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The nuclear crisis in Japan has many people in California worried about possible radiation exposure here on the West Coast.
The South Coast Air Quality Management District says there has been no change in background levels of radiation.
The agency operates three stations around Southern California for the Environmental Protection Agency, which has deployed more radiation monitors in the western United States and Pacific territories after growing concerns by Americans.
Some computer models suggest the radioactive plume from the damaged Japanese plant could reach Southern California as early as Friday. Health officials have said there's no danger to the West Coast or Pacific territories.
They’re advising the public that potassium iodide tablets are not recommended at this time.
"Potassium iodide is used to protect the body from one specific type of radioactive material known as radioiodine," said Eric McDonald, M.D., M.P.H., County Deputy Public Health Officer. "Potassium iodide should only be used in cases of exposure to significant amounts of radioiodine."
Meantime, the Department of Homeland Security is screening passengers and cargo entering the United States from Japan for "even a blip of radiation."
Customs and Border Protection agents have been advised this week to pay particular attention to arrivals from Japan.
Napolitano said the screening of passengers and cargo is being done "in an exercise of caution."