Environ. Sci. Techno/. 1995, 29, 2504-2512
Differential Bisaccurnulation of Nonlorlho-SuWtuted and Other PCB Comeners in Coastal Arctic Invertebrates and Fish DOUG A. BRIGHT,* S T E P H E N L . GRUNDY, A N D KENNETH J. REIMER Environmental Sciences Group, Royal Roads Military College, FMO Victoria, British Columbia, Canada VOS 1BO
The composition of 47 ortho- and seven non-orthosubstituted PCBs in sediment, water, invertebrates, and fish collected from Cambridge Bay, Northwest Territories, Canada, is presented. The congener composition in sea urchins (Strongylocentrotus droebachiensis) was attributed to differences in the log KO, of individual congeners during uptake from ingested sediment and aqueous solubility during secondary uptake from the water column. Fourhorn and short-horn sculpins exhibited selective bioaccumulation of the recalcitrant congeners: those lacking two non-chlorinated carbons in adjacent meta and para positions on the biphenyl ring. The presence of methyl sulfone PCBs in four-horn sculpin liver provided direct evidence for metabolism. The percent composition of total PCB levels in four-horn sculpin livers, contributed by non-ortho-substituted PCBs 77 and 126 (those with potential for dioxin-like toxicity), was relatively constant regardless of total PCB concentration, suggesting that for a given species increased exposure to PCBs does not lead t o increased relative concentrations of non-ortho-substituted congeners. Limited data on congeners 77 and 126 in sediment, sea urchins, or four-horn sculpins suggests that, with increasing trophic status, these congeners were diminished rather than enriched relative to the total PCB concentration.
Introduction Polychlorinated biphenyls (PCBs) are among a group of chlorinated organic contaminants that are ubiquitous (1, 2 ) . The effect of PCBs on vertebrate and other large predators is undoubtedly related to the tendency of these substances to biomagnify; that is, increase in concentration from lower to higher trophic levels in the food web. A large amount of research (3,4)has focused on the measurement * Author to whom correspondence should be addressed: e-mail address:
[email protected].
2504
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 29, NO. 10, 1995
of PCBs and various other chlorinated pesticides in marine vertebrates in the Canadian Arctic. Many arctic marine mammals contain organochlorines at levels that could result in adverse effects or have negative consequences for humans using these mammals as food (5). There is little published research, however, on organochlorine inputs to sediment,water, and animals near the base of arctic marine food chains or the associated impact. The toxicity of individual PCB congeners is related to the molecular structure. Few of the 209 congeners are considered to exhibit toxicity (61, in spite of public perceptions about the dangers of PCBs. Although PCBs may have adverse effects on animals via severaldifferent biochemical pathways, one of the major molecular mechanisms of PCB toxicity has come to light within the last decade (6, 7). Nonortho-substituted PCBs have a high affinity for the Ah (dioxin)receptor due to their tendency to assume a planar configuration, which is isosteric with 2,3,7,8-tetrachlorodibenzo -p- dioxin. The congener signature of PCBs in mammals is generally a reflection of differential rates of enzyme-mediated hydroxylation and excretion (8). Many animals are capable of enzymatically modifylng congeners that exhibit at least one site where adjacent carbons in the meta and para positions lack chlorine substituents; the net result is the production of dihydroxy or other intermediates that lead to more readily excreted compounds. Metabolism of congeners with adjacent unsubstituted ortho, meta positions has also been demonstrated for some marine mammals (8). There are other theories on the observed differential bioaccumulation of PCB congeners. The partitioning of organic contaminants between water and an aquatic organism tends to be higher for more hydrophobic, more lipophilic compounds (for example, as estimated by the octanol-water partitioning coefficient, IC,) (9). In the case of PCBs, the log IC,, increases with degree of chlorination (IO)from 4.09 for biphenyl to 8.18 for decachlorobiphenyl. Shaw and Connell(11) noted that the bioaccumulation of PCBs by mullet and polychaetes was related to both log KO, and stereochemistry (especially