Dioxin and heavy-metal contamination of shellfish and sediments in St. Louis Bay, Mississippi and adjacent marine waters.

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

Shellfish collected with the Mississippi dredge on or close to the substrate surface were brought on board and rinsed clean of visible sediments using ambient water at the end of each dredge collection. The objective was to collect American oysters (Crassostrea virginica, Gmelin 1791), but at a few locations incidental collections of common Rangia clams (Rangia cuneata G. B. Sowerby I, 1831) and hooked mussels (Ischadium recurvum Rafinesque 1820) were made. The shellfish were blotted dry and packed in aluminum foil (precleaned by treatment in a muffle oven for a minimum of 3 h at a minimum temperature of 450[degrees]C) and then packed inside plastic bags. The shellfish were cooled in heavily insulated containers with frozen ice packs. At the end of each sampling day, small amounts of dry ice were added to the samples and a programmed temperature recorder (Optic Stowaway Temp, Onset Computer Corp., Bourne, Massachusetts) was added to each container. All samples were shipped to the processing laboratory in Sequim, Washington by overnight courier on July 13, 2004, for delivery on July 14. Temperature was maintained between 1[degree]C and 4[degrees]C in all containers. All samples were assigned a predetermined sample number and entered into a chain of custody logging system. The shellfish sample collection locations are shown in Figure 2 and Figure 3 and labeled in numerical order as collected. Some numerical sample designations were subdivided into sequential alphabetical designations (e.g., 7A and 7B) representing two or more dredge samples with a given sample number. Start and end points are labeled S and E, respectively. All sample transfers were accompanied by chain-of-custody documentation.

[FIGURE 3 OMITTED]

After processing, samples for dioxin and furan analysis were submitted to the analytical laboratory on July 19, 2004. Additional oysters from most collection sites were stored frozen and whole at the processing laboratory at -20[degrees]C for later possible analysis. Samples for metals analysis were submitted to the analytical laboratories between September 3 and October 27, 2004. Samples were collected according to protocols acceptable for both dioxin and metals analysis, as referenced in the following methods, but as an added precaution, control oysters from a non-industrialized site in Puget Sound, Washington were also processed using part or all of the dioxin-preparation procedure to verify that no artifact from the dioxin sample preparation process would affect the metals analysis.

Sediment Collection and Handling

Sediments were collected with a Petite Ponar grab sampler, precleaned with Alconox Laboratory Detergent (Alconox Corp., White Plains, New York). Each sediment sample was removed from the grab sampler using individually prepared nonmagnetic, noncorrosive stainless-steel sediment spoons wrapped in aluminum foil and precleaned by washing in laboratory detergent and heating as described previously. Samples were placed into certified precleaned 4 ounce (118.4 ml) amber glass sampling jars (Environmental Sampling Supply [ESS], Oakland, California) according to a method validated for collection of both organic contaminant and metals sample collection (PSEP 1997). Sediment was stored and shipped to the laboratory as described for shellfish samples. Sediment blanks were included for a manual reading of temperature in shipping containers using a calibrated thermometer on arrival at the laboratory. Sediment samples were logged and tracked using the chain-of-custody system described for shellfish samples. Sediments from a Puget Sound, Washington site were also handled with and without the sediment spoons used in St. Louis Bay to verify that no artifactual metals were added to the samples that would affect the metals analysis. Sediment samples were taken independently from shellfish samples and labeled from 1 to 13 as shown on Figure 4.

Sediment samples for grain-size analysis and total volatile organic content were removed from the grab sampler while onboard the sampling vessel and placed in freezer bags with paper tracking labels to match exterior marking with waterproof felt-tip pens.

Sample Processing and Storage at Laboratory

Upon receipt at the laboratory, the recorded temperature data from each shipment container were downloaded and examined to ensure that temperature had not exceeded 4[degrees]C. Sediment samples were then frozen at -20[degrees]C in a non-self-defrosting freezer. Shellfish samples for dioxin and furan analysis were maintained between 0[degree] and 4[degrees]C until processing. Shellfish were either archived within their precleaned foil wraps, shucked and archived for metals analysis, or processed for dioxin analysis as follows.

All instruments and glassware for shellfish tissue processing for dioxin and furan analysis were precleaned and recleaned between individual sample processing by scrubbing thoroughly while immersed in Alconox soapy water, then rinsed by immersion and agitation in laboratory 18-M[OMEGA] reagent-grade water, followed by unused rinse water poured over the instruments. The instruments or materials were then rapidly air dried on paper, rinsed with reagent grade 100% absolute methyl alcohol (Certified Analytical Reagent, ACS, USP Reagent), rinsed with dichloromethane (Certified Analytical Reagent, ACS, USP Reagent), and allowed to air dry. A method blank consisting of rinse water was also collected and analyzed.

Each replicate sample of oysters contained between l0 and 20 individuals, except as noted in Table 3 (see Table 3 later in text). Prior to shucking, each oyster was scrubbed with fresh tap water in a laboratory sink and measured for shell "length" the linear distance between the dorsal umbo tip and the ventral shell margin (the morphologic shell height). The oysters were opened on a cleaned surface (Alconox scrubbed and rinsed). The oyster meats did not contact the work surface during preparation and only oysters that were previously tightly closed were selected for analysis. The soft tissues were placed in aluminum weigh "boats" that were cleaned by heating as previously described, to determine individual wet weights.

A section for histological examination was removed and placed in a histological cassette, followed by immersion into fixative. The remaining oyster meat was placed in a cleaned beaker and homogenized to a liquid slurry form using a Pro Scientific (Oxford, Connecticut) 200-series homogenizer with a 20-mm, saw-tooth generator. Depending on the amount of homogenized tissue available, one or two laboratory splits of the samples were then poured into the ESS-certified clean amber-glass jars and the net amount of tissue weighed. Samples were then stored at <4[degrees]C. Replicates not submitted to the laboratory within 2 days of processing were stored at -20[degrees]C.

Shellfish tissues for analytical chemistry analysis were dispatched to the analytical laboratory packed in a solid cooler with labels and matching chain-of-custody forms. Ice packs and a small quantity of dry ice (0.5 -1.0 kg) were included within the sample containers. A blank sample for temperature recording upon receipt was included. Samples were sent by overnight courier for dioxin and PCB analysis and hand delivered or sent by courier for metals analysis.

For metals analysis, shellfish were opened using nonmagnetic corrosion-resistant stainless-steel shucking knives, previously validated for handling bivalve tissues used for trace-metals analyses (PSEP 1997; Stephensen et al. 1979). In addition, control oysters from a non-industrialized site were processed and analyzed in an identical manner to ensure that no artifactual metals were added to the samples.

Chemical Analysis of Shellfish Tissues and Marine Sediments 

Dioxin and Furans

Frozen shellfish tissue homogenates and sediments were shipped as described above to Paradigm Analytical Laboratories (Wilmington, North Carolina) for analysis of sample content for 17 dioxin/furan congeners using the United States Environmental Protection Agency method SW846, method 8290 (USEPA 1997).

Polychlorinated Biphenyls 

The same sample set used for dioxin and furan analysis was analyzed for polychlorinated biphenyls (PCBs) by Paradigm Analytical Laboratories using the United States Environmental Protection Agency, method 1668A. (USEPA 1999).

Trace Metals

An initial set of sediments and shellfish tissue samples were analyzed for total metals by the Battelle Marine Sciences Laboratory, Sequim, Washington using inductively-coupled, plasma-mass spectrometry (ICP/MS) as the analytical technique (except for mercury) using EPA methods 1638 and 200.8 (USEPA 1996a & 1994, respectively), adapted for analysis of solid-sample digestates. Mercury was determined by cold-vapor atomic-absorption spectroscopy (CVAA), based on EPA method 245.5 (USEPA 1991a). For these analyses, samples were freeze dried and homogenized using a ball mill prior to digestion with nitric acid, hydrofluoric acids and peroxide in a Teflon vessel, and heated in an oven at 130[degrees]C ([+ or -] 10[degrees]C) according to the laboratory standard operating procedure and quality assurance/quality control documentation. This sample procedure was expected to yield total metals, including those that are bound as crystal silicates.

A second set of sediment and tissue samples were analyzed by the same ICP/MS method (EPA Method 200.8 [USEPA 1994], but were digested using EPA method 3050B (USEPA 1996b) which is not designed to be a total digest for most samples but will dissolve almost all elements that could become environmentally available and is thus comparable to the United States Environmental Protection Agency method used by Lytle and Lytle (1982). These samples were analyzed by Analytical Resources, Tukwila, Washington.

All shellfish were processed whole so that measured metals may have been either incorporated into the tissues or resident in the digestive tracts. This processing represents the potential ingestion exposure of the metals to human consumers because oysters are commonly eaten whole or the entire oyster body is used in preparing the oysters for consumption.

Grain Size-Analysis and Volatile-Organic Content of Sediments

Grain-size analysis and percent volatile solids were determined using methods ASTM D422-63 and EPA 160.4, respectively (ASTM 2003; USEPA 1979). These analyses were performed by Aquatic Research Inc. of Seattle, Washington. Grain size and volatile organics were examined and compared with prior data from St. Louis Bay (Isphording 1985).

