Toenails measure toxic exposure, Neighborhood looks very Extremely normal single-family homes and apartment buildings packed together, dogs barking from postage-stamp-size lawns, parents hustling down narrow sidewalks to fetch their children from school. But something with very dangerous potential lies below the surface, officials say. The residents' toenails will provide confirmation. A plume of hexavalent chromium, a metal used in industrial production that the Centers for Disease Control and Prevention calls a "well-established carcinogen," has spread under Garfield, putting about one-tenth of the city's homes — about 600 structures and 3,600 residents — at risk. The Environmental Protection Agency is about to start drilling on the spill site to determine how much chromium is pooled beneath and remove tainted soil. The agency is also testing the broader area to determine how it will be cleaned up. Now a group of scientists from New York University is working to as