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Toxic chemicals


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 (see Hormone Disrupters) 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 (see Declining sex ratios). 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) 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, 1997d).

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 osteoperosis 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 manmade 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 http://www.chem.unep.ch/pops/.

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. http://www.grida.no/amap/assess/soaer-cn.htm

Boyce, Nell. 1998. "A necessary evil". New Scientist, 7 February 1998, pp. 18-19.

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.

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

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

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

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

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.



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