[ RadSafe ] [EXTERNAL] Bq/kg soil

Jim Hardeman Jim.Hardeman at dnr.state.ga.us
Mon Dec 5 21:51:59 CST 2011

Karen --
I'll try to give you a short answer to a complex question.
Were an incident such as the Fukushima accident to occur in the US, the response at the federal level would be governed by the National Response Framework (NRF), and more particularly the Nuclear / Radiological Incident Annex (NRIA). Both of these documents can be found on the FEMA and DHS websites.
A fundamental concept expressed in these documents is that "decisions" are made at the local and state level, with the federal government providing support when resources are exhausted or when special expertise is required. Two primary examples of such expertise are the Federal Radiological Monitoring and Assessment Center (FRMAC) and the Advisory Team for Environment, Food and Health (Advisory Team). These multi-agency federal assets, and others, provide assistance to state and local governments in assessment of ANY major radiological incident, including a significant reactor accident.
At the present time, there are two (2) federal guidance documents for protective measures such as evacuation, sheltering, relocation (essentially what we're seeing in Japan right now), reentry, return and recovery -- and measures designed to prevent the consumption of contaminated food. These two documents are:
EPA-400-R-92-001, "Manual of Protective Action Guides and Protective Actions for Nuclear Incidents" (EPA, 1992), and
"Accidental Radioactive Contamination of Human Food and Animal Feeds: Recommendations for State and Local Agencies" (FDA, 1988).
Please note than EPA has for several years been in the process of revising EPA-400-R-92-001, and in fact briefly released the revision in January 2009; that revision was withdrawn and the 1992 guidance is still in force.
These documents do not provide a limit for radionuclides in soil, per se. The limits are expressed in terms of dose. For example, any combination of deposited radionuclides that would produce a total effective dose equivalent of 2 rem in the first year after a contaminating incident would warrant relocation.
Likewise, for foodstuffs, the "limit" is in terms of dose. Here, however, for a limited number of radionuclides, FDA pre-calculated a derived intervention level (DIL) at which protective measures would be warranted. The DIL is expressed in terms of activity per unit mass or volume in food as prepared for consumption. For example, the limit for Cs-134 + Cs-137 is 1,200 Bq/kg.
Assessments performed by FRMAC in conjunction with state radiological health organizations include ALL radionuclides present, and as already indicated by another commenter, you will see separate values for each radionuclide, rather than a "gross" limit for all radionuclides. However, limits may also be expressed in terms of an easily measured "marker radionuclide" if the radionuclide mix is sufficiently characterized to allow this. These calculations are performed with computer codes similar to RESRAD, and in fact RESRAD has been used, at least in exercises, to perform calculations for specific pathways -- for example, contamination limits on roadways or building surfaces. 
Bottom line -- there is no pre-existing limit, in particular for the concentration of a particular radionuclide in soil, especially in the case where more than one contaminating radionuclide may be present.
Please let me know if you need any additional information, or if I can point you to some of these documents. Sorry for the long answer, but I didn't want you to come away from this discussion with the idea that there was a "simple" answer to your question.
Jim Hardeman, Manager
Environmental Radiation Program
Environmental Protection Division
Georgia Department of Natural Resources
4220 International Parkway, Suite 100
Atlanta, GA 30354
(404) 362-2675
Fax: (404) 362-2653
Personal fax: (404) 521-4485
E-mail: Jim.Hardeman at dnr.state.ga.us 

>>> Karen Street <Karen_Street at sbcglobal.net> 12/5/2011 20:44 >>>
Dennis, thanks. You're talking local consumption, not use for agriculture, but hobby gardening, or eating all one's food from that plot of land? You are using physical rather than ecological half life? It sounds as if the effect on agriculture is fairly small.


Thanks, and you are doing great so far!

Cesium from Chernobyl had an ecological half life of months in most locations . Is enough known about what affects ecological half life to make predictions for Japanese agriculture?

I would think that plants with shallow roots pick up little of the radioactivity compared to roots that extend deep into the soil, but that is because I live in CA where the clay layer seems to be 2 mm or so below the soil layer.

I know that water standards are very different in the EU and Japan, with drinking water standards 4x greater in the EU; they would never have banned Tokyo water. So if the accident had been in the EU or US, would the standards for ag have been different?

> Hi, Karen.
> The first point to keep in mind is that all becquerel are not created
> equal, especially when trying to start with soil concentrations and end
> up with dose from ingestion.  You really can't say anything until you
> know what isotope you are dealing with.  You need to know this for two
> reasons:
> First, knowing the isotope lets you know the element, which will usually
> give you an idea about how well the plants in question will remove the
> isotope from the soil and make it part of the plant (you obviously need
> to know what plant you are talking about, too).  Different elements
> differ wildly on how, or even if, they are taken up by different plants.
> Second, knowing the isotope lets you know the half-life, which gives you
> important information about how long the radioactive material is going
> to be around.  This lets you know if it is potentially going to be a
> problem.  If, for example, the isotope of concern is iodine-131 (I131),
> with an 8 day half life, you know it will be an issue if it is on a
> field of lettuce scheduled to be harvested this week.  If it is on
> pumpkins to be harvested in three months, then canned for consumption
> next year, it is much less of an issue.
> In an event like Fukushima, it can be a challenge figuring out which
> isotope is the one to be most concerned about in a given area, for a
> given crop, at a given time (as time goes by the isotope that will
> produce the greatest dose will change, as the ones with the shortest
> half lives decay away).
> If this is a useful level of detail, let me know, and I will continue.

Best wishes,
Karen Street
Friends Energy Project
blog http://pathsoflight.us/musing/index.php 

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