Combined toxicity assessment of myclobutanil and thiamethoxam to zebrafish embryos employing multi-endpoints

It is necessary to understand the interactions between different pesticides in ecotoxicology because pesticides never appear as individual compounds but rather in combinations with other compounds. In this study, we planned to explicate the combined toxic effect of myclobutanil (MYC) and thiamethoxam (THI) on the zebrafish (Danio rerio) by adopting multiple biomarkers. Results unraveled that the 96-h LC₅₀ values of MYC to D. rerio at various life phases ranged from 5.2 to 10.3 mg L^-1, which were lower than those of THI ranging from 147 to 246 mg L^-1. Combinations of MYC and THI exhibited synergetic toxicity to zebrafish embryos. The activities of antioxidative enzymes (T-SOD, Cu/Zn-SOD and POD) and detoxification enzyme (GST) were obviously varied in most of the MYC, THI and combined exposures compared to the control. The mRNA expressions of eight genes (Cu-sod, cas3, il-8, cxcl, erα, crh, cyp17 and dio1) involved in antioxidation, apoptosis, immunity and endocrine were obviously altered in the combined exposure of MYC and THI compared to their individual exposures. Our findings hinted the threats when YMC and THI co-existed, which would be beneficial for the risk assessments of pesticide mixtures.

Effect of nano zinc oxide on the acute and reproductive toxicity of cadmium and lead to the marine copepod Tigriopus japonicus

Given the absorbability of nZnO and its inevitable coexistence with trace metals such as Cd and Pb in coastal environment, nZnO can adsorb these pollutants thereby affecting their distribution in different media of marine ecosystem. The marine copepod Tigriopus japonicus was applied in the present study to investigate the combined effect of nZnO and Cd or Pb on mortality and reproduction in marine organisms. For acute exposure, presence of 1.0 mg/L nZnO increased the toxicity of both Cd and Pb, as their LC₅₀ decreased from 5.9 and 75.4 mg/L to 3.95 and 48.0 mg/L, respectively. For 21 d chronic exposure, the reproduction of the copepod was influenced by Cd and Pb at environmental relevant concentrations, and the interaction between nZnO and Cd or Pb appeared to be antagonistic. The waterborne Cd and Pb concentration was affected by nZnO for neither acute nor chronic exposure, indicating no adsorption of these two metals to nZnO at relative low concentration. The overall findings of this study suggested the binary exposure to nZnO/Cd or nZnO/Pb might have potential different toxic mechanisms between acute and chronic exposure.

Quantification of the combined toxic effect of polychlorinated biphenyls and nano-sized polystyrene on Daphnia magna

It has been reported that nanoplastics (NP) could cause serious toxicity and accumulative effects on aquatic organisms as well as interact with organic pollutants and influence potential hazards when exposed to biota. The current study aimed to quantitatively investigate the combined acute toxic effect of polychlorinated biphenyls (PCBs) and nano-sized polystyrene (PS) plastic on aquatic organisms based on analyte speciation. First, the combined acute toxicity of PCB-18 and 100 nm PS to Daphnia magna (D. magna) in water was evaluated. Then, speciation analysis of the exposure system was conducted by measuring the sorption coefficients (logK_NP) of PCBs to nano-sized PS (ranging from 5.28 to 6.56), which demonstrated the PS could substantially decrease the free concentrations of PCBs. The results showed that a low concentration of the PS could decrease the toxicity to D. magna., which might be originated from the decreased free concentration of PCB-18. However, when the PS concentration was high enough, an opposite effect was observed because the PS dominated the lethality instead of PCB-18. The current study is helpful to clarify the PCB occurrence in ecosystems and provide an in-depth understanding of the eco-toxicological effects of nanoscale plastics.