Given all the hype over the greening of corporate America, and the regulatory schemes of the clean air and water acts, you’d think old-style pollution problems–the kind where manufacturers foul the air or water– would be behind us. They’re not. Today’s CNNMoney column is about a few environmental laggards in the chlorine industry who use an outdated technology that emits mercury into the air.

On a global scale, chlorine plants aren’t a huge problem. Far more mercury comes from coal-fired power plants and natural sources like volcanoes. But the column is a reminder that there’s still lots of work to be done to clean up big business. Here’s how it begins:

As a growing number of well-known companies promote themselves as friends of the earth, it’s easy to overlook the fact that others still pollute, unnecessarily. But they do.

So, at least, says Oceana, a Washington, D.C., environmental group that accuses four companies – Olin Corp., PPG Industries, Ashta Chemicals and ERCO Worldwide – of operating five manufacturing plants that release vast quantities of toxic mercury into the air every year. The plants make chlorine, which is used in swimming pools, plastics and paper towels, among other things.

The story’s a little more complicated than it seems; cleaning up the plants is very expensive, and there’s some argument about how much mercury they actually emit. But Oceana, which brought me the story, persuaded me that this is a problem than can and should be fixed. You can read the rest of the column here.