Silver speciation during chronic toxicity tests with the mysid, Americamysis bahia

Abstract

A 28-day chronic toxicity test and two 7-day chronic estimation toxicity tests were conducted with silver nitrate (AgNO 3) and the marine invertebrate, Americamysis bahia, in 20‰ (parts-per thousand) salinity seawater. One 7-day test was initiated with 7-day-old mysids and the second was initiated with <24-h-old mysids. There was very good agreement between the three toxicity tests. The no-observed-effect concentration (NOEC) values from the 28-day test, the 7-day test initiated with 7-day-old mysids, and the 7-day test initiated with <24-h-old mysids were 34, 65 and 38 μg/l silver, respectively. The 96-h LC50 values from the 28-day toxicity test and the 7-day toxicity test initiated with 7-day old mysids were 260 μg/l, and the 96-h LC50 value from the 7-day toxicity test initiated with <24-h-old mysids was 280 μg/l. Free ionic silver, Ag +, concentrations measured with a silver electrode were in good agreement with concentrations calculated using total dissolved silver and chloride concentrations. Mean measured concentrations of Ag + in the test solutions ranged from 0.99 to 25 ng/l for the dissolved silver concentrations that ranged from 34 to 410 μg/l silver, indicating that free ionic silver varied from 0.003 to 0.006% of the silver dissolved in the 20‰ salinity seawater. Understanding the relationship of salinity and silver speciation, and the effect of this relationship on chronic invertebrate toxicity, will be useful for development of a marine biotic ligand model (BLM) and a water quality criterion for silver. This model could provide an important tool for improving the relationship of laboratory toxicity test results and predicted effects in natural environments, where variations in salinity may act to modify the toxicity of silver and other metals.