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Cytotoxicity of silver nanoparticles (Ag NPs) is attributed to silver internalization, which can be depressed by dissolved organic matter (DOM) to form Ag-DOM. Ag-DOM are bioavailable and then silver internalization could be increased. Herein, 3 and 48-h Escherichia coli viability bioassays were employed to evaluate effect of fulvic acid and humic acid (10 mg L-1) on cytotoxicity of 30 and 100 nm PVP-Ag NPs. Moreover, zebrafish embryos were used as reference model to understand silver internalization routes. Ag ions or Ag-DOM internalization varied in routes to Escherichia coli and zebrafish embryos. Cytotoxicity mechanisms of PVP-Ag NPs are dynamic. In 3-h bioassays, cytotoxicity of PVP-Ag NPs mainly involves Ag particle-related toxicity. DOM significantly mitigated cytotoxicity of PVP-Ag NPs (p

Cyanobacterial blooms are a major problem in many lakes and can negatively impact public health and ecosystem services. The bioflocculation technique has proven to be a cost-effective, environmentally friendly technique with no secondary pollution to harvest multiple microalgae; however, few studies have focused on its effect on and potential for controlling cyanobacterial blooms in eutrophic lakes. In this study, the bioflocculation efficiencies of different Microcystis species under Glyptotendipes tokunagai (Diptera, Chironomidae) stress conditions and the interactions between secreted silk from Chironomid larvae and extracellular polymeric substances (EPS) from Microcystis were compared. The results indicated that G. tokunagai presented better bioflocculation efficiency on M. wesenbergii than on M. aeruginosa. The formation of “Large Algal Aggregate” flocs was promoted by the derived-soluble extracellular polymeric substances (i.e., proteins and polysaccharides, sEPS) from M. wesenbergii and silk from G. tokunagai. Both M. wesenbergii and midge silk had abundant functional groups, which was beneficial to the formation of the large aggregate. G. tokunagai secreted a large amount of silk to bridge with the sEPS of M. wesenbergii, forming a network structure via interaction between filamentous substance (i.e., complex of sEPS and silk) that plays an important role in the aggregation of Microcystis and the removal of the Microcystis biomass in the water column. The findings provide further insights that will benefit the existing efforts of combating Microcystis blooms in the water column via bioflocculation and will provide a new sustainable approach for inhibiting early bloom formation from the perspective of its provenance in the sediment-water interface.

Silver nanoparticles (AgNPs) have been increasingly manufactured and thus are increasingly detected in aquatic systems. However, there are still some overlooked factors (e.g., organism sex) in the field of nano-toxicological assessment. In this study, to explore the role of sex in nanotoxicity, adult male and female zebrafish were exposed to 100 μg/L of two uncoated commercial AgNPs with primary sizes 20 nm and 80 nm for 2 weeks, after which the impacts of AgNPs on intestines and livers of both male and female zebrafish were assessed using a suite of biomarkers. Results demonstrated that the intestinal Na/K-ATPase activity as well as the superoxide dismutase activity in male zebrafish differed significantly between 20-nm AgNPs and 80-nm AgNPs treatments (p 0.05), indicating 20-nm AgNPs showing higher toxicity to zebrafish than the 80-nm AgNPs. Also, we noted that the used AgNPs induced sex-dependent effects on growth indices, oxidative/anti-oxidative status, neural signaling and hepatic lipid metabolism, with the male zebrafish being more sensitive to AgNPs than the females. Further, the tested AgNPs impaired the intestine much more seriously than the liver, as evidenced by the disruptions of Na/K-ATPase and antioxidant system in intestine but not in liver. These findings imply that prolonged exposure to AgNPs might induce size-related, sex-dependent, and organ-specific toxicity to adult zebrafish, thereby may significantly extend our understanding of the toxic effects of AgNPs in aquatic environment.

Silver nanoparticles (Ag NPs) have been inevitably introduced into ecological environment during their extensive applications in daily human life. Thermodynamically, Ag NPs are unstable and transform into other species under various aqueous conditions. Ag NPs and their transformation products pose potential threats to environment and humans. However, the complex environmental conditions and transformations of Ag NPs complicate their human health and environmental risk assessment. To bridge the knowledge gap, four essential environmental transformations, oxidative dissolution, sulfidation, chlorination and photoreduction, of Ag NPs are reviewed herein. The mechanism, morphology and size change, as well as the toxicity of Ag NPs during these transformations under certain aqueous conditions are detailed. In particular, these environmental transformations have shown strong correlations that are discussed. The transformation, fate, bioavailability, morphology and toxicity of Ag NPs are critical factors and should be considered in a complete human health and environmental risk assessment of Ag NPs. The fluctuation of these factors in the realistic environment is also vital and should be considered.