"Eighty-seven percent of the city's heating oil soot pollution is created by burning the dirtiest heating oils available in only one percent of all buildings in New York City, according to this report. As a result of burning this toxic sludge (No. 4 and 6 oil)--which New York uses more than any other big city--9,000 large buildings spew out about 1,000 tons of toxic soot pollution every year. Soot pollution aggravates asthma, increases the risk of cancer, exacerbates respiratory illnesses and can cause premature death. EDF's study, "The Bottom of the Barrel: How the Dirtiest Heating Oil Pollutes Our Air and Harms Our Health," shows that the city's levels of nickel--a heavy metal that increases the risk of cardiovascular disease by thickening the walls of arteries--are nine times higher than other U.S. cities."