The first radioactive fallout from Japan's multi-reactor nuclear accident arrived on the East Coast late last week, Progress Energy and other nuclear plant operators reported.

More trace amounts of radioactive material are expected to be picked up this week by measurement equipment used by Progress Energy, Duke Energy and Scana Corp., the regional power companies that operate nuclear plants in the Carolinas.

The amounts detected so far are minuscule and pose no public health risks, nuclear experts and health officials said Sunday. A roundtrip international airline flight exposes a person to 100,000 times as much radiation, according to the U.S. Environmental Protection Agency.

"You could continue to receive that kind of dosage and not accumulate anything because it's so small," said Brian McFeaters, disaster preparedness coordinator for Wake County Human Services.

Last week Raleigh-based Progress Energy said it picked up very low levels of iodine-131, a radioactive byproduct of nuclear fission, at its Robinson nuclear plant in South Carolina and at the Crystal River plant in Florida.

The company expects to pick up similar readings this week when it takes periodic tests at the Shearon Harris nuclear plant in Wake County and the Brunswick plant near Wilmington, Progress spokesman Drew Elliot said.

The samples detected on the East Coast traveled half-way around the planet from Japan since several reactors were disabled by a tsunami March 11.

Elliot said the radioactive traces are not from Progress nuclear plants, because they were measured in isolation without the presence of other isotopes that would be present if the radioactive release took place locally.

"It's just above the threshold of detectability in our very sensitive measuring devices," Elliot said.

In much greater amounts, iodine-131 can cause thyroid cancer. Iodine-131 deteriorates rapidly, losing half its radioactivity every eight days.

U.S. authorities detected trace amounts of radioactive material on the West Coast early last week. The EPA reported small amounts of iodine, cesium and tellurium.

Japanese authorities have been scrambling to limit radioactive releases since emergency cooling equipment was knocked out at multiple nuclear reactors.

Since the natural disaster struck northern Japan, nuclear fuel at several reactors has melted, releasing radioactive materials into the atmosphere. The levels would be most dangerous near the damaged plants.

john.murawski@newsobserver.com or 919-829-8932