LOS ANGELES — Radioactive particles released in the nuclear reactor meltdown in Fukushima, Japan, after the March 2011 earthquake and tsunami were detected in giant kelp along the California coast, according to a recently published study.

Radioactive iodine was found in samples collected from beds of kelp in locations along the coast from Laguna Beach to as far north as Santa Cruz about a month after the explosion, according to the study by two marine biologists at California State University, Long Beach.

The levels, while most likely not harmful to humans, were significantly higher than measurements prior to the explosion and comparable to those found in British Columbia, Canada, and northern Washington state after the Chernobyl disaster in 1986, according to the study published in March in the journal Environmental Science & Technology.

Giant kelp, or Macrocystis pyrifera, is a particularly good measure of radioactive material in the environment because it accumulates iodine, researchers said. They wrote that radioactive particles released into the atmosphere, in particular radioactive isotope iodine 131, made its way across the Pacific, then was likely deposited into the ocean during a period of significant rain shortly after the meltdown in Japan.

The highest levels were found in Corona del Mar in Orange County. Researchers wrote that the levels were probably highest there because the kelp is also exposed to urban runoff, which may have increased the amount of rainfall it received.

The study’s authors said that while the effect of radioactive material in kelp is not well known, it would have been consumed by organisms that feed on the kelp such as sea urchins or crustaceans. Certain species of fish, including opaleye, halfmoon or senorita may be particularly affected because their endocrine systems contain iodine, according to researchers.

“Radioactivity is taken up by the kelp and anything that feeds on the kelp will be exposed to this also,” Steven Manley, the study’s lead author, said in a statement released by the university. “It enters the coastal food web and gets dispersed over a variety of organisms. … It’s not a good thing, but whether it actually has a measurable detrimental effect is beyond my expertise.”

The researchers also analyzed kelp from Sitka, Alaska, for comparison, but did not find radioactivity. The kelp there may not have been exposed to the same degree because of atmospheric patterns.

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