A global treaty that bans certain long-term pollutants that have been linked to a range of human health problems is to come into force. The countdown towards implementation of the Stockholm Convention on Persistent Organic Pollutants was triggered on 17 February, when France became the 50th country to ratify the treaty. The first phase of the agreement will ban the use of 12 types of pollutant of limited economic importance. Environmentalists hope to expand the range of pollutants covered by the agreement, but chemical manufacturers are likely to fight constraints on more financially valuable compounds.