feeding on a PCB-contaminated food chain might consume enough toxicant to 



alter their semen quality in that breeding season; when coupled with altered 



courtship, this could reduce the fertility of the eggs and reproductive 

 fitness of the individual (Bird et al . 1983). 



Among comparatively resistant species of birds, no significant 

 reproductive effects were observed during long-term exposures at high Aroclor 

 1254 feeding levels in Japanese quail Coturnix coturnix japonica (50 ppm in 

 diets), northern bobwhites Colinus virginianus T^D ppm) (NAS 1979), and 

 mallards (25 ppm) (Custer and Heinz 1980). ScFeech owls ( Otus asio ), given 3 

 ppm of Aroclor 1248 in their diets for two breeding seasons, laid eggs 

 containing 3.9 to 17.8 mg PCBs/kg fresh weight compared to control values of 

 0.0 to 0.6; however, reproductive variables, including eggs per clutch, 

 hatchability, chick malformations, survival, and eggshell thickness, were not 

 affected (McLane and Hughes 1980). 



For most avian species, a reduction in eggshell thickness of 15 to 20% is 

 suggested as a critical value beyond which population numbers will decline 

 (Nygard 1983). Pheasants fed 50 mg of Aroclor 1254 weekly produced fewer 

 eggs, but an effect on eggshell thinning was not apparent before other effects 

 became obvious (Roberts et al. 1978). However, eggshell thickness of the 

 peregrine falcon ( Falco peregrinus ) from Norway declined 85% between 1854 and 

 1976; addled eggs containing dead embryos collected in 1976 had 724 ppm of 

 PCBs in lipids, and up to 110 ppm on a fresh weight basis (Nygard 1983). 

 Peregrine populations have declined in Norway, but the high DDT levels (which 

 cause eggshell thinning) in tissues and eggs--together with measurable 

 residues of dieldrin and mercury--made it difficult to ascribe thinning or 

 population declines exclusively to PCBs (Nygard 1983). Mean PCB residues were 

 significantly lower in eggs from successful nests of the American bald eagle 

 than unsuccessful nests (1.3 ppm fresh weight vs. 7.2), and may be associated 

 with eggshell thinning (Wiemeyer et al . 1984). PCB concentrations in eggs were 

 inversely correlated with shell thickness in the bald eagle (Wiemeyer et al. 

 1984) as well as the black-crowned night-heron (McEwen et al . 1984; Henny et 

 al. 1984). However, PCB content is frequently correlated positively with DDE 

 content (Norheim and Kjos-Hanssen 1984), which is known to interfere with 

 avian calcium metabolism and to induce thin eggshells. The observed 

 thickening of eggshells in black-crowned night-heron eggs between 1973 and 

 1979 in colonies from Rhode Island locations was associated with marked 

 reductions in both PCBs and DDE (Custer et al . 1983a, b). At present, the 

 evidence implicating PCBs as a major source of eggshell thinning is 

 inconclusive. 



Loss rates were followed in common grackles fed 150 ppm dietary Aroclor 

 1254 for 8 days, then given untreated food and killed at 1 to 32 weeks 

 posttreatment (Stickel et al . 1984). PCB levels in bodies of grackles 

 declined from 1,300 ppm fresh weight on the day clean food was restored, to 

 169 ppm 32 weeks later. The overall loss rate was estimated at 0.77% daily 

 with a calculated biological half-life of 89 days. Similar loss rates were 

 observed in pheasants given a single capsule dosage of Aroclor 1254 (as quoted 

 in Stickel et al . 1984). In general, PCB residues in brain are good 



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