Mercury is a potent neurotoxin that accumulates in the food chain and can pose a threat to people who eat fish tainted with the metal. It can impair neurological development in fetuses, infants and children, according to the EPA.
"People can live and be healthy with some level of mercury in their bodies, but it really has an impact on a developing fetus," said Bowden Quinn, conservation director for the Hoosier chapter of the Sierra Club.
U.S. Geological Survey studies have found elevated levels of mercury in Indiana's rivers and streams and the fish that live in those waterways.
Much of that is traced to emissions from Indiana's coal-fired power plants. In 2011, Indiana got about 85 percent of its electricity from such plants, Quinn said.
The new EPA standards are estimated to cut mercury pollution from coal by 90 percent, lung-damaging acid gases by 88 percent and soot-producing sulfur dioxide by 41 percent.
IPL has about 470,000 customers in Indianapolis and surrounding counties.