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TOXIC CHEMICALS IN ATLANTIC CANADA - THE NATURE OF PAHs The comforting fire that graces your hearth or keeps your car or furnace humming is really a chemical reactor. Although most of the substances it produces (such as water and carbon dioxide) are more or less harmless, the burning of fuel can also produce a variety of chemicals which are harmful to the environment. One of the most prominent groups of chemicals in smoke, soot and exhaust are polynuclear aromatic hydrocarbons or PAHs natural products of the incomplete combustion of carbon compounds. When released directly into the atmosphere through burning, PAHs may attach to small particles and be transported for considerable distances before returning to earth directly, or in rainfall. PAHs are frequently transported to Atlantic Canada through the atmosphere from outside the region. In fact, they have been found in precipitation in relatively pristine Kejimkujik National Park in south-central Nova Scotia. Present in low concentrations virtually everywhere, PAHs occasionally reach elevated concentrations as the result of prolonged industrial activities involving burning, or by releases of materials, such as creosote-based wood preservatives, which contain PAHs in high concentrations. PAHs are a concern because some of them can cause cancers in humans and are harmful to fish and other aquatic life. Individual Emissions:
Industrial Emissions:
Natural Emissions
The Tar Ponds in Sydney, Nova Scotia, is one of the largest sources of PAHs in Canada, and the site of a massive clean-up program. Elevated concentrations of PAHs have also been found in soils as well as ground and surface waters at wood preservation facilities in the Maritimes which use creosote. Elevated PAH concentrations are restricted mostly to areas which have received industrial or urban discharges containing PAHs over long periods, such as the harbours at Sydney and Halifax, Nova Scotia, and Saint John, New Brunswick; and at some wood preservation plants. THE UPS AND DOWNS OF PAHs PAHs are a group of more than a hundred organic compounds composed of two or more carbon rings derived from benzene. As a rule, when PAH compounds grow in molecular weight, their solubility in water decreases, solubility in fat tissues increases, and their melting and boiling points increase. Various PAHs usually occur together at a contaminated site, and their overall properties and effects vary according to the combination of PAH compounds involved. THE BEHAVIOUR AND FATE OF PAHs Forest fires, volcanic eruptions and decaying organic matter are all natural sources of PAHs. Industrial processes such as aluminum production using old technology and iron smelting, petroleum refining, coal coking, thermal power generation, tar paper production, and wood preservation operations using creosote, are all examples of major human sources. PAHs enter water directly from the air with dust and precipitation, or on particles washed from the soil by runoff. PAHs dissolved in water can be "taken up" by plants, and are released into soil and water when the plants die, decompose or are burned. PAHs also find their way directly into the aquatic environment through discharges from various human activities, including: industrial and domestic sewage effluents; spills and leaks of PAH- containing materials such as oils; runoff from paved roads, parking lots, and the grounds of wood preservation plants; offshore drilling; and leaching and disposal of refinery effluents. Despite these releases, concentrations of PAHs in ground and surface waters in the Atlantic region are generally low. PAHs are slow to degrade in the environment, and sediments in particular are "sinks" where chemicals tend to concentrate. Some PAHs can also accumulate in tissues of marine organisms, although they tend to stay at the lower levels of the food chain. High concentrations of PAHs in organisms can occur, however, when they are directly exposed to high concentrations in the environment. For instance, high PAH concentrations have been found in lobster from heavily contaminated Sydney Harbour, Nova Scotia; and in mussels and periwinkles near creosoted wharf pilings throughout the Atlantic provinces. ENVIRONMENTAL CONCERNS Elevated concentrations of PAHs in the air and water can lead to significant environmental effects. In marine and freshwater systems, PAH concentrations are rarely high enough to kill aquatic organisms outright. Physical and biochemical changes often result from prolonged exposure to lower levels. Elevated PAH concentrations in sediments have resulted in liver damage and tumours in flatfish (which live on or near the bottom), and can also cause liver enlargement and effect reproduction. Some fish, however, increase their production of enzymes which break down PAHs, possibly reducing the chemicals' toxic effects. Organisms such as mussels and oysters lack the enzyme systems which break down PAH compounds, and sometimes accumulate high concentrations. Instances of extreme PAH contamination in Atlantic Canada tend to be localized at sites where chemicals and combustion by-products containing PAHs were poorly managed in the past. The Sydney Steel plant and coke ovens is a case in point, serving as the source of high quantities of PAHs for more than 80 years. PAHs deposited at the site continue to enter the environment long after the coke ovens ceased operation in 1988. Releases from the facility to the marine environment led to elevated concentrations of PAHs in marine organisms in Sydney Harbour and closure of the lobster fishery there. Concentrations of benzo(a) pyrene, a highly carcinogenic PAH, in the livers of lobster averaged 200 times greater than lobster from uncontaminated areas. Mussels in Sydney Harbour have been found to have total PAH concentrations 40 to 80 times higher than those from uncontaminated areas. All major industries using fossil fuels generate PAHs, and higher concentrations are usually found near heavy industry. Many of the industrialized harbours in the Maritimes have above normal PAH concentrations. The wood preservation industry is a major source of local PAH contamination which occurs mainly in soils on the plant premises, but also in ground water and adjacent surface waters. Creosote can also leach from treated lumber in utility poles, railway ties, bridges, wharves and pilings into marine and freshwater systems, ground water and soil where it leads to increased concentrations of PAHs. Increased use of wood as an industrial and residential fuel has also led to greater releases of PAHs into the atmosphere throughout the Atlantic region. Concerns about smoke from extensive use of home wood-burning appliances in some urban areas led Environment Canada to carry out studies of PAH and particulate levels in Truro and Sackville, Nova Scotia, in 1984 and 1985. The studies indicated, however, that there were no public health impacts. REGULATING PAHs PAHs are controlled under various laws, regulations and agreements designed to protect the environment and human health. PAHs were assessed for environmental and human health effects under the Canadian Environmental Protection Act's (CEPA) Priority Substances Assessment Program. PAHs were judged to be toxic to the environment based, in part, on observed effects on aquatic life at several sites in Canada including industrialized harbours. In addition, five specific PAHs were judged to be toxic to human health based on studies in which long-term exposure to high concentrations of those substances was associated with an increased incidence of cancer in laboratory animals. Due to the pervasive nature of PAHs and their sources of release, reducing exposure presents a significant challenge; the federal government will consult key stakeholders on the means of reducing exposure to PAHs. PAHs are included in ocean dumping provisions of CEPA, which regulate allowable levels of contaminants in materials disposed of at sea. In addition, Environment Canada administers Section 36 of the Fisheries Act which prohibits depositing harmful substances, such as PAHs, in waters used by fish. Other federal legislation which deals with the regulation of PAHs includes the Pest Control Products Act, the Transportation of Dangerous Goods Act and the Food and Drug Act. Finally, Environment Canada has published technical guidelines for the safe design and operation of wood preservation facilities which use creosote-based pesticides. EN40-226/3-1995E ANY QUESTIONS: For more information contact: Phone: (902)426-5048
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