Silver toxicity across salinity gradients: the role of dissolved silver chloride species (AgCl x ) in Atlantic killifish (Fundulus heteroclitus) and medaka (Oryzias latipes) early life-stage toxicity
The influence of salinity on Ag toxicity was investigated in Atlantic killifish (Fundulus heteroclitus) early life-stages. Embryo mortality was significantly reduced as salinity increased and Ag+ was converted to AgCl(solid). However, as salinity continued to rise (>5 ‰), toxicity increased to a level at least as high as observed for Ag+ in deionized water. Rather than correlating with Ag+, Fundulus embryo toxicity was better explained (R2 = 0.96) by total dissolved Ag (Ag+, AgCl2 −, AgCl3 2−, AgCl4 3−). Complementary experiments were conducted with medaka (Oryzias latipes) embryos to determine if this pattern was consistent among evolutionarily divergent euryhaline species. Contrary to Fundulus data, medaka toxicity data were best explained by Ag+ concentrations (R2 = 0.94), suggesting that differing ionoregulatory physiology may drive observed differences. Fundulus larvae were also tested, and toxicity did increase at higher salinities, but did not track predicted silver speciation. Alternatively, toxicity began to increase only at salinities above the isosmotic point, suggesting that shifts in osmoregulatory strategy at higher salinities might be an important factor. Na+ dysregulation was confirmed as the mechanism of toxicity in Ag-exposed Fundulus larvae at both low and high salinities. While Ag uptake was highest at low salinities for both Fundulus embryos and larvae, uptake was not predictive of toxicity.
KeywordsFundulus heteroclitus Silver Ionoregulation Bioavailability Salinity Na+ balance
We would like to thank Dr. Bryan Clark for his laboratory assistance; Drs. David Hinton and Kevin Kwok for providing medaka embryos, and Dr. Jason Unrine of the University of Kentucky for ICP-MS assistance. This material is based upon work supported by the National Science Foundation (NSF) and the Environmental Protection Agency (EPA) under NSF Cooperative Agreement EF-0830093 and DBI-1266252, Center for the Environmental Implications of NanoTechnology (CEINT). Additional support was provided by NSF (CBET-1066781). Any opinions, findings, conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NSF, or the EPA. This work has not been subjected to EPA review and no official endorsement should be inferred. The authors also thank the CNRS for funding the iCEINT consortium.
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Conflict of interest
The authors declare that they have no conflict of interest.
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