Raja Chakir
email: raja.chakir@grignon.inra.fr

Maia David
email: maia.david@agroparistech.fr

Estelle Gozlan
email: esgozlan@grignon.inra.fr.

Aminata Sangare

Elodie Brahic

Jeanne Dachary-Bernard

Arnaud Estoup

Bérénice Fassote

Marc Kenis

Eric Lucas

Jayson Lusk

Valuing the impacts of an invasive biological control agent: a choice experiment on the Asian ladybird in France

Keywords: Non-market valuation, Discrete choice experiment, Biological Invasion, Biological Control, Biodiversity, Pesticides. JEL Classification: Q10, Q51, Q57, C35

Initially used as a biological control agent against Aphids, the Asian ladybird has become highly invasive in many regions, including Europe. While biological control is usually considered as an environmentally-friendly alternative to chemical pesticides in controlling pests in crops, there is growing concern that these environmental benefits could be outweighed by the negative consequences of the invasion. These include (i) biodiversity losses as populations of native ladybirds suffer from intraguild predation and competition for resources; (ii) human nuisance in houses, including risks of allergy and (iii) potential losses to wine-growers. The aim of this paper is to provide an economic valuation of environmental and private characteristics affected by the Asian ladybird's invasion. We conduct a discrete choice experiment among a representative sample of the French population. Our results show that the consequences of the Asian ladybird's introduction do affect significantly the population's welfare. Among these, the impact on biodiversity through the threat on native species appears to be a significant concern. The tradeoffs elicited suggest that people are willing to accept a small increase in pesticides to preserve native ladybirds.

Introduction

Biological control is usually considered as an efficient and environmentally-friendly method of pest management. Its advocates indicate that biological control outperforms chemical control on many aspects: specificity, success ratio, benefit/cost ratio and less harmful side effects [START_REF] Van Lenteren | Internet Book of Biological Control[END_REF]. In particular, in comparison to chemical insecticides, biological control avoids the release of toxic substances harming non-targeted species (including humans) and avoids the development of resistance in targeted pests. Public concern about chemical pesticides has grown dramatically over the last decades with mounting evidence of their health and ecological effects. Recent studies suggest that citizens in developed countries have a positive willingness to pay (WTP) to avoid exposure to pesticides (see for example [START_REF] Florax | A meta-analysis of the willingness to pay for reductions in pesticide risk exposure[END_REF] for a meta-analysis).

However, adverse non-target effects of biological control have been observed in a number of situations. These include the release and spread of exotic species that have become invasive.

Invasive species are considered as a major environmental concern and represent one of the top drivers of global biodiversity loss [START_REF] Issg | IUCN guidelines for the prevention of biodiversity loss caused by alien invasive species[END_REF]. Even though there is general agreement that sound risk assessment procedures should precede the release of exotic invertebrate biological control agents, there is no consensus on how to judge the magnitude of non-target effects and whether these effects could outweigh the benefits of biological control [START_REF] De Clercq | Benefits and risks of exotic biological control agents[END_REF].

Our study aims at providing some economic insights in this debate. In particular, we value individual preferences with regard to some of the costs and benefits associated with the use of the Asian ladybird as a biological control agent and with the consequences of its invasion.

Section 2 presents the background, recalling the reasons for the release of the Asian ladybird in Europe, highlighting the main problems associated with its spread, and discussing the possible options to mitigate these impacts (2.1); it also provides a quick survey of the economic non-market valuation literature addressing similar issues and highlights our original contribution (2.2). Section 3 focuses on the methodology we used to conduct our study. Results are presented in section 4 and discussed in section 5.

2 Background and insights from the literature 2.1 A tale of a good insect that has become a problem

The Asian ladybird (Harmonia axyridis, see Figure 1) is an aphid predator that was voluntarily released in Europe in the 1990s as a biological control agent because of its voracity. It has been effective at controlling pest insects in a variety of crop systems. For reasons which remain unknown, it recently suddenly became highly invasive on four continents, including Europe Comment citer ce document : Chakir, R., David, M., Gozlan, E., [START_REF] Chakir | Valuing the impacts of an invasive biological control agent: a choice experiment on the Asian Ladybird in France[END_REF]. Valuing the impacts of an invasive biological control agent: a choice experiment on the Asian Ladybird in France. Journal of Agricultural Economics, 67 (3), 619-638. DOI : 10.1111/1477-9552.12160

where it has spread at the rate of approximately 200 km/yr [START_REF] Brown | Harmonia axyridis in europe: spread and distribution of a non-native coccinellid[END_REF][START_REF] Brown | The global spread of harmonia axyridis (coleoptera: Coccinellidae): distribution, dispersal and routes of invasion[END_REF]. For

France, the following maps (Figure 2) illustrate the progression of the invasion between 2004 and 2011.

Figure 1: The multicolored Asian ladybird (Harmonia axyridis)

The Asian ladybird is now considered as one of the world's most invasive insects [START_REF] Roy | Harmonia axyridis: A successful biocontrol agent or an invasive threat?[END_REF]. The negative consequences of the invasion include:

• Biodiversity losses as populations of native ladybirds and other aphidophagous insects suffer from intraguild predation and competition for resources. According to a recent study for England, Belgium and Switzerland [START_REF] Roy | Invasive alien predator causes rapid declines of native european ladybirds[END_REF]: "the decline in the distribution and abundance of previously widespread and common native ladybirds after the arrival of H. axyridis is striking. The dramatic decline of the European two-spot ladybird

Adalia bipunctata [see picture on Figure 3 a.] over the five years following the arrival of H. axyridis is of particular note", with a decrease in native populations ranging from 30% (Belgium) to 45% (England) and even 99% (Switzerland). [START_REF] Brown | Intraguild predation by harmonia axyridis (coleoptera: Coccinellidae) on native insects in europe: molecular detection from field samples[END_REF] provide recent evidence of the predation on native species by the Asian ladybird in France, England, Slovakia and the Czech Republic;

• Human nuisance because the beetle aggregates in buildings when seeking overwintering sites in the autumn, thousands being reported in a single household (CABI Invasive Species Compendium). Human nuisances that have been reported include aesthetic inconvenience due to aggregates in the housing (see Figure 3 c.). Moreover, reflex bleeding ladybirds may stain furnishings and walls and result in unpleasant odors. Also, exposure

to reflex blood may in some cases trigger allergic reactions in sensitive persons [START_REF] Majerus | The potential impacts of the arrival of the harlequin ladybird, harmonia axyridis (pallas)(coleoptera: Coccinellidae), in britain[END_REF][START_REF] Koch | Bad side of a good beetle: the north american experience with harmonia axyridis[END_REF]; • Potential losses to wine-growers (Figure 3 b.), because the taste of wine can be spoiled when beetles are crushed with grapes [START_REF] Pickering | Influence of harmonia axyridis on the sensory properties of white and red wine[END_REF]. This impact has been reported in North America 1 where the invasion of H. axyridis is also a concern, and to a lesser extent in Europe, including France. that used to be a symbol of the "good beetle". Could these impacts be mitigated by public intervention or private actions ? [START_REF] Kenis | Current and potential management strategies against harmonia axyridis[END_REF] have surveyed current and potential management strategies against H. axyridis. These include mechanical control, trapping, chemical control, the use of deterrents, and even biological control. Some of the presented methods could solve the problems caused by beetles aggregating in houses and vineyards, while research needs to be pursued regarding methods to lower population densities in natural environments and to limit the impact of the Asian ladybird on native species 2 .

Comment
Pursuing research has a cost and economic questions arise. Should public money be spent to search and implement solutions to address the negative consequences of the invasion of the Asian ladybird? If so, what is the approximate budget that should be allocated? Since the impacts of the invasion are multiple and have both a private and a public good dimension, what are the priorities for public action? More generally, was the introduction of this insect as a biocontrol agent economically sound, i.e. do benefits overweight the costs? Should we 1 In 2003, over a million litres of Harmonia-tainted wine had to be destroyed in Ontario, Canada [START_REF] Ejbich | Producers in ontario and northern us bugged by bad odors in wines[END_REF].

2 Among ongoing research, a sexually transmitted mite inducing host sterility could be a promising candidate for lowering the populations of H. axyridis [START_REF] Rhule | Potential role of the sexually transmitted mite coccipolipus hippodamiae in controlling populations of the invasive ladybird harmonia axyridis[END_REF]. Understanding the reasons why the native ladybird populations seem to be less declining in some countries (Germany) could also be of interest. relies on the assumption that the costs that the invasion has put on our societies outweigh the benefits -while such a conclusion cannot be reached without an economic valuation of these costs and benefits. In particular, if the disappearance of native ladybirds does not matter to the citizens (either because they don't care about ladybirds, or because the Asian ladybird is considered a close substitute), and if the nuisances do not affect their utility significantly, while the use of pesticides does, then the conclusion of a cost-benefit analysis could be in contradiction to that of the environmental risk assessment.

An economic analysis of the use of the Asian ladybird is thus needed. By trying to elicit public preferences with regard to some of the consequences of the release of the Asian ladybird in France, providing willingness to pay estimates and highlighting tradeoffs, this article brings an original quantified contribution in this debate.

Insights from the non-market valuation literature

We wish to value, in monetary terms, the weight the French population grants to the positive and negative impacts of the Asian ladybird (reduction of pesticides, threat on native species, ...).

Several non-market valuation methods are used in the literature to estimate the monetary value associated with environmental services or damages (stated preference methods and revealed preference methods).

In recent years, there has been an increasing use of choice experiments (also named discrete choice experiments, DCE) in non-market valuation (see [START_REF] Hoyos | The state of the art of environmental valuation with discrete choice experiments[END_REF] for a survey). Like other stated preference methods such as contingent valuation, this method captures the non-use value of environmental goods (existence value, bequest value...), which is useful when valuing endangered species or biodiversity. Moreover, it reveals more detailed information than a contingent valuation by yielding the willingness to pay for different aspects (i.e. attributes) of an environmental issue. On the other hand, its main disadvantage is that the survey is generally heavier than for other valuation methods, which may induce some cognitive difficulties [START_REF] Hanley | Modelling recreation demand using choice experiments: Climbing in scotland[END_REF] and more complex econometric estimations. Although there are numerous contingent valuations dedicated to endangered species (see [START_REF] Richardson | The total economic value of threatened, endangered and rare species: An updated meta-analysis[END_REF] for a meta-analysis of 43 such studies), and several related to the consequences of invasive species [START_REF] Nunes | Can people value protection against invasive marine species? evidence from a joint tc-cv survey in the netherlands[END_REF][START_REF] Mcintosh | Invasive species and delaying the inevitable: Valuation evidence from a national survey[END_REF] and the use of pesticides (see [START_REF] Florax | A meta-analysis of the willingness to pay for reductions in pesticide risk exposure[END_REF] for a meta-analysis), there are only a few DCEs in these fields.

