Descriptions of some toxic contaminants found in the Pacific and Yukon Region

Chlordane

Chlordane was used as an insecticide in Canada and the United States from 1949 to 1995. It is not a single chemical, but a mixture of chlordane and many related chemicals. It bioaccumulates in the tissues of fish, birds and mammals.

Use: Chlordane was registered in Canada in 1949 for the control of insect pests in crops and forests, as well as for domestic and industrial applications. It was never manufactured in Canada. Most uses of chlordane were phased-out by the mid-1970s prior to regulatory control in Canada and in response to environmental and safety concerns. It adheres strongly to surface soil particles and can stay in the soil for 20 years. It does not easily dissolve in water. Most chlordane leaves the soil by evaporation to the air, where it may be redistributed by air currents, contaminating areas far from their original application site.

Chemical Structure: Chlordane (C₁₀H₆Cl₈)

Legislation: In December 1985, the use of chlordane was suspended with the exception of its use to control subterranean termites. Even its use against termites was voluntarily discontinued by the registrant in 1990, with the understanding that the existing stock would be sold, used or disposed-of by the end of 1995. After this date, any sale or use of chlordane in Canada represents a violation of the federal Pest Control Products Act

DDE

DDE (dichlorodiphenyldichloroethylene) is a breakdown product of DDT (dichlorodiphenyltrichloroethane) that can cause a wide variety of health problems in humans and wildlife. In humans it may cause cancer and damages to the liver and to the nervous and reproductive systems. In birds it can also result in eggshell thinning. DDT-related compounds bioaccumulate in the tissues of fish, birds and mammals and biomagnifie in the ecosystem. DDE is the most persistent of all the DDT metabolites.

Use: DDT is a toxic synthetic insecticide used to kill agricultural pests, as well as control mosquito-borne diseases in tropical regions. Although it has been banned in North America, Europe and several other countries, it continues to be used in Asia, Africa and Central and South America in part for the control of life-threatening malaria and typhus. Recently some tropical countries have reluctantly resumed use of DDT because of rising cases of malaria following the phase-out of DDT use. The DDE present in the Canadian environment originates from two sources: a) residues from historic application to agriculture and b) atmospheric transportation from other regions.

Chemical Structure: DDE (C₁₄H₈Cl₄)

Legislation: Most uses of DDT was banned in Canada in 1974. However, the consumption of existing stocks of DDT was permitted until 1990. As of January 1, 1991 the sale and use is no longer permitted under the federal Pest Control Products Act. The World Health Organization has called for a worldwide ban on DDT by 2007 because of its probable link to cancer and other health problems in humans and its persistence in the environment.

Dieldrin

Dieldrin and aldrin are chemicals that were widely applied in agricultural areas throughout Canada and the world. Both chemicals are toxic and bioaccumulative. Aldrin does break down to dieldrin in living systems but dieldrin is known to resist bacterial and chemical breakdown processes in the environment.

Use: Aldrin was used to control soil pests (namely termites) on corn and potato crops. Dieldrin was an insecticide used on fruit, soil and seed. It persists in the soil with a half-life of five years at temperate latitudes (Orris et al. 2000). Both aldrin and dieldrin may be volatilized from sediment and redistributed by air currents, contaminating areas far from their sources. Aldrin and dieldrin have been measured in Arctic wildlife suggesting long range transport from southern agricultural regions (Orris et al., 2000).

Chemical Structure: Dieldrin (C₁₂H₈Cl₆O)

Legislation: Both aldrin and dieldrin have been banned in most developed countries but aldrin is still used as a termiticide in Malaysia, Thailand, Venezuela and other parts of Africa. In Canada, the sale of dieldrin and aldrin was restricted in the mid-1970s, with the last registered use of the compounds in Canada being withdrawn in 1984.

