Clinical audit: a useful tool for reducing severe postpartum haemorrhages?

Objective. Reducing the rate of severe postpartum haemorrhage (PPH) is a major challenge in obstetrics today. One potentially effective tool for improving the quality of care is the clinical audit, that is, peer evaluation and comparison of actual practices against explicit criteria. Our objective was to assess the impact of regular criteria-based audits on the prevalence of severe PPH.

Design. Quasi-experimental before-and-after survey Setting. Two French maternity units in the Rhône-Alpes region, with different organisation of care.

Participants. All staff of both units.

Intervention. Quarterly clinical audit meetings at which a team of reviewers analysed all cases of severe PPH and provided feedback on quality of care and where all staff actively participated.

Main outcome measures. The primary outcome was the prevalence of severe PPH. Secondary outcomes included the global quality of care for women with severe PPH, including the performance rate for each recommended procedure. Differences in these variables between 2005 and 2008 were tested.

Results. The prevalence of severe PPH declined significantly in both units, from 1.52% to 0.96% of deliveries in the level III hospital (p=0.048) and from 2.08% to 0.57% in the level II hospital (p<0.001). From 2005 to 2008, the proportion of deliveries with severe PPH that were managed consistently with the guidelines increased for all of its main components, in both units.

Conclusion. Regular clinical audits of cases severe PPH were associated with a persistent reduction in the prevalence of severe PPH.

Introduction

Severe postpartum haemorrhage (PPH) is the main component of severe maternal morbidity in developed countries, and reducing its rate is a major challenge in obstetrics today. In France, PPH is the leading cause of maternal mortality, and data from the French Confidential Enquiries into maternal deaths show that 80% of deaths due to PPH might have been prevented by timely and appropriate care [START_REF]Third Report[END_REF]. The French College of Obstetrics & Gynaecology (CNGOF) issued the first national clinical guidelines on PPH prevention and management in France in November 2004 [START_REF] Goffinet | Postpartum haemorrhage: recommendations for clinical practice by the CNGOF (December 2004)[END_REF]. However, the passive dissemination of guidelines is by itself insufficient to change professionals' practices [START_REF] Dupont | Incidence and management of postpartum haemorrhage following the dissemination of guidelines in a network of 16 maternity units in France[END_REF].

Clinical audit is a quality improvement process that seeks to improve patient care and outcomes by looking at current actual practices through the review of cases according to explicit criteria and uses the findings to modify the organisation and the content of care if necessary [START_REF]Principles for best practice in clinical audit[END_REF][START_REF] Buljac-Samardzic | Interventions to improve team effectiveness: a systematic review[END_REF]. Few studies have assessed the impact of clinical audits in obstetrics [START_REF] Pattinson | Critical incident audit and feedback to improve perinatal and maternal mortality and morbidity[END_REF][START_REF] Wilson | The Leeds University Maternity Audit Project[END_REF][START_REF] Chaillet | Evidence-based strategies for implementing guidelines in obstetrics: a systematic review[END_REF], and none, to our knowledge, has focused specifically on PPH. Information on the feasibility of clinical audits of deliveries with severe PPH and the results that can be expected from this tool would be useful to clinicians [START_REF] Lombarts | Application of quality improvement strategies in 389 European hospitals: results of the MARQuIS project[END_REF]. The Pithagore6 trial was a cluster-randomised trial, with the maternity unit as the unit of randomisation, to evaluate a multifaceted educational intervention for reducing the rate of severe PPH.

It included 106 French maternity units and finally found no significant difference in the severe PPH rate between the hospitals with the intervention and the control hospitals [START_REF] Deneux-Tharaux | Educational multifaceted intervention to decrease the rate of severe postpartum haemorrhage-the Pithagore6 cluster-randomized controlled trial[END_REF]. The intervention included a clinical audit of deliveries with severe PPH in all maternity units in the intervention arm.

Two of these hospitals decided to continue the clinical audit meetings on a regular basis. The objective of this report is to describe the change in the prevalence of severe PPH and in the quality of care provided in these cases after the implementation of routine audits in two hospitals with different levels and organisation of care.

