A federal appeals court on Tuesday upheld regulations adopted by the Environmental Protection Agency to cut mercury and other emissions from large power plants, a setback for states and energy trade groups that have been challenging Clean Air Act regulations during the Obama administration.

The decision by a three-judge panel at the U.S. Court of Appeals for the District of Columbia Circuit means that coal- and oil-fired plants must purchase scrubbers and other equipment to prevent 91 percent of mercury from being released into the air during the burning of coal.

States led by conservative governors — among them Michigan, Idaho, Ohio, Alaska and Kansas — joined trade groups in claiming that EPA overstepped its authority by crafting the mercury rule without considering its $9.6 billion per year cost to the economy, risking 16,000 jobs.

When Congress granted EPA the authority to limit emissions of hazardous air pollutants in 1990, lawmakers were more concerned with the impact on human health than costs, Judge Judith W. Rogers wrote in the opinion.

“Congress was focused on the health hazard of emissions and the slowness of EPA regulation of them, and concluded it was reasonable to make decisions without considering costs,” Rogers wrote. There was no congressional requirement for the agency to focus on the economic hit.

Other factors weighed against the financial impact to industry, including health and environmental improvements worth more than $100 billion a year, the EPA said. The American Lung Association claimed it would prevent 11,000 premature deaths, about 5,000 heart attacks and 130,000 asthma attacks.

The court was not in full agreement in the case. Although Judge Brett M. Kavanaugh concurred with Rogers and Chief Judge Merrick B. Garland on many points, he dissented on the EPA’s failure to consider the cost of its regulations.

“In my view, it is unreasonable for EPA to exclude consideration of costs in determining that it is ‘appropriate’ to impose significant new regulations on electric utilities,” Kavanaugh wrote.

“To be sure, EPA could conclude the benefits outweigh the costs. But the problem here is that EPA did not even consider the costs. And the costs are huge . . . $9.6 billion a year, by EPA’s own calculation.”

Through several pages of the opinion, the judge’s debated the meaning of the word “appropriate.” A dictionary was consulted. In the end, the meaning, in relation to the case, was ambiguous.

Rogers ended the argument — for now. Lawmakers said nothing about considering costs in 1990 revisions to the Clean Air Act. “Basically, the petitioners and our dissenting colleague seek to impose a requirement that Congress did not,” she wrote.

National Mining Association President Hal Quinn called the court’s decision unfortunate, saying utilities had already spent $100 billion to reduce mercury since 2005. “The costs of EPA’s rules are significant and substantial,” he said. “Already more than 40,000 [megawatts] of electricity capacity have been scheduled for closure because of these rules. The Department of Energy forecasts that capacity retirements will reach 60,000 — enough electricity to power almost 30 million homes.”

Coal-fired power plants are among the nation’s greatest sources of stationary pollution, according to a January 2011 report by the Congressional Research Service. In 2005, they accounted for 70 percent of emissions of sulfur dioxide, nearly half of the mercury and 20 percent of the nitrogen oxide.

Mercury is among the most dangerous toxins. Studies link it to cancer in adults and neurological disorders in young children. Emissions of mercury from utilities fall on land and water, contaminating humans and fish.

In water, it develops into a more toxic strain called methylmercury and concentrates in large predator fish such as tuna. A recent study of small fish off the Maine coast found that their metabolism races as waters warm with the climate, compelling them to eat more in waters contaminated with methylmercury.

Smaller fish are eaten by larger fish up to the very top of the food chain, where methylmercury is concentrated in high doses. One of the predator fish, tuna, often winds up in small cans in kitchen pantries.

“Mercury from power plants is a leading source of the pollution that has led to fish consumption advisories in rivers and streams around the country as well as here in the Chesapeake Bay region,” said Jon Mueller, the Chesapeake Bay Foundation’s vice president for litigation. “Those contaminated fish put the health of many, including those who fish to feed their families, at risk.”