Autumn is high season for freshly harvested “shinmai,” the new rice marketed as a seasonal favorite in Fukushima Prefecture. But the farmers there fear their fare will go unsold because harvests around three cities have turned up excessive levels of radioactive cesium, prompting shipment bans.

Consumers are deeply worried as well. Where was the contaminated rice found? What about rice from other prefectures? How are authorities measuring the contamination?

Following are questions and answers on rice contaminated by fallout from the Fukushima No. 1 power plant.

Where was tainted rice found?

Rice exceeding the government’s cesium threshold of 500 becquerels per kilogram has been found in five districts in the cities of Fukushima, Nihonmatsu and Date.

No rice over that limit been found in other prefectures so far.

How badly is the rice contaminated and what are the risks of consuming it?

The highest contamination level so far is 1,240 becquerels per kilogram of unpolished rice grown in Date.

If the isotope is assumed to be cesium-134, the internal radiation dose will amount to 0.02356 millisieverts per kilogram consumed.

A dose of 100 millisieverts increases one’s lifetime cancer risk by 0.5 percent, according to the International Commission on Radiological Protection and other bodies.

Where in the prefecture was the tainted rice grown?

The first crop found with cesium above the provisional limit came from a farm in the Onami district in the city of Fukushima, resulting in the first government ban on shipments on Nov. 17.

Onami is just 80 km away from the Fukushima No. 1 plant.

Shortly afterward, more findings prompted bans on grain shipments from the Oguni and Tsukidate districts of Date, which has known “hot spots” where annual exposure can exceed the 20-millisievert limit.

The central government also banned shipments of rice grown on the outskirts of the capital, and from the Shibukawa district in the city of Nihomatsu.

Hadn’t Fukushima Gov. Yuhei Sato declared rice from his prefecture safe?

Sato made the declaration in October, after tests on rice samples in the prefecture had already been completed. The first batch of tainted grain turned up in mid-November, when an Onami farmer took unmilled rice individually to a local agricultural cooperative for inspection.

Despite the ban, Sato said on Nov. 30 that he won’t retract the proclamation because the prefecture won’t allow rice to be shipped even if it contains more than 10 becquerels of cesium per kilogram — a limit much more stringent than the government’s.

How did the prefecture test the rice?

Officials basically followed the rules set by the Agriculture, Forestry and Fisheries Ministry, except that they doubled the number of inspection locations.

According to the farm ministry, 17 prefectures required to inspect rice screened the produce in two stages using preharvest tests and postharvest tests.

Preharvest tests on unmilled rice are carried out in areas where soil has been found to contain 1,000 becquerels of cesium per kilogram, which means it radiates more than 0.15 microsievert per hour.

If rice containing more than 200 becquerels per kilogram is found, the crop must undergo a postharvest test for every 15 hectares harvested.

After that, experts say that cesium levels will decline quickly as the rice is polished. About 70 percent of the cesium ends up in the straw, with another 10 percent ending up in the bran and 7 percent in the chaff and the rice itself.

Areas in the 30-km hot zone around the Fukushima power plant and unusually hot spots — including the village of Iitate — are not allowed to grow rice in fiscal 2011.

Aomori, Iwate, Miyagi, Akita, Ibaraki, Tochigi, Gunma, Chiba, Kanagawa, Saitama, Tokyo, Yamagata, Niigata, Nagano, Yamanashi and Shizuoka prefectures are also inspecting rice.

Did Fukushima Prefecture find excessively tainted rice during the postharvest tests?

No, the cesium levels in the four named districts were well below the government’s limit in early inspections.

But the case of the Onami farmer suggests tainted rice can still slip through government inspections.

Was the contaminated rice shipped to market?

Some of it. One of the two farms in the Oguni district said 9 kg of its rice was sold at a local store and the remainder was stored at homes and agricultural cooperatives. The prefecture has been trying to identify the buyers.

Other excessively tainted rice in Onami, Tsukidate and the city of Fukushima was not shipped.

It is possible that rice harvested in the four areas was sold through direct sales channels before the government ban, as Japan Agricultural Cooperatives allows rice from areas measuring under 10 becquerels of cesium per kilogram to be distributed. Private wholesalers purchase rice only from such areas.

The prefectural government is therefore investigating the circulation channels involving farms in the four districts.

What is Fukushima doing to prevent tainted rice from being shipped?

Officials plan to check about 25,000 farms whose rice was found tainted in either stage of testing in September and October — even if that level was below the provisional limit. Those farms account for nearly 40 percent of the farms in the prefecture.

When will the new inspections end?

Probably next year. It takes time because officials are also examining cesium levels in beef and only have 10 germanium detectors, which can measure food radiation precisely but cost from ¥15 million to ¥20 million apiece, according to the Health, Labor and Welfare Ministry

The prefecture thus opted to conduct simpler inspections on rice containing 200 becquerels or less per kilogram. Nonetheless, only 4,000 farms can be checked per week.

The farm ministry announced early this month that it would support Fukushima by sending staff and lending out detectors.

Is the farm ministry going to revise its rice inspections?

Probably. Agriculture, Forestry and Fisheries Minister Michihiko Kano hinted in November that changes are needed.

“We will focus on areas with radiation hot spots and areas surrounded by mountains and investigate there thoroughly,” Kano said.

The prefecture is probing with experts the reasons why rice in the certain districts ended up with higher levels of cesium.

All of the four districts where cesium-tainted rice was found are situated in areas where the rice paddies are surrounded by mountains.

The Weekly FYI appears Tuesdays. Readers are encouraged to send ideas, questions and opinions to hodobu@japantimes.co.jp