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Magnitude and Extent of Chemical Contamination and Toxicity in Sediments of Biscayne Bay and Vicinity
The toxicity of sediments in Biscayne Bay and many adjoining canals and tributaries was determined as part of bioeffects assessments performed by NOAA's National Status and Trends Program. The objectives of the survey were to determine: (1) the spatial patterns in chemical contamination and toxicity throughout the study area; (2) the spatial extent of contamination and toxicity; (3) the severity of contamination and toxicity; and (4) the relationships between chemical concentrations in the sediments and measures of toxicity. The survey was conducted over two years - 1995 and 1996.
Surficial sediment samples were collected from 226 randomly-chosen locations throughout nine major regions. Four toxicity tests and complete chemical analyses were conducted on all samples.
Contamination and toxicity were most severe in several peripheral canals and tributaries, including the lower Miami River , adjoining the main axis of the bay. In the open basins of the bay, chemical concentrations and toxicity generally were higher in areas north of the Rickenbacker Causeway than south of it. Sediments from the main basins of the bay generally were less toxic than the adjoining tributaries and canals.
Both the degree and spatial extent of chemical contamination and toxicity in this study area generally were similar to or less severe than those observed in many other areas in the U.S. The spatial extent of toxicity in all four tests performed throughout the bay were comparable to the "national averages" calculated by NOAA from many previous surveys conducted with the same methods.
Several trace metals occurred in concentrations in excess of those expected in reference sediments. Mixtures of substances, including pesticides, petroleum constituents, trace metals, and ammonia, were associated statistically with the measures of toxicity. Substances most elevated in concentration relative to numerical guidelines and associated with toxicity included PCBs, DDTs, PAHs, HCHs, lead, and mercury. These (and other) substances occurred in concentrations greater than effects-based guidelines in the samples that were most toxic in one or more of the tests.
Project Partners
State of Florida
Miami-Dade County, Florida
National Park Service