Polychlorinated Biphenyls (PCBs)

Tom Harrington's backyard in Queensbury, N.Y., looks much as it used to, except for a few telltale signs: the maple tree is smaller, the swing set is in a different place, and the lawn has strange lines running through it, like a bad hair implant.

For 25 years, environmental groups and state officials have concentrated on the problems posed by toxic PCB's in the Hudson River, but now they are starting to focus on dozens of contaminated spots in landfills and backyards in the upper Hudson Valley.