Tiny amounts of radioactive isotopes of sulfur, believed to have traveled by wind across the Pacific Ocean from the Fukushima Dai-ichi nuclear plant, were detected in California, scientists say.
But the amounts detected weren't in any way harmful, says Mark Thiemens, a professor of chemistry at the University California, San Diego.
"It took me three years to figure out the chemistry, to be able to measure things that low," Thiemens told USA Today.
The California chemists were able to get their estimate based on air sampling.
Thiemens and his team were measuring the levels of sulfur-35 as part of climate research they were doing, and collected the readings between March 22 and April 1.
This was after the March 11 tsunami in Japan, and their readings indicated that there were 1,500 atoms of sulfur-35 per square meter in the air in La Jolla, Calif., which was an increase above normal levels, according to the Los Angeles Times.
"The tsunami came and we were measuring, but we didn't expect to see anything because reactors don't make sulfur," Thiemens told USA Today.
The results are published in Monday's issue of the journal Proceedings of the National Academy of Sciences.