Studies have shown that killer whales are some of the most contaminated marine mammals in the world.
Killer whales are apex (top) predators in the ocean’s food web and consequently receive high contaminant loads from their prey.
Persistent Organic Pollutants (POPs) and Cetaceans
Accumulation up the food web
Cetaceans are particularly vulnerable to Persistent Organic Pollutants (POPs), as they will accumulate in their thick layer of blubber. These toxins are difficult to metabolize and eliminate, especially in long-lived top predators – such as killer whales (Orcinus orca) – who feed higher up the food chain12, 13, 14. In fact, studies have shown that killer whales are some of the most contaminated marine mammals in the world14, 15, 16. Killer whales are apex (top) predators in the oceans’ food web, and consequently receive high contaminant loads from their prey. Research by the Coastal Ocean Research Institute’s Dr. Peter Ross has shown that Bigg’s (transient) killer whales, which prey on marine mammals, have the highest level of PCBs compared to resident, fish-eating killer whales13.
Toxins increase with age
In addition to accumulating more pollutants as they move up the food chain, cetaceans also gain more pollutants over time. PCB concentrations have been shown to increase with age in both resident and Bigg’s killer whales13, 17. Mongillo et al.18 found a similar trend in PBDEs; PBDEs increase over time as an individual ages, with concentrations doubling in individuals every three to four years.
Passing along generations
POPs are not only acquired by consuming contaminant-laden prey, but are also passed from female to calf during gestation and nursing through their rich, fatty milk. A killer whale female’s first calf receives the largest contaminant load compared to the load received by subsequent calves16. While this transfer of contaminants from female to calf may be very harmful for the calf, it does mean that females reduce their contaminant load significantly every time they rear young16, 19. This release of toxins through lactation implies that the POP load of juveniles can be much higher than their mothers19.
The transfer of pollutants from female to calf has also been observed in other species of cetaceans. Using earwax from a stranded six-month-old blue whale calf, Trumble et al. found that the calf had already accumulated approximately 20% of the total amount of POPs a blue whale (Balaenoptera musculus) would have in its body over an entire lifetime20. They suggested that for this to have occurred, a significant amount of pollutants must be passed from female to calf within the first twelve months of life. Desforges et al. found that female beluga whales (Delphinapterus leucas) in the St. Lawrence pass along a larger concentration of POPs to their offspring, not just through lactation21, but also via transplacental transfer 22. This study found that female belugas transferred 11.4% of the PCBs and 11.1% of the PBDEs within their blubber to their fetuses in the womb.
More contaminants near-shore
The location where cetaceans choose to forage can affect the contaminant load they receive. For example, the POP load of northern and southern resident killer whales is significantly different. While both populations have the same preference for Chinook salmon (Oncorhynchus tshawytscha), the toxin levels of southern resident killer whales are four to six times higher than that of the northern resident population13, 23. Southern resident killer whales spend most of summer and fall foraging for Chinook salmon in near-urban waters of the Salish Sea (the Strait of Georgia, Strait of Juan de Fuca and Puget Sound), while the northern residents forage in more remote waters along the central and northern coasts of B.C. during this time. Chinook in urbanized areas are exposed to greater toxin levels from being in more containment-laden environments. Consequently, the salmon consumed by southern resident killer whales contain higher POP concentrations, causing a discrepancy in toxin levels between the two resident killer whale populations. Furthermore, Chinook from these near-shore environments that have higher POP concentrations also contain less fat than northern Chinook23. As a result, southern resident killer whales have to consume more individual fish to satisfy their nutritional requirements, ultimately increasing their contaminant intake.
Noe even the Arctic is safe from pollutants
The Arctic is a region that appears seemingly untouched by modern human existence – sadly, this is not the case. POPs from all over the world arrive in the Arctic via atmospheric and oceanic circulation. Consequently, top predators – such as belugas, narwhals and polar bears – accumulate large amounts of contaminants, the way killer whales and other marine mammals do in southern latitudes closer to direct pollution sources24. Not just top predators are exposed to pollutants in the Artic, even baleen whales that feed on krill and smaller fish obtain high contaminant loads. Artic minke whales (Balaenoptera acutorostrata) that feed at lower levels of the food web – foraging mainly for krill, herring and capelin25 – are still subjected to accumulating high levels of pollutants. Minke whales in the Arctic contained 1.5 to 7 times higher levels of POPs than minke whales observed off of Japan, the North Sea and the North Atlantic26.
The toxic problem with food scarcity
Contaminants are problematic for cetaceans in years of limited prey availability. POPs that have accumulated in their fatty tissues (blubber) can be mobilized in years of food shortage, when these fat stores are metabolized for energy27. Once these fat tissues are broken down, the stored POPs are released causing higher concentrations of toxins within the body. Fat stores are also mobilized more readily during lactation, causing high contaminant loads to be passed from female to calf – and contaminant loads especially high for the female’s first-born calf27. For southern resident killer whales, a decrease in salmon abundance is related in increased periods of mortality28 and a decrease in females producing new calves 29.
Food web bioaccumulation of contaminants in killer whales (Miller et al. 2020)
Contaminants move after entering the marine environment, and sediment has been shown to be both a place of “storage” and a subsequent “source” of contaminants, making it an important component of marine contaminant monitoring. Through deposition and resuspension of sediment, contaminants are stored and remobilized, respectively, re-exposing aquatic organisms (Alava and Gobas, 2016).
