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Virginia Institute of Marine Science
Gretchen Rupp and Michelle D. White
Fish Physiology, Toxicology, And Water Quality - Proceedings of the Seventh International Symposium, Tallinn, Estonia May 12-15, 2003
U.S. Environmental Protection Agency
Fish are suddenly exposed to hypoxic conditions during diverse events such as seiche- or turnover-related water movements, bottom water release from reservoirs, ice-over of eutrophic arctic lakes, and rapid shifts in respiration: photosynthesis associated with cultural eutrophication. In each case, chemical equilibria established under hypoxic conditions that result in metal dissolution and accumulation suddenly shift toward chemical equilibria of oxic conditions. Critical changes in speciation include those determining the free ion activity that, as expressed by the Free Ion Activity Model (FIAM), is often the most bioactive form of a dissolved metal. Metal phase can also change rapidly and, in some cases, result in a precipitate on respiratory surfaces. Exposure of fish gills to metal (and integument of larval or small fish) changes O2 exchange dynamics. Changes in mucus quality and production and lamellae morphology decrease the amount of effective gill exchange surface and increase the diffusive layer thickness. These changes exacerbate those associated with the reduced O2 partial pressure gradient. Consequent shifts in blood chemistry (e.g., pH and ion composition) and ventilation also affect metal transport and deposition within fish tissues. Some of these changes have immediate consequences, but others can continue for long periods after the hypoxic conditions pass. Long-term metal effects can influence fish tolerance during future hypoxic episodes.
A joint, similar action model can be applied if the parsimonious assumption is made that asphyxiation constitutes a common mode-of-action for both acute metal effects and hypoxia. Joint action models are applicable based on either conventional dose-effect or survival time approaches. Expansion of such models to a physiologically-based toxicokineticstoxicodynamics framework (e.g., framed around the Fick equation) would be desirable, provided that model parameter requirements remain realistic. Long-term effects may be better addressed with models such as the binary logistic models used by epidemiologists.
Newman, Michael C., "Can We Predict Joint Effects Of Hypoxia And Metals On Fish Survival?" (2004). VIMS Books and Book Chapters. 15.