Pesticides Occurrence in an Alfisol of Sudano-Sahelian Agricultural Watershed (Korokoro, Mali)

Soil contamination by pesticides (organochlorine, organophosphates and pyrethroids) has been studied in the agricultural watershed (60.6 km 2) of Korokoro in Mali. Farmers of this watershed produce cotton and cereals (sorghum, maize, millet). Soil samples (0-20 cm) of an alfisol used for cotton cropping were collected at the end of the cropping seasons 2010 and 2011. Samples were analyzed by gas chromatography and mass spectrometer for quantifying the main pesticides (profenofos, acetamiprid, atrazine and cypermethrin) frequently used in the watershed and others organochlorine pesticides (DDT, endosulfan and HCH) that could be still detected. The results showed that soils were contaminated by DDT and its metabolites (0.1 to 3.5 µg.kg-1) due to past agricultural uses for African migratory locust control while those of endosulfan sulfate (detection limit to 4.2 µg.kg-1) and cypermethrin (2.5 to 6.2 µg.kg-1) were due to their actual application on cotton. According to mass balances calculation cypermethrin residues are stocked in the soil compartment of the watershed after its application on cotton. This accumulation was evaluated at 13 ± 0.4% of applied quantities.