In the present study, we evaluated the individual and combined toxic effects of herbicide atrazine and three insecticides (chlorpyrifos, lambda-cyhalothrin and imidacloprid) on the earthworm, Eisenia fetida. Results from 48-h filter paper test indicated that imidacloprid had the highest toxicity to E. fetida with an LC50 of 0.05 (0.041-0.058) μg a.i. cm(-2), followed by lambda-cyhalothrin and atrazine with LC50 values ranging from 4.89 (3.52-6.38) to 4.93 (3.76-6.35) μg a.i. cm(-2), while chlorpyrifos had the least toxicity to the worms with an LC50 of 31.18 (16.22-52.85) μg a.i. cm(-2). Results from 14-days soil toxicity test showed a different pattern of toxicity except that imidacloprid was the most toxic even under the soil toxicity bioassay system. The acute toxicity of atrazine was significantly higher than that of chlorpyrifos. In contrast, lambda-cyhalothrin was the least toxic to the animals under the soil toxicity bioassay system. The binary mixture of atrazine-lambda-cyhalothrin and ternary mixture of atrazine-chlorpyrifos-lambda-cyhalothrin displayed a significant synergistic effect on the earthworms under the soil toxicity bioassay. Our findings would help regulatory authorities understand the complexity of effects from pesticide mixtures on non-target organisms and provide useful information of the interaction of various pesticide classes detected in natural environment.
Keywords: Acute toxicity; Combined toxicity; Ecotoxicology; Pesticide; Soil invertebrate.