WASHINGTON — The Supreme Court is taking up a challenge by industry groups and Republican-led states that want to roll back Obama administration environmental rules aimed at reducing power plant emissions of mercury and other hazardous air pollutants that contribute to respiratory illnesses, birth defects and developmental problems in children.

The justices are hearing arguments today in a case about the authority of the Environmental Protection Agency to take action against coal- and oil-fired power plants that are responsible for half the nation’s output of mercury. The EPA’s rules on emissions of chromium, arsenic, acid gases, nickel, cadmium as well as mercury and other toxic substances is supposed to begin taking effect in April, and be in full force next year.

The court is to decide whether the Clean Air Act requires that costs be a factor in the initial decision on whether to regulate hazardous air pollutants from power plants, or whether health risks are the only consideration.

The EPA did factor in costs, but only at a later stage when it wrote the standards are expected to reduce the toxic emissions by 90 percent.

The costs of installing and operating equipment to remove the pollutants before they are dispersed into the air are hefty — $9.6 billion a year.

But the benefits are much greater, $37 billion to $90 billion annually, the agency said. The savings stem from the prevention of up to 11,000 deaths, 4,700 nonfatal heart attacks and 540,000 lost days of work, the EPA said.

Mercury accumulates in fish and is especially dangerous to pregnant or breastfeeding women and young children, because of concern too much could harm a developing brain.