To the best of our knowledge, [START_REF] Travisi | Valuing environmental and health risk in agriculture: A choice experiment approach to pesticides in italy[END_REF] and [START_REF] Chalak | Pesticides, preference heterogeneity and environmental taxes[END_REF] are among the only DCEs directly dedicated to the valuation of the impacts of chemical pesticides 4 . [START_REF] Travisi | Valuing environmental and health risk in agriculture: A choice experiment approach to pesticides in italy[END_REF] analyze the perception of pesticide risks in Italy, taking into account potential impacts on biodiversity, groundwater quality and human health. According to their results, biodiversity seems to be one of the main concerns related to pesticides. [START_REF] Chalak | Pesticides, preference heterogeneity and environmental taxes[END_REF] have driven two DCEs in the UK: one on the use of pesticides in cereal production and the other on fruits and vegetables. Their study aims at disentangling the respective weight of environmental impacts and health impacts in the willingness to pay for a reduction in pesticides.

In comparison with our work, the designs used in these two papers do not involve the same trade-off between biodiversity and pesticides, as biodiversity losses are a consequence of chemical pesticides use, while in our problem, a decline in biodiversity is driven by an alternative to chemical pesticides. [START_REF] Hanley | Economics and the design of nature conservation policy: a case study of wild goose conservation in scotland using choice experiments[END_REF][START_REF] Hanley | Economic values of species management options in human-wildlife conflicts: Hen harriers in scotland[END_REF]; [START_REF] Bartczak | Valuing the chances of survival of two distinct eurasian lynx populations in poland : Do people want to keep the doors open?[END_REF] and [START_REF] Wallmo | Valuing improvements to threatened and endangered marine species: an application of stated preference choice experiments[END_REF] use DCEs to value endangered species and species preservation policies. The species studied in these articles are respectively birds, mammals and fish. Insect species do not seem to have been the object of DCEs up to now, when according to [START_REF] Richardson | The total economic value of threatened, endangered and rare species: An updated meta-analysis[END_REF] the willingness to pay to preserve an endangered species depends crucially on the species' type.

Our work contributes to the literature in three main ways. First, we provide a first DCE estimation of the willingness to pay of the French population for a reduction of chemical pesticides, in a context where their use has become controversial in this country. Second, we obtain some first DCE estimates of the value of an endangered species of the insect type, namely the emblematic two-spot ladybird (A. bipunctata). These two contributions meet the need for local monetary values of environmental goods linked to biodiversity and ecosystemic services (see Chevassus-au [START_REF] Louis | Approche economique de la biodiversite et des services liés aux écosystèmes[END_REF]). Third, we give valuable insights towards a first cost-benefit analysis of the introduction of the Asian ladybird. Such an economic analysis was crucially lacking according to the ecological literature on the topic [START_REF] Pervez | Ecology and biological control application of multicoloured asian ladybird, harmonia axyridi s: A review[END_REF]).

4 Other DCEs address topics linked to pesticides, such as [START_REF] Michaud | Willingness to pay for environmental attributes of non-food agricultural products: a real choice experiment[END_REF] and [START_REF] Yue | Organic or local? investigating consumer preference for fresh produce using a choice experiment with real economic incentives[END_REF], who examine, respectively, the willingness to pay for eco-labeled (non-food) and organic (food) agricultural products.

Comment citer ce document : Chakir, R., David, M., Gozlan, E., Sangare, A. ( 2016). Valuing the impacts of an invasive biological control agent: a choice experiment on the Asian Ladybird in France. Journal of Agricultural Economics, 67 (3), 619-638. DOI : 10.1111/1477-9552.12160

3 Methodology

Survey design and choice experiment

A discrete choice experiment consists of six main steps: the choice of the relevant attributes and their levels; the experimental design which consists in selecting a satisfactory sub-set of all the possible combinations among the attributes' levels; the design of the questionnaire; the data collection; the econometric estimations; the interpretation of the results.

The choice of the attributes and their levels

In our survey, respondents were asked to indicate which situation they would prefer, in a fiveyears time, between three options including the status quo situation, that is the situation in five years if nothing is done. Each option was characterized by different levels of several attributes, including a monetary attribute.

A fundamental question when designing a DCE is whether to present the choice sets in a labeled or an unlabeled form. In DCEs, labeled alternatives typically allow to link environmental and economic outcomes (measured by the level of selected attributes) to a specific policy option. In unlabeled DCEs, each alternative is named generically (eg. A, B, C...) and respondents differentiate among the proposed alternatives only through the attributes and their levels. Both methods have been commonly used in the literature and have their strengths and weaknesses. In particular, while labeled alternatives may make the choice task more concrete for respondents, recent contributions found evidence that a proportion of respondents chose on the basis of the label only [START_REF] Doherty | Examining labelling effects within discrete choice experiments: An application to recreational site choice[END_REF], and that unlabeled DCEs may be more suitable to investigate tradeoffs between attributes [START_REF] Bekker-Grob | Labeled versus unlabeled discrete choice experiments in health economics: an application to colorectal cancer screening[END_REF]. Such tradeoffs appear to be important in our investigation as one of our aims is to highlight priorities for the future policies. We therefore opted for an unlabeled DCE. Our main aim is to infer from respondents' choices their monetary value associated with each attribute as a first step to design policy action.

Discussions were held with experts in ecology and non-market valuation methods in order to identify the most significant attributes and their levels, and to characterize the status quo in terms of our chosen attributes. With the same aim, a focus group was organized allowing informal discussions with non-expert people. The chosen attributes were:

1. The level of pesticides used in agriculture. Three levels were associated with this attribute:

the business-as-usual level, i.e. level in five years if nothing is done (status quo), a 3% increase compared to the business-as-usual level, a 3% decrease compared to the businessas-usual level5 .

Comment citer ce document : Chakir, R., David, M., Gozlan, E., Sangare, A. ( 2016). Valuing the impacts of an invasive biological control agent: a choice experiment on the Asian Ladybird in France. Journal of Agricultural Economics, 67 (3), 619-638. DOI : 10.1111/1477-9552.12160

2. The state of the population of the two-spot ladybird A. bipunctata (the most threatened European native ladybird species), representing the impact of the invasion on biodiversity. Three levels were associated with this attribute: disappeared (status quo), rare and abundant.

3. The damages caused by the Asian ladybird to human beings, their housing and fruit cultures were grouped in a unique attribute. Three levels were associated with this attribute, in proportion to the affected human population: high (status quo, 15% of the population), moderate (5% of the population) and insignificant (1% of the population).

4. The cost attribute was chosen as an increase of yearly local taxes, with three possible values: e0 (status quo), e5 and e10. Taxation was preferred to voluntary donations to avoid free-riding effects [START_REF] Whitehead | A practitioner's primer on the contingent valuation method[END_REF]

Experimental design

Once the attributes and their levels were chosen, the next step was to choose which options (i.e. combinations of attributes' levels) to include in the questionnaire. With four attributes and three associated levels each, the full factorial range of combinations (3 4 ) was too wide to collect the respondents' opinion on all of them. We selected a statistically optimal sub-set of biological control agent, the use of pesticides to control the Asian ladybird in vineyards, etc. The chosen levels were selected after the pre-test, because it appeared that (i) respondents needed some quantitative elements to make a decision, (ii) in our case, the variations in the use of chemical pesticides were not major at the country level.

Comment citer ce document : Chakir, R., David, M., Gozlan, E., Sangare, A. ( 2016). Valuing the impacts of an invasive biological control agent: a choice experiment on the Asian Ladybird in France. Journal of Agricultural Economics, 67 (3), 619-638. DOI : 10.1111/1477-9552.12160

these combinations using a Bayesian D-optimal design. This is the aim of experimental design techniques (see [START_REF] Louviere | Stated choice methods: analysis and applications[END_REF]) and the dedicated software6 . There are different types of experimental designs. The orthogonal design is widely used in the literature and selects the choice sets that procure the maximal information without any a priori information on the population's preferences. The efficient design yields more information for a given number of choice sets but requires a priori values (priors) on the population's preferences. These priors can be issued from previous studies in the literature or pilot studies. The efficient design, although less common than the orthogonal given its requirements, is recognized as superior in the literature7 .

As a first step, we implemented a pilot study on a sample of students based on an orthogonal design. This allowed us to obtain priors in order to implement an efficient design on a representative sample of the population. The pilot study was administered to 204 French students on an engineering school campus in the Paris area (AgroParisTech). The efficient design was then obtained resulting in 9 choice sets. Each choice set is composed of the status quo and two alternative scenarios, as shown in the example presented below (Figure 4, translated from French), in which the pesticide attribute is labeled "Pesticides", the state of Adalia bipunctata's population attribute is labeled "Biodiversity", the attribute related to damages on humans is labeled "Nuisances" and the cost attribute is labeled "Cost".

Data collection and presentation of the questionnaire

The survey was administered online in May 2014 by a survey institute, yielding 503 answers from a representative sample by quota of gender, age, place of residence (urban/rural) and socioprofessional category of the French population. The questionnaire was designed to last less than 15 minutes. After a short introduction on the topic of the survey, some general questions were asked related to the respondent's environmental attitudes (consumption of organic products, past voluntary donations, etc.). A summary of our problem was then presented through a video and slides. The meaning and detailed definition of each attribute was explained, along with examples. The information provided to the participants also included (i) general information about biological vs. chemical control of pests in agriculture, (ii) details about the various consequences of the invasion of H. axyridis and (iii) information about conceivable measures that could be thought of to address these impacts within a five-years time. The survey was explained to be a preliminary step in order to assess the population's willingness to pay to address the consequences of the problem, and thus to inform on the appropriate budget to dedicate to this field.

Comment citer ce document : Chakir, R., David, M., Gozlan, E., Sangare, A. ( 2016 to carefully consider their current budget and expenditures in making their choices. The order of the choice sets was randomized so that declining attention issues would not systematically affect the same choice sets. In one of the choice sets, there was one dominated option (same monetary contribution but worse levels for all other attributes) which allowed to control for the respondent's consistency8 . At the end of the nine choice sets, participants were asked whether they were satisfied with their answers and, in the case they were not, to explain why.

Socio-demographic information on the respondent such as income level, gender, age and level of education were collected at the end of the questionnaire.

Among the respondents, 70 individuals (14% of the sample) indicated they were not entirely satisfied with their answers. Most of them seemed to have understood the questions quite well and were simply frustrated by the trade-offs they had to make, for instance having to choose between less pesticides or more biodiversity. For this reason, we chose not to systematically exclude them from the sample. Note, moreover, that our econometric results are robust to their exclusion.

