Barry, the CLEA uptake model didn't just rely on one paper. The regression
analysis for the uptake model was put together from data numerous papers
where, for example, plant Cd concentration, soild Cd concentration and soil
pH was measured. If you get hold of a copy of the old SGV3 document for
cadmium you'll find the list of papers that were cited in a review of the
literature.
The problem though, is that the papers that were referenced had widely
varying soil Cd concentrations and widely varying soil types and so on.
Now, this data was used in an attempt to show a correlation between soil pH
and plant concentration factor (separating the data into those for leafy
veg and those for root veg), but the regression analysis completely ignore
the fact that concentration factor also varies as a result of soil Cd
concentration, plant species and variety, and umpteen other soil
properties. These other factors all contribute to a very large uncertainty.
No attempt was made to separate out the different factors affecting
concentration factor, and with the data used (38 points) there isn't
enough data to be able to do this anyway with any degree of confidence.
Furthermore, the data was log transformed prior to the regression analysis,
so when glancing at the graph one sees what looks like a fairly small range
of ln(CF) values and it's easy to overlook the fact that most of them lie
outside the confidence interval shown, and also that this range of ln(CF)
values actually equates to a very wide range of CF values in linear space.
I've got a copy of the SGV3 document as a pdf file - if you would like me
to email it to you then I'm more than happy to do so.
Pete Millis
Centre for Environmental Research
School of Life Sciences
University of Sussex
Falmer
Brighton BN1 9QJ
and
Rottingdean Garden and Landscape Services Ltd
Old School House
Telscombe Village
Nr Lewes BN7 3HY
--On 15 November 2009 09:04 +0000 Barry Croft <[log in to unmask]>
wrote:
>
>
>
> Thanks Pete. That's the most honest answer to date. A couple of comments:
>
> - surely there must be umpteen papers correlating pH with plant uptake,
> so why does CLEA rely on just one?
> - in the light of this and the many other question marks over CLEA, does
> the jury think that even believing the output to ONE significant figure
> is optimistic, and perhaps we should only believe CLEA output order of
> magnitude?
>
>
>
> Barry Croft, Director
> MSc DIC MIEnvSci CEnv
>
> GREEN BRAIN
>
> Consultancy & Training in Environmental Permits,
> Contaminated Land, Landfill Gas and Waste
>
> www.greenbrainassociates.co.uk
>
>
>
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