High PCB Concentrations in Free-Ranging Pacific Killer Whales, Orcinus orca: Effects of Age, Sex and Dietary Preference

Blubber biopsy samples were obtained for contaminant analysis from two discrete populations of killer whales (Orcinus orca) which frequent the coastal waters of British Columbia, Canada. Detailed life history information for the fish-eating ‘residentʹ population, comprising two distinct communities, and the marine mammal-eating ‘transientʹ killer whale population, provided an invaluable reference for the interpretation of contaminant concentrations. Total PCB concentrations (sum of 136 congeners detected) were surprisingly high in all three communities, but transient killer whales were particularly contaminated. PCB concentrations increased with age in males, but were greatly reduced in reproductively active females. The absence of age, sex and inter-community differences in concentrations of polychlorinated- dibenzo-p-dioxins (PCDDs) and- dibenzofurans (PCDFs) may have partly reflected low dietary levels, but more importantly, metabolic removal of dioxin-like compounds in killer whales. While information on toxic thresholds does not exist for PCBs in cetaceans, total 2,3,7,8-TCDD Toxic Equivalents (TEQ) in most killer whales sampled easily surpassed adverse effects levels established for harbour seals, suggesting that the majority of free-ranging killer whales in this region are at risk for toxic effects. The southern resident and transient killer whales of British Columbia can now be considered among the most contaminated cetaceans in the world.