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Heavy metalsIn the right concentrations, many metals are essential to life. In excess, these same chemicals can be poisonous. Similarly, chronic low exposures to heavy metals can have serious health effects in the long run. The main threats to human well-being are associated with lead, arsenic, cadmium and mercury, and it is these substances that are targeted by international legislative bodies. In 1996, the OECD agreed to phase out many uses of lead (OECD, 1996b), and in June 1998, the ECE added a protocol on heavy metals to the Convention on Long-range Transboundary Air Pollution (link to Protocol; link to UN/ECE press release with summary description).
Lead poisoning in children causes neurological damage leading to a reduction in intelligence, loss of short term memory, learning disabilities and problems with coordination. Prenatal exposure can cause reduced birth weight and immune suppression or oversensitisation, which could explain why some children develop asthma and allergies (Day, 1998). It has also been suggested that lead can affect behavioural inhibition mechanisms with a consequent increase in violence (Masters, 1998), and that it can contribute to tooth decay (Gil et al, 1996). Many developed countries had significantly reduced lead levels in children by 1992, mainly by introducing lead-free fuel. The US, for instance, showed a 77 percent reduction (Pirkle et al., 1994), although 2 million children were still at risk (Brody et al., 1994); in Britain, blood-levels of lead have fallen by two thirds since 1987 (IEH, 1998). However lead pollution levels have been rising in the urban areas of many developing countries, with more than 90% of the children in some African cities suffering from lead poisoning (Nriagu et al., 1996). The impacts on their development prospects can easily be imagined. Recent work has also found that waste incineration contributes a substantial amount of the lead fallout over urban areas (Chilrud et al, 1999). Most incinerators have been shut in Europe and North America, but they are increasingly used in developing countries, including China and Pakistan, which may help account for the increases.
High concentrations of arsenic in drinking water have been documented in specific parts of Argentina, Canada, Chile, China, Japan, Mexico, the Philippines and the USA. The problem is particularly acute in West Bengal and Bangladesh, where an estimated 30 million people are drinking arsenic-poisoned water (WHO, 1997). Some 62% of wells supply arsenic-contaminated water above WHO's limits with some containing as much as 400 times the limit (Bagla et al, 1996). The effects of arsenic include cardiovascular problems, skin cancer and other skin effects, peripheral neuropathy (WHO 1997) and kidney damage. And yet, one can filter out the arsenic and supply one person with clean water for about 15 US cents per year (Beard, 1998).
Cadmium exposure occurs mainly through cereals and vegetables grown on soils contaminated by mining activities and use of phosphorus fertilizers. Shellfish and animal organs also contain high levels. Cadmium accumulates in the kidneys and is implicated in a range of kidney diseases (WHO, 1997).
Mercury accumulates at the top of aquatic and marine food chains and fish is the major source of dietary exposure (WHO, 1997). The principal health risks associated with mercury are damage to the nervous system, with such symptoms as uncontrollable shaking, muscle wasting, partial blindness, and deformities in children exposed in the womb. At levels well below WHO limits, it can damage the foetal and embryonic nervous systems with consequent learning difficulties, poor memory and shortened attention spans (Jorgensen et al, 1997). Low-level exposures can also adversely affect male fertility (Dickman et al, 1998).
Like POPs (see POPs below), mercury is a global problem. Most of the mercury found in high concentrations in the Everglades in Florida comes from thousands of miles away, traveling on trade winds from Europe and Africa (Zarrella, 1998). Although it appears that less mercury than previously thought is polluting Greenland (Boutron et al, 1998), global transfers of mercury to the poles are still substantial, with base-levels three times what they were two centuries ago. Every spring, a toxic rain of mercury falls on the arctic, at the time when ecosystems are most active. (Pearce, 1997c). As a consequence, one in six Greenlanders have potentially harmful blood-levels of mercury, from eating contaminated fish and whales.
Bagla, Pallava and Jocelyn Kaiser. 1996. "India's Spreading Health Crisis Draws Global Arsenic Experts". Science, vol 274, number 5285, 11 October 1996, pp. 174-175.
Beard, Jonathan. "Safe to drink". New Scientist, 28 March 1998, p. 10.
Boutron, CF. Vandal, GM. Fitzgerald, WF. Ferrari, CP. 1998. "A 40-year record of mercury in central Greenland snow". Geophysical Research Letters, Vol. 24, no. 17, 1998, p. 3315.
Boyce, Nell. 1998. "A necessary evil". New Scientist, 7 February 1998, pp. 18-19.
Brody, Debra J., J.L. Pirkle, R.A. Kramer, K.M. Flegal, T.D. Matte, E.W. Gunter and D.C. Paschal. 1994. "Blood lead levels in the US population - Phase-1 of the 3rd National Health and Nutrition Examination Survey (NHANES-III, 1988 to 1991)." JAMA Journal of the American Medical Association 272(4):277-283. 27 July 1994.
Chilrud, SN, RF Bopp, HJ Simpson, JM Ross, EL Shuster, DA Chaky, DC Walsh, CC Choy, LR Tolley, A Yarma. 1999. "Twentieth Century Atmospheric Metal Fluxes into Central Park Lake, New York City". Environmental Science and Technology, vol. 33 (5), 1999, pp.657-662.
Day, Michael. 1998. "Lead in the womb". New Scientist, 23 May 1998, p. 7.
Dickman, MD, CKM Leung, MKH Leong. 1998. "Hong Kong male subfertility links to mercury in human hair and fish". The Science of the Total Environment, Vol 214 (1-3), 1998, pp. 165-174.
Gil, F., Facio, A., Villanueva, E., Perez, M.L., Tojo, R., Gil, A. "The Association of tooth lead content with dental health factors". The Science of the Total Environment, vol. 192, issue 2, 2 December 1996, p. 183.
IEH. 1998. Institute of Environment and Health at Leicester University. Report: Recent UK Blood Lead Surveys. 1998. ISBN 1 899110 13 5.
Jorgensen, PJ, R.Dahl, P.Grandjean, P.Wahl, R.F.White, N.Sorensen. 1997. "Cognitive Deficit in 7-Year-Old Children with Prenatal Exposure to Methylmercury". Neurotoxicology and Teratology, vol. 19, issue 6, November 1997, pp. 417-428.
Masters, Roger. 1998. "Environmental Pollution, Neurotoxicity and Criminal Violence". In ed. Rose, J. Environmental Toxicology, Gordon and Breach, 1998, London.
Nriagu, Jerome, et al. 1996. in The Science of the Total Environment. Cited in Motluk, Alison. "Lead blights the future of Africa's children." New Scientist, 23 March 1996, p. 6.
OECD. 1996b. Declaration on risk reduction for lead. Adopted at the Meeting of Environment Ministers, 20 February 1996.
Pearce, Fred. 1997c. "Mercurial storms rage in the Arctic". New Scientist, 21 June 1997, p. 17.
Pirkle, J. L., Debra J. Brody, E.W. Gunter, R.A. Kramer, D.C. Paschal, K.M. Flegal and T.D. Matte. 1994. "The decline in blood lead levels in the United States - The National Health and Nutrition Examination Surveys (NHANES)." JAMA Journal of the American Medical Association 272(4):284-291. 27 July 1994.
WHO. 1997. Health and Environment in Sustainable Development. WHO, Geneva.
Zarrella, John. 1998. CNN environment, 13 February 1998.
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