Intraorgan Distribution of Chemical Contaminants In Tissues of Harbor Porpoises (Phocoena phocoena) From the Northwest Atlantic
John E. Stein, Karen L. Tilbury, Donald W. Brown, Catherine A. Wigren, James P. Meador, Paul A. Robisch, Sin-Lam Chan and Usha VaranasiNational Marine Fisheries Service
Northwest Fisheries Science Center
Environmental Conservation Division
2725 Montlake Blvd. E.
Seattle WA 98112
U.S. DEPARTMENT OF COMMERCE
Barbara Hackman Franklin, Secretary
National Oceanic and Atmospheric Administration
National Marine Fisheries Service
The National Marine Fisheries Service through its National Marine Mammal Tissue Bank and Stranding Network Program is developing baseline data on the concentrations of chemical contaminants in marine mammals that are endangered or that could be used as sentinel species in monitoring studies. The Program is also archiving marine mammal tissues to be used for retrospective analyses of chemical contaminants as improved analytical methodologies are developed.
The possible heterogeneous partitioning of chemical contaminants within tissues of marine mammals, however, is a factor affecting whether a tissue sample is representative of the entire organ. This potential partitioning is of particular concern in marine mammals where the analytical sample is quite often a very small proportion of the whole organ. Accordingly, blubber and liver samples were taken from different anatomical locations in these organs of three apparently healthy harbor porpoises (Phocoena phocoena) caught in a gill-net fishery in the northwest Atlantic. Concentrations of chlorinated hydrocarbons (CHs), such as polychlorinated biphenyls (PCBs), DDTs, and chlordanes, were measured in the blubber (n = 7) and liver (n = 5) samples, and selected toxic elements (e.g., mercury, lead, cadmium) were also measured in the liver. Additionally, individual samples were taken from brain, lung, kidney, and gonad to assess the disposition of toxic chemicals within harbor porpoise.
Based on the analysis of a total of 21 blubber and 15 liver samples, the mean concentrations of PCBs ranged from 13,000 to 33,000 and 390 to 1,200, ng/g (ppb) wet weight tissue, respectively. Further, the concentrations of DDE in blubber and mercury in liver ranged from 3,900 to 5,600 and 610 to 2,500 ng/g, respectively. The PCB concentrations in blubber were comparable to concentrations in harbor porpoise from the west coast of the United States, whereas the concentrations of DDE in blubber and mercury in liver were considerably lower in the present study than the DDE concentrations in harbor porpoise from the west coast of the United States or of mercury in porpoise from the British Isles.
Statistical analyses of the results showed that the anatomical location of the blubber or liver sample had no statistically significant effect on concentrations of either CHs in blubber and liver or of toxic elements in liver. However, the concentrations of CHs and level of total lipids in blubber from a lateral site slightly anterior to the peduncle were consistently less than those in most of the other subsamples. Thus, these results show that sampling blubber and liver from different anatomical locations contributes little to the variation in tissue concentrations of CHs and toxic elements among individual harbor porpoise. Nevertheless, the designation of a specific site for sampling tissues of marine mammals for archival in a tissue bank is recommended, because of potential differences among species in the distribution of contaminants and the potential of analyses, in the future, for compounds for which there may be substantial differences in distribution within an organ.
In addition to determining if tissue concentrations of CHs and toxic elements were dependent on the anatomical location of the sample, the analyses of CHs in the brain, gonad, kidney, and lung of one porpoise provided an initial assessment of the distribution of CHs among harbor porpoise tissues. The results showed that the CH concentrations, based on wet weight, were considerably higher in the blubber than in the other tissues; however, the concentrations of CHs in the different tissues were comparable when values were based on total lipid weight. An exception was the brain where lipid normalized concentrations were lower than in all other tissues. The low relative accumulation of lipophilic contaminants in the brain tissue may be due to a lower proportion of neutral lipids in brain. Previous studies suggest that the level of total lipid, and specifically neutral lipid, in a tissue is an important factor influencing the uptake of lipophilic CHs, such as PCBs. Accordingly, in addition to measuring the total content of lipids in a tissue, the composition of lipids should be determined to provide proper assessment of the distribution of lipophilic contaminants among tissues.
