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Kai Ryssdal: We’ve known for decades that mercury is incredibly toxic. The government regulates factory emissions of the stuff. And the newest in that category as of this week is cement plants.

From the Marketplace Sustainability Desk, Scott Tong reports.

Scott Tong: Cement is the glue that holds together concrete, which as the industry puts it, is the foundation of the construction economy.

Andrew O’Hare: In fact, it is the second most used material on earth, second to water.

Andrew O’Hare is with Portland Cement Association. He says plants can’t avoid spewing mercury; it’s in the limestone that gets crushed and heated to make cement. Regulations will force plants to install expensive pollution filtering equipment — or shut down.

O’Hare: We were looking at shuttering as many as 40 cement plants, which represents about 40 percent of our current U.S. cement-manufacturing capacity.

On the other side, EPA says the rules will cut mercury emissions every year by 16 tons. And this is toxic stuff: Remember, even a broken old-school thermometer is cause for alarm.

John Walk at the Natural Resources Defense Council is a fan of the new rules. He’s an even bigger fan of the Obama administration’s EPA.

John Walk: The mindset at EPA under the current administration is vastly different than the deregulatory agenda of the Bush administration.

And the agency’s just getting started. It’s expected to put out mercury rules for coal-fired power plants, which may put the oldest plants out of business. And greenhouse gas rules are coming, too. Congress hasn’t acted, but the EPA believes it can regulate carbon dioxide under the existing Clean Air Law, and the regulators have withstood a recent court challenge.

In Washington, I’m Scott Tong for Marketplace.