Joint toxic impacts of cadmium and three pesticides on embryonic development of rare minnow (Gobiocypris rarus)

Although rare minnow (Gobiocypris rarus) has been employed in many toxicological investigations, most of them have only assessed the impacts of single chemical. In our current work, we investigated the single and joint toxic impacts of heavy metal cadmium (Cd) and three pesticides (thiamethoxam, bifenthrin, and tebuconazole) on G. rarus embryos. Results from the 96-h semi-static toxicity assay exhibited that bifenthrin possessed the highest intrinsic toxic effect on rare minnows with an LC50 value of 1.86 mg L−1, followed by tebuconazole with LC50 values of 4.07 mg L−1. Contrarily, thiamethoxam elicited the least toxic effect with an LC50 value of 351.9 mg L−1. Seven chemical mixtures (four binary mixtures of Cd-bifenthrin, thiamethoxam-bifenthrin, thiamethoxam-tebuconazole, and bifenthrin-tebuconazole, two ternary mixtures of Cd-thiamethoxam-tebuconazole and thiamethoxam-bifenthrin-tebuconazole, and one quaternary mixture of Cd-thiamethoxam-bifenthrin-tebuconazole) displayed synergistic impacts with equivalent concentration and equitoxic ratio on G. rarus. Our results offered valuable insights into ecological risk assessment of these chemical combinations to aquatic vertebrates. The simultaneous existence of a few chemicals in the aquatic ecosystem might result in elevated toxicity, leading to severe harm to the non-target organisms compared with single compound. The observed synergistic interactions underlined the necessity to revise water quality standards, in which the detrimental joint effects of these chemicals are likely to be underestimated.