Toxicity and speciation of inorganic arsenics and their adverse effects on in vivo endpoints and oxidative stress in the marine medaka Oryzias melastigma.

Here, we investigate the effects of acute and chronic exposure to arsenate (AsV) and arsenite (AsIII) in the marine medaka Oryzias melastigma. In vivo effects, biotransformation, and oxidative stress were studied in marine medaka exposed to the two inorganic arsenics for 4 or 28 days. An investigation of embryonic development revealed no effect on in vivo parameters, but the hatching rate increased in the group exposed to AsIII. Exposure to AsIII also caused the greatest accumulation of arsenic in medaka. For acute exposure, the ratio of AsV to AsIII was higher than that of chronic exposure, indicating that bioaccumulation of inorganic arsenic can induce oxidative stress. The largest increase in oxidative stress was observed following acute exposure to AsIII, but no significant degree of oxidative stress was induced by chronic exposure. During acute exposure to AsV, the increase in the enzymatic activity of glutathione-S-transferase (GST) was twice as high compared with exposure to AsIII, suggesting that GST plays an important role in the initial detoxification process. In addition, an RNA-seq-based ingenuity pathway analysis revealed that acute exposure to AsIII may be related to cell-cycle progression. A network analysis using differentially expressed genes also revealed a potential link between the generation of inflammatory cytokines and oxidative stress due to arsenic exposure.

Synergistic adverse effects of microfibers and freshwater acidification on host-microbiota interactions in the water flea Daphnia magna.

Microfibers are the most common type of microplastics in freshwater environments. Anthropogenic climate stressors, such as freshwater acidification (FA), can interact with plastic pollution to disrupt freshwater ecosystems. However, the underlying mechanisms responsible for the interactive effects of microfibers and FA on aquatic organisms remain poorly understood. In this study, we investigated individual Daphnia magna-microbiota interactions affected by interactions between microfibers and FA (MFA). We found that the accumulated amount of microfibers in pH-treatment groups was significantly higher than in the control groups, resulting in negative consequences on reproduction, growth, and sex ratio. We also observed that MFA interactions induced immunity- and reproduction-related biological processes. In particular, the abundance of pathogenic bacteria increased only in MFA groups, indicating that MFA interactions can cause intestinal damage. Our integrated analysis of microbiomes and host transcriptomes revealed that synergistic adverse effects of MFAs are closely related to changes in microbial communities, suggesting that D. magna fitness and the microbial community are causally linked. These finding may help elucidate the toxicity mechanisms governing the responses of D. magna to microfibers and acidification interactions, and to host-microbiome-environment interactions.