Toxic Chemicals

Submitted by Arthur Dahl on 5. June 2011 - 23:31
e-learning centre on sustainable development


Heading: Environment    Topic: Toxic chemicals

Qualitative information suggests that environmental emergencies, particularly those involving chemicals such as industrial accidents, toxic spills, explosions and chemical fires, are increasing steadily and can be expected to occur more widely with the increasing manufacture, transport and use of dangerous materials in developing countries. The 1984 Bhopal toxic gas leak and 1995 cyanide poisoning of the Essequibo river in Guyana are but two of the larger recent disasters. Often a natural emergency such as an earthquake or flood in an industrialized area can trigger technological emergencies as well, and also make them more difficult to control.

Heavy metals

In 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, 1996), 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.


One of the most pressing environmental issues today is that presented by persistent organic pollutants (POPs). POPs take a long time to break down in the environment and it is very difficult, if not impossible, to contain them once they have been released.

Over the past few years, there has been an increasing body of evidence documenting their devastating effects on wildlife, including wasting syndromes, shrinking populations, birth defects such as missing eyes and deformed reproductive organs, and behavioural disorders such as same-sex nests and loss of sex drive. POPs accumulate exponentially in fatty tissue as they move up the food chain, such that concentrations can be 70,000 times the background levels in a top predator. The same chemicals have been reported in human blood and body fats, with high concentrations in breast milk (Colborn et al., 1996).

POPs present serious health risks including mimicking reproductive hormones and a suspicion of immune suppression and are thought to assist carcinogenic substances or cause cancer directly. Of great concern is their effect on the human embryo and infants, which are exposed to POPs at various developmental stages via the placenta and breast feeding, with effects on neurological development and sexual differentiation. The effects on children exposed when in the womb include lowered intelligence, poor short-term memory, a shortened attention span, and difficulties learning to read. These children are also born sooner and are smaller than average (Colborn et al., 1996; Pearce, 1997b). The effects are long-term, as can be seen from Vietnamese children born today with birth defects such as twisted or missing limbs and eyes without pupils. It is thought that these defects are due to dioxin-containing defoliants (e.g. Agent Orange). In the face of these facts, it is alarming that POPs are found with increasing frequencies in a variety of food products with millions of people potentially exposed to dangerous levels.

Furthermore, POPs are transported globally. For example, dioxin in the Great Lakes comes from as far away as Florida and California (Kleiner, 1996b) and potentially damaging levels of DDT, PCBs and dioxin-like compounds have been found in wildlife on remote Pacific islands thousands of kilometers from heavily populated areas.

There is a systematic transfer of these chemicals from warmer to colder areas through the process of global distillation. The pollutants evaporate from soils in warm areas such as the tropics, are transported as vapour around the globe, and condense over cold areas as toxic snow or rain. If bound in snowflakes, the spring melting causes a toxic flush just when biological activity is at its most intense.

As a result, one of the most serious environmental POP-related crises is the widespread contamination of the arctic and antarctic ecosystems, with high levels found in wildlife and people (Van den Brink, 1997; Pearce, 1997b). POPs accumulate in the fat of seals and beluga whales, which are then eaten by Inuits. Thus, chlordane levels in the breast milk of Inuit women are 10 times higher than in the south of Canada, and PCB levels are 5 time higher (AMAP, 1997). In some traditional Inuit villages, two thirds of children have blood-PCB levels above Canadian health guidelines. Men are more affected than women, as lactation drains some of the poison - straight to the children - and older people have higher levels, as they have been accumulating the poisons over longer periods of time. And the problems are not limited to POPs, as heavy metals (see Heavy metals above) also end up in the Arctic (Pearce, 1997b).

Many countries do not control releases of POPs, or fail to implement existing legislation. These problems are often compounded by lack of treatment, unsafe transport, concentration in urban areas and inadequate management. Thus, some countries have imposed tough standards which have resulted in largely dioxin-free emissions from incinerators. However, the dioxin remains in the ash, which is often used as landfill, such that the dioxin merely reaches the environment by another route (Pearce, 1997c).