Methods

A before-and-after survey was designed to assess the impact of the routine use of clinical audits.

Population

The study was conducted in France in two maternity hospitals located in the Rhône-Alpes region. Both were part of the Pithagore6 research program [START_REF] Deneux-Tharaux | Educational multifaceted intervention to decrease the rate of severe postpartum haemorrhage-the Pithagore6 cluster-randomized controlled trial[END_REF] and decided, after the study's conclusion, to integrate the clinical audit into their routine practice. Croix-Rousse Hospital is a level III university hospital, that is, a reference centre with an onsite neonatal intensive care unit and around 3000 deliveries a year. Valence Hospital is a level II hospital that has a neonatal unit and around 2000 annual deliveries. Both units have an anaesthetist and a junior and a senior obstetrician on site at all times, as well as an onsite blood bank, arterial embolisation facilities and an adult intensive care unit.

They also have written protocols, consistent with national guidelines, for the management of obstetric haemorrhages.

From 2005 through 2008, the obstetrics departments of both hospitals held clinical audit meetings every three months to analyse all cases of severe PPH in the preceding quarter. Severe PPH was defined as a PPH associated with one or more of the following: blood transfusion, arterial embolisation, arterial ligation, other conservative uterine surgery, hysterectomy, transfer to an intensive care unit, peripartum haemoglobin drop of 4 g/dl or more, or maternal death. Women with transfusions during the postpartum period but not clinically diagnosed with PPH were not included.

Deliveries with severe PPH were prospectively identified and reported at the daily obstetric staff meeting, and one midwife in each hospital was responsible for collecting cases and checking that all pertinent information was included in the file.

Clinical audit

In each unit, all cases of severe PPH that occurred during the previous 3 months were reviewed during a quarterly meeting of the local clinicians. All members of maternity unit's medical staff (obstetricians, midwives and anaesthetists) were asked to participate. Participation in this meeting was considered working time. From 20 to 25 people attended each meeting. In each unit, a three-member audit team an obstetrician, a midwife and an anaesthetistconducted the clinical audit. A member of the team caring for the woman at the time the PPH occurred presented each case. The content of the obstetric files was also available to the audit team.

The clinical audit included three steps. First, the appropriateness of the care provided was critically analysed by the audit team in a discussion with the other clinicians. Management was assessed according to explicit criteria derived from the main components of the national guidelines: examination of the uterine cavity and/or manual removal of the placenta within 15 minutes of the PPH diagnosis; instrumental examination of the vagina and cervix; intravenous administration of oxytocin; and if PPH persisted and was due to uterine atony, intravenous administration of sulprostone (second line oxytocic) within 30 minutes of the initial diagnosis. A standardised audit form (available on request to the authors) was completed for each case and stated whether each recommended procedure was performed.

At the end of this analysis, the audit team offered an oral synthesis of the practices, feedback about what was done wrong and what was done well, and a consensus was then made by the audit meeting on the global quality of care provided (optimal, suboptimal, non-optimal). Care was considered optimal if the following four major components of recommended care were performed within the required time: examination of the uterine cavity/manual removal of placenta; call for additional staff; administration of oxytocin; and administration of sulprostone if uterine atony persisted. If at least one of these major components was absent, care was considered non-optimal. Care was considered suboptimal if all major procedures were performed but at least one was not done within the recommended time or another minor component of care did not comply with the recommendations.

The second step of the audit consisted in an active discussion involving all meeting participants and facilitated by the audit team to identify the specific reasons for sub-or non-optimal care, both in terms of content and organization. Finally, the group analysed the reasons identified in the second step and defined practical ways to improve the specific non-optimal aspects, in view of local constraints and the specific context. One person, usually a senior midwife, was in charge of monitoring implementation of the recommended actions. After the meeting, the senior midwife reduced these conclusions to writing and sent them by email to each participant. They were also made available to all staff of the maternity unit in the labour ward.

