The Coast Guard and the Department of Environment and Natural Resources yesterday were racing against time to prevent a major environmental disaster as oil seeped from a tanker that sank between Guimaras and Negros Islands Friday. The spill is threatening marine life and the tourism industry of Western Visayas, officials said, and moving closer to Negros Occidental. The Coast Guard in Bacolod had a Marine Environment Protection Unit, assisted by trained personnel of oil firms in the province, on standby to set up spill booms in case the oil slick approaches Negros, to help prevent its entry into the area, Chief Petty Officer Cornelio Barbasa said.