Occurrences, distribution and risk assessment of polar pesticides in Niger River valley and its tributary the Mekrou River (Niger Republic)
Résumé
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 herbi-
cides) 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 assess-
ment 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.
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