8.1 Effects
Most of the literature on toxicity of PCBs to wildlife concerns the consumption of PCBs in their diet. In reviewing data gathered from various sources, Eisler (1986) noted that, as a group, birds were more resistant to acutely toxic effects of PCBs than mammals. LD50s ranging from 604 to more than 6 000 mg Aroclor/kg of diet were reported for various species of birds. Also, for all avian species, PCB residues of 310 mg/kg fresh weight of the bird were associated with an increased likelihood of death from PCB poisoning,
Among mammals, the mink (Mustela vison ) is the most sensitive wildlife species tested. Diets containing 6.7 mg Aroclor 1254/kg fresh weight and 8.6 mg Aroclor 1242/kg fresh weight killed 50% of the mink in 9 months (Ringer 1983). In comparing primary toxicity (where animals were fed a diet containing a PCB formulation) and secondary toxicity (where the diet contained the same concentrations of the metabolised xenobiotic or PCBs in this case) of Aroclor 1254 to mink, Aulerich et al. (1986) found that the mean feed consumption and body weight gains were lower for the animals fed metabolised Aroclor 1254 (secondary toxicity) than for animals that received the same concentrations of the technical grade of Aroclor 1254 (primary toxicity). The tests yielded 28- and 35-day LC50 values, respectively, of 79.0 and 48.5 mg Aroclor 1254/kg fresh weight of feed for the primary toxicity test and 47.0 and 31.5 mg/kg fresh weight of feed for the secondary toxicity test.
Signs of PCB poisoning in mink include anorexia, weight loss, lethargy, and un-thrifty appearance. In studying sublethal effects, Aulerich et al. (1985) found that diets supplemented with as little as 2 mg Aroclor 1254/kg of feed for 8 months, or 5 mg Aroclor 1254/kg of feed for 4 months, resulted in near reproductive failure with normal breeding and whelping, but a high death rate of kits; reproduction was not affected at dietary levels of 1.0 mg Aroclor 1254/kg. Two of the 12 female minks died in 129 days, when exposed to a PCB level of 0.64 mg/kg fresh weight in a diet containing meat from cows which had been fed Aroclor 1254 (Platonow and Karstad, 1973). Death was not reported in the mink population fed a control commercial diet containing 0.3 mg PCBs/kg. Although poor reproduction at the rate of 1.81 kits/female bred (satisfactory production is considered to be 4 kits/female) was noted by these investigators, lesions referable to the PCB content of the control ration were not seen in the mink of this herd, which were used for research on aleutian disease during the course of these PCB experiments.
The data relating toxicity of individual PCB congeners to wildlife are limited. Recently, it has been shown that certain hexachlorobiphenyls, such as 3,4,5,3',4',5'-hexachlorobiphenyl (PCB #169), are extremely toxic to mink ; concentrations as low as 0.1 mg/kg fresh weight in their diet killed 50% of the animals exposed to the congener. However, other hexachlorobiphenyls, such as 2,4,5,2',4',5'-hexachlorobiphenyl (PCB #153) and 2,3,6,2',3',6'-hexachlorobiphenyl (PCB #136) were non-fatal to mink under similar conditions, and did not produce adverse reproductive effects (Aulerich et al., 1985). Note that PCB #169 is a coplanar biphenyl while the other two hexachlorobiphenyls are not.
8.2 Criteria from the Literature
The Province of Manitoba recommended a surface water quality objective of 0.014 µg total PCB/L to protect wildlife from the adverse effects of PCBs. This guideline is the same as suggested by the US EPA (1980) for freshwater aquatic life, to provide protection for fish-consuming wildlife against excessive accumulation of PCBs in fish.
Based on an acceptable level of 0.1 µg PCB/g wet weight in whole fish for the protection of fish-consuming birds (and a bio-concentration factor of 1 x 105), the IJC (1977) estimated that a concentration of 0.001 µg PCBs/L in water would be required to reach the recommended fish tissue level. The safe level of 0.1 µg PCBs/g in whole fish was derived, in part, from the Platonow and Karstad (1973) study, where the lowest dietary concentration observed to cause a deleterious biological effect was 0.64 µg Aroclor 1254/g (see Section 8.1). A safety factor of five was applied to obtain the recommended level for fish tissue (whole fish) of 0.1 µg PCBs/g wet weight. Note that, in latter reviews (Eisler, 1986), birds were found to be more resistant to PCBs than mammals.
No other jurisdiction recommended levels for PCBs in water for the protection of wildlife.
8.3 Recommended Criteria
Criteria for PCBs in waters consumed by wildlife are not recommended at this time.
To protect wildlife (e.g., mink) from harmful effects of PCBs in the diet, it is recommended that the concentration of total PCBs in fish and shellfish should not exceed 0.1 µg/g wet weight in whole fish and shellfish.
8.4 Rationale
Criteria for PCBs in waters consumed by wildlife are not recommended at this time, primarily due to the lack of pertinent information (e.g., the toxicity of PCBs in water to wildlife). As with human drinking water (section 6) and livestock (section 9.2), PCB levels in ambient waters consumed by wildlife were considered to pose an insignificant threat to wildlife.
For waters inhabited by aquatic life, the criterion recommended for the protection of aquatic life and their consumers appears more than adequate to protect wildlife.
The major source of PCBs in wildlife is food (e.g., fish and shellfish). The criteria for PCBs in fish consumed by wildlife are primarily based on the results of the Platonow and Karstad (1973) study with minks. Platonow and Karstad observed some adverse effects in female minks, fed a diet (0.64 µg PCBs/g) containing meat from cows exposed to PCBs (Aroclor 1254). In this document, a rounded figure of 0.1 µg PCBs/g wet weight in whole fish was chosen to be the acceptable level for fish-consuming wildlife (see Section 7.4.2 for more detail). This concentration is more than 5 times lower than the lowest observed effect level (LOEL) noted by Platonow and Karstad (1973) with minks.
The CCREM (1987) did not recommend a guideline for the protection of wildlife.