RESULTS

Dioxins and Furans

Dioxin and furan concentrations expressed as toxic equivalencies for shellfish collected in and near St. Louis Bay are shown in Table 1. Toxic equivalencies (TEQs) are expressed as WHO-TEQs (Vanden Berg et al. 1998) and I-TEQs (USEPA 1989), for comparison with a previous evaluation of oysters from southern Mississippi (Fiedler et al. 1997). The set of international toxic equivalency factors (I-TEFs) returns TEQ values that are higher than those derived from using the World Health Organization TEFs due to differing TEF values for three congeners. In addition, the data available from the Fiedler et al. (1997) paper are based on using one half the limit of quantification value (1/2 LOQ) for nondetects. The LOQ is defined as 10 times the standard deviation of the average of a series of blank measurements and likely overstates the contribution of non-detects (Jensen & Bolgar 2001). Therefore, our comparison, from data derived using one half detection limit values for non-detects, to the Fiedler et al. (1997) values is a conservative estimate of the difference between the two data sets, because the 1997 values may have been lower than reported if the raw data had been presented as we present our raw data. Congeners measured are shown in Table 2. The shellfish tissue values for data generated in this study were converted to I-TEQs and WHO-TEQs with appropriate TEFs using the EPA-referenced method (USEPA 1989) advising that the common conservative approach for non-detected congeners is to set their value at one-half of the detection limit (ND = 1/2).

In addition, the I-TEQs were expressed adjusted for lipid so that they could be compared with the prior study by Fiedler et al. (1997) of dioxins and furans in oysters collected as part of a market-basket assessment of food products from southern Mississippi. Only the specific congener analytes common to both studies were used in the comparison. Table 1 shows that the WHO-TEQ values (ND = 1/2) for the 17 congeners of dioxins and furans in oysters (total tissue basis) from within and near St. Louis Bay ranged from 0.312 pg/g to 0.463 pg/g wet tissue weight with an average value of 0.378 pg/g. Rangia clams collected from shellfish collection track 1 had a higher WHO-TEQ of 0.581 pg/gm. Oysters from inside the bay only (collection tracks 2 to 8) had an average WHO-TEQ of 0.398 pg/g and oysters collected from open harvest sites between the highway and railroad bridges at the mouth of the bay and from sites outside the bay had an average WHO-TEQ of 0.343 pg/g. The shellfish collection track with the highest WHO-TEQ inside the bay was collection track-7B, located in the midbay region, and the site with the highest TEQ outside the bay was shellfish collection track-17 (located ~7 km southwest of the center of the bay mouth and between 0.67 and 1.48 km offshore).

When the I-TEQ values for shellfish tissues were lipid adjusted (i.e., expressed as a concentration in the lipid fraction only) for comparison with those reported by Fiedler et al. (1997), the I-TEQ values for the clam sample was 165.5 pg/g lipid, the average value for oysters within the bay was 98.2 pg/g lipid, and the average value for oysters south of the highway bridge and outside the bay was 58.8 pg/g lipid. The two highest values for lipid adjusted I-TEQ were shellfish collection track 2 (152.4 pg/g lipid), located just south of the refinery outfall in St. Louis Bay and shellfish collection track 3 (247.9 pg/g lipid) also located nearby the outfall and southeast of Grassy Point (Fig. 2).

Total dioxins and furans and TEQ values for sediments are shown in Table 2. The two highest WHO-TEQ values in St. Louis Bay (11.41 and 11.78 pg/g sediment dry-weight basis) were located at sediment stations 2 and 3, respectively, which were the stations closest to the titanium dioxide refinery effluent outfall point, labeled as a sewer on National Oceanic and Atmospheric Administration (NOAA) Nautical Charts 11371 and 11372A and in Figure 2 and Figure 4. These two stations were also the only in-bay stations with detectable levels of 2,3,7,8-TCDD, the most toxic of the dioxin congeners. Sediment station 2 is located approximately 260 m south of the discharge of the refinery outfall pipe, and sediment station 3 is located approximately 1.6 km to the south-southwest of the outfall discharge (Fig. 4). The highest value outside the bay (15.33 pg/g) was located at sediment station 12 between Henderson Point and Square Handkerchief Shoal, which was also the only out-of-bay station with a detectable level of 2,3,7,8-TCDD. The average sediment WHO-TEQ value inside the bay (sediment stations 1 to 8) was 8.57 pg/g, and the average WHO-TEQ value for the stations outside of the bay (sediment stations 9 to 13) was 7.92 pg/g. Due to variation in half-life of constituent congeners (Sinkkonen & Paasivirta 2000) and lack of source test data, we did not attempt a quantitative comparison of congeners from the various stations.

Sediment Grain Size, Volatile Solids, and Association with Dioxin Concentrations

The sediments in this study were largely sandy-silts (median diameter, 82 [micro]m). Sediment grain size did not correlate well with total dioxin, but total volatile solids, consisting of all organic material and carbonates, showed a higher inverse correlation coefficient for sites inside the bay (r = 0.86; n = 8) than for sites outside the bay (r = 0.73; n = 5).

Total Dioxin Load Estimate for St. Louis Bay Sediments

The total load of the measured 17 congeners of dioxins and furans in St. Louis Bay sediments was estimated by using the average concentration of all congeners at each sediment site located within the bay, north of US Highway 90. The surface area of the bay was estimated at 40.9 [km.sup.2] and the area of the bay and surrounding marshlands was estimated at 54.1 [km.sup.2]. However, a figure of only 75% of the bay surface area was used as a conservative factor in estimation of a minimum burden number. The marshlands surrounding the bay and comprising an additional 13.2 [km.sup.2] were not included in the minimum estimate calculation, although they may be periodically inundated with seawater at high tide. The maximum estimate calculation included the full area of the bay and the surrounding marshlands or an area 76% greater than the minimum estimated area (consisting of 75% of the bay surface area). Therefore the minimum calculation is conservative.

To estimate the total burden of the 17 measured dioxin and furan congeners in St. Louis Bay, the sediment concentration per gram was calculated by converting the dry weight concentrations of dioxins and furans to wet weight concentrations using an average moisture content of sediments of 66% (determined in the analytical preparation of sediments) and the empirically measured average of 1.35 g of wet sediment per cubic centimeter. Because sediment samples were taken and mixed from the top 4 cm of sediment, the burden was calculated for the top 4 cm of sediment only. This calculation yielded a total burden of measured dioxins and furans in the sediments of 3.72 kg for 75% of the area of St. Louis Bay, to a depth of 4 cm, assuming that the bay bottom was a planar surface. If the entire area of the bay as well as the marshlands were to be included, this estimate would increase by 76% to 6.56 kg. In addition, dioxins and furans may be present at sediment depths >4 cm.

Polyehlorinated Biphenyls

The WHO-TEQs for PCBs (ND = 1/2) for sediment samples ranged from 0.113-0.225 pg/g on a dry-weight basis for all sample sites. The WHO-TEQs for PCBs (ND = 1/2) for oyster samples ranged from 0.108-0.125 pg/g on a wet-weight basis.

Trace Metals--Shellfish Tissues

Trace-metal values for shellfish, derived using the extraction method for bioavailable metals (second analytical set), inside St. Louis Bay and in locations near the mouth of the bay are shown in Table 3, referenced to sample locations shown in Figures 2 and 3. For edible oysters inside the bay, these values show large increases from the 1978 study in arsenic (percent value of 404% compared with 1978), chromium (percent value of at least 1,167% compared with 1978), and nickel (percent value of at least 467% compared with 1978). Selenium increased 48% and the other metals showed decreases from the 1978 study. In Rangia clams, also evaluated in the 1978 study, there were increases in the content of all metals measured, which registered above detection limits (Table 3) and were measured in the 1978 and 2004 studies, with the exception of zinc. There was only a minor increase in mercury in clams. The increased concentrations in Rangia clams were greater than that for oysters with the largest increases in arsenic (percent value of 1,920% compared with 1978) and nickel (percent value of at least 1,225% compared with 1978). A value for chromium in Rangia clams was not reported in the 1978 study. Hooked mussels, considered a non-edible species, showed the lowest concentrations of metals. Based on this data set, the highest concentrations of chromium and nickel in any of the shellfish were from oysters taken at shellfish dredge site 16 (Fig. 3), an area open to oyster harvest, located about 1.7 km south of Henderson Point, which forms the eastern aspect of the mouth of St. Louis Bay.

