Potatoes may be more dangerous than other vegetables
2011/05/29
A farmer crushes vegetables earmarked for disposal in a hothouse in Nihonmatsu, Fukushima Prefecture, on March 23. (Jun Kaneko)
Potatoes may be more liable to be contaminated by radioactive materials released by the stricken Fukushima No. 1 nuclear power plant than other types of fruits and vegetables, according to a study by Japan's agriculture ministry.
Researchers looked at the absorption rates of 17 types of vegetables and four fruits and found that sweet potatoes and potatoes were significantly more likely to take in radioactive materials than other fruits and leafy vegetables.
The maximum absorption rate of a sweet potato was 17 times higher than that for a lettuce, for instance.
"If potatoes are grown in farmlands where high concentration levels of cesium have been detected in the soil, they could contain more (radioactive material) at the time of harvesting than safety standards," a ministry official said.
The research, released by the government on May 27, was based on data drawn from foreign countries with a similar climate to Japan.
The absorption rate was calculated as the proportion of the cesium present in the soil that finds its way into a fruit or vegetable's edible portions at harvest.
For example, if sweet potatoes with a maximum absorption rate of 0.36 were grown in soil with 5,000 becquerels of cesium per kilogram, the agriculture ministry researchers would project about 1,800 becquerels of radioactive material per kilogram in the vegetable itself if the maximum rate was applied.
The study gave three different absorption figures for each foodstuff: a maximum ratio, a minimum ratio, and an average ratio.
According to the data, the average absorption rate of sweet potatoes was 0.033. The maximum and minimum rates were 0.36 and 0.0020, respectively. The corresponding figures for Irish potatoes were 0.011 (average), 0.13 (maximum) and 0.00047 (minimum).
Other fruits and vegetables had considerably lower absorption ratios. The average rate for a lettuce was 0.0067, with a maximum rate of 0.021 and a minimum of 0.0015.
Apples showed a 0.0010 average absorption rate and a 0.0030 maximum.
Under the Food Sanitation Law, the maximum permissible level of cesium in a kilogram of vegetables is 500 becquerels.
In April, the agriculture ministry and the Fukushima prefectural government jointly conducted a soil survey in farmland beyond a 30-kilometer radius of the Fukushima plant.
They found about 5,000 becquerels of cesium per kilogram of soil in Iitate village, Kawamata town, Otama village, Nihonmatsu city and Motomiya city. Residents of Iitate village and part of Kawamata town have already been told to leave their homes.
The ministry decided to look at contamination levels to about 15 centimeters below the surface because cesium leaked from the plant is likely to be mixed into the soil when farmers prepare the land before planting.
It gathered overseas data on soil contaminated by cesium-137, which has a half-life of about 30 years, to a depth of 10 to 20 cm.
"The amount of data is limited, so the absorption rates are just for reference. We want each local government or farmer to decide which agricultural products to plant," a ministry official said.
The ministry has already banned rice planting in some areas, but has no plans for similar embargoes on the planting of vegetables and fruits.
Instead, it plans to stop shipments if agricultural products are found to exceed safety standards for radioactive materials when they are harvested.
An official of JA Michinoku Adachi, an agricultural cooperative in Nihonmatsu, said: "The absorption rates released by the agricultural ministry are just a guide. But in areas where high concentrations of radioactive materials are detected, we could change to products which have low absorption rates."
(This article was written by Satoshi Otani and Keishi Nishimura.)
沒有留言:
張貼留言