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Treated wastewater as a source of sediment contamination in gulf of Mexico near‐coastal areas: A survey

The primary objective of this baseline survey was to provide some needed perspective on the magnitude of sediment contamination associated with wastewater outfalls discharged to Gulf of Mexico near‐coastal areas. The chemical quality and toxicities of whole sediments and pore waters collected from three coastal rivers and four coastal bays receiving wastewaters were assessed during a 2‐year period. Rooted plants, invertebrates, and fish were used to assess the acute and chronic toxicities of sediments associated with a total of 10 industrial, municipal, steam electric‐power generation and forest product wastewater outfalls. Effects on bacterial bioluminescence, early seedling biomass, survival, reproduction, fertility, and growth were determined in bioassays ranging from 30 min to 28 d duration. Sediment chemical contamination was localized and decreased with increasing distance from the discharge areas. The major sediment contaminants, with few exceptions, were divalent trace metals, which increased, on average, by 69% below 8 of the 10 outfalls. However, only a few concentrations exceeded proposed threshold sediment quality assessment guidelines. Toxicity to either the plant or animal test species was observed occasionally below 7 of the 10 outfalls, but its detection was dependent on the type of bioassay and the frequency of use. Consequently, a suite of bioassays conducted on multiple occasions appears to be needed for toxicity assessments of sediments collected below wastewater discharges in the Gulf region to ensure relevancy of the results. This is particularly true for low to moderately contaminated sediments where acute toxicity is uncommon, which was the case in this study.