The Transfer of Insecticides Used in Cotton Production to Aquatic Ecosystems in the Cotton Basin in Northern Benin

Abstract

The transfer of two insecticides (acetamiprid and chlorpyrifos) from cotton fields to a nearby water reservoir together with the ecotoxicological risks involved for this receiving environment were assessed by measuring their concentrations in runoff water and sediment samples collected both at the exit of the crop plots and in the reservoir after treatment. The multi-residue method by UPLC-MS/MS was used to determine the concentration of the different active substances in the collected samples. The results obtained indicate that acetamiprid and chlorpyrifos are almost always present regardless of the treatment period. The physico-chemical properties (solubility in water and adsorption to soil particles) explain a difference in behaviour between acetamiprid, present mainly in water, and chlorpyrifos, more concentrated in sediments. Calculations show that 0.005% of the acetamiprid applied in the basin around Gambanè flows to the reservoir, compared to 0.0003% of the chlorpyrifos applied. Depending on the sampling dates, the average runoff quantities for acetamiprid vary from 0.002 to 0.156 g/ha over 96 g/ha and from 0.001 to 0.039 g/ha for chlorpyrifos. The study shows that the transfer by runoff from the fields is relatively fast but is nevertheless influenced by rainfall, the distance of the fields to the reservoir, the slope and the characteristics of the environment. At the concentrations of acetamiprid observed in this receiving environment, the ecotoxicological risk would be negligible (Environmental Risk Index = 4) for aquatic organisms, earthworms and birds. However, concentrations of chlorpyrifos in the environment could be harmful to these organisms (Environmental Risk Index = 272). The aquatic ecosystem in this area is therefore exposed to the harmful effects of these active substances. Key words: acetamiprid; chlorpyrifos; UPLC-MS/MS; cotton