planarity) of individual congeners. If stereochemistry influences the differential adsorption and bioaccumulation of PCBs in marine animals, then this raises the possibility that the concentrations of non-ortho-substituted congeners,with dioxin-liketoxicity, could increase or decrease relative to other congeners during food chain-mediated uptake and transfer. The impact on an organism is undoubtedly related to the congener composition and concentration of the original PCB contaminant source as well as to changes in congener composition during food chain transfer. Parkinson and Safe (12) provide a review of studies in which the PCB congener composition found in human breast milk was 5-10 times more potent an inducer of cellular responses for a given total congener concentration than the industrial PCB mixture. This resulted from the enrichment of monoand di-ortho-substitutedcongeners capable of eliciting toxic responses via induction of the cytosolic Ah receptor. Recent work has focused on the molecular mechanisms of PCB toxicity and PCB bioaccumulation in large marine mammals in the Arctic (4, 13,14). There are still, however,
0013-936X/95/0929-2504$09.00/0
0 1995 American Chemical Societv
large gaps in our understanding of critical pathways of contaminant transfer from sediment or water into lower trophic level organisms and, subsequently, to higher order consumers. This study employs data from Cambridge Bay, Northwest Territories, Canada, to examine the PCB congener composition associatedwith uptake and metabolism in marine animals near the base of the food chain in coastal Arctic waters. There are local sources of PCB input into Cambridge Bay (15); in particular, runoff from areas contaminated with an Aroclor 1254 technical mixture near the DEW Line site and the hamlet dump. The congener composition of the source is known and serves as a baseline for examining food chain-mediated changes. The mechanisms associated with changes in congener composition following local inputs are also applicable to inputs associated with long-range transport events where the congener composition of the inputs has not been clearly elucidated. In addition, data on non-ortho-substituted PCBs (especially congeners 77 and 126)are used here to provide an indication of possible changes in the toxicity of PCB mixtures as they are assimilated by Arctic marine predators.
Experimental Section Sampling. Environmental samples, comprising sediment, water, and bottom-dwelling fish and invertebrates, were collected from Cambridge Bay and Queen Maud Gulf in August 1991 and 1992 (15)as well as in August 1993 (17). Cambridge Bay is located at latitude 69’07” and longitude 105O 07’W. The embayment occupies an area of approximately 15 km2 and is the site of a hamlet of 1100 residents as well as a militaryradar site operated from 1957 to the present time. Samples from Queen Maud Gulf, to the south of Cambridge Bay, and Wellington Bay, to the west of Cambridge Bay, were collected as reference samples. There is no evidence of the direct input of anthropogenic materials in these areas. Sediment samples were collected from 65 sites in or near Cambridge Bay over the three years, either directly into a contaminant-free amber I-CHEM jar by scuba divers or using a stainless steel sediment grab deployed from a surface vessel. Fish were either hand-collected by scuba divers or by using a gdl net. Invertebrate species collected and analyzed for PCBs included amphipods (Orchomene sp.) (collected using baited amphipod traps), bivalves (Arctica islandica, Mya truncata, and Mytilus edulis), and sea urchins (Strongylocentrotus droebachiensis). Fish samples included four-horn sculpins (Myoxocephalusquadricornis), short-horn sculpins (Myoxocephalus Scorpius), Greenland cod (Gadusogac), and Arctic char (Salvelinus alpinus). All invertebrate samples were pooled for each site to make up a wet tissue mass of approximately 10-25 g. Two to four individuals of each species of sculpin from each collection site were pooled to make up a sample of total wet tissue mass of 15-50 g. Livers were dissected and pooled separately. Greenland cod and Arctic char were analyzed as individual fish (whole tissue minus livers or excised liver tissue). All samples were wrapped in baked aluminum foil, immediatelyfrozen, and shipped to Victoria, British Columbia, for analysis. Analytical. Biota samples and sediment samples collected in 1991-1992 were analyzed for 47 individual or co-eluting ortho-substituted PCB congeners using gas chromatography (GC) coupled with electron capture detection (ECD) (modified EPA Method 608/8080)or mass
