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TOXIC CHEMICALS IN ATLANTIC CANADA - LEAD WHAT IS LEAD AND WHAT ARE ITS USES? Some materials are so commonplace that we take them for granted. One of those materials is a greyish metal that has been with us for thousands of years. That metal is lead, still one of the world's most useful substances, and one that never ceases to find a role in human society. The earliest known applications were in pottery glazes 4,000 years ago, but it is suspected that lead was used as much as a thousand years earlier. It was used in ancient times for making coinage, art objects and water pipes. One of the first known toxic substances, lead was used by the Romans for lining aqueducts and in glazes on containers used for food and wine storage; and it is suspected to have resulted in widespread lead poisoning. Members of the famous Franklin Expedition to the Northwest Passage in the mid-1840s met a similar fate, being poisoned from lead in solder, widely used at the time to seal tins used to store foods. In modern times, lead has found a wide range of uses, and world demand for lead and its products has steadily increased. Lead's usefulness stems from the metal's many desirable properties: softness, high density, low melting point, ability to block radiation, resistance to corrosion, readiness to form alloys and chemical compounds, and ease of recycling. Until recently, one of the most significant uses was an anti-knock additive in gasoline. In the 1970s and 1980s, steps were taken to reduce the use of leaded gas. By 1990, these actions had virtually eliminated the use of lead in gasoline. Lead is also one of the best and earliest examples of recycling about 55 percent of the lead used in Canada comes from recycled material. Despite its positive qualities, lead is a significant environmental contaminant because it is toxic, persistent, and can be "taken up" and stored in biological tissues. THE BEHAVIOUR AND FATE OF LEAD Lead enters the environment from a variety of natural and human sources. Natural processes such as soil weathering and erosion, volcanoes and forest fires contribute to significant releases of lead. Natural processes rarely result in elevated concentrations in the environment; in fact, human activities release the most lead and frequently result in incidents of local contamination. The burning of leaded gas in automobiles was once the largest human source of lead in the environment, but industrial releases now exceed automotive emissions. Lead mining, smelting and refining operations, battery manufacture, and industrial and municipal effluents are major sources of lead. Lead from batteries, tin cans and other products winds up in landfills and incinerators, and can eventually enter the atmosphere and aquatic systems. Elevated concentrations now occur principally near mines and smelters and in urban centres. Since lead is largely insoluble in water, it is usually a minor constituent of surface and ground water. It tends to be absorbed by soil particles and organic materials, especially those near the source of the lead. And because of lead's low solubility in water, its "uptake" in plants is usually limited. Due to these properties, elimination of major localized sources of lead contamination can result in immediate reductions in concentrations of lead in the water and organisms near the sources. Like other heavy metals, lead dissolves more readily in acidic waters. When the pH level is raised (and acidity is lowered), some of the lead forms lead hydroxide solids, which settle out. Mine tailings ponds are commonly treated with lime to raise the pH level to keep lead and other dissolved metals from reaching nearby watercourses. Lead released into the atmosphere is a major source of environmental contamination. Deposited on the soil, in surface waters and on plants, lead can enter the food chain. Lead particles can be transported in the air for considerable distances, up to thousands of kilometres from their source, before being deposited through precipitation. ENVIRONMENTAL CONCERNS Lead concentrations in the environment in Atlantic Canada have been monitored extensively by various federal and provincial agencies. Normal concentrations of lead in water are often attributable to natural processes of weathering and erosion of lead in rock formations and soils in the locations where the measurements are made. Higher than normal concentrations are found frequently in urban areas; alongside roads; near mining, smelting and shipping facilities; and at industrial sites including battery manufacturing operations. Domestic drinking water may have elevated concentrations of lead, primarily as a result of lead leaching from water mains, connecting pipes and in-house plumbing. Corrosion of lead pipes and lead solder in some plumbing, aggravated by low pH levels, can contribute significant quantities of lead to drinking water. Elevated concentrations of lead were at one time found in soils in orchards where lead arsenate, once a popular fruit tree insecticide, was applied. The chemical has been replaced by other less persistent pesticides and is no longer registered for use in Canada. Mining and smelting are significant sources of lead in the Atlantic region, and one of Canada's two lead smelting operations is located in northern New Brunswick. Lead enters the environment in emissions from the smelting process, as dust from the various processing steps, and during shipping and transferring activities. Effluent from metal mines frequently has elevated concentrations of lead and other heavy metals, due to runoff from waste rock piles and tailings, and mine drainage. In some cases, these effluents have degraded aquatic environments. In 1993, eight lead mines were operating, or under development, in the Atlantic region. Sites where ore and concentrated lead products are loaded onto ships are also potential sources of lead in the environment due to