Answer to Question #9784 Submitted to "Ask the Experts"

Category: Nuclear Accidents — Fukushima

The following question was answered by an expert in the appropriate field:

Q
What types of foods would most likely take up the longer-lived radionuclides that were deposited in the soil from the Fukushima reactor accident fallout that came down in precipitation across the United States? For crops already growing this spring, I have heard that plants with large leaves, like spinach, were particularly likely to absorb contamination from precipitation. For crops just coming up (both now and in future growing seasons), which foods are most likely to take up contamination from the soil? Which types of crops are least likely to take up or absorb cesium and other radionuclides?

There have also been reports about radionuclides turning up in milk—mostly short-lived iodine, which is not much of a concern at this point (several months after the accident), but also some instances of cesium being detected in milk as well. Are contaminants like iodine and cesium (or other radionuclides from nuclear fallout) also likely to end up in eggs (which typically have a high iodine content)?

A

The degree of uptake by plants of radionuclides deposited on soil depends on many factors, including the specific radionuclide and its chemical form, characteristics of the soil, available moisture, season of the year, and stage of plant growth. Soon after the initial fallout deposition of radiocesium and radioiodine from Fukushima, for example, most of the material that might be measured in plants would likely be through direct interception on the foliage, so leafy plants such as lettuce, spinach, etc., would likely contain higher levels than fruits, tubers, root crops, etc. Over time, the distribution changes, as material washes off leaves and gets into the soil, and then some fraction might be taken up by roots and translocated to different plant parts.

Although there are significant differences among different plant species in their ability to take up radiocesium from soil, other factors, particularly the abundance and type of clay minerals in the soil, have a much greater influence. Generally, soils with reasonably high amounts of micaceous clay minerals will bind radiocesium over time and largely prevent plant roots from absorbing it. One example study, of many, on plant uptake of radiocesium is by J.F. Seel, F.W. Whicker, and D.C. Adriano, "Uptake of 137Cs in Vegetable Crops Grown on a Contaminated Lakebed," Health Physics 68(6):793-799 (1995). Both radioiodine and radiocesium will find their way into animal products such as meat, milk, and eggs if sufficient quantities are ingested by the animals involved. While radioiodine and possibly radiocesium have been found in some samples of food products in the United States, the amounts have been extremely small and close to the limits of detection ability of existing technology.

Ward Whicker, PhD
Professor Emeritus, Colorado State University

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