Persistant Organic Pollutants
Environmental contaminants are a serious concern for killer whales. Recent studies have shown that the killer whales of the Pacific Northwest are some of the most contaminated marine mammals in the world. The main contaminants of concern are known as persistent organic pollutants (POPs) and include PCBs, PBDE’s and dioxins and furans. These chemicals break down extremely slowly in the environment or in the bodies of animals that ingest them. Predators 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 like killer whales end up with extremely high levels.
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.
Polybrominated diphenyl ethers (PBDEs) are a relatively new class of fire retardant chemicals. They are widely used in plastic products including fabric, furniture and carpets and in computers and other electronic devices. They are still produced and used in North America.
Dioxins and furans
Dioxins and furans are produced and released into the environment when organic material is burned in the presence of chlorine. Common sources include coal-fired generators, municipal waste incinerators, metal smelting, diesel engines, sewage sludge, and the burning of preservative-treated wood and trash.
Killer whales are top predators in the oceans’ food chain and therefore receive high contaminant loads from their prey. Research by Dr. Peter Ross of the Institute of Ocean Sciences has shown that transients, being mammal predators, feed highest up the food chain and therefore have the highest level of POPs. Southern residents, living in a more urbanized coastal area, have higher loads than their northern counterparts.
POPs are stored in the fat of animals that consume them. These toxins are difficult to metabolize and eliminate in long-lived species such as killer whales. They are known to affect the endocrine system in marine mammals, potentially causing impairment of reproduction, development and immune system function, making them more susceptible to infectious disease and cancers.
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 milk produced by the female. A female’s first calf receives the largest contaminant load (at least 14 years worth of accumulated POPs) 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 a calf. This release of toxins through lactation means that the POP load of adult females is roughly 30% less than that of adult males, on average.
Oil spills are also a significant threat to all killer whales. Killer whales 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 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, particularly transient killer whales that may consume oil adhering to the bodies and fur of their mammalian prey. Ingestion of oil can cause serious long-term damage to internal organs.
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.
Photo: Graeme Ellis
Killer whales are one of the most polluted marine mammals on earth
The load of PCBs is greatest in Transient killer whales.
Photo: Alana Phillips
Killer whale calves receive toxins from their mothers while nursing.
Photo: Caitlin Birdsall
Male killer whales carry a higher load of persistant organic pollutants than their female counterparts.