Sediment Toxicity in Galveston Bay in a Nationwide Context
The National Oceanic and Atmospheric Administration (NOAA) determines the spatial extent and severity of sediment toxicity in the estuaries and other coastal waters of the United States. The study in Galveston Bay was based on a total of 75 randomly selected stations from 22 strata encompassing the entire bay and adjacent coastal waters. Sediment toxicity tests were selected to ensure different modes of contaminant exposure (i.e., bulk sediment, porewater, and chemical extracts of sediments) to a variety of test organisms (invertebrates, bacteria, and vertebrate cells) and to measure different assessment end-points (i.e., mortality, impaired reproduction, physiological stress, and enzyme induction). None of the samples was found to be toxic based on results of the amphipod mortality test. However, results of sub-lethal tests show widespread toxicity. The Microtox test indicated significant toxic response over 85 percent of the study area; a reduction in fertilization success in sea urchin eggs was noted over 32 percent of the study area; and impaired sea urchin larval development was noted over 23 percent of the study area. The human reporter gene system (HRGS) response, measured as induction of a cytochrome P-450 enzyme upon exposure to certain xenobiotic compounds, was very limited. The mean value was 5 mg benzo[a]pyrene equivalents per kg of dry sediment. Values less than 10 are not likely to be associated with adverse biological effects. Based on results of NOAA's sediment toxicity from 23 different coastal areas and data compiled in 1998, seven percent of total studied area was classified as toxic based on the amphipod mortality tests; 39 percent based on sea urchin fertilization test, and 66 percent based on the Microtox test. On a nationwide basis, the highest observed value of the spatial extent of sediment toxicity was 85 percent based on the amphiopod mortality (in Newark Bay), 98 percent based on the sea urchin fertilization test (in San Pedro Bay), and 100 percent based on the Microtox test (in Choctawhatchee Bay). In light of these results and consistent with previous studies, severity of sediment toxicity in Galveston Bay is spatially quite limited, and generally reflective of low levels of trace metals and organic contaminants. Only 2 of the 75 stations had chemical contaminants exceeding the median values associated with adverse biological effects.