Study variables

The data routinely collected by the units includes characteristics of pregnancy and delivery known to be risk factors for severe PPH: previous caesarean delivery, multiple pregnancy, placenta praevia or accreta, mode of delivery, and foetal macrosomia (baby's weight > 4000 g), as well as any postpartum haemorrhage (clinically assessed by the caregivers). These data were extracted for this study, together with their proportions among annual deliveries (from each unit's annual report).

The primary outcome was the prevalence of severe PPH, calculated as the number of cases divided by the total number of deliveries. Secondary outcomes included the rates of the principal recommended interventions for PPH management, extracted from the data collected during the audits. Specifically, we calculated the rate of calls for additional staff and administration of oxytocin for all cases. The rates of examination of the uterine cavity within 15 minutes of diagnosis and of instrumental examination of the vagina and cervix were assessed for severe PPH following vaginal delivery. Lastly, the rate of administration of sulprostone within 30 minutes of the diagnosis was assessed for the cases due to uterine atony.

Analysis

Differences between the before (2005) and after (2008) periods for primary and secondary outcomes were tested with the chi-square test or Fisher's exact test, as appropriate, as were differences in the prevalence of individual risk factors for severe PPH between these periods.

Results

The characteristics of parturient women did not change significantly from 2005 to 2008 in the level II unit, although in the level III unit, the rate of instrumental vaginal deliveries increased significantly, from 7.3% in 2005 to 10.5% in 2008, as did the rate of deliveries with PPH, from 4.0% of deliveries in 2005 to 6.1% in 2008 (Table 1). This global increase in the PPH annual rate resulted from the combination of a decrease in PPH after spontaneous and instrumental vaginal deliveries (from 2.0% to 1.85% and from 7.9% to 3.5%, respectively) and a concomitant significant increase in the PPH rate after caesarean deliveries, from 9.6% in 2005 to 20.4% in 2008.

A significant reduction in the prevalence of severe PPH occurred in both hospitals between 2005 and 2008, from 2.1% to 0.6% in the level II hospital and from 1.5% to 1.0% in the level III hospital (Table 2). In the level II unit, the prevalence of severe PPH decreased for both vaginal and caesarean deliveries. In the level III unit, on the other hand, the prevalence of severe PPH after vaginal deliveries fell significantly, but the prevalence after caesareans did not change.

The global quality of care provided to women with severe PPH improved in both units between 2005 and 2008, although the difference reached statistical significance only in the level III hospital (Table 3). The proportion of cases for which management was considered optimal increased from 47% to 73% in the level II unit and from 22% to 61% in the level III unit.

In both units in 2005, the main deviations from recommended care once PPH was diagnosed were no or delayed examination of the uterine cavity (57% in the level II and 74% in the level III unit), the absence of instrumental examinations of vagina and cervix (76% and 59% of severe PPH cases, respectively), and no or delayed administration of second-line uterotonics when uterine atony persisted (71% and 86%).

From 2005 to 2008, the proportion of deliveries with severe PPH that were managed consistently with the guidelines increased for all of the principal components, in both units. In particular, this improvement was statistically significant in both units for the components of care that were the most inappropriate in 2005.

Discussion

This study shows that routine clinical audits can easily be implemented in obstetrics settings and that their regular performance is associated with an improvement in PPH-related practices and with a significant reduction in the prevalence of severe PPH.

Several limitations must be noted. First although the initial audit meeting was part of a research programme, the routine use of the audit that followed was a local initiative in both units, and the external validity of the results may thus be questionable. Our findings nonetheless suggest that clinical audits are a simple and potentially effective tool for units willing to assess and improve the care they provide.

The quality of care for PPH and the specific components of that care were analysed only in cases of severe PPH. A complete assessment of the audit impact would theoretically have required us to analyse practices in all cases of PPH, or in a representative sample of them, and not only in the most severe cases. These data, however, were not available. It is possible that the improvement in practices was actually greater than that observed in cases of severe PPH, since, by definition, the severe cases have worsened and are thus more likely to have received inappropriate care.

