Sediment organic matter content as a confounding factor in toxicity tests with Chironomus tentans

Abstract

AbstractPhysicochemical characteristics of sediment unrelated to contaminant levels and bioavailability may influence the outcome of toxicity tests. In particular, sediment organic matter content has the potential to be a confounding factor in toxicity tests using the midge larva Chironomus tentans because the larvae are infaunal and feed on organic matter in the sediments. To examine this possibility, we conducted a series of tests using formulated sediments with varying organic matter contents (0–20%) following the standard U.S. Environmental Protection Agency (U.S. EPA) 10‐day C. tentans growth and survival protocol. Formulated sediments made with peat moss, α‐cellulose, and maple leaves were tested. An organic‐rich natural sediment diluted with formulated sediment to achieve a range of organic matter contents was also examined. In a final experiment, sediments containing each of the four organic matter sources at the same concentration were tested against one another. Survival was not greatly affected by concentration of organic matter, except at the lowest concentrations in natural sediment (6–7%), where survival dipped below 70%. In experiments using peat moss, α‐cellulose, and maple leaves, significant differences in C. tentans growth (measured as ash‐free dry weight) were found at different organic matter concentrations. In contrast, concentration of organic matter in the natural sediment dilution series had little effect on growth, perhaps because much of this material was highly refractory. In the comparison experiment, growth differed significantly among the four sediments, with best growth achieved with α‐cellulose and leaves. These results suggest that both organic matter quantity and quality can be confounding factors in toxicity tests using C. tentans.