Speciation and Microalgal Bioavailability of Inorganic Silver

Abstract

Silver accumulation in aquatic organisms is primarily attributed to the bioavailability of the free Ag ion (Ag+). Some reports suggest that AgCl(aq) is also available for biological uptake, but few studies of Ag bioavailability used the range of chloride concentrations over which AgCl0(aq) is the dominant Ag species. None used environmentally realistic, low Ag concentrations (10−200 pM). To assess the bioavailability of inorganic Ag species and the importance of the low polarity AgCl(aq) complex to biological uptake, we determined the octanol−water partition coefficient of Ag over a range of chloride concentrations (0−50 mM) representative of fresh to brackish waters and measured short-term Ag uptake rates in the euryhaline marine microalga Thalassiosira weissflogii exposed to a total silver concentration of 50 pM. Overall octanol−water partition coefficients (Dow) of inorganic silver ranged from 0.02 to 0.06. The Kow of AgCl(aq) calculated using Dow values measured at 0.5, 5, and 50 mM Cl- and the Kow of...