The inherent limitations of our observational design prevent this study from proving that the regular audits caused the reduction in the prevalence of severe PPH, and other factors external to the audit may have contributed to this decrease. Obstetrics professionals in France have been focusing on the issue of PPH since the late 1990s, and global improvement in PPH-related practices might have been underway as part of this national context and could explain the decrease in the prevalence of severe PPH found in the 2 units of our study. We consider this hypothesis seems unlikely, however. Firstly, passive dissemination of recommendations for clinical practice has repeatedly been shown to be insufficient to improve practices [START_REF] Freemantle | Withdrawn: Printed educational materials: effects on professional practice and health care outcomes[END_REF] . Secondly, the dramatic reduction found herewith the prevalence of severe PPH after vaginal delivery divided by three --seems unlikely to have happened in the absence of active intervention. Finally, a regional study in all maternity units of another French region showed no significant decrease in the rate of severe PPH during this time period [START_REF] Audureau | Practices for prevention, diagnosis and management of postpartum haemorrhage: impact of a regional multifaceted intervention[END_REF]. Another possible explanation of our results is that the proportion of women at risk for PPH decreased over time. However, neither the prevalence of PPH risk factors among parturient women nor the annual rate of all PPH decreased over this period. Indeed, an inverse trend was observed in the level III unit, where the rates of two important risk factors increased between 2005 and 2008: the number of instrumental deliveries and of women with previous caesareans. These changes may have contributed to the increase in the PPH rate. Under these circumstances, the reduction we observed in the prevalence of severe PPH suggests a decline in the proportion of the PPH that worsened and became severe, probably due to better management of early PPH. The specific PPH-related practices used as criteria for determining quality of care improved concomitantly. Finally, the implementation of routine audits was associated with a significant reduction in severe PPH in two different maternity units providing different levels of care in different settings. All these elements suggest that the organisation of regular clinical audits is likely to have had a positive effect on the prevalence of severe PPH.

Although there are reports of interventions aimed at improving the global quality of care delivered to mothers and children, or targeting other specific issues in obstetrics, previous studies of interventions to decrease the rate of severe PPH are scarce [START_REF] Rizvi | Successful reduction of massive postpartum haemorrhage by use of guidelines and staff education[END_REF][START_REF] Skupski | Improving hospital systems for the care of women with major obstetric hemorrhage[END_REF]. Because those few tested the impact of complex or multifaceted interventions, they are not easily reproducible, and it is difficult to attribute the global effect to one component or another. Only one reported a significant reduction in the rate of severe PPH, obtained over a 3 year period in one centre [START_REF] Rizvi | Successful reduction of massive postpartum haemorrhage by use of guidelines and staff education[END_REF]. The present study provides a description of the routine use of one specific tool, the clinical audit, and our findings suggest it has a significant impact on the prevention of severe PPH through effective management of early bleeding. The precise description of the agenda of the audit meetings should make them easily reproducible in other units. In addition, the continuous monitoring of the prevalence of severe PPH and of the proportion of adequate care provides evidence that the audit's impact is sustained over time.

A major strength of regular clinical audits is that they bring practitioners together frequently to discuss the management of severe cases and to define relevant improvement objectives appropriate to the local context and based on the audit's findings [START_REF] Zwarenstein | Interprofessional collaboration: effects of practice-based interventions on professional practice and healthcare outcomes[END_REF]. Severe PPH is a very pertinent event for clinical audits, because of the availability of management guidelines and its obviously multidisciplinary nature, involving midwives, obstetricians, and anaesthetists. Such multidisciplinary meetings with a facilitator team applying strategies to encourage collaboration, both at the meeting and during care, are likely to increase the audit activity and to improve care.

