A decision by Chiquita Brands International to stop using fuel from refineries linked to Canadian tar sands oil is a sign of a growing trend, advocates said. Environmental advocacy group ForestEthics said it was working with Chiquita to stop using fuel from tar sands refineries in vehicles that deliver its products in the United States. \"Canada\'s tar sands is all risk and no benefit for leading American brands like Chiquita that are resolved to reduce environmental problems, so they are working hard to get Tar Sands out of their transportation footprint,\" Aaron Sanger, an official at ForestEthics, said in a statement. Canada is a major supplier of oil to the United States. Concerns over the environmental impact of so-called tar sands oil have escalated since a spill of Canadian crude into rivers in southern Michigan last year. ForestEthics said producing crude from tar sands projects releases more greenhouse gases than conventional crude. Residents downwind and downstream from Alberta oil refineries, the group said, have elevated levels of cancer. \"Tar sands crude is the dirtiest oil on Earth,\" Kate Colarulli of The Sierra Club said in a statement. The environmental groups said Chiquita\'s decision is a sign the United States doesn\'t need the planned Keystone XL oil pipeline, which would carry Alberta crude to refineries along the southern U.S. coast.