There is no published research on what iodine 131 might do to fish at the levels found in the kelp.
“That is a good question and one we don’t really know the answer to as yet,” said Christopher Lowe, a biology professor and director of Cal State Long Beach’s Sharklab, which studies sharks and game fish. Lowe was co-author of the kelp study.
“Without actually measuring this, my guess is that the effects on fish thyroids from this limited exposure are probably negligible. However, that may not be the case for herbivorous fish species exposed closer to the release site” in Japan, Lowe said.
One toxicologist who works with fish said fish thyroids are sensitive to radioactive iodine but there is no data on its effects. High levels might cause thyroid tumors in the exposed fish or alter their cells’ genetic material.
Although radioactive iodine would move up the food web, it would be decaying at the same time that it is being concentrated, so it would be gone from the fish within days.
“It’s definitely not harmful to humans,” Manley said.
Any effects on marine life would be “below minimal -- negligible, undetectable,” said Nicholas Fisher, Distinguished Professor in the School of Marine and Atmospheric Sciences at State University of New York, Stony Brook.
“Do I think it’s a public health concern? Absolutely not in California” and probably not in Japan marine life, either, Fisher said.
Iodine 131, found in nuclear fission products, is not naturally occurring and is not naturally found in oceans. It was a significant part of the plume from Fukushima, and a major contributor to the cancers and other health hazards from atomic bomb testing in the 1950s and the Chernobyl disaster.
The ocean and everything in it, however, contain many other naturally radioactive materials.
“The reality is there are far more natural radionuclides in marine life than manmade ones,” Fisher said. “There are naturally occurring radioisotopes that have been in the ocean for billions of years, before man ever showed up and they occur at pretty high concentrations in organisms, much more than the artificial radioactivity introduced by
Fukushima, or even Chernobyl, which was worse. Even at its peak, it was probably very low compared to the natural radionuclides.”
Manley said that natural radiation in the ocean water is around 15 becquerel per liter. And if they calculated the levels in the water squeezed out of the kelp, "it would be 400 Bq per liter, which is well above the ocean average for natural radiation,” he said. In the kelp itself, the amounts of Fukushima radioactivity were about the same as natural radioactive potassium found in other research.
The scientists only measured iodine 131, although other isotopes were in the plume from Japan that also accumulate in kelp. One of them, Cesium 137, has a 30-year half-life.
Fisher and chemist Ken Buesseler from Woods Hole Oceanographic Institution studied fish off the coast of Japan for Cesium 137 and 134, which accumulate in muscle tissues or filets. Their results are expected to be published next week.
Fisher said the levels they found in the fish 30 kilometers off Japan “are not a problem…Detectable, but not at high levels.”
In Southern California, the kelp was collected after rainstorms, which would have washed the radioactive material from the air onto land and then into the ocean.
Other sites that were measured – including Orange County’s Laguna Beach and Crystal Cove – were less contaminated than Corona del Mar, since the latter gets urban runoff via a creek that winds through much of Orange County.
“A whole confluence of things were happening. You’ve got this plume that moves along, and then when it rains, that’s when the material comes out in the rain,” Manley said.