Persistent Organic Pollutants in Seals

The marine environment is at the receiving end of thousands of chemicals being released intentionally or nintentionally every year. Persistent contaminants including polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are found throughout the global environment and accumulate in the aquatic food chain. Many marine mammals are long-lived, have a thick blubber layer, and are at the top of the food chain. These factors predispose them to accumulating persistent organic pollutants (POPs) at harmful levels (Figure 1).

Despite the implementation of regulations on the production and use of these chemicals, they are still found in the marine environment and wildlife at relatively high concentrations due to their persistence and ability to move in the environment. PCBs were widely used as stable, heat resistant coolants and lubricants for electrical transformers and capacitors – they were banned in 1977 in Canada. PBDEs were widely used as flame retardants in electronics, furniture, and other products. Two of the three commercial formulations of PBDEs (penta- and octa-) were withdrawn from the market in 2004 while the third product was phased out in 2013.

Figure 1. Some chemicals introduced into the environment persist there, moving between water, sediments, and the atmosphere. These chemicals accumulate in the food web, ending up in toxic concentrations in marine mammals such as killer whales.

B.C.’s killer whales exhibit high concentrations of flame retardant chemicals. (Photo: Marie Noel)

PCBs represent a major toxicological concern for many high trophic level species. They have been associated with reproductive problems, tumors, disruption of the immune system, and hormonal imbalances. While less is known about the toxicity of PBDEs to marine mammals, similarities in chemical structures suggest similar toxic effects. PBDE-associated disruption of the immune system has been reported in harbour seals.

British Columbia’s killer whale (Orcinus orca) populations are among the most PCB-contaminated marine mammals in the world and also exhibit one of the highest concentrations of PBDEs. Contaminants have been identified as a threat to the recovery of all four B.C. killer whale populations under the auspices of the Species at Risk Act (SARA). It is therefore important to monitor such contaminants in order to identify priorities, design mitigation measures, and monitor progress.

Harbour seals (Phoca vitulina) provide insight into local killer whale habitat quality and help shed light on source, transport, fate, exposure, and effects of contaminants of concern to SARA-listed resident and transient killer whales. Harbour seals have proven to be useful indicators of marine environmental quality, and research on contaminants in harbour seals has helped to identify regional hotspots and emerging contaminants of concern. The utility of the harbour seal as a sentinel of food web contamination can be ascribed to their widespread distribution in B.C., their ease of capture and handling, and the extensive knowledge of their biology and ecology. Contaminants of concern have been monitored in the blubber of harbour seal pups since 1984. In this context, harbour seals can be considered as “canaries in the coal mine” in the B.C. marine environment to track POPs and monitor the health status of the ecosystem at spatial and temporal scales over the long-term.

PCB levels in harbour seal pups have been declining since 1984 indicating that regulations enacted in North America have reduced PCB inputs into the local coastal food web (Figure 2). PBDE levels in harbour seal pups increased exponentially from 1984 to 2003, but appear to be declining since then, reflecting the regulations put into place in early 2000s.

Figure 2. While PCB levels in harbour seal pups have been declining since 1984 in Puget Sound, USA, PBDEs levels increased exponentially until 2003 before declining. Source: Ross et al (2013).

Toxicity reference values (TRV) have been developed for PCBs in marine mammals. The most conservative toxicity reference value of 1.3 mg of PCBs per kilogram of lipid weight is the threshold above which disruption of the immune system, hormonal imbalances, and genetic effects have been observed in harbour seals. While PCB-associated health risks in harbour seals have been declining following regulations, all the pups sampled at Gertrude Island (Puget Sound, USA) exceeded the toxicity reference value (Figure 3). Similarly, PCB concentrations in 80 percent of Steller sea lions (Eumetopias jubatus) sampled in the Strait of Georgia exceeded the toxicity reference value for PCBs. There are currently no toxicity reference values for PBDEs.

Figure 3. The PCB-related health index of harbour seal pups sampled in British Columbia is relatively good (67–88 percent), however all of the seal pups sampled in the industrialized Puget Sound, USA, exceeded the toxicity reference value for PCBs, giving them a PCB-related health
index of zero. Source: Ross et al (2013).

Individual and Organization Actions:

• Learn more about contaminants of concern using the resource links in the full article.
• Reduce or eliminate the use of chemicals for cleaning or gardening.
• When buying furniture, ask about any flame retardants that might be found in products and try to avoid buying items that contain PBDEs.
• Take electronic equipment to a recycling and disposal centre near you.

Government Actions and Policy:

• Develop regulations to prohibit and control currently-used pesticides, flame retardants, and plasticizers that have the same properties that made PCBs problematic – namely chemicals that are persistent, toxic, and accumulate in organisms faster than they can be excreted.