WASHINGTON — Elevated levels of cesium found in fish off Japan's east coast 18 months after the Fukushima nuclear disaster suggest a "continuing source" of radiation in the ocean, a new study has revealed.
Marine chemist Ken Buesseler of the Woods Hole Oceanographic Institution reviewed official Japanese data on radiation levels in fish, shellfish and seaweed collected near the crippled nuclear plant.
Buesseler concluded the lingering contamination may be due to low-level leaks from the facility or contaminated sediment on the ocean floor, according to his research, published Thursday in the US magazine Science.
He estimated that about 40 percent of fish caught near Fukushima are considered unfit for consumption under Japanese regulations.
"To predict how the patterns of contamination will change over time will take more than just studies of fish," said Buesseler, who led an international research cruise in 2011 to study the spread of radionuclides from Fukushima.
"What we really need is a better understanding of the sources and sinks of cesium and other radionuclides that continue to drive what we're seeing in the ocean off Fukushima."
A huge tsunami, sparked by a massive 9.0-magnitude undersea earthquake, swamped the Fukushima Daiichi nuclear plant in March 2011.
Reactors went into meltdown, spewing radiation over a large swathe of Japan's agriculture-heavy northeast, in the planet's worst atomic disaster for a generation. Around 19,000 people were killed or remain missing.
The study called it the "largest accidental release of radiation to the ocean in history".
Cesium levels vary across fish types, though Buesseler also found that demersal, or bottom-dwelling fish, consistently showed the highest cesium counts from the damaged nuclear plant.
Levels of contamination of almost all types of fish are not declining, even though the levels vary, the study showed.
The scientist stressed that the levels of radiation found in the vast majority of fish caught off Japan's northeastern coast remain within safe limits and the fish is fit for consumption.
Fears about food safety, which was once a given in Japan, have only slightly abated in the wake of the Fukushima disaster, with many consumers still eschewing products from the affected area despite government reassurances.
Japan's powerful farming and fishing industries have suffered both at home and abroad, with exports of farm products taking a major hit in 2011, falling 7.4 percent compared to the previous year.
Buesseler and Mitsuo Uematsu of the University of Tokyo are organising a scientific symposium in Tokyo on November 12 and 13 to present the latest findings on how the nuclear disaster has affected the ocean and marine life.