Moreover, 38 individuals (7.5% of the sample) selected the dominated option in one of the choice sets. This choice was consistent only if the person had a preference for an increase in pesticides. Therefore we checked in their responses along the other choice sets whether they were consistent with a positive willingness to pay for an increase in pesticides: they were not, so these 38 answers were excluded from our analysis. We also excluded one participant who had chosen the same option to all the choice sets, exhibiting inconsistent choices. The final sample used in the estimation therefore comprised the remaining 503-39=464 respondents.

France [START_REF] Olsen | Choosing between internet and mail survey modes for choice experiment surveys considering non-market goods[END_REF].

Comment citer ce document : Chakir, R., David, M., Gozlan, E., Sangare, A. ( 2016). Valuing the impacts of an invasive biological control agent: a choice experiment on the Asian Ladybird in France. Journal of Agricultural Economics, 67 (3), 619-638. DOI : 10.1111/1477-9552.12160

Econometric model

The discrete choice experiment technique is an application of the characteristics theory of value [START_REF] Lancaster | A new approach to consumer theory[END_REF], combined with random utility theory [START_REF] Mcfadden | Conditional logit analysis of qualitative choice behavior[END_REF]. As suggested in the literature, we assume that the utility for each individual i (i = 1, ..., N ) and each option o (o = 1, ..., O) in each choice set s (s = 1, ..., S) is composed of a linear-in-parameters part, that depends on observable variables and an error term:

U ios = β x ios + γ i z ios + ε ios (1)
where x ios and z ios are the observed variables associated with option o in choice set s, β

is the vector of fixed coefficients, γ is a vector of random coefficients with mean zero and ε ios is a vector of error terms. Option o will be chosen over some other option o if and only if

U ios > U io s .
The econometric model depends on the assumption on the distribution of error terms. If the ε ios are independent identically distributed (IID) type I extreme value, we have a random parameter logit (or mixed logit model) [START_REF] Train | Discrete Choice Methods with Simulation[END_REF]. The standard logit is a special case of this model where γ has a zero variance. The random parameter logit is a highly flexible model that can approximate any random utility model [START_REF] Mcfadden | Mixed mnl models for discrete response[END_REF]. It enables to avoid the three limitations of standard logit by allowing for random taste variation, unrestricted substitution patterns and correlation in unobserved factors over time [START_REF] Train | Discrete Choice Methods with Simulation[END_REF].

In the random parameter logit model, it is necessary to make an assumption regarding the distribution of each of the random coefficients. The choice is often limited by the difficulty of the model estimation and availability in econometric software. We assume here that the random parameters are normally distributed, which is the most easily applied distribution and which allows for both negative and positive preferences.

For a given value of γ, the conditional choice probability is a standard logit:

L io (γ) = e β x io +γ i z io o ∈O e β x io +γ i z io (2)
and the unconditionnal choice probability, in the random parameter logit model, is the logit formula in equation ( 2) integrated over all values of γ weighted by the density of γ:

P io = L io (γ)f (γ/Ω)dγ, (3)
where f (L io (γ)) is the density of γ and Ω is the fixed parameter of the distribution. The choice probability in equation ( 3) cannot be calculated exactly because the integral does not have a closed form in general. This integral is approximated through simulations. For a given value of the parameters Ω, a value of γ is drawn from its distribution. Using this draw, the logit formula in (2) is calculated. This process is repeated for many draws, and the mean of the resulting L io (γ) is taken as the approximate choice probability yielding equation ( 4):

SP io (γ) = 1 R R r=1 L io (γ r ), (4)
where, R is the number of draws of γ, and SP is the simulated probability that an individual i chooses option o.

In the analysis of the collected data, we estimate three types of models: the standard logit (SL), the conditional logit (CL) and the random parameter logit (RPL). The latter is the most flexible as it has the advantage of assuming that the alternatives are not independent and it takes into account unobserved heterogeneity as well as random taste variations among individuals [START_REF] Train | Discrete Choice Methods with Simulation[END_REF]. In our model, the utility coefficients vary among individuals, but are constant among the choice situations for each individual. This reflects an underlying assumption of stable preference structures for all individuals [START_REF] Train | Mixed logit models for recreation demand[END_REF].

We use the estimated parameters to calculate the willingness to pay (WTP) associated with each attribute k and each level l as follows:

W T P kl = - γ l k β cost (5)
where γ l k are the estimated parameters, which measure the variation of the utility associated with a variation of the attribute k from the status quo level to the level l. β cost is the parameter associated with the cost attribute, i.e. the marginal utility of income which is assumed constant as is common in the literature [START_REF] Hensher | The mixed logit model: the state of practice[END_REF]. W T P kl thus represents the willingness to pay to move from the status quo level of attribute k to a level l.

In calculating a WTP, it is important that both parameters used in the calculation be statistically significant, otherwise no meaningful WTP measure can be established.

Results and interpretation

The estimation results of the three econometric models are shown in Table 4. The term cte SQ refers to the alternative specific constant (ASC) associated with the status quo; it captures the utility associated with the status quo. As we have unlabeled options 9 , we only include an ASC for the status quo alternative [START_REF] Hoyos | The state of the art of environmental valuation with discrete choice experiments[END_REF].

γ 2 pesticide and γ 3 pesticide are respectively the variation in utility due to a 3% increase and 3% decrease in pesticides compared to the status quo situation. γ 2 biodiv and γ 3 biodiv are respectively 9 Each option in the choice sets does not necessarily correspond to a precise policy alternative which could be labeled, it is just a random combination of attributes' levels. As mentioned in subsection 3.1.1, the use of unlabeled options is common in the DCE literature.

Comment citer ce document : Chakir, R., David, M., Gozlan, E., Sangare, A. ( 2016). Valuing the impacts of an invasive biological control agent: a choice experiment on the Asian Ladybird in France. Journal of Agricultural Economics, 67 (3), 619-638. DOI : 10.1111/1477-9552.12160

the variation in utility when increasing A. bipunctata's population from a "disappeared" level to a "rare" and "abundant" level. γ 2 nuisance and γ 3 nuisance are respectively the variation in utility when reducing the human nuisances due to the Asian ladybird from a "high" level to a "moderate" and a "insignificant" level. The parameters β SQ sex , β SQ income , β SQ organic , β SQ donation and β SQ rural are the coefficients associated with individual characteristics: sex, income, organic, donation and rural respectively (see Table 3). These individual characteristics are assumed to affect the variation of utility when moving away from the status quo.

The RPL model was estimated using logitm procedure of STATA 12. In the RPL model, all the parameters except the payment attribute and those associated with socio-demographic variables were specified to be normally distributed. The results of the RPL estimations are reported in the third and fourth columns of Table 4. They show that the standard deviations of the coefficients are significant, indicating that a RPL provides a significantly better representation of the choices than a SL, which assumes that coefficients are the same for all respondents.

This indicates that the data supports choice specific unconditional unobserved heterogeneity for the considered attributes. Moreover, recent applications of the RPL model have shown that this model is superior to the CL model in terms of overall fit and welfare estimates [START_REF] Lusk | Demand for beef from cattle administered growth hormones or fed genetically modified corn: a comparison of consumers in france, germany, the united kingdom, and the united states[END_REF]. For all these reasons, we focus our interpretations on the results of the random parameter logit model.

The parameters of all the attributes in the RPL model are statistically significant and have the expected signs. Unsurprisingly, the signs of β cost and γ 2 pesticide are negative, meaning that an increase in costs or in the pesticides' use reduce the respondents' utility. The estimates of the parameters associated with the socio-demographic variables show that the gender, as well as the fact of living in rural areas, has no impact on the utilities of the respondents.

Similarly, results show that giving donations for humanitarian or other reasons does not impact the utilities of respondents. However, frequent organic purchasers and respondents from higher income classes decrease their utility when staying in the status quo rather than moving away from this situation.

The choice experiment approach then allows us to estimate the WTP associated with each level of each attribute. Using equation ( 5), results of WTP are presented in Table 5. All the WTP estimates obtained with the RPL model are highly significant. They show that respondents are ready to pay on average e10 per year to increase European native ladybird population from the status quo level ("disappeared") to a level "abundant". Respondents seem also concerned by pesticides' use in agriculture as they are willing to pay on average e3 per year to decrease their level by 3% compared to their business-as-usual level. The WTP associated with an increased level of pesticides in agriculture are negative which means that the respondents need to receive on average e6.5 to compensate the utility loss associated with a 3% increase of pesticides. Regarding the human damages caused by the Asian ladybird, respondents have an The standard-deviation of WTP were calculated by the delta method.

Table 5: WTP estimates in e

As shown in our results, there is a significant willingness to pay to preserve the endangered two-spot ladybird, A. bipunctata. A household's willingness to pay to avoid the disappearance of this species in five years and reach an abundant population ranges from e8.6 to e11.4 per year. It is difficult to compare our results with the value obtained in the literature on DCEs valuing endangered species (ranging approximately from e10 to e70, depending on the species' type, whether the payment prevents extinction, on the extent of the variation of the population induced by the payment, whether it is a one time or annual payment, whether the concerned species is emblematic [START_REF] Richardson | The total economic value of threatened, endangered and rare species: An updated meta-analysis[END_REF]). Most of these studies are dedicated to mammals, birds and fishes rather than insects, which explains the variation in the obtained values. Multiplying the obtained individual WTP by the number of households in France in 2010, we find that the total budget that could be dedicated to preserve A. bipunctata in France ranges from e198 million to e266 million per year.

The willingness to pay for a 3% pesticides reductions is e3 per year and per household. This estimate is not directly comparable to those obtained in the literature, due to differences in the analytical framework. [START_REF] Travisi | Valuing environmental and health risk in agriculture: A choice experiment approach to pesticides in italy[END_REF] focus on the consequences of the variations in pesticides on several attributes, including biodiversity, while our motivation was to highlight some potential tradeoffs of biological control, requiring to consider chemical pesticides and biodiversity as two separate attributes. [START_REF] Chalak | Pesticides, preference heterogeneity and environmental taxes[END_REF] found a willingness to pay of £0.425 a week (through higher expenditures in fruits and vegetables), i.e. around e28 a year for a 5% decrease in a wide class of chemical pesticides. The relative small willingness to pay we obtain for reducing pesticides might be due to the small extent of the reduction considered (3% in five years may not seem substantial for a portion of the population 10 ) or to a lack of awareness on risks associated with pesticides 11 .

Furthermore, one may note the strong asymmetry between the willingness to pay for a reduction of pesticides and the willingness to accept for a same extent increase of pesticides.

The total French population is willing to pay from e45 million to e119 million per year to decrease pesticides by 3% whereas it needs to receive between e138 million and e222 million to accept a 3% increase. This confirms a well-known result in the literature according to which a willingness to accept is higher than a willingness to pay for a same variation of the environmental quality.

