FISHERY BULLETIN: VOL. 84, NO. 1 



a wide range of this species' occurrence in the north- 

 western Atlantic and includes information on or- 

 ganic, La, polychlorinated biphenyls (PCB), polynu- 

 clear aromatic hydrocarbons (PAH) from combustion 

 and petroleum sources, and bulk levels of the petro- 

 leum hydrocarbon (PHC) class, and seven trace metal 

 contaminants. The study includes the first known 

 set of PCB data for this species. 



MATERIALS AND METHODS 



Ocean quahog samples were obtained at random 

 stations from wide areas on the continental shelf of 

 the northwestern Atlantic (Fig. 1). These were col- 

 lected from annual, summer hydraulic dredge shell- 

 fish surveys of NOAA's Northeast Fisheries Center 

 from 1981 and 1982. At most stations, 10-12 

 medium-sized clams were selected, as available Half 

 of the collection was prepared for organic analysis 

 by wrapping them in aluminum foil that had been 

 prewashed with spectral grade acetone followed by 

 dichloromethane; the remaining half for trace metals 

 were placed in polyethylene plastic bags. All were 

 quickly frozen at -20°C. In certain areas where 

 there were not sufficient samples at a particular sta- 

 tion to provide material for both organics and trace 

 metal analyses, samples were collected at a nearby 

 station, with similar environmental characteristics, 

 to complete the collection for the area. These paired 

 station samples were not intermixed. 



Chemical Analysis - Organics 



In the laboratory, the thawed whole meats of each 

 of the five or six individual clams in each station sam- 

 ple were removed from the shells, pooled, and homo- 

 genized in a high-speed blender. A 100 g (wet weight) 

 aliquot was removed from the homogenate and pro- 

 cessed according to the extraction, fractionation, and 

 analytical methodology described by Warner (1976), 

 as modified by Boehm et al. (1982). After aqueous 

 caustic (0.5N KOH) digestion of the tissue for 12 h, 

 the digestate was back-extracted three times with 

 hexane The hexane extract was concentrated by ro- 

 tary evaporation, then fractionated on a 5% deacti- 

 vated alumina/activated silica gel column. The first 

 eluting fraction from the alumina/silica column (fj) 

 contained the saturated PHC; the second fraction 

 (f 2 ) contained the PCB and PAH. Quantitation pro- 

 cedures closely followed those by Boehm (1983b). 

 PHC factors were quantified using the internal 

 standard method whereby all peaks are quantified 

 relative to androstane in the fj fraction and 0-ter- 

 phenyl in the f 2 fraction. 



PCBs were quantified relative to the internal 

 standard tetrazene (2, 3, 5, 6 tetrachloronitroben- 

 zene). The average relative response factors of two 

 or three isomers in each of the di-, tri-, tetra-, penta-, 

 hexa-, hepta- and octachlorobiphenyls groups were 

 applied to the sum of the peaks in each grouping. 

 Thus, PCBs were quantified by isomer group rather 

 than according to the Aroclor 4 -type quantification 

 (Duinker et al. 1980, 1983; Boehm 1983b). PHCs 

 were determined by the total of f : and f 2 fractions, 

 as analyzed by high resolution (fused silica capillary) 

 gas chromatography with flame ionization detection 

 (GC 2 /FID). A Hewlett Packard model 5840A gas 

 chromatograph was used for all GC 2 deter- 

 minations. A 30 m fused silica SE-30 (0.25 mm i.d.; 

 J and W Scientific) column was used to analyze the 

 saturated hydrocarbon (f t ) fraction. A 30 m SE-52 

 fused silica column was used to analyze the aroma- 

 tic/olefinic (f 2 ) fraction by GC 2 /FID and the same 

 fraction by gas chromatograph/mass spectrometer 

 (GC/MS) (see below). The f 2 fractions were analyzed 

 by GC 2 /ECD (electron capture detection) to obtain 

 the PCB concentrations. PCBs were analyzed on a 

 30 m SE-52 fused silica column. The f 2 fraction was 

 also analyzed by a Finnegan MAT model 4530 

 computer-assisted GC/MS system for PAH deter- 

 minations. GC/MS conditions were as follows: ioniza- 

 tion voltage, 70 ev; electron multiplier voltage 2,000 

 volts; scan conditions 45-450 amu at 400 amu/s. 



Chemical Analysis - Trace Metals 



Whole clams, 5 or 6 per station, were thawed, and 

 the whole body removed from the shells. Each indivi- 

 dual clam was weighed in Pyrex beakers and dried 

 for 16-20 h at 105°C. Twenty mL of 70% trace metal 

 grade nitric acid were added to each beaker, which 

 was covered with a Pyrex watch glass and heated 

 (70° -75°C) on a ceramic hot plate until dry. After 

 cooling to room temperature, another 20 mL of con- 

 centrated nitric acid were added and the dissolution 

 continued. After 3 or 4 repeated acid additions and 

 evaporations, 10 mL of 30% hydrogen peroxide were 

 added, the solutions evaporated to near dryness and 

 removed from the heat. When cooled, samples were 

 filtered through Whatman #4 filter paper and 

 brought to a final volume of 25 mL in a Pyrex glass- 

 stoppered graduated cylinder by adding 5% (w/v) ni- 

 tric acid. Analysis was performed on a Perkin Elmer 

 model 5000 atomic absorption (AA) spectrophotom- 

 eter employing an air-acetylene flame and conven- 



4 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



134 