The first data set (i.e., metals obtained by total digestion) yielded similar but somewhat higher values for metals, as expected. Because this could have been due to a contribution of mineral-bound and nonbioavailable metals and a small artifactual increase during processing (measured at 1 [micro]g/g for Cr and about 0.5 [micro]g/g for Ni, for tissue samples only) of the samples for dioxin analysis (not conducted on or applicable to the second sample set), we have excluded this data set from comparative evaluation with the 1978 data. However, it is included in summary form (Table 4) because it confirms the high values of metals in oysters from an open harvest area and emphasizes the need for public health agencies to consider these data in regard to the suitability of such oysters for human consumption and, at a minimum, to provide public notice of the potential for negative health effects to specific groups of the population. Examination of metals content from shellfish from data set 1 shows that values as high as 12.3 [micro]g/g for chromium and 7.54 [micro]g/g for nickel were found in edible oysters from open harvest shellfish collection site 15. Even allowing for a reduction in up to 1 [micro]g/g in these values, based on control studies applying only to this data set, these are still high values with regard to human consumption, as will be discussed in following text. Using the first and second data sets for metals, respectively, the chromium content of oysters in Mississippi Sound, adjacent to St. Louis Bay showed percent values of at least 11,300% and 7,700% compared with the 1978 values (below detection limit) reported for in Bay oysters in 1978. However, in utilizing the US Food and Drug Administration estimated safe and adequate daily dietary intake for specific metals (USFDA 1993a, b, c), we used only metals data set 2, designed to analyze for bioavailable metals.

Trace Metals-Sediments

The 1978 values for trace metals in sediments from St. Louis Bay were from sampling and analysis reported by Lytle and Lytle (1982) prior to the construction and operation of the titanium dioxide refinery. Based on comparison of the 1978 data with our values for sediment station 2, chromium, beryllium, nickel, arsenic, and lead increased (listed in descending order of magnitude) in St. Louis Bay sediments between 1978 and 2004 (Table 5). The percent value for copper in 2004 was 90% of that in 1978 and the similar value for zinc in 2004 was 80% of that in 1978. Cadmium, antimony, and selenium were below detection limits in the 1978 study and this data set from 2004. Mercury was detected at 0.107 [micro]g/g in 1978 and found to be 0.095 [micro]g/g in 2004. Although there were no 1978 data to compare sites outside of the bay with the 2004 values, chromium and nickel values from sites outside but near St. Louis Bay were higher in 2004 than the values reported for these metals inside the bay in 1978.

The increase noted in some of these metals is undoubtedly an anthropogenic effect. Particle size analyses carried out by Isphording (1985) in St. Louis Bay versus those in the present investigation clearly show a coarsening trend for bay sediments over the past 20 y. The 1985 sediments were largely silty-clays (median diameter, 14.1 [micro]m) whereas those at present are chiefly sandy-silts (median diameter, 57 [micro]m, in-bay). As such, the expected trend would be for lower natural levels of heavy metals to be found in the sediments. Sorption of heavy metals in sediments is closely related to grain size (see Cordi et al. 2003) because sand-sized sediment (i.e., >62 [micro]m) and medium to coarse silt-size sediment (those 10-62 [micro]m) will consist almost entirely of the mineral quartz (Si[O.sub.2]). Quartz shows almost no tendency to adsorb contaminants because it closely approaches its stoichiometric composition under natural conditions and has few site vacancies that produce positions where ions can "attach." The clay-sized sediments (by definition, those <4 [micro]m in size) in St. Louis Bay, in contrast, consist largely of the Smectite Group clay mineral montmorillonite, (Ca,Na)[(Al,Mg,Fe).sub.4][[(Si,A1).sub.8][O.sub.20]][(OH).sub.4] * n[H.sub.2]O). This mineral is characterized by numerous Schottky-Wagner (missing ion) defects that render the clay micelle surfaces "charged." Hence the mineral can abundantly adsorb organic and inorganic impurities and contaminants. Montmorillonite clays also possess very high cation exchange capacities (100-300 milliequivalents/liter). This property, similarly, renders them capable of adsorbing a wide variety of metals and organo-metallic species. Not unexpectedly, then, when the median diameters of the 13 samples collected in this study were compared with the total dioxin and furan levels from Table 2, an inverse correlation of r = 0.70 was obtained. A less strong, but statistically significant inverse correlation (r = 0.54) was also obtained when dioxin and furan levels from Table 2 were compared with the percentage of sediments in each sample in the 3- to 12-micron range. This size fraction is important because it includes the size range of particles that are ingested by filter feeding oysters. Given that the sediments demonstrably contain elevated levels of both dioxins and furans, it is not therefore surprising that St. Louis Bay shellfish exhibit heightened levels of both of these compounds.

In addition to contaminants associated with the clay minerals, the fine silt and clay fraction (particles <10 [micro]m) also contains significant quantities of iron and manganese oxide and oxyhydroxide compounds. These, similarly, are marked by extensive substitution of a wide variety of metal ions for both iron and manganese. Hence, a decrease in the quantity of fine silt and clay-size sediments over the 20-y period would be expected to produce a decrease in metal levels and other contaminants. The increase observed in this investigation must therefore be the result of "loading" of the reduced quantities of fine silt and clay due to high levels of contaminant influx.

DISCUSSION

Toxic Equivalents of Dioxins, Furans, and PCBs in Shellfish

The WHO-TEQ values based on a whole-shellfish soft tissue wet-weight basis averaged 0.392 pg/g for oysters and was 0.581 pg/g for the single sample of Rangia clams. While there is no defined action level in the United States, the US Food and Drug Administration advises that "Since there are no tolerances or other administrative levels for dioxins in food or feed, the appearance of these compounds in a food or feed supply is of gravest concern" (USFDA 2000). The European Union (EU) has defined action levels of between 0.5 and 4.5 pg/g (based on WHO-TEQ) for dioxins, furans, and dioxin-like biphenyls in various seafoods related products (EC 2002). Because these action levels include dioxin-like biphenyls, and in setting the action level, studies showed that only 25% to 50% of the total dioxin equivalents came from dioxins and furans, the effective EU action level for dioxins and furans separately is closer to 1.0-2.0 pg/g. In 1981, The US Food and Drug Administration recommended a 25-pg/g maximum dioxin level to address contamination of fish in the Great Lakes. Subsequently, in 1997, the USFDA (1997) issued prohibition of the sale of catfish containing more than 1 pg/g dioxin, but subsequently rescinded this restriction (USFDA 1997). We compared the values for oyster dioxin and furan TEQs from this study with those reported previously by Fiedler et al. (1997). Only the congeners reported by Fiedler et al. (1997) that were also evaluated in this study were used, and I-TEQ (ND = 1/2) values for nondetects in our data were used. The Fiedler values could be an overestimate of the actual toxic equivalents present because they use 1/2 LOD values for nondetects. Thus, our comparison to their values of the increase in dioxins and furans includes a conservative estimation factor, due to the necessity of using their values based on 1/2 LOD. The Fiedler et al. (1997) study was a market-basket survey of various food stuffs, including oysters, from grocery stores and seafood markets in southern Mississippi, although the source location of the oysters was not specified. Fiedler et al. (1997) report lipid-adjusted values (i.e., they expressed the total dioxin and furan analytes as a concentration of the lipid portion only of the animal) because, as they noted, dioxins and furans accumulate in the lipid compartment of animal tissues.

Using this lipid-adjusted means of expression, these authors reported values of from 21.0-31.4 pg/g I-TEQ for the oysters. Using the same method of calculation (but using 1/2 detection limit values for nondetects), we found lipid-adjusted I-TEQ concentrations ranging from 54.2-247.9 pg/g for oysters in St. Louis Bay, 165.5 pg/g for Rangia clams in St. Louis Bay and concentrations ranging from 36.6-79.1 pg/g for oysters from open harvest areas south of and adjacent to St. Louis Bay. Thus, the comparison of lipid adjusted values from the 1997 paper to those of the current study indicates a doubling to near an order of magnitude greater values for dioxin and furan TEQs for St. Louis Bay oysters versus those from southern Mississippi in 1997. In most circumstances, this would be surprising because a number of studies have indicated that dioxin concentrations in the environment, in food stuffs, as well as human exposure levels, have been decreasing for several decades (e.g., USEPA 1991b; Smith et al. 1995, Pearson et al. 1995, Pinsky & Lorber 1998, Winters et al. 1998). Dioxin and furan concentrations in St. Louis Bay in 2004 were about 2.6 to 7.9 times higher than the low and high values, respectively, reported in the 1997 study. Dioxin and furan values outside of St. Louis Bay in 2004, in open harvest areas, are about 1.8 to 2.5 times higher than the low and high values, respectively, reported in 1997. The actual increase may be higher due to the use of 1/2 LOQ values by Fiedler et al. in 1997. Our average value for total dioxin and furan TEQs is lower than a national average (0.448 ppt) reported by Jensen and Bolgar (2001) for mollusks (using 1/2 detection limit values for nondetects). However, that study did not specify the collection sites or mix of species used in the reported number. The more significant comparison is the rise in values of contaminants in oysters collected in southern Mississippi between 1997 and 2004, during a time period when dioxins were generally decreasing in the environment.

It should be noted that the female oysters collected for this study were not in a condition of peak reproductive development, when lipid levels would be expected to be higher. At that time, lipid levels can range from 10% to 15% as a proportion of total body weight, even after peak reproductive conditioning (Barber et al. 1988a, Barber et al. 1988b). Rather, the average lipid levels of oysters from all sites in our study were low, only 0.59%. Assuming an equal proportion of males and females, this indicates that the lipid content could be greater by a factor of 8.5-12.7, assuming no lipid increase in reproductively mature males. This indicates that at certain times of the season, the dioxin content of oyster samples could similarly increase by a factor of 8.5-12.7 to levels that would be of public health concern, although the rate of accumulation is unknown and thus the maximum potential accumulation is also unknown. However, the high potential accumulation rates would be of particular concern for sites outside of, but near, St. Louis Bay that are open for harvest.

