Chlorinated hydrocarbon contaminants in arctic marine mammals

Abstract

By 1976, the presence of chlorinated hydrocarbon contaminants (CHCs) had been demonstrated in fur seal ( Callorhinus ursinus), ringed seal ( Phoca hispida), hooded seal ( Cystophora cristata), bearded seal ( Erignathus barbatus), walrus ( Obdobenus rosmarus divergens), beluga ( Delphinapterus leucas), porpoise ( Phocoena phocoena) and polar bear ( Ursus maritimus) in various parts of the Arctic. In spite of this early interest, very little subsequent research on contaminants in Arctic marine mammals was undertaken until the mid-1980s. Since that time, there has been an explosion of interest, resulting in a much expanded data base on contaminants in Arctic marine mammals. Except in the Russian Arctic, data have now been obtained on the temporospatial distribution of PCBs and other contaminants in ringed seal, beluga and polar bear. Contaminants in narwhal ( Monodon monoceros) have also now been measured. On a fat weight basis, the sum of DDT-related compounds (S-DDT) and PCB levels are lowest in walrus (< 0.1 μg/g), followed by ringed seal, (0.1–1 μg/g range). Levels are an order of magnitude higher in beluga and narwhal (1–10 μg/g range). It appears that metabolism and excretion of S-DDT and PCBs may be less efficient in cetaceans, leading to greater biomagnification. Polar bears have similar levels of PCBs as cetaceans (1–10 μg/g), but with a much simpler congener pattern. DDE levels are lowest in polar bear, indicating rapid metabolism. Effects of age and sex on residue levels are found for all species where this was measured. Among cetaceans and ringed seal, sexually mature females have lower levels than males due to lactation. Although PCB levels in adult male polar bears are about twice as high as females, there is only a trivial age effect in either sex apart from an initial decrease from birth to sexual maturity (age 0–5). Comparison of levels of S-DDT and PCBs in Arctic beluga and ringed seal with those in beluga in the Gulf of St. Lawrence and ringed seal in the Baltic Sea, indicate that overall contamination of the Arctic marine ecosystem is 10–50 times less than the most highly contaminated areas in the northern hemisphere temperate latitude marine environment. Geographic distribution of residue levels in polar bears indicates a gradual increase from Alaska east to Syalbard, except PCB levels are significantly higher in eastern Greenland and Svalbard. Information on temporal trends is somewhat contradictory. S-DDT and PCB levels declined in ringed seal in the Canadian Arctic throughout the 1970s, whereas polar bear data indicate levels in the late 1960s were lower than in the 1980s. Interpretation is confounded by insufficient data on sex, age and condition of the early samples, and lack of intermediate time points for polar bear. Application of gas-chromatography-mass spectrometry techniques in the 1980s has resulted in the identification of many previously unmeasured contaminants in Arctic marine mammals. HCH, HCB, dieldrin and a number of chlordane-related compounds were first reported in polar bear and ringed seal from the Canadian Arctic. Polychlorinated camphenes (PCCs) have been found in polar bear, ringed seal, beluga and narwhal. The major PCCs have been identified as a octochloro- and nonachlorobornane found in technical toxaphene. Geographic distribution of HCH, HCB, dieldrin, chlordane and PCC residues in the Arctic is more even than that of S-DDT and PCBs. Low levels (< 20 pg/g) of 2,3,7,8-TCDD and other PCDD and PCDF congeners have been identified in ringed seal and polar bear. Geographic distribution of TCDD is the most non-uniform of the CHCs. Highest levels occurred in the high Arctic and Spitzbergen. TCDD-like non- ortho and mono- ortho PCBs have been measured mainly in ringed seal, beluga and narwhal. TCDD toxic equivalent concentrations are highest in narwhal and beluga, in the order of 100–500 pg/g, and are dominated by PCBs. TCDD equivalents in ringed seal are about 10 times lower than in beluga and narwhal, but TCDD itself makes a proportionately larger contribution. Recently, μg/g levels of tris(4-chlorophenylmethanol) and methylsulphone metabolites of PCB congeners and DDE have been identified in polar bear tissues.