POPs present a special challenge to developing countries, which typically lack the capacity to identify and respond to sources of releases of POPs to the air, water and soil. They have also been victims of shipments of toxic chemicals from industrialised countries. In addition, other public health considerations, such as the fight against the malarial mosquito and tse-tse fly, make developing countries reluctant to agree to curtail the use of effective pesticides like DDT. Alternatives to DDT are often more toxic. For example, chronic low-level exposure to organophosphate pesticides can cause irreversible neurological and physical damage, such as osteoporosis and osteopenia (Day, 1997). They must also be reapplied more frequently, making them more expensive, and may be less effective than DDT, as mosquitoes rapidly develop multiple resistance to them (Boyce, 1998). In contrast, some countries that are subjected to global distillation, are pushing for restrictions on the use of all persistent chemicals, whether they are known to be toxic or not, pointing to the fact that we have 300 to 500 measurable man-made chemicals in our bodies that would not have been found there 50 years ago (Lowrie, 1997).

Reconciling these concerns is difficult, but building a global defence through a legally binding convention is vital for the protection of public health and the environment. Action is being taken against the most threatening chemicals. In June 1998, in Aarhus, Denmark, thirty-three countries and the European community agreed the UN/ECE Protocol on Persistent Organic Pollutants to the Convention on Long-range Transboundary Air Pollution (link to protocol), which bans 16 different POPs. In September 1998 in Rotterdam, a legally binding convention requiring the prior informed consent (link to PIC at FAO, or PIC homepage) of countries to international shipments of toxic chemicals was signed by sixty-one countries. And under the aegis of UNEP, 103 governments are currently negotiating a legally binding international agreement to reduce and/or eliminate releases of 12 of the POPs most widely implicated in damage to human health and the environment. The 12 POPs are the pesticides aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex and toxaphene; the industrial chemicals polychlorinated biphenyls (PCBs) and hexachlorobenzene which is also a pesticide; and the unintended by-products of combustion and industrial processes, dioxins and furans. The mandated deadline for reaching an agreement is the year 2000. Reports of the Intergovernmental Negotiating Committees (INCs) and the meetings of the expert group mandated to devise criteria and a procedure to add POPs to the treaty in the future, as well as other official UNEP documents, are available at

Two useful online resources on toxic chemicals are the State of the Arctic Environment Report on Arctic Pollution Issues at the Arctic Monitoring and Assessment Programme (AMAP) website and the National Centre for Environmental Assessment website.


AMAP, 1997. Report: State of the Arctic Environment: Arctic Pollution Issues. Arctic Monitoring and Assessment Programme, 1997.

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.

Colborn, Theo, Dianne Dumanoski, and John Peterson Myers.  1996.  Our Stolen Future.  Dutton, New York.

Day, Michael. 1997. "Sheep dip clue to broken bones". New Scientist, 24 May 1997 , p. 6.

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.

Kleiner, Kurt. 1996b. "Long-lived pollutants threaten the great Lakes". New Scientist, 13 July 1996.

Lowrie, Margaret. CNN environment, 27. June 1997.

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. 1997b. "Northern Exposure". New Scientist, 31 May 1997, pp. 24-27.

Pearce, Fred. 1997c. "Mercurial storms rage in the Arctic". New Scientist, 21 June 1997, p. 17.

Pearce, Fred. 1997d. "Errors of emission". New Scientist, 4 October 1997, p. 21.

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.

Van den Brink, NW. 1997. "Directed transport of volatile organochlorine pollutants to polar regions: the effect on the contamination pattern of Antarctic seabirds". The Science of the Total Environment, vol., 198 (1), 1997, pp. 43-50.

WHO. 1997. Health and Environment in Sustainable Development. WHO, Geneva.

Zarrella, John. 1998. CNN environment, 13 February 1998.

Based partly on materials originally prepared for UN System-wide Earthwatch

Article last updated 9 July 1999

Return to IEF sustapedia


Return to e-learning centre

Last updated 8 September 2010