In our experience, the results that can be expected from a clinical audit meeting depend on several aspects of the audit process: institutional support, by treating participation in the meetings as actual working time; respect for the facilitator team and their leadership skills; consideration for every participant's words; objective assessment of care provided with the help of a standardised form; analysis of the mechanisms that led to the severe event, focused not on individual mistakes, but on understanding individual and collective decision-making processes; and conclusions expressed in terms of improvement strategies. In addition, long-term repetition of the audit appears necessary for it to improve practices and health outcomes. In the level III unit, clear improvement appeared only during the third year of audits. This finding is consistent with the previous report from Rizvi et al of an intervention to decrease the rate of severe PPH [START_REF] Rizvi | Successful reduction of massive postpartum haemorrhage by use of guidelines and staff education[END_REF]. This is also likely to explain why no significant improvement was obtained in the Pithagore6 trial where only one audit meeting took place [START_REF] Deneux-Tharaux | Educational multifaceted intervention to decrease the rate of severe postpartum haemorrhage-the Pithagore6 cluster-randomized controlled trial[END_REF]: a single meeting is probably insufficient for identifying suboptimal care and its reasons and is certainly insufficient for verifying its improvement.

An interesting finding is the differential changes in the prevalence of severe PPH for vaginal and caesarean deliveries. Caesarean delivery is a recognized risk factor for severe PPH, and the baseline rates of severe PPH in 2005 were higher for caesarean than vaginal deliveries in both units. During the subsequent years and following the implementation of routine audits, the prevalence of severe PPH after vaginal delivery fell quite appreciably in both units. However, severe PPH at caesarean deliveries decreased only in the level II unit; it remained stable in the level III unit and these cases accounted for most of the severe PPH in 2008. The clinical guidelines for PPH management offer more detailed measures for dealing with bleeding after vaginal delivery; it is thus unsurprising that the audits might have had a greater impact on this type of PPH. The concomitant increase in the rate of all PPH after caesarean delivery found in the level III unit may indicate that the procedure itself was associated with a higher risk of bleeding in 2008 than in 2005. Although the mechanisms and management of PPH at caesarean deliveries include surgical issues that may be more difficult to standardise, the current continuous rise in caesarean rates indicates that guidelines focusing on the management of bleeding at caesarean delivery are needed.

The prevalence of severe PPH and the high proportion of inadequate management found at baseline in the two units of this study suggest that room for improvement exists. Because passive dissemination of guidelines does not change practices, specific interventions are required. One feasible tool is the regular clinical audit of severe PPH, and in this study, it was associated with a persistent reduction in the prevalence of severe PPH.

Table 2 :

 2 Number and Rate (% of deliveries) of severe PPH*, 2005 to 2008, in the 2 units severe PPH defined as a PPH associated with one or more of the following: blood transfusion, arterial embolisation, arterial ligation, other conservative uterine surgery, hysterectomy, transfer to an intensive care unit, peripartum haemoglobin delta of 4 g/dl or higher, or maternal death **Difference between 2005 and 2008

	2005	2006	2007	2008

*

Table 3 :

 3 Characteristics of care provided for severe PPH, 2005 to 2008, in the 2 units

	2005	2006	2007	2008

* Difference between 2005 and 2008

Acknowledgements

The authors thank Mrs Anne Lafon for her help in data monitoring.

Disclosure of interests

The authors have nothing to disclose

Contribution to authorship

CD and CDT participated in the design and the implementation of the study, the collection and the analysis of the data and the drafting and revision of the paper. ST, CC, MHBC and JL participated in the design of the study and the revision of the paper.

RR initiated the collaborative project, participated in the design and the implementation of the study, the management of the audit meetings, the analysis of the data and the drafting and revision of the paper.

ST, CB, GP, and MPF participated in the organisation of the audit meetings, the collection of the data and the revision of the paper.

Funding

The work was supported by the French Ministry of Health under its Clinical Research Hospital Program (contract n° 27-35). The Ministry had no role in the design of the trial, the collection, analyses, or interpretation of the data, the writing of the manuscript or the decision to submit it for publication.

Ethics approval

Approval for the Pithgaore6 trial was obtained from the Sud Est III Institutional Review Board and from the French Data Protection Agency (CNIL). No specific ethics approval for this ancillary study was required because outcome data were routinely collected at maternity units and analysed in an aggregate format.


