As contaminated water leaks into the ocean from the the damaged Fukushima Daiichi nuclear power station, and the soil near the plant tests positive for plutonium, Japanese authorities have updated the list of the nation's contaminated foods.
Milk, spinach, and other leafy greens grown in Miyagi and neighboring prefectures were already known to contain elevated levels of radioactive iodine-131 and cesium-137, but now 99 more products have tested positive for radioactive contamination—although most still at levels considered safe to eat for everyone but infants and pregnant women.
According to NPR, wasabi (shown above in its raw state) had some of the highest recorded levels, exceeding legal guidelines for iodine-131. Other more unusual foods on the list included chrysanthemum leaves (shungiku), which are eaten in salads, and mizuna, or mustard leaves.
As the New York Times explained last week, the movement of radioactive contamination through the food chain is complex and hard to predict. Big edible leaves are initially susceptible, as are the thyroid glands of livestock such as cows and goats (and hence their milk). Radioactive iodine, with its extremely short half-life, is only dangerous for the initial couple of weeks following a leak, but cesium is much longer lasting and can accumulate in an ecosystem for decades, depending on the type of soil—crops grown in sandy soil accumulate more radioactivity—wind direction, and rainfall.
F. Ward Whicker, an expert in radioecology, described the difficulty in predicting how radiactivity will move through the food chain, and thus the stupidity of creating blanket import bans:
There is an extremely complex interaction between the type of radionuclide and the weather and the type of vegetation. There can be hot spots far away from an accident, and places in between that are fine.
For now, the FDA is stopping all produce imported from the affected Japanese prefectures at U.S. ports for testing. So if it's on the shelves, it should be safe to eat.