A Lecomte

R Salmon

M Purvis

S Prusek

Glowny S Bock

Instytut Gornictwa

L Gajda

J Dziura

Kompania Weglowa

Sa Muñoz Niharra

( Geocontrol

Case studies and analysis of mine shafts incidents in Europe

Entry to mine workings is normally gained by means of vertical shafts or horizontal or inclined tunnels called adits. Other mining objects such as fan drifts and wheel pits are often associated with mine shafts. Such mining objects may or may not have been filled, wholly or partially, or otherwise sealed to prevent entry when the mine was abandoned. Nowadays mine entries are usually adequately protected on abandonment to prevent accidental ingress. Many earlier mine entries remain open, however, and may pose a threat to human safety. Within the framework of MISSTER (Mine shafts: improving security and new tools for the evaluation of risks), a European RFCS project (Research Fund for Coal and Steel), a selection of representative cases of mine shafts incidents was reviewed. This work was carried out by INERIS (France), GEOCONTROL (Spain), University of Nottingham and Mine Rescue Service Ltd (United Kingdom), Central Mining Institute and KWSA (Poland). The experience accumulated through this work will allow a fuller determination of risk scenarios associated with mine shafts.

INTRODUCTION

MISSTER is a European Project within the framework of RFCS (Research Fund for Coal & Steel). It is a three year research project that aims to develop innovative costeffective tools to:

• enhance the understanding of hazards that may affect mining shafts and • optimize safety conditions for active shafts maintenance and disused shaft treatments. The project partners include research institutes, universities and mining companies from France (INERIS), United Kingdom (University of Nottingham and Mines Rescue), Poland (Central Mining Institute and Kompania Węglowa), Germany (DMT) and Spain (GEOCONTROL). An important work was carried out to collect representative case history data concerning shaft instability in Europe. Rather than being comprehensive of all events, the case data are representative of a range of potential behaviour in European conditions. In all coal mining areas, several cases of incidents or accidents relevant to mining shafts are related. These may occur both during and after mining operations (during design, mine extraction, after closure). The design, monitoring, and maintenance of mine shafts all incur significant costs during the operational lifetime of a mine. In addition, at the end of mining operations, closure of shafts often constitutes an sizeable expensive, depending on the treatment technique applied.

Although fatalities associated with past incidents are rare, they constitute a important constraint on mining operations as well as on land planning. Collapse of shaft linings or of shaft walls (particularly in unconsolidated superficial deposits) and collapse of shaft fillings (especially if partially filled or founded on wooden staging part way down the shaft) pose an obvious threat to life and safety as well as to any buildings or structures in the vicinity. In unconsolidated superficial deposits, a funnel-shaped crater may form which is considerably more extensive than the area of the original shaft.

METHODOLOGY

In order to provide a representative analysis of cases relative to incidents directly involving mine shafts, a collection of incidents has been researched by each partner for their respective country. To obtain the most representative cases, a list of the incidents which can be induced by the presence of a mine shaft has been created. The different kinds of incidents and accidents considered are:

a collapse of the filling material column

In the case of a shaft, collapse of the shaft filling material is a rough and dynamic remobilisation of the filling material which propagates down abruptly and rushes into the old works, generating a collapse of the surface if no structure or protection was installed at the head of the shaft. Collapse of the shaft filling material occurs generally after a slow degradation of the conditions of the filling material, in particular during mine water rising within the shaft column after exploitation. These progressive modifications end in the establishment of a limit balance and the intervention of an aggravating factor can be enough to activate the dynamic mobilization of the column. Some collapses of the shaft filling material result from the formation of a void in the column during the dumping of filling material. These voids can result from the blocking of materials within the shaft column. Examples: Cases of shafts n°8 and n°8 bis, at Noeux-les-Mines in France, illustrate this kind of collapse. A detailed analysis is presented in Section 3. The case of Lancashire n°6 upcast shaft, in England, also illustrates this kind of incident. This 4.1 m diameter circular shaft, around 200 m deep, was filled in 1927 with soft material. In January 2007, a void about 4 m diameter at 20 m depth was observed from ground level. Brick lining remained suggesting a collapse of filling material that did not lead to the rupture of shaft head (Figure 1). 2. a failure of the shaft head Many shafts were closed by old techniques presenting no guarantee of sustainability. Some old mine shafts were closed by a single on-surface or near-surface wooden platform, eventually completed by filling material on the shaft head but leaving the whole column empty. The case of West Midlands Shaft, in England, illustrates this kind of situation. This 3 m diameter circular shaft, 144 m deep, suffered a collapse of ground approximately 3 m diameter and 2.5 m deep in a car park area in 2000. Collapse became apparent when surfacing failed over a void due to weight of a car (Figure 2). Two occupants in the car escaped with only minor injuries. Some structures, such as more recent concrete slabs, can break when they are subjected to excessive loads (motor vehicle transit, building…), or when surface ground materials on which they rest fail.

This kind of failure is illustrated by South Yorkshire shaft, in England. This 3 m diameter circular shaft, 170 m deep, was filled and closed in 1919. A depression in a wooded land at the location of a recorded shaft was reported on 1 March 2005. Three features on the site were observed. Firstly, a feature appeared that was shaft like, some 3 m in diameter, and the fill within the feature appeared to have sunk by about 1m with parts of brick lining exposed. Secondly, there was a ground collapse some 1.5 m diameter and 1.2 m deep. Both of the two features are associated with the area around the South Yorkshire filled shaft. Thirdly, a brick structure some 4 m square projecting 600 mm above ground level with 150 mm thick concrete slab on top was found. It is believed that this is the surface cap for the shaft. According to the desk investigation, it was found that the shaft was 170 m deep and was filled in 1919.

While excavating the shaft top a brick lined inset was uncovered. The Inset roof was collapsed which probably caused the depression of land.

a failure of the shaft lining

The most frequent failures of the shaft lining result from a decrease of its resistance or from an increase of the pressure of grounds. When the strength of the lining is exceeded, the lining (bricks, stone blocks, concrete, cast iron and steel) deforms and eventually breaks. It may collapse in the shaft with part of the surrounding ground. The decrease of the mechanical properties of a lining material with time is an inevitable phenomenon resulting from the progressive ageing of the constituent materials. Shaft backfilling operations made without sufficient precautions may also damage linings. Stones or blocks dumped from the surface opening are subjecte to free-falls of several hundreds of meters and can sometimes damage sections of the lining. Also, closure structures badly or insufficiently designed may sometimes stress the shaft lining. Examples:

-Coal shaft V, Knurow-Szczyglowice colliery, in Poland. A detailed analysis is presented in Section 3. -Shaft n°1 and n°2 at Barony Colliery Ayrshire Scotland (England): sunk between 1906 and 1912, shaft n°1 and n°2 are rectangular (resp. [6.4 m x 3.3 m] and [4.9 m x 3.3 m]), wood lined and 633 m deep. In 1960/62, modification of ventilation systems took place. N°1 shaft was originally used as the Downcast / coal winding until 1962. Following completion of works at the shaft head, it was re-commissioned as an upcast. N°2 shaft was an Upcast. After conversion of ventilation system, shaft n°2 collapsed following deterioration of wood lining (Figure 3), that may have been caused by contact with upcast air of high humidity. 4. a failure of deep closure structure located into the shaft galeries Galleries or mining works with connecting shafts may have been closed before the shaft was backfilled in order to avoid spreading of the backfilling material in the galleries. Structures generally consist of walls in hollow blocks, metal dams or concrete plugs. For old mining shafts, galleries may have been closed with remaining items but without particular design. Because of various causes, for example concrete segregation or poor lining design, a rupture of this deep closure structure can occur allowing the filling material to spread into the galleries, resulting in a collapse of the shaft. Monitoring of shaft n°1 and n°2 (Vieux Condé, France) backfilling has illustrated this problem. Shaft n°2 in Vieux-Condé (France) is a 5 m diameter circular shaft, 501m deep. It was filled in 1982 after the construction of a concrete plug at the bottom of the shaft. Other stages of shaft were closed by various undefined remaining elements. The follow up of the stowing shows that filling material volume is similar to shaft column volume (i.e. the shaft was completely filled). In 1987, the first 305 m of shaft n°2 were observed empty from the surface. Also illustrating collapse of filling material column, this incident suggests that filling material spread through shaft galeries because of poor design of their closure.

a specific focus on surface development

Occasionally, a brutal collapse may occur in the vicinity of a mining opening due to the constraints applied on surface. Several causes are likely to lead to these instabilities of the ground level. For example, an overload on the surface, in the immediate surroundings of the shaft head, such as storage of exploited material, heavy vehicles or construction. Vibrations generated by explosions or blasting near the shaft head or by intense circulation of very heavy vehicles can also cause instability.

Examples:

-West Midlands shaft (England), introduced previously.

