CONCLUSIONS:

Home Background Purpose and Scope Approach and Methods Results and Discussion Conclusions

Some of the SVOCs and trace elements sampled in October 1998 show patterns of distribution that relate to local point or nonpoint sources, whereas others appear to have more widespread sources such as the atmospheric transport of phthalate esters or the natural distribution of trace elements. Bottom-sediment characteristics such as organic carbon or clay content also influence the observed concentrations of many organic compounds or trace elements, respectively; but we used the normalizing techniques to minimize that influence. However, other sediment characteristics, such as particle size, composition, and residence time may also affect concentrations of trace substances in bottom sediments.

Some concentrations of PAHs normalized to organic carbon concentrations show peak concentrations along the Barron River canal at CR-858, at Jerome, and at sites downstream of Jerome. While the roadway and associated vehicular activity are probably a general source of PAHs in the Barron River Canal, the peaks in the normalized concentrations are probably related to contamination near CR-858 and the former creosote wood treatment facility at Jerome. Fluoranthene and pyrene, in particular, peak 8 km downstream of Jerome, and it is possible that these compounds have migrated downstream over the decades since the wood creosote treatment facility ceased operations in about 1956.

The highest concentrations of the phthalate esters and the trace elements arsenic, cadmium, and zinc occurred at the Turner River background site where the organic carbon concentration was the highest. The normalized distributions of the phthalate esters and arsenic, cadmium, and zinc suggest that their concentrations are influenced by widespread processes such as atmospheric transport of the phthalate esters; the natural distribution of arsenic, cadmium, and zinc; and the tendency of many trace substances to adsorb onto organic matter. Within the Barron River Canal, normalized values of arsenic, chromium, copper, and zinc peaked at either CR-858 or Jerome. The normalized concentrations of lead, copper and zinc at some sites indicate that they may be enriched above natural levels by human activities.

Concentrations of SVOCs and trace elements were below criteria that indicate potential adverse effects on aquatic life. However, most sites had measurable concentrations of several compounds, some of which approached the probable effect levels. Mixtures of SVOCs and other contaminants found at some sites could behave synergistically to cause adverse biological effects that are not indicated by criteria recommended for each individual contaminant.

ACKNOWLEDGMENTS

We thank Robert Sobczak and Christine Bates of the Big Cypress National Preserve in Ochopee, Florida, for their part in the project design and acquisition of funding for the sediment analyses and report preparation. Water analyses were funded by the Southern Florida National Water Quality Assessment project in Tampa, Florida.

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