Last, the WTPs for a reduction of human nuisances due to the Asian ladybird are significant.

For instance, a household's willingness to pay to reduce these nuisances from a high level (15% of the population) to an insignificant level (1% of the population) ranges from e6.3 to e8.5 per year. We thus find that the total budget that could be dedicated to solve H. axyridis's effects in housings and vineyards in France ranges from e174 million to e235 million per year.

Finally, the comparison of WTP-estimates in Table 5 provides some interesting insights on the tradeoffs in policy outcomes. It shows that the amount of money required for respondents to accept a small increase in pesticide use (3%) is less -or comparable to -their willingness to pay for an improvement in the populations of the native two-spot ladybird. This is also the case for an important reduction of nuisances to humans and vineyards.

Conclusion and discussion

The objective of this paper was to provide an economic valuation of environmental and private characteristics affected by the use of the Asian ladybird as a biological control agent and by its 10 As a comparison, [START_REF] Chalak | Pesticides, preference heterogeneity and environmental taxes[END_REF] explore the willingness to pay for a 5%, 10%, 20% and a 50% reduction of pesticides. However, we have chosen this level as a higher reduction would not be realistic as a consequence of the introduction of the Asian ladybird.

11 In our will to stay as neutral as possible regarding the information delivered before the choice sets, we did not give a long description of the potential negative effects of chemical pesticides. Instead a short sentence mentioned potential effects on the environment and health. Detailing the impacts of pesticides on topics as sensitive as health and fertility might have distorted the results by shocking the population.

Comment citer ce document : Chakir, R., David, M., Gozlan, E., Sangare, A. ( 2016). Valuing the impacts of an invasive biological control agent: a choice experiment on the Asian Ladybird in France. Journal of Agricultural Economics, 67 (3), 619-638. DOI : 10.1111/1477-9552.12160

invasion. A discrete choice experiment with efficient design was conducted among a representative sample of the French population. Three econometric models were estimated (standard logit, conditional logit, random paramter logit) yielding statistically significant estimates of the population's willingness to pay for various attributes linked to our topic : pesticides' use, local biodiversity and nuisances to humans and fruit cultures.

Our results show that all the attributes considered have a significant effect on the utility of respondents. In particular, regarding biodiversity, we highlight the existence value of the two-spot ladybird for which respondents are ready to pay e10 per year in average to increase the population from a "disappeared" level to an "abundant" level. Conversely, respondents would need to receive a payment of e6.5 per year in average to compensate the loss of welfare associated with a 3% increase of pesticides' use in agriculture.

Our quantitative analysis sheds some light on the questions raised in the introduction.

Clearly, measures should be taken to address the negative consequences of the invasion, as they affect welfare significantly. Based on our evaluation of preferences, significant budgets -several hundred million euros in France -could be spent to solve the problems associated with this issue.

The tradeoff between the environmental benefits of biological control by Asian ladybirds (less chemical pesticides) and the environmental cost of the invasion on native species implies a balance between an environmental attribute with some private good characteristics (perceived effects of pesticides on one's individual health) and a pure public good (biodiversity). Here, free-riding effects -typical with pure public goods -do not seem to dominate as respondents are clearly taking both the private and public good into consideration. They are in average willing to accept a small increase in pesticides to avoid the disappearance of a native ladybirds species.

This may be due to an irreversibility effect, making respondents reluctant to select an option where a species disappears (A. bipunctata), even when it is replaced by a close substitute (H.

axyridis).

Our economic valuation gives support to van Lenteren et al. ( 2008)'s environmental risk assessment, stating that H. axyridis should probably not have been released in Northwest Europe : in France, the private and environmental costs of the invasion of H. axyridis appear to be significant in comparison to the environmental benefits of its use as a biological control agent. This result calls for the greatest caution in the future when considering the introduction of exotic species as biological control agents, while this importation process (classical biological control) remains common practice in many countries [START_REF] Cock | Do new access and benefit sharing procedures under the convention on biological diversity threaten the future of biological control?[END_REF].

Figure 2 :

 2 Figure 2: Invasion of the Asian ladybird in France 2004-2011 (Source: Observatoire Permanent pour le suivi de la coccinelle asiatique en France)

Figure 3 :

 3 Figure 3: a. The threatened native species Adalia bipunctata ; b. Asian ladybird nuisance in vineyards; c. Asian ladybird aggregate in housing

  ). Valuing the impacts of an invasive biological control agent: a choice experiment on the Asian Ladybird in France. Journal of Agricultural Economics, 67 (3), 619-638. DOI : 10.1111/1477-9552.12160

Figure 4 :

 4 Figure 4: Example of a Choice Set

  Comment citer ce document : Chakir, R., David, M., Gozlan, E., Sangare, A. (2016). Valuing the impacts of an invasive biological control agent: a choice experiment on the Asian Ladybird in France. Journal of Agricultural Economics, 67 (3), 619-638. DOI : 10.1111/1477-9552.12160

  Comment citer ce document : Chakir, R., David, M., Gozlan, E., Sangare, A. (2016). Valuing the impacts of an invasive biological control agent: a choice experiment on the Asian Ladybird in France.

	consider its introduction in other regions 3 ?
	The result of van Lenteren et al. (2008)'s environmental risk assessment stated that "in the
	H. axyridis case, current knowledge would lead to the conclusion that, although the predator is
	capable to effectively control several pest species (a strong benefit), its risks are manifold (...),
	and it should, thus, not have been released in Northwest Europe". However, this conclusion
	Journal of
	Agricultural Economics, 67 (3), 619-638. DOI : 10.1111/1477-9552.12160

Table 1 :

 1 Attributes and levels

	Attributes	Description	Levels
	Pesticides	Use of chemical pesticides in agriculture Business-as-usual level (SQ);
			Reduction (-3%); Increase (+3%)
	Biodiversity State of Adalia bipunctata's population Disappeared (SQ); Rare; Abundant
	Nuisance	Damages on humans, housing and wine High (15%, SQ); Moderate (5%);
		(% of the population affected)	Insignificant (1%)
	Monetary	Increase in yearly local taxes	e0 (SQ); e5 ; e10
	contribution

and this payment vehicle did not seem to meet major objections during the focus group.

See the table below for a summary of the attributes and their levels. The status quo level is indicated by "SQ".

Table 2 :

 2 Comparison between our sample and the French population characteristics

	Sample

istics of the sample are very close to the French population's characteristics (see Table

2

); our sample exhibits a slight over-representation of people in upper socio-professional categories, as it is usual in Internet and mail surveys

Table 4 :

 4 Comment citer ce document : Chakir, R., David, M., Gozlan, E., Sangare, A. (2016). Valuing the impacts of an invasive biological control agent: a choice experiment on the Asian Ladybird in France. Journal of Agricultural Economics, 67 (3), 619-638. DOI : 10.1111/1477-9552.12160 Estimation results average WTP of respectively e5 and e7 per year to reduce these damages from their actual "high" (15% of the population concerned) level to a "moderate" level (5% of the population) Comment citer ce document : Chakir, R., David, M., Gozlan, E., Sangare, A. (2016). Valuing the impacts of an invasive biological control agent: a choice experiment on the Asian Ladybird in France. Journal of Agricultural Economics, 67 (3), 619-638. DOI : 10.1111/1477-9552.12160and "insignificant" level (1% of the population).

		SL	CL	RPL
		Param	Param	Param	SD
	cte SQ	-0.669 * * * 0.737 * * *	-0.131	3.173 * * *
		(-9.27)	(6.20)	(0.37)	(11.70)
	γ 3 pesticide	0.813 * * * 1.006 * * *	0.536 * * *	0.541 * *
		(9.39)	(11.07)	(5.08)	(2.88)
	γ 2 pesticide	-0.695 * * * -0.263 * *	-1.172 * * *	1.806 * * *
		(-7.97)	(-2.82)	(-6.58)	(10.79)
	γ 2 biodiv	0.460 * * * 0.917 * * *	1.509 * * *	0.140
		(4.53)	(8.63)	(10.58)	(0.81)
	γ 3 biodiv	1.022 * * * 1.324 * * *	1.807 * * *	0.734 * * *
		(16.26)	(19.81)	(15.37)	(5.20)
	γ 2 nuisance	-0.138	0.391 * * *	0.926 * * *	0.512 * * *
		(-1.83)	(4.62)	(8.11)	(3.92)
	γ 3 nuisance	0.705 * * * 1.028 * * *	1.331 * * *	1.019 * * *
		(6.99)	(9.77)	(9.91)	(8.74)
	β cost	-0.178 * * * -0.124 * * *	-0.180 * * *
		(-22.50) (-14.60)	(-13.92)
	β SQ sex	-0.0611	-0.0813	-0.0878
		(-0.81)	(-0.92)	(-0.20)
	β SQ organic	-0.497 * * * -0.665 * * *	-1.218 * *
		(-5.38)	(-6.29)	(-2.92)
	β SQ donation	-0.506 * * * -0.663 * * *	-0.750
		(-3.50)	(-4.08)	(-1.71)
	β SQ income	-0.413 * * * -0.570 * * *	-0.992 *
		(-5.52)	(-6.49)	(-2.54)
	β SQ rural	-0.278 * * * -0.384 * * *	-0.404
		(-3.69)	(-4.36)	(-1.19)
	LogL	-7407.72 -6467.23	-3422.87
	N	464	464	464
	N × S	4176	4176	4176
	t statistics in parentheses. * p < 0.05, * * p < 0.01, * * * p < 0.001

For example,[START_REF] Pervez | Ecology and biological control application of multicoloured asian ladybird, harmonia axyridi s: A review[END_REF] argued in 2006 that H. axyridis's "field releases in tropical countries like India should be encouraged; however, only after a thorough analysis of the cost and benefit of beneficial and non-target fauna". Nowadays, it seems highly debatable that new introductions of this insect should be encouraged given its invasive character.

Note that, in our case study, several factors can affect the level of pesticides: the use of ladybirds as a

We used NGene which is a reference in this field.

Given the priors, NGene has basic information on respondents' preferences which allows a more targeted design, yielding more information for a given number of choices.

This is proposed in the NGene design.

This project is supported by Agropolis Fondation under the reference ID 1001-001.


H Huot

M O Simonnot

F Watteau

P Marion

J Yvon

P De Donato

J L Morel

Early transformation and transfer processes in a Technosol developing on iron industry deposits

Large surface areas covered with man-made materials are subject to pedogenetic evolution. However, pedogenetic processes in the resulting Technosols are seldom fully assessed. This work was conducted to identify and characterize the processes occurring on deposits of industrial technogenic materials.