INTRODUCTION

Groundwater with a high F concentration is encountered in many places around the world and various geological settings (Edmunds & Smedley, 2005), whereas an excessive intake of F is dangerous for human health and provokes a potentially highly disabling disease called fluorosis. In India, endemic fluorosis has been identified in 17 states, affecting more than 60 million people because of consumption of water with high fluoride concentration [START_REF] Rao | Incidence of fluorides in drinking water resources in Andhra Pradesh[END_REF]. The Maheshwaram watershed is a typical Southern India rural watershed; in response to the development of agricultural activities, its hard rock aquifer is overexploited leading to a progressive depletion of water resources as indicated by declining water tables [START_REF] Maréchal | Combined estimation of specific yield and natural recharge in semi-arid groundwater basin with irrigated agriculture[END_REF]. This watershed has also to face groundwater quality problems and an increase of fluoride concentration has been reported for several years, leading to cases of dental fluorosis (Pauwels et al., 2010). The present work, based on the detailed study of chemical and isotopes composition of groundwater under paddy fields in the Maheshwaram watershed and supported by chemical modeling, aims at determining: 1) the key parameters of fluoride accumulation in groundwater in response to paddy fields development; 2) evaluate the potential impact of land use and climate change on fluoride concentration.

METHOD

General feature of the watershed

The Maheshwaram watershed is located 35 km south of Hyderabad, Andhra Pradesh, Southern India (Fig. 1). With an annualpotential evapotranspiration close to 2,000 mm and an annual rainfall of 750 mm over a 4-to 5-months monsoon period, the climate of the region is classified as semi-arid. The geology is relatively homogeneous and composed of Archean granites, which is representative of the whole region. It is also a typical rural watershed with a population of 15,000 inhabitants, whose principal economic activity is agriculture: rice, vegetables and flowers being the main crops. Irrigated agriculturehas developed since the beginning of 1980', im-

Shakeel Ahmed

IFCGR-NGRI, Hyderabad, Inda

ABSTRACT: A geochemical study was conducted to obtain a comprehensive understanding of fluoride concentration increase in groundwater from a crystalline (hard-rock) aquifer in a small Indian agricultural watershed, where groundwater is intensively abstracted for paddy irrigation. A reactive1-D geochemical model using PHREEQC was used to reproduce fluoride concentrations under rice paddies taking into account evaporation and return flow related to paddies and water-rock interactions processes, namely dissolution of biotite, allanite and fluoro-apatite as well as absorption onto Al and Fe-hydroxides. This model can be applied to evaluate vulnerability to high fluoride concentration for several land use and climate change scenarios. plying a significant water table depletion, leading to an endoreism of the basin (i.e., basin closure). The irrigation return flow (IRF) is largely variable in the area and is a function of the land use (higher in rice paddies than in flower-or vegetable plots).

Sampling and analytical techniques

Samples were collected from i) some of the 900 borewells drilled for irrigation which are equipped with submersible pumps and ii) boreholes drilled for scientific purpose at selected depth by using a down hole hammer. Water samples were collected for major and trace elements determination using ionic chromatography and ICP-MS. Water samples were also collected for stable isotopes measurements using a Finnigan MAT 252 mass spectrometer with a precision of 0.1‰ vs. SMOW (e.g. Standard Mean Ocean Water) for δ 18 O and 0.8‰ for δ 2 H.

Modeling

The software PHREEQC (Parkust and Appelo, 1999) is used to simulate and confirm some of the hydrogeochemical processes that occur during infiltration of water from paddy fields to groundwater.

RESULTS AND DISCUSSION

Impact of paddy fields and return flow on F accumulation

Groundwater F concentrations depend on the land use activities and are mostly above the drinking-water limit (1.5 mg/l) where the paddy fields prevail, whereas they remain at more acceptable levels elsewhere (Fig. 2). Stable isotopes of the water molecule present also a particular signature in groundwater beneath paddy fields compared to other areas. From the δ 18 O and δ 2 H of groundwater and monsoon rainfall samples, it has been possible to calculate the "D-excess", namely the deviation from the Local Meteoric Water Line, represented by the formulae [START_REF] Negrel Ph | Understanding groundwater systems and their functioning through the study of stable water isotopes in a hard-rock aquifer (Maheshwaram watershed, India)[END_REF]:

