ABSTRACT Dioxins, furans, and trace metals were evaluated in shellfish and sediments from St. Louis Bay, Mississippi and adjacent waters of Mississippi Sound. Highest concentrations and the most toxic dioxin congener were found in St. Louis Bay sediments in closest proximity to the effluent outfall from the titanium dioxide refinery on the northern shore of the bay. Using conservative assumptions, we estimated the dioxin and furan burden of 17 measured congeners in St. Louis Bay sediments to be between 3.72 and 6.16 kg. Comparison of lipid-adjusted dioxins and furans in oysters (Crassostrea virginica) from this study with those collected from seafood markets and grocery stores in southern Mississippi in 1997 shows dioxin and furan contamination about 1.7 to 8 times higher in the samples from this study, depending on collection location. Oysters from St. Louis Bay and adjacent marine waters may accumulate higher concentrations of dioxins and furans than measured here, at other times during the year, due to the low lipid content of oysters in this single-season study. At other times, with typical higher oyster lipid levels, the dioxin content of oysters could increase by a factor of 8.5 to 12.7 times, commensurate with the expected increase in oyster lipids, although the rate of uptake of these contaminants is not known. Certain trace metals have increased markedly in St. Louis Bay shellfish since a 1978 baseline study that was conducted prior to the operation of the titanium dioxide refinery that produces large quantities of soluble waste metals such as chromium, nickel, and lead. In 2004, the percent value of chromium in oysters in St. Louis Bay was at least 1,167% greater than the 1978 values, and the percent value for nickel in oysters in the bay was at least 467% greater than the 1978 value. The percent value for chromium in 2004 from oysters outside the bay was between 7,700% and 11,300% greater than the 1978 reported in bay values. Rangia clams (Rangia cuneata) from St. Louis Bay tended to have greater increases than did oysters for all metals measured above detection limits in both studies, except for zinc, which declined in both shellfish species. Metals also increased in sediments, but soluble metals which are produced by, and apparently released from, the titanium dioxide refinery may be flushed out of the bay to higher salinity seawater before becoming adsorbed on fine silt and clay-size particles which are consumed by shellfish and/or deposited in sediments. Oysters from waters near the mouth of St. Louis Bay were also contaminated with dioxins, furans, and heavy metals. Based on widely published estimated safe and adequate daily dietary intake for chromium and nickel (the latter standard for hypersensitive individuals) the values recorded in this study indicate that less than one oyster per day should be consumed from the open harvest site sampled in adjacent Mississippi Sound. An evaluation of other regional sources of dioxin and dioxin-like compounds and heavy metals was conducted using data reported to the United States Environmental Protection Agency. Because of the lack of other identifiable large sources of these contaminants, the transport dynamics of soluble metals and the occurrence of highest dioxin and dioxin-like compound concentrations near the titanium dioxide refinery outfall, we conclude that the refinery is the most likely and most significant source of the measured dioxins, dioxin-like compounds, chromium, and nickel contamination found in St. Louis Bay and adjacent marine waters of Mississippi Sound.
KEY WORDS: dioxin, furan, trace metals, chromium, nickel, St. Louis Bay, oysters
INTRODUCTION
St. Louis Bay is a 3,860-ha elliptical-shaped, shallow embayment with a narrow entry to the western end of Mississippi Sound (Fig. 1). The bay receives freshwater input from 2 primary rivers, the Jourdan and the Wolf, and, according to a 1978 study (Lytle & Lytle 1982), suffered the least of all bays along the Mississippi coast from sources of anthropogenic pollutants. The study of Lytle and Lytle (1982) was part of a characterization of St. Louis Bay because of concerns about potential pollution resulting from the future placement and operation of a titanium dioxide refinery near the northern shore of the bay in 1979. The refinery is reported to produce quantities of dioxins, furans, PCBs, and heavy metal by-products as well as other hazardous chemicals, based on the refinery's annual reporting requirements to the United States Environmental Protection Agency's Toxic Release Inventory (TRI) (USEPA 2003). Such by-products are injected into ground wells on the site, disposed of at on-site landfills, released as point source air emissions, fugitive air emissions, and surface water discharges according to the reporting data. There is an effluent pipe from the refinery, labeled as a sewer pipe on National Oceanic and Atmospheric Administration (NOAA) nautical charts 11371 and 11372A (NOAA 2001; NOAA 2004), located on the northern shore of St. Louis Bay, and releases from this pipe may constitute a portion of the reported surface-water discharges. In addition, airborne emissions from the refinery could be deposited, in part, by settling into the marine waters of St. Louis Bay, surrounding tidal marshes and the adjacent Mississippi Sound.
