Mean survival of the marine amphipods (A. virginiana) in the 22 Saglek sediments ranged from 72 to 96%, including 72 to 87% in the reference sites (n = 5, PCB concentrations <5 ng/g) and 78 to 96% in the more contaminated sites (n = 17; Supplemental Data, Table S1). The mean survival of amphipods for two control sediments—which were collected together with the amphipods at Martinique Beach, Nova Scotia, Canada—was 94% and 85%. Based on the regression analysis, the results from the amphipod survival test and Microtox (V. fischeri) assay versus sediment PCB concentrations were not statistically different (p > 0.05). All samples were below the Microtox solid-phase toxic hazard level (EC50 < 1,000 mg/L) 31.
In total, 96 taxa were found in the benthic community analysis. Samples were numerically dominated by the polychaetes Capitella capitata, Eteone longa, Marenzellaria viridis, Microspio sp., Ophelia limacina, and Spio filicornis; the amphipods Oediceros saginatus and Protomedia fasciata; and the nemertean Cerebratulus sp. Based on the regression analysis, the number of individuals, taxa, and diversity versus sediment PCB concentrations were not statistically different (p > 0.05). Analyses of similarity among reference and contaminated sites were not significantly different (R = 0.06, p > 0.05). Analysis of the benthic community structure using nonmetric multidimensional scaling (nMDS) also showed reference sites interspersed among, or lying close to, contaminated sites. Thus, the results of sediment toxicity testing and a benthic community survey provide no evidence of adverse effects on benthos associated with the PCB-contaminated sediments in Saglek Bay.
The finding of no adverse effects on benthos from the contaminated sediments at Saglek may seem surprising, especially in view of the relatively high PCB concentrations (average PCB concentrations within 1.5 km of the contaminated beach = 884 ng/g dry wt 12) compared with the Canadian sediment quality guideline (21.5 ng/g dry wt) and probable effects levels (189 ng/g dry wt), which are designed to be protective of benthic invertebrates 10. However, there is limited information about the toxicity of PCB-contaminated sediments to benthos under conditions in which cocontaminants are present at negligible levels, as they are at Saglek. It is possible that toxicity is significantly reduced 20. Furthermore, slight differences in sediment characteristics (e.g., grain size or total organic carbon) can have an effect on the survival of certain benthic organisms 35. Therefore, the effects levels established from previous studies in areas of fine-grained sediments (e.g., harbors) might not be transferable to the sand-dominated (with low organic carbon content) benthic community at Saglek. A study of benthic community health in relation to PCB contamination in San Francisco Bay also found no relationship between species diversity and PCB concentrations within the range of 9 to 1570 ng/g, which is a range similar to that at Saglek 36.
Literature-derived toxicity values. Polychlorinated biphenyls have been associated with toxicity related to a variety of endpoints in fish, including lethality, immune suppression, liver lesions, impaired reproduction, growth inhibition, cellular changes, and biochemical effects 37. Two endpoints (lethality and reproductive success) were selected, for which a literature-derived PCB threshold concentration served to guide the interpretation of PCB risks to sculpin health. An exhaustive review of the literature concerning the response of aquatic organisms to PCB exposure 37 proposed a threshold level for lethality in adult male and female fish and reproductive effects in adult females of about 100,000 ng/g wet weight. For progeny, Niimi 37 proposed a threshold level for reproductive effects of about 50,000 ng/g wet weight. Other laboratory studies reviewed by Kime 38 showed adverse effects on reproduction, including impaired ovarian growth and hormonal changes, at concentrations ranging from 50 to 5,000 ng/g wet weight. Establishing a threshold of risk to fish survival and reproduction based on the literature data is complicated by various studies reporting contradictory results for PCB effects. Also, thresholds vary among different species, among tissues analyzed, and with the mix of PCB congeners analyzed. However, based on the literature, the threshold for risk to reproductive effects in fish appears to be in the range of 1,000 to 5,000 ng/g wet weight, with some risk of effects occurring with as low as 100 to 1,000 ng/g wet weight. The former part of the range coincides with the average sculpin PCB exposures (2,660 ng/g wet wt) in the beach group (Table 1). Based on the sediment–sculpin PCB relationship established for the exposure assessment (Fig. 3), the sediment PCB concentration associated with this sculpin exposure is approximately 750 ng/g dry weight. The higher sculpin PCB concentrations measured at the other sites as far as 3 km east or west of the beach approach the lower end (1,000 ng/g wet wt) of this threshold concentration (Table 1).
