Comparative Study of the Sediment-Toxicity Index, Benthic Community Metrics and Contaminant Concentrations

This paper demonstrates how a new tool for integrating the results of a battery of sediment toxicity tests can be effective in assessing the relative toxic potential of freshwater sediments to aquatic organisms. This tool, called the Sediment-Toxicity (SED-TOX) Index, was applied to laboratory toxicity data derived from two larger projects conducted on freshwater sediments. The SED-TOX Index generates a single value that represents all the results of the different STTs on a common, easily interpreted scale. The SED-TOX results were tentatively correlated with four benthic community metrics (species richness, number of taxa in the orders Ephemeroptera, Plecoptera and Trichoptera, the Shannon-Wiener diversity index, and the ICI-SL, which is a version of the invertebrate community index modified for the St. Lawrence River) and levels of sediment contamination. Although not significant (p = 0.07), SED-TOX scores were most closely related with ICI-SL values; high SED-TOX scores (≥2.0) were always associated with lower ICI-SL scores (<8), which suggests benthos degradation. Agreement was observed between chemistry and SED-TOX results in extreme situations. Indeed, 70% of the sites showing a high hazard potential (≥2.0) in the SED-TOX Index had mean sediment quality guideline (SQG) quotients >5, while 86% of those with a marginal SED-TOX score (0.1 to 0.9) had mean SQG quotients <1. The SED-TOX Index was useful for discriminating sediments based on their hazard potential to a variety of test species and for predicting most (but not all) of the extreme chemistry and benthic community results.