The recent strandings of marine mammals and the decline in populations of some species has heightened the concern that environmental pollution may have a role in these events and has pointed to the need for high quality samples from marine mammals for assessing the role, if any, of environmental contaminants. In response to this need, the National Marine Fisheries Service (NMFS), in 1989, initiated the development of the National Marine Mammal Tissue Bank (NMMTB) at the National Biomonitoring Specimen Bank located in the National Institute of Standards and Technology (NIST). The NMMTB archives selected marine mammal tissues that have been collected and processed using rigorous well-documented protocols. These tissue samples are stored under the best conditions currently available (-150° C) for maintaining sample integrity. As part of the NMMTB, the NIST and the Environmental Conservation (EC) Division are cooperating in the development and application of quality assurance procedures and materials for chemical analysis of marine mammal samples. Additionally in 1989, enhanced support for the Marine Mammal Stranding Network (MMSN) began. The stranding network has a primary role in the collection of tissues for anthropogenic contaminant analyses and for the NMMTB, but it was also recognized that additional biological data should be collected to enhance the monitoring of the health of marine mammal populations and their relationships to chemical contaminant exposure.
In 1991, the NMFS combined the NMMTB and the MMSN into a single broader program, now known as the National Marine Mammal Tissue Bank and Stranding Network Program (NMMTB&SN Program), which includes a contaminant monitoring component presently conducted by the EC Division of the Northwest Fisheries Science Center, NMFS. The monitoring component includes real-time analyses to determine concentrations (based on current methods) of environmental contaminants and biotoxins in marine mammals, as well as research on ways to enhance methods and procedures used by the program.
This report presents the results of a study to assist in developing a protocol for the NMMTB&SN for sampling marine mammal tissues for the measurement of chemical contaminant concentrations. Specifically, the present study determined if there is heterogeneity in the distribution of persistent chemical contaminants, such as chlorinated hydrocarbons (e.g., polychlorinated biphenyls) and certain toxic elements (e.g., mercury), in tissues of harbor porpoise (Phocoena phocoena). Any significant heterogeneity in the distribution of chemicals is of particular concern in marine mammals where the tissue sample for chemical analysis is often a very small proportion of the entire organ.
To address the public and scientific concern that chemical contaminants may be affecting the health of marine mammals, the National Marine Fisheries Service (NMFS), through its National Marine Mammal Tissue Bank and Stranding Network (NMMTB&SN) Program, is developing baseline data (primarily by the NMFS laboratory in Seattle) on the concentrations of chemical contaminants in marine mammals that are endangered or that could be used as sentinel species in monitoring studies. Additionally, the NMMTB&SN is archiving (conducted by the National Institute of Standards and Technology) marine mammal tissues to be used for retrospective analyses of chemical contaminants as improved analytical methodologies are developed. The availability of baseline data and high quality archived samples will greatly aid in documenting and refining information on long-term trends in chemical contaminants presently of concern and those that may emerge as potential toxicopathic agents.
The possible heterogeneous partitioning of chemical contaminants within tissues of marine mammals, however, is a factor that could affect whether a tissue sample that is collected is representative of the entire organ. This is of particular concern for marine mammals where the sample of tissue for detailed chemical analysis quite often represents a very small proportion of the mass of the whole organ. Thus, information on the distribution of chemical contaminants within tissues sampled as part of marine mammal monitoring programs is needed in designing sampling protocols for the NMMTB&SN Program.
Currently, there are limited data available on the anatomical distribution of chemical contaminants, such as chlorinated hydrocarbons (CHs), within tissues of marine mammals. Aguilar (1985) in his review of sampling procedures for surveys of concentrations of CHs in cetaceans discussed the distribution of CHs among different types of tissues as well as potential limitations of using blubber as a representative tissue in assessing CH exposure in cetaceans. Aquilar (1985) suggested that because of differences in compositions of lipids in blubber and mobilization of lipids in starved animals, blubber may not be a homogeneous tissue, and therefore, there may be significant differences in contaminant concentrations in areas of the blubber, both with respect to location on the body where it is sampled and whether the entire thickness of blubber is sampled. In contrast to the data reported by Aguilar, Calambokidis (1986) reported that the concentrations of CHs in blubber (all strata) sampled from different anatomical locations on two harbor porpoises (Phocoena phocoena) from the west coast of the United States were very similar. Further, there are very limited data available for other tissues that are commonly sampled, such as liver, or for tissue concentrations of elements (e.g. mercury) of toxicological concern.