A former settling pond of the iron and steel industry was chosen where a forest has established since termination of the industrial activity, approximately 50 years ago. A 2-m deep pit was opened, and a series of layers of the soil profile were sampled. Macro-and micro-structure were studied, and soil samples were analysed for structural, chemical and mineralogical assessment (chemical analyses, X-ray diffraction, infrared and Mössbauer spectroscopies, scanning and transmission electron microscopies coupled with energy dispersion spectrometry).

Results showed that the profile was composed of a succession of sub-horizontal layers arranged in two groups according to their structure and composition linked to the composition of the industrial effluent. Group 1 was composed of iron-, carbonate-and aluminosilicate-rich layers exhibiting a compact structure. Group 2 contained manganese-rich layers with a friable structure. Pedogenetic processes of various intensities were detected at different depths. Besides an accumulation of organic matter at the surface, transformations of minerals were recorded all along the soil profile, with weathering, leaching and precipitation of new phases. Phenomena occurred primarily in specific zones, such as cracks and interfaces between two layers. In conclusion, the soil maintained characteristics of the original industrial material and displayed several stages of pedogenesis, which were controlled chronologically by climatic and biological factors.

Introduction

In densely populated areas, human pressure has become the main factor of soil pedogenesis. Human activities affect soil formation through the generation of technogenic parent materials and changes in soil evolution conditions [START_REF] De Kimpe | Urban soil management: a growing concern[END_REF]. Technosols are a soil group of the World Reference Base for Soil Resources (WRB; IUSS Working Group WRB, 2006) taking into account soils wherein properties and pedogenesis are dominated by their technogenic origin [START_REF] Lehmann | Technosols and other proposals on urban soils for the WRB (World Reference Base for Soil Resources)[END_REF][START_REF] Rossiter | Classification of urban and industrial soils in the World Reference Base for Soil Resources[END_REF]. They include a large range of soils and especially those developing on industrial or urban wastes (landfills, sludge, cinders, mine spoils and ashes).

In a similar way to natural bedrock, technogenic parent materials originating from man's activities may undergo a set of physical, chemical and biological processes under the influence of pedogenetic factors: climate, biological activity, topography and time [START_REF] Jenny | Factors of Soil Formation[END_REF]. In contrast to most natural environments, pedogenesis is recent, and affects young and heterogeneous materials originating from man's activities. Intense and rapid weathering seems to be a common feature of Technosols when compared with natural soils [START_REF] Zevenbergen | Clay formation and metal fixation during weathering of coal fly ash[END_REF][START_REF] Rossiter | Classification of urban and industrial soils in the World Reference Base for Soil Resources[END_REF][START_REF] Séré | Early pedogenic evolution of constructed Technosols[END_REF]. Little is known about the pedogenetic processes that affect technogenic materials, and pedogenesis is often considered as unimportant because of the short period of development. Understanding the processes of evolution of Technosols would provide useful knowledge about the changes in man-made materials, which may contain toxic compounds, under the influence of the environmental factors and their impact on adjacent environments (water bodies, natural ecosystems) and add to our general understanding about processes affecting soil development.

Different processes have been described in Technosols. Accumulation of organic matter at the soil surface is often reported as the primary pedogenetic process that occurs in them [START_REF] Sourkova | Accumulation of carbon, nitrogen and phosphorus during soil formation on alder spoil heaps after brown-coal mining, near Sokolov (Czech Republic)[END_REF]. Also, solute movement (carbonates, sulphates) as well as changes in structure and hydrodynamics have been shown to occur [START_REF] Zikeli | Initial soil development in lignite ash landfills and settling ponds in Saxony-Anhalt, Germany[END_REF][START_REF] Hartmann | Changes in soil physical properties of forest floor horizons due to long-term deposition of lignite fly ash[END_REF][START_REF] Séré | Early pedogenic evolution of constructed Technosols[END_REF] and specific aggregation phenomena involving mineral and organic technogenic materials have been demonstrated [START_REF] Monserié | Technosol genesis: identification of organo-mineral associations in a young Technosol derived from coking plant waste materials[END_REF][START_REF] Séré | Early pedogenic evolution of constructed Technosols[END_REF]. However, transformations of minerals are rarely considered despite their value as indicators of pedogenesis [START_REF] Uzarowicz | Technogenic soils developed on mine spoils containing iron sulphides: Mineral transformations as an indicator of pedogenesis[END_REF]. In general, investigations about the weathering of industrial materials (metallurgy by-products, incineration residues, smelter-derived particles) are conducted within a context of risk assessment related to pollutant fate and impact. Nevertheless, these studies may also reveal strong mineral transformations of primary phases and the formation of secondary phases [START_REF] Ettler | Primary phases and natural weathering of old lead-zinc pyrometallurgical slag from Pribram, Czech Republic[END_REF][START_REF] Ettler | Natural alteration products of sulphide mattes from primary lead smelting[END_REF].

Pedogenetic processes can be assessed from detailed studies of the soil profile, in comparison with unaltered material parents [START_REF] Van Breemen | Soil Formation[END_REF]. In contrast to natural soils, this approach is more difficult with Technosols because of the unknown initial composition of the source materials (such as industrial sludge), strong heterogeneity (several depositing events) and a short period of pedogenesis (a few decades). Therefore, pedogenesis assessment of Technosols must rely on changes in a large set of properties. First, characterization of the mineral constituents and their transformations, together with historical information are useful tools to trace the industrial processes [START_REF] Vassilev | Mineralogy of combustion wastes from coalfired power stations[END_REF][START_REF] Gregurek | Mineralogical fingerprints of industrial emissions -an example from Ni mining and smelting on the Kola Peninsula, NW Russia[END_REF]. Mineralogical approaches can be used to describe weathering sequences of by-products under natural conditions and to predict their long-term behaviour [START_REF] Yvon | Long-term stability in landfills of Municipal Solid Waste Incineration fly ashes solidified/stabilized by hydraulic binders[END_REF][START_REF] Saffarzadeh | Impacts of natural weathering on the transformation/neoformation processes in landfilled MSWI bottom ash: A geoenvironmental perspective[END_REF]. Finally, analysis of the soil structure at several scales (from profile to micro-structure) may provide a large range of information on the physical, chemical and biological processes occurring in the Technosol [START_REF] Bullock | Handbook for Soil Thin Section Description[END_REF].

A Technosol that developed in a former settling pond of the iron industry and covered by a forest ecosystem was studied as a relevant model to understand the process of pedogenesis better. In a previous examination of this Technosol, bulk chemical and physical properties were characterized [START_REF] Huot | Characteristics and potential pedogenetic processes of a Technosol developing on iron industry deposits[END_REF]. The chemical (large CEC, alkaline pH) and physical properties (low bulk density, large micro-porosity, strong water retention capacity) indicated that the soil was a Spolic Technosol (Calcaric, Laxic, Hydric, Thixotropic, Andic, Toxic) (IUSS Working Group WRB, 2006). A strong vertical heterogeneity in composition was recorded along the profile, resulting from the successive sludge deposits. The structure and composition of materials seemed to be mostly derived from the former industrial processes; however, some indication of mineral weathering and solute transfer were detected in the soil profile.

Here we report efforts to identify and characterize the pedogenetic processes that occurred in the early stages of evolution of this very complex Technosol. General methods were based on the study of the soil constitution at several scales and the characterization of mineral constituents in order to distinguish processes directly connected to the iron and steel industry, and processes which could be attributed to early pedogenesis of the Technosol.

Materials and methods

History of the site and the industrial processes

The iron and steel industry of Pompey-Frouard-Custines (Lorraine, France), situated along the Moselle river, existed from 1872 to 1986 and it produced special and well-known pig iron and steels. In particular, a manganese (Mn)-rich ferroalloy (ferromanganese) was made in one blast furnace from 1922 until the industry ceased [START_REF] Truffaut | La fabrication du ferro-manganèse au haut-fourneau en France, 1875-2003[END_REF].

During pig iron production, the gas leaving the blast furnace contains particulates and so requires cleaning before recycling. Generally, dry cleaning to remove coarser particles is followed by wet cleaning which is commonly performed by spraying water into the gas to capture finer particles. Sludge resulting from wet cleaning is not recycled because it contains zinc (Zn), lead (Pb) and alkali metals that can damage the blast furnace. Therefore, the sludge is often dumped into settling ponds [START_REF] Mansfeldt | Chemical and mineralogical characterization of blast-furnace sludge from an abandoned landfill[END_REF].

In Pompey, the sludge was transported by pipe to the settling ponds situated on an island at the confluence of the Meurthe and Moselle rivers. Generally, dams were gradually built with slag or other materials around ponds during the filling by successive sludge supplies, thereby generating stratified deposits about 10-m deep. The pond in the southwestern part of the island has a surface area of 2.6 ha. The alluvial groundwater table is at 7-8 m from the pond surface. It is assumed that sludge dumping was abandoned in the 1950s. The site was restored after the industry closed for further economic development [START_REF] Schwartz | Le pédologue en milieux industriels et urbains. I. Sols d'une friche industrielle[END_REF]. However, the former settling pond remained unchanged and was colonized by vegetation leading to a forested ecosystem.

Profile description and samplings

A 2-m deep pit was opened in June 2009 in the north-western flat part of the pond (48°46'6.98"N, 6°8'6.47"E) [START_REF] Huot | Characteristics and potential pedogenetic processes of a Technosol developing on iron industry deposits[END_REF]. The pit was in a small clearing covered by herbaceous species and surrounded (more than 1.5 m from the pit) by deciduous woody species (Sambucus nigra L., Populus tremula L., Betula pendula L.). Colours of the different layers of the profile were assessed with the Munsell Soil Color Chart. According to the Référentiel Pédologique [START_REF] Afes | Référentiel Pédologique[END_REF], the soil displayed an A/C profile with a C horizon composed of numerous layers of various colours.

Among the 24 layers visible in the 2-m pit, 12 were selected as representative of the whole soil profile, and, except for the A horizon, layers of the C horizon were chosen for their contrasting colours and structure (Figure 1). Layers were sampled in May 2010 for chemical analyses and mineralogical characterization. Blocks of undisturbed soil samples were also collected using Kubiena boxes (90  60  50 mm) at eight depths, within layers or at the interface between layers (Figure 1). Kubiena boxes with two open faces were slowly inserted into a ledge excavated at the desired depth in the soil. After extraction from the soil with a knife, the boxes were wrapped, secured against any disturbance in a container and transported to the laboratory.

To determine cyanide contents in the soil, samples were collected in March 2004 in an older pit in the north-eastern part of the pond. Four layers were collected at 35-40 cm (corresponding to layer 2), 40-55 cm, 55-70 cm (corresponding to layer 3) and at 70-80 cm (corresponding to layer 4).

