Ecological risk assessment of pesticides on earthworms on the southeast slopes of Mount Cameroon

Agrochemicals misuse is a common practice in developing countries with many environmental implications. This work assessed the ecological risk of pesticides, utilised by farmers, on earthworms at the lower slopes of Mount Cameroon using the Pesticide Risk in the Tropics to Man, Environment and Trade (PRIMET) model. PRIMET was developed in 2008 by modellers in The Netherlands for use in tropical regions. Data on usage scheme and ecotoxicological information was collected and keyed into PRIMET for three main outputs: Predicted Exposure Concentration (PEC), No Effect Concentration (NEC), and Exposure Toxicity Ratio (ETR = PEC/NEC). Pesticides that were predicted for no acute and no chronic risk to earthworms included fipronil and chlorothalonil. A few compounds were predicted for an acute risk to earthworms, and they comprised acetamiprid; imidacloprid; lambda-cyhalothrin; carbendazim when used on maize (PEC = 2.69 mg.kg-1; ETR = 5) and tomato (PEC = 16.15 mg.kg-1; ETR = 30); 2, 4-D; abamectin when used on tomato; and ethoprophos. Insecticides exhibiting a possible chronic risk to earthworms comprised acetamiprid, cypermethrin, emamectin benzoate, imidacloprid, indoxacarb, lambda-cyhalothrin, oxamyl, and thiametoxam. The majority of fungicides assessed (83%) posed a possible chronic terrestrial risk, with carbendazim at the top position when applied on tomato (PEC = 16.15 mg.kg-1; ETR = 81). Other pesticides predicted for possible chronic risk to earthworms included 2, 4-D, diuron, glyphosate, ethoprophos, and metaldehyde. Pesticides with the highest risk to earthworms comprised chlorpyrifos-ethyl, imidacloprid, ethoprophos, and nicosulfuron. The riskiest pesticides should hereby be regulated or replaced by less risky ones. The measurement of pesticide residues in water and food in the various agroecological zones of Cameroon is a necessity to put more light on pesticide ecotoxicology.