Cetaceans, PCBs

When compared to other cetaceans, PCB residues in blubber of harbor porpoises (Phocoena phocoena) from the Black Sea showed a measurable sexual difference. PCB concentrations were lower in older female porpoises possibly due to lactational transfer to their calves, while in males the PCB concentrations were positively correlated with increasing age (Tanabe et al. 1997). In stellar sea lions (Eumetopias jubatus), the transfer rate of PCBs through lactation was estimated at 80% of the total body PCB burden of adult females (Lee et al. 1996). PCB concentrations in liver of the stellar sea lion from the Bering Sea increased with increasing age and correlated positively with those of blubber (Lee et al. 1996). In ringed seals (Phoca hispida) from the Russian Arctic, lactational transfer of PCBs was estimated at 25% of whole-body burden in the mature female (Nakata et al. 1998), or about one third that of stellar sea lions. In grey seals (Halichoerus... 

Levels of POPs in two local marine mammals, the Indo-Pacific humpback dolphin (Sousa chinensis) and Unless porpoise (Neophocaena phocaenoides), were measured in two ad hoc studies of stranded cetaceans in 1995-2000 and 2000-2001, respectively (Jefferson et al., 2002 Imanishi et al., 2004). Cetacean tissue samples were collected from stranded animals found in Hong Kong and analyzed for DDT, mirex, toxaphene and PCBs. High mean blubber concentrations of DDT (32.8 mg kg-1 ww) and PCBs (8.19 mg kg-1 ww) were reported. 

Results of the ecological risk assessment of POPs in the marine environment to local cetaceans (the hump-backed dolphins and the Unless porpoises) showed the HQs for eight POPs studied (chlordane, DDT, dieldrin, heptachlor, HCB, toxaphene, PCBs and dioxins/furans) were all less than unity, suggesting that there was no unacceptable risk of toxicological significance associated with exposure of local cetaceans to the current contamination level of these POPs in the marine environment (Table 7.17). 

Troisi, G.M., Haraguchi, K., Simmonds, M.P., Mason, C.F., 1998. Methyl sulphone metabolites of polychlorinated biphenyls (PCBs) in cetaceans from the Irish and Aegean Seas. Arch. Environ. Contam. Toxicol. 35, 121-128. 

Figure 18.3. Geographical distribution of PCBs, DDTs and PBDEs in Asian cetaceans. Black and white bars indicate coastal and offshore species, respectively.

Separately living populations of wildlife species may show differences in patterns of environmental contaminants like PCBs. PCB and PCDD/F congener patterns may differ in the same species from various locations as a result of the difference in patterns already present in their (differing) food, as has been demonstrated for seals fed with fish.35 Such differences also relate to selective biotransformation capacities of the organisms involved.20 Large differences in metabolic capacity have been observed between pinnipeds and cetaceans (c/. biotransformation section). This does not only hold for CACs, but also for chlorinated pesticides. For instance, porpoises have been shown to have a... 

Similar species differences in biotransformation abilities can be observed in the marine environment.2019 Molluscs and polychaeta are not able to metabolize any PCB group. Fish seem to be able to metabolize globular but not planar congeners. In cetaceans the CYP2B isozymes seem to be relatively underdeveloped, because whale species can metabolize planar congeners only. Freshwater and other small cetaceans have an even lower capacity than larger marine species,68 69... 

Characterization of enantiomer composition in the food web demonstrated enantioselective detoxification of POPs, including PCBs, in cetaceans. In the Bering-Chukchi-Beaufort Sea area, bowhead whales Balaena mysticetus) had nonracemic amounts of some chiral PCBs, while their Calanus zooplankton prey had racemic levels [189]. Given the simpUcity of the bowhead whale food chain, these observations indicate that these cetaceans had biotransformed PCB atropisomers enantioselectively. The EEs of PCB 91 were significantly correlated with body length in males only, while those of PCBs 95 and... 

There are consistent attempts in the literature to interpret specific biotransformation of PCBs that occurred in an organism from the relative ratio of X-CB to that of a reference CB-Y. The later could be CB-153, CB-138 (2,2, 3,4,4, 5-hexa CB), and CB-180 (2,2, 3,4,4, 5,5 -hepta CB) [52]. Such structure-dependent metabolism studies predicted induction of Cytochrome P450 isozymes in the marine food chain [59], small cetaceans [52], beluga and narwhal [60], river dolphins [61], pinnipeds [52], aquatic fauna including invertebrates [62], and in humans [63]. Comprehensive characterization of xenobiotic metabolizing enzymes in whales and pinnipeds has been carried out to show the utility of this approach [51,64]. 

Small cetaceans from the North Sea and Atlantic Ocean, North Atlantic coast of US, Baltic Sea, Scandinavian waters, and Atlantic coast of Canada were analyzed for specific CB congeners and a few large whale species have been analyzed thoroughly for PCBs, such as the sperm whale, beaked whale, killer whale, minke, fin, blue, and humpback whales [52]. 

Marine mammals are the most vulnerable and most prohahle target organisms to PCBs. The metabolic potential to degrade organochlo-rine contaminants and therefore accumulate relatively high concentrations of persistent PCBs is lower in marine mammals, particularly in cetaceans, than in terrestrial mammals. Dead harhor porpoises (Phocoena phocoena)... 

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