How Bad Is Japan’s Radioactive Contamination of the Ocean?

Clownfish swimming near sea anenome. Credit:
Clownfish swimming near sea anenome. (Image credit:

On Friday (April 8), Japan officials announced that workers at the stricken Fukushima nuclear power plant would be able to stop pumping contaminated water into the ocean on Saturday.

Now that the radioactive release is finally drawing to a close, experts on the ecological effects of radioactivity are stepping back to assess its impact. They say the contamination is probably a mere drop in the ocean.

While iodine-131 and cesium-137 concentrations near the nuclear reactors' drainage outlets are high, "the diluting capacity of the ocean is great, and radioactivity concentrations decrease with distance from the source," said Pal Andersson, a radioecologist with the Swedish Radiation Safety Authority.

Contaminants quickly disperse and sink to the seafloor. As a result, "the concentration in sea water 30 km [19 miles] from the nuclear power plant is comparable to levels suggested as reference values, below which there is no concern about effects on wildlife," Andersson told Life's Little Mysteries, a sister site to LiveScience. Radioactive substances such as uranium are naturally present in the ocean.

The ecological impact will thus be limited in scope, according to Ward Whicker, professor emeritus in the Department of Environmental and Radiological Health Sciences at Colorado State University and author of several books on the environmental impact of radiation.

"Any ecological effects are likely to be somewhat localized near the points of discharge," Whicker said.

The Fukushima fish

Even in the vicinity of the plant, seawater has probably shielded the marine life from a lot of the harmfulness of radioactivity. "The relatively high mineral (potassium, iodine and calcium) concentrations in seawater tend to reduce marine food chain concentrations of cesium-137, iodine-131 and strontium-90 dramatically, as compared to freshwater systems," Whicker said. The data he has seen from offshore water samples indicates that levels of radioactivity would need to be "orders of magnitude higher" to yield dangerous doses to local fish.

Any mutant fish that have been born are likely to quickly die out.

"Genetic effects can occur as a result of the releases, but it seems unlikely that they will be observed because of rapid natural selection of abnormal individuals in such a huge, open environment," Whicker explained.

"Levels of cesium-137 especially, and possibly iodine-131 for a few more weeks, may approach concentrations in fish, shellfish and seaweed that might exceed guidelines for human consumption."

Even so, consumption poses minimal danger. As Robert Peter Gale, a hematologist who helped coordinate medical relief efforts after both the Chernobyl and Fukushima nuclear disasters, told Bloomberg last week, "No one could afford to consume enough sushi to get radiation damage."

The future is bright

"Any local ecological effects are likely to be temporary due to the vast marine ecosystem and its ability to re-colonize local areas," Whicker said.

Even the ocean ecosystem of the Bikini Atoll, which was severely radiation-damaged by 20 nuclear tests conducted there in the late 1940s and 1950s, recovered in good stead, he said. "The atoll recovered significantly within a decade or so and now provides spectacular diving." The marine life there is flourishing, and safe to eat.

This article was provided by Life's Little Mysteries, a sister site to LiveScience. Follow Natalie Wolchover on Twitter @nattyover

Natalie Wolchover

Natalie Wolchover was a staff writer for Live Science from 2010 to 2012 and is currently a senior physics writer and editor for Quanta Magazine. She holds a bachelor's degree in physics from Tufts University and has studied physics at the University of California, Berkeley. Along with the staff of Quanta, Wolchover won the 2022 Pulitzer Prize for explanatory writing for her work on the building of the James Webb Space Telescope. Her work has also appeared in the The Best American Science and Nature Writing and The Best Writing on Mathematics, Nature, The New Yorker and Popular Science. She was the 2016 winner of the  Evert Clark/Seth Payne Award, an annual prize for young science journalists, as well as the winner of the 2017 Science Communication Award for the American Institute of Physics.