Physiology and modeling of mechanisms of silver uptake and toxicity in fish

In this review, we outline the physiological and toxicological effects of s ilver (Ag) in freshwater and marine fish. For freshwater fish, the acute to xicity of Ag appears to be caused solely by ionic Ag+ interacting at the gi lls, inhibiting basolateral Na+,K+-ATPase activity. Disruption of this enzy me inhibits active Na+ and Cl- uptake and therefore osmoregulation by the f ish. Silver is much less toxic to marine fish, mainly because ionic Ag+ is complexed by Cl-, but the mechanisms of acute toxicity and the toxic specie s of Ag are poorly understood. Osmoregulatory failure occurs in marine fish exposed to high concentrations of Ag, and the intestine appears to be a pr imary toxic site of action, perhaps along with a gill component. Modeling a pproaches to calculate Ag interactions at biological surfaces are used to i llustrate the effects of water chemistry on Ag speciation and therefore tox icity to freshwater and marine fish. In these models, the most important co mponents affecting Ag speciation are the complexing agents Cl- and dissolve d organic matter followed by the competing agents Na+ and Ca2+, although a particulate component may be important to incorporate into the models in fu ture. More precise knowledge of the actual toxic sites of Ag is necessary i f we are to fully understand the effects of waterborne Ag in the environmen t.