Mono(2-ethylhexyl) phthalate modulates lipid accumulation and reproductive signaling in Daphnia magna.

Mono(2-ethylhexyl) phthalate (MEHP) is a primary metabolite of di(2-ethylhexyl) phthalate (DEHP), which is widely used in industry as a plasticizer. Both DEHP and MEHP have been identified as endocrine disruptors affecting reproduction systems in natural aquatic environments. However, the effects of MEHP exposure on aquatic invertebrates such as Daphnia magna are still poorly understood. In the present study, lipid alterations caused by MEHP in D. magna were identified by analyzing lipid accumulation and nontarget metabolomics. In addition, reproductive endpoints were investigated. MEHP exposure under any conditions upto 2 mg/L was not associated with mortality of D. magna; yet, the number of lipid droplets and the adult female daphnids reproduction rates increased after 96 h of exposure and 21 days of exposure, respectively. MEHP also enhanced lipid metabolism, as evident from 283 potential lipid metabolites, including glycerolipids, glycerophospholipids, and sphingolipids, identified following 48 h of exposure. The MEHP-treated group exhibited significantly higher ecdysone receptor (EcR) and vitellogenin 2 (Vtg2) expression levels at 6 and 24 h. At 48 h, EcR and Vtg2 expression levels were downregulated in the 1 and 2 mg/L MEHP exposure groups. Our data reveal that the EcR pathway changes over MEHP exposure could be associated with lipid accumulation, owing to increased lipid levels and the subsequent increase in the reproduction of MEHP-exposed D. magna.

Quantitative prediction of mixture toxicity of AgNO3 and ZnO nanoparticles on Daphnia magna.

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.