[ RadSafe ] [EXTERNAL] Bq/kg soil

Dennis Quinn dqdx at aol.com
Tue Dec 6 09:11:26 CST 2011

Yes, this is local consumption; however, the dose if used for a large
agricultural farm would be similar, assuming an individual received all the
food from that farm.  Most likely individuals would only receive part of
their food source from any one farm.  
The term ecological half life I assume means that it's related to the amount
of time the radionuclide is available to the ecosystem.  Resrad considers
that to an extent, but only to the extent that it is available on the
surface (or not).   Cesium tends to bind with soil and is not transferred
down through the soil to the water table easily, so the dose will primarily
be from the direct dose from the gamma rays due to surface cesium.  Other
radionuclides will be different.  
Since most of the dose is from the surface, remediation of the surface layer
(removal) or covering with a layer of clean soil could be effective.
Dennis Quinn   

Dennis Quinn, CHP
dqdx at aol.com

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Karen Street
Sent: Monday, December 05, 2011 8:44 PM
To: The International Radiation Protection (Health Physics) Mailing List
Subject: Re: [ RadSafe ] [EXTERNAL] Bq/kg soil

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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