LONG BEACH, Calif. – Kelp off Southern California was contaminated with short-lived radioisotopes a month after Japan’s Fukushima accident, a sign that the spilled radiation reached the state’s urban coastline, according to a new scientific study.
Scientists from California State University, Long Beach tested giant kelp collected in the ocean off Orange County and other locations after the March, 2011 accident, and detected radioactive iodine, which was released from the damaged nuclear reactor.
The largest concentration was about 250-fold higher than levels found in kelp before the accident.
“Basically we saw it in all the California kelp blades we sampled,” said Steven Manley, a Cal State Long Beach biology professor who specializes in kelp.
The radioactivity had no known effects on the giant kelp, or on fish and other marine life, and it was undetectable a month later.
Iodine 131 “has an eight-day half life so it’s pretty much all gone,” Manley said. “But this shows what happens half a world away does effect what happens here. I don’t think these levels are harmful but it’s better if we don’t have it at all.”
A year ago, Manley watched coverage of the tsunami and Fukushima accident and wondered what impact it might have on California’s marine life, particularly his favorite subject matter – kelp.
Spread in large, dense, brown forests across the ocean off California, Macrocystis pyrifera, known as giant kelp, is the largest of all algae and grows faster than virtually any other life on Earth. It accumulates iodine so Manley realized it would be a useful dosimeter to check how far radioactive material spreads.
“Kelp forests are some of the most productive ecosystems on Earth,” he said. “I thought this would be an opportunity because one thing about macrocystis is it has a large surface canopy,” which means it is continually exposed to the air – and whatever contaminants are in it.
In addition, giant kelp concentrates radioactive iodine 10,000-fold – for every one molecule in the water there would be 10,000 in its tissues.
Kelp was collected at three sites off Orange County, as well as Palos Verdes Peninsula in Los Angeles County, Santa Barbara, Pacific Grove and Santa Cruz. The highest concentration of iodine 131 was found in the kelp off Corona del Mar, which receives runoff from a large portion of Orange County. Its kelp was collected on April 15 of last year and tested five days later.
The level of radioactive iodine found there – 2.5 becquerel per gram of dry weight -- was “well above” levels sampled in kelps prior to the Fukushima release, according to the paper, published online earlier this month in the journal Environmental Science & Technology.
It was about 250 times higher than the concentration found in giant kelp off British Columbia before Fukushima.
When kelp from the same California sites was re-sampled a month later, in May of 2011, it contained no detectable amounts of radioactive iodine.
The scientists estimated that the entire kelp tissue on the surface at Corona del Mar contained about one millicurie.
“In terms of overall exposure to the kelp bed itself, it’s not a huge amount,” said Manley.
It would not have harmed the kelp, a species that grows from northern Baja to southeast Alaska, he said.
Some radioactive material probably accumulated in fish that eat the kelp – opaleye, halfmoon and senorita.
“If they were feeding on it, they definitely got dosed. We just don’t know if it was harmful. It’s probably not good for them. But no one knows,” Manley said. “In the marine environment it was significant, but probably not harmful at the levels we detected it, except it may have affected certain fish’s thyroid systems, the ones that fed on the kelp.”