-Low Hall n°7 (New Zealand Pit) at Abrams Lancashire, in England. The shaft is circular (3.66 m) and 305 deep and was sunk circa 1885. All mining via the shaft was abandoned in 1919 (1924?) although the shaft was retained for ventilation until 1932 (1931?) when it was filled with a reported 8,120T of debris. In April 1945, some 13 years after the mine shaft had been filled the locomotive was shunting a train of 13 loaded coal wagons (full length 86m) when the ground beneath the line cratered and collapsed (Figure 4). The last wagon entered the crater pulling the rest of the train and eventually the locomotive with it. A few days later, when the dust cleared, the front of the locomotive could be made out 30m below pointing upwards. Not later than the first days after the aforementioned event the craters united into one that continuously grew. What caused the catastrophe was the inrush of a quicksand strata into the shaft. The strata found a way into the shaft in a leak of the shaft lining at the connection of the ventilation drift to the shaft. This caused loosening of ground under the drift and its vertical displacement by about 2,0 m (Figure 6). The catastrophe of shaft Bolesław took place on 6 September 1975. On the western side of the shaft a crater came into being that uncovered foundations of the shaft bank house. After several hours the increasing crater caused a collapse of the shaft bank building which leaned against the headframe's angle struts breaking them and causing a collapse of the headframe (Figure 7). The event was characterised by a very dynamic course and lasted merely 15 hours. The primary cause of the accident was a quicksand inrush into the shaft at a depth of 24 m. An increased outflow was observed during the nightly shaft inspection before the catastrophe and a vertical fracture of the lining was located below the outflow point. As a result of falling out of an concrete gutter element a 0,8-m long and 0,2-m wide vertical fissure came into being throughout the whole thickness of the shaft lining. Although a provisional packing had been placed in the gap in lining, made of ventilation fabric and planks, a considerable and violent increase of the gap in the lining was observed after a short time since it began, along with an intensive outflow of sand and water. As a result of water influence and changes in load exerted on the shaft lining the latter began breaking along a considerable length. The quicksand inrush caused that it was necessary to fill the shaft at a depth of from 6,0 m to 160,0 m.

a risk of gas release

The presence of harmful or potentially explosive gases (monoxide and carbon dioxide, methane…) in old mining works can result from: a concentration of gas in the rock which is released into cavities generated by the mining; the decomposition or the chemical weathering of materials or products which remain within the mine. Shaft may constitute a preferential flow path from mine working up to the surface for gas. The release on the surface can occur during the exploitation, but also during the phase of filling the void after the end of the works (the gases migrating to the surface by piston effect). These gases can migrate to the surface according to various phenomena: thermal variation, due to the difference between gases' temperature or openings altitude; variations of the external atmospheric pressure: gases dilate in period of decline of the outside barometric pressure. On the contrary, in case of increase of the external pressure, the air rushes into the mine; rise of water levels: under its effect, gases are pushed upward through the openings of access. The level of the underground aquifer can vary according to the seasons or the precipitation and induce slow or rough rises of gas. Example: Coal shaft Barrois at Creutzwald, in France: this 4 m diameter shaft is 512 m deep. Closed in 1988, it was equipped with various device in order to monitor gas migration during and after mine water rising. The monitoring since 2005 shows that gas migration (CH 4 , CO 2 ) between mine working and surface is mainly governed by variations of pressure. When atmospheric pressure decrease, shafts flow out because pressure in mining voids is larger and differential pressure is sufficient [START_REF] Lagny | Gas flow mechanisms and mine gas emissions in the Lorraine coal basin before, during and after mine water flooding[END_REF].

CASES

Two detailed cases are presented in this paper. The first case illustrates the collapse of the filling material column (failure scenario 1 from above), which is one on the most frequent scenarios found. The second case illustrates a collapse due to the rupture of shaft lining (scenario 3) leading to the shaft head rupture (scenario 2).

COLLAPSE OF THE SHAFT FILLING MATERIAL -COAL SHAFT N°8 AND N°8 BIS, NOEUX-LES-MINES, FRANCE

LOCATION AND CHARACTERIZATION OF THE SHAFT(S)

Pithead of shafts n°8 and n°8 bis is located on the territory of the municipality of Verquin (North region of France, Coal mine closed in 1990). Both shafts n°8 (main shaft) and 8 bis were dug in 1899 and opened in 1901. The distance between the two shafts is 40 m (Figure 8). Considering a density of 1,7 t / m 3 to for backfilling material (schists and ashes), the expected equivalent tonnage required to backfill shaft n°8 is 23,000 t and the shaft n°8 bis of 14,800 t, that is a total tonnage of 37,800 t.

GEOLOGIC AND HYDROGEOLOGIC CONTEXTS

The cross section of shafts head shows the following succession of near surface grounds:

DESCRIPTION OF THE INCIDENT

The follow-up of stowing indicates the following quantities:

1968/69 shaft n°8 backfilling :

o Tonnage of schists: 11,900 t (equivalent volume: 7,100 m 3 ) ;

o Tonnage of ashes: 3,600 t (equivalent volume: 2,200 m 3 ).  Total volume of 9,300 m 3 (that is 67 % of the theoretical volume)

1968/69 shaft n°8 bis backfilling:

o Tonnage of schists: 8,900 t (equivalent volume: 5,300 m 3 ) ;

o Tonnage of ashes: 2,500 t (equivalent volume: 1,500 m 3 ).  Total volume of 6,800 m 3 (that is 76 % of the theoretical volume) The actual poured tonnages are much less than the theoretical volumes. On November 24th, 1999 (30 years after shafts backfilling), it was noticed that shafts n°8 and n°8 bis had unrammed. The level of backfilling materials were measured at a depth of 45 m for shaft n°8 and 186 m for shaft n°8 bis. Note that on November 2 nd , 1987, approximately 20 years after the backfilling, a complement of backfill material was made for both shafts: 9 m 3 of backfill material were added to shaft n°8 and 13 m 3 to shaft n°8 bis. The small volume of missing material in shaft head, indicate that it is a classic phenomenon of progressive and residual settlement of backfill material. On the other hand, decrease of 1999 measured levels, rough and of great amplitude, cannot be the result of the only phenomenon of collapse of backfill material.

PROPOSITION OF ANALYSIS

The historic curves deducted from the follow-up of backfill data show sharply the appearance of void formed from the first works of stowing. Figure 9 and Figure 10 show a sensitive and constant distance between the level of backfill material measured in the column of shafts and the level equivalent to the volume of the dumped backfill material. The first one is upper than the second indicating the presence of one or several voids in the column of shafts. Let us note that shafts were not deinstalled before the stowing and the presence of metallic structures within the column of shafts can ease the creation of backfill material vaults. the adjustment of the level of the backfill material by filling of the void created previously;

the failure of the system of closure of one or several stations the departure of backfill material in one or several corresponding galeries.

The volume of backfill material unrammed in the column of the shaft n°8 bis is equal to the volume of missing backfill material during the stowing (2,100 m 3 opened for 2,100 m 3 missing). The volume of backfill material unrammed in the column of the shaft n°8 is less than the volume missing of backfill material during the stowing (814 m 3 unrammed for 4 528 m 3 of missing backfill material). Even in the hypothesis where backfill material does not dump in galeries, the risk of unramming of the backfill material within the column of the shaft n°8 is not to be excluded long term basis. The case of shafts n°8 and n°8 bis illustrates the risk of unramming due to the creation of void within the column of shafts during the phase of stowing.

RUPTURE OF THE SHAFT LINING AND SHAFT HEAD -COAL SHAFT V, KNUROW-SZCZYGLOWICE COLLIERY, POLAND

LOCATION AND CHARACTERISATION OF THE SHAFT(S)

Pithead of shaft V is located on the territory of the municipality of Knurow in Poland. The ventilation shaft V was sinked to the depth of 326. The shaft has a diameter of 6.0 m and contains 5 stations: Up to a depth of 41.5 m the shaft has a brick lining with a thickness of 0.5 m -0.9 m and below a concrete lining with a thickness of 0.3 m -1.3 m. The water inflow to the shaft sump was below 35 l/min.

GEOLOGIC AND HYDROGEOLOGIC CONTEXTS

The geological cross-section around shaft V encompasses Quaternary formations

DESCRIPTION OF THE INCIDENT

On 4 September 2008 at 4.35 o'clock a catastrophe took place which resulted in shaft lining damage up to a depth of circa 70 m, and afterwards the shaft was spontaneously filled with overburden soil material. This caused that a large crater came into being at the surface that in turn caused damage of building facilities present in its impact zone. The crater had a diameter at the ground surface about 60 m, a depth of around 11 m and an estimated volume of about 30,000 m³. Horizontal range of fracture zone at the ground surface affirmed on 4 September 2008 amounted to 67 m.

ANALYSIS

The primary cause of the accident at the shaft was damage to its lining at a depth of 61 m -67 m. The damage was a consequence of:

1.

Irregular mining repeatedly performed in the neighborhood of the safety pillar of the shaft which influenced hydrogeological conditions which in turn destroyed building-engineering stability of the groundlining system.

Crater area

2.

Poor technical condition of the lining of shaft V.

The dimensions of the collapse are exceptionally great compared to other shaft head collapses. This is inducing by the nature of ground surface materials surrounding the shaft head. The quaternary formations are constituted by arenaceous clays with interlayers of sand that is to say a great fraction of low cohesive material more than 18 m thick. The angle of stability of such a material is very low and may be affected by possible surface or near-surface water circulation.

Considering the characteristics of the surface collapse, the equivalent angle of stability of ground surface material is around 15° which is coherent with the nature of geological surface materials.

The measures to eliminate consequences of the catastrophe were undertaken right after it occurred. Firstly building emergency stoppings were set in order to make the ventilation stable. At the next stage 2 m thick isolation-and-pressure-resistant stoppings were built using mineral binders located in the shaft insets vicinity at levels 350 m, 450 m, 550 m and 650 m. The space between theses stoppings and the shaft fill was filled with an ash-and-water mixture using the hydraulic-filling installations existing in the colliery. Empty spaces in the shaft section where the lining damage took place up to the crater bottom were filled with a binder characterised by compression strength of not less than 15 MPa. The spaces were filled after building stoppings at levels 450 m and 350 m. The filling material was supplied through holes drilled from the ground surface in the direction to the shaft at 10 m distance one to another. Before they set to injection, an exploration borehole was drilled to assess the crater's range and scope of damage. Locations of the injection boreholes and the exploration hole are presented in Figure 14. The fine graining and fluidity of the binding material ensured good penetration between the protruding elements of the headframe, large-dimension reinforcedconcrete elements and building debris. The compression strength allowed obtaining high parameters of the monolith set. The fill of binding material after setting became a plug that effectively stopped and stabilised the above lying shaft fill material. At the second stage (Stage II) the crater was filled with a ca. 1 m thick layer so as to completely cover protruding elements of the steel headframe. The material used was a binding material with a compression strength of not less than 10 MPa, which, after setting, allowed light building machines to ride on it. The layer allowed using of mechanised equipment during demolishing and planting the building debris at the third stage. The third stage (Stage III) included further filling the crater up to the ground surface by means of a mixture of building debris (stemming from demolishing) and a binding material with compression strength of at least 5 MPa. Moreover all fissures that came into being in the vicinity of the crater were filled with the binding material used at the second stage. The fourth stage (Stage IV) was a form of reclamation, at which the crater was covered with a layer of clay slate up to a height of 1.5 -2 m in the central part of the crater with a slope in the direction from the middle to the outside of the crater so as to make precipitation waters to run outside the reclaimed area.

