Kelp along the California  coast was found to be contaminated with radioactive material from a nuclear plant damaged in the March 2011 earthquake and tsunami that struck Japan, according to a recent study.

Researchers at California State University, Long Beach  found that the kelp contained radioactive iodine, cesium, xenon and other particles at levels unlikely to be detrimental to human health  but much higher than the amounts measured before the disaster.

The levels were also about the same as those measured in British Columbia and Washington state after the 1986 Chernobyl nuclear power plant explosion.

The researchers  also expressed worry that the radioactivity could have made it into the coastal food chain, although they weren't sure what impact that could have.

"Radioactivity is taken up by the kelp, and anything that feeds on the kelp will be exposed to this also," said co-author Steven Manley in a news release.

Medical experts, however, said the disaster's impact on U.S. public health was likely insignificant. Exposures of large numbers of people in past nuclear accidents, such as Chernobyl, have indicated that any radiation that reached the West Coast  wouldn't have much of an effect.

"But in Japan, the effects are as serious as we thought.  There's still a lot of contamination there," said Dr. Nagy Elsayyad, an assistant professor of radiation oncology at the University of Miami Sylvester Cancer Center.   "Some areas are still getting contamination in the fish, and some of the radiation is very long-lasting."

Manley and his co-author, Christopher Lowe, wrote that exposures along the North American coast should continue to be monitored.

"The resulting data would reveal the pattern of plume dispersal and the degree of contamination of the coastal community."