Radiation in Japan Seas: Risk of Animal Death, Mutation?


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Sailors wearing protective suits bring pure water to the Fukushima Daiichi nuclear power plant.

Aboard a boat pulling a barge with water for Japan’s overheating Fukushima nuclear plant Thursday.

Photograph from Japan Maritime Self-Defence Force via Reuters

Christine Dell’Amore

National Geographic News

Published April 1, 2011

If radioactive material from the Fukushima Daiichi nuclear power plant—disabled by the March11 Japan earthquake and tsunami—continues to enter the ocean, marine life could be threatened, experts say.

(See related photos: “Japan Tsunami: 20 Unforgettable Pictures.”)

In the past week, seawater samples taken near the nuclear power plant, on Japan‘s eastern coast, have shown elevated levels of radioactive isotopes, including cesium 137 and iodine 131, according to the New York Times. (See “Japan Tries to Avert Nuclear Disaster.”)

All life on Earth and in the oceans lives with exposure to natural levels of ionizing radiation—high-frequency radiation with enough energy to change DNA. Most such genetic damage heals, but the addition of human-made radiation can make it harder for the body to repair broken genes.

Radiation concentrations in the Japanese seawater samples have fluctuated in past days, but on Wednesday the amount of iodine spiked to 3,355 times the legal limit for seawater, Japanese nuclear safety officials told the Associated Press.

That level is the highest so far—and an indication that more radiation is entering the ocean, though how is still unknown, the agency reported. Cesium was also found to be 20 times its safety limit on March 28, according to the Times.

Radiation Can Cause “Bizarre Mutations”

Once in seawater, radiation can hurt ocean animals in several ways—by killing them outright, creating “bizarre mutations” in their offspring, or passing radioactive material up the food chain, according to Joseph Rachlin, director of Lehman College’s Laboratory for Marine and Estuarine Research in New York City.

“There will be a potential for a certain amount of lethality of living organisms, but that’s less of a concern than the possible effects on the genetics of the animals that become exposed,” Rachlin said.

“That’s the main problem as I see it with radiation—altering the genetics of the animal and interfering with reproduction.”

Even so, according to radioecologist F. Ward Whicker, the concentrations of iodine and cesium levels “would have to be orders of magnitude larger than the numbers I’ve seen to date to cause the kind of radiation doses to marine life that would cause mortality or reductions in reproductive potential.

“I am very doubtful that direct effects of radioactivity from the damaged reactors on marine life over a large area off the coast of Japan will be observed,” Whicker, professor emeritus at Colorado State University, said via email.

Likewise, using legal limits to gauge damage to marine life is of little value right now, he said.

To make a “credible assessment” of the risk to marine animals, scientists would have to know the actual concentrations of radioactive iodine in the water and fish or other marine animals off Fukushima Daiichi, he said.

Radiation Hardest on the Little Ones

It’s possible that levels of radioactive contamination near the Fukushima nuclear reactors could increase and cause some harm to local marine life, Whicker said.

“If this happens, the most likely effects would be reductions in reproductive potential of local fishes. … ,” he said.

Marine organisms’ eggs and larvae are highly sensitive to radiation, since radioactive atoms can replace other atoms in their bodies, resulting in radiation exposure that could alter their DNA, Whicker said. (Get the basics on genetics.)

Most such deformed organisms don’t survive, but some can pass abnormalities on to the next generation, Lehman College’s Rachlin said. Either way, the radiation exposure could hurt the population’s ability to survive long-term.

Rachlin thinks the most susceptible critters would be soft-bodied invertebrates such as jellyfish, sea anemones, and marine worms—which can take up the radiation more quickly than shelled creatures—though Whicker said fish may be most at risk.