INDEXES OF BENTHIC COMMUNITY TOLERANCE IN CONTAMINATED GREAT-LAKES SEDIMENTS - RELATIONS WITH SEDIMENT CONTAMINANT CONCENTRATIONS, SEDIMENTTOXICITY, AND THE SEDIMENT QUALITY TRIAD

We evaluated the toxic-units model developed by Wildhaber and Schmitt (1996) as a predictor of indices of mean tolerance to pollution (i.e., Lenat, 1993; Hilsenhoff, 1987) and other benthic community indices fr om Great Lakes sediments containing complex mixtures of environmental contaminants (e.g., polychlorinated biphenyls -PCBs, polycyclic aromat ic hydrocarbons PAHs, pesticides, chlorinated dioxins, and metals). Se diment toxic units were defined as the ratio of the estimated pore-wat er concentration of a contaminant to its chronic toxicity as estimated by U.S. Environmental Protection Agency Ambient Water Quality Criteri a (AWQC) or other applicable standard. The total hazard of a sediment to aquatic life was assessed by summing toxic units for all contaminan ts quantified. Among the benthic community metrics evaluated, total to xic units were most closely correlated with Lenat's (1993) and Hilsenh off's (1987) indices of community tolerance (T-L and T-H, respectively ); toxic units accounted for 42% (T-L) and 53% (T-H) of variability in community tolerance as measured by Ponar grabs. In contrast, taxonomi c richness and Shannon-Wiener diversity were not correlated (P > 0.05) with toxic units. Substitution of order-or family-level identificatio ns for lowest possible (mostly genus-or species-) level identification s in the calculation of TL and TH indices weakened the relationships w ith toxic units. Tolerance values based on order-and family-level iden tifications of benthos for artificial substrate samples were more stro ngly correlated with toxic units than tolerance values for benthos fro m Ponar grabs. The ability of the toxic-units model to predict the oth er two components (i.e., laboratory-measured sediment toxicity and ben thic community composition) of the Sediment Quality Triad (SQT) may ob viate the need for the SQT in some situations.