Toxins

Environmental contaminants are a serious concern for marine animals. Many of these human produced chemicals are bioaccumulated, meaning that organisms absorb these chemicals at a rate faster than they are lost. The higher an animal is up the food chain the greater its exposure to these chemicals from their prey – they are biomagnified, as animals higher in the food chain will receive the chemical load from each of their prey.

An example is chinook salmon and northern resident killer whales. The salmon carry a load of the toxins known as PCBs in the range of 20 parts per billion. The northern resident killer whales that feed on them carry a load of up to 40 parts per million – a level approximately two thousand times higher – by eating 10 to 25 fish a day.

The main environmental toxins that are currently a concern for populations of marine mammals are primarily persistent organic pollutants (POPs) such as PCBs, PBDE’s and dioxins and furans.

Polychlorinated biphenyls (PCBs)
PCBs were used extensively in industrial processes beginning in the early 1900s. As early as 1947 it was understood that PCBs were toxic chemicals. They were used in a variety of adhesives, sealants and paints and as hydraulic fluids, however, they were especially common in large quantities as coolants and insulating fluids in electric transformers. In 1966, it was determined conclusively that they were a serious environmental contaminant and PCB production was eventually banned in the 1970s.

PCBs are now classified as persistent organic pollutants. This means that they are easily absorbed and not easily eliminated by animals. Additionally, they are biomagnified, in that they become more concentrated in animals that are higher in the food chain. PCBs 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. These effects have been implicated in population level impacts including reproductive failure and outbreaks of disease.

PCB concentrations declined rapidly in the environment following the implementation of regulations in the 1970s. However, as PCBs are difficult to metabolize and eliminate, large, long-lived species, such as killer whales continue to have high levels of PCBs. In killer whales, the northern resident population has the lowest level of PCBs at 40 parts per million (ppm), southern resident males carry 150 ppm and transients (feeding higher up the food chain on marine mammals) carry 250 ppm. Female killer whales carry roughly 1/3 the level of the male, likely as a result of transferring large concentrations of contaminants in milk to their first calf. Human females in BC, by comparison, carry from 49 to 1,454 parts per billion (ppb), with an average level of 180 ppb in milk fat. This means that transient male killer whales carry PCB loads 170 times higher than those levels found in women in BC that are a considered a health risk.

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 of these contaminants in the environment are:

- Coal fired utilities
- Municipal waste incinerators
- Metal smelting
- Diesel engines
- Land application of sewage sludge
- Burning treated wood
- Burning of trash

In BC, up until the early 1990s, pulp and paper mills produced high levels of dioxins and furans as by-products and released them to the environment in their effluent. Since chlorine bleaching in pulp mills was banned in 1992, levels of dioxins and furans in BC waters have dropped over 90%.
Dioxins and furans persist in the marine environment and are extremely toxic in minute amounts – the most toxic dioxin (TCDD or 2,3,7,8-Tetrachlorodibenzo-p-Dioxin) is ten times more toxic than the most toxic PCB. These chemicals easily accumulate in fatty animal tissues. Once in tissues of fish, dioxins and furans can be passed up the food chain to seabirds, marine mammals and humans.

Short-term exposure of humans to high levels of dioxins may result in skin lesions (a type of acne), patchy darkening of the skin, and altered liver function. Long-term exposure is linked to disruption of the immune system, the endocrine system and reproductive functions. Chronic exposure of animals to dioxins has resulted in several types of cancer. Killer whales are more able to metabolize dioxins and furans (Tanabe et al. 1988; De Swart et al. 1995; Ross et al. 2000) and thus carry much lower levels of these than they do PCBs.

Polybrominated diphenyl ethers (PBDE)
PBDEs are flame retardants that have been added to a variety of plastic products, including fabrics, furniture, and especially in electronics such as computers. There are three types of PBDEs; penta, octa and deca, representing the number of bromine atoms in the molecule (5, 8, and 10 respectively). The lighter penta and octa-PBDEs were determined to bioaccumulate easily in the environment and were subsequently banned in 1998. It was thought that the heavier deca-PBDEs were less likely to leak into the environment and less able to bioaccumulate, however, some recent studies raise the concern that this is not so. PBDEs are a relatively new chemical and are present in increasing concentrations in the environment.
PBDEs are chemically similar to PCBs. While PBDEs are less likely to cause dioxin-like effects, 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.

Transient and southern resident killer whales carry approximately 1 ppm of PBDEs with northern residents slightly lower at 200 ppb. Recent studies have shown that PBDE concentrations are increasing in marine and terrestrial mammals.

WHAT YOU CAN DO
The biggest source of toxins in the environment from individuals comes from the use of pesticides and from the backyard burning of trash and treated wood. Investigate the use of natural alternatives to pesticides and herbicides, and dispose of trash and treated wood in an environmentally sensitive manner.

Citizens can also petition their governments to restrict the emission / dumping of toxic contaminants into the environment.