Thin sections

Thin sections were prepared from blocks of undisturbed soil. Blocks were dried with acetone and embedded in resin and polymerized at 35° C, and 30 µm-thick sections (50  80 mm) were extracted from each block. Some cracks appeared during drying. A general description of thin sections was made at 8  and in more detail at 60  magnification with a stereomicroscope Leica MZ FLIII (Leica Microsystems AG, Heerbrugg, Switzerland). Conventional descriptions were made following guidelines recommended by [START_REF] Bullock | Handbook for Soil Thin Section Description[END_REF] and [START_REF] Stoops | Interpretation of Micromorphological Features of Soils and Regoliths[END_REF] including the assessment of mineral and organic phases, porosity, micro-structures and pedo-features. Specific structural features were further analysed with a scanning electron microscope JSM J7600F (JEOL, Tokyo, Japan) equipped with an analysis system EDS (20 mm² of SDD type) coupled with a spectrometer WDS INCA (Oxford Instruments, Oxfordshire, United-Kingdom) on some areas of the thin sections after thin carbon coating.

Chemical analyses

The 12 sampled layers were freeze-dried and ground manually with an agate mortar for chemical and mineralogical analyses. Elemental composition was performed by the Service d'Analyse des Roches et des Minéraux (CNRS, Vandoeuvre-lès-Nancy) according to the method described by [START_REF] Carignan | Routine analyses of trace elements in geological samples using flow injection and low pressure on-line liquid chromatography coupled to icp-ms: A study of geochemical reference materials BR, DR-N, UB-N, AN-G and GH[END_REF]. Major elements are reported in the Table 1. Forms of aluminium (Al), iron (Fe), silicon (Si) and Mn were determined according to the methods of [START_REF] Tamm | Eine methode zur bestimmung der anorganischen komponente des gelkomplexes im boden[END_REF] and [START_REF] Mehra | Iron oxide removal from soils and clays by a dithionite-citrate system buffered with sodium bicarbonate[END_REF] by the Laboratoire d'Analyse des Sols (INRA, Arras), as described in [START_REF] Huot | Characteristics and potential pedogenetic processes of a Technosol developing on iron industry deposits[END_REF]. Analysis of total cyanides was conducted on four layers in 2004 according to the standard method described by AFNOR XP X31-430 (2001). Available cyanides, which include cyanide compounds in a solid that can form HCN during the distillation at pH 4 (AFNOR XP X31-430, 2001), were determined on the soil sample collected at 70-80 cm (corresponding to layer 4).

Table 1 Major elements (%) in the 12 selected layers along the Technosol profile. Two groups of deeper layers were defined according to their morphology and structure.

Layer

Layer group

Depth

Major elements /% (w/w) /cm 1 -0-18 Fe : 21.0 C : 14.0 Ca : 8.4 Si : 6.2 Al : 3.6

Mineralogical analyses

X-ray diffraction (XRD) was performed by reflection on randomly dispersed powders, using a diffractometer Bruker D8 Advance (Bruker, Karlsruhe, Germany) with Co Kα radiation (λ = 1,789 Å) in the Laboratoire Interdisciplinaire des Environnements Continentaux (CNRS-UL, Vandoeuvre-lès-Nancy). Diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) was conducted with a Bruker Equinox IFS 55 device (Bruker, Ettlingen, Germany), after dilution in KBr, without preparing pellets, in the Laboratoire Géoressources (CNRS-UL, Vandoeuvre-lès-Nancy). These global characterizations were completed by observations and elemental analyses on six samples (layers 1, 2, 4, 5, 7 and 11) by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) coupled with energy dispersion spectrometry (EDS). Analysis by SEM-EDS was performed on polished sections after vaporization of a thin carbon layer with a SEM S-4800 (Hitachi, Japan) equipped with a EDS Si(Li) diode (Noran, Middleton, USA) and the SEM JSM J7600F. Images were obtained in back-scattered electron (BSE) mode. Analysis by TEM-EDS was carried out on samples dispersed in ethanol and deposited on carbon films supported by Cu grids, using a TEM CM20 (FEI, USA) equipped with a EDS Si(Li) diode (PGT, Princeton, USA) at 200 kV. The microscopy analyses were conducted in the Service Commun de Microscopie Electronique et de Microanalyses (CNRS-UL, Vandoeuvre-lès-Nancy).

The three most Fe-rich samples (layers 1, 2 and 11) were subjected to Mössbauer analysis in the Laboratoire de Chimie Physique et Microbiologie pour l'Environnement (CNRS-UL, Vandoeuvre-lès-Nancy) using a constant acceleration spectrometer and a 512 multichannel analyser, (Halder Elektronic GmbH, Seehausen, Germany), a scintillation detector (Crismantec, St Pierre-lès-Nemour, France) and a 50 mCi source of 57 Co in Rh matrix maintained at room temperature. The velocity was calibrated with a 25 μm foil of α-Fe at room temperature and the centre shifts are given with respect to this reference. Samples were placed in the sample holder and introduced into the cryostat (Advanced Research Systems, Macungie Pennsylvania, USA). After the amount of sample materials had been optimized (10 mg Fe cm -2 ), spectra were computed and fitted by χ 2 minimization using a sum of Lorentzian shape lines as implemented in the Recoil software. Measurements were performed with a velocity range of ±11 mm s -1 . The larger range allowed possible detection of magnetically split patterns from Fe oxides.

Results

Soil structure (from the profile scale to the micro-morphology)

The Technosol profile was composed of a superimposition of sub-horizontal layers of various colours, thickness and structure. At the profile scale, layers were clearly delimited. However, in some cases wavy limits between layers were observed (limit 1/2 or 7'/8) (Figure 2b) and series of cracks (2 to 5-mm wide and a few cm deep) were detected at some interfaces between layers (limit 8/9). In general, cracks were filled with fine materials originating from the layers above (layer 4) (Figure 3c). Roots were present throughout the profile with a varying density according to the layer (Figure 1a). The 20-cm thick surface layer exhibited a granular structure, a brown colour (5 YR 2.5/2) and a large root density (data not shown). Figure 3 Structure in layer 4 (group 1) and at the limits with the surrounding layers (3' and 5) (group 2). Microstructure was observed in a thin section with a stereomicroscope: (a) whole thin section (63-71 cm) with the locations of the detailed pictures, (b) particular structure of layer 3' composed of 100 to 1500 µm particles, (c) crack in layer 4 filled with the finer material from above layer 3', (d) roots in macropores and between two laminae in layer 5 and (e) biodegraded root in macropore under the limit of layers 4 and 5.

Deeper in the profile, light layers with compacted laminar structure (a few mm to 15-cm thick) alternated with dark layers with massive structure (one to 20-cm thick) (Figure 1b). Two groups of deeper layers could be identified. Group 1 (layers 2, 4, 9 and 11) included layers with a laminar structure resulting from the superimposition of millimetric consolidated laminae. They were various shades of grey (10 YR 7/1 to 7.5 YR 4/0), rust (10 YR 5/6 to 5 YR 3/3) and beige (10 YR 8/1-8/2 to 7.5 YR 8/0-8/2). Their composition was dominated by calcium (Ca) or Fe (Table 1). Layer 12 could be linked to this group regarding its composition despite its crumblier structure.

Group 2 was composed of crumbly layers (3, 5, 6, 7, 8 and 10). Most of them (layers 3, 5, 8 and 10) were uniformly coloured black (5 YR 3/1 to 10 YR 2/1), the others showed a succession of black and rust (10 YR 6/4 to 2.5 Y 6/6) laminae (layer 7') or the superimposition of thin laminae (one to 8-mm thick) of rust to beige colours (7.5 YR 3/4 to 10 YR 6/4 in the layer 5 and 10 YR 5/3 to 10 YR 7/2 in layer 8). Manganese was the major element of these layers (Table 1).

Micro-structure analysis showed the laminar structure of the materials of group 2 (Figure 3d). Also, it revealed areas with a particular structure composed of distinct particles (50-1500 µm), especially in layers 3 and 6 (Figure 3b). Layers 5, 7, 8 and 10 exhibited more or less curved sub-vertical cracks with or without fillings (Figure 1b). Black coatings, composed of 0.5-to 3-mm thick black (10 YR 2/1 to 10 R 2.5/2) compacted and brittle materials, covered the faces of cracks in layers 5, 7 and 8 (Figure 4a-d-e). In the latter, a whitish coating (10 YR 6/3 to 6/4) developed inside the cracks and on the faces of the blocky structures that they delimited (Figure 2a). This coating was composed of a fine layer of translucent crystals (100-500 µm) which reacted with acid (HCl 0.05 M) and might be a calcitic coating (Figure 2c). In some places, this formed a fine and delicate beige coating, which was also found in some cracks (5-cm deep) in the underlying layer 9. According to SEM-EDS elemental analyses of layer 7, the black coatings were more enriched in Mn and depleted in Si than the lighter material covered by the coating (Figure 5). The material of the black coatings seemed to diffuse inside the adjacent lighter materials (Figure 5a). This phenomenon was recorded on the rims of the cracks (Figure 4e), around large black nodules and at the limits between two laminae (Figure 4b). Diffusion from the darker layers towards the lighter ones formed black dendrites upward or black droplets downward (Figure 4c-g-h). This effect followed the stratification and its deformation or added to the pre-existing stratification (layer 9) (Figure 4f). Spherical black or rust nodules (50-200 µm in diameter) were present in the lighter layers 4, 7, 9, 10 and 11 (Figure 4c). Their composition was dominated by Mn and they contained also substantial amount of Fe, according to SEM-EDS elemental analyses (layers 7 and 9).

The presence of roots as well as fecal pellets including Oribatid mites provided evidence of significant biological activity in most of the layers (layer 5) (Figure 3e). As expected, activity was more intense in the surface layer than deeper in the profile. The presence of a network of macro-pores (100 to more than 5000 µm in diameter) was also recorded. Roots were often found in the macro-pores or at the limit between two laminae (Figure 3d).

Figure 4 Black coatings in cracks, dendrites and droplets in layers 5, 7 (group 2) and 9 (group 1). Micro-structure was observed in thin sections with a stereomicroscope: (a) crack with black coating crossing over the laminar structure of layer 5: whole thin section, (b) black droplets at the limit of layer 5 and below fine laminar grey layer : detail of the thin section (a), (c) black droplets and nodules in layer 7: detail of the thin section (d), (d) cracks with black coatings in closed loop in layer 7 and laminar structure of layer 7': whole thin section, (e) black coatings in cracks and diffuse black precipitates around: detail of the thin section (d), (f) laminar structure in layer 9 with black figures of diffusion and nodules: whole thin section, (g) black precipitates with downward movement: detail of the thin section and (h) black precipitates with upward movement (dendrites) : detail of the thin section (f).

