But exemptions for some toxins such as DDT were maintained to allow their use to fend off deadly insects despite their harmful effects.

"We are very satisfied. The results here are not academic achievements but they are achievements for all people in the world," said Klaus Toepfer, executive director of the United Nations Environment Program, which organized the conference.

About 800 officials from around the world gathered in the Uruguayan beach resort of Punta del Este to bolster the Stockholm Convention to eliminate so-called persistent organic pollutants, or POPs.

The convention has been ratified by 98 of the 151 countries that signed it. The United States and Russia are among those nations yet to ratify the accord.

"Four chemicals have already been mentioned for further research and integration, for example lindane, a pesticide widely used around the world. These are very important chemicals," said Toepfer.

POPs build up in fatty tissues and traces can be found in every person in the world.

The candidates for being phased out include two flame retardants called pentabrominated diphenyl ether (penta-BDE) and hexabromobiphenyl (Hexa-BB).

The other two culprits are the insecticide lindane and the pesticide chlordecone.

The working group to study these four will meet in October or November. It could take up to three years before they are formally included in the ban.

Environmentalist group WWF had proposed 20 chemicals be added to the ban.

EXEMPTIONS UPHELD

The conference upheld exemptions for some toxins -- most importantly the anti-malarial DDT and termite killer mirex -- in some countries because the death and damage caused by their disuse was considered to be worse than the harm they cause. The list of exemptions is reviewed every three years.

"The convention required this meeting to determine whether DDT continues to be essential to health protection and the decision was yes," said John Buccini, acting executive secretary of the Stockholm Convention.

While DDT is banned for use on crops, about 20 countries spray some 7,500 tonnes of the chemical every year in their homes to kill mosquitoes. Malaria kills 1 million people a year.

The UN estimates termites cause $30 billion a year in damage by chomping through wooden buildings, bridges and crops.

Environmentalists were pleased with the possible widening of the ban but said the commitment from some governments was still too weak.

They say countries need to find ways of financing poor countries who adopt more costly alternatives to the hazardous chemicals.