|August 13, 2013|
With radiation fears rekindled, researchers seek truth off Fukushima coast
|SHINCHI, Fukushima Prefecture--Although researchers have yet to confirm a trend in the radioactivity levels of marine life off the coast of Fukushima Prefecture, there have been reasons for optimism.|
Studies showed that the waters around the stricken Fukushima No. 1 nuclear plant had become safer. Radioactivity levels in marine creatures greatly fluctuated, but the highest levels were attributed to cesium sticking to the seabed mud.
Beaches reopened, plans were announced to resume fishing operations, and coastal communities felt that a sense of normalcy could finally return to their lives.
However, Tokyo Electric Power Co. admitted on July 22 that contaminated water from its Fukushima plant had been flowing into the ocean. In fact, the radioactive spillage had likely continued since the meltdowns in March 2011.
Although studies show that marine animals with high radioactivity levels have been concentrated right next to the nuclear plant, TEPCO's belated announcement has rekindled fears that all waters off the Fukushima coast are filled with radioactive substances, dealing a further blow to fishermen in the area.
"The image of contamination started spreading again just as we were preparing to resume operations," said Yuichi Manome, an official with the Iwaki city fishing cooperative.
On May 28, nearly two months before TEPCO's announcement, all restrictions on entering the ocean off Fukushima were lifted. Only those who work within a 5-kilometer radius off the coast from the Fukushima No. 1 nuclear plant must report to the local coast guard office.
For researchers from two universities, their work to determine the full effects of the nuclear disaster on marine life started last fiscal year. It may still be a while before they can comfortably give an accurate assessment.
One team of researchers, from Tohoku University, departed from a harbor near Tsurushihama beach in Shinchi about 50 kilometers north of the Fukushima No. 1 plant on Aug. 9. The tsunami following the Great East Japan Earthquake on March 11, 2011, swept away buildings in the area around the harbor.
About 500 meters off the coast, the water temperature was 21 degrees and the ocean about 5.9 meters deep. The murky water and the swirling sand were reminders that radioactive cesium is known to attach to sand and mud particles. Mud tends to accumulate on the sea bed in areas like this that are close to a river mouth.
The three-member team led by Yukio Agatsuma, a professor of marine plant ecology at Tohoku University, collected about 20 types of seaweed and 30 kinds of marine creatures from three areas on the seabed. They remained in each area for 30 to 40 minutes.
Seaweed was pulled up by the roots. Sea urchins, abalone, starfish and "hoya" sea squirts were placed in separate bags.
Along with the water and dirt brought up, the total amount collected reached about 100 kilograms.
After returning to land, the marine life was sorted by type and sent by frozen delivery for measurement. A minimum of 200 grams of a particular type of marine life is required for a radioactivity test.
At Tokyo University of Marine Science and Technology, the marine plants and creatures are cut into smaller pieces and sent to an agency for analysis.
One difficulty in swiftly determining the effects of the radioactive substances on marine life is that it takes about two months for the results of the analysis to be returned.
Past studies by Fukushima Prefecture found that as time passed, radioactivity levels declined at a faster pace for fish and shellfish in deeper parts off the coast than those on the seabed closer to the coast.
The aim of the Tohoku University team was to test marine life in shallow seabeds near the coast that could only be collected by diving.
"We want to confirm where and to what extent cesium still remains, and to also allay concerns that the cesium will go up the food chain to larger fish," Agatsuma said.
Tohoku University researchers have focused their studies off the coast of Soma about 50 km north of the Fukushima No. 1 plant. Researchers from Tokyo University of Marine Science and Technology have handled the area off the coast of Iwaki 35 to 50 km south of the plant.
Both teams have been working with the Fukushima prefectural government since the last fiscal year to measure radioactivity levels in marine life.
The researchers have also attached transmitters to fish to track their movements.
"We have been unable to determine trends yet because radioactivity levels have been different even for the same type of marine life depending on the sample and location where it was collected," said Agatsuma, who has made three dives off the Fukushima coast since the nuclear accident.