Figure 5 Observations and elemental map of the black coating in a crack in the layer 7 (group 2). The backscattered electron image (b) and the EDS X-ray map (Al, Si, Ca, Mn and Fe) obtained with SEM-EDS on the rim of a black coating and black nodules around on a thin section of layer 7 observed with a stereomicroscope (a).

Mineralogy

At the profile scale, groups determined according to the morphology were confirmed with mineralogical analysis. Group 1 layers (1, 2, 4, 9, 11 and 12) were dominated by carbonates, aluminosilicate phases and Fe (hydr)oxides in layers 2 and 11 and contained cyanide compounds. The surface layer displayed mineralogy similar to layer 2. Group 2 layers (3, 5, 6, 7, 8 and 10) had a large content of Mn (hydr)oxides, and sulphate phases were recorded only in the deepest layers (7, 8, 9, 11 and 12) (Table 2). X-ray diffraction analyses revealed the weak extent of crystallinity of mineral phases in group 2 layers (3, 5, 6, 7, 8 and 10) (Figure 6). Also, numerous phases exhibited compositional zonings, while others resulted from the association of several phases.

Calcite (CaCO 3 ) was detected in all layers by XRD in variable amounts (Figure 6). Group 1 layers were generally more calcareous than group 2. Layer 8 was an exception, as already reported [START_REF] Huot | Characteristics and potential pedogenetic processes of a Technosol developing on iron industry deposits[END_REF]. Calcite was present as individual crystals or as crystals around another phase (Figure 8a).

O O ox x o X X X x o oX x 2 O O ox o X X X X x 3 x X 4 O O o x X x 5 o o O ox oX 6 X 7 o o O oX o 8 x X x 9 X x 10 x X 11 O O x ox X X X oX o x o x x 12 x x X x x x
Tamm and Mehra-Jackson extractable-Si and Al contents indicated poorly crystalline oxalate-extractable aluminosilicates phases, assigned to 'allophane-like' phases as defined by [START_REF] Huot | Characteristics and potential pedogenetic processes of a Technosol developing on iron industry deposits[END_REF]. Spherical and fibrous aluminosilicate phases were observed mainly in layers 1, 2, 4 and 11 (group 1) and as minor phases in layers 5 and 7 (group 2) (Table 2). Small spheres (100 to 750 nm diameter) of silico-calcic glass had an average Al:Si ratio of 0.5 ±0.1, an average Ca:Si ratio of 0.6 ±0.3 and variable contents of alkaline (Mg) and metal (Fe, Mn) elements (Table 3) . Some phases with a 1:1 Ca:Si ratio were assigned to wollastonite. These glass-like spheres were often surrounded with aluminosilicate phases comprising 50-nm fibrous components (Figure 7). Fibrous phases could correspond to the 'allophane-like' phases. They were more depleted in Ca than the glass-like phases with an average Ca:Si ratio of 0.1 ±0.1 and an average Al:Si ratio of 0.6 ±0.2 (Table 3). Some clay minerals (Fe chlorites, berthierines and kaolinite) and quartz were detected as minor phases by XRD in some layers of group 1 (Figure 6 and Table 2). Iron and Mn oxides and hydroxides had different levels of oxidation and crystallinity as well as various morphologies. Manganese (hydr)oxides were the major phases in layers 5 and 7 (group 2). They appeared as filled spheres (plerospheres, 10-50 µm in diameter) (Figure 8a-c), and in some cases displayed concentric zonings reflecting a change of composition (Figure 8b). The smaller phases (< 5 µm) had a poorly crystalline fibrous structure (Figure 9a). However, some crystalline phases of manganese oxide 2 were observed (Figure 9b) and detected with XRD (peak corresponding to 4.70 Å interplanar spacings) in group 2 layers (3, 4, 5 and 8) (Figure 6). The observed phases were mainly made of MnO 2 and to a lesser extent MnO and also contained observable amounts of Si, Al and other metals (EDS spectra in Figures 8 and9).

Several Fe (hydr)oxides, such as ferrihydrite (5Fe 2 O 3 .9H 2 O), haematite (Fe 3 O 4 ) and goethite (FeO(OH)), were detected by XRD (Figure 6) and Mössbauer spectroscopy (Figure 10a andTable 4) and analysed by SEM-and TEM-EDS (Figure 10c), in particular in group 1 layers (1, 2 and 11). Iron was also present in its metallic form (Figure 10a andTable 4). Plerospheres (25-100 µm in diameter) made of reduced Fe (Fe or FeO) were observed in layer 1 (Figure 10b). Some Fe-and Mnbearing compounds showed a strong compositional heterogeneity and a concentric structure. Several phases were observed with an Fe (hydr)oxide core and a Mn-rich shell.

Table 4 Mössbauer parameters for three layers (1, 2 and 11) along the Technosol profile. Each line corresponds to a Fe-bearing phase or a Fe site with characteristic parameters: isomer shift with respect to metallic α-Fe at room temperature (δ), quadrupole splitting (Δ), hyperfine magnetic field (H) and their relative abundance (RA) and their content calculated with respect from the total Fe content. Spectra were recorded at room temperature. Sulphate phases, such as gypsum, anhydrite and ettringite were detected by XRD in deeper layers 11 and 12 (group 1). Observations revealed also the presence of Ba sulphates in layers 7 (group 2) and 11 (group 1). These phases appeared as automorphous crystals (10-30 µm) and contained small amounts of strontium (Sr). Sulphate phases, such as gypsum, anhydrite and ettringite were detected by XRD in deeper layers 11 and 12 (group 1). Observations revealed also the presence of Ba sulphates in layers 7 (group 2) and 11 (group 1). These phases appeared as automorphous crystals (10-30 µm) and contained small amounts of strontium (Sr).

Total cyanide contents varied along the profile and seemed to be greater in the layers of group 1. Contents were as much as 1179 mg CN kg -1 dried soil in the layer at 35-40 cm (corresponding to layer 2), 435 mg CN kg -1 at 40-55 cm, 113 mg CN kg -1 at 55-70 cm (corresponding to layer 3) and 3445 mg CN kg -1 at 70-80 cm (corresponding to layer 4). In the latter, available cyanides were present at 4 mg CN kg -1 , showing the very poor mobility of cyanide compounds in the soil. X-ray diffraction patterns and DRIFTS spectra indicated the presence of group 1 of potassium zinc hexacyanoferrate(II) nonahydrate (K 2 Zn 3 (Fe(CN) 6 ) 2 .9H 2 O) in some layers. This finding was supported by the presence of a light absorption band between 2094 and 2105 cm -1 on DRIFTS spectra of the layers 4, 9 (Figure 11b), 11 and 12, which corresponds to the stretching band of the triple bound -C≡N in this cyanide compound [START_REF] Rennert | Identification of Iron-Cyanide Complexes in Contaminated Soils and Wastes by Fourier Transform Infrared Spectroscopy[END_REF]. Diffractograms of these layers showed peaks corresponding to 4.06 Å interplanar spacings and, to a lesser extent, 5.41 and 4.51 Å (Figure 11a), which are typical of this cyanide compound [START_REF] Mansfeldt | Identification of a crystalline cyanide-containing compound in blast furnace sludge deposits[END_REF].

Discussion

The Technosol is the result of a series of successive processes, from the deposition and formation of parental materials generated by the iron and steel industry to the early pedogenetic processes (weathering, transfer and accumulation) under the influence of environmental factors for approximately half a century. From analysis of the structure and mineral phases, combined with the knowledge of the industrial processes (particle (trans)formation in the blast furnace, sludge production and sludge discharge, the origin and transformations of the constituents can be inferred and a chronological reconstitution of the formation of the Technosol proposed.

(Trans)formation processes of particles in the blast furnace Some mineral phases in the Technosol could result from the fine particles leaving the blast furnace during the introduction of the raw materials (ores, fuel, fluxes). For instance, the Fe ore formerly used by the steel industry in Lorraine ('Minette') is composed of goethite, Fe-bearing chlorites and calcite [START_REF] Dagallier | Caractérisation minéralogique et microtexturale du vieillissement anthropique du minerai de fer lorrain[END_REF].

However, most minerals are decomposed in the blast furnace and fine particles are (trans)formed by the thermic and reduction processes. The large range of Fe oxides and particularly the presence of metallic Fe in the Technosol could result from the more or less complete reduction of Fe oxides (Truffaut, 1989). At temperatures from 1200 to 1600° C, ore melts and some compounds are volatilized and partly evacuated with gas at the top of the blast furnace. Glass-like phases originating from the fast cooling of a silicate liquid and spherical phases from the solidification of droplets are present in suspension in the gas [START_REF] Vassilev | Mineralogy of combustion wastes from coalfired power stations[END_REF]. The presence of Mn oxide in the Technosol could be explained by the condensation and oxidation of volatilized Mn during upflow in the blast furnace which forms micronic particles (1-10 µm) (Truffaut, 1989). Carbon from the coke and N from the blown pre-heated air react to form hydrogen cyanide (HCN), which is also partly evacuated with the gas.

Formation and settling of blast furnace sludge

During wet cleaning of the gas containing particulate materials , condensing processes continue, and other chemical reactions occur in contact with water and the atmosphere (hydration, carbonation), resulting in mineralogical transformations. For instance, alkali or even more complex cyanides could be formed, such as K 2 Zn 3 (Fe(CN) 6 ) 2 .9H 2 O, which is a typical compound of blast furnace sludge [START_REF] Mansfeldt | Identification of a crystalline cyanide-containing compound in blast furnace sludge deposits[END_REF]. The stratified deposit with an alternation of dark layers rich in Mn (hydr)oxides and lighter-coloured layers dominated by aluminosilicates, carbonates and Fe (hydr)oxides resulted from the settling of successive sludge supplies. Sludge composition varied according to the raw materials and industrial processes, and black layers were probably connected with ferromanganese production. Moreover, other wastes used in the iron and steel industry could have been deposited in the pond.

Signs of evolution processes of the industrial parental materials

The presence of cracks, crossing the laminar structure of some layers, at the limit between two layers suggests that deposition was not a continuous process and there were periods of desiccation between supplies of liquid sludge supplies. The andic properties (low bulk density, large porosity and water retention capacity) developed by these materials [START_REF] Huot | Characteristics and potential pedogenetic processes of a Technosol developing on iron industry deposits[END_REF] favour shrinkage with drying [START_REF] Bartoli | Shrinkage of initially very wet soil blocks, cores and clods from a range of European Andosol horizons[END_REF]. Suspension flows have filled cracks with the material above, and displaced finer particles explaining the particular structure in some areas. Coatings of Mn-rich material or calcite in some cracks reflected solute movements and seemed to be restricted to specific layers or at the interface between two consecutive layers. The presence of Ca sulphates in deeper layers only could result from leaching processes through the soil profile.