spectrometry (MS). Congeners quantified include (according to their order of elution) IUPAC Numbers 18,151 17,54,31,28,52,49,44,40/103,61/94/74, 121,56/60,90/ 101,86/97,87,77/154/110,151,135/144,149,118,143,114, 132/153,105,141/179,137,138/158,129/126,187/182/159, 183,128,185,174/181,202/171/156,173/201,180,181,170, 199, 2031196, 189, 208/195,207, 194, 205, and 206. The concentration of co-eluting congeners complexes was generally assigned to the congener dominant in Aroclor 1254 (18). Sediment samples collected in 1993 were analyzed for the PCBs as Aroclors (Aroclor 1242,1254,and 1260)and the aforementioned 47 ortho-substituted congeners by gas chromatography/high-resolutionmass spectrometry (GCI HRMS). Details of the extraction and instrumental analysis of sediment and biota samples for PCBs, as Aroclors and individual congeners, were provided previously (15, 16). Sample extracts (combined F1 and F2 fractions) were also analyzed for non-ortho-substituted PCBs in a subset of samples. An aliquot of surrogate standard 13C-labeled PCB 77,80,126, and 169 was added to the extract prior to additional cleanup. The combined fractionwas loaded onto a prepared carbon/celite column and eluted with hexane, 1:1 hexane:dichloromethane, and then ethyl acetate (all of which were discarded). The coplanar PCBs were eluted with 1:1 toluene:ethylacetate, reduced to dryness, and redissolved in hexane. The extract was cleaned up further on an alumina column eluted with hexane followed by 1:1 hexane:dichloromethane,concentrated, and transferred to a microvial. l3C-Labe1ed PCB 153 was added as a recovery standard, and the extract was analyzed by GC/HRMS. Chromatographic separation was carried out on a 30 m long, 0.25 mm i.d. Restekx-5column (with a 0.25 pm film thickness). A Finnigan Incos 50 MS was operated in the E1 mode (70eV) using multiple ion detection (MID)to enhance sensitivity,acquiring two characteristicions for each target analyte and surrogate standard. Additional cleanup on some samples was required to remove interferences during analysis of non-ortho-PCBs. This involved elution through a carbonlglass fiber column. Quantitative data were achieved for non-ortho-congeners 77,80, 126,and 169. Data for congeners 79,78, and 81, without 13C-labeledsurrogate standards, were obtained by applying similar response factors to those for congeners with surrogate standards (above). There is a small possibility that other substances in the samples may have coeluted with congeners 79,78,and 81,which could lead to errors in quantification. Additional cleanup on a carbon/ glass fiber column might not have removed co-eluting substances if they also exhibited a planar stereochemistry. The data for these congeners, therefore, have been interpreted semiquantitatively; we examined primarily the presence or absence of these congeners invarious samples. Methyl sulfone PCBs, products of metabolism, were examined in four composite liver samples from four-horn sculpins according to the methods of Bergman et al. (19). Briefly, tissue samples were spiked with surrogate standard 3-methylsulfonyl-4-methyl-5,2’,3’,4’,5’-pentachlorobiphenyl, ground with anydrous sodium sulfate,and extracted by elution with dichloromethane:hexe. The extract was subjected to a series of cleanup steps prior to analysis by high-resolution gas chromatography on a 60 m (0.25mm i.d., O.lpm6lmthickness) DB-5 columnwithlow-resolution (quadrupole) mass spectrometric detection operated in electron capture negative chemical ionization mode. VOL. 29, NO. 10, 1995 /ENVIRONMENTAL SCIENCE &TECHNOLOGY
B
2505
d
to 0-
Mavd GUN
FIGURE 1. Distribution of PCBs in the sutficial sediment (approximately 0-5 cm depth) of Cambridge Bay. NWI, in 1993: concentration contours. in nglg, or ppb dry weight.
Quality control for ortho-substituted PCBs included the monitoring of accuracy through analysis of NRC reference sediments HS-1 and HS-2, internal laboratory sediment standards certified for Aroclor 1254, and NIST. Cod liver oil (1588) certified for PCB congeners 101, 138, 153, 170, and 180. AU sediment and tissue blanks were below the limits ofdetection for all analytes. The ranges of detection limits for individual ortho-substituted congeners in sediment and tissuesampleswereasfollows: sediment,