Dioxins and Furans

Chlorinated dioxins are a group of 75 compounds consisting of two benzene rings linked by two oxygens and with at least one chlorine atom. Chlorinated furans are a group of 135 compounds consisting of two benzene rings linked by one oxygen and with one or more chlorine atoms. The dioxins and furans with chlorine atoms at the 2, 3, 7, and 8 positions are the most toxic. Of these, 2,3,7,8-chlorodibenzo-p-dioxin (T4CDD) has the highest toxicity, is the most studied and best known, and is the standard to which the toxicity of the other dioxins and furans are compared.

Use: Dioxins and furans are byproducts of a wide variety of industrialized activities, such as chlorine bleaching in kraft pulp and paper mills and incineration of municipal and industrial wastes. Levels of dioxin and furans, are highest in BC and Yukon wildlife living near pulp and paper mills. These compounds are highly persistent, with the potential to become increasingly concentrated in living tissues as it moves up the food chain.

Chemical Structure: Dioxin (C₁₂H₄Cl₄O₂) Furan (C₁₂H₄Cl₄O)

Legislation: In 1992, the  Pulp and Paper Mill Effluent Chlorinated Dioxins and Furans Regulations were introduced under the Canadian Environmental Protection Act (CEPA). The regulations required that all mills using chlorine bleaching process achieve the maximum discharge limit in the final effluent of 15 parts per quadrillion (ppq) for dioxin (2,3,7,8-TCDD) and 50 ppq for furan (2,3,7,8-TCDF) by January 1, 1994.

Mercury

Mercury (Hg) is a highly toxic element that is found both naturally and as an introduced contaminant in the environment. Although its potential for toxicity in highly contaminated areas such as Minamata Bay, Japan, in the 1950's and 1960's, is well documented, research has shown that mercury can be a threat to the health of people and wildlife in many environments that are not obviously polluted. The risk is determined by the likelihood of exposure, the form of mercury present (some forms are more toxic than others), and the geo-chemical and ecological factors that influence how mercury moves and changes form in the environment.

The toxic effects of mercury depend on its chemical form and the route of exposure. Methylmercury [CH₃Hg] is the most toxic form. It affects the immune system, alters genetic and enzyme systems, and damages the nervous system which impacts coordination and the senses of touch, taste, and sight. Methylmercury is particularly damaging to developing embryos, which are five to ten times more sensitive than adults. Exposure to methylmercury is usually by ingestion, and it is absorbed more readily and excreted more slowly than other forms of mercury. Elemental mercury, Hg(0), familiar liquid (quicksilver) form in thermometers and motion switches, causes tremors, gingivitis, and excitability when vapors are inhaled over a long period of time. If elemental mercury is ingested, it is absorbed relatively slowly and may pass through the digestive system without causing damage. Ingestion of other common forms of mercury, such as the salt HgCl₂, which damages the gastrointestinal tract and causes kidney failure, is unlikely from environmental sources. Emissions of mercury to the environment can have serious effects on human health when humans consume fish and wildlife from contaminated areas.

Like PCBs, dioxins, furans and DDE, mercury undergoes bioaccumulation. Bioaccumulation is the process by which organisms (including humans) can take up contaminants more rapidly than their bodies can eliminate them, thus the amount of mercury in their body increases over time. If for a period of time an organism does not ingest mercury, its body burden of mercury will decline. If, however, an organism continually ingests mercury, its body burden can reach toxic levels. The rate of increase or decline in body burden is specific to each organism. For humans, about half the body burden of mercury can be eliminated in 70 days if no mercury is ingested during that time. Adding to this problem is the fact that mercury concentrates in the muscle tissue of fish. So, unlike organic contaminants (for example PCBs and dioxins), which concentrate in the skin and fat, mercury cannot be filleted or cooked out of consumable game fish.

Use: Mercury is a naturally occurring volatile metal that will be released from any environment with elevated temperature such as volcanoes. The primary human-related sources of mercury include: coal combustion, chlorine alkali processing, waste incineration, and metal processing. It has been used at gold mine sites to extract gold. Best estimates to date suggest that human activities have about doubled or tripled the amount of mercury in the atmosphere, and the atmospheric burden is increasing by about 1.5 percent per year. Mercury residues can persist from past industrial and agricultural releases. However, recent concerns focus on mobilization of mercury from man-made reservoirs and deposition of atmospherically transported mercury from coal-fired utilities and municipal waste incineration. These continental to global scale occurrences of mercury contamination cannot be linked to individual emissions of mercury, but instead are due to widespread air pollution. In Canada, methylmercury is released during mining and other industrial activities. Most emissions come from base metal smelting.