The even higher TEQ values of sediments, compared with shellfish TEQ values, and potential new dioxins and furans added to the marine environment, provide the source for such additional accumulation of these carcinogens. A paper published in 1996 (Comber et al. 1996) indicated that relatively high values of dioxins and furans were acceptable in freshwater sediments. However, these guidelines were based on toxicity of the sediments to trout eggs and fish and did not address toxicity to organisms residing in marine sediments. The risk posed by sediment dioxins and furans to mollusks residing in or near the sediments is a function of multiple factors including sediment resuspension, congener half-life, sediment transport, addition rate of new congeners, and removal rate of dioxins by natural processes.

Calculation of TEQ values for PCBs in shellfish and sediments showed that they were below recognized levels of concern.

Estimation of Total Dioxins and Furans in Bay Sediments

As noted in the Results section, we conservatively estimated the total load of the measured 17 congeners of dioxins and furans in sediments of St. Louis Bay at 3.72 kg. This estimated value would increase by 76% to 6.56 kg if marshlands and the total bay area were included.

Visual inspection of the data (Table 2) suggests similarity between the dioxin and furan content of all the sites with relatively high proportions of OCDD and 1,2,3,4,6,7,8-HpCDD; 1,2,3,7,8,9 HxCDD; and 1,2,3,6,7,8 HxCDD in all samples, both inside and outside St. Louis Bay. However, we judged that a numerical analysis of the similarity of congener composition between sites in this study and between our values and the reported discharge values from the titanium dioxide refinery (USEPA 2003) would not be meaningful because the residence time of the dioxin and furan components at each site is unknown, and the half-life of congeners in sediments varies markedly (Sinkkonen & Paasivirta 2000).

Heavy Metals in Shellfish and Sediments of St. Louis Bay and Adjacent Marine Waters

Our study found a marked increase in the bioavailable heavy metals, namely chromium, nickel, and arsenic in oysters in St. Louis Bay and adjacent waters of Mississippi Sound compared with the prior survey. Chromium and nickel were not detected in oysters in St. Louis Bay in 1978 and arsenic was detected at about 25% of the 2004 concentration in 1978 oyster samples. Evaluation of Rangia clams shows that the burden of all metals measured above detection limits, except zinc, have increased in shellfish in St. Louis Bay since 1978, with the greatest increases in arsenic and nickel.

Metals appear to have also increased in sediments in St. Louis Bay and adjacent marine waters. However, because the large increases in chromium and nickel accumulation in shellfish appear spatially linked to the titanium dioxide refinery, which produces soluble metal chlorides, the discharge of such compounds may, in large part, be carried outside of St. Louis Bay where precipitation and dispersion in the higher salinity waters of Mississippi Sound would occur. Thus, sediment data are of limited value in estimating the contamination of St. Louis Bay waters by metals from the titanium dioxide refinery because the refinery process that utilizes the chloride-ilmenite process (USEPA 2001) results in acidified soluble metal chlorides (MDEQ 2003) which, assuming these are the most likely source of contaminants, would be expected to be largely flushed out of St. Louis Bay as dissolved matter, where they would tend to precipitate and be dispersed in the more saline waters of Mississippi Sound. It is also presumed that this process produces primarily chromium-III, rather than the more highly toxic and carcinogenic chromium-VI.

Metal Content of Edible Oysters and Recommended Safe Consumption Levels

Table 6 shows the estimated safe and adequate daily dietary intake (ESADDI) for chromium-III and nickel and compares these to the content of the metals in oysters from St. Louis Bay and adjacent waters of Mississippi Sound in this 2004 study (USFDA 1993b, USFDA 1993c). Although these values are stated to represent only the historical record, according to the US Food and Drug Administration, they have not been replaced by new USFDA recommendations or guidelines and have been widely adopted as the standard for ESADDI (Beers & Berkow 2004; PDR 2004). Using these ESADDI values indicates that the oysters, which previously had no detectable chromium and nickel in 1978 and about 25% of the 2004 value of arsenic, are now sufficiently burdened with these metals that less than one oyster per day can be consumed from open harvest areas near St. Louis Bay without exceeding the ESADDI levels for chromium-III and nickel for hypersensitive individuals. The oysters inside St. Louis Bay, currently a closed area due to bacterial contamination, have lower concentrations of these metals but are markedly elevated compared to 1978.

The increases in chromium and nickel are the most significant in terms of ESADDI of these metals (Table 6). Based on these values, and assuming that oysters are the only source of dietary chromium, for example, the consumption of oysters from inside St. Louis Bay should not exceed about 3 1/2 per day. However, oyster harvest from the bay is not permitted because of bacterial contamination. More significantly, based on average chromium levels (assumed to be chromium-III) in oysters from adjacent waters outside the bay, such oysters should not be consumed at a rate of more than two medium oysters per day. At the site with the highest chromium level, medium-sized oysters should not be consumed at a rate of more than 0.8 oysters per day to not exceed the ESADDI. For individuals hypersensitive to nickel (estimated to be about 10% of females and 2% of males in a European population, for example [Flyvholm et al. 1984]) and who are thus susceptible to nickel eczema, oysters with average nickel concentrations outside the bay should not be consumed at a rate of more than 0.5 oyster per day or at a rate of more than 0.2 oyster per day from sites with the highest recorded nickel content, based on the ESADDI. Based on the USFDA (1993a) advisory, arsenic levels are probably not of concern, although elevated over those of 1978, because 90% or greater of the arsenic found in shellfish is usually in organic form, rather than the toxic inorganic form. The analysis performed in this study did not discriminate between organic and inorganic arsenic. All of the above computations of the ESADDI of these metals assume that oysters are the sole dietary source of the metal.

The relatively high chromium content in the oysters in this study is surprising due to the discrimination of Eastern oysters against accumulation of chromium in relation to other metals (Huanxin et al. 2000). These authors found that chromium concentrations were lowest in relation to sediment concentrations when compared with several other metals. Our study established the content of chromium in whole oyster meats, some of which may have been in the digestive tract, associated with food particles, including those that would have complexed with soluble chromium compounds. However, as indicated previously, the total content of bioavailable chromium is important due to the consumption of whole oysters as a food product.

Transport of Contaminants out of St. Louis Bay

Studies of St. Louis Bay and the adjacent waters of Mississippi Sound indicate that a salinity gradient exists across the mouth of St. Louis Bay, and that the low salinity outflow of the bay consistently occurs on the western side and continues to follow the shoreline westward for some distance (Eleuterius 1976). This circulation pattern helps explain the higher than average TEQs for dioxins in shellfish from sample tract number 17 and the relatively high value for total dioxins and furans at sediment site 13 as well as the lower values at sediment sites 9 and 10. However, considerable mixing occurs outside the mouth of St. Louis Bay and depends on weather and sea state conditions. Weather fronts from autumn through spring may push waters south of the bay either northeastward or southeasterly depending on the wind direction. Such conditions could account for mixing and higher accumulation of contaminants such as total dioxins and furans at sediment station 12 and chromium in oysters in shellfish dredge tract 16. According to a circulation model of the bay (Cobb & Blain 2002), there can be a net west to east flow south of the mouth of St. Louis Bay resulting from ebb tide flows and wave induced currents. Chromium, presumed to be released in soluble form into St. Louis Bay, would be likely to accumulate in oysters near the bay than in sediments because soluble chromium compounds would be expected to precipitate or complex with fine particles that are ingested by filter-feeding oysters.

Other factors acting to control distribution of contaminants observed in the fauna and sediments again involved both the grain-size distribution of sediments at a given site and mineral speciation at the site. Higher levels of furans and dioxin are found where the content of fine silt and clay-size sediment is greatest. Clay minerals, however, are more likely to settle out where a change to a higher salinity is encountered. This causes the clay particles (micelles) to flocculate and thus "clump" to form hydraulically larger sized sediment, which settles more quickly to the bottom. This is particularly apparent at sites 7, 8, 12, and 13, each of which contains approximately 20% or more of clay-size particles. Each of these sample locations is also the site of elevated congeners of dioxin and furans that are similar, or exceed levels found immediately offshore from the titanium-dioxide refinery.

Sources of Contamination

Potential sources for dioxin, chromium, and nickel contamination of St. Louis Bay and the nearby waters of Mississippi Sound were reviewed using the United States Environmental Protection Agency Toxic Release Inventory (TRI) Program's TRI Explorer (www.epa.gov/enviro/html/tris/) and the EPA Envirofacts Warehouse (http://www.epa.gov/enviro/index.html). The Toxic Release Inventory Program makes data available to the public. However, it is important to recognize that the program does not mandate monitoring, and some of the TRI data are based on monitoring protocols whereas other data are derived by using various estimation techniques. Because facility activities and patterns of disposal or other releases can vary dramatically from one year to the next multiyear data were evaluated, as available.

