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Insect pollinators are routinely exposed to a complex mixture of many pesticides. However, traditional environmental risk assessment is only carried out based on ecotoxicological data of single substances. In this context, we aimed to explore the potential effects when worker honey bees (Apis mellifera L.) were simultaneously challenged by thiamethoxam (TMX) and flusilazole (FSZ). Results displayed that TMX possessed higher toxicity to A. mellifera (96-h LC 50 value of 0.11 mg a. i. L−1) than FSZ (96-h LC 50 value of 738 mg a. i. L−1). Furthermore, the mixture of TMX and FSZ exhibited an acute synergistic impact on the pollinators. Meanwhile, the activities of SOD, caspase 3, caspase 9, and PPO, as well as the expressions of six genes (abaecin , dorsal-2 , defensin-2 , vtg , caspase-1 , and CYP6AS14) associated with oxidative stress, immune response, lifespan, cell apoptosis, and detoxification metabolism were noteworthily varied in the individual and mixture challenges than at the baseline level. These data revealed that it is imminently essential to investigate the combined toxicity of pesticides since the toxicity evaluation from individual compounds toward honey bees may underestimate the toxicity in realistic conditions. Overall, the present results could help understand the potential contribution of pesticide mixtures to the decline of bee populations. [Display omitted] • Thiamethoxam showed a higher acute toxic effect on the honey bees than fluconazole. • Thiamethoxam in combination with fluconazole produced synergistic toxicity. • CYP450s had important roles in the synergism of fluconazole and thiamethoxam. • mRNA levels of 6 genes in mixtures elicited greater alterations than individuals. • Joint effects should be incorporated into ecological risk assessment of pesticide. [ABSTRACT FROM AUTHOR]

Pesticides often occur as mixtures of complex compounds in water environments, while most of studies only focus on the toxic effects of individual pesticides with little attention to the joint toxic effects. In the present study, we aimed to the mixture toxicity of beta -cypermethrin (BCY) and thiacloprid (THI) to zebrafish (Danio rerio) employing multiple toxicological endpoints. Results displayed that the 96-h LC 50 values of BCY to D. rerio at various developmental stages ranged from 2.64 × 10 (1.97 × 10–3.37 × 10) to 6.03 × 103 (4.54 × 103–1.05 × 104) nM, which were lower than those of THI ranging from 2.97 × 104 (1.96 × 104–4.25 × 104) to 2.86 × 105 (2.19 × 105–5.87 × 105) nM. Mixtures of BCY and THI exhibited synergistic response in embryonic zebrafish. Meanwhile, the enzyme activities of antioxidants (CAT and SOD) and detoxification enzyme (CarE), endogenous T-GSH and MDA contents, as well as gene expressions (tsh , crh , cxcl and bax) involved in oxidative stress, cellular apoptosis, immune system and endocrine system were obviously changed in the mixture exposure compared with the respective BCY or THI treatment. Consequently, the increased toxicity of pesticide mixture suggested that the toxicological data acquired from individual pesticide tests might underrate the toxicity risk of pesticides that actually arise in the real environment. Taken together, our present study provided evidence that mixture exposure of BCY and THI could induce additional toxic effect compared with their respective individual pesticides on D. rerio , offering valuable insights into the toxic mechanism of pesticide mixture. Image 1 • Beta -cypermethrin exerted greater toxicity than thicloprid to zebrafish. • Mixtures of beta -cypermethrin and thicloprid had synergistic effect on zebrafish. • Expressions of 4 genes exerted greater changes in pesticide mixtures. • Mixture effects should be considered in the ecological risks of pesticide. Synergistic effects and underlying mechanism of beta -cypermethrin and thiacloprid on zebrafish. [ABSTRACT FROM AUTHOR]

Aquatic organisms are usually exposed to a mixture of pesticides instead of individual chemicals. However, risk assessment of pesticides is traditionally based on toxicity data of individual compounds. In this study, we aimed to examine the joint toxicity of two fungicides cyprodinil (CYP) and kresoxim-methyl (KRM) to zebrafish ( Danio rerio ) using a systematic experimental approach. Results from 96-h semi-static test indicated that the LC 50 values of KRM to D. rerio at multiple life stages (embryonic, larval, juvenile and adult stages) ranged from 0.034 (0.015–0.073) to 0.61 (0.39–0.83) mg a.i. L −1 , which were higher than those of CYP ranging from 1.05 (0.88–1.52) to 4.42 (3.24–6.02) mg a.i. L −1 . Pesticide mixtures of CYP and KRM exhibited synergistic effect on embryonic zebrafish. The activities of carboxylesterase (CarE) and cytochrome P450 (Cyp450) were significantly altered in most of the individual and combined exposures compared with the control group. The expressions of seven genes ( Mnsod , cyp17 , crhr 2 , crh , gnrhr 4 , gnrhr 1 and hmgrb ) were significantly altered upon exposure to combined pesticides compared with their individual pesticides. Collectively, these findings suggested joint effects should be considered in the risk assessment of pesticides and development of water quality criteria for the protection of aquatic environment. [ABSTRACT FROM AUTHOR]