Transboundary river water pesticide pollution in historical agriculture areas in West Africa: a case study in the Comoe, Bia, and Tanoe rivers (Cote d’Ivoire)

Pesticides’ contamination status was determined in water samples at the Bia, Tanoe, and Comoe Rivers’ mouths to understand their occurrences and the potential ecological and human health risks in Cote d’Ivoire, West Africa. A total of 26 out 30 pesticides measured including five organophosphates, eleven N-substituted ureas, nine triazines, and one carbamate, triazinone, pyrimidine, and two chloroacetanilides/organochlorines were detected in the three estuaries at concentrations far above international standards. The triazinone herbicides were the most frequently detected followed by pyrimidine rodenticides. Simazine herbicide showed the highest concentration of 120.7 μg/L in the rivers. The Tanoe River bordering Cote d’Ivoire and Ghana recorded more pesticide occurrences per water sample than the Bia and Comoe Rivers; the Bia River hosting large cocoa and rubber plantations in Cote d’Ivoire had significantly higher pesticide concentrations than in the other rivers. The Bia River showed significantly higher concentration during the rainy season than in the flood and dry seasons while no seasonal trend was found in the Comoe and Tanoe Rivers. The risk quotient data suggest that the Bia, Tanoe, and Comoe Rivers present chronic high risks to aquatic organisms; pesticide concentrations in the Bia River are likely to pose chronic health risks to children from 0 to 11 years.