Occurrences, distribution and risk assessment of polar pesticides in Niger River valley and its tributary the Mekrou River (Niger Republic).

The increase in food needs due to high population growth in Niger has led to the intensification of urban agriculture and the increased use of pesticides. The objective of this study is primarily to assess the polar pesticide contamination (mainly herbicides) of the Niger River and its tributary, the Mekrou River, in Niger, using both grab sampling and POCIS (Polar Organic Chemical Integrative Samplers), and then to evaluate the risk to the aquatic environment. Two water sampling campaigns were carried out during the wet and dry seasons. The polar pesticides were analyzed by liquid chromatography coupled with tandem mass spectrometry, which allowed the identification of compounds with concentrations in the grab samples above the WHO guide values and the EU directive: diuron with 2221 ng/L (EU quality guideline: 200 ng/L), atrazine with 742 ng/L (EU quality guideline: 600 ng/L) and acetochlor with 238 ng/L (EU quality guideline: 100 ng/L). The risk assessment study indicated that diuron and atrazine present a high risk for the aquatic environment during the wet season. The main source of water contamination is the intensive use of pesticides in urban agriculture near the city of Niamey, and the intensive cotton farming in the Benin. Moreover, the surveys (30 producers interviewed) showed that 70% of the pesticides used are not approved by the Interstate Committee for Drought Control in the Sahel (CILSS) and some are prohibited in Niger. The inventory of pesticides sold in the zone showed that active ingredients used by producers are 48% insecticides, 45% herbicides, and 7% fungicides.

Development and implementation of a multi-criteria aggregation operator to estimate the contributions of the natural geochemical background and anthropogenic inputs in groundwater in former mining regions: An application to arsenic and antimony in the Gardon river watershed (southern France).

Establishing the contribution of natural enrichment of a substance and anthropogenic inputs has become a major issue for the management of groundwater systems. The issue is made more complex when the geology of the concerned territories is heterogeneous, at variable geographical scales, at a site that has experienced mining activity that has left behind mining remains. Several studies have tried to answer this problem using different approaches: statistical, geostatistical, geological, and geochemical. The limits of these studies are seen through the incomplete integration of geological and geomorphological parameters in the results. The aim of the present research is, therefore, to look deeper into an approach to estimate the respective contributions of the natural geochemical background and anthropogenic inputs, by simultaneously considering the heterogeneity of the geology, the variability of the spatial scale, and the combination of geological, geomorphological and statistical factors. A multi-criteria aggregation operator was thus developed and implemented on underground water bodies delimited by the Gardon watershed in the Cevennes (a region with former mining activities - France), in order to produce quantitative and qualitative maps for discriminating between the natural geochemical background and anthropogenic inputs. 176 geochemical observation points on groundwater quality were collected by sampling and through the acquisition of public data on water sources (ADES database), wells and boreholes, to reconstruct the spatial distribution of arsenic and antimony in the study site. An aggregation operator was developed, which enabled the determination of the formulae to calculate the natural geochemical background and hence deduce the anthropogenic contributions. Cartography of the quantitative and qualitative aspects of the geochemical concentrations that have been impacted by anthropogenic activity made it possible to determine remarkable focal points located on the Cevennes fault and other specific points of geochemical interest.