Absorption of arsenic by edible plants

Bill Morgan wtmorgan at pilot.msu.edu
Mon Mar 27 10:37:39 EST 2000


In article <38de9883.18292221 at nntp.uio.no>,
alf.christophersen at basalmed.uio.no (Alf Christophersen) wrote:

> On Sun, 26 Mar 2000 22:49:17 GMT, alf.christophersen at basalmed.uio.no
> (Alf Christophersen) wrote:
> 
> >I'm afraid that the addition by leakage will be less than 1 promille
> >of the background concentration of As in soil, maybe less than 1 ppb
> >of the background, how could you then detect that difference ? If you
> >have a background concentration of 10 ppb and the leakage is about
> >1/1000 og ppb pr year, how would you quatitate that leakage without
> >selectively marking the leakage?
> 
> Have now checked background concentrations, and the above is very
> optimistic pure.

I'm afraid you are missing the point here.

The question is whether or not you need to use radioisotopes to get a good
handle on the significance of leaching. The answer is "No". 

What you're talking about is rather beside the point. Concentration changes
in the amounts you speak about are so minute as to be meaningless. You
don't *need* to detect that much of a difference. No matter what method of
measurement is used, there will be some small margin of error in it. That's
unavoidable in most experimental designs, and certainly unavoidable in
chemical analysis. The question is whether or not that error is meaningful.
Here it is not. Additional arsenic in the amounts you mention is not going
to make much of a difference. If you increased the background concentration
by a factor of ten, that might be of concern. Adding a part per billion
doesn't seem to be something worth being too concerned about.

So for real-world applications, you needn't use radioisotopes. That's a
horribly expensive method. And at the end of that, you also come down to a
tiny, unavoidable experimental error. It may be a smaller error than with
other methods, but why go to the expense of using a radioisotope when you
don't need it? You don't need to nail down the change to the last molecule
of arsenic compound (and can't anyway, regardless of the method used). You
do need to be fairly precise, but certainly not so precise as to detect one
part in a billion change over background.

[Remainder snipped: it goes off on irrelevant tangents.]

Regards,
Bill

-- 
Bill Morgan <wtmorgan at pilot.msu.edu>

Those who do not learn the lessons of science fiction are condemned to live
them. 




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