Combined effects of four pesticides and heavy metal chromium (VI) on the earthworm using avoidance behavior as an endpoint

In natural ecosystems, organisms are commonly exposed to chemical mixtures rather than individual compounds. However, environmental risk is traditionally assessed based on data of individual compounds. In the present study, we aimed to investigate the individual and combined effects of four pesticides [fenobucarb (FEN), chlorpyrifos (CPF), clothianidin (CLO), acetochlor (ACE)] and one heavy metal chromium [Cr(VI)] on the earthworm (Eisenia fetida) using avoidance behavior as an endpoint. Our results indicated that CLO had the highest toxicity to E. fetida, followed by Cr(VI), while FEN showed the least toxicity. Two mixtures of CPF + CLO and Cr(VI) + CPF + CLO + ACE exhibited synergistic effects on the earthworms. The other two quaternary mixtures of CLO + FEN + ACE + Cr(VI) and Cr(VI) + FEN + CPF + ACE at low concentrations also displayed synergistic effects on the earthworms. In contrast, the mixture of Cr(VI) + FEN had the strongest antagonistic effects on E. fetida. Besides, the quinquenary mixture of Cr(VI) +FEN + CPF + CLO + ACE also exerted antagonistic effects. These findings highlighted the importance to evaluate chemical mixtures. Moreover, our data strongly pointed out that the avoidance tests could be used to assess the effects of combined effects.