The Arctic at Risk:
A Circumpolar Atlas of Environmental Concerns
The Arctic at Risk:
Lead (Pb) is another heavy metal that can combine with an organic group (as does mercury); in this case, lead combines with four ethyl groups to form tetra-ethyl lead. Like cadmium, lead is a conservative pollutant that is never lost from the environment. Lead is soluble in dilute nitric acid, but is somewhat resistant to hydrochloric and sulfuric acid. It dissolves in water in the ionized form, and also combines with some other chemicals to form lead salts. It generally does not bioaccumulate in marine organisms.
Production and Use
Lead occurs naturally in the environment and is also released by human activities. The inadvertant contamination of samples, particularly in glass, is a major concern and has led to inaccurate assessments of environmental contamination in the past. By including in this study only data reported since 1980, we hope that the values are accurate.
The total world production of lead is about 43 million tons/year (Clark, 1992). Lead in metallic form--for example in battery casings and plates, and in sheets and pipes--is often recovered and recycled. Nearly 10% of the world lead production is in the form of tetra-ethyl lead, a gasoline additive, and much of it is lost to the atmosphere (Clark, 1992). As a result, today the primary source of lead in the environment is from leaded automobile fuels. Some insecticides also contain lead compounds. Worldwide, human activities release much more lead to the atmosphere (449,000 tons/year) than do natural inputs (19,000 tons/year); (Clark, 1992).
The US EPA required a phase-out of the use of leaded gasoline in automobiles. These regulations have decreased the amount of lead emitted from the United States and some other countries.
Transport Pathways
Lead aerosols deposit in both wet and dry deposition all over the globe. Finer particles transport lead longer distances and enhance its toxicity (Sadiq, 1992). Lead has a residence time in the atmosphere of about five days (Clark, 1992).
Lead deposited from the atmosphere, as well as lead that occurs naturally in rocks and soils, may be mobilized in lakes if they are acidified to a pH of less than 3.5 by acid rain (Galloway et al., 1982).
The major pathway of lead to the marine environment is through atmospheric deposition (Schaule and Patterson, 1983), with automobiles and smelters as the major sources of contamination (Sadiq, 1992). Once in the marine environment, lead adsorbs onto settling particles and is transported to the sea floor, where it deposits (Sadiq, 1993). Therefore marine sediments serve as a lead sink.
Environmental Distribution
Atmospheric lead deposited in the Canadian High Arctic has been tracked back to sources in eastern Europe, Russia, and the Baltic states, as well as in Quebec and the northeastern United States (Cheng et al., 1993).
Atmospheric deposition of lead in Norway appears to have decreased by nearly a factor of two between the mid 1970's and the early 1980's (Steinnes, 1990).
Worldwide, surface waters range from 10 ng/l in remote areas to nearly 27,000 ng/l in the Baltic Sea (Sadiq, 1992). Concentrations in rivers may be 3,000 ng/l (Kennish, 1994), while coastal and estuarine waters near industrial centers may exceed 1,000 ng/l. Seawater with a concentration below 100 ng/l is considered to be relatively uncontaminated (Sadiq, 1992), and values of 30 ng/l are fairly typical for the ocean (Kennish, 1994).
In the Arctic, relatively clean surface ocean water is observed in the vicinity of Svalbard (Mart 1983). Elevated concentrations of lead in the Arctic are reported from the Piasina River which drains the industrial complex of Norilsk (8,000 ng/l), and the Ob' and Yenisey river estuaries (ca. 2,000 ng/l, Melnikov and Vlasov, 1992). However, a recent detailed study of the Ob' and Yenisey casts doubt on these reports: lead concentration in the Ob' was found to be only 17 ng/l, 6 ng/l in the Yenisey (Dai and Martin, 1995). Martin et al. (1993) found 0.08 nM in the Lena River. These values must be considered as pristine.
McCrea and Fischer (1986) found elevated concentrations in the Ontario rivers that drain into Hudson Bay (1,000 ng/l).
