The public panic over the threat of radioactive food has subsided in the four years since the Fukushima No. 1 nuclear power plant experienced three reactor core meltdowns and spewed massive amounts of fallout, but worries persist.

Seikatsu Club, a mail-order food delivery co-op, maintains an online database that includes more than 700,000 results of radiation tests on food items. Page views have fallen to about one-tenth of their peak in 2012, said Hiroshi Tsuchida, a quality management division chief with the co-op, but there are people who still visit the site almost daily.

“For such members, we are continuing testing and disclosing all the data on our website,” Tsuchida told The Japan Times. “In Ukraine, there are screening devices at markets where people check food even today, nearly 30 years since the (start of the Chernobyl) nuclear disaster. I believe we should do the same.”

Despite the lingering fears, however, overall contamination levels of farm produce and seafood from Fukushima and neighboring prefectures have declined significantly.

For the first time since the 2011 start of the nuclear disaster, all Fukushima rice harvested in 2014 cleared mandatory radiation tests, meaning none exceeded the state-set safety levels of 100 becquerels of radioactive cesium per kilogram.

The same goes for beef, pork, chicken, leafy vegetables, fresh fruit, eggs and milk, as none of the samples checked by the central and local governments exceeded the threshold for the past one or two years, according to health ministry data.

But concern remains over fish, wild vegetables and wild game. Between April 1 last year and March 1, around 292,000 such samples were tested for radioactive cesium and 502, or 0.17 percent, exceeded the safe threshold, the health ministry said. In fiscal 2012, that ratio stood at 0.85 percent.

Wild vegetables, wild game, mushrooms, freshwater fish and bottom-dwelling ocean fish made up most of the contaminated food that exceeded the threshold over the past year, and was thus banned from shipment.

In February, wild boar meat from Fukushima Prefecture was found to contain 15,000 becquerels of cesium per kilogram, the highest figure since last April 1.

Highly contaminated wild game was also found in Miyagi, Iwate, Ibaraki, Tochigi, Gunma, Niigata and Saitama prefectures, including wild boar meat from Miyagi that contained 1,300 becquerels of cesium per kilogram and deer meat from Saitama that contained 530 becquerels of cesium per kilogram, according to government data.

As for mushrooms and wild vegetables, samples from 11 prefectures, including Fukushima, Yamanashi, Nagano and Shizuoka, exceeded the threshold between April 1 last year and March 1, according to the data.

The threshold of 100 becquerels per kilogram is intended to curb the total internal exposure to cesium from food to less than 1 millisievert per year.

Cumulative exposure of 100 millisieverts would increase the chance of death by cancer by 0.5 percent, according to the International Commission on Radiological Protection.

According to the Food Safety Commission of Japan, an adult weighing 60 kg usually maintains a natural level of 7,000 becquerels of radioactive materials, including 4,000 becquerels of radioactive potassium, in their body.

The overall contamination levels in fish have also declined over the past couple of years, despite ongoing leaks of highly radioactive water from Tokyo Electric Power Co.’s crippled Fukushima No. 1 power plant into the Pacific.

According to sample test results released by the Fisheries Agency, of 3,766 fish tested in Fukushima between October and last month, only 13 of them, or 0.3 percent, exceeded the government threshold. Between October 2011 and March 2012, that figure was 30.5 percent.

In 2012, a total of 18 fish caught in Fukushima and Miyagi contained over 1,000 becquerels of cesium per kilogram, or 10 times the state threshold. The highest reading of cesium-134 and -137 was 3,300 becquerels per kilogram, found in iwana mountain trout from Fukushima, according to sampling data of the Fisheries Agency.

But between last April 1 and March 1, the highest cesium level in iwana from Fukushima was 740 becquerels per kilogram. As for bottom fish, 510 becquerels of cesium per kilogram was the highest level of contamination found by the central and local government sampling tests.

But the decline in contamination has been very slow among bottom fish, including karei flat fish and ainame greenling caught off Fukushima. The same is true of freshwater fish, including iwana, caught from rivers, lakes and ponds in Fukushima, Miyagi, Tochigi, Gunma and Chiba prefectures.

Toyoji Kaneko, a professor of aquatic bioscience at the University of Tokyo, said that in a pond, for example, radioactive cesium that accumulated in the water and soil and pond-bed would have no outlet and thus would tend to remain there. The fish would ingest the isotope, expel it and ingest it all over again, he said.

To reduce radioactive contamination, some suggest removing the highly contaminated surface soil at the bottom of ponds, lakes and river mouths. But the removal process would only stir up more radioactive substances in the water and dirt, Kaneko said, and there would be no way to dispose of such residue. A realistic option would be to leave the sites alone and wait for the cesium to decay, he said.

Jota Kanda, a professor of chemical oceanography at Tokyo University of Marine Science and Technology, said that in the case of bottom fish, the route of their contamination has yet to be established. Some experts believe the bottom fish become contaminated by eating radioactive matter on the seabed, while others note that such fish have a slow biological half-life, which is usually around 50 days for a marine fish.

“Even though there are issues regarding whether consumers will purchase such fish, eventually the contamination will decline to a level that will allow Fukushima fishermen to resume commercial fishing,” Kanda said.

But the revitalization of Fukushima fisheries once the contamination is gone is a different matter, he said.

Currently in Fukushima only trial fishing is conducted on 58 kinds of marine produce that have shown very low or undetectable levels of radioactive cesium, including squid, octopus and mackerel.

But the latest announcement by Tepco that radioactive rainwater has been running into the ocean since last spring has devastated local fishermen, further damaging the image of fish from Fukushima.

One positive outcome of the unprecedented duration of the Fukushima ban is that fish have grown in abundance since the curbs were initiated.

The quality of fish caught off Fukushima also seems to be improving, as fatty, tasty-looking fish are often caught, Kanda said.

By carefully managing such increased resources and catching only a limited amount, Fukushima may be able to somehow create a brand for its fish, he said.