A FIELD-STUDY OF METAL TOXICITY AND ACCUMULATION BY BENTHIC INVERTEBRATES - IMPLICATIONS FOR THE ACID VOLATILE SULFIDE (AVS) MODEL

The toxicity and accumulation of Cd from sediment by benthic invertebrates was measured along a Cd gradient created in nature. The efficacy of acid-volatile sulfide (AVS) concentrations in improving the prediction of biological effects in nature is also evaluated for the first time. The Cd concentration of sediments from a shield lake in Quebec was adjusted to obtain Cd:AVS ratios of from 0.05 to 10. The sediments were then subjected to in situ colonization by invertebrates over a 1-yr period. Cd concentrations in pore waters were very low at Cd:AVS molar ratios < 1 but increased markedly at ratios > 1. The results of previously published laboratory bioassays suggest that Cd would not be toxic to invertebrates when the molar ratio of Cd:AVS was < 1. The biological effects of contaminated sediment varied greatly among taxa, as determined by both an animal's sensitivity to Cd and the animal's behavior. The abundance of only one of the insect taxa present, Chironomus (salinarius gp.) sp., was significantly related to the Cd: AVS molar ratio. For the other taxa present, there was no relationship between either abundances or growth rates and the Cd:AVS molar ratio. The general lack of expected toxicity at the high Cd:AVS molar ratios in our field study can be explained by the differing sensitivities to Cd for the animal species used in the laboratory and in the field and by the relatively low concentrations of Cd in excess of AVS even at the highest Cd:AVS molar ratio.