At the end stage of the work a borehole with a diameter of 200 mm was drilled along the shaft centre line up to a depth of ca. 75 m in order to observe settling of the material in the shaft. Moreover the mine workings in the locality of shaft V at level 250 m were filled with a material with compression strength of min. 10 MPa through boreholes drilled from the surface.

CONCLUSION

Mine shafts, during or after mining operation, may induce risks for operational staff or people and buildings in their vicinity. This paper details two historical cases illustrating three scenarios associated with mine shafts: collapse of backfilled shaft column and failure of a shaft lining leading to a surface collapse. These cases enable the understanding of key parameters in the securing process of shaft, or the evaluation of risks associated with old shafts, choice of backfilling material nature, follow up of backfilling process, ageing or deterioration of lining, impact of ground surface geology on shaft head collapse extension. Many other incident cases underline other key parameter.

Cross exchange between mining countries of mine shafts incidents should be developed in order to help mining operators to better anticipate mine shaft closure constraints. In post mining contexts, it constitutes a reference list of possible scenario for a better long term risks evaluation.

Figure 1 :

 1 Figure 1 : Collapses of LancashireNo.6 Upcast Shaft (Source: UK Coal Authority).

Figure 2 :

 2 Figure 2 : Collapse of ground in the car park area (Source: UK Coal Authority)

Figure 3 :

 3 Figure 3 : N°2 Shaft following Collapse (Source: MRSL)

Figure 4 :

 4 Figure 4 : Infilling Shaft Post Collapse (Source: MRSL)

Figure 5 :

 5 Figure 5: the collapsed shaft at road between Brithdir and Tirphil (Source: UK Coal Authority)

Figure 6 :

 6 Figure 6 : The crater in the neighborhood of shaft "V" (Source: GIG / KWSA) -Coal shaft BolesŁaw, Bobrek-centrum colliery (Poland). Sunk from 1906 to 1910 to the depth of 779 m, this shaft is 6.4 m diameter circular. The geological cross-section around shaft Bolesław encompasses formations of the Quaternary (represented by sands and clays from 0,0 to 63,0 m), Tertiary (mostly formed of limestones and dolomites from 63,0 to 114,0 m) and Carboniferous (represented by clay slates, arenaceous shale, sandstones and coal from 114,0 to 779,0 m). The catastrophe of shaft Bolesław took place on 6 September 1975. On the western side of the shaft a crater came into being that uncovered foundations of the shaft bank house. After several hours the increasing crater caused a collapse of the shaft bank building which leaned against the headframe's angle struts breaking them and causing a collapse of the headframe (Figure

Figure 7 :

 7 Figure 7 : View of the collapsed headframe (Source: GIG / KWSA)

Figure 8 :

 8 Figure 8 : Location of shafts n°8 and n°8 bis (Source: INERIS) They were intended for the extraction of thin coal veins. The concerned veins are about ten, rather flat and regular, with a dip of 30-35°. The total production of the site was 14,5 Mtons. The closure was pronounced in 1968, and their backfilling began in 1968 and ended in 1969. Shaft n°8 is a circular 100 m deep shaft with a regular diameter of 4.8 m (that is 13,800 m 3 ). It contains 13 stations. Shaft n°8 bis is a circular 600 m deep shaft with an irregular diameter ((3,6 m from the surface to depth 102 m, then 4,1 m from depth 102 to 539 m, and finally 4.2 m from depth 539 to 600 m) that is around 8,900 m 3 ). It contains 14 stations.Considering a density of 1,7 t / m 3 to for backfilling material (schists and ashes), the expected equivalent tonnage required to backfill shaft n°8 is 23,000 t and the shaft n°8 bis of 14,800 t, that is a total tonnage of 37,800 t.

  From 5.15 m to 31.71 m From 5.05 m to 31.47 m chalk with flint From 31.71 m to 55.17 m From 31.47 m to 62.10 m

Figure 9 :Depth

 9 Figure 9 : backfill level evolution -Shaft n°8from 01/07/68 till 17/01/69

  5 m from May 1972 to May 1973. In the period from March 1985 to May 1986 the shaft was sinked to the final depth of 632.05 m.

  (from 0.0 to 18.4 m), Tertiary formations (from 18.4 to 165 m) and Carboniferous formations (from 165 to 632.05 m). The Quaternary formations are represented by arenaceous clays with interlayers of sand. The Tertiary formations with a thickness of about 120 m mainly occurring in a form of hard-plastic clays are prone to swelling under water influence. At depths from 73 m to 84 m the clays are interbedded with gypsum and marls. Below in an interval from 142 m to 146 m and 161 m to 165 m (i.e. up to the Carboniferous top) fine-grained sandstones, arenaceous dusts with interbeddings and interlayers of water-bearing dusty sand with a small thickness and prone to become liquid. The Carboniferous formations are composed of strata of argillaceous shales, arenaceous shales and sandstones, among which coal seams with a thickness of up to 4.5 m occur. A fragment of geological cross-section along shaft V is presented in Figure 12. It represents the geological setting in the area of the catastrophe.

Figure 12 :

 12 Figure 12 : Geological cross-section in the area of catastrophe occurrence

Figure 13 :

 13 Figure 13 : General view of the scene of the catastrophe of shaft V from the south (Source: GIG / KWSA) Displacement of ground into the shaft caused its filling. The shaft inset workings were also filled with ground material at the following levels: Level 650 minset opening was filled over a length circa 30 m, Level 550 m -inset opening was filled over a length circa 50 m, Level 450 m -inset opening was filled over a length circa 16 m, Level 350 m -inset opening was filled over a length circa 10 m, Level 250 mno data as the level was earlier abandoned.

Figure 14 :

 14 Figure 14 : Schematic illustration of the crater resulting from the catastrophe of shaft V and its fill The crater was filled in four stages. At the first stage (Stage I) the crater was filled up to a height of 6 m above gathered water level with a fine-grained binding material with a compression strength of not less than 15 MPa and a fluidity of 150 ÷ 160 mm.

  Figure 15 and Figure 16 present results of work performed at Stage II and III.

Figure 15 :

 15 Figure 15 : The load-bearing layer at the crater -5 May 2010 (Source: GIG / KWSA)

Acknowledgements

The authors wish to acknowledge the contributions of partners of MISSTER European project, which made this paper possible. Thanks also goes to the UK Coal Authority for providing access to its database of mine shafts within the UK.


INERIS, L Cauvin

Combined video and laser camera for inspection of old mine shafts

For the cases where the location of a shaft is known but not its fundamentals characteristics, INERIS has developed a combined video and laser camera to face with problems of characterization of body of shafts or underground cavities.

The system is able to product videos, pictures, punctual manual measures, and automatic measure cycles to establish cross-sections, profiles and contour lines as well as the estimate volume of voids in dry or flooded cavities. For inspection of shafts, developments are within the framework of MISSTER 1 project (RFCS, Research Fund for Coal and Steel). The work is principally based on the development of the second camera for flooded voids. The development of the data analysis systems to obtain direct results like cross section and also obtain a direct geo-referenced 3D point cloud to fit into existing GIS is based on field's tests in old shallow mines.

STATE OF THE ART

European mining industries and local authorities are dealing with risks and harmful effects due to underground extraction sites. After mine closure, in the "post-mining" period, mining sites may indeed generate consequences that may affect people and goods located in the vicinity of mining works. One of the main issues is linked with mining works located near the surface (< 100 m). This is notably due to the fact that shallow works often correspond to very old mining period with very high sensitivity to long term mechanical stability. Today, these disused mines may become dangerous. Currently, most of the systems used to inspect old mine shafts or underground cavities which can be reached by borehole are based on modified video cameras for water wells. Their most important drawbacks are:

An important electrical consumption due to lighting The weight of the system for deep shafts (which implies to fix it in a vehicle) A low viewing distance Low quality of video and pictures

No possibility to target upward with camera To estimate size and orientation of the underground voids, actual systems are based on manual measures, 3D Laser scanning systems in dry voids or sonar in flooded voids. Their most important drawbacks are: implementation difficulties for 3D Laser systems and sonar Only punctual measures for manuals systems Thus, to obtain a complete state of a void, different systems are required what increases length and inspections costs. This developed tool does not replace high accurate systems like 3D scanners which product high density point cloud (with thousands of measure points) but must be specific enough for a good initial diagnosis of an underground void or shaft stability.

MAIN CHARACTERISTICS OF THE PRODUCT

INERIS has developed a specific camera to face with problems of characterization and localization of old underground cavities or old mine shaft when a direct inspection is not possible or is difficult for safety reasons. This camera can reach cavities from the surface through a borehole or can inspect directly the inside body of shafts. The objective of INERIS was to develop a multipurpose tool suitable in most of the shallow cavities we have to inspect. The general specifications of the product were:

Built in 3 parts (cameras, winder on a trolley, remote control unit) to be transportable in a small van, the total weight is less than 100 kg Based on two interchangeable cameras (for dry and flooded voids) Can be used directly on its own wheel (photo 1), usable in a house in case of inspection of a shaft underneath a house, (the trolley of the winder was built to get through in standard house door) Implementation by one or two no specialist operator Independent power supply (small generator, 2000 VA) Cameras had to be waterproof, dustproof and shockproof The system had to be able to product videos, pictures, punctual manual measures, and automatic measure cycles to establish cross sections, profiles and contour lines as well as estimate volume of the void in dry cavities. Most of the shallow cavities INERIS has to inspect are situated in metallic ores or stone quarries which are rarely concerned by the risks of explosion and inflammation of gas mine. Thus, the orientation of the probe is fixed by a gyroscopic device to face with the problem of the use of a magnetic compass in metallic ores and it was not built to operate in explosive atmosphere.

SPECIFICATIONS OF THE CAMERAS

The first camera (photo 1) is built to work in dry condition or in accidental immersion (<100 kPa). It requires a drilling of 125 mm diameter.

