Levels of soil pollution by pesticides in market gardening sites in the department of Madaoua, Niger

In Madaoua Department-Niger, market gardeners have adopted peasant practices of using pesticides that can pollute the soil. The objective of this study is to quantify pesticide residues in the soils of these market garden sites in order to highlight their level of pollution. Sixteen (16) composite soil samples, including five (5) in Galma, six (6) in Madaoua and five (5) in Sabon Guida were taken in the first twenty centimeters using an auger. The extraction and analysis of pesticide residues were carried out by the QuEChERS method. Residues of twenty-seven (27) pesticides belonging to eight (8) chemical families were quantified in soils at average concentrations ranging from 3.6 to 678 µg.kg-1. According to the maximum residue limits (MRLs) of pesticides fixed in the soil in the Netherlands, Canada, the United States and India, 44.44% of the quantified residues have average concentrations, which are 1.01 to 2194 times higher than MRLs in soils. Pesticides with average concentrations above their MRLs are: DDT (84.2-238 µg.kg-1), aldrin (9.6-20 µg.kg-1), dieldrin (3.6-5.67 µg.kg-1), alpha-endosulfan (126.4-227.7 µg.kg-1), beta-endosulfan (59.4-113.8 µg.kg-1), heptachlor (40.6-146.8 µg. kg-1), lindane (34.8-109.7 µg.kg-1), dicofol (54-86.8 µg.kg-1), chlorpyrifos methyl (164.8-278.6 µg.kg-1), pyrimifos methyl (144.4-277.2 µg.kg-1), profenofos (53.6-94.2 µg.kg-1) and malathion (193.4-304.5 µg.kg-1). The very high concentrations of lindane are worrying. Indeed, they exceed its MRL by 696 to 2194 times (0.05 µg.kg-1). Some pesticides such as DDT, aldrin, dieldrin, endosulfan, and lindane are even banned according to Annex III of the Rotterdam Convention for health or environmental reasons.  This study therefore revealed soil pollution by pesticide residues from the market garden sites investigated