Accordingly, in the present study the profiles and concentrations of CHs (Table 1) in both blubber and liver, and of selected toxic elements in liver from three apparently healthy harbor porpoises incidentally caught in gill nets were determined to improve our understanding of potential intratissue differences in accumulation of these chemicals by marine mammals. Such information will aid in refining sampling procedures for the NMMTB&SN Program. Additionally, the concentrations of CHs and toxic elements were determined in kidney, brain, lung, and testis of one porpoise to make a preliminary assessment of the distribution of toxic chemical contaminants among harbor porpoise tissues. The availability of information on the distribution of contaminants in various tissues of apparently healthy animals will aid in interpreting data from stranded animals.
Multiple samples of blubber (all strata of blubber, from skin to muscle) (Fig. 1) and liver (Fig. 2 and 3) were taken from a harbor porpoise (MH-91-424) that was caught in a gill net off Boston Harbor, Massachusetts, and from two harbor porpoises (MH-91-504, MH-91-506) that were caught in gill nets off Boothbay Harbor, Maine. The Boston Harbor animal was a yearling female (MH 91-424; length, 120.0 cm) and the Boothbay Harbor porpoises were both males; one yearling (MH-91-504; length, 120.0 cm) and one approximately 4 years old (MH-91-506; length, 136.5 cm). Additionally, kidney, gonad, lung, and one-half of the brain were collected from all three animals. A biologist from Northwest Fisheries Science Center's Environmental Conservation (EC) Division and personnel from the National Institute of Standards and Technology and the New England Aquarium conducted the necropsies of the animals. The frozen samples were shipped on dry ice to our laboratories in Seattle, Washington. Samples of blubber and liver from each animal were also archived for the NMMTB at the National Institute of Standards and Technology.
The subsamples of blubber from the three harbor porpoises were analyzed for CHs (Table 1), percent lipid, and percent dry weight, and the subsamples of liver were analyzed for CHs, percent lipid, percent dry weight, and selected toxic elements (arsenic, cadmium, copper, lead, selenium, mercury). Additionally, samples of kidney, brain, gonad, and lung from animal MH-91-506 were analyzed for CHs, percent lipid, percent dry weight, and toxic elements.
Toxic Element Determinations
The concentrations of toxic elements were determined using analytical methodologies and quality control procedures used in the National Benthic Surveillance Project of NOAA's National Status and Trends Program. Briefly, thawed tissue (1.0 to 1.8 g) was digested with 10 mL of concentrated ultrapure nitric acid for 2 hours at room temperature in a sealed Teflon bomb. The bomb was then heated in a microwave oven at 650 watts for 6 minutes. The digestate was further treated to destroy organic matter by digestion with 4 mL hydrogen peroxide and again heated in the microwave oven. The digestates were diluted with deionized water to a final volume of 25 mL. Concentrations of elements were determined by atomic absorption spectrophotometry using the following techniques: 1) cold vapor hydride generation was used for determining mercury; 2) graphite furnace was used for copper; and 3) Zeeman-corrected graphite furnace was used for arsenic, selenium, cadmium, and lead.
Chlorinated Hydrocarbon Determinations
The concentrations of CHs (Table 1) were determined by modifying the National Benthic Surveillance Project method to account for the lipid-rich blubber tissue of marine mammals. Briefly, samples of thawed tissue were extracted using modified procedures of Krahn et al. (1988). Tissue (1 g) was macerated with sodium sulfate and methylene chloride. The methylene chloride extract was filtered through a column of silica gel and alumina, and the extract concentrated for further cleanup. Size exclusion chromatography with high performance liquid chromatography (HPLC) (flow rate of 5 mL/min vs. 7 mL/min in the original method) was used and a fraction containing the CHs was collected. The HPLC fraction was exchanged into hexane and the extracts were analyzed for CHs by capillary column gas chromatography (GC) equipped with an electron capture detector. Identification of individual CHs was confirmed using GC-mass spectrophotometry (MS).
