Environmental contaminants are a serious concern for many marine species. The main environmental toxins that are currently a concern for populations of marine mammals are known as persistent organic pollutants (POPs) and include PCBs, PBDE’s and dioxins and furans. Many of these human produced chemicals are bioaccumulated, meaning that organisms absorb these chemicals at a rate faster than they are lost. Predatory animals acquire the lifetime accumulation of POP’s of the animals they eat. This leads to biomagnification, whereby the concentration of POP’s increases greatly at every step in the food chain, and top predators, such as killer whales, end up with extremely high levels.
Polychlorinated biphenyls (PCBs)
Polychlorinated biphenyls (PCBs) were first introduced into the environment in the early 1900s where they were used in a variety of adhesives, sealants, paints, hydraulic fluids, coolants and electric transformer insulating fluids. PCBs were banned in Canada and the US in the 1970s but persist in the environment. They are still produced and used in some parts of the world.
According to Dr Peter Ross at the Institute of Ocean Sciences, PCBs are considered of highest concern to marine life. PCB’s have been associated with toxic effects in marine mammals such as endocrine disruption, which can cause impairment of reproduction, development, and other hormonally mediated processes, and immunotoxicity, giving rise to an increased susceptibility to infectious diseases and cancers.
Concentrations of polychlorinated biphenyls (PCB’s) in killer whales and humans.
Polybrominated diphenyl ethers (PBDE)
PBDEs are a relatively new class of flame retardants that have been added to a variety of plastic products, including fabrics, furniture, and especially electronics such as computers. PBDEs are present in increasing concentrations in the environment and are still produced and used in North America. PBDEs are chemically similar to PCBs and the metabolites of PBDEs (the chemical that forms when the body attempts to break down PBDEs) are likely to interfere with hormones, uptake of Vitamin A, neurological development and the immune system.
Dioxins and Furans
Dioxins and furans are closely related chemicals that are produced when organic material is burned in the presence of chlorine. Common sources include coal-fired generators, municipal waste incinerators, metal smelting, pulp and paper mills, diesel engines, sewage sludge, and the burning of preservative-treated wood and trash. Dioxins and furans persist in the marine environment and are extremely toxic in minute amounts – the most toxic dioxin is ten times more toxic than the most toxic PCB.
POPs and Cetaceans
POPs are stored in the fat of animals that consume them, which makes marine mammals particularly vulnerable as contaminants will accumulate in their thick layer of blubber. Endocrine system disruption and immunotoxicity are the two serious issues that arise from POP exposure, and these toxins are difficult to metabolize and eliminate in long-lived species such as killer whales. In fact, recent studies have shown that killer whales of the Pacific Northwest are some of the most contaminated marine mammals in the world. Killer whales are top predators in the oceans’ food chain and therefore receive high contaminant loads from their prey. Research by Dr. Peter Ross has shown that Bigg’s killer whales (transients), being mammal predators, feed highest up the food chain and therefore have the highest level of POPs.
Where the animals forage may also affect the contaminant load they receive. For example, the difference in northern and southern resident killer whales’ POP accumulation is significantly different. While both populations have the same preference for chinook salmon, the southern residents killer whales, who spend the summer months around the Puget Sound area of Washington and in the southern Strait of Georgia in British Columbia, have accumulated toxin levels four times higher than the northern resident population, found along the central and northern coasts of British Columbia during the summer and fall. Cullon et al found that the cause of this discrepancy is the Chinook that these populations eat. The salmon consumed by southern resident killer whales is exposed to higher toxin levels in more urbanized areas. Southern residents also need to eat more of this contaminated prey, as Chinook nearing the end of their migrations in the south are less fatty.
POP’s are not only acquired by consuming contaminant-laden prey, but are also passed from female to calf during gestation and nursing. They are mainly transferred via the rich, fatty milk produced by the mother. A female’s first calf receives the largest contaminant load compared to the load received by subsequent calves. 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 young. This release of toxins through lactation means that the POP load of adult females is roughly 30% less than that of adult males.
The Arctic is a region that appears seemingly untouched by modern human existence, but sadly this is not the case. POPs from all over the world arrive in the Arctic via atmospheric and ocean circulation. The result is that animals at the top of the food chain, such as belugas, narwhals and polar bears, accumulate tremendous amounts of contaminants the way killer whales and other marine mammals do in more southern latitudes, closer to direct pollution sources. Research by Desforges et al. attests to the issue of Arctic pollution and female POP offload to offspring, although in this case it was via transplacental transfer and not lactation. This study found that female belugas transferred 11.4% of their PCB’s and 11.1% of their PBDE blubber burden to their fetuses in utero.
Oil spills are also a major threat to marine life and 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 eye sight, they don’t appear to recognize surface oil as a hazard. Oil vapour is very toxic and causes respiratory distress when inhaled. Whales are also in danger if they eat oiled prey. Bigg’s killer whales (transients) 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 organs. Baleen whales are also particularly vulnerable to oil while feeding, as oil may stick to their baleen while they “filter feed” near oil slicks.
The 1989 Exxon Valdez disaster in Alaska sadly illustrated the damaging effects of oil on killer whale groups. One resident pod (AB) was photographed in an oil slick shortly after the spill and suffered the loss of 33% of its members within a year. 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 recovery.
WHAT YOU CAN DO
• 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-dependant 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 POP’s 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 in streams and rivers. Maintain your vehicles to prevent oil from leaking onto the road which will then go down a drain and into the water.
• Recycle all oil and chemicals. Most communities have recycling centers 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.
Cullon, D.L., M.B. Yunker, C. Alleyne, N.J. Dangerfield, S. O’Neill, M.J. Whiticar, P.S. Ross. 2009. Persistent organic pollutant in chinook salmon (Oncorhynchus tshawytscha): Implications for resident killer whales of British Columbia and adjacent waters. Environmental Toxicology and Chemistry 28(1): 148-161
Desforges, J.P., Ross, P.S., Loseto, L.L. 2012. Transplacental transfer of polychlorinated biphenyls and polybrominated diphenyl ethers in arctic beluga whales (Delphinapterus leucas). Environmental Toxicology and Chemistry 31(2): 296-300.
Ross, P.S., De Swart, R.L., Reijnders, P.J.H., Van Loveren, H., Vos, J.G., and Osterhaus, A.D.M.E. 1995. Contaminant-related suppression of delayed-type hypersensitivity and antibody responses in harbor seals fed herring from the Baltic Sea. Environ. Health Perspect. 103: 162–167.
Ross, Peter S. 2006. Fireproof killer whales (Orcinus orca): flame retardant chemicals and the conservation imperative in the charismatic icon of British Columbia, Canada. Can. J. Fish. Aquat. Sci. 63: 224–234