Once metal-based engineered nanoparticles (NPs) are released into the aquatic environment, they are expected to interact with other existing co-contaminants. A knowledge gap exists as to how the interaction of NPs with other co-contaminants occurs. Here we selected ZnO NPs among various NPs, with Ag ion existing as a contaminant in the aquatic environment by Ag NPs widely used. A novel modeling strategy was demonstrated enabling quantitative and predictive evaluation of the aqueous mixture nanotoxicity. Individual and binary mixture toxicity tests of ZnO NPs and silver (as AgNO3) on Daphnia magna were conducted and compared to determine whether the presence of Ag ions affects the toxicity of ZnO NPs. Binary mixture toxicity was evaluated based on the concentration addition (CA) and independent action models. The CA dose-ratio dependent model was found to be the model of best fit for describing the pattern of mixture toxicity. The MIX I and MIX III suspensions (higher ratios of ZnO NPs to AgNO3) showed a synergism, whereas the MIX II suspension (lower ratio of ZnO NPs to AgNO3) showed an antagonism. The synergistic mixture toxicity at higher ratios of ZnO NPs to AgNO3 was caused by either the physiological or metabolic disturbance induced by the excessive ionic Zn or increased transport and accumulation in D. magna via the formation of complex of ionic Ag with ZnO NPs. Therefore, the toxicity level contributed via their aggregation and physicochemical properties and the dissolved ions played a crucial role in the mixture toxicities of the NPs.
Mono(2-ethylhexyl)-phthalate (MEHP) is the primary metabolite of di(2-ethylhexyl)-phthalate (DEHP), which is widely used in industry as a plasticizer. Previous studies showed that both DEHP and MEHP have been found in not only human urine samples but also natural aquatic environments, and well documented as toxicants for reproduction and endocrine disruptors, However, the effects of MEHP exposure on aquatic organisms, including invertebrates such as Daphnia magna (D. magna), are still scarce. In the present study, the lipid alterations caused by MEHP in D. magna have been identified by analyzing lipid accumulation and nontarget metabolomics. Additionally, the expressions of reproduction were investigated. Ecotoxicologically relevant concentrations (1 to 2 mg/L) and exposure time ranges (24 h to 21 days) have been tested. MEHP resulted in no mortality to D. magna with all exposure conditions, but the number of lipid droplets increased after 96 h of exposure and enhanced reproduction of female adult daphnids was observed in the 21-day of exposure. Besides, we observed that MEHP enhanced lipid metabolism with the identification of 283 potential lipid metabolites, including glycerolipids, glycerophospholipids, and sphingolipids, following 48 h of exposure. MEHP treated group exhibited significantly higher expression of ecdysone receptor (EcR) and vitellogenin 2 (Vtg2) at 6 h and 24 h. Meanwhile at 48 h, EcR and Vtg2 were downregulated in 1 and 2 mg/L MEHP exposure. Our data show that the changes in EcR pathway with different exposure time could be associated with the lipid accumulation due to lipids increment subsequently to increased reproduction in MEHP-exposed D. magna.
Mono(2-ethylhexyl)-phthalate (MEHP) is the primary metabolite of di(2-ethylhexyl)-phthalate (DEHP), which is widely used in industry as a plasticizer. Previous studies showed that both DEHP and MEHP have been found in not only human urine samples but also natural aquatic environments, and well documented as toxicants for reproduction and endocrine disruptors, However, the effects of MEHP exposure on aquatic organisms, including invertebrates such as Daphnia magna (D. magna), are still scarce. In the present study, the lipid alterations caused by MEHP in D. magna have been identi ed by analyzing lipid accumulation and nontarget metabolomics. Additionally, the expressions of reproduction were investigated. Ecotoxicologically relevant concentrations (1 to 2 mg/L) and exposure time ranges (24 h to 21 days) have been tested. MEHP resulted in no mortality to D. magna with all exposure conditions, but the number of lipid droplets increased after 96 h of exposure and enhanced reproduction of female adult daphnids was observed in the 21-day of exposure. Besides, we observed that MEHP enhanced lipid metabolism with the identi cation of 283 potential lipid metabolites, including glycerolipids, glycerophospholipids, and sphingolipids, following 48 h of exposure. MEHP treated group exhibited signi cantly higher expression of ecdysone receptor (EcR) and vitellogenin 2 (Vtg2) at 6 h and 24 h. Meanwhile at 48 h, EcR and Vtg2 were downregulated in 1 and 2 mg/L MEHP exposure. Our data show that the changes in EcR pathway with different exposure time could be associated with the lipid accumulation due to lipids increment subsequently to increased reproduction in MEHP-exposed D. magna.
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