To determine extractable lipids, an aliquot of the initial methylene chloride extract of tissue was filtered through filter paper with diatomaceous earth as a filtering aid and the solvent was removed from each sample using a rotary evaporator. After the solvent was evaporated, the flask was weighed and the weight of lipid determined. The percent lipid was determined by dividing the weight of lipid by the original sample wet weight and multiplying by 100. Evaluation of this method using sea lion blubber (n = 5) and liver (n = 5) samples showed that this procedure gave results for total lipids comparable to those obtained using the method of Hanson and Olley (1963), a modification of the Bligh and Dyer method. The percent total lipids in blubber determined by our method and the Hanson and Olley method were 84 ± 0.7% and 80 ± 2.2%, respectively, and for liver were 2.7 ± 0.1% and 2.2 ± 0.2%, respectively.
Quality control procedures included the use of standard reference materials (SRMs) and certified reference materials (CRMs). The reference material SRM 1974 (mussel (Mytilus edulis) tissue), analyzed for CHs, and CRM 1566a (oyster tissue), used for toxic elements, were from the National Institute of Standards and Technology. The reference materials for toxic elements also included the National Research Council of Canada's DOLT-1 (dogfish liver), DORM-1 (dogfish muscle), LUTS-1 (nondefatted lobster hepatopancreas), and TORT-1 (lobster hepatopancreas). The quality control procedures for CHs and toxic elements also included analyses of method blanks, solvent blanks, certified calibration standards, and replicate samples. Replicate analyses (n = 2) for CHs in samples of porpoise liver and blubber agreed within ± 15% (Tables 2 and 3) and the analyses of replicates for toxic elements agreed within ± 16%. Further, as an indication of the accuracy of the analytical method, the grand mean recovery (110 ± 2%) of selected CH analytes in SRM 1974 was calculated from the mean recoveries for selected CH analytes by calculating the ratio of the concentrations of analytes from this series (n = 4) to those of previous analyses (n = 19). The mean recovery of the toxic elements in the CRMs was 99 ± 25%.
Samples of blubber were taken from seven different anatomical locations on the body (Fig. 1) and from five different sites in the liver (Fig. 3) of the three harbor porpoises to assess the effect of anatomical location of the sample on the distribution of chemical contaminants. The data on chemical concentrations (based on wet weight and lipid weight) were analyzed by two-way analysis of variance (ANOVA), with tissue sampling location within the animal and the animal itself as the factors. This approach has the advantage of taking into account variability among animals in the concentration of chemicals in a tissue, but at the same time allows determination of whether there are intraorgan differences in the concentrations. Further, the data were log transformed (log (x + 1)) to reduce deviations from normality. The results of the statistical analyses were very similar whether concentrations were expressed on a wet weight or dry weight basis, thus only the results for the analyses using concentrations based on wet weight are discussed. The significance level was set at P < 0.05.
The data on concentrations (ng/g wet weight) of CHs (the sum of PCBs, DDTs, DDEs and DDDs which are metabolites of DDTs, and _other CHs), percent lipid and percent dry weight in samples of blubber and liver from each of the three porpoises are presented in Tables 2 and 3. The concentrations (ng/g wet weight) of arsenic, cadmium, copper, lead, selenium, and mercury in liver samples are presented in Table 4. Detailed results on concentrations of individual DDTs, DDEs, DDDs, other CHs, selected polychlorinated biphenyls (PCB) congeners, and PCBs by homolog class (tri- to nonachlorobiphenyls) are given in Appendix A (Tables A1-A14). The detailed quality control results for analyses of CHs and of toxic elements are presented in Appendix B (Tables B1-B4 and B5, respectively).
