Nairobi, Kenya — A convention which scientists say will deliver a healthier world for people and wildlife is set to be signed 22-23 May in Stockholm by more than 100 countries.

The signing of the Convention on Persistent Organic Polutants (POPs), according to Klaus Topfer, Executive Director of the UN Environment Programme (UNEP) under whose auspices the treaty was negotiated, will be another milestone in environmental health and conservation.

Topfer says the treaty will signal mankind's willingness to phase out some of the world's most hazardous chemicals.

"Persistent organic pollutants threaten the health and well- being of humans and wildlife in every region of the world", Topfer said in statement Monday.

"It is therefore vital that after adopting and signing the Convention in Stockholm, governments should follow up quickly by ratifying the treaty so that it can enter into force by 2004 at the latest."

For the agreement to be legally binding, it requires 50 ratifications.

The United States is among countries willing to sign the convention, Topfer said, noting that the gesture underlined the importance of international cooperation on environmental issues.

The treaty's text was finalised at a meeting held in December 2000 in Johannesburg, South Africa.

The 12 initial POPs are aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex, toxaphene, polychlorinated bipehnols (PCBs) hexachlorobenzene, dioxins and furans.

Of all the pollutants released into the environment every year by human activity, POPs are among the most dangerous. They are highly toxic, causing an array of adverse effects --including death, disease, and birth defects among humans and animals.

Specific effects can include cancer, allergies and hypersensitivity, damage to the central and peripheral nervous systems, reproductive disorders, and disruption of the immune system.

In addition, POPs concentrate in living organisms through another process called bioaccumulation.

Though not soluble in water, POPs are readily absorbed in fatty tissue, where concentrations can become magnified by up to 70,000 times the background levels.

"Fish, predatory birds, mammals, and humans are high up the food chain and so absorb the greatest concentrations. When they travel, the POPs travel with them and as a result, POPs can be found in people and animals living in regions such as the Arctic, thousands of kilometers from any major POPs source", Topfer explained.

While control measures will apply to the initial 12 chemicals, a Review Committee will consider additional candidates for the POPs list on a regular basis to ensure that the treaty remains dynamic and responsive to new scientific findings.

However, a health-related exemption has been granted for DDT, which is still needed in many countries to control malarial mosquitoes.

Similarly, in the case of PCBs, which have been widely used in electrical transformers and other equipment, governments may maintain existing equipment in a way that prevents leaks until 2025 to give them time to arrange for PCB-free replacements.