Mercury, which damages the brains and nervous systems of children from the time they're in the womb, is just one of the toxic pollutants from coal-fired power plants. New EPA regulations would require high-tech scrubbers to limit emissions. Arguments before the US Supreme Court today pitted the coal industry against the Environmental Protection Agency. Twenty states joined the opposition to power-plant regulation, while 17 other states said it's needed. But does the Clean Air Act require the agency to balance the potential health benefits against the cost of the technology? Did the justices provide any clues about rulings to come on Obamacare and actions against climate change?