Cormorant eggs, PCDD

Table 8 Concentrations (ng kg 1 fresh weight) of PCDD/Fs in double-crested cormorant eggs from the Great Lakes, 1988-1991... 

Ryckman et al. [74] studied the incidence and temporal trends of bill deformities in double-crested cormorants in the Canadian Great Lakes. While the prevalence of bill-deformities was higher than in reference sites (Lake Nipigon and Lake-of-the-Woods), there were no differences in incidence among colonies in the Great Lakes between 1988 and 1996. Given the relatively low (and even) concentrations of PCDD/Fs in cormorant eggs (Table 8), if the cross-bill deformity was AHR-mediated, it was likely to be due to PCBs. 

Three studies have looked at PCDD/F concentrations in eggs of double-crested cormorants in the Great Lakes. These are summarized in Table 8. 

Similar to cormorants, it appears that most of the PCDD/Fs found in Caspian tern eggs are accumulated outside the Great Lakes prior to nesting, however, there may be some local influence, especially on 2378-TeCDF concentrations. 

Total PCDDs and PCDFs were usually used for comparison, however, it should be noted that different studies used different standards to calculate total PCDDs/PCDFs. The eggs of double-crested cormorants that were collected from Mandarte Island, and Crofton and Mitlenatch Islands, in the Strait of Georgia, in British Columbia, Canada, between 1973 and 1998 have been analyzed for PCDDs and PCDFs (Harris et al., 2003). The study showed that the levels of total PCDDs and PCDFs in 1998 were lower than those from 1973 to 1989 (Table 8.9). In another study, the PCDDs/PCDFs levels in white-tailed sea eagle livers were analyzed (Kannan et al., 2003). It showed that no significant difference in the total PCDDs/PCDFs in adult females that were collected from 1985 to 1995 was observed. However, this observation was confounded by small sample sizes and associated inherent biological variations. 

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