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Re: More on DU
I think Bob Cherry's point of quantifying how much 238-U is already in a square mile of soil to a depth of three feet was intended to show how insignificant 290 tonnes of DU would be over many square miles of earth contaminated by DU rounds. For example, 100 square miles already contains 823 tonnes to three feet (previous assumptions applied). So, in terms of epidemiology (radiological or not) that would be a useful datapoint.
>>> keith bradshaw <Keith.G.Bradshaw@soc.soton.ac.uk> 06/08 5:55 AM >>>
Hi all
Thanks to everyone who replied to my question on chemical/ radiological
toxicity of nat-U and DU.
The consensus of sensible replies seems to be that the limit of
200microgramU/m3 set by the American Conf. of Gov. Induustrial Hygenists is
based on chemical toxicity. The Rand report says this limit applies to both
soluble and insoluble forms. But there is a problem with this, because for
insoluble forms, such as uranium oxides resulting from combustion of
uranium metal, it's clear that the radiological dose calculation is MUCH
more restrictive than 200microgram/m3. This applies to both nat-U and DU.
So basically, the Rand report is incorrect by saying that protection from
chemical effects will automatically guard against radiological hazard. In
fact, the primary concern for respirable forms of insoluble uranium oxides
is radiological, and this applies to both nat-U and DU.
I calculated an Annual Limit of Intake (inhalation) of 32Bq, which
corresponds to 2100microgram of DU for members of the public (1mSv/yr
limit). At 2000 hr per year and a breathing rate of 1.2m3/hr, you obtain a
Derived Air Concentration (DAC) of 0.013 Bq/m3 which corresponds to
0.88microgram/m3. This is a factor of 227 times more restrictive than the
ACGIH limit.
The above is for DU with an isotopic composition (taken from the Rand
report) of
238U = 99.800%
235U = 0.200%
234U = 0.001%
The dose coefficients are 3.1, 3.3, 3.5 E-05Sv/Bq respectively (English
NRPB 1987).
I think calculating the amount of U in x tonnes of surface soil etc is
missing the point. It's clearly impossible to inhale several kg of dirt.
But it might be possible to inhale 2mg uranium oxide whilst you are
cleaning out tanks if you're not careful. Having said that, the symptoms of
Gulf War syndrome seem to point to chemical effects, so my money is still
on pesticides.
We still have not really settled the question of the presence (or not) of
Pu, 233U and 236U in DU.
Regards
Keith Bradshaw Southampton University UK
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