spillage, runoff and windblown dust. Substantial amounts of lead/zinc concentrate from such sources entered the harbour at Dalhousie, New Brunswick, from the 1960s through to the early 1980s. This led to problems in dredging the harbour, as metal concentrations were too high to permit ocean disposal of the dredged material. Lead and other metals have also been found at ship loading sites in Newfoundland, although levels there were not high enough to threaten fish or other aquatic life. Concentrations of lead in the atmosphere of urban centres in the Atlantic region have shown a steady improvement from the peak levels of the early 70s, which occurred prior to controls on lead in gasoline. Greater controls of the mining and smelting of lead have also resulted in reductions in emissions from these facilities. For example, lead emissions from the mining and smelting operation at Belledune, New Brunswick, were reduced by 50 percent through various measures between 1975 and 1988, and now meet emission guidelines for the amount of lead in the atmosphere. Although air emissions have largely been controlled, metals have accumulated in soils and vegetation near the plant. Vegetables, cows' milk and water from within a 20 km radius of the facility, however, show no significant contamination. A lead-acid battery plant in Springhill, Nova Scotia, was a source of lead and cadmium contamination of the air, vegetation, and soil in the 1960s and 1970s. The plant has subsequently made changes which resulted in a 95 percent reduction of lead and particulate emissions. Elevated concentrations of lead have also been found in ports and harbours throughout the Maritimes. Sediments in Halifax Harbour for example, have lead concentrations from sources such as sewage, refuse, wastes from ship repair and products which prevent corrosion. Contaminated sediments in Halifax Harbour have lead concentrations that are approximately 10 to 140 times higher than those at uncontaminated sites. Industrial sites including mines, smelters, and battery manufacturing operations, also frequently have increased lead concentrations in nearby sediments. Lead in sediments tends to be fairly immobile and becomes a concern only in the case of dredging, or when ecosystem changes threaten to release it. Lead is also used in pure form as lead shot and fishing tackle such as sinkers and lures, which often harm waterfowl and other wildlife. When ingested by waterfowl, lead can cause poisoning and subsequent death of the birds. At least two percent of all North American waterfowl are estimated to die each year as a result of ingesting lead shot. Environment Canada has been monitoring the occurrence of lead shot in their gizzards, as well as other measures of lead contamination of waterfowl in the Maritimes. And "lead-free" hunting areas have been established in several areas of the Atlantic Provinces where only steel shot can be used. GETTING THE LEAD OUT.....OF DUCKS In recent years, black ducks that over-winter in urban areas in Nova Scotia have been found to have high concentrations of lead in their blood, in many cases at levels considered to be a threat to their health. The Canadian Wildlife Service has found that many of those birds do not have lead shot in their gizzards, therefore they are not ingesting lead shot used in hunting, but are getting lead from other sources. An Environmental Protection Branch study found very high concentrations of lead in urban pond sediments; the average lead concentrations were up to 50 times higher than those at uncontaminated sites. Since urban ponds used by ducks are usually located in small parks surrounded by roads with medium to high density traffic, the likely source of lead contamination of urban pond sediments was the use of leaded gasoline in vehicles prior to 1990. During that period, lead from automobile exhaust was either directly deposited in the ponds or was deposited indirectly through runoff from contaminated roadside plants or soils, or from contaminated leaves in the autumn. Since lead is quite immobile in sediments, the lead in urban pond sediments will pose a lingering hazard to ducks unless the contaminated sediments are removed from the ponds. REGULATING LEAD The use and release of lead and its compounds fall under various laws, regulations and agreements designed to protect the environment and human health. Lead was one of the first "toxic substances" written into law in Canada. Its listings in the Canadian Environmental Protection Act (CEPA), the primary federal legislation that deals with toxic substances in the environment, allows the federal government to control the importation, manufacture, distribution and use of lead and lead compounds in Canada. Regulations under CEPA restrict the use of lead in gasoline and control its release from secondary lead smelters. The Act also regulates the disposal at sea of material containing specified concentrations of lead. Under the federal Fisheries Act, the release of any substance which is deleterious to fish or fish habitat is prohibited. Metal Mining Liquid Effluent Regulations, as well as Metal Finishing Liquid Effluent Guidelines under the Fisheries Act limit releases of lead from metal mines and processing facilities. Shipping or transport of substances containing lead are regulated under the federal Transportation of Dangerous Goods Act, while use of compounds containing lead are controlled by the Hazardous Products Act, the Food and Drug Act, and the Pest Control Products Act. The discharge of lead and lead compounds from ships in Canadian territorial waters is regulated under Pollutant Substances Regulations of the Canadian Shipping Act (1991). Lead is also included in the Workplace Hazardous Materials Information System, operated by Health Canada. EN 40-226/1-1995E ANY QUESTIONS: For more information contact: Phone: (902)426-5048 Return to our Programs and Priorities Index Page |
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