Results for lipid content (%), condition factor (CF), hepatosomatic index (HIS), and EROD activity have been reported by Kuzyk et al. 1. Lipid content, CF, and HIS were similar between sexes and among the four groups, and EROD activity was significantly different among the four groups (p < 0.0001). The average activity in sculpins from the beach group was nearly fourfold greater than average levels at the next most contaminated site (west 1 km) and 25-fold greater than the average levels at the reference sites 1. Furthermore, there was a strong correlation between EROD activity and tissue PCB concentrations (r2 = 0.60, p < 0.05). To interpret the observed biological responses in the context of ecological risk, Kuzyk et al. 1 used an upper estimate of background EROD activity as a threshold for EROD induction, above which there may be an increase in EROD activity associated with PCB concentrations. The determined threshold for EROD induction for Saglek Bay sculpin was 3,620 ng/g lipid weight and 50 ng/g wet weight in the whole body minus liver tissue 1. Average concentrations of PCBs in sculpin tissue 4.5 km from the beach of Saglek Bay substantially exceeded the established threshold 1. Based on the sediment–sculpin PCB relationship established for the exposure assessment (Fig. 3), the sediment PCB concentration associated with this sculpin exposure is approximately 5 ng/g dry weight 1.
Jorgensen 39 related EROD induction to PCB exposure in a northern pelagic fish population (Arctic char) and proposed a threshold level of between 100 and 1,000 ng/g wet weight in the carcass tissue. For shorthorn sculpin, EROD results were generally consistent with the lower end of this proposed threshold range 1. The threshold determined by Kuzyk et al. 1 was also in agreement with the lower end ranges reported for other fish species 40. Ethoxyresorufin-O-deethylase induction is one of the best known sublethal responses to dioxins, polyaromatic hydrocarbons, and PCBs and is used often as an early-warning indicator for levels that might have adverse effects on fish health 12. The biological significance of EROD induction in sculpin from Saglek Bay remains unknown; however the results suggest that sculpin collected within 4.5 km of the beach elicit a sublethal response to elevated PCB levels in the area.
The results for the guillemot endpoints studied are summarized in Table 3. Results for liver biomarkers (EROD, liver retinol concentration, porphyrin concentrations, and malic enzyme activity) have been reported by Kuzyk et al. 11. Among the 13 endpoints, several showed no relationship to PCB exposure: malic enzyme; thyroid mass and activity; mass of the bursa, spleen, heart, and adrenal glands; chick growth; and hatching success (Table 3). Malic enzymes, the thyroid, the heart, and the adrenal are all direct or indirect physiological indicators of metabolic functioning, and growth is a functional endpoint strongly linked to metabolism. Therefore, the nonsignificant response for this set of endpoints is biologically consistent and provides quite convincing evidence that guillemot metabolism has not been significantly affected by PCB exposure at Saglek.
Table 3. Summary of biological effects data for the black guillemots exposed to polychlorinated biphenyls in Saglek Baya
|1. MFO induction||Sublethal effects threefold|| ||×|| || || || |
|2. Adaptive organ enlargement (liver)||Sublethal effects 25%||×|| ||750||50|| || |
|3. Malic enzyme||Sublethal effects 30%|| || || || || || |
|4. Thyroid activity||Sublethal effects twofold increase or 50% increase|| || || || || || |
|5. Liver porphyrin||Sublethal effects twofold||Indeterminate|| || || || || |
|6. Change in organ mass||Sublethal effects|| || || || || || |
| Thyroid|| −30%|| || || || || || |
| Thymus|| −25%||×|| ||1,090||87|| || |
| Bursa|| −30%|| || || || || || |
| Spleen|| −50%|| || || || || || |
| Heart|| −50%|| || || || || || |
| Adrenal|| −50%|| || || || || || |
|7. Retinoid levels||Sublethal effects 40%||×|| ||1,050||82|| || |
|8. Steroid hormones|| || || || || || || |
| a. Testosterone and estradiol||Sublethal effects 20%|| || || || || || |
|Survival/reproduction 40%||×|| || || ||1,000||77|
| b. Corticosterone||Sublethal effects 40%|| || || || || || |
|9. Genetic variation||N/A rejected due to data quality|| || || || || || |
|10. Gonad histology||Survival/reproduction; presence of any abnormalities that could compromise reproductive capacity||×|| || || ||×||×|
|11. Growth||Sublethal effects 20%|| || || || || || |
| ||Survival/reproduction 30%|| || || || || || |
|12. Immune function||Sublethal effects 25%||×|| ||275||11|| || |
| ||Survival/reproduction 50%||×|| || || ||2,750||355|
|13. Hatching success||Survival/reproduction; statistically significant reduction of at least 10%|| || || || || || |
In contrast, statistically significant effects related to nestling PCB exposure were found for liver porphyrin content, MFO induction, liver enlargement, thymus mass, retinoid levels, steroid hormone levels, and the PHA skin test immune response (Table 3). Liver porphyrin content showed unexpected decreases with increasing PCB concentrations, given the results of previous studies 41, so these results were considered to be indeterminate in terms of risk to guillemot health. The MFO induction results were significantly related (R2 = 0.26, p = 0.004, n = 31) to PCB exposure, but the magnitude (1.5-fold increase for the beach compared with reference) of the responses was not great enough to be considered indicative of risk (Table 3). However, for the rest of the endpoints (liver enlargement, decrease in thymus mass, retinoid levels, steroid hormone levels, and PHA skin test immune response), the results strongly indicated the presence of PCB-related adverse effects.
