Mixture toxicity of thiophanate-methyl and fenvalerate to embryonic zebrafish (Danio rerio) and its underlying mechanism

Though pesticide mixtures can reflect the real-life situation in the water ecosystem, the quantification of their toxicity is still not fully understood. Combined effects of thiophanate-methyl (THM) and fenvalerate (FEN) on embryonic zebrafish (Danio rerio) and underlying mechanism were conducted in this study. Results showed that the 96-h LC50 values of THM to D. rerio at different growth periods ranged from 12.1 to 26.1 mg L-1, which were lower in comparison with those of FVR ranging from 0.025 to 2.8 mg L-1. Mixture of THM and FVR exhibited a synergetic response to zebrafish embryos. Activities of Cu/Zn-SOD, POD, caspase 3 and caspase 9 were significantly different in most of single and mixture administrations compared with the control group. In addition, live genes (P53, Cu/Zn-sod, crh, ER alpha and IL-8) associated with oxidative stress, cellular apoptosis, immune system and endocrine system showed greater variations of expressions when administrated to pesticide mixtures compared with single chemicals. Our experimental results exhibited that mixtures of thiophanatemethyl and fenvalerate produced higher toxicity towards aqueous vertebrates than when determined singly. Collectively, upcoming environmental risk assessments established according to single administrations might not be enough to protect the water ecosystem. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study found that the mixture of thiophanate-methyl and fenvalerate showed higher toxicity to zebrafish embryos compared to individual chemicals, and had a greater impact on the expression of related genes in zebrafish. Therefore, future environmental risk assessments need to consider the effects of pesticide mixtures on aquatic ecosystems.