Legislation: Since 1988, Canada’s major copper and lead smelters have made major changes to reduce emissions by 94%. By 2008, these smelters will reduce mercury emissions by a further 800 kg/year to less than 2 grams of mercury per tonne of product. Canadian Standards are among the most stringent limits anywhere.

PCBs

Polychlorinated biphenyls are mixtures of up to 209 individual chlorinated compounds (known as congeners). PCBs are either oily liquids or solids that are colorless to light yellow. Some PCBs can exist as a vapor in air. PCBs have no known smell or taste. Many commercial PCB mixtures are known in North America by the trade name Aroclor. Polychlorinated biphenyls (PCBs) persist in the environment and are passed up the food chain, with the highest levels accumulating in predatory birds and mammals.

Use: PCBs were predominantly used as coolant insulants and heat transfer agents in a number of electrical products such as transformers and capacitors. PCBs were also used in a wide variety of products including printing inks, adhesives and paints. There are no known natural sources of PCBs.

Chemical Structure: General structure C₁₂H_10-xClx where x = 1 to 10

Legislation: Although the manufacture, import and most non-electrical uses of PCBs has been banned in North America since 1977, some uses of PCBs are still allowed. Release of materials containing small concentrations of PCBs to the receiving environment is permitted but is highly regulated.

Polybrominated diphenyl ethers

Polybrominated diphenyl ethers (PBDEs) are a group of substances primarily used as flame retardant additives and they are identical to PCBs except the chlorine atoms of the PCB molecule is replaced with a bromine. Like PCBs they are complex substances composed of many congeners and isomers (a total of 209 possible) of which more than 30 are regularly measured in environmental samples. PBDEs have been measured in air, sediments, fish, sewage sludge, birds, marine mammals and in human tissue. Research has shown that they can be persistent, bioaccumulative and toxic. Results from archived biological samples provide evidence that levels of PBDEs are on the rise in North America and Canadian data are showing that high PBDE levels measured are approaching those of some PCBs. This compound in the breast milk of North American women has increased from 2 to 200 parts per billion in the 1990s (from K. Betts 2001) and by 300-400 times in Canadian lake trout from 1975 to 2000 (from M. Alaee 2003). The significance of elevated burdens of these chemicals in humans and in wildlife is unknown but their toxicology is currently under investigation. However, some research suggests liver and neurodevelopment toxicity and potential impact on thyroid function.

Use: PBDEs have been used extensively over the past two decades as flame retardants in most types of polymers. They are used in textiles, polyurethane foam, plastics, computers, wire and cable insulation, furniture, building materials, carpets and in vehicles.

Chemical Structure:

Legislation: Although there is currently no legislation on PBDEs in Canada, Environment Canada and Health Canada are currently researching the effect of PBDE’s on the environment and human health. This may result in the restriction of this chemical. Recently the European Union (EU) has voted to ban two PBDE formulations by July 1, 2003 and a third formulation could be banned by 2006.

Toxaphene

Toxaphene (C₆H₁₀C_l8) is an insecticide composed of a complex mixture of chlorinated compounds (up to 1400 possible compounds). It is a persistent organochlorine contaminant found in water and soil and does bioaccumulate in aquatic and terrestrial biota. It can also be transported atmospherically to areas where it has never been used.

Use: It was one of the world's most widely used insecticides in the 1970s because it replaced DDT as an insecticide in many agricultural uses. In the United States it was one of the most heavily used insecticides until 1982. It was used primarily in the southern US to control insect pests on cotton and other crops. In the early 1990s, toxaphene was produced in Africa and Central America; the heaviest current use is thought to be in Africa (WWF Fact sheet on Toxaphene). Presently it is prohibited in Canada, USA and in 57 other countries worldwide, and is severely restricted in another 12. The only known use in British Columbia was to rid lakes of competing fish species prior to stocking them with sport fish species, such as rainbow trout. Toxaphene levels in fish of Yukon lakes have been found high enough to be of health concern to human consumers while elevated levels have also been measured in fish from the Rocky Mountains and the Fraser River basin. The primary source of toxaphene is likely atmospheric deposition.

