Combined toxic impacts of thiamethoxam and four pesticides on the rare minnow (Gobiocypris rarus)

To examine pesticide mixture toxicity to aqueous organisms, we assessed the single and combined toxicities of thiamethoxam and other four pesticides (chlorpyrifos,beta-cypermethrin, tetraconazole, and azoxystrobin) to the rare minnow (Gobiocypris rarus). Data from 96-h semi-static toxicity assays of various developmental phases (embryonic, larval, juvenile, and adult phases) showed thatbeta-cypermethrin, chlorpyrifos, and azoxystrobin had the highest toxicities toG. rarus, and their LC(50)values ranged from 0.0031 to 0.86 mg a.i. L-1, from 0.016 to 6.38 mg a.i. L-1, and from 0.39 to 1.08 mg a.i. L-1, respectively. Tetraconazole displayed a comparatively high toxicity, and its LC(50)values ranged from 3.48 to 16.73 mg a.i. L-1. By contrast, thiamethoxam exhibited the lowest toxic effect with LC(50)values ranging from 37.85 to 351.9 mg a.i. L-1. Rare minnow larvae were more sensitive than embryos to all the pesticides tested. Our data showed that a pesticide mixture of thiamethoxam-tetraconazole elicited synergetic toxicity toG. rarus. Moreover, pesticide mixtures containingbeta-cypermethrin in combination with chlorpyrifos or tetraconazole also had synergetic toxicities to fish. The majority of pesticides are presumed to have additive toxicity, while our data emphasized that the concurrent existence of some chemicals in the aqueous circumstance could cause synergetic toxic effect, leading to severe loss to the aqueous environments in comparison with their single toxicities. Thence, the synergetic impacts of chemical mixtures should be considered when assessing the ecological risk of chemicals.

Automated summary

The study revealed varying levels of toxicity of different pesticides to the rare minnow, with thiamethoxam exhibiting the lowest toxicity. Additionally, pesticide mixtures were found to elicit synergistic toxic effects, emphasizing the importance of considering the combined impacts of chemical mixtures on aquatic environments.