Mineral weathering and precipitation of new phases were recorded. Coatings rich in Mn originated probably from the solubilization of Mn and Fe in reduced environments allowing their transport, followed by their precipitation in more oxygenated area (along cracks) as is commonly observed in seasonally flooding soils [START_REF] Richardson | Wetland Soils: Genesis, Hydrology, Landscapes, and Classification[END_REF]. These phenomena may explain the formation of Mn nodules in soil [START_REF] Mckenzie | Manganese oxides and hydroxides[END_REF]. Also, black Mn precipitates present as upward or downward features (dendrites and droplets, respectively) might be evidence of diffusion from the Mn-rich coatings towards the Mn-depleted adjacent materials. Dissolved Mn 2+ might have been transported by mass flow under the action of the gravity or capillarity in the vicinity of the cracks.

Among secondary phases are carbonates as suggested by calcite coatings. Calcite was formed from hydrolysis of Ca oxides or calcic silicates and carbonation in contact with water and atmospheric CO 2 . Similarly, Fe released from primary phases contributed to the formation of new phases, such as ferrihydrite [START_REF] Schwertmann | Iron Oxides[END_REF] or complexes with cyanides and then K and Zn to form K 2 Zn 3 [Fe(CN) 6 ] 2 .9H 2 O. Also, weakly crystalline fibrous aluminosilicates probably originate from Al and Si released by weathering of glass-like phases. We can assume that sludge pH was initially high and controlled by the reaction of Ca and alkali oxides, and then decreased in the presence of atmospheric CO 2 to reach its current value of 8 [START_REF] Huot | Characteristics and potential pedogenetic processes of a Technosol developing on iron industry deposits[END_REF]. A high pH (> 9) favoured the dissolution of both Al and Si from silicate glass and industrial aluminosilicates, whereas a decrease in pH caused the precipitation of secondary aluminosilicates [START_REF] Zevenbergen | Clay formation and metal fixation during weathering of coal fly ash[END_REF]. Zeolites could also be formed in such an environment from Si released at high pH [START_REF] Sauer | The occurrence and distribution of various forms of silica and zeolites in soils developed from wastes of iron production[END_REF].

After the termination of sludge discharges, organisms have colonized the deposit, which is currently covered by a forest. As a consequence, organic matter has accumulated at the top of the soil profile, and a thick organo-mineral horizon has developed with the mixing of organic and mineral phases resulting from the industrial process (glass, metallic Fe compounds). Biological activity (roots, fauna) is observable down the profile but is more intense in the surface layer. Roots are present in all layers and develop preferentially in the cracks and macro-pores or at the boundary between two layers.

Proposed outline of pedogenesis on the iron deposit

Physical and chemical processes occurred preferentially at the top of the layers or at the interface of two consecutive layers. This suggests that pedogenetic change was initiated during the pond filling, which left sludge layers under the direct influence of the climate. At this time, materials in the pond underwent dramatic changes in their surrounding water environment. Wetting-drying cycles, producing shrinkage and oxidation, were probably the driving factors of dissolution and precipitation, which developed primarily in the cracks. Also, during this period of intense change, the high pH contributed to accelerated weathering of industrial aluminosilicate phases. This first step of weathering depended on the time span between two successive sludge supplies.

The spreading of a new sludge layer with a different composition caused infilling of the cracks by fine material and could induce a new cycle of reduction reactions along with the diffusion of solutes, leaving traces at the interface between two layers and around the crack coatings. Gradual burying of the sludge layers modified the physical and chemical conditions (lower oxygenation, subsidence), and reduced the influence of climate in the deeper layers. Hence, the initial physical and chemical pedogenetic processes initiated during the pond filling either stopped or were substituted by new processes (diffusion, root activity). In the absence of roots, drying in deeper layers is unlikely because of the large water retention capacity of these materials [START_REF] Huot | Characteristics and potential pedogenetic processes of a Technosol developing on iron industry deposits[END_REF]. So, some mineral transformations or mass and solute transfers seem to be evidence of an early stage of pedogenesis, producing 'fossilized' pedogenetic structures with no further changed occurring.

Later, biological activity became the new driving factor of pedogenesis of thisTechnosol, particularly in the upper layers. Roots as well as associated microorganisms and fauna have colonized the deeper layers taking advantage of the previous steps of weathering, such as in cracks. Organisms may play a role in the weathering and evolution of the material as they contribute to the development of flow pathways, modify chemical ambiance (pH, redox potential) in the rhizosphere and create organo-mineral associations.

Conclusions

The profile of a Technosol developing on a deposit of blast furnace sludge, and currently supporting a forested ecosystem, was investigated by the analysis of the structure at different scales and the mineral phases. This approach, combined with the knowledge of the industrial operations and of pedogenetic processes occurring in 'natural' soils, enabled us to infer the origin and transformations of the constituents and to propose a scenario for the Technosol formation.

The investigations provided evidence of an evolution of the industrial parental materials following several stages with areas of more intense changes (interfaces between layers, cracks). An early stage, and driven by drying-wetting cycles and changes of physico-chemical conditions (redox, pH) occurred during the deposition of sludge and produced shrinkage, mass and solute transport and mineral transformation. Then, gradual burying changed the conditions further, reducing the influence of climate as driver of pedogenesis. The current changes are driven mainly by biological processes, as is evident in the accumulation of organic matter in the upper layer. A study of the role of roots, which are present throughout the soil profile, is underway.

Tracing the formation of Technosols provides information on pedogenetic processes occurring in these soils and helps us to understand their functioning and to predict their evolution better. Characterization of the anthropic constituents and knowledge of the specificity of pedogenetic processes in such soils appeared to be relevant criteria for the establishment of a functional classification of Technosols.

Figure 1

 1 Figure1The Technosol profile with the 12 selected layers: (a) variation in layer limits and structure along the Technosol profile and (b)A/C profile showing the 12 selected layers with the location of samples for thin sections.

Figure 2

 2 Figure 2 Structure in layer 8 (112-134 cm) (group 2) featured by cracks with calcitic coatings: (a) crack in layer 8 with black coating and calcite deposit inside the crack, (b) calcite coatings in layer 8 and the wavy limit between layers 7' and 8 and (c) calcite coatings comprising crystals. cc : calcitic coating ; bc : black coating ; wl : wavy limit.

Figure 6 X

 6 Figure6X-ray diffraction patterns for 6 selected layers (1, 2, 4, 5, 7 and 11) along the Technosol profile. Layer 1 is the organo-mineral surface layer. Layers 2, 4 and 11 belong to group 1, and layers 5 and 7 to group 2. Ak: akermanite ; Cal: calcite ; Cy: cyanide compound ; Fe: metallic iron ; Go: goethite ; Gyp: gypsum ; Hm: hematite ; Lc: lamellar compound of the chlorite or kaolinite groups ; Mg: magnetite ; Ox-Mn: Mn oxide (MnO 2 ); Qz: Quartz.

Figure 7

 7 Figure 7 Aluminosilicate phases observed by TEM-EDS in layer 4 (group 1). Silico-calcic glass-like spherical phases (a) surrounded by fibrous crystalline aluminosilicate phases (b).

Figure 8

 8 Figure 8 Manganese-bearing phases on polished sections in layers 5 and 7 (group 2) observed by SEM-EDS: (a) plerospheres of Mn (hydr)oxides surrounded by a aluminosilicate matrix and CaCO 3 crystals surrounded a Mn-bearing compound (layer 5), (b) plerosphere of Mn (hydr)oxides showing concentric zoning (layer 7) and (c) plerospheres of Mn (hydr)oxides containing Al, Si and metals (spectrum (d)) surrounded by weathered products (layer 7).

Figure 9

 9 Figure 9 Manganese-bearing phases displaying different levels of crystallinity and forms observed by TEM-EDS: (a) fibrous and poorly crystalline Mn (hydr)oxide containing Al, Ca, Si and metals (layer 1) and (b) crystalline Mn oxide of MnO 2 type (d=4,70 Å) (layer 5) (group 2).

  Figure 10Iron-bearing phases detected in layer 1 (0-18 cm): (a) Mössbauer spectrum recorded at room temperature showing the presence of Fe (hydr)oxides, metallic Fe, and of Fe(II) and Fe(III) probably in silicates, (b) plerosphere of Fe oxides (FeO) observed by SEM-EDS and (c) haematite (Fe 3 O 4 ) observed by TEM-EDS.

Figure 11

 11 Figure 11 Details of XRD patterns: (a) and FTIR spectrum and (b) highlighting the presence of a ferrocyanide compound K 2 Zn 3 (Fe(CN) 6 ) 2 .9H 2 O in the layer 9 (135-140 cm) (group 1). The d spacings in Å are indicated on the peaks corresponding to this compound.

Table 2

 2 Recap chart of the detected and observed mineralogical phases in the 12 selected layers along the Technosol profile. O: phase frequently observed by SEM-EDS and/or TEM-EDS; o: phase rarely observed by SEM-EDS and/or TEM-EDS; X: major phase detected by XRD, DRIFTS and/or Mössbauer spectroscopy; x: minor phase detected by XRD, DRIFTS and/or Mössbauer spectroscopy.

		aluminosilicates	Mn (hydr)oxides		Fe (hydr)oxides		carbo-nates		sulphates		other phases
	layer	allophane-like	silicate glass	phyllosilicates/zeolites	silica -feldspars	poorly crystalline	Mn (hydr)oxides	crystalline Mn (hydr)oxides	ferrihydrite	haematite	goethite	magnetite -spinels	wuestite	calcite	gypsum	anhydrite	ettringite	barite	metallic Fe	cyanides
	1

Table 3

 3 Average elemental composition of aluminosilicate spherical and fibrous phases. Average content and standard deviation were calculated from the TEM-EDS analyses performed on n phases in layers 1, 2, 4, 11 and to a lesser extent, layers 5 and 7.

Acknowledgements

This work was conducted within the framework of the GISFI program (www.gisfi.fr) and supported by the Région Lorraine, Institut Carnot Energie Environnement Lorraine (ICEEL) and ArcelorMittal Real Estate France (AMREF). The authors wish to thank Patrick Charbonnier and Emmanuelle Depré (AMREF) for their advice and help, Jean-Claude Bégin, Adeline Bouchard and Romain Goudon (LSE) and Cindy Messana and Lucas Charrois (GISFI) for the sampling and the production of thin sections, Mustapha Abdelmoula (LCPME) for Mössbauer spectroscopy analyses, Odile Barrès (LEM) for IR spectroscopy analyses, Guirec Ollivier (LEM) for XRD analyses, Jaafar Ghanbaja, Sandrine Mathieu and Ludovic Mouton (SCMEM) for SEM-EDS and TEM-EDS analyses, M.C. Rouillier (LEM) for the cyanide analyses and Camille Morel for her work on mineralogical characterization.