Oil Spills and Cetaceans
Oil spills are a major threat to marine life, especially for cetaceans that must interact with the surface to breathe. Cetaceans do not appear to avoid areas affected by oil. They have little, if any, sense of smell and are unable to detect oil vapour in the air. While they do have excellent eyesight, they do not appear to recognize surface oil as a hazard. Oil vapour is very toxic and causes respiratory distress when inhaled. Furthermore, cetaceans are in danger if they eat oiled prey. Bigg’s (transient) killer whales can consume oil adhering to the bodies and fur of their mammalian meals, and ingestion of oil can cause serious long-term damage to internal organs30. Harbour porpoise are a high-risk species for oil spill due to their high preference for squid, which is highly susceptible to being coated in oil. Baleen whales are particularly vulnerable to oil while surface feeding, as oil may stick to their baleen while they “filter feed” near oil slicks30. Oil spills affect cetaceans at the population level, due to dramatic losses of individuals. These deaths have drastic long-term effects on the population, and years can go by before the population begins to recover. In addition to increase mortality rates, cetaceans exposed to oil have been shown to have reduced reproductive success and many long-term health effects that make them more susceptible to pathogens31. The 1989 Exxon Valdez disaster in Alaska sadly illustrated the damaging effects of oil spills on killer whale populations. Alaska’s AB resident killer whale population was photographed in an oil slick shortly after the spill, and suffered the loss of 33% of its members within a year32. Its rate of reproduction has been lower than average ever since, and the pod fractured following the death of a matriarch. Members of the AT1 transient population were also photographed in oil from the Exxon Valdez, and 41% of its members were lost in the following year. There has been zero reproduction in this group since the spill and this genetically distinct transient population is on the verge of extinction with almost no chance of recover
Regulating Contaminants in Canada
The Government of Canada has aided in measures to reduce the release of POPs through stricter regulations regarding disposal of chemicals and wastewater discharge. PCBs have been banned from use in North America since the 1970s; PBDEs are prohibited in Canada under the Prohibition of Certain Toxic Substances Regulations, 2012 ; and the Canadian government has implement measures to reduce emissions of dioxins, furans and mercury33. In addition, the Government of Canada is working with other countries to reduce POPs from outside sources. The ban on PCBs in the 1970s appears to have been effective at reducing the amount of PCBs in the marine environment. Concentrations of PCBs within marine sediments have begun to decrease due to reduced input from human sources and through the natural process of sedimentation – the burying of sediments. The reduction of PCBs within the marine environment is seen in killer whales born after the ban, which are not accumulating higher concentrations with age18. However, acts such as marine dredging or natural displacement due to benthic organisms can release these toxins back into the water column to reenter the food web, which is one of the reasons PCBs are still present in the marine environment today. Possible solutions to reduce the risk of POPs with marine sediments reentering the water column involve disposing highly contaminated sediments in non-critical areas containing high sedimentation rates in order to bury contaminants – limiting their release into the food web34. To improve overall water quality, the Government of Canada introduced the Wastewater System Effluent Regulations in 2012, which placed stricter regulations on wastewater treatments. These protocols must be implemented by high-risk treatment facilities starting in 2020, with all facilities meeting regulations by 2040. As wastewater is the main source of PBDE contamination, these regulations were made to reduce their concentrations within the marine environment. Under the Environmental Response System, the Government of Canada has put protocols in place to respond to an oil spill. Under this mandate, dedicated teams based out of Victoria, Richmond and Prince Rupert are available 24-7 to respond to an oil spill. Oil spills are reported directly to the closest regional Canadian Coast Guard Station – in B.C., this would the Pacific Station (1-800-889-8852). In addition, the Government of Canada also employs the National Aerial Surveillance Program to conduct aerial surveillance to better detect oil spills in Canadian waters. Canada’s Marine Oil Spill Preparedness and Response Regime of the Environmental Response System makes polluters accountable for their spills, and responsible for the cleanup and response costs. Furthermore, all ships transiting Canada waters and all oil-handling facilities must have an oil response plans in place.
What can you do to help?
- Use your consumer power to demand PBDE-free products. Choose furniture, carpet and electronic products that do not use these hazardous chemicals.
- Reduce the use of hazardous chemicals by choosing household cleaners, pesticides and fertilizers, which are not toxic to your surroundings. If chemicals are toxic to the oceans, they are also a danger to you and your family. Support companies that make clean products and consume less pesticide-dependent foods, thereby reducing the amount of pesticides used.
- Compost your household, kitchen and yard wastes, which makes an excellent fertilizer.
- Never burn treated wood and trash. This releases POPs into the environment.
- Recycle all electronic equipment responsibly.
- Never pour any oil or other chemicals onto the ground or into drains. Many of these chemicals make their way to the ocean. Even if you live far from the ocean, the chemicals from your area can be transported to the ocean via local streams and rivers. Maintain your vehicles to prevent oil from leaking onto the road, which can go down drains and end up in the ocean.
- Report all spills. All pollution and potential spills should be reported to the Canadian Coast Guard at 1-800-889-8852 (Pacific Division) or on Marine Channel 16. When reporting a spill please provide: your name, telephone number, location of the spill, quantity of the spill, type of product spilled and on scene weather.
- Recycle all oil and chemicals. Most communities have recycling centres that will accept used oil and other chemicals for recycling.
- Your voice counts. Citizens can also petition their governments to restrict the emission / dumping of toxic contaminants into the environment.
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