A Physiologically Based Biotic Ligand Model for Predicting the Acute Toxicity of Waterborne Silver to Rainbow Trout in Freshwaters

Abstract

An early silver-gill binding model using conditional equilibrium binding constants (K) was fitted to actual toxicity data for rainbow trout (Oncorhynchus mykiss) and subsequently modified to produce a mechanistically based acute toxicity model for predicting silver toxicity. The model used an "off the shelf" aquatic geochemistry software program (MINEQL + ) and physiologically based log K values to predict the acute effects of waterborne silver in rainbow trout. The final version of the model does not predict total gill-silver loading, as the early model did, but rather predicts the binding of Ag + to key toxic sites on the gill and incorporates the effects of cation competition at these sites. The acute toxicity model for Ag + provided the best fit to toxicity data when a log K value for the affinity of these sites was 7.6 with cationic competition log K values for Na + and Ca 2+ of 2.9 and 2.3, respectively. A log K for Ag-DOM of 9.0 was used representing strong Ag + binding to dissolved organic matter. The model we present is easy to use and provides a good match with previously published acute AgNO 3 toxicity data for rainbow trout from 31 data sets in 10 studies. The modified model is now ready for full verification with a greater range of laboratory and natural waters.

Is Cl− protection against silver toxicity due to chemical speciation?

“…It should be acknowledged that different Cl − uptake pathways and requirements perhaps are not the only explanations for the observed differences among species. For example, it is puzzling that the enzyme Na + /K + -ATPase apparently receives protection from ambient Cl − against silver inhibition (McGeer et al, 2000), an observation which may be explained by differences in cellular silver speciation.…”

“…In efforts to evaluate the bioavailability and acute toxicity of waterborne metals, a biotic ligand model (BLM) has been developed as a predictive tool that will allow site-specific water quality standards to be generated when the water chemistry of the site is known (McGeer et al, 2000;Di Toro et al, 2001). This model takes into account a variety of water chemistry parameters, including Cl − concentration, to predict the amount of free metal ion available to bind to the fish gill.…”

Binding of Silver(I) Ions by Alfalfa Biomass (Medicago Sativa): Batch PH, Time, Temperature, and Ionic Strength Studies

“…Although silver ions are not considered highly toxic to human life, there remains a secondary maximum contaminant level (SMCL) of 0.5 ppm of Ag in drinking water (U.S. Environmental Protection Agency, 1995). In addition, ionic silver (Ag + ) has been considered to be highly toxic to zooplankton (Hook and Fisher, 2001), aquatic life (Erickson et al, 1998;McGeer et al, 2000;Wood et al, 1996a), and mammals (Warila et al, 2001) when it is supplied as silver nitrate (AgNO 3 ), a form considered relatively soluble if compared to other silver salts. Although no direct relationship has been found between silver toxicity and photographic wastes containing silver (Hogstrand and Wood, 1998;Wood et al, 1996b), studies have established that other chemicals present in photographic waste are toxic to aquatic life (Edgar, 1995).…”

Modeling chemical speciation of copper in River Yamuna at Delhi, India

“…The next generation equilibrium models such as REDEQL (Morel and Morgan, 1972) and GEOCHEM (Sposito and Mattigod, 1980) incorporated methods of convergence, interfacing NewtonRaphson and successive approximation methods. The Biotic Ligand Model (BLM, Pagenkopf, 1983), almost a derivative of the Free-Ion Model (FIM), is a recent development relating chemical forms of metals with toxicity to organisms (Bell et al, 2002;Campbell 2002;Campbell et al, 2002;Chapman et al, 2003;Di Toro et al, 2001;McGeer et al, 2000;Morgan and Wood, 2004;Playle, 1998;Playle et al, 1993;Tipping, 1994). The model aims at predicting interactions of dissolved metals with aquatic organisms that eventually affect them.…”