The results of the statistical analyses (Tables 5-7) showed that the concentrations of the selected CHs in blubber and liver were significantly different among the three porpoises (P < 0.001). For example, concentrations (mean ± standard error (SE)) of the sum of PCBs in subsamples (n = 7) of blubber of each of the animals were 33,000 ± 1,100, 22,000 ± 1,600, and 13,000 ± 770 ng/g wet weight (Table 2), and in liver were 1,200 ± 68, 620 ± 4, and 390 ± 14 ng/g wet weight (Table 3). Additionally, the concentrations of toxic elements in subsamples of liver were significantly different among the three porpoises (P < 0.004), except for the concentrations of lead (Table 4), which were not significantly different (P = 0.06). The lack of significant differences for lead would appear to be related to the low (< 5 ng/g) concentrations measured and thus greater variation in concentrations among the subsamples of liver from each porpoise.
The comparison of concentrations of CHs and toxic elements in tissues of harbor porpoise in the present study to results from other studies must be made with caution because of differences in methodology and lack of availability of quality control data in some studies. With this in mind, the concentrations of the sum of PCB and hexachlorobenzene (HCB) (23,000 ± 5,900 and 520 ± 180 ng/g wet weight, respectively) in blubber of the three porpoises in the present study appear to be comparable to the concentrations (14,000 ± 1,900 and 510 ± 60 ng/g wet weight, respectively) reported for harbor porpoises from the west coast of the United States (Calambokidis and Barlow 1991). However, the concentrations (31,000 ± 4,500 ng/g wet weight) of the sum of DDE in harbor porpoise from the west coast were six times greater than the concentrations (4,800 ± 500 ng/g wet weight) in porpoises from the northwest Atlantic. For the toxic elements, the concentrations of cadmium and copper in livers of harbor porpoise from the British Isles were 200 ± 60 and 24,000 ± 8,900 ng/g wet weight, respectively (Law et al. 1991) and were comparable to concentrations (150 ± 80 and 11,000 ± 3,600 ng/g wet weight, respectively) for these elements in porpoises in the present study, whereas the concentrations (14,000 ± 7,400 ng/g wet weight) of mercury in porpoise from the British Isles were 10 times as great as the concentrations (1,400 ± 570 ng/g wet weight) reported here. The data on the toxic elements can be compared with greater confidence because the same CRMs were used in both studies and the results of analysis of the CRMs confirmed the accuracy of the methods used.
Chlorinated Hydrocarbon Concentrations
Sampling blubber from different locations on the body of the porpoises had no statistically significant (P > 0.05) effect on concentrations (wet weight) of the CHs measured (Table 5). However, even though there were no statistically significant differences in the mean concentrations of the CHs in subsamples of harbor porpoise blubber, the concentrations of CHs in the subsamples (Fig. 4) from site 5 (a lateral site slightly anterior to the peduncle) were consistently lower than the mean concentrations in most of the other subsamples. This finding is similar to previous results (Calambokidis 1986) showing agreement in PCB and DDE concentrations among most subsamples of blubber taken from various locations on the bodies of harbor porpoises from the west coast of the United States, except that a dorsal site near the peduncle also had the lowest concentrations.
Similar to blubber, the mean concentrations (wet weight) of selected CHs in subsamples of liver from each of the three harbor porpoises also showed no significant differences (P > 0.05) among subsamples with the exception of the concentrations of the sum of DDDs (P = 0.02) (Table 6). Even though there were statistically significant differences among concentrations of this CH among subsamples, the difference between the subsamples with the highest and lowest concentrations (Fig. 5) was only 17%. Overall, the statistical results also illustrated that the major source of variation in both liver and blubber concentrations of CHs was due to differences among porpoises and that only a small proportion of the variation was due to sampling from different anatomical locations.
An important factor in the accumulation of lipophilic CHs by marine mammals is the lipid content of the tissue (Aguilar 1985). The results of the analysis of the replicate samples of blubber and liver showed no significant differences (P > 0.05) in percent lipid among different anatomical locations (Tables 5 and 6). Further, statistical analyses of concentrations of CHs in blubber when based on total lipid (Table 5) showed that the probability of significant differences with respect to anatomical location was not affected in a consistent manner when compared to the results of the analyses done using concentrations of CHs based on wet weight tissue. This result is consistent with the finding that the lipid content of the subsamples of tissues was not markedly different (Table 3). However, lipid normalization of the concentrations of CHs did result in the concentrations of CHs in blubber from site 5 being generally comparable to the other subsamples, rather than being less than the other sites when the concentrations are expressed on a wet weight tissue basis (Fig. 6). This result reflects the lower percent total lipid for site 5 (74 ± 1.0%, n = 3) compared to the other sites (83 ± 1.0%, n = 18). Calambokidis (1986) also found that the percent total lipid for blubber from the dorsal peduncle area was less than that for blubber from other anatomical locations in harbor porpoise from the west coast. Thus, overall these results suggest that although there were no statistically significant differences in the lipid content of blubber from different anatomical locations, variation in lipid content among the subsamples does appear to account for some of the variation in the concentrations of CHs. This supports the accurate measurement and reporting of the lipid content of tissues from stranded animals when concentrations of CHs are determined.