Mine wastes containing lead have been disposed of in the North American Arctic at several locations. The following summary of mining activities is from Asmund et al. (1991): Maarmorilik, in western Greenland; Nanisivik in Strathcona Sound on the northern tip of Baffin Island, North West Territories, Canada; and Ivittuut in southern Greenland. Since the opening of the mine in 1973, tailings were disposed of in the fjord near Maarmorilik, resulting in lead contamination of the marine ecosystem, including bivalves, shrimp and seaweed. In addition to marine pollution, contaminated dust is emitted from the production facilities associated with the mine. The concentration factor between seaweed and ambient seawater is about 6,200, while it is about 220,000 between seawater and the blue mussel.
The mine at Nanisivik went into production at 1976. Tailings are disposed of in West Twin Lake. However, contaminants spilled from ships during loading and leachate draining into a creek also contribute to pollution of Strathcona Sound.
At Ivittuut, mining has been carried out to varying degrees since 1854. Waste rock has been used for landfill, causing high concentrations of lead in interstitial water. Transport to the adjacent Arsuk Fjord resulted in elevated concentrations of lead in seawater, sediment, and seaweed.
In all three cases, the greatest lead contamination was found at distances less than 5 km from the source, but effects were detectable as far as 30 km away (Johansen et al., 1991).
Ringed seals from the Strathcona Sound area in the Northwest Territories had very high lead levels, and were found to be affected by mining activities in that region (Wagemann, 1989).
Also notable are the high lead concentrations found in the livers of walrus from Hudson Bay, northern Quebec. These values are on average twice as high as for animals sampled to the north in Foxe Basin (Wagemann and Stewart, 1994). They are comparable to samples from belugas from the St. Lawrence and from white-beaked dolphins from the eastern Canadian and US seaboards, which had some of the highest recorded lead levels in marine mammals (Muir et al., 1988; Wagemann and Stewart, 1994). Wagemann and Stewart (1994) propose that walrus may have ingested lead when they ate contaminated clams and cockles. The source of metals taken in by the clams and cockles is not yet identified.
Potential Health Effects
Lead and lead-containing compounds are highly toxic to animals and people; children are particularly sensitive. Sources of lead include food, water, soil, dust and smoking. Lead pollution is considered by some to be the chief environmental problem facing the modern world (Meyer, 1989). The US Center for Disease Control (CDC) considers lead poisoning the major environmental health threat to children in the United States. However, according to Dewailly (pers. comm., 1995), exposure to lead is not a problem of particular concern for most Arctic populations, where the concentration of lead in people is generally low.
The toxicology of inorganic lead is well understood and documented in people, less so in animals. Lead is taken up from the air, from food, and, to a lesser extent, by direct contact with skin. Lead is carried in the blood and sequestered in bone, from where it is slowly released. The best and most common measure of exposure and dose in humans is blood concentration (expressed in micrograms per deciliter = ug/Dl) because this measure avoids the problem of uptake and absorption estimates. A blood-lead level of 10 ug/Dl is considered unsafe for children.
Lead retained in the body and accumulated over a long period of time may lead to cumulative lead poisoning. Overexposure to lead causes both acute and chronic effects on a wide range of physiological systems and organs. Chronic overexposure affects the nervous, cardiovascular, gastrointestinal, immune, reproductive and kidney systems. Lead impairs the formation of red blood cells at several steps in the process; there appears to be no threshold for effects of lead on blood formation (ATSDR). It can harm reproductive, endocrine, hepatic (liver), and gastrointestinal processes, and damage the central nervous system in general (Meyer, 1989). In the workplace, OSHA regulates exposure to 50 ug/m3 in air.
The most serious health concerns over lead poisoning are the long-term chronic ones, especially in children. The most dramatic effects are neurological and behavioral alterations in children with blood lead above 10 ug/Dl. There is a dose-dependent decrement in cognitive function and increase in hyperactivity with increasing blood lead. In adults, lead provokes increases in miscarriages and decreased sperm counts .
The US EPA drinking-water standard for lead is 0.015 mg/l. The ambient water quality criteria for protection of aquatic organisms in freshwater is 82 ug/l for 1-hour average acute effects (3.2 ug/l for 4-day average chronic effects), and in marine environments 140 ug/l for 1-hour average acute effects (4.5 ug/l for 4-day average chronic effects).
The lead criterion for marine waters to protect marine animals is 5.6 ppb (= 5,600 ng/l; ATSDR 1993).
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