Toxic release data from facilities in Hancock and Harrison Counties, the Mississippi counties directly adjacent to St. Louis Bay, were complied for all years available. TRI data are available through 2002, with early release of 2003 TRI data making those numbers available in November 2004, but with the caveat that "... the traditional public data release, which includes more quality checks ..." is expected in Spring 2005. At this time, the 2003 data are in the form of an electronic facility data release, which have not completed all verification. However, as the 2003 data are consistent with prior years for the facilities that have been reviewed for this study, and the EPA website states that the data have "undergone the majority of the data quality checks routinely conducted by EPA's TRI Program," we included this year in the multiyear compilations.

EPA Toxic Release Inventory records report release of dioxins only for the years 2000 to 2003, due to regulatory changes effective in the year 2000, when certain new persistent bioaccumulative toxic (PBT) chemicals were added to the TRI list of reportable chemicals.

In reviewing the EPA TRI records, no significant sources of dioxin contamination were found in the St. Louis Bay watershed, other than the titanium dioxide refinery on the northern shore of St. Louis Bay. In fact, TRI records show no release of dioxin or dioxin-like compounds reported in Hancock County for 2000 to 2003. In Harrison County, only 2 facilities reported release of dioxins: the titanium dioxide refinery and the Mississippi Power Company Jack Watson Power Plant. Total reported release of dioxin and dioxin-like compounds for the Mississippi Power Company Watson Plant for the years 2000, 2001, and 2002, was, respectively, 0.3691 g, 0.3425 g, and 0.3109 g. For the same years, the titanium dioxide refinery reported release of 19,493.17 g, 18,201.2 g, and 20,078.11 g. The total amount of dioxins released on-site for the years 2000 to 2003 for the Mississippi Power Company Jack Watson Power Plant was 1.39 g, compared with 72,817.41 g disposed of or released on-site by the titanium dioxide refinery for the same time period. Dioxin release by facilities in the other counties in the Mississippi Coastal Watershed was examined also. In 2002, a representative year, the total amount of dioxin and dioxin-like compounds reported released was as follows: Jackson County, 3.8 g; Lamar County, 1.57 g; Pearl River County, 1.2 g; and Stone County, 4.47 g.

Over 99.99% of the dioxin and dioxin-like compounds released by the titanium dioxide refinery are listed as being disposed of in "other on-site landfills." "Other landfills" (Section 5.5.1B on the TRI Form R) are defined by the EPA TRI program as "those landfills which are not authorized under Subtitle C of the Resource Conservation and Recovery Act (RCRA) to accept hazardous wastes. These landfills are commonly referred to as non-hazardous waste landfills and may be regulated under a variety of other Federal, state, and local programs." (USEPA TRI Explorer, http:// yosemite 1.epa.gov/oiaa/explorers_fe.nsf/Doc1/Other+Landfills?). The titanium dioxide refinery does not use RCRA Subtitle C landfills for disposal of dioxins, as indicated in Section 5.5.1A on the TRI Form R completed for dioxins in 2000 to 2003. The RCRA Subtitle C landfill is designed and authorized to accept hazardous waste for disposal, with requirements for lining to prevent leakage of landfill contents.

Given the large quantity of dioxin and dioxin-like compounds that are disposed of on-site, the type of disposal, the plant's proximity, and the lack of any other significant sources of dioxins in the vicinity, it seems likely that the titanium refinery is the most significant source of the dioxins found in St. Louis Bay. The distribution of dioxin and furan compounds in St. Louis Bay also implicates the refinery as the source. Such compounds could enter the bay by several pathways, including fallout from airborne emissions as well as fugitive emissions from surface-water runoff or discharges. The latter inference is supported by the fact that the two highest concentrations of dioxins and furans in St. Louis Bay sediments were found at the two stations closest to the facility's surface-water discharge pipe (identified as the "sewer" noted in Fig. 1, Fig. 3). In addition, the two oyster samples with the highest lipid-adjusted I-TEQ values were from shellfish dredge sites 2 and 3, nearest to and close to, respectively, the facility's surface-water discharge pipe.

The potential for shellfish to accumulate greater concentrations of dioxin as the lipid content increases is suggested by the higher TEQ values for the measured dioxins and furans in sediments in and near St. Louis Bay. These WHO-TEQ values ranged from 4.17-11.78 pg per gram for in bay sites, with the highest sites recorded closest to the titanium dioxide refinery outfall (sediment collection sites 2 and 3, Fig. 3). However, relatively high sediment values were recorded at two open harvest sites near the mouth of St. Louis Bay (sediment collection sites 12 and 13). The elevated concentrations in sediments at these sites may be due to waterborne transport out of the bay and local current patterns in the vicinity of sediment collection sites 12 and 13. As noted earlier, during wave-tidal coupled action there is consistent flushing of the mouth of the bay into Mississippi Sound during all phases of the tide.

The US Environmental Protection Agency Toxic Release Inventory (USEPA 2003) was examined for potential sources of chromium and nickel in the St. Louis Bay watershed. The titanium dioxide refinery on the northern shore of St. Louis Bay was found to release the largest amounts of chromium and nickel, and appears to be the only facility in close enough proximity to significantly affect the metals levels in St. Louis Bay. According to the figures reported by the titanium dioxide refinery to the USEPA Toxic Release Inventory, the refinery disposed of 304,928 kg (672,252 lb) of chromium compounds and 32,888 kg (72,505 lb) of nickel compounds in 2002. These are assumed to be metal chlorides based on the described manufacturing process for the refinery (USEPA 2001; MDEQ 2003). The majority of the chromium (303,907 kg = 670,000 lbs) and nickel (32,659 kg = 72,000 lb) were disposed of in Class l wells, whereas only 6.4 kg (14 lb) of chromium compounds and 45.5 kg (100 lb) of nickel compounds were reported to be released to surface water discharges (into St. Louis Bay) in 2002.

Multi-year data compilations were done to compare the amounts of chromium and nickel released by the titanium dioxide refinery with the two other sources of chromium and nickel in the counties bordering St. Louis Bay. For the years 1995 to 2003, the only years that the titanium dioxide refinery reported release of chromium and nickel compounds, the total quantity released was 238,872 kg (526,623 lbs) of nickel compounds and 3,168,142 kg (6,984,558 lbs) of chromium compounds. As noted earlier, most of the chromium and nickel compounds were injected into Class 1 wells. However, over this 9-y period, nickel compounds were also released as follows: 160 kg (353 lbs) stack or point source air emissions, 1260 kg (2778 lbs) discharged into St. Louis Bay, and 1996 kg (4400 lbs) placed in "other landfills" (not RCRA Subtitle C landfill). The corresponding amounts of chromium compounds for this 9 y period were: 131 kg (287 lbs) stack or point source air emissions, 156 kg (344 lbs) discharged into St. Louis Bay, and 10,841 kg (23,900 lbs) placed in "other landfills".

The Mississippi Power Company Watson Plant in Harrison County reported release of nickel compounds for the years 1998 to 2003 totaling 1299 kg (2864 lb) stack or point air emissions and 1134 kg (2501 lb) discharged to surface waters. The corresponding amounts for chromium compounds for these years (except no Cr release reported in 2002) were 946 kg (2085 lb) stack or point source air emissions and 349 kg (770 lb) discharged to receiving streams or water bodies. Plant Watson is located 28.2 km (17.5 air miles) east-northeast of Grassy Point in St. Louis Bay and at least 72.4 km (45 water miles) from Grassy Point via Biloxi Bay and Mississippi Sound. An examination of the prevailing winds in the area indicates that no significant heavy-metal components in the plant's air emissions would be expected to reach St. Louis Bay; likewise, the water distance and the lack of a direct water route to St. Louis Bay makes it highly improbable that the Bay would be affected by discharges from the Mississippi Power Company power plant. In addition to these two release routes, this plant places nickel and chromium compounds in surface impoundments; however, this release of chromium and nickel would not affect St. Louis Bay.

The other source of chromium compounds and nickel compounds in the vicinity is General Electric Plastics, located at Port Bienville in Hancock County, MS. This plastic polymer facility is located approximately 30.6 km (19 air miles) southwest of Grassy Point in northern St. Louis Bay and at least 45.1 km (28 water miles) via the Pearl River and Mississippi Sound from Grassy Point. This facility reports their toxic releases in ranges, as permitted by the EPA. These ranges are large enough to make it impossible to know how much nickel or chromium has been released to the air over the years reported (1999-2003). For each of these years, the amounts for chromium compounds and nickel compounds in fugitive air releases are noted to be 5.0-226.5 kg (11-499 lbs). The yearly amounts for both compounds released to water are noted to be 0.45 to 4.5 kg (1-10 lbs) for each of two water bodies. However, the total quantity released on-site is only 45.5 kg (100 lbs) of each metal compound per year, so the total amount of chromium compounds for the 5-y period is 227.0 kg (500 lbs), and for nickel compounds, the total released on-site for this period is also 227.0 kg (500 lbs). Given the relatively modest amounts of chromium and nickel released, coupled with the distances (via air and water) from St. Louis Bay, it seems unlikely that the releases from this facility affected the bay.