δ 2 H = 7.64 ± 0.26 δ 18 O + 7.80 ± 1.18 (R2 = 0.989, n = 12)
Actually, the 'D-excess" in groundwater is always below 10 and generally within the -0.6 to 7.6 range, with a value as low as -4. The "D-excess" values of around 7 and 8 are considered as being inherited from precipitation with a minor evaporation [START_REF] Negrel Ph | Understanding groundwater systems and their functioning through the study of stable water isotopes in a hard-rock aquifer (Maheshwaram watershed, India)[END_REF], whereas the lower value, particularly those less than 5 suggest significant evaporation of water. It is worth pointing out that all values below 3.5 are related to groundwater where paddy fields prevail, indicating a higher evaporation in these areas (Fig. 2). From a balance between yield and recharge at the scale of the watershed, the extent of Irrigation Return Flow (IRF) mainly related to paddy fields has been already highlighted by [START_REF] Maréchal | Combined estimation of specific yield and natural recharge in semi-arid groundwater basin with irrigated agriculture[END_REF]. From the present study, it is clear that IRF leads to a significant evaporation of water, which is known for its negative impact on groundwater quality because it increases the overall salinity of water. This result is also in agreement with a solute recycling model, which includes the reservoir geometry and hydraulic properties, the pumping rate and the irrigation surface area of the watershed [START_REF] Perrin | Solute recycling: an emerging threat to groundwater quality in southern India[END_REF] and which simulates an increase in concentration of any mobile element by 2.8 over the last 13 years.

Simulating F accumulation beneath a paddy field

Fluoride concentrations as well as evaporation linked to IRF are higher beneath paddy fields suggesting the impact of evaporation on F accumulation. However, the lack of clear relationship between "D-excess" and fluoride suggest the occurrence of other processes involved within fluoride accumulation, among them contribution from variability of water-rock interactions processes and inputs from fertilizers. A 1D PHREEQC column has been conceptualized in order to understand the relative contributions of the above mentioned processes on the control of fluoride accumulation in groundwater (Fig. 3). In this model, return flow is simulated by successive infiltration of pumped groundwater (last cell in column PHREEQC) after flowing through the column. At each daily step of recharge, an average evaporation flux is applied to the inflowing solution. The calculations are made for an average thickness of 20m above the groundwater level and an average infiltration velocity corresponding to the geometric mean of hydraulic conductivity in the laminated layer of 5.1 x10 -5 m.s -1 (about 4.4 m/day) [START_REF] Dewandel | A Generalized 3-D geological and hydrogeological conceptual model of granite aquifers controlled by a single or multiple weathering[END_REF].

Water-rock interactions processes taken into account are based on observations. Biotite, apatite, allanite and sphene are the main F-bearing minerals of the granite from the watershed. As sphene is an unalterable phase, it cannot be considered as a main contributor to F accumulation. Therefore, only biotite (F: 1.08%), fluorapatite (F: 3.42%) and allanite (F: 0.97%) must account for the fluoride accumulation. On one hand, the presence of some undesirable elements such as uranium at concentrations that can exceed the drinking water limit supports the contribution of allanite (U= 0.3%). On the other hand, a lack of vanadium in some of the high-F-groundwater samples, despite the significant content in biotite (V=0.03% ) and allanite (V= 0.03%), suggests a significant contribution from fluorapatite (V<0.003%) in some samples. Thus, the three Fbearing minerals almost certainly contribute through water-rock interaction processes and have been taken into account in the PHREEQC 1D conceptual model of water infiltration beneath a paddy field.

