SEDIMENT CORE VERSUS GRAB SAMPLES - EVALUATION OF CONTAMINATION AND TOXICITY AT A DDT-CONTAMINATED SITE

Four sites from a stream system near Huntsville, Alabama, contaminated with DDT and its metabolites, were sampled using a coring device. Gra b samples were also collected at these and five other sites. Analytica l and toxicological evaluations were made on both sets of samples. Cor e samples provided vertical delineation of toxicity and contamination in sediments, and documented periods of sedimentation with clean mater ial, which appears to be isolating the contaminated sediments from ben thic communities. Grab samples yielded less information about the site s. Relationships between DDT concentration and sediment toxicity to Ch ironomus tentans were similar regardless of the sampling method. Subst antial increases in toxicity occurred in most samples when concentrati ons exceeded 3000 mug of DDT residue/g organic carbon. (C) 1994 Academ ic Press, Inc.