No other USEPA-permitted discharges of chromium or nickel compounds were identified from either Hancock or Harrison Counties. As noted, General Electric Plastics and Mississippi Power Company Watson Plant likely do not contribute to the metal contamination of St. Louis Bay. The distances via air and water over which these contaminants would have to travel to reach St. Louis Bay and the physical, meteorological, and hydrological barriers to migration would preclude, in our opinion, any significant addition by these two sources to the metal contaminants in St. Louis Bay.

The titanium dioxide refinery has been discharging nickel and chromium compounds into the water of St. Louis Bay and into the air near the bay for at least 9 y. In addition, it seems possible that some of the nickel and chromium compounds placed in the landfills could, over time, leach out and contribute to the contamination of the bay.

Because the metals are likely to be metal chlorides, they would be expected to be soluble but likely precipitate and form particle-bound complexes when released and mixed into waters of increasing salinity. Thus, leakage of such compounds from the northern aspect of St. Louis Bay would likely result in a substantial portion of such metal chlorides being transported to the mouth of the bay and out of the bay to the higher salinity waters of Mississippi Sound where they would tend to precipitate out of solution. Therefore, the measured amounts of leachable and bioavailable chromium and nickel remaining in St. Louis Bay would represent only a fraction of the amount released into the bay. This further explains why a source of metal chlorides in the bay could result in higher accumulations of the metals in shellfish outside the bay than in the bay.

We also examined the potential for heavy-metal aerosols to reach St. Louis Bay from air-emission point sources along the Mississippi River industrial corridor. That corridor runs from Baton Rouge downriver past New Orleans, Louisiana, and includes numerous petroleum refineries and chemical-manufacturing plants. Baton Rouge is 160 km (100 mi) due west of St. Louis Bay and New Orleans (the closest point along the industrial corridor) is 80 km (50 mi) southwest of the bay. Year 2002 EPA-TRI data (USEPA 2003) show that 134.4 kg (296 lb) of chromium and chromium compounds and 3,778 kg (8,322 lb) of nickel and nickel compounds were released from industrial sources within the "River Parishes" along the corridor.

We analyzed windrose data from the years 1987, 1988, 1990, and 1992 recorded at Louis Armstrong International Airport at New Orleans (MSY) to determine the potential for heavy-metal aerosols to reach St. Louis Bay from the industrial corridor. The windrose data show that winds that could potentially transport chromium and nickel aerosols occur only 11.8% of the time from the west through the southwest. Theoretically, only 11.8% of the chromium and nickel had the potential to be transported directly to the bay (15.8 kg = 34.9 lb of Ct; 445.8 kg = 982.0 lb of Ni). At least 75% of those westerly-through-southwesterly winds had velocities of 18.5 km/h (11.5 mi/h) or less; and the average velocity was 15.0 km/h (9.3 mi/h) for the entire period from all quadrants. Given the significant distances over which those aerosols would have to travel to reach St. Louis Bay (80-160 km; 50-100 mi), and the tendency of those aerosols to continually settle out before reaching the bay, we believe those aerosols would have no significant impact on chromium and nickel levels we found in sediments and shellfish in that bay.

Because of the specific source of metals, particularly chromium and nickel, the increase of these in sediments and particularly in shellfish, the association of dioxin with the refinery outfall, and the lack of other reporting large sources of these contaminants in the watershed, we conclude that the most likely source of these elevated contaminants in St. Louis Bay and the adjacent waters of Mississippi Sound is the titanium dioxide refinery on the northern shore of St. Louis Bay.

TABLE 1.
Dioxin toxicity equivalent concentrations for St. Louis Bay,
Mississippi shellfish samples. (1)

                                                              I-TEQ
                                                           (ND = 1/2)
Shellfish                        WHO-TEQ        I-TEQ       [corected
Sample                         (ND = 1/2)    (ND = 1/2)     for lipid
Tract               Percent      [[pg/g]       [[pg/g]       [[pg/g]
Number               Lipid       .sup.2]       .sup.3]       .sup.4]

1                    0.35%        0.581         0.579        165.544
2                    0.55%        0.444         0.838        152.407
3                    0.35%        0.376         0.868        247.866
4                    0.70%        0.381         0.379         54.147
5                    0.66%        0.412         0.413         62.505
6                    0.53%        0.395         0.400         75.474
7A                   0.54%        0.378         0.364         67.429
7B                   0.71%        0.463         0.451         63.568
7C                   0.60%        0.382         0.379         63.118
8                    0.34%        0.348         0.330         96.995
9C                   0.46%        0.335         0.364         79.124
9D                   0.64%        0.337         0.352         55.038
15                   0.58%        0.312         0.294         50.627
16                   0.46%        0.327         0.334         72.654
17                   1.07%        0.405         0.391         36.561
Average all                       0.392         0.449         89.537
  samples:
Average oysters
  only (all
  except #1):                     0.378         0.440         84.108

(1) Toxicity equivalencies (WHO-TEQ and I-TEQ) calculated using World
Health Organization toxic equivalence factors (WHO-TEF, Vanderberg et
al. 1997) and International toxic equivalency factors (I-TEF, USEPA
1989), respectively. All values expressed as pg dioxin equivalent
per g of shellfish tissue, wet weight. Congeners measured are shown
in Table 2.

(2) Values in this column are calculated using values for non-detects
at 1/2 the detection limit (ND =1/2) (USEPA 1989).

(3) Values in this column are given to provide a basis for comparison
with Fiedler et al. (1997) who used I-TEF conversion factors and used
1/2 the limit of quantification for no detect congener values.

(4) Values in this column are adjusted for lipid, assuming that all
dioxins and furans are contained in lipids, and thus represent the
calculated concentration using such an assumption. Thus the values
in the far right column are comparable to the values published by
Fiedler et al. (1997), after adjustment so that only the congeners
measured in each study are included in a comparison.

TABLE 2.
Dioxin compounds and dioxin toxicity equivalent concentrations for
St. Louis Bay, Mississippi sediment samples. (1,2)

Sediment Collection Station Number

Analyte                    1           2            3           4

2378-TCDD                              0.449       0.407
12378-PeCDD                1.22        1.7         1.78        1.74
123478-HxCDD               3.4         5.26        5.41        5.01
123678-HxCDD               6.49        9.67       10.6         9.75
123789-HxCDD              14.7        22.2        23.4        22.9
1234678-HxCDD            245         377         403         362
OCDD                   5,590       7,950       7,910       6,920
2378-TCDF                  0.462       1.2         0.805       0.755
12378-PeCDF                0.313       0.796                   0.398
23478-PeCDF                0.353       0.787       0.582       0.532
123478-HxCDF               1.01        2.27        1.72        1.37
123678-HxCDF               0.989       1.76        1.6         1.36
234678-HxCDF               1.02        1.89        1.75        1.68
123789-HxCDF               0.356                   0.505       0.395
1234678-HpCDF              7.25       15.1        13.5        14.5
1234789-HpCDF                          2.04        1.46        1.31
OCDF                      15.4        40.6        26.7        31.5
Sums (total dioxins
  and furans):         5,888       8,433       8,403       7,375
Average at in bay                                          6,594
  stations (1 to 8):
WHO-TEQ
  (ND = 1/2)               7.25       11.41       11.78       10.66

                            Sediment Collection Station Number

Analyte                     5           6          7       8

2378-TCDD
12378-PeCDD                0.717       0.803       1.31        1.37
123478-HxCDD               1.99        2.32        4.09        4.22
123678-HxCDD               3.63        4.53        8.57        8.2
123789-HxCDD               8.41        9.77       18.4        18.4
1234678-HxCDD            140         179         332         336
OCDD                   3,460       4,120       6,750       7,140
2378-TCDF                  0.301       0.389       0.612       0.657
12378-PeCDF                0.179       0.198       0.348       0.387
23478-PeCDF                0.232       0.249       0.484       0.489
123478-HxCDF               0.432       0.543       1.14        1.13
123678-HxCDF               0.449       0.568       1.23
234678-HxCDF               0.525       0.656       1.51        1.36
123789-HxCDF               0.184
1234678-HpCDF              3.91        5.08       11.4        10.5
1234789-HpCDF              0.441       0.453       1.19        1.08
OCDF                       0.769      10.10       22.3        18.9
Sums (total dioxins
  and furans):         3,622       4,335       7,155       7,543
Average at in bay                               Average at out bay
  stations (1 to 8):                            stations (9 to 13):
WHO-TEQ
  (ND = 1/2)               4.17     5.05           9.11        9.12

                       Sediment Collection Station Number

Analyte                     9           10         11

2378-TCDD
12378-PeCDD                0.286                   1.31
123478-HxCDD               0.691       2.73        3.91
123678-HxCDD               1.39        5.34        6.98
123789-HxCDD               2.99       10.8        13.4
1234678-HxCDD             54.7       214         247
OCDD                   1,220       4,330       4,630
2378-TCDF                  0.152
12378-PeCDF                            0.241       0.3
23478-PeCDF                            0.346       0.493
123478-HxCDF                           0.642       0.79
123678-HxCDF               0.213                   0.777
234678-HxCDF               0.226       0.809       1.06
123789-HxCDF                           0.293
1234678-HpCDF              1.74        0.692       7.22
1234789-HpCDF              0.138       0.623       0.733
OCDF                       3.54       13          11.9
Sums (total dioxins
  and furans):         1,286       4,579       4,926
Average at in bay      Average at out bay      5,864
  stations (1 to 8):   stations (9 to 13):
WHO-TEQ
  (ND = 1/2)               1.62        4.93        7.18

