LOS ANGELES (CBS/AP) — The Department of Homeland Security has begun screening passengers and cargo arriving in LAX from Japan for “even a blip of radiation” as radiation from the ongoing nuclear disaster is expected to arrive in Southern California.

KNX 1070’s Ed Mertz reports the first particles from the Japanese nuclear plant could arrive in southern California by late Friday, according to a United Nations forecast.

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Homeland Security Secretary Janet Napolitano said Thursday that no harmful levels of radiation have reached the U.S. since the nuclear crisis in Japan sparked by last week’s devastating earthquake and tsunami.

Air quality officials are monitoring the atmosphere on an hourly basis, and Neal Sheehan with the Nuclear Regulatory Commission says any amount of radioactive particles would be minimal.

Customs and Border Protection, which monitors ports, routinely screens passengers and cargo for radiation. Agents have been advised this week to pay particular attention to arrivals from Japan.

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KNX 1070’s John Brooks reports detectors are now being used at LAX after low-level radiation has reportedly been found in Dallas and Chicago on passengers and planes coming in from Japan.

Napolitano said the screening of passengers and cargo is being done “in an exercise of caution.”

The agency handles more than half a million radiation alarms a year, though most are related to medical procedures.

While online and brick-and-mortar vendors have seen a run on potassium iodide pills, health officials warn they should not be taken without proper guidance.

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