In the calculations, thermo-kinetic dissolution of primary aluminosilicate phases (allanite and biotite, among others) and iron oxides (goethite) are based on the general form:

Where eff m i k , is the rate constant, Q i is the ion activity product and m i K is the thermodynamic equilibrium constant for the reaction [START_REF] Lasaga | Kinetic Theory In the Earth Sciences[END_REF]. Dissolution rate of fluorapatite (Ca 10 (PO 4 ) 6 F 2 ) depends on pH and is expressed according to [START_REF] Chaïrat | Kinetics and mechanism of natural fluorapatite dissolution at 25°C and pH from 3 to 12[END_REF]. Precipitation of secondary mineral at thermodynamic equilibrium is allowed for chalcedony, calcite, fluorite, gibbsite, kaolinite, dolomite, ferrihydrite. Adsorption processes, including fluoride adsorption, are described by [START_REF] Dzombak | Surface complexation modeling[END_REF] theory for both ferrihydrites and gibbsite minerals. The model also includes ion exchange capacity of clays. The evolution of the chemical composition is simulated as a function of time and depth (Fig. 4). During infiltration, through-flow column and return flow, pH value stays near neutrality because of the buffering effect due to calcite precipitation. Cl -concentration increases yearly by 9.4%. Fluoride concentration varies with depth in response to infiltration of evaporated water and water-rock interaction processes. It also increases with time despite possible fluoride adsorption onto precipitating mineral phases and the potential fluorite (CaF 2 ) precipitation according to the reaction:

Ca 2+ + 2F -↔ CaF 2
Fluoride concentration increase exceeds that of chloride but depends on the dissolution rate of the primary mineralogy (biotite, allanite and fluorapatite). The strong mobilization of F is due to the inhibition of fluorite precipitation by calcite stability in the system, which precipitation consumes calcium, making it unavailable for fluorite.

Impact of climate change

The 1D PHREEQC column can be applied to evaluate groundwater vulnerability to high fluoride concentration for several land use and climate change scenarios. In particular, climate change, by changing rainfall rates and temperature may have a additional negative impact on groundwater quality, notably by enhancing F accumulation. Increase of temperature contributes to evaporation increase. With the change of rainfall rates, they promote salinization of the groundwater system. For the considered study area, by applying a lumped reservoir model, [START_REF] Perrin | Solute recycling: an emerging threat to groundwater quality in southern India[END_REF] simulated the concentration evolution of any conservative elements for different scenarios during the next 35 years . Decrease of rainfall rates by 10 % would lead to an increase of any conservative element concentration by a factor of about 2 and evaporation increase by 10 % would increase concentration by about 1.8 compared to today's values. For fluoride, higher factors have even to be expected because of additional dissolution of F-bearing primary minerals. Apart from evaporation, temperature increase may also modify water-rock interactions and in turn impacts F concentration. Thus, we have shown that calcite stability within soils is a key parameter of fluoride increase in groundwater, and increase of temperature favors calcite stability, although the sensitivity of this parameter need to be assessed. According to these results, F concentration in groundwater beneath paddy fields would systematically exceed the drinking water limit rapidly (1.5 mg/l).

CONCLUSIONS

Fluoride accumulation in groundwater constitutes a threat to drinking water for local communities in hard-rock regions of India. Although fluoride originates from dissolution of rock aquifer during groundwater flow, some land use practices can contribute to its accumulation. Our work shows that evaporation in paddy fields and subsequent water-rock interaction during return flow increases F concentration by several mg/l, by a factor higher than that of overall salinity and leading rapidly to groundwater exceeding the drinking water limit. The 1D geochemical model can be applied to evaluate groundwater vulnerability to high fluoride concentration for several land use and climate change scenarios. Climate change is expected to enhance F accumulations in groundwater, in particular through the decrease of rainfall and increase of evaporation. Within a near future, all groundwater around paddy fields would reach F concentration exceeding drinking water limit.

  Figure 1: Site Location

Figure 2 :

 2 Figure 2: 'D-excess' vs. fluoride plot for groundwater from the Maheshwaram watershed

Figure 3 .

 3 Figure 3. PHREEQC 1D Column conceptual model of return flow simulation beneath a paddy field.

Fig. 4 :

 4 Fig.4: F concentration pattern with depth on a daily basis and at different periods of time.

  Vulnerability of intensively-exploited hard-rock aquifers to fluoride contamination in India: impact of global change Hélène Pauwels, Marie Pettenati, Jérôme Perrin, Philippe Negrel

	BRGM, Orléans, France