Normalizing the concentrations of CHs in liver to total lipid also had no consistent effect on the probability of significant differences among sampling locations (Table 6) because, as with blubber, there were no consistent differences in percent lipid among the subsamples (Table 3). However, the results shown in Figure 7 indicate that the variation among subsamples was increased, with site 5 generally exhibiting higher lipid-based concentrations of CHs than in the other subsamples. The increased variability in lipid-based concentrations of CHs among liver subsamples was a consequence of relatively low percent lipid (~ 1.5%) in liver and the magnification of differences among subsamples when the values were converted to concentrations based on total lipid.
Toxic Element Concentrations
The concentrations of the selected toxic elements in liver taken from different anatomical locations also showed no significant differences (P > 0.05) among subsamples (Table 7). However, the concentrations of lead in the subsamples were more variable than the concentrations of the other toxic elements (Fig. 8). The greater variability in lead concentrations is expected at the low concentrations found (not detected to 57 ng/g wet weight). There are apparently no published data on the distribution of toxic elements within liver for other marine mammals for comparison.
Overall, the results for CHs and toxic elements showed that the anatomical location of the sample had minimal effects on concentrations of CHs in blubber and liver or toxic elements in liver, regardless of the basis used for expressing the concentrations (CHs: wet or dry weight tissue or total lipids; toxic elements: wet or dry weight tissue). However, the findings of somewhat lower concentrations of CHs based on wet weight tissue in blubber near site 5 suggest that this area should be avoided when sampling blubber. The finding of lower concentrations of CHs in blubber from site 5 was due, in part, to the lower percent lipid in this site compared to other sites. Differences in composition of lipid in blubber strata in going from the skin to the muscle may also introduce a heterogeneous distribution of CHs in blubber. Because the present study did not address the issue of vertical stratification of CHs in blubber, additional study is needed to provide information for interpreting data from studies analyzing biopsy samples or samples from the large marine mammals where the entire thickness of blubber may not be routinely sampled or analyzed.
Samples of kidney, gonad, brain, and lung were also analyzed from one porpoise (MH-91-506) as an initial assessment of the distribution among tissues of CHs (Table 8) and toxic elements (Table 9). Consistent with previous data (Aguilar 1985) the present results indicate that the concentrations (wet weight) of CHs were considerably higher in the blubber than in the other tissues analyzed. However, when the concentrations are expressed on total lipid weight, the concentrations of CHs in the different tissues are comparable (Table 8), with the exception of brain, in which the concentrations were lower than in all the other tissues. These findings are also similar to the results from previous studies (reviewed in Aguilar 1985) with several marine mammal species showing that the concentrations in blubber of the sum of PCBs and DDTs on a total lipid basis were on average approximately equal to the concentrations in liver, muscle, or kidney; whereas for brain the concentrations of these CHs on a total lipid basis were considerably lower than the concentrations in blubber. Similarly in the present study, the blubber-to-brain concentration (total lipid basis) ratios were 4.3, 13, and 7.9 for the sum of PCBs, DDTs, and other CHs, respectively.
Analysis by Aguilar (1985) of the data of Fukushima and Kawai (1981) on CHs in tissues of the striped dolphin (Stenella coeruleoalba) shows that the high blubber-to-brain concentration ratios are in large part due to low proportions of neutral lipids (triglycerides and nonesterified fatty acids) comprising total lipids in brain. For example, concentrations based on total lipids of the sum of DDTs and PCBs in 14 tissues were highly correlated (the sum of DDTs, r = 0.86, P = 0.001; the sum of PCBs, r = 0.75, P = 0.005) with the proportion of the neutral lipids in the tissues (Aguilar 1985). These results demonstrate that measurement of neutral lipids should also be considered when determining concentrations of lipophilic contaminants such as CHs. Currently, we are evaluating methodologies for determination of triglycerides as markers of neutral lipids in tissues of aquatic species.