Photo 1 -camera for dry voids

The lightening is composed of 12 ultra high intensity white LED fixed in the body of the camera. The rotating head can move in 360° in the azimutal plane and 155° in elevation (zenith). The head position is located in three directions in reference with the body camera by pitch and roll sensors and a gyroscopic device. The video camera and the laser distance meter are situated in the rotating head.

The second camera (photo 2) is built to work in flooded condition (max <14 kPa) like in some old mine shafts. It requires a drilling of 100 mm diameter.

Photos 3 and 4: two examples of inspection of a shaft directly from the winder on its wheels Photo 5 -inspection of a cavity through a 200 mm diameter nude borehole directly from the van Photo 6 -inspection of a cavity through a 140 mm diameter tubed borehole directly from the van

The second case is by using a suspended pulley or a tripod to guide the probe in the center of a larger shaft or when the shaft or the borehole cannot be reached with the van or the trolley.

When the use of a tripod (photo 7) or a deviation pulley is needed, the reachable depth is directly affected by the distance between the winder and the centering system.

Photos 7 and 8 -Inspection of an inclinated shaft through a 125 mm diameter borehole, the distance between the winder (in the van

) and the tripod is about 80 m.

EVALUATION OF THE OPTIMAL OR ACCEPTABLE WORKING CONDITION OF THE PROBE

In all case, the minimum access size of a void is 100 mm. The maximum depth which can be reached is about 140 m. When the diameter of the access in the shaft or in a void is more than 140 mm and the void is dry, the system (based on camera 1) is able to product video and pictures, manual laser measures and automatic laser measures (3D point-cloud).

When the diameter of the access is between 100 and 140 mm and the void is dry, the system (based on camera 2) is able to product video and pictures and manual laser measures in an azimutal plan.

For an access between 100 and 140 mm and a flooded void, the system (based on camera 2) is only able to product video and pictures.

The depth of the void is established by a mechanical counter, coupled with an electronic counter which measures the length of cable paid out by the winder. The 0 value of the depth counter is fixed by the operator. If the winder cannot be positioned on the top of the void, the reachable depth is directly affected by the distance between the winder and the centring system.

DATA AND VIDEO ANALYSIS

Using the control software, the operator can produce a full report during inspection. Whenever an anomaly is encountered, he can choose a description of the fault from the list proposed (to which he can make additions according to his particular needs).

A digital photograph (photos 9 and 10) of the void is then taken automatically by the video acquisition card and printed in the report.

Photos 9-example of digital picture taken by the acquisition card

Our objective was to make visualization and analysis in GIS. Currently, the 3D point cloud is exported in software like ENCOM DISCOVER 3D® (figure 2) and MAPINFO® (figure 3). Finally, after positioning of the borehole or the shaft with GPS, the result is projected directly on a map in the GIS to verify the goods on surface situated in the vicinity it can be also used to product hazard and risk map.

FIELD TESTS: EVOLUTIONS OF THE SYSTEM

The current developments are carried out along two axes.

The first part of development concern old shaft characterization.

SHAFTS CHARACTERISATION

Figure 2 -

 2 Figure 2analysis of point cloud in DISCOVER 3D Figure 3evaluation of the sizes of the void in MAPINFO

  France (INERIS), United Kingdom (University of Nottingham and Mines Rescue), Poland (Central Mining Institute (GIG) and Kompania Węglowa (KWSA)), Germany (DMT) and Spain (GEOCONTROL). The actual developments are part of a work package including INERIS, GIG and KWSA whose objectives are the design, the construction and field's test of probes, to deal with the characterizations of old mine shafts. These tests are at the time in progress and are based on the second camera. The second part of the development concern INERIS activities to face with problems of old abandoned shallow mines mainly with the estimations of the sizes and volumes of voids.

  Tests are realized in the state of MISSTER project. It is a European Project within the framework of RFCS (Research Fund for Coal & Steel). It is a three years research project that aims to develop innovative cost-effective tools to:Enhance the understanding of hazards that may affect mining shafts Optimize safety conditions for active shafts maintenance and disused shaft treatments The project partners include research institutes, universities and mining companies from

MISSTER : MIne Shafts : improving Security and new Tools for the Evaluation of Risks.

Photo 2 -camera for flooded voids

The body of the camera is totally cylindrical. The rotation of the head in only an azimutal plane (360°) is located in direction in reference with the camera's body and by a gyroscopic device. The video camera and the laser distance meter are situated in the rotating head between 2 directives ultra high intensity white LED. A second onboard nose cone camera used to view the borehole with an additional white LED light source is situated in the front of the body.

USE CONDITIONS

The first case is the inspection of cavities and shaft from the surface to 140 m deep when the winder is directly at the top of the shaft (photos 3 and 4) or at the top of a borehole (photos 5 and 6).

Photo 10example of digital picture taken by the acquisition card

The second part of the software is built to automate measure cycles (max 1800 measuring points at each cycle) of the laser distance meter (figure 1). This 3D scanning process products a data file containing series of 3D coordinates, what we call a 3D point cloud. A 3D point cloud of less than 10 000 points cannot be correctly exploited in specific 3D analysis softwares like Polyworks®(InnovMetric Software). In any case, the use of such specific software requires particular abilities.

OLD SHALLOW MINES CHARACTERISATION

In these cases the voids are generally reachable by a borehole. The current development based on field's tests of the data analysis systems aims to obtain direct results like cross section and also direct geo-referenced 3D point cloud to fit into existing GIS directly by the operator. The first results of the field's tests of our camera were not in accordance with our expectations because of the swaying of the camera due to inertia during automatic rotation in a void. The maximum number of point measured was only 800 and not 1800 as predicted. The solution could be to create a new type of cycle to increase the number of 3D point. In order to solve this problem, the proposal is to change the automatic measure cycle. In present, the unfolding of a measure cycle is:

The elevation is fixed at one value (increment each 5°) Measure during a 360° rotation of the head (the head need to be stop at each measure) The modifications of the software are based on the observation of inertia of the head of the camera during a measure cycle. The new measure cycle we propose is the following:

The rotation (azimutal) is fixed each 3 or 5° Measure during the elevation of the head (increment each 3 or 5°) A manual measure cycle will also be developed in order to product a point cloud based on manual pointing of the rotating head of the camera. This version is currently in development and will be tested in April or May 2012.

Somme other modifications resulting from the field's tests are proposed. For example, the addition of a stabilized power device in order to protect data acquisition in case of loss of the electric power supply by.


C Lagny

R Salmon

Z Pokryszka

INERIS S Lafortune

Impact of mine closure and access facilities on gas emissions from old mine workings to surface: examples of French iron and coal Lorraine basins

Closure methods and techniques of mine shafts located in the iron Lorraine basin, in the Lorraine and in North-East coal basins are quite different.

For the first, they are associated with adits. Some are closed by a simple grid to avoid entrance in mine workings but gas entrance and exit are allowed. Coal shafts are secured and can be equipped with a vent to enable mine gas outflow in specific conditions.

Measurements stations were installed on mine accesses to monitor mine gas parameters (oxygen, carbon dioxide and methane volumetric content, radon volumetric activity, flow velocity, gas temperature and differential pressure) and external parameters (temperature and barometric pressure).

The results show that gas flow can be regulated mainly by temperature gradient between external atmosphere and mine workings (in iron mines) or by barometric pressure (in coal mines). Gas emissions from iron mines may require extra securing protocol that prevents population exposal to noxious gas.

Introduction

Scientific publications show that gas flows from old mines are regulated by various parameters. [START_REF] Grabowski | Emissions gazeuses à partir des vides miniers dans le bassin ferrifère lorrain[END_REF] highlighted the link between external temperature and direction and intensity of gas flow from adits of an old iron mine located at Moyeuvre-Grande town (Lorraine iron basin East of France). The atmospheric pressure does not have any significant influence. On the contrary, [START_REF] Hall | Is minewater a source of hazardous gas ? IAEG[END_REF], [START_REF] Burrell | The influence of minewater recovery on surface gas and water discharges in the Yorkshire Coal Field[END_REF] have written that old coal mines are affected by atmospheric pressure possibly leading to dangerous situations (noxious gas exposure). Indeed, a drop in atmospheric pressure leads usually to an outflow of mine gas. The closing of mine accesses, mine gas characteristics and gas flow mechanisms are important to understand and prevent a dangerous situation. This paper deals with different French old mines that have already flooded:

• Two coal basins: in Lorraine (East of France) and in the North and Pas-de-Calais region (North of France). • One iron basin located in Lorain.

The risks encountered with gas mine depend on the exploited ore but usually consist of explosion, inflammation, intoxication, radiation exposure or asphyxia. The risks of explosion and inflammation are usually related to coal mines. Some basins were safely closed because mine shafts configuration and treatment made possible gas emission control. It is not always the case. The different data collected and their interpretations are presented hereafter.

Context of coal basins and iron-ore basin

2.1

The Lorraine and North and Pas-de-Calais coal basins

The Lorraine coal basin

This basin presents variations in surface altitude (200 to 400 m NGF in La Houve concession). Coal extraction was made from shafts due to the depth of the coal seams (more than one hundred meters). The number and the location of the shafts are known. At the end of the exploitation in late 1990's, early 2000's, dewatering was stopped and the accesses were closed (with concrete plug or flag). Some were equipped with a vent1 to enable mine gas exit in specific conditions. Some parts of the basin are under gas capture stations influence. This is not the case in "La Houve" concession. Two accesses were instrumented: one shaft (Barrois) and one venting borehole (SDEC OUEST 1). This basin does not present significant variations in altitude. Coal extraction was made from shafts due to the depth of the coal seams (only one adit is known). The number of the shafts is high (near 600) but their location is not always known. The majority of the accesses are filled and closed and some shafts can be equipped with a vent. Some boreholes can have been drilled in the basin and a great part of the basin is under the influence of gas capture stations. Dewatering was stopped after the end of exploitation.

