The danger posed by the Gulf oil spill to the U.S. food supply is worse than previously thought, and could make testing of seafood necessary for decades to come, officials and scientists say.

The National Oceanic and Atmospheric Administration (NOAA) said Tuesday it was doubling the area in the Gulf where commercial and recreational fishing are temporarily off-limits as the oil slick spreads to the south and east. The prohibited area is now about 46,000 square miles, roughly the size of Pennsylvania or one-fifth of federal waters in the Gulf.

Federal officials had already shut down fishing in some offshore waters from the Mississippi River to the Florida Panhandle.

The spill “will affect the Gulf, and possibly the entire North American region, for maybe years, if not decades,” said Rowan Gould, acting director of the U.S. Fish and Wildlife Service.

Gulf products account for about 5% of the seafood consumed in the United States. Since the Deepwater Horizon oil rig exploded April 20, opening a gusher of oil from the ocean floor, testing has not found “substantial” quantities of contaminated seafood, said Roy Crabtree, the regional administrator for NOAA’s Southeast regional office.

Oil contains harmful chemicals such as polycyclic aromatic hydrocarbons that can cause cancer if ingested by humans in high concentrations, said LuAnn White of the Tulane University Center for Applied Environmental Public Health. However, she said monitoring efforts by the government and the seafood industry make the possibility of significant levels of toxic contamination “extremely unlikely   in anything that gets to market.”

“For the sake of people and the industry, it’s better to take some short-term hits than let anything tainted get in there,” said White, who participated in a meeting last week with Environmental Protection Agency officials to help contain fallout from the spill.