The U.S. Supreme Court on Monday dealt a blow to an Obama administration regulation cutting mercury and other toxic emissions from power plants. The court ruled that the Environmental Protection Agency didn’t do enough to consider the costs of complying. As a result, the EPA will have to reexamine and perhaps alter its rules.

But since the regulation went into effect earlier this year, many power plants have already installed equipment reducing mercury, a neurotoxin linked to lower IQs and other health effects in children, as well as other toxic substances. “Investments have been made and most plants are already well on their way to compliance,” according to an EPA statement.

Based on 2013 EPA data, here is the list of the