Assessment of ecotoxicological effects of agrochemicals on bees using the PRIMET model, in the Tiko plain (South-West Cameroon)

Pesticide utilization in agriculture has many harmful effects of non-target organisms. This study assessed pesticide risk to bees using PRIMET (Pesticide Risks in the Tropics to Man, Environment and Trade), a pesticide risk model. Data was collected on pesticide application scheme (active ingredient, crop, dose, number of applications, application interval) and ecotoxicological properties (LD(50-Bee)). These two groups of variables were introduced one after the other in PRIMET 2.0 to obtain the Predicted Exposure Concentration (PEC(bee)), No Effect Concentration (NEC(bee)) and Exposure Toxicity Ratio (ETR(bee) = PEC(bee)/NEC(bee)). Eight insecticides (out of 15 assessed) and 1 nematicide (out of 1) posed a Definite Risk to bees with imidacloprid (PEC = 4412 g/ha; ETR = 1.09E+07) at the top position. Six insecticides (out of 16), and 1 nematicide (out of 1) posed a Possible Risk to bees. The insecticide oxamyl (PEC = 2044g/ha, ETR = 87) had the highest ETR in this category, followed by the nematicide ethoprophos (PEC = 5.4E+04 g/ha; ETR = 69). The results of this study revealed that 27 compounds, including 1 insecticide (out of 15), 10 herbicides (out of 10) and 16 fungicides (out of 16) posed No Risk to bees. Herbicides and fungicides appeared “safer” for bees as compared to other pesticide families. The fungicides, mancozeb (PEC = 1 g/ha, ETR = 0.006) and maneb (PEC = 1 g/ha, ETR = 0.006) had the lowest ETR out of all the 43 compounds assessed in the study. Regulation on the importation, distribution and use should be reinforced for very hazardous compounds such as imidacloprid, carbofuran, thiamethoxam and metaldehyde. Substituting the most toxic pesticides with less toxic ones such as novaluron (insecticide), oxadiazon (herbicide), mancozeb (fungicide) and maneb (fungicide) may help to reduce pesticide pressure on the environment.