                        Sediment Collection
                          Station Number

Analyte                    12           13

2378-TCDD                   0.564
12378-PeCDD                 2.3         1.83
123478-HxCDD                7.36        5.27
123678-HxCDD               14.2        10.3
123789-HxCDD               29          18.7
1234678-HxCDD             546         384
OCDD                   10,100       7,310
2378-TCDF                   0.937
12378-PeCDF                 0.575       0.473
23478-PeCDF                 0.857       0.728
123478-HxCDF                1.62        1.33
123678-HxCDF                1.67
234678-HxCDF                2.24        1.69
123789-HxCDF                            0.489
1234678-HpCDF              16.8        12.3
1234789-HpCDF               1.79        1.36
OCDF                       31.1        25.5
Sums (total dioxins
  and furans):         10,757       7,774
Average at in bay
  stations (1 to 8):
WHO-TEQ
  (ND = 1/2)               15.33       10.56

(1) Toxicity equivalent factors (WHO-TEQ) calculated using World Health
Organization toxic equivalence factors (TEFs). All values expressed
in pg analyte per gram of sediment dry weight. TEQ values
calculated using 1/2 the detection limit value (ND = I/2) for
non-detect analytes (USEPA 1989).

(2) Blanks in analyte table indicate non-detects or values below
the detection limit.

TABLE 3.
Metals in shellfish in St. Louis Bay, Mississippi and out of
bay locations. (1)

                                      Metal Element Measured in shell-
                                      fish (micro]g/g wet weight) (2)

     Shellfish Collection
     Site Number and Species           Ag       As      Be      Cd

     1978 values for Eastern
       oysters (Crassostrea
       virginica) in
       St. Louis Bay                         0.1222   <0.08    1.61
     1978 values for wedge clams
       (Rangia cuniata) in
       St. Louis Bay                         0.056    <0.08   <0.05
3C   Wedge clams (n = 4)              0.39   0.93     <0.04    0.12
7A   Eastern oysters (n = 12)         0.57   0.63     <0.04    1.12
7A   Wedge clams (n = 5)              2.01   1.22     <0.04    0.10
7B   Eastern oysters (n = 6)          0.53   0.55     <0.04    0.95
7B   Ischadium recurvum
       (hooked mussels) (n = 15)      0.05   0.74     <0.04    0.24
7C   Eastern oysters (n = 3)          0.30   0.30     <0.04    0.62
9B   Eastern oysters (n = 12)         0.58   0.70     <0.04    0.92
15   Eastern oysters (n = 10)         0.71   0.77     <0.04    1.03
15   Hooked mussels (n = 15)          0.05   0.90     <0.04    0.17
16   Eastern oysters (n = 5)          0.87   0.99     <0.04    1.37
     Average in bay Eastern
       oysters, this study            0.47   0.49     <0.04    0.90
     Average in bay wedge clams,
       this study                     1.20   1.08     <0.04    0.11
     Percent value, 2004 compared
       to 1978, Eastern oysters (3)          404%               56%
     Percent value, 2004 compared
       to 1978, wedge clams                  1920%             220%

                                      Metal Element Measured in Shell-
                                      fish (micro]g/g wet weight) (2)

     Shellfish Collection
     Site Number and Species             Cr      Cu       Hg      Ni

     1978 values for Eastern
       oysters (Crassostrea
       virginica) in
       St. Louis Bay                   <0.1     31.5    0.0746   <0.2
     1978 values for wedge clams
       (Rangia cuniata) in
       St. Louis Bay                    NR      2.46    0.107    <0.2
3C   Wedge clams (n = 4)                2.30    3.60    0.04      3.30
7A   Eastern oysters (n = 12)           1.20   37.00    0.01      0.90
7A   Wedge clams (n = 5)                1.00    4.00    0.03      1.60
7B   Eastern oysters (n = 6)            1.70   34.00    0.02      1.40
7B   Ischadium recurvum
       (hooked mussels) (n = 15)        0.50    1.70    0.02      0.60
7C   Eastern oysters (n = 3)            0.60   22.00   <0.01      0.50
9B   Eastern oysters (n = 12)           0.80   33.00   <0.01      0.80
15   Eastern oysters (n = 10)           0.20   28.00   <0.01      0.40
15   Hooked mussels (n = 15)            0.90    1.80    0.02      0.50
16   Eastern oysters (n = 5)            7.70   49.30    0.02      7.30
     Average in bay Eastern
       oysters, this study              1.17   31.00   <0.01      0.93
     Average in bay wedge clams,
       this study                       1.65    3.80    0.12      2.45
     Percent value, 2004 compared
       to 1978, Eastern oysters (3)   >1170%     98%      17%    >467%
     Percent value, 2004 compared
       to 1978, wedge clams                     154%     112%    >1225%

                                      Metal Element Measured in Shell-
                                      fish (micro]g/g wet weight) (2)

     Shellfish Collection
     Site Number and Species            Ph      Sb      Se       Zn

     1978 values for Eastern
       oysters (Crassostrea
       virginica) in
       St. Louis Bay                  <0.5    <0.05   0.248   821
     1978 values for wedge clams
       (Rangia cuniata) in
       St. Louis Bay                  <0.5    <0.05   0.493    16.5
3C   Wedge clams (n = 4)              <0.20   <0.04    0.50     9.90
7A   Eastern oysters (n = 12)         <0.20   <0.04    0.40   543.00
7A   Wedge clams (n = 5)              <0.20   <0.04    1.10     8.50
7B   Eastern oysters (n = 6)          <0.20   <0.04    0.30   549.00
7B   Ischadium recurvum
       (hooked mussels) (n = 15)      <0.20   <0.04    0.60     7.10
7C   Eastern oysters (n = 3)          <0.20   <0.04   <0.40   342.00
9B   Eastern oysters (n = 12)         <0.20   <0.04    0.50   486.00
15   Eastern oysters (n = 10)         <0.20   <0.04    0.60   252.00
15   Hooked mussels (n = 15)          <0.20   <0.04    0.90     7.90
16   Eastern oysters (n = 5)          <0.20   <0.04    0.60   580.00
     Average in bay Eastern
       oysters, this study            <0.20   <0.04    0.37   478.00
     Average in bay wedge clams,
       this study                     <0.20   <0.04    0.80     9.2
     Percent value, 2004 compared
       to 1978, Eastern oysters (3)                    148%      58%
     Percent value, 2004 compared
       to 1978, wedge clams                            162%      56%

(1) Data set 2, as referenced in text, extraction using
EPA Method 3050B.

(2) Values listed as < indicate the detection limit and therefore the
concentration is less than the detection limit.

(3) Change values listed as > indicate that the percent value in 2004
is at least the indicated percentage in comparison to the 1978 values
because the latter were below the indicated detection limits. Blank
values in the comparison rows indicate that both 1978 and 2004 values
were below the limits of detection.

TABLE 4.
Metals in shellfish in St. Louis Bay, Mississippi and out of bay
locations. (1)

                           Metal Measured in Tissue ([micro]g/g wet
                           weight) (2)

                                   Ag                        As

Avg. of 4 in-bay sites
  (7A, 7B, 7C, 8)
  [+ or -] SD (3)          0.31 [+ or -] 0.02        0.34 [+ or -] 0.03
Range of same 4
  in-bay sites                 0.29-0.34                 0.32-0.39
Avg. of 3 sites
  south of bay
  (9, 15, 17)
  [+ or -] SD  (3)         0.31 [+ or -] 0.01        0.44 [+ or -] 0.10
Range of same 3
  sites south of
  bay (4)                      0.21-0.40                 0.34-0.53

                           Metal Measured in Tissue ([micro]g/g wet
                           weight) (2)

                                   Ni                        Pb
Avg. of 6 in-bay
  sites (1, 2, 3,
  5, 7, 8) [+ or -]
  SD (3)                   2.75 [+ or -] 1.96        0.08 [+ or -] 0.02
Range of same 4
  in-bay sites                 0.92-5.28                 0.06-0.10
Avg. of 3 sites
  south of bay
  (9, 11, 13)
  [+ or -] SD (3)          4.43 [+ or -] 2.70        0.05 [+ or -] 0.01
Range of same 3
  sites south of
  bay (4)                      2.67-7.54                 0.04-0.07

                           Metal Measured in Tissue ([micro]g/g wet
                           weight) (2)

                                   Be                        Cd

Avg. of 4 in-bay sites
  (7A, 7B, 7C, 8)
  [+ or -] SD (3)         0.003 [+ or -] 0.001       0.63 [+ or -] 0.08
Range of same 4
  in-bay sites                0.002-0.003                0.54-0.73
Avg. of 3 sites
  south of bay
  (9, 15, 17)
  [+ or -] SD  (3)        0.002 [+ or -] 0.000     0.53 [+ or -] 0.12
Range of same 3
  sites south of
  bay (4)                   0.0014 (U)-0.002             0.46-0.66

