More than a year after the March 2011 tsunami that struck Japan, devastating the region and crippling the nuclear power plant at Fukushima, the effects are still apparent. Of utmost concern, is the effects of nuclear radiation on the environment and the potential threat of this to human health. To get a better understanding of these effects, scientists are focusing their attention on marine fish.
Tsunami Damages Fukushima Nuclear Plant
On March 11, 2011, an undersea earthquake measuring 9.0 on the Richter scale – reportedly the 4th largest earthquake ever recorded – triggered a 40-foot tsunami that engulfed the northeastern coastline of Japan. The tsunami not only resulted in the death of an estimated 20,000 people, it also caused major damage to the Fukushima nuclear power station, resulting in a catastrophic radiation leak into the surrounding ocean waters.
Fukushima Radiation Contaminates Seafood
Japan is one of the highest consumers of seafood products in the world, prompting concern over the associated health risks of consuming seafood contaminated with radionuclides. Consequently, many in-shore fisheries have been closed since the radiation leak, and the Japanese Ministry of Agriculture, Forestry and Fisheries have been sampling fish, shellfish, and other seafood products, such as seaweed, to ascertain levels of radiation.
Marine chemist Ken Buesseler from Woods Hole Oceanographic Institution, conducted an analysis of available data on the radiation levels of marine organisms, which was provided by the Japanese Ministry of Agriculture, Forestry, and Fisheries who tested approximately 9,000 samples collected from different sites in areas surrounding Fukushima.
In a Perspectives article published in the journal Science (October 25, 2012), Buesseler reveals that while 60% of fish caught in waters off the northeastern coast of Japan have radionuclide levels that are below the limits considered safe for human consumption, 40% of fish have cesium levels that are too high to be safe for human consumption – with most of the fish that contain radionuclide contaminants higher than the set limits being caught in the waters off Fukushima Perfecture. What was interesting, however, is that demersal fish that live on the bottom of the ocean consistently showed the highest levels of the radionuclide cesium in their tissue. Buesseler also noted that while radionuclide levels in the fish sampled varied, in almost all types of fish sampled, the levels of contamination were not declining.
Continued Source of Radioactive Contamination
Cesium is typically released from saltwater fish fairly quickly and does not remain in their body tissue for long, therefore the levels of cesium should be diminishing much quicker than what is being observed. As this is not happening, and given the continued high radionuclide levels detected in bottom dwelling fish, Buesseler believes that either radiation could be continuing to leak into the ocean from the nuclear plant, or radiation that is lingering in contaminated sediments on the seabed could be being reintroduced into the ocean water to contaminate the fish.
“To predict the how 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.”
When Will Fish be Safe to Eat?
Because levels of contamination vary widely across fish species and catch dates, this makes it very difficult for fishery managers to determine when to close or reopen different types of fisheries. Furthermore, different fish species may absorb and release the contaminants in different ways and at different rates, which makes it difficult to regulate fisheries generally or to communicate the reasons why certain fisheries remain closed while others may be reopened, to a public that is eager to continue consuming their staple diet – fish.
K. O. Buesseler. Fishing for Answers off Fukushima. Science, 2012; 338 (6106): 480 DOI: 10.1126/science.1228250