Abstract

  A Toxicity Identification Evaluation (TIE) of sediments from various reaches of the Calcasieu Estuary was performed to improve the technical basis for Total Maximum Daily Loads (TMDLs) under development of this water body ensure future compliance with Louisiana Water Quality Standards. The TIE methodology involves manipulations of the physical/chemical properties of sediment pore water samples to target each of the major classes of contaminant compounds and confounding factors. Toxicity tests performed in conjunction with these manipulations provide evidence to directly correlate contaminant classes that cause toxicity with observed changes in toxic effects. Evaluation of the potential toxicity from chemical contamination versus confounding factors relied upon multiple lines of evidence, including the full toxicity results (Superfund and TIE studies), TIE signals (Filtration, STS, EDTA and C18 treatments), Hazard Quotients from multiple exposure sources (based on sediment, particulates in porewater, dissolved porewater concentrations) and finally, application of a site-specific PRG process where collocated toxicity and chemistry results were evaluated based on the larger Superfund risk assessment database.   Sediment porewaters from seven locations were tested using water-only exposures to the amphipod, Ampelisca abdita and the mysid, Americamysis bahia. TIE results demonstrated improved survival after filtration, indicating that suspended particulates and associated contaminants were a significant source of toxicity. Subsequent treatments with C18 and EDTA reduced toxicity, indicating both organics and metal constituents of porewaters as contributors to toxicity. The analysis of the filters used in the TIE revealed that particulate copper in the porewater exceeded AWQC in the majority of samples, and measured porewater concentrations were also above criteria values. The identification of specific contaminant classes as well as particulate effects as sources of acute toxicity from TIE results indicate that present sediment loadings (via porewater flux and resuspension) are sources of water quality impairment and should be considered in the TMDL development.