The highest level detected in samples collected by the Tohoku team was 74 becquerels of cesium per kilogram in a type of sea squirt.
Most marine life samples collected south of the Fukushima No. 1 plant have had levels of 50 becquerels or less. However, one type of sea urchin had a reading of 483 becquerels.
"It was likely due to the mud containing cesium that was collected at the same time," said Hisayuki Arakawa, a professor in the Ocean Sciences Department at Tokyo University of Marine Science and Technology.
Although marine life is washed and cut up into samples for measurement, it is difficult to remove all the sand and mud.
Studies by the prefectural government of the edible parts of sea urchin and sea squirts have not detected cesium. Experts also said it is unlikely for cesium to be transferred to fish that eat such marine life.
Among the seaweed collected, the highest radioactivity levels have been 59 becquerels.
CURRENTS DISBURSE CONTAMINATION
The level of radioactivity in water samples from the Pacific has fallen drastically since the accident because of the dispersal of the substances by ocean currents, according to the prefecture.
In May 2011, a water sample taken near the area of the latest dive by the Tohoku University team showed radioactive cesium levels of 6.37 becquerels per liter. By August 2011, the level could not be detected.
Although the readings showed the water is safe for swimming and diving, cesium has continued to be found in the seabed.
Before the Fukushima nuclear accident, the central government found cesium levels of between 0.19 and 3.5 becquerels per kilogram in samples collected from the seabed in 14 prefectures around the nation.
However, in June this year, dirt from the seabed off the coast of Soma showed a cesium level of 522 becquerels per kilogram. At the same time, samples from only a few kilometers away had cesium levels of only about 10 becquerels.
Tsuneo Fujita, an official with the Fukushima Prefectural Fisheries Experimental Station, said there were differences in cesium levels even 10 meters apart. He added that swells and waves affected the levels.
The radioactivity levels found in the seabed are much lower than on land. In wide areas of farmland in eastern Fukushima Prefecture, cesium levels of between 1,000 and 5,000 becquerels have been detected.
"When cesium is attached to inorganic materials, such as sand and mud particles, it is believed that the cesium will leave the body along with those materials," Fujita said. "There should be no concerns about swallowing the sand that may swirl up in the ocean."
FISHING DELAYED AFTER TEPCO ADMISSION
A totally different situation can be found in the port surrounded by a levee next to the Fukushima No. 1 nuclear plant.
TEPCO, which is in charge of radiation measurements within a 20-km radius of the plant, began testing fish in the port last October.
In December, a type of ocean perch caught in a net at the port had a radioactive cesium level of 254,000 becquerels. The net cannot capture all the fish because it has to be lifted whenever a boat passes through the area.
Later, a fat greenling was caught with cesium levels of 740,000 becquerels.
Outside of the 20-km radius, radiation measurements are conducted by the central and prefectural governments. The radioactivity levels in fish much further from the plant have significantly decreased. Only an occasional fat greenling, ocean perch or flounder now shows radioactivity levels exceeding the government standard of 100 becquerels, according to the researchers.
Amid that situation, moves have been made to resume fishing far off the coast of Fukushima.
One test fishing operation started in June 2012 in the northern part of the prefecture in waters about 150 meters deep. It began with three types of seafood, including octopus, and has since expanded to 15 types.
In the southern part of Fukushima Prefecture, plans were made to begin test fishing off the coast from September.
Closer to the coast, fishing for Japanese sand lance resumed this spring in northern Fukushima, and plans were announced to begin fishing for whitebait in September or October, even in the southern part of the prefecture.
A Fukushima prefectural government study did not find any sharp increase in radioactivity levels after TEPCO admitted on July 22 that contaminated water had been flowing into the ocean.
But fishing cooperatives in all parts of Fukushima decided to postpone the resumption of operations. Due to consumer fears about radiation poisoning, fishermen are worried that they will be unable to sell their catch even if the safety of the seafood is confirmed.