2.2

The Iron Lorraine basin This study only concerns the north basin. This basin is a part of the iron basin of Briey-Longwy-Thionville (see Fig. 2) which is divided in three main parts, separated by main faults. These parts are hydraulically independent and dewatering was stopped at different dates. Iron mine shafts are associated with adits. The iron north basin presents variation in surface altitude (from 355 to 441 m NGF for shafts and from 210 to 330 m NGF for adits). Some mine shafts and adits are closed by a simple grid to avoid human entrance in old workings but gas entrance and exit are allowed. Generally, shafts are located on plateau (they usually constitute topographically high points) while adits are located on hillsides (they usually constitute topographically low points). These accesses are open and protected only by a grid at the entry. They do not show any significant resistance to gas outflow or inflow.

Monitoring

A monitoring system was installed in order to understand gas flow mechanisms and to evaluate mine gas composition and its intensity and evolution with time for the different old mines.

At each site, several parameters were measured:

• External parameters such as barometric pressure and atmospheric temperature.

• Gas parameters such as gas velocity and flow direction, O 2 , CO 2 , and CH 4 gas content, radon volumetric activity, gas temperature, differential pressure 2 . Fig. 4 shows a typical measurement station. 2 Difference between mine pressure and atmospheric pressure; if positive, the gas should flow out from the mine; if negative, atmospheric gas flows in the mine. This behaviour is typical and has already been observed in other coal basins where the mine voids represent a significant volume and where the accesses between mine and daylight are essentially closed shafts which are not under gas capture influence. This is the case of the east part of the North and Pas-de-Calais coal basin. We can observe for all accesses (equipped with a vent) and for venting boreholes that the differential pressure shows variations that are the opposite of those of the barometric pressure [START_REF] Lagny | Modélisation de la pression du réservoir post-minier et des débits de gaz passant par les exutoires du secteur Est du bassin houiller du Nord et du Pasde-Calais[END_REF]. The absolute pressure measured at the top of the vents is therefore practically constant, except when a severe barometric depression passes through. This behaviour may be illustrated by Fig. 7 which shows ten minutes data acquisition intervals monitoring of the barometric pressure and of the differential pressure on a decompression borehole S11 (called Taffin) at the Vieux concession over a period of ten days. We can observe that the variations in the barometric pressure induce differential pressure fluctuations between -550 and +2000 Pa. The old mine voids that make up a closed system (shafts that are mostly closed off and/or filled-in and a lack of clearly open floor-surface accesses) operate as follows: the variations in barometric pressure lead to fairly significant differential pressure variations. As a result, the barometric pressure serves as the main parameter driving mine gas towards the surface.

In the Lorraine coal basin, rising of water resulted in the filling of mine voids. The last stage of flooding immediately leads to a fall in differential pressure that then vanishes.

A progressive fall in mine gas content (methane and carbon dioxide) is observed while the oxygen content is increasing. The variations of atmospheric pressure have no more effect on the differential pressure. Mine gas exit is stopped at the instrumented accesses. Gas shaft temperature change, is influenced by seasons. CO 2 volumic gas content presents seasonal variations like radon volumetric activity which can reach respectively 2 % and 5000 Bq/m 3 . Water overflowing did not change shaft gas flow behavior and characteristics. Similar remarks can be made on Algrange adit, but a small decrease in CO 2 gas content can be observed with dewatering. On the contrary, radon volumetric activity is stable and stays around 9000 Bq/m 3 . According to the season and for each access, gas flow direction is changing due to the variations of atmospheric temperature. Noxious gas is emitted to the surface through the grids of the accesses and preferentially during summer conditions for François shaft, Algrange adit and Ottange incline.

Iron basin

Conclusions

5.1

Coal basins For all instrumented accesses (equipped with a vent and for venting boreholes), the differential pressure shows variations that are the opposite of those of barometric pressure [START_REF] Lagny | Modélisation de la pression du réservoir post-minier et des débits de gaz passant par les exutoires du secteur Est du bassin houiller du Nord et du Pasde-Calais[END_REF]. This behavior is typical and has already been observed in other coal basins where the mine voids represent a significant volume and where the accesses between mine and daylight are essentially the shafts like in the North and Pas-de-Calais and Lorraine coal basins. On the studied area, uncontrolled outflow of mine noxious gas was avoided thanks to the shaft closure and venting boreholes realisation. These shafts and the boreholes are usually isolated by an enclosure or an enclosing wall to prevent human intrusion. A notice warns people of the danger eventually encountered.

Iron basin

The way of closure in the iron basin is not the same as in coal basins. The rising of water does not have a significant effect on the gas flow and on the influence of external temperature. This observation highlights that natural thermal convection plays a significant role in the creation of the gaseous flow between the mining reservoirs and the surface. This phenomenon is due to the temperature difference between the external atmosphere and the old workings. In the old workings, the temperature is usually almost constant (it is estimated between 12 and 14°C, in this case), contrary to the atmospheric temperature, whose value varies according to the annual seasonal cycle. Also, a surface topography over the mining reservoir and the closure way of the accesses seem to facilitate thermal convection. During summer, a part of the atmospheric air in contact with the upper old workings (openings badly closed or exploitation fractures) is subjected to a progressive cooling. An increase in the bulk density, due to the effect of cooling, causes gas migration towards the lowest parts of the old emerged mine workings. For G7 adit located at Moyeuvre-Grande town in Moselle department (East of France), during summer, under-oxygenated and noxious gas is emitted [START_REF] Grabowski | Emissions gazeuses à partir des vides miniers dans le bassin ferrifère lorrain[END_REF]. It was necessary to put a deflector (Fig. 12) which deflects the gas flow and an enclosure to avoid human exposure to this gas due to its composition [START_REF] Tauziède | Mise en sécurité de la galerie G7 à Moyeuvre-Grande (57). Résultats de l'installation d'un déflecteur d'air[END_REF].

Figure 1 :

 1 Figure 1: Photographs of the vent SDEC OUEST 1 (left) and BARROIS shaft with a vent (right).

  North and Pas-de-Calais coal basin

Figure 2 :

 2 Figure 2: Position of selected instrumented openings in the north part of the iron-ore basin of Lorraine.

Figure 3 :

 3 Figure 3: François shaft (left) and Algrange adit (right).

Figure

  Figure 4: Monitoring station.

Figure 5 :

 5 Figure 5: Variations in gas and radon content at Barrois shaft from 09/10/2007 to 10/10/2007.

Figure 6

 6 Figure6shows that the variations in differential pressure levels are opposite to the variations in barometric pressure. During the investigated period, the differential pressure variations hit approximately 450 Pa.

Figure 6 :

 6 Figure 6: Variations in differential pressure (measured at Barrois shaft) and in barometric pressure.

Figure 7 :

 7 Figure 7: Barometric pressure, differential pressure and absolute pressure over time on the S11 boreholes at the Vieux Condé concession.

Fig. 8

 8 and Fig.9are parts of the plots of the data registered at François shaft.

Figure 8 :

 8 Figure 8: CO 2 volumic gas content and temperature recorded at François shaft.

Figure 9 :

 9 Figure 9: Radon volumetric activity and temperature recorded at François shaft.

Figure 11 :

 11 Figure 10: Gas flow exchange during summer.

Figure 12 :

 12 Figure 12: Deflector and enclosure set up at G7 adit exit.

A vent or a venting borehole (when not put on a shaft) is a pipe of a given height and diameter which passes through the plug or the floor of a shaft and which is in connection with the old mine workings. It is fitted with a flame arrestor and a non-return valve. The non-return valve should inhibit any intake of atmospheric air and is set to only open if the difference in pressure between inside of the pipe and outside exceeds

Pa (for Lorraine coal basin).

Acknowledgements

The work is a part of a research programme carried out by INERIS for the Ministry in charge of mines and for GISOS (Groupement de recherche sur l'Impact et la Sécurité des Ouvrages Souterrains) -Research Group for the impact and safety of underground cavities.


Manier Nicolas
email: nicolas.manier@ineris.fr

Bado Anne

Resve Amélie

Delalain Patrice

Aguerre-Chariol Olivier

Pandard Pascal

Effect of non-ageing and ageing ceria nanoparticles suspensions on fresh water micro-algae

When assessing the hazards properties of nanomaterials in the environment, the main research challenges are numerous. Firstly, determining if nanomaterials are more or less toxic than the bulk forms of the same materials and the extent to which toxicity is governed or influenced by the physico-chemicals properties of the nanoparticles. Secondly, it appears necessary to study the effect of nanomaterials and nanoparticles throughout their life cycle including both initial forms and physico-chemically modified form (i.e. aggregated or agglomerated forms) resulting from an ageing process.

Our work focused on the effect of commercial ceria nanoparticle (nCeO 2 ) suspensions, towards freshwater micro-algae assessing the effect nCeO 2 suspensions with different agglomeration/aggregation state obtained by using an artificial ageing process. Both ageing and non-ageing nCeO 2 suspensions were fully characterized using dynamic light scattering (ZetaSizer, Malvern Instruments) or laser diffraction (MasterSizer, Malvern Instruments) and transmission electron microscopy (TEM). In addition, the interaction between NPs and algae were investigated using flow-cytometry and environmental scanning electron microscope technique (E-SEM).

The results obtained showed that the algae growth inhibition was similar after exposure to nonageing or ageing nCeO 2 suspensions. The results obtained from flow-cytometry and E-SEM proved that the ceria NPs are able to tightly entrap the algae cells, which could in part contribute to the effect recorded. Those results also support the fact that aggregation or agglomeration has a few influences when focusing on the standardized algae ecotoxicity test. Moreover by comparison to our previous studies performed with other ceria suspensions, it was shown that the primary particle size and consequently the particle surface area is a relevant parameter in assessing the ecotoxicity of nanoparticles.

