U.S. car makers such as General Motors, Ford, and Nissan are purchasing steel made from pig iron that is smelted using large amounts of illegally logged timber from the Amazon rainforest, according to a two-year investigation by Greenpeace. The environmental group also said that the pig iron smelting, fueled by charcoal produced from tropical forest trees, has resulted in virtual slave labor and illegal logging of indigenous lands in northeastern Brazil. The Greenpeace investigation said that Brazil’s Carajas region — where three-quarters of the forests have been cleared, mainly for charcoal production — is home to 43 blast furnaces used by 18 different companies. Two of the major companies, Viena and Sidepar, sell pig iron to a U.S. steel mill operated by Severstal, Greenpeace said. That mill sells steel to General Motors, Nissan, BMW, and Mercedes, according to Greenpeace. As illegal charcoal operations have decimated the forests in Carajas, loggers have entered conservation areas belonging to indigenous tribes, who have lost 30 percent of their lands to illegal loggers, Greenpeace said.