Horizon-specific oxidation of acid volatile sulfide in relation to the toxicity of cadmium spiked into a freshwater sediment

Abstract

The effects of oxidative processes on acid volatile sulfide (AVS) concentrations in various horizons of whole sediment cores were evaluated in relation to the toxicity of a metal (cadmium). An artificial system was used to “age” cadmium-spiked sediment samples under a constant flow of fresh Lake Superior water. Sediments from Pequaywan Lake, Minnesota (12 μmol AVS/g) were spiked to achieve (nominal) cadmium: AVS molar ratios of 0.02 (control), 0.2, 0.8, 1.2, and 3.0. At 0, 24, and 48 days post-spiking, sediment cores were removed from the aging system and tested for toxicity to the amphipod Hyalella azteca. At the same time, horizons from replicate sediment cores were prepared for analysis by freezing, and then cutting them into 10–20 mm increments. The sediment horizons were analyzed for AVS and simultaneously extracted cadmium concentrations, and pore water concentrations of cadmium. Relatively little oxidation of surficial AVS concentrations was observed, even at aging times up to 48 d. By 48 d, pore water concentrations of cadmium were slightly elevated at all spiking concentrations, but were increased greatly at cadmium:AVS ratios greater than one. Hyalella azteca mortality was generally predictable based on surficial cadmium:AVS ratios or pore water cadmium concentrations.