Silver toxicity to Chironomus tentans in two freshwater sediments

Abstract
Sediment collected from two freshwater lakes, West Bearskin Lake(Cook, MN, USA) and Bond Lake (Douglas, WI, USA), was characterized for grain size, total organic carbon, (TOC), acid‐volatile sulfides (AVS), simultaneously extracted metals (SEM), and iron (Fe). Both sediments had low levels of TOC (3 in a series of concentrations, some of which were intended to exceed the total silver (Ag)‐binding capacity of the sediments, allowing for the appearance of dissolved Ag in pore water (PW). Sediment toxicity tests were then designed such that the AgNO3 amendment levels would result in PW concentrations that bracketed the 10‐d concentration causing 50% lethality (LC50) for dissolved Ag of 0.057 mg/L, as determined in a toxicity test in water alone (i.e., without sediment present). The 10‐d LC50 values for Chironomus tentans, based upon nominal additions of Ag to the sediments, were 2.75 and 1.17 g Ag per kilogram dry sediment for West Bearskin and Bond Lake sediments, respectively. An LC50 value based upon dissolved Ag in the PW was determined only for Bond Lake sediment and was approximately 275 times greater than the water‐only LC50 value. This indicated that a high proportion of the dissolved fraction was not readily bioavailable to cause lethality. A reduction in PW pH and the displacement of other metals from sediment into PW with Ag additions to the sediment likely contributed to the observed mortalities and weight losses, particularly at the higher exposure levels. The concentrations of Ag in these sediments that resulted in biological effects are considerably higher than levels reported in the environment.

This publication has 35 references indexed in Scilit: