After the Three Mile Island nuclear reactor meltdown in Pennsylvania in 1979, regulators moved to overhaul safety requirements for nuclear power plants. This led to the temporary closure of some older nuclear power plants governed by the Tennessee Valley Authority (TVA) when they couldn’t meet the Nuclear Regulatory Commission’s (NRC) newly tightened standards.

Now, Carnegie Mellon assistant professor of economics and public policy Edson Severnini says those closures may have caused reduced birth weight in children in the area at the time, due to pollution exposure from the increased reliance on coal-burning power plants. The sudden removal of nuclear power, which doesn’t emit any greenhouse gases, led to a ramp-up in the amount of power being provided by nearby coal plants, Severnini wrote. That led to increases in particle pollution in areas adjacent to coal power plants, measured by the Environmental Protection Agency (EPA) in total suspended particulates (TSP).

At the same time, average birth weight for infants declined 134 grams.