"It is a major step even for the developed countries which will have to introduce significant changes to the information they make available," said Jeremy Wates, of the United Nations Economic Commission for Europe (ECE), which hosted the talks.

Under the pact, which ECE countries will formally sign at a ministerial meeting in May in Kiev, states pledged to set up national registers of industrial pollutants released into the water, air and soil.

These "pollutant release and transfer registers" will be publicly accessible, user-friendly and updated annually with information on 86 pollutants considered to pose the most significant threats to the environment or health.

They include greenhouse gases, acid rain pollutants, heavy metals and cancer-causing chemicals such as dioxins.

Amongst industries required to report under the plan are refineries, thermal power stations, chemical and mining concerns, waste incinerators and larger farms, ECE said in a statement after the final weeklong talks.

Ten European Union countries and Canada were among those that negotiated the pact, which will be a legally binding protocol to the 1998 Aarhus Convention, the flagship U.N. treaty on environmental democracy issues.

But the United States, which has some of the toughest disclosure rules in the world, pulled out of the talks earlier, arguing the pact did not go far enough.

The ECE groups Europe, countries in the former Soviet Union and North America.

Environmentalists welcomed the deal, although they regretted that some toxic materials such as radioactive waste had been excluded from the list of substances, under pressure from industry lobbyists.

"It is going to be a huge improvement in many countries, even within the European Union," said Mary Taylor, of Friends of the Earth. "Activists will be looking to widen the list (of substances) but it is a good start."