Key words: Ceria nanoparticles, Pseudokirchneriella subcapitata, agglomeration state, ageing suspensions

Introduction

When assessing the hazards properties of nanomaterials to the environment, the effect of nanomaterials and nanoparticles including both initial form and altered form should be addressed. Thus, the present work aimed at investigating the effects of a commercial ceria nanoparticle composite suspension (nCeO 2 ) toward freshwater algae. The ecotoxic effects were investigated using both non-aging (freshly prepared) or aging (artificially altered) nCeO 2 suspensions. The standardized green algae Pseudokirchneriella subcapitata was used for the algae growth inhibition experiments. All the suspensions were fully characterized using dynamic light scattering (ZetaSizer, Malvern Instruments) or laser diffraction (MasterSizer, Malvern Instruments) and transmission electron microscopy (TEM). In addition, the interaction between NPs and algae were investigated using flow-cytometry and environmental scanning electron microscope technique (E-SEM).

Nano-ceria suspensions

Commercial nCeO 2 were obtained as 248 g/L stable suspension in water. A primary particle size of 10 nm was reported by the supplier. For the ecotoxicity tests, an initial nCeO 2 suspension (25 mg/L) was prepared by dilution of the commercial suspension into the algae growth media (OECD 201 growth media). This suspension was artificially aged under light and slow magnetic stirring for 3 days. Another freshly (nonageing) nCeO 2 suspension was prepared 15 minutes prior to the experiment using the same dilution protocol but without ageing process. For the ecotoxicity tests, nCeO 2 suspensions with nominal concentrations from 0.195 to 25 mg/l (8 concentrations) were then prepared by dilution of the ageing and non-ageing initial nCeO 2 suspensions in the algae growth media. The average specific growth rate of P. subcapitata in each concentration was calculated each day up to 72h for both ageing and non-ageing nCeO 2 suspensions.

Characterization of non-ageing and ageing suspensions

Investigation of the initial nCeO 2 suspensions in algae growth medium showed that ageing and nonageing suspensions mainly differ in term of agglomeration/aggregation state. As illustrated by figure 1, the non-ageing suspension were mainly composed of small nCeO 2 agglomerates or aggregates around 30 nm with some of them up to 500 nm. By comparison, the ageing suspension showed large and loose agglomerated particles up 10 µm (Figure 1).

Algae growth inhibition test

The results obtained clearly show that nCeO 2 are ecotoxic towards micro algae. Moreover, the effects recorded were similar after both ageing and non-ageing nano-ceria suspension. We have calculated EC 50 values of 1.4 mg/L and 1.8 mg/L for the non-ageing and the ageing ceria suspensions, respectively. This observation suggested that whatever the agglomeration state, the algae growth inhibition is similar when focusing on the algae growth inhibition test. Moreover, compared with our previous works with other nano-ceria suspensions [START_REF] Manier | Behaviour of ceria nanoparticles in standardized test mediainfluence on the results of ecotoxicological tests[END_REF], our data support the view that the primary particle size and consequently the surface area might be an important parameter to take into account, as previously suggested by Van Hoecke et al. [START_REF] Van Hoecke | Fate and effects of CeO 2 nanoparticles in aquatic ecotoxicity tests[END_REF].

Nanoparticles-Algae interaction

The interaction between ceria NPs and algae were investigated by flow-cytometry and using E-SEM) technique. The cytogram distributions showed an increase in cell complexity with increasing nCeO 2 concentration which suggests a potential adsorption onto the cell wall or a potential internalization into the cell. Without demonstrating the NPs internalization in cells, the results obtained from E-SEM confirmed that the ceria NPs are able to tightly entrap and wrap the algae cells (figure 2). These observations suggest that the algae ecotoxicity could, in part, be due to this close interaction by limiting the transport of metabolites and nutrients across the cell wall, or by inducing cell membrane disruptions and oxidative stress [START_REF] Rogers | Physico-chemical behaviour and algae toxicity of nanoparticulates CeO 2 in freshwater[END_REF].

Figure 1 :

 1 Figure 1: Particle size distribution and TEM micrographs of the non ageing (a) and ageing (b) nano-ceria suspensions in the OECD algae growth medium (25 mg/L).

Figure 2 :

 2 Figure 2: E-SEM micrographs of Pseudokirchneriella subcapitata exposed to nCeO2 suspension (a) and in the control media without nCeO2 (b)


Pierre Huguier
email: pierre.huguier@ineris.fr

Nicolas Manier

Camille Meline

Pascal Pandard

Pascale Bauda

Huguier Pierre

Manier Nicolas

Meline Camille

Pandard Pascal

Bauda Pascale

Applicability of the Caenorhabditis elegans survival, growth and reproduction test to assess the effects of biosolids used in agriculture

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

In the context of environmental sustainability, more and more materials are intended to be valuable instead of being wasted. Modern high productivity agriculture has led to an impoverishment of nutrients and organic carbon in field soils, and as a consequence plants nutrition complements like fertilisers or biosolids have to be used to keep high yield. These complex materials are a source of nutrients for plants; they could also be a source of pollutants depending on their origin. As these materials are applied in field, they can be potentially harmful to soil fauna, plants and humans. So there is a necessity to assess the environmental effects of these materials before field use.

In this study, environmental effects of biosolids were assessed on the survival, growth and reproduction of a microfauna organism of the nematoda family, Caenorhabditis elegans, following the standardized protocol ISO 10872 [START_REF]Water quality -Determination of the toxic effect of sediment and soil samples on growth, fertility and reproduction of Caenorhabditis elegans (Nematoda)[END_REF]. This widespread organism was chosen due to the possibility of testing soils and mixtures of soil and biosolids as well as water extracts of these matrices.

Performing tests with the ISO standard showed that protocols for sediment and water testing were clearly defined. These tests also demonstrated that the standard could be improved for testing soils and mixtures of soil and biosolids. Indeed, according to their respective water holding capacities (WHC), addition of growing media and food leads to a two phase system (e.g. water on top of the matrix). This can be explained by two reasons: soil moistening in the standardized protocol is based on soil dry weight and the food volume added to the wet sample is too important in comparison with the mass of the tested soil.

In order to harmonize test conditions and to allow comparison between results for soils and/or soils mixed with biosolids, optimization of the protocol aspects mentioned above were carried out: 1) a range of suitable percentage of water holding capacities was determined, to base sample moisture on WHC instead of dry weight; 2) food was inoculated at a higher concentration, to reduce the added volume. Then, different biosolids (limed sludge, manure ...) were tested using this protocol. An example for a limed sludge is given in this extended abstract.

Optimization of the test protocol concerning soil water input

Tests were conducted on five soils with different texture classes (Table 1). These soils were selected to cover a wide range of WHC. In addition to these experiments, extraction ratios on 75 and 1200 juveniles (Table 1) were carried out on the studied soils in optimized conditions, to ensure that the modification of test conditions didn't affect the recovery after the exposure period.

In order to determine if juveniles of C. elegans can develop in unsaturated as well as in saturated matrices, growth and reproduction of this nematode were recorded. The range from 40% to 100% of WHC was tested on each of the selected soils. Food (Escherichia coli) volume was decreased to be able to be included in the soil moistening volume. In the current protocol, growing media is added at 40% of soil dry weight and another volume of food is added. For comparison, expressions of results for soils moistened as the standardized protocol are given in Table 1 as a percentage of WHC of each of the selected soils.

To minimize the input of bacteria solution added to the soils, the volume was decreased by a factor of 10 and the concentration was increased by the same factor, to ensure that the same amount of food is provided as in standardized conditions. To determine if decreasing food volume can influence C. elegans endpoints responses, a comparison were made between the above mentioned soils, moistened according to the standardized method and moistened at 80% of their respective WHC, including food. Regarding improvements of the test protocol, our results showed that: 1. In the range of soils moisture tested, 40% of WHC was not adapted for C. elegans reproduction. Growth was not impacted by this condition. Moreover the soils textures studied were shown to be suitable for C. elegans survival, growth and reproduction, as the test validity criteria for each soil were all satisfied. 2. The range from 60% to 100% WHC of the selected soils was suitable, 80% of WHC were selected to carry further tests on solid matrices. This condition allows to keep samples unsaturated and avoid soil drying during the exposure period. 3. Decreasing food volume and including it in the soil moistening volume didn't significantly affect neither C. elegans growth nor reproduction endpoints for the selected soils.

Assessing biosolids with Caenorhabditis elegans: an example of a limed sludge

To assess the effect of biosolids, different methods are available. As the studied biosolids are spread on agricultural field, it seems more logical to assess their effects based on their agricultural use rather than to determine a dose-effect relationship of the biosolid itself. In this example, the limed sludge application rate (3 tons.ha -1

, equivalent to 1X in figures) was used as a basis for the preparations of mixtures with standard soil (LUFA 2.2, control soil) and their respective water extract [START_REF]Characterization of waste. Preparation of waste samples for ecotoxicity tests. Acknowledgement -The authors thank the french Ministry of Ecology, Sustainable development, Transport and Housing (MEDDTL)[END_REF]. Different rates were tested, from one time to one hundred times the application rate. Results of C. elegans growth and reproduction in soil mixtures and in their water extracts are presented respectively in Figure 1 a and b. These results showed that reproduction is the most sensitive endpoint for both solid and liquid media. Indeed, it significantly decreased at a hundred times of the application rate on standard soil and from one fold this rate for water extracts. No significant differences were found for growth in solid matrices but it significantly decreased for the water extracts of soil and limed sludge mixtures. Surprisingly, water extracts of soil mixtures were more toxic than the mixtures themselves. These effects cannot be attributed to a pH increase.

Conclusions

There was a need to harmonize moisture conditions of soils and soil/biosolid mixtures to test this kind of materials with Caenorhabditis elegans. Growth and reproduction results for soils moistened based on their water holding capacities demonstrate that the range from 60% to 100% of samples WHC is suitable for the development of this invertebrate and 80% were chosen to run these tests and further ones. In order to determine if food volume can be lowered for C. elegans soil tests, it was included in the total volume used to moisten the soils and soil/biosolid mixtures.The endpoints results for these conditions were compared to those got for the same soils in standardized conditions and no significant differences were found between the two protocols. Moreover, soils textures studied had no effect on the endpoints studied. With regards of the effects of soils and biosolids mixtures on C. elegans growth and reproduction, moistening the samples on a WHC basis is adequate to assess this kind of materials. Endpoints results of C. elegans in solid and liquid phases demonstrated again the relevance of this organism to assess toxic effects on both media.

