Physicists argue that the Fukushima nuclear disaster was less damaging to the global fishing industry than early media reports led people to believe, according to a new report published today in PNAS. This report comes on the heels of United Nations prouncement that no foreseeable health effects are expected from the accident among the general public and the vast majority of workers from the plant. 

The 2011 nuclear meltdown at Fukushima not only raised concerns over the damaging impact to local wildlife near Japan, but also fears that cancer-causing radioactivity may spread internationally, via aquatic species in the Pacific Ocean.  

Two surveys in 2012, also published in PNAS, calculated radioactive contamination in marine life in waters near the accident as well as from tuna that had migrated to shores near San Diego, Calif. In contrast to the ports in immediate vicinity of Fukushima, which remain closed to fishing to this day, the offshore regions of Japan and California were deemed safe.

"[Radiation] Doses to Japanese consumers were calculated to be higher than to American seafood consumers, but were still very low in most circumstances," said co-author Dr. Nicholas Fisher, Ph.D., distinguished professor at SUNY Stony Brook School of Marine and Atmospheric Sciences.

Both studies identified nuclear particles - cesium-134 and cesium-137 - in these marine ecosytems, but maintained that "radiation risks are below those generally considered harmful to marine animals and human consumers."

Despite this reassuring conclusion, over 1,000 stories appeared in newspapers, television, internet media, and radio outlets, with much of the coverage exaggerating the dangers posed to the seafood industry.

To assuage public fears, the authors of the 2012 studies have returned with a follow-up analysis of their original data to assess the threat that migratory bluefin tuna from Japan posed to California seafood.

"In our earlier publications we presented radioactivity concentrations in fish (bequerels per kilogram) but people could not translate those units to doses (and risks)," Fisher told Medical Daily.

Pacific bluefin tuna were surveyed because they are heavily fished along the coasts of both nations.

Rather than conveying radioactive exposure in terms of what was found in fish, the researchers expressed the dose that human consumers and fishermen in the U.S. and Japan may have experienced in the months after the meltdown.

By the time Japanese tuna completed their three- to four- month journey across the Pacific and reached the California coast, the authors concluded the fish would have excreted most of the nuclear particles from Fukushima and would contain non-harmful levels of radiation.

 

Natural Glow

All living beings - fish, humans, and otherwise - are already filled with radioactive elements. In fact, our bodies have evolved to maintain precise levels of natural radioactive compounds, like potassium-40, and excess amounts are quickly removed from our systems.

Some may argue that the nuclear particles from Fukushima are more dangerous than natural radioactivity. Not all radiation is the same, in terms of energy state, and there are four common forms in order of increasing peril: alpha particles, beta particles, gamma rays, and neutrons.

The radioactive material from Fukushima - cesium-134 and cesium-137 - falls into the gamma ray category, while natural particles like potassium-40 and polonium-210 are beta and alpha particles, respectively.

While they have varying levels of risk when exposed externally, they are all dangerous if high doses are present inside the body.

The authors calculated that the Fukushima-related radiation from cesium in California tuna would be between 200 to 1,000 times less potent than naturally occurring radioactivity - potassium-40 and polonium-210 - that was already present in the fish.

"The main point of this paper is that the radiation doses (and attendant risks) to human consumers eating Pacific bluefin tuna are likely to be extremely low, indeed orders of magnitude lower than that from naturally occurring radiation in the fish," said Fisher.

The researchers estimated that, on an annual basis, the average seafood lover would consume 600 times more natural radiation than Fukushima-related radioactivity. They argue that 95 percent more radioactive potassium would be ingested by eating a common banana.  

For a recreational fisherman, who the authors assumed eat about five times more seafood, the radiation dose from Pacific bluefin tuna would amount to a routine dentist's X-ray, which would increase their chances of developing cancer by 0.00002 percent.

Overall, this would amount to two additional fatal cancer cases per 10,000,000 similarly exposed people. 

One of the main highlights that was missed in the media coverage of the 2012 reports, according to Fisher, is the Fukushima disaster provides a unique opportunity to track the migration patterns of Pacific marine life.

"Radionuclides present in the fish could be used to trace migration patterns and timing for those animals that spend part of their lives in the western Pacific (such as bluefin tuna)," said Fisher.

While the current study did not address this point, it remains an interesting topic for future studies and raises a possible scientific benefit from the Fukushima disaster.

 

Source: Fisher NS, Beaugelin-Seillerb K, Hinton TG, Baumanna Z, Madiganc DJ, Garnier-Laplaceb J. Evaluation of radiation doses and associated risk from the Fukushima nuclear accident to marine biota and human consumers of seafood. PNAS. 2013.