London

The clock is ticking for a troublesome set of chemical pollutants. Last week, a three-month countdown began towards the day when the Stockholm Convention on Persistent Organic Pollutants (POPs) comes into force.

But environmental-health specialists warn that the first phase of the agreement, drawn up in 2001, represents a relatively easy win. From May, the convention will ban the use of 12 types of pollutant of limited economic importance; but subsequent constraints on more financially valuable compounds will be fiercely fought by chemical manufacturers, the specialists predict.

The countdown towards implementation was triggered on 17 February, when France became the fiftieth country to ratify the agreement. Several countries, including the United States and Britain, have yet to ratify it, but are preparing legislation to do so.

Environmentalists have campaigned for years against POPs, a group of very stable compounds that includes dioxins and the pesticide chlordane. POPs accumulate in animals and plants at the end of the food chain, and have been linked to a range of human health problems.

Chemical manufacturers accept that the 12 substances covered by the first phase of the convention are dangerous, and have already phased some of them out. But Bo Wahlstrom, a Geneva-based scientific adviser at the United Nations Environment Programme, which brokered the treaty, predicts that it will be far harder to incorporate compounds that are still made and sold in large quantities.

Substances that are likely to spark disagreement include brominated flame retardants such as hexabromocyclododecane (HBCD) and decabromodiphenyl ether (decaBDE). Tens of thousands of tonnes of these compounds are made every year, primarily as flame-retarding additives for textiles, electrical equipment and building materials. The retardants can enter the environment during manufacture and disposal, and their stability means that they can build up in humans and animals over time.

The jury is still out on whether the current level of exposure to these compounds presents a health risk to people and animals, say environmental-health researchers. But, they add, HBCD and decaBDE meet some of the criteria for being classed as POPs.

Steve Robinson, chemicals assessment manager at the Environment Agency in Wallingford, near Oxford, UK, says that HBCD is toxic and accumulates in living tissue. He adds that industry is now running tests to assess another criterion for it to be classed as a POP: whether or not it persists in the environment. So far, the only evidence for decaBDE as a possible POP is that it has been shown to build up in the tissue of animals at the end of the food chain, such as harbour seals, birds of prey and dolphins (L. S. Birnbaum and D. F. Staskal Environ. Health Perspect. 112, 9–17; 2004).

The status of such contentious compounds will become clear when European Union nations complete a risk assessment of flame retardants later this summer. The Bromine Science and Environment Forum, which represents bromine manufacturers, says that the industry is working with officials on this assessment and that, so far, the studies show no need for decaBDE or HBCD to be added to the convention.

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