They are found everywhere, including the most remote areas, far from any industrial activities. Even though they are present in the environment at very low levels, they have been linked to many health and environmental effects. They are known as POPs, or persistent organic pollutants.

POPs have been shown to cause serious immune and metabolic effects, neurological defects, reproductive anomalies and cancer in both humans and wildlife. In addition, they are highly toxic, remain in the environment for long periods, bioaccumulate (become more concentrated as they rise in the food chain), and can spread thousands of miles from the point of emission.

The most important class of compounds among POPs are the organochlorines, chemicals containing chlorine. Many of these are pesticides. POPs are nearly all of human origin, such as from:

1. the manufacture and use of certain organic chemicals, including many pesticides
2. certain metal and refining processes
3. pulp and paper manufacturing processes that utilise chlorine
4. leaks, spills and dumping of these materials;
5. the combustion of certain fuels and waste

Because increasing evidence shows that POPs are a global problem, international action is needed. Twelve POPs have been identified by governments for initial action:

• aldrin, chlordane, DDT, dieldrin, dioxins, endrin, furans,
• heptachlor, hexachlorobenzene, mirex, PCBs, toxaphene

There are many different toxic effects associated with POPs. However, there are many subtle effects which are of concern. These have been linked mostly to organochlorine compounds, the most important group of POPs.

Recent studies of humans exposed to POPs through their food have shown a possible relationship to disruptions to the immune system. Several chemicals have been found to cause immune effects at very low levels. For example:

There is mounting evidence that organochlorine compounds can act as hormones. These compounds, including DDT, PCBs, and endosulfan, may also be part of the cause for the decrease in the quality of semen, an increase in testicular and prostate cancer, an increase in defects in male sex organs; and increased incidence of breast cancer which has been observed in the last fifty years. (Hileman,1994; Soto;1993)

It has been suggested that exposure to organochlorines has resulted in a reduction in fertility in men (lower sperm count, sperm deformities). Some POPs act as hormones. These could impact the developing foetus. The chemicals listed below have been linked to adverse reproductive effects.

DBCP, DDT, dieldrin, dioxins, endosulfan, hexachlorobenzene, methoxychor, mirex, PBBs, PCBs. (Colborn,1993; Allsopp,1995; IEM,1995)

Many organochlorines pesticides have been classified as having sufficient evidence of cancercausing effects in animals. For example:

chlorophenols, chlorophenoxy-herbicides, DDT, dioxin (TCDD), hexachlorobenzene, hexachlorocyclohexane, mirex, toxaphene.

Several POPs have been shown to act as tumour promoters or to have genotoxic effects. The following chemicals have been associated with breast cancer:

Chlordane & oxy-chordane, DDD, DDE, DDT, dieldrin, heptachlor-epoxide, hexachlorobenzene, hexachlorocyclohexane, trans-nonachlor, PCBs. (Davis, 1993; Allsopp, 1995; IEM,1995)

It has been suggested that the endocrine disrupting effects of organochlorines is having major impact on wildlife. Exposure during critical moments of development can have major impact. Endocrine disrupters has been associated with:

1. abnormal thyroid function in birds and fish;
2. decreased fertility in birds, fish shellfish, and mammals (seals);
3. masculinisation and defeminisation of female fish, gastropods, and birds;
4. demasculinisation and feminisation of male fish, birds, reptiles and mammals;
5. alteration of immune system in birds and mammals. (Colborn, 1993; Guillette,1994)

Immune disruption has been suggested as a cause for the increased incidence in marine mammal die-offs and strandings among seals and whales.

A Science assessment by Environment Canada in 1994 concluded that there were three levels of biodiversity threatened by POPs:

It noted that population declines in certain birds reversed when the levels of POPs was reduced, showing that POPs did have an impact on ecosystem health.

By definition, POPs are persistent in the environment. Another characteristic is that they can be found at great distances from where they are used or released. The global distillation effect means that POPs evaporate from the warmer regions, where they are used or released, and then condense in the colder regions, finally concentrating in the Arctic and Antarctic. POPs also attach to soil particles, moving through the air or water. POPs bioaccumulate and the highest concentrations are found in animals such as birds, fish, seals, whales, and among some of the native peoples in the Arctic. (IEM,1995)

Allsopp, M. et al. 1995. Body of evidence: the effects of chlorine on human health. Greenpeace International, Amsterdam.

Colborn, T. et al. 1993. Developmental effects of endocrine-disrupting chemicals in wildlife and humans. Environmental Health Perspectives (101/5): 378-384.

Davis, L.D. et al. 1993. Medical hypothesis: xenoestrogens as preventable causes of breast cancer. Environmental Health Perspectives (101/5): 372-377.

Guillette, L.J. et al. 1994. Developmental abnormalities of the gonad and abnormal sex hormone concentrations in juvenile alligators from contaminated and control lakes in Florida. Environmental Health Perspectives (102/8): 680-687.

Hileman, B. 1994. Environmental estrogens linked to reproductive abnormalities, cancer. C&EN (31 January): 19-23.

(IEM) 1995. Towards global action. Meeting background report, International Experts Meeting on Persistent Organic Pollutants, June 4-8, 1995, Vancouver, B.C. Environment Canada, Hull, Quebec.

Soto, A.M. 1993. Testimony before the Subcommittee on Health and the Environment, U.S. House of Representatives, 21 October 1993.

Prepared by:
Ronald Macfarlane,
Pesticide Action Network - Asia and the Pacific.

PAN AP, P.O. Box 1170, 10850 Penang, Malaysia.
Tel: (60-4) 657 0271; (60-4) 656 0381; Fax: (60-4) 657 7445;
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