Figure

  Figure 1a & b : Limed sludge effect on C. elegans growth and reproduction, tested in mixture (a) and as water extracts (b). a,b,c : significant differences among reproduction results, after ANOVA and Tukey HSD test (α=0.05); *: significant differences against LUFA for growth results after Kruskal-Wallis test (α=0.05).

Table 1 : Soils classification, WHC, extraction ratio and water addition for standardized conditions.

 1

	Soil	Soil classification	WHC (%)	Extraction ratio (mean %) 75 ind. 1200 ind.	Standardized water addition (% of WHC)
	LUFA	Loamy sand	45	87	76	280
	Agricultural	Sandy loam	40	93	85	350
	Forest	Sandy clay loam	70	94	72	200
	Garden 1	Sandy loam	65	77	81	215
	Garden 2	Light clay	36	81	90	388


Romain Achard
email: romain.achard@ineris.fr

Anne Benard

Brice Campredon

Patricia Merdy

Yves Lucas

Environmental behavior of inorganic pollutants present in raw and desalinated French marine sediments

Keywords: Dredged sediment, metal mobilization, Acid Neutralization Capacity

In the frame of long-term management of contaminated dredged sediments, this paper is centered on the determination of the mobility of inorganic contaminants. A methodology derived from waste characterization has been developed and applied to marine sediments from Lazaret bay (Toulon, southern France) to determine the potential mobilization of inorganic pollutants in specific conditions. It consists of mineral and textural analysis combined with leaching tests. This methodology was applied to untreated, 5.8 % organic matter, light sandy silt harbor sediment and to the same sediment after a desalinization treatment. In both untreated and desalinated sediments, the contaminant content was around 26. 1, 0.18, 42.5, 34, 31, 35 and 99 mg kg -1 for As, Cd, Cr, Cu, Ni, Pb and Zn, respectively. After 24 hours of time contact between deionized water and sediments, contaminant release of metals was very low (ca. <0.7 total mass %, for all studied elements) due to low solubility of the bearing solid phases (organic matter, carbonates and sulfides), while Mo and B were widely released. After 48 hours, Cd, As, Mo and B release was higher while more significant but no clear differences for other metal appeared.

1-Introduction

Seaworthiness of waterways and harbors was guaranteed by annual dredging of about 40 million tons of marine sediments in France. Dredged sediments were defined as complex matrices, of variable particular size classes, with different minerals, organic matter content as well as highly variable concentration of organic and inorganic contaminants [START_REF] Cappuyns | Kinetics of elements release during combined oxidation and pHstat leaching of anoxic river sediments[END_REF]. Based on the august 9 th 2006 French decree and especially N1 and N2 thresholds, about 8 million of these sediments could be contaminated by inorganic and organic pollutants and could require a terrestrial management. According to French regulation, contamined dredged sediments were considered as waste but sediments management stay problematic due to high content of water, salt, organic matter as well as large volume. Since a couple of years different studies and research programs have been developed to improve sediment treatment and reuse channels or/and to assess environmental impacts of the reuse and deposit [START_REF] Lions | Etude hydrogéochimique de la mobilité de polluants inorganiques dans des sédiments de curage mis en dépôt : expérimentation, étude in situ et modélisations[END_REF][START_REF] Lions | Zinc and cadmium mobility in a 5year-old dregded sediment deposit : experiments and modelling[END_REF][START_REF] Piou | Changes in the geochemistry and ecotoxicity of a Zn and Cd contaminated dredged sediment over time after land disposal[END_REF]. Today, it is necessary to have information on long term environmental behavior of sediment in reuse scenario. The study dealt with this topic and evaluated the mobilization of inorganic pollutants present in fresh raw marine sediment from Toulon Bay (South of France) and its desalinated analogue, in a target of reuse. The methodology applied was inspired by waste characterization [START_REF] Kosson | An integrated framework for evalution leaching in waste management and utilization of secondary materials[END_REF] and linked textural, mineral and organic matter characterization with different leaching tests in laboratory and outside lysimeter. A model will then created with experimental data to validate the different assumptions and to be applied for other types of sediments or reuse scenarii.

2-Materials and Methods:

2-1 Sampling and preparation.

The studied marine sediment was chosen to present an intermediate contamination content between thresholds N1 and N2, according to French regulation (august 9, 2008 decree). Therefore, the dredging area was established from previously available data concerning the spatial distribution of inorganic contaminants in the sediments from Toulon Bay, France [START_REF] Tessier | Study of the spatial and historicl distribution of sediment inorganic contamination in the Toulon Bay (Franc)[END_REF]. The sediments from the Lazaret Bay (43°05.3644 N, 05°54.6679 S) were selected to be studied and the first 20 centimeters of the sediments was sampled by divers at 7 meters-depth. About 900 kg of sediment were this way collected on April 2011. One part of the sediment was sieved at 2 mm, homogenized and stored at 4°C to the shelter of the light and under a 20 cm sea water layer or freeze-dried, in order to preserve its physico-chemical properties until analysis and experiments. Another part of the sediment was desalinated with tap water until an electrical conductivity (EC) was lower than 4.5 mS.cm -1 . About 1600 L of tap water were used to desalinate 550 kg of raw sediment. Before reuse, some marine dredged sediments are sometime washed and the desalinated sample was done in take into account this pre-treatment.

2-2 Physical and chemical characterization

Size particles distribution was determined using a laser diffraction particle-size analyzer (LS 200 Beckman Coulter) with a range from 0.03 µm to 2000 µm. Total concentrations of trace metals and major elements were measured by Inductively Coupled Mass spectrometry (Perkin Elmer Elan DRC II) and ICP-Atomic Emission Spectroscopy (Perkin Elmer-Optima 7200-DV) respectively, after optimized semi-total aqua regia digestion. 100 mg of sediment and 10 mL of aqua regia (HNO 3 : HCl 1 V:3 V, Fisher Scientific_ Trace Analysis grade, HNO 3 70%-16 M, HCl 37%-12 M) were placed in 50 mL Teflon (PTFE) bombs and submitted to a controlled elevation of pressure and temperature in a microwave oven (Anton Paar_ Multiwave 3000). Sample extractions and analysis were realized in triplicate and the accuracy and precision of the analysis was checked using an international certified reference material (PACS, Table 1). Particulate organic and inorganic carbon (POC and PIC, respectively) concentrations were determined using a TOC-V analyzer (Shimadzu) coupled with a SSM-5000A [START_REF] Benner | A critical evaluation of the analytical blank associated with DOC measurements by high-temperature catalytic oxidation[END_REF]. Organic carbon was calculated by difference between total and inorganic carbon contents. The mineralogy of the raw and desalinated sediment were identified by X-Ray Diffraction (Panalytical X'pert pro NPD) Following the recommendations of [START_REF] Kosson | An integrated framework for evalution leaching in waste management and utilization of secondary materials[END_REF], single and sequential selective extractions were realized in order to evaluate the behavior and speciation of each contaminant. Single extraction was performed using deionized water and acetic acid and aims at determining respectively soluble and available fractions of the sediment [START_REF] Lebourg | Intérêt de différents réactifs d'extraction chimique pour l'évaluation de la biodisponibilité des métaux en traces du sol[END_REF]. Liquid on solid (L/S) ratios were 10 and 40 mL g -1 for deionized water and acetic acid, respectively; and time contact was 24 and 48 hours for water and 16 hours for acetic acid. Sequential extractions were performed in triplicate using the BCR protocol [START_REF] Tessier | Sequential extraction procedure for the speciation of particulates metals[END_REF]Quevauviller et al., 1997). Four fractions were obtained: the first one was acid-extractable (0.11 M of acetic acid), the second one reducible (0.5M hydroxylamine hydrochloride), the third one oxidizable (8.8M H 2 O 2 adjusted to pH2 with HNO 3 concentrated at 85°C followed by ammonium acetate 1M adjusted to pH2) and the last one is residual fractions (calculated by difference with total contents obtained using aqua regia digestion) (J. Morillo et al., 2003). Acid neutralization capacity tests (ANC) [START_REF] Kosson | An integrated framework for evalution leaching in waste management and utilization of secondary materials[END_REF], Chatain et al., 2004;[START_REF] Cappuyns | Assessment of acid neutralizing capacity and potential mobilization of trace metals from land-disposed dredgred sediments[END_REF][START_REF] Dijkstra | Leaching of Heavy Metals from Contaminated Soils: An experimental and Modeling Study[END_REF] were realized to evaluate the sediment buffering capacity and the liquidsolid partitioning of the different targeted elements. About 80.8 grams of wet sediments (which corresponded to 30 grams of dry matter) were leached with a 10 mL g -1 L/S ratio during 48 hours in HNO 3 and NaOH solutions in order to obtain final pH values ranging from 4 to 12 for raw sediment and from 1 to 12 for desalinated sediment. All the obtained leachates were filtered using 0.45 µm pore size acetate-cellulose syringe membranes (Minisart, Sartorius-stedim biotech) and then analyzed using ICP-AES and ICP-MS. Anions and cations ( including, phosphates, sulphates and chlorides) were analyzed by ion chromatography (Dionex-120). Dissolved concentrations of TOC (Total Organic Carbon) were estimated by the difference between total carbon and inorganic carbon measured by the carbon analyzer (Shimadzu TOC-5000A).

3-Results and discussion

3-1 Sample characterization

The raw sediment was characterized by high moisture content, around 61%. The physical fractionation results are given in Table 2. Both raw and desalinated sediments were mainly fine and silty with 65 and 51% of particles smaller than Ø 50 µm, respectively. According to the USDA triangular diagram of textural classes of soils, both materials are light sandy silt. Desalinated sediment had values lower for silt-sized particles (2-50 µm) and higher for coarse sand particles (200-2000 µm), indicating aggregation during desalination process. Organic matter (OM) content was relatively low (5.6 and 6.02 %) for raw and desalinated sediment, respectively). This concentration was closed to the values of Spanish harbor [START_REF] Guevara-Riba | Assessment of metal mobility in dredged sediments from Barcelona, Spain[END_REF]Casado-Martinèz et al., 2009) Total elements contents are given in Table 3. Ca was the most important major element and it would be present in calcite, aragonite and to a less extend in dolomite in both sediments, from the XRD results. The other major elements would be constituent of quartz, phyllosilicates (muscovite, kaolinite, clinochlore), plagioclase (albite), pyrite and halite for both sediments. Alunite, a sulfate mineral, was only present in the desalinated sediment. Total As and Hg contents were higher than thresholds proposed by the environmental French group GEODE within the framework of OSPAR convention, when Cu and Ni were nearby the N1 threshold.

