Radioactivity from Japan’s damaged Fukushima Daiichi nuclear power plant made its way in the atmosphere across the Pacific to the North American west coast in a matter of days following the March 11, 2011, earthquake and tsunami.
One of the major contaminants was the radioactive isotope iodine 131 (131-I), and because ocean kelps are one of the strongest plant accumulators of iodine, California State University, Long Beach (CSULB) marine biology professors Steven L. Manley and Christopher G. Lowe examined kelp samples and determined that iodine 131 was indeed present in California kelp more than a month after the tsunami.
Their findings appear in an article, “Canopy-Forming Kelps as California’s Coastal Dosimeter: 131I from Damaged Japanese Reactor Measured in Macrocystis pyrifera,” in the online edition of the journal Environmental Science & Technology.
Rainstorms contributed to depositing the airborne contaminants into the ocean, said Manley, an expert in marine algae and kelp. “We measured significant, although most likely non-harmful levels of radioactive iodine in tissue of the giant kelp Macrocystis pyrifera. Although it is probably not harmful for humans because it was relatively low levels, it may have affected certain fish that graze on the tissue because fish have a thyroid system that utilizes iodine.”
Moreover, he noted, “Although we measured iodine 131 because we were limited in what our instrumentation allows us to do, the big question was, is another major isotope that came over in the cloud, cesium 137, present in the kelp, too? It has a half-life of 30 years, where iodine 131 has a half-life of eight days,” so cesium may still be present.
Manley said he initiated the study as a follow-up to a 1980s study of radiation contamination from Ukraine’s Chernobyl nuclear disaster conducted by Professor Louis Druehl of Simon Fraser University in British Columbia. Druehl was the first to detect radioactivity from a reactor leak (Chernobyl) in an intertidal brown rockweed named Fucus.
“He was harvesting intertidal seaweed, which at high tides is covered in water and at low tides is exposed to air,” Manley said. “Most of this fallout comes from the atmosphere primarily in rain, which is what delivers it to the ground. Most of Fucus would be covered in seawater, so it wouldn’t get the full exposure as when it was exposed to the air at low tide. But one of the nice things about Macrocystis is that it’s a canopy-forming kelp and it’s not influenced by tides because it’s out in the subtidal area. It has these big canopies that are at the water-air interface and are continually exposed to whatever falls out of the sky.
“I have a graduate student, Danielle Burnett, and she was already sampling kelp blades for another study for me, so I asked her to sample some kelp blades at her three study sites along Orange County,” at Corona del Mar, Laguna Beach and Crystal Cove, Manley said. “She brought back some blades and I processed them and counted them and found radioactivity in them. But because our instrument is rather old, it couldn’t identify what the isotopes were right away. You have to look for the decay profile. I’d count them every few days and then you’d see a decay. I thought, ‘I’ve picked up something. I wonder what it is?’ We let it decay away and calculated the half-life and it was eight days and it was I-131.”
He then called upon Lowe, director of the CSULB Shark Lab and an expert in marine fisheries, to ask his graduate students working in the field to also obtain kelp samples. Lowe also helped obtain funding for the study from USC Sea Grant, which engages in a variety of coastal ecosystem and marine biology studies.
In addition to Orange County, Manley and Lowe obtained samples collected by CSULB students as well as marine biologists from UC Santa Barbara, UC Santa Cruz and the University of Alaska Southeast. California samples contained varying low levels of iodine 131, but a closely related kelp in Alaska, Macrocystis integrifolia, had none. “We didn’t find any activity there, but it could have been that it decayed away and we didn’t detect it or it could also be that the plume never did get up there in a high enough concentration,” Manley said.
“Radioactivity is taken up by the kelp and anything that feeds on the kelp will be exposed to this also,” he continued. “Even though we detected low levels, it still got into the environment and we don’t know anything about the other radioisotopes like cesium 137, which stays around much longer than iodine. In fact, the values that we reported for iodine probably underestimate what was probably in there. It could be two to three times more because we were just sampling the surface tissue; the biomass estimates were based on canopy tissue and a lot of kelp biomass is underneath. So, probably two or three times more was in the tissue at its height. Then it enters the coastal food web and gets dispersed over a variety of organisms. I would assume it’s there. It’s not a good thing, but whether it actually has a measureable detrimental effect is beyond my expertise.”
Manley hopes to engage CSU’s Coastal Affairs, Science and Technology (COAST) consortium of all CSU campus marine biology programs in follow-up studies. “Through them, I’d like to see if we can organize a standardized monitoring system where we can get tissue and background samples every few months so that if another event occurs, we’ll have some baseline information. It would be a good way to monitor our coastal environment.
“I was thinking of writing a grant to study cesium accumulation in kelps, in Macrocystis in particular. But that study can only work if we have a vibrant graduate program, because if we don’t have graduate students, we really can’t go out and collect the samples and do the experiments,” he said, adding that potential state funding cutbacks may have a detrimental effect on CSULB’s graduate programs, which are a source of many professionals and educators in the sciences and a variety of other fields.
“Chris and I are pretty happy with this study,” Manley said, “because it was just one of those spur of the moment things and it panned out really well.”