Environmental groups and several states are cheering a Feb. 8 court decision that strikes down a 2005 Environmental Protection Agency rule governing air emissions of mer cury. The regulation, which was to take effect in 2010, would have let coal- and oil-fired powerplants that couldn’t meet mercury standards buy credits from plants that could. The U.S. Court of Ap peals for the District of Columbia said EPA must draft a new rule.

EPA says its 2005 rule would have cut mercury emissions na tionwide by 70%. But under the court decision, “The U.S. has no na t ional regulation to cut mercury emissions from existing powerplants,” says EPA spokesman Jon athan Shradar. He says EPA is re viewing the ruling to determine its next step.