People living in Ohio, Pennsylvania and Florida are most at risk in the United States from toxic emissions spewing from coal and oil-fired power plants, two leading American environmental groups said in a report.

Electricity generation and chemical processing were the top culprits for dangerous emissions, which can lead to or worsen ailments such as asthma and cancer, according to the report by the Natural Resources Defense Council and Physicians for Social Responsibility.

While Ohio topped the list of 20 states most affected by toxic air pollution, Kentucky and Maryland were ranked fourth and fifth. Next were Indiana, Michigan, West Virginia, Georgia and North Carolina.

"Power plants are the biggest industrial toxic air polluters in our country, putting children and families at risk by dumping deadly and dangerous poisons into the air we breathe," said Dan Lashof, director of the climate center at the Natural Resources Defense Council.

The study, an analysis of toxic emissions data from 2009 released last month by the U.S. Environmental Protection Agency, found that coal and oil-fired plants were responsible for nearly half of all toxic air pollution in America.

The report was prepared by comparing data from the electric utilities sector to those from other industry sectors and ranked on the basis of total emissions by sector.

In 2009, electricity generation in America was responsible for 49 percent of all industrial toxic air pollution and accounted for about 75 percent of all mercury air pollution, the study said.

The findings underline the need for strong action by the Environmental Protection Agency to spur industry to clean up the emissions, Lashof said.

Amendments designed to block the U.S. environmental regulator's air pollution standards are expected to be brought before the U.S. House of Representatives this week, the groups said.

In February, the Republican-led House, in a bid to cut government spending and avoid a U.S. default on financial commitments, voted to thwart the EPA from making rules to limit mercury and other toxic emissions from cement plants.