The desalination protocol has leached more than 90% of Na and Cl, 31% of Fe and about 18% of S. Fe and S leaching were probably associated to pyrite (FeS2) oxidation, and alunite (KAl3(SO4)2(OH)6) formation. Pyrite often contains trace contaminants, like Ni, Cu, Zn, Pb, Hg [START_REF] Lions | Etude hydrogéochimique de la mobilité de polluants inorganiques dans des sédiments de curage mis en dépôt : expérimentation, étude in situ et modélisations[END_REF][START_REF] Lors | Effects of bacterial activities on the release of heavy metals from contaminated dredged sediments[END_REF][START_REF] Caille | Solubility of metals in an anoxic sediment during prolonged aeration[END_REF]. In this case, desalination and pyrite oxidation seem not to be responsible of inorganic contaminants release. For the contaminants, only B could be significantly released during the desalination.

3-2 Determination of water and acido-soluble extractible fractions

Long term behavior of chemical contaminants depends on its speciation within the matrix. Trace contaminants are retained by minerals, organic matter and as adsorbed species; the behavior of the bearing phases during leaching (dissolution, precipitation, mineralization…) explains the more or less mobility of the contaminants [START_REF] Chaurand | Environmental impacts of steel slag reused in road construction: A crystallographic and molecular approach[END_REF]. Contaminant release was first studied using deionized water and acetic acid solution, then the bearing phases were evaluated using sequential selective extractions. The physico-chemical parameters of solutions obtained after water extraction during 24 hours and a liquid/solid ratio of 10 L/kg (W24) were quite similar for both sediments. The pH was 7.8 and 7.5 for the raw and desalinated sediments, respectively; the redox potential was greater than 190 mV/ENH for both sediments. The electro-conductivity diminished from 10.9 mS.cm -1 in raw sediment to 2 mS.cm -1 in desalinated sediment, due to the washing process. treatment) between 6.5 and 9.6 Tw% (percent of total weight) in both sediments. Ni was released by AA treatment with 16.9 and 17.3 Tw% in raw and desalinated sediment, respectively. A contact time of 48h was necessary to release Cd with water which was also extracted with acid acetic. Cd suffered a similar release by W48 and AA treatment (19.9 and 15 Tw% in raw sediment and 9.3 and 12.8 Tw% in desalinated sediment, respectively). As was leached with acid acetic for both sediments (9.2 and 4.4 Tw% in raw and desalinated sediment, respectively), but was weakly released (3.7 Tw%) with water (48 hours) only for the raw sediment. The B and Mo were strongly extracted for all treatment. B extraction with acetic acid was greater than water extraction, while Mo was more extracted with water; about 55% were extracted with water for the raw sediment. Generally, inorganic contaminant extraction was more strongly emphasized for raw sediment compared to desalinated sediment, a higher ionic strength might promote inorganic contaminant extraction. Similar results were found for cadmium which presents an affinity for chlorides [START_REF] Lions | Etude hydrogéochimique de la mobilité de polluants inorganiques dans des sédiments de curage mis en dépôt : expérimentation, étude in situ et modélisations[END_REF]. The results indicated that Cu wasn't bounded to bearing phases soluble in water or acetic acid. Ni, Pb, Zn and Co were associated with carbonates extracted in acetic acid such as calcite. As, Cd, B and Mo were both leached with water and the acetic acid treatment, and the release of pollutants was increased by a longer time contact.

3-3 Operational speciation: fractionation by sequential selective extractions

Sequential selective extractions showed similar distribution of contaminants in the four fractions, for both raw and desalinated sediments. More than 20% of B and Mn were bound to the acid-extractable fraction, indicating high availability and easy release. More than 15% of Ni and Cd were also in this acid-extractible fraction. Cr and Cu were mainly bound to the oxidisable fraction, i.e. organic matter as already observed for Cu by [START_REF] Caplat | Heavy metals mobility in harbor contaminated sediments: The case of Port-en-Bessin[END_REF] on harbor contamined sediments. Cd was dominantly in the reducible fraction, i.e. bound to Fe-and Mn-oxides. Ni, Co, Zn, As, Mo and Pb were more distributed between fractions when Al and Fe were mainly in the residual fraction, indicating that they are included in the low soluble mineral phase [START_REF] Caplat | Heavy metals mobility in harbor contaminated sediments: The case of Port-en-Bessin[END_REF]. These results showed the complexity of sedimentary matrix : inorganic minerals were associated with different phases of the sediments. Nevertheless, some elements like Cu, Cr, B and Mn showed affinity for, respectively, organic matter or acid-extractible fraction. Evolution of the pH in the water solution containing increasing protons concentration, i.e. sediments acid neutralization capacity, is shown on figure 3. ANC titration (Fig. 3) showed that the desalinated sediment had a strong buffering capacity for pH values comprised between 5.5 and 6.8. Such buffering capacity is likely due to a high content of carbonate originating from seashells. The liquid-solid partitioning of Cu, Pb, Zn and As at various pH are given in Figure 4 for desalinated sediment; the same trends were found for raw sediment. The solubility of these elements presented a typical "V shape", with lower solubility between pH 3.8 and 8.0 for Cu and As, as already observed by Chatain et al. (2005), and between pH 6.5 and 8 for Pb and Zn. Behavior of Zn was close to these of Pb, when behavior of Cu was close to these of As (correlation coefficient R²=0.89 for pH values above 2) . Zn and Pb were the more released at acid pH (from pH<5.5), although a significant release Most of the variations of the considered metals with pH can be explained by the solubility in water of their cationic and hydroxylated species. However, the shape of the solubility curve at basic pH can be also determined by the release of organic matterelement complexes. This hypothesis is strengthen by high correlation coefficient between dissolved organic carbon (DOC) and Cu and As for pH higher than 5.5 (R² = 0.946 and 0.93 for Cu and As, respectively), same trends were found for raw sediment.

4-Conclusion

A combination of methods used in the present study allowed a differentiated characterization of the behavior of potentially toxic elements present in the studied sediments. With regard to elements having concentrations over the environmental threshold in the raw sediment, results indicated that Cu appeared poorly mobile at pH between 5 and 7.5, and mainly retained by the oxidizable fraction of the sediment, i.e. organic matter. This leaching behavior could change with time due to an oxidation of the sediment natural organic matter, as a result of changing physico-chemical conditions during oxidation/reduction cycles [START_REF] Calmano | Bondong and mobilization of heavy metals in contaminate sediments by pH and redox potential[END_REF] or of bacterial action [START_REF] Lors | Effects of bacterial activities on the release of heavy metals from contaminated dredged sediments[END_REF]. Arsenic has a similar leaching behavior; it was strongly associated to organic matter. Arsenic could also be As Cu mobilized after oxides dissolution. Ni is released with acetic acid attack, it was easily mobilisable. Mo was mainly dissolved in water, it was easily available. The sediment desalination released Na, Cl but also Fe and S, probably due to pyrite oxidation into alunite. Desalination also promotes particle aggregation and elements leaching, but the contaminants distribution into the different sediments fractions remains quite the same. Treatment of the outside lysimeter results and modeling are in process.

Figure 1 .

 1 Figure 1. Comparison of metal concentrations extracted by deionized water and acetic acid

Figure 2 .

 2 Figure 2. Element fractionation by sequential extraction (% of total weight).

Figure 3 .

 3 Figure 3. Evolution of the pH of water sediments versus added H + mol

Figure 4 :

 4 Figure 4: Zn, Pb, Cu and As solubilization in leachate as a function of pH (time contact 48 hours, L/S 10)

  .

	Table 1 Results (mean ± standard deviation) obtained from
	certified reference materials analysis
	Certified value (mg/Kg)	Measured value (mg/Kg)
	PACS 2
	Cu	310±12	316 ± 0,89
	Pb	183±8	136 ± 0,82
	Zn	364±23	368 ± 1,35
	Ni	39,5±2,3	38,4 ± 0,11
	Cd	2,11 ± 0,15	2,6 ± 0,03
	Cr	90,7±4,6	73,9 ± 0,84
	As	26,2±1,5	29,8 ± 0,17
	Table 2 General properties of both sediment
	type of sediment	Raw	desalinated
	pH		7,8	7,5
	Total Organic carbon (%)	3,3	3,6
	Inorganic Carbon (%)	3,4	3,5
	Particule size distribution	% of total mass
	2000 -200 µm	8,7	22,9
	200 -50 µm	26,6	26,9
	50 -20 µm		19,6	15,5
	20 -2 µm		37,6	29,8
	<2 µm		7,5	5,2
	Total fraction	100	100

Table 3

 3

	Total concentration of elements. Rw: untreated sediment; Ds: desalinated sediment; N1, N2:
	environmental thresholds *values from Eurofins Cofrac Lab

  High As and Cu release occurred at both acid (<3.5) and basic (>8) pH. Under acidic conditions, Pb release occurred at higher pH than observed by[START_REF] Cappuyns | Assessment of acid neutralizing capacity and potential mobilization of trace metals from land-disposed dredgred sediments[END_REF] from landdisposed dredged sediments.

	occurred at pH >8.
				Desalinated sediment
	pH	1 2 3 4 5 6 7 8 9 13 12 11 10					pH
		-0,3	-0,1	0,1	0,3	0,5	0,7	0,9
					added H + mol

Acknowledgements:

This work was supported by INERIS and Provence-Alpes-Côte d'Azur Region. The authors thank the divers of DDTM 83 for sediment sampling in the Lazaret Bay, Toulon, south of France.