Legislation: Toxaphene was banned in Canada in 1985 and in 1990 in the USA. Sale or use is illegal under the Canada federal Pest Control Products Act.

Toxic Equivalence (TEQ)

Because dioxins, furans and PCBs may elicit similar toxic effects, a system has been developed to estimate the combined toxic effect of exposure to these types of chemicals. The most common dioxin, furan and PCB congeners having "dioxin-like" activity have been assigned a “toxic equivalence factor” (TEF) relative to the most toxic chlorinated dioxin congener with chlorine atoms at the 2,3,7 and 8 positions. For example, the TEF of dioxin 2378-TCDD is 1, whereas the TEF of PCB 126 is 0.1, as research has determined that PCB 126 is 1/10th as toxic as 2378-TCDD. The TEFs quoted here are the TEFs appropriate for birds; because other animal taxa, such as mammals or fish have different physiologies, they also have different sensitivity to individual congeners and thus different TEF values. The toxicity of a combination of PCBs, dioxins and furans is calculated by multiplying the concentration of the contaminant by its TEF. This produces a toxic equivalent quotient (TEQ) and the total toxicity of a mixture of chemicals can be estimated by summing the TEQs for all contaminants present.

Toxic Equivalence Factors (TEF) for selected dioxins and furans.

Toxic Equivalence Factors (TEF) for selected PCBs.

Bioaccumulation and biomagnification

Many toxic contaminants are bioaccumulated in organisms and biomagnify in the ecosystem. Bioaccumulation is when a compound accumulates in a single organism because its excretory system is unable to eliminate the compound at the same rate as it ingests it. Biomagnification is when concentrations of a compound increase through the food chain due to bioaccumulation. For example, the biomagnification of TCDD as it is bioaccumulated by different organisms is illustrated in the figure. As shown, the dioxin TCDD is bioaccumulated in many organisms and biomagnified by the food chain. For example, from a pollution source with a TCDD level of 0.01 ppt, levels in top predators such as Bald Eagles and Great Blue Herons are thousands of times higher.

Reference:

Some of the following references contain Web sites that are not under the control of Environment Canada (EC) and they are provided solely for the convenience of users. Environment Canada is not responsible for the accuracy, currency or the reliability of the content. Environment Canada does not offer any guarantee in that regard and is not responsible for the information found through these links, nor does it endorse the sites and their content. Users should be aware that information offered by non Government of Canada sites that are not subject to the Official Languages Act, and to which Environment Canada links, may be available only in the language(s) used by the sites in question.

• Alaee, M. 2003. Flame Retardants: A Threat to the Environment. Environment Canada, National Water Research Institute, web sitehttp://www.nwri.ca/sande/may_jun_2002-2-e.html.
• Betts, K.S. 2001. Rapidly rising PBDE levels in North America. Environmental Science & Technology, Science News - December 7, 2001.
• Orris, P., L. Kaatz Chary, K. Perry and J. Asbury. 2000. Persistent organic pollutants (POPs) and human health. A publication of the World Federation of Public Health Associations (WFPHA). Washington, DC. 45pp.
• U.S. Environmental Protection Agency. 2003. PCB ID - Toxicity Equivalency Factors (TEFs), web sitehttp://www.epa.gov/toxteam/pcbid/tefs.htm.
• Van den Berg, M., et al. (World Health Organization - WHO), Toxic Equivalency Factors (TEFs) for PCBs, PCDDs, PCDFs for Humans and Wildlife, Environmental Health Perspectives, Volume 106, Number 12, December 1998, pp. 775 - 791.
• World Wildlife Fund. Toxics - Fact Sheets, web site http://www.worldwildlife.org/toxics/pubs.cfm.