Validation study of the acute biotic ligand model for silver

Abstract

An important final step in development of an acute biotic ligand model for silver is to validate predictive capabilities of the biotic ligand model developed for fish and invertebrates. To accomplish this, eight natural waters, collected from across North America, were characterized with respect to ionic composition, pH, dissolved organic carbon, and sulfide. Tests were conducted with the cladoceran Ceriodaphnia dubia (48-h static) and the fish Pimephales promelas (96-h static renewal) to determine the concentrations causing lethality to 50% of the organisms (LC50s) for silver in each of these waters. Overall, the biotic ligand model adequately predicted silver toxicity to C. dubia; however, in some cases, predicted LC50 values exceeded measured values. The accuracy of the biotic ligand model predictions was less convincing for silver toxicity to P. promelas with pronounced problems in low-ionic strength waters. Another issue was the use of acclimated organisms in toxicity studies because the biotic ligand model has been developed with the use of a mix of studies with acclimated and nonacclimated test organisms of varying ages and sizes. To evaluate whether effects of acclimation to test waters influence biotic ligand model predictions, a subset of the natural waters were also tested with P. promelas that had been acclimated to the natural water for 7 d before testing. These experiments revealed no differences in toxicity between acclimated and nonacclimated P. promelas. To determine the influence of organism size, which has been previously correlated to Na(+) turnover and acute silver toxicity across multiple species, Na(+) and Cl(-) influx rates were measured in P. promelas of different sizes. Our results show that Na(+) and Cl(-) influx rates were inversely related to fish mass and positively correlated with silver sensitivity.

The effect of food on the acute toxicity of silver nitrate to four freshwater test species and acute-to-chronic ratios

“…The acute toxicity of silver was also investigated by other researchers. Kolts et al (2006) reported a 48-h EC50 of 0.30 lg dissolved Ag/l while Bielmyer et al (2007) reported a 48-h EC50 of 0.76 lg dissolved Ag/l. Bielmyer et al (2007) also performed acute studies with C. dubia in HT water (non-reconstituted) and reported a 48-h EC50 of 1.28 lg dissolved Ag/l.…”

“…Kolts et al (2006) reported a 48-h EC50 of 0.30 lg dissolved Ag/l while Bielmyer et al (2007) reported a 48-h EC50 of 0.76 lg dissolved Ag/l. Bielmyer et al (2007) also performed acute studies with C. dubia in HT water (non-reconstituted) and reported a 48-h EC50 of 1.28 lg dissolved Ag/l. For comparison, we observed a 48-h EC50 of 0.27 lg dissolved Ag/l in reconstituted HT water using a 5 min (approximate) equilibration period (Naddy et al 2007a).…”

“…Karen et al (1999) reported values of 5.57-17.1 lg/l, at a similar DOC concentration but results varied depending on the chloride level (nominal of 0 and 3 mg/l, respectively). It should be noted that silver toxicity studies that used KCl to adjust Cl -(i.e., Karen et al 1999;Bielmyer et al 2007) may have underestimated its protective effects. Potassium (ion) concentrations in excess of *10 mg/l has been found to exacerbate the toxicity of ion regulatory inhibitors such as Ag ?…”

A biotic ligand model-based toxicodynamic approach to predict arsenic toxicity to tilapia gills in cultural ponds

“…For a specific water body, the determination of water effect ratios (WERs) is crucial while generating site-specific AWQC (Di Bielmyer et al 2007). The WER is defined as the ratio of the effective concentration of the site-specific water to the effective concentration of the reference laboratory water.…”

“…The biotic ligand model (BLM), derived from the gill surface interaction model and the free ion activity model, has been widely used to predict the toxicological effects of metals on aquatic organisms in the last decade (Paquin et al 2000;Niyogi and Wood 2004;Bielmyer et al 2007). In the BLM, the metal toxicity is resulted from the free metal ions reacting with the binding sites (i.e., biotic ligand) at the site of action for aquatic organisms.…”