Creosote, coal-tar creosote, coal-tar pitch
Coal-tar creosote is a greasy black liquid used as a wood preservative. Before the advent of pressure-treated wood, it was available from hardware stores for consumers looking to weather-seal their fences and mailbox posts. Both the International Agency for Research on Cancer and the EPA have determined that the coal-tar version of creosote is a carcinogen. Eating food or drinking water contaminated with it can cause burning in the mouth and throat, and stomach pains; contact can cause rashes, chemical burns on the eyes, convulsions, kidney or liver problems, and death. And take note: Even if you don't have a can of the stuff lurking in the basement, it might be coating the old railroad ties the previous owner used to build a raised vegetable garden.