In its ruling, the court rejected state and major industry challenges to appeal rules designed to reduce chromium, arsenic, nickel and cadmium as well as mercury and other toxins.

In a 61-page ruling, a divided three-judge panel of the US Court of Appeals for the District of Columbia Circuit rejected several legal oppositions raised by challengers.

The challengers included more than 20 coal-dependent states and major companies such as Peabody Energy and the National Mining Association.

The challengers argued that the EPA didn’t thoroughly consider costs in drafting the pollutant standards, which would be applied to around 1400 units in more than 600 plants.

The cost of enforcing the ruling is estimated by the EPA at $US9.6 billion ($A10.27 billion).

However, since the estimate in 2007 the effects have likely been reduced because companies have since shifted away from coal-fired plants and budgeted for compliance expenses.

According to the Energy Information Administration, since November 2013, companies have announced plans to close nearly 30 units at nine coal-fired power plants, producing a total of 5.4 gigawatts of coal-fired capacity.

The EIA predicts that between 2012 and 2020, the capacity to produce a total of 60GW will be retired due to stricter emissions rules and other factors, with 90% of these retirements occurring by 2016.

The EPA rules were first mandated by Congress in 1990 but were delayed by litigation, petitioning and legislative opposition.

The rules require coal utilities to cut a minimum of 90% of their emissions of mercury, a neurotoxin the EPA believes causes brain damage and other health problems, chiefly in developing foetuses and young children.