Among the male guillemots, qualitative analysis of the gonads revealed three significant testis abnormalities. Two males—one from the beach group and one from the island group—had disconnected medullar tissue that extended outside the cortex 5. Normal medullar tissue is located and contained within the cortex. Another male from the island group had seminiferous tubules extending through the cortex to the outside of the testis. If this tubule persisted during sexual maturity, growing sperm that traversed it would eventually be displaced to the outside of the testis within the abdominal cavity 5. No medullary abnormalities were observed in nestlings from the reference group. However, males of all groups showed a relatively high frequency of disrupted capsules (2 of 6 reference males, 4 of 7 island males, and 4 of 5 beach males, including the two males that had disconnected medullary tissue). Among the quantitative parameters examined, only the number of Sertoli cells varied significantly among the exposure groups. Major testicular abnormalities are extremely rare, and their presence in any member in a sample of wild, prefledgling birds is typically considered indicative of some developmentally disruptive factor, such as an estrogenic contaminant 42. This sample size, however, was very small and limited the statistical power of the analysis. Among females, histological analysis revealed neither significant structural abnormalities nor qualitative cellular changes related to PCB concentration. Relative ovarian weight results were inconclusive.
The results of the multiendpoint guillemot effects study were biologically consistent with each other and were also consistent with previous results indicating that the immune system and the developing reproductive system are the most sensitive systems in terms of contaminant-related effects. Liver enlargement, thymic atrophy, and retinoid depletion are all believed to share a common mode of toxicity (aryl hydrocarbon [Ah] receptor mediated) 43–45. Mixed function oxygenase induction also shares the Ah receptor-mediated mode of toxicity 43. Although MFO induction results were not high enough to be indicative of risk, they did show a significant relationship with PCB exposure. These results were also consistent with the observed effects on the PHA skin test immune response and the observed abnormalities in nestling gonads. The PHA skin test measures the T-cell–mediated portion of the immune response; the thymus is the site of T-cell maturation in the body. Therefore, the results show corresponding structural (thymus mass) and functional (immune response) changes in relation to PCB exposure. Contaminants that have caused atrophy and (or) histological changes in immune organs are usually associated with altered immunological function 46.
The observed depletion of retinoids is also consistent with this set of responses in that inadequate retinoid levels are related to immunosuppresion as well as overall susceptibility to disease 47. Retinoids are also associated with reproductive and developmental effects such as changes in secondary sexual characteristics, testes weight, spermatogenesis, and embryo survival 48. Elevated concentrations of estradiol and testosterone were observed in the guillemot nestlings at the beach area. These results are consistent with the presence of other reproductive effects and suggest that there is some potential for risk to guillemot reproduction. Abnormal concentrations of sex hormones are believed to be a causal factor related to developmental gonad abnormalities 42.
For each of the statistically significant endpoints, the relationship between the observed response and nestling PCB exposure was used to estimate the nestling liver PCB concentrations associated with risk to guillemot health. Nestling liver PCB concentrations were then translated into estimates of sediment PCB concentration using the exposure equation (Fig. 4) and are presented in Table 3. In terms of sublethal health risks, nestling liver PCB concentrations ranged from 750 to 1,090 ng/g wet weight, and corresponding sediment PCB concentrations were estimated at 50 to 87 ng/g dry weight. The PCB concentrations associated with sublethal immune effects were estimated at 275 ng/g wet weight and 11 ng/g dry weight for nestling livers and sediment, respectively. In terms of risk to guillemot reproduction or survival, nestling liver PCB concentrations were 1,000 and 2,750 ng/g wet weight for two endpoints, with corresponding sediment PCB concentrations at 77 and 355 ng/g dry weight. These values represent the best estimates of the sediment PCB concentrations associated with the effects observed in the present study; however, the values may either underestimate or overestimate risk.