Distinctive patterns and low concentrations of persistent organic pollutants in Northwestern Pacific killer whales (Orcinus orca)

Persistent organic pollutants (POPs) in killer whale (Orcinus orca) populations in the Northwestern Pacific Ocean are much less studied compared to the Northeastern Pacific and North Atlantic populations. The objective of this study was to address that knowledge gap by analysis of biopsy samples obtained as part of studies of killer whale feeding and habitat use in coastal waters of the Russian Far East. Skin/blubber biopsies collected from 26 killer whales at five locations in coastal waters of the Kamchatka Peninsula (Avacha Gulf), North Kuril Islands, Western and Northern Sea of Okhotsk, and further north in Chukotka, between 2012 and 2016, were analysed for a suite of organochlorine pesticides and byproducts (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs). DDT related compounds and PCBs were the most prominent POPs in the biopsy samples with geometric mean concentrations in the 5 regions ranging 34.4 to 161 ng/g (wet weight, ww) for total DDT and 8.10 to 58.5 ng/g ww for total PCBs. Principal components analysis using the data for OCPs showed that key contributors to the geographic differences were DDT isomers as well as the more volatile OCPs, hexachlorobutadiene and pentachlorobenzene. The concentrations of individual OCPs and PCBs agreed with previous reports for female killer whales sampled in the Northwestern Pacific region in 2002–2004 but were up to 180-fold lower than reported in transient males. Overall concentrations of POPs in killer whales in this region are among the lowest for killer whale populations in the northern hemisphere.