The distribution of toxic elements (Table 9) among different organs of porpoise MH-91-506 (liver, kidney, gonad, brain) appeared to be more variable relative to the distribution of CHs. The concentrations of mercury in liver were 4 to 17 times greater than that found in other organs and the concentrations of cadmium were highest in the kidney and not detected in the brain. The concentrations of copper were similar in liver, kidney, and brain. The present results for mercury, cadmium and copper are similar to those for harbor porpoise from the east coast of Scotland, reported by Falconer et al. (1983). In the present study, the concentrations of selenium were highest in the kidney (tenfold higher than in liver), while the concentrations of arsenic appeared to be similar in all tissues analyzed. The concentrations of lead were low in liver (11 ± 3 ng/g wet weight) and in the other tissues examined.
In conclusion, the present study shows that there were no marked differences in the concentrations of either CHs or selected toxic elements among subsamples of blubber or liver of harbor porpoise in which the concentrations of PCBs in blubber, for example, ranged from 12,000 to 33,000 ng/g wet weight. It is recommended, however, that blubber should not be sampled from near the dorsal peduncle because the concentrations, based on wet weight tissue, were consistently lower compared to samples from most of the other anatomical locations. These differences in concentrations were, in part, due to lower levels of total lipid in blubber from this location.
An additional factor in the similarity of concentrations of CHs among subsamples of blubber from different anatomical locations in the present study may also be that all strata of blubber were sampled and analyzed. Vertical differences (skin to muscle) in the composition of lipids in blubber, however, would be expected to affect the accumulation of CHs. Thus, additional studies are needed to determine the vertical distribution in blubber of both CHs and the composition of lipids in large marine mammals in particular. Such information is important for interpreting results from studies using samples from biopsies or from studies with large marine mammals where the full thickness of blubber may not be routinely sampled or analyzed.
The preliminary results on the distribution of CHs among tissues also support previous results showing that the lipid content of a tissue may be an important factor controlling accumulation of lipophilic CHs in tissues. However, in the present study, the lack of correlation of total lipid normalized concentrations of CHs in brain to those in other tissues supports the hypothesis (Aguilar 1985) that the proportion of neutral lipids rather than content of total lipids is an important factor affecting the accumulation of lipophilic CHs in tissues of marine mammals. The high quality of the samples of tissue from the harbor porpoises in the present study warrants analysis of the remaining tissue samples (e.g., brain, kidney, lung) to substantiate this finding and to expand the database on distribution of toxic chemicals in apparently healthy harbor porpoise. The results on the distribution of toxic chemicals among tissues would provide a sound basis for interpreting results from stranded animals.
We are grateful to our colleagues Dr. Nancy Foster and Cmdr. Ted Lillestolen in the NMFS Office of Protected Resources for providing valuable assistance in organizing the project and for funding support. We also appreciate the assistance of Greg Early of the New England Aquarium and Barbara Koster from National Institute of Standards and Technology in the collection of samples. Finally, a number of EC Division scientists and technicians ably assisted in the collection of samples, sample analyses, and data management. In alphabetical order they are Nicolaus Adams, Jill Andrews, Stacie Aspey, Christine Blea, Jennie Bolton, Daryle Boyd, Richard Boyer, Kristin Bryant, Douglas Burrows, Todd Crawford, Katherine Dana, Wayne Dyer, Donald Ernest, Tara Felix-Slinn, Jennifer Hagen, Tom Hom, Stephanie Johansen, Thomas Merculief, Hannah Morris, Susan Pierce, Casimir Rice, Paul Robisch, and Dana Whitney. We also thank Dr. Cheryl Krone and Gina Ylitalo for reviewing the manuscript, Sharon Giese and Barbara Bennett for editorial comments and assistance, and Shirley Perry for typing the manuscript.
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