                           Metal Measured in Tissue ([micro]g/g wet
                           weight) (2)

                                   Sb                        Se

Avg. of 6 in-bay
  sites (1, 2, 3,
  5, 7, 8) [+ or -]
   SD (3)                 0.005 [+ or -] 0.00        0.21 [+ or -] .01
Range of same 4
  in-bay sites                 0.005 (U)                 0.20-0.22
Avg. of 3 sites
  south of bay
  (9, 11, 13)
  [+ or -] SD (3)         0.005 [+ or -] 0.00       0.32 [+ or -] 0.093
Range of same 3
  sites south of
  bay (4)                      0.005 (U)                 0.23-0.42

                           Metal Measured in Tissue ([micro]g/g wet
                           weight) (2)

                                   Cr                        Cu

Avg. of 4 in-bay sites
  (7A, 7B, 7C, 8)
  [+ or -] SD (3)         4.213 [+ or -] 3.35        20.5 [+ or -] 1.01
Range of same 4
  in-bay sites                 1.15-8.68                 19.5-21.7
Avg. of 3 sites
  south of bay
  (9, 15, 17)
  [+ or -] SD  (3)         6.91 [+ or -] 4.68        17.2 [+ or -] 5.70
Range of same 3
  sites south of
  bay (4)                      3.86-12.30                11.6-23.0

                           Metal Measured in Tissue ([micro]g/g wet
                           weight) (2)

                                   TI                        Zn

Avg. of 6 in-bay
  sites (1, 2, 3,
  5, 7, 8) [+ or -]
   SD (3)                 0.001 [+ or -] .000         461 [+ or -] 68
Range of same 4
  in-bay sites                0.001-0.002                 407-550
Avg. of 3 sites
  south of bay
  (9, 11, 13)
  [+ or -] SD (3)         0.002 [+ or -] 0.001        256 [+ or -] 101
Range of same 3
  sites south of
  bay (4)                     0.001-0.002                 159-361

                           Metal Measured in Tissue ([micro]g/g wet
                           weight) (2)

                                   Hg

Avg. of 4 in-bay sites
  (7A, 7B, 7C, 8)
  [+ or -] SD (3)         0.006 [+ or -] 0.001
Range of same 4
  in-bay sites                0.005-0.007
Avg. of 3 sites
  south of bay
  (9, 15, 17)
  [+ or -] SD  (3)        0.006 [+ or -] 0.002
Range of same 3
  sites south of
  bay (4)                     0.004-0.007

                           Metal Measured in Tissue ([micro]g/g wet
                           weight) (2)

Avg. of 6 in-bay
  sites (1, 2, 3,
  5, 7, 8) [+ or -]
   SD (3)
Range of same 4
  in-bay sites
Avg. of 3 sites
  south of bay
  (9, 11, 13)
  [+ or -] SD (3)
Range of same 3
  sites south of
  bay (4)

(1) Data set 1, as referenced in text, extraction using hydrofluoric
acid method.

(2) Values followed by U indicate that the value is the detection limit
and the value for that indicated site and element is thus below the
detection limit.

(3) Site numbers refer to site locations shown in Figure 3.

(4) For silver, arsenic, cadmium, chromium, nickel, and selenium the
highest values for open harvest areas south of St. Louis Bay, indicated
by the upper range number, were for shellfish collection site 15, as
indicated on Figure 2.

TABLE 5. Comparison of sediment metals in St. Louis Bay 1978 versus
2004. (1)

                            Metal Element Measured in Sediment
                            ([micro]g/g dry weight)

                             As        Be         Cd        Cr
1978 Average Value
  in St. Louis
  Bay (SLB)                 7.05     0.789     <0.087    10.67
2004 Value in SLB
  (Site 2)                  8.55     1.05      <0.50     16.50
Percent value,
  2004 compared
  to 1978 (in bay
  values)                 121%     133%                 155%
2004 Average
  Value outside
  SLB (Sites 12 & 13)       6.1      0.85      <0.5      15

                            Metal Element Measured  in Sediment
                            ([micro]g/g dry weight)

                             Ni       Pb         Sb        Se

1978 Average Value
  in SLB                    9.35    15.4       <0.025    <0.013
2004 Average Value
  in SLB                   11.5     17         <0.5      <1.0
Percent value,
  2004 compared
  to 1978 (in bay
  values)                 123%     111%
2004 Average
  Value outside
  SLB (Sites 12
  & 13)                    13.5     13         <0.5      <1.0

                            Metal Element Measured in Sediment
                            ([micro]g/g dry weight)

                            Cu        Hg

1978 Average Value
  in St. Louis
  Bay (SLB)                10.04     0.107
2004 Value in SLB
  (Site 2)                  9        0.095
Percent value,
  2004 compared
  to 1978 (in bay
  values)                  90%      88.8%
2004 Average
  Value outside
  SLB (Sites 12 & 13)      10        0.090

                            Metal Element Measured in Sediment
                            ([micro]g/g dry weight)

                           Zn

1978 Average Value
  in SLB                   69.35
2004 Average Value
  in SLB                   55.5
Percent value,
  2004 compared
  to 1978 (in bay
  values)                  80%
2004 Average
  Value outside
  SLB (Sites 12
  & 13)                    53

(1) Data set 2, as referenced in text, extraction using EPA Method
3050B.

TABLE 6.
Estimated safe consumption levels of oysters from St. Louis Bay and
near Bay open harvest areas. (1)

                                              Nickel         Nickel
                                             (general      (hypersen-
                              Chromium       popula-      sitive indi-
                               III (2)      tion) (3)     viduals) (3)

Estimated safe and
  adequate daily dietary
  intake (ESADDI):               200           1200            50
                              [micro]g/     [micro]g/      [micro]g/
                              person/day    person/day     person/day

Average concentration
  in oysters from in Bay
  sites ([micro]g/g wet
  weight)                        1.17           0.93           0.93
Specific consumption
  level of concern from
  in Bay sites (g
  oysters per day)             171           1290             54
Number of oysters
  (34 g) consumed daily
  to reach consumption
  level of concern               5.0           38.0            1.6
Maximum concentration
  in oysters from in Bay
  sites ([micro]/g wet
  weight)                        1.7            1.4            1.4
Specific consumption
  level of concern from
  in Bay sites (g
  oysters per day)             118            857             36
Number of oysters
  (34 g) consumed daily
  to reach consumption
  level of concern               3.5           25.2            1.1
Average concentration
  in oysters from near
  Bay sites ([micro]g/g
  wet weight)                    2.9            2.8            2.8
Specific consumption
  level of concern from
  near Bay sites (g
  oysters per day)              69            424             18
Number of oysters
  (34 g) consumed daily
  to reach consumption
  level of concern               2.0           12.5            0.5
Maximum concentration in
  oysters from near Bay
  site ([micro]g/g wet
  weight)                        7.7            7.3            7.3
Specific consumption
  level of concern from
  near Bay sites (g
  oysters per day)              26            164              7
Number of oysters (34 g)
  consumed daily to
  reach consumption
  level of concern               0.8            4.8            0.2

(1) These calculations of estimated safe consumption levels of oysters
are based on the more conservative metals data set 2.

(2, 3) USFDA 1993. Values from guidance documents for chromium and
nickel in shellfish (also PDR 2004, Beers & Berkow, 2004).

ACKNOWLEDGMENTS

The authors thank Mr. Glen Strong for providing and operating the boat used for sample collection and Mr. Joe Jewell and Ms. Traci Floyd of the Mississippi Department of Marine Resources who provided the scientific collection permit used for these studies. The Enforcement Division of the MDMR assisted in ensuring that sample collection trips were logged as required by Mississippi law. Mr. James Humphrey III assisted under supervision in the preparation for sampling and processing of the samples and Mr. Derek Elston assisted under supervision in the collection of samples. Mr. Read Hendon of Gulf Environmental Associates assisted with the GIS area determinations and preparation of Figure 1. Mr. Mark Gruber of Stone Lions Environmental Corporation, Roiling Hills Estates, California 90274 prepared the windroses for Keesler Air Force Base, Biloxi MS, and Louis Armstrong International Airport, New Orleans, LA, used in the analysis. Funding for this study was provided by contract from Baron & Budd, P.C., Dallas, Texas to AquaTechnics Inc., Sequim, Washington and to Gulf Environmental Associates, Ocean Springs, Mississippi.

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RALPH ELSTON, (1) * EDWIN W. CAKE, JR, (2) KAREN HUMPHREY, (1) WAYNE C. ISPHORDING (3) AND J. E. (JACK) RENSEL (4)

(1) AquaTechnics Inc., PO Box 687, Carlsborg, Washington 98324; (2) Gulf Environmental Associates, 2510 Ridgewood Road, Ocean Springs, Mississippi 39564; (3) Department of Earth Sciences, University of South Alabama, Mobile, Alabama 36688; (4) Rensel Associates Aquatic Sciences, 4209 234th Street NE, Arlington, Washington, 98223

* Corresponding author. E-mail: [e-mail]