Ecological risk assessment of pesticides in the Ngouoh Ngouoh watershed of the Foumbot Municipality in the west region of Cameroon using the PRIMET model.

Abstract

The use of pesticides near water bodies poses significant risks to non-target organisms. This work aimed at assessing risks related to pesticide utilization on common tropical crops along the Ngouoh Ngouoh stream (West Cameroon) using PRIMET (Pesticide Risks in the Tropics to Man, Environment, and Trade), a pesticide risk model. Data on the physicochemical and ecotoxicological characteristics of pesticides, pesticides application scheme and water abiotic variables were measured and input one at the time into the PRIMET model to get the PEC (Predicted Exposure Concentration), PNEC (Predicted No Effect Concentration) and ETR (Exposure Toxicity Ratio = PEC/PNEC). Among the 13 pesticides assessed, the PRIMET model predicted 8 pesticides to pose acute risk while two were predicted for a chronic risk. Imidacloprid (PEC = 4.53µg/L; ETR = 7.6), mancozeb (PEC = 4.05µg/L; ETR = 5.6), copper hydroxide (PEC = 4.05µg/L; ETR = 23.81), chlorothalonil (PEC = 2.59µg/L; ETR = 15.2) posed a possible acute hazard risk while cypermethrin (PEC = 4.52µg/L; ETR = 7694), emamectin benzoate (PEC = 3.17µg/L; ETR = 317), paraquat (PEC = 33.13µg/L; ETR = 1440) and lambda-cyhalothrin (PEC = 4.52µg/L; ETR = 2.83E + 04) posed definite risks. Cypermethrin also posed a possible chronic hazard to fish (ETR = 32.8) and lambda-cyhalothrin posed a possible risk to daphnia (ETR = 2.7). The Ngouoh Ngouoh stream physicochemical properties exhibited significant changes across sampling stations. Decision-makers should take measures to limit the use of pesticides that are harmful for aquatic biodiversity.