Assessment of Pesticide Contamination in Agricultural Soils According to Crop Type in the Niayes Zone

The Niayes constitute a unique ecosystem in Senegal, providing the bulk of the country's horticultural production. However, this area is undergoing severe ecological degradation due to the combined effects of several factors, including agricultural activities, urban and industrial development and climate change. Agriculture is becoming increasingly intensive, with high levels of chemical inputs, including pesticides. In 2021, studies showed that 100% of agricultural soils contained pesticides that could have harmful effects on soil health. Soil samples were taken in the study area in 2022 and 2023 and analyzed for residues of thirty-five pesticides, including persistent organic pollutants. The results obtained in 2022 revealed that 100% of the study sites were contaminated by pesticides, including profenofos (88% of plots), dimethoate (89%), bromacil and chlorpyrifos (64%) and abamectin (48%). The same trend was observed in 2023, when all sites were contaminated, with abamectin (89% of plots), cypermethrin, bromacil and profenofos (80%) the most frequently found molecules. These were followed by lambda-cyhalothrin, trifluralin and pendimethalin (76%), chlorpyrifos (71%), DDT (62%) and lindane (38%). These results were used to map contamination in the Niayes area in 2022 and 2023 using Geographic Information System (GIS) software, and to identify the most polluting crops. As a result, all soils hosting onions, carrots, turnips, peppers and tomatoes were contaminated. In addition, the highest pesticide residue levels were found in the soils of onion and tomato fields.