The use of chironomid deformation in an in situ test for sediment toxicity

An in situ bioassay using mouthpart deformities in Chironomus riparius larv ae was developed to monitor sediment toxicity, Second-instar larvae, along with a standardized amount of food and sediment taken from the study locati ons, were enclosed in cages that were placed on the sediment surface of riv ers, Mouthpart deformities were screened after larval molting to the fourth instar (exposure time: 7-10 days). Mouthpart deformities of caged and fiel d larvae (when present) were related to the estimated sediment toxicity, By summing toxicant concentrations and normalizing them to the organic matter and clay contents, a significant relationship between toxicity levels and mouthpart deformities in the mentum was revealed. Results suggest that the pattern of observed deformities was indicative of site toxicity rather than a characteristic of the laboratory larval population used. The main advant age of the proposed in situ bioassay is the possibility to assess the incid ence of deformities at sites where C, riparius does not occur naturally. (C ). 2000 Academic Press.