Oysters as Biomonitors of Oil in the Ocean
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ABSTRACTOysters collected from 70 Gulf of Mexico sites, removed from known point source inputs, contained low concentrations of toxic polynuclear aromatic hydrocarbons (PAH). The PAH concentration remained relatively constant at most sites over 5 years of sampling. Other sites apparently experienced inputs from episodic events such as small oil discharges.INTRODUCTIONAs part of the National Oceanic and Atmospheric Administration, National Status and Trends (NS&T) Mussel Watch Program, oyster samples have been collected from approximately 70 Gulf of Mexico sites in the winters of 1985 through 1989. The sampling sites represent all major Gulf Coast estuaries. Sampling sites are located in areas not influenced by any known point source inputs of oil. Twenty oysters were collected at three stations at each site and analyzed for polynuclear aromatic hydrocarbons (PAH) and other environmental contaminants (1,2) Oysters have been employed as sentinel organisms because they are cosmopolitan, sedentary, bioaccumulate, able to provide an assessment of bioavailability, not readily capable of metabolizing PAH, able to survive pollution loading, readily found as locally stable populations, transplantable, and commercially valuable. Oysters are, therefore, excellent biomonitors for hydrocarbon contamination in estuarine areas. The geographical distribution of PAH as well as trends in PAH concentrations are discussed.MATERIALS AND METHODSThe collection and analytical methods for NS&T samples have been detailed elsewhere (1), and only a brief overview will be given here. Oysters (20) were collected (three stations at each site) and analyzed after homogenization. Sample locations and designations are given elsewhere (3). The accuracy and precision of the PAH analyses have been established by several intercalibration exercises overseen by the National Institute of Standards and Testing (NIST). The oysters are extracted with methylene chloride after drying with Na2S04. The samples are then purified by column and high-performance liquid chromatography. PAR are analyzed by gas chromatography/mass spectrometry in the selected ion mode (GC/MS/SIM). All concentrations are reported as ng of analyte per gram dry weight of sample or ppb. Concentrations in the procedural blanks were, in all cases, below reporting levels for each individual analyte. The PAH analyzed are listed in Table 1. mean of Year 4 are shown. The smaller bars represent plus one standard deviation derived from the three stations from each site. Concentrations range from the method detection limit (20 ng/g) to over 7000 ng/g. Between 1986 and 1988 the highest total PAH concentrations were found in oyster samples from Laguna Madre (LMPI), Corpus Christi (CCNB, CCIC, and CCBH), Aransas(ABHI), Copano(CBCR), and Galveston (GBOB and GBSC) Bays in Texas; Barataria Bay (BBMB) and near the Mississippi River mouth (MRTP) in Louisiana; and Pensacola (PBPH), Choctawhatchee (CBSR), St. Andrew (SAWB), Apalachicola (APDB and APCB) and Roockery (RBHC) Bays in Florida. Significant changes in total PAH concentrations were observed at several sites during the fourth year sampling. For example, changes of one to two orders of magnitude were detected in samples from Barataria (BBSD) and Pensacola (PBPH) Bays. One way to summarize a large data set such as this one for NS&T PAH data is to use a frequency distribution.