[FIGURE 1 OMITTED]
Based on the reported chemical production in close proximity to St. Louis Bay, the potential for release of a portion of the chemicals and their entry into the bay ecosystem and adjacent offshore marine waters, and the availability of the baseline study, we undertook the current study to assess the degree of contamination of marine shellfish and sediments in the bay and adjacent offshore waters of Mississippi Sound in the summer of 2004.
MATERIALS AND METHODS
Field Collection of Samples
Sediment and shellfish collections were made on July 11 and 12, 2004, from a 15.2-m length (50 foot) oyster dredging vessel, the F/V Nova Star, fitted with a 16 tooth oyster dredge weighing about 265 kg, known as a Mississippi dredge. Samples were collected under permit from the Mississippi Department of Marine Resources inside St. Louis Bay, between US Highway 90 and the CSX railroad bridges at the mouth of the bay and in adjacent waters of Mississippi Sound outside of St. Louis Bay at the locations shown in Figure 2 and Figure 4 (see Fig. 4 later in text).
[FIGURES 2 & 4 OMITTED]
A GPS (global positioning system) receiver (Garmin GPSMAP 76, WAAS-enabled) was used onboard the sampling vessel for tracking the sampling vessel's path and marking sediment sampling station waypoints. The receiver was mounted vertically on the bow of the vessel, as far as possible from all other electronics, to increase accuracy and reduce any possible interference. Observed accuracy was approximately 3.0 m. Track locations and time were automatically recorded about once per minute along all oyster-collection trawls. Waypoints and collection time were manually saved at appropriate locations. Tracks and waypoints were downloaded to a computer for plotting on digital versions of NOAA nautical charts 11371 and 11372A using GIS software. Start and stop endpoints of the shellfish dredges were also noted by hand recording and cross referenced to locations recorded by a separate GPS system used on board the sampling vessel.
The surface area of St. Louis Bay, north of the US Highway 90 bridge, south of Interstate Highway 10, including the adjacent tidal marshlands, was estimated using ArcView GIS software (ESRI, Redlands, California).
Sediments collected in July 2004 were compared with samples that had earlier been analyzed as part of a 1984 Mississippi-Alabama SEA GRANT investigation. The 1984 study (see Isphording, 1985) encompassed the entire Mississippi Sound, as well as all adjacent bays (as well as Lake Borgne, Louisiana). A total of 109 2-meter vibracores were collected, 6 of which were obtained in St. Louis Bay. Each was subjected to mineralogic analysis to determine the mineralogy of the clay-size (-4 [micro]m) fraction, using x-ray diffraction, chemical analysis, using a Perkin-Elmer Model 6500 ICP spectrophotometer, carbon analysis, using a LECO carbon-sulphur analyzer, and sediment texture analysis. A bottom sediment texture map of the Mississippi Sound was constructed by carrying out size analyses on the upper 10-cm portion of each core using ASTM method D 422-63 (also used in the present study). The size frequency distribution of each sediment sample was obtained and also a complete description of the measures of central tendency and dispersion. The same computer algorithm used to analyze the 1984 samples was similarly used to process sediment data for the July 2004 samples in order that meaningful comparisons could be made.
Shellfish Collection and Handling
