[ RadSafe ] [EXTERNAL] Bq/kg soil

Karen Street Karen_Street at sbcglobal.net
Mon Dec 5 19:44:02 CST 2011

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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