On Wed, 24 May 2000 22:45:31 -0500, Mike Miller wrote:
>Does anybody know if this zinc sulfate was from a naturally contaminated
>source or was recycled from an industrial process? Mike Miller
My father was a metallurgist by profession, and he gave me a 'heads-up'
on this one almost thirty years ago. Cadmium is metallurgically almost
identical to zinc, to the point of being virtually impossible to
separate completely.
He felt that from an agricultural point of view the greatest risk of
cadmium contamination in the system was via galvanised water troughs,
especially in areas with slightly acidic water. Apparently
galvanisation zinc (even if it is reasonably pure) can contain 1-2% Cd.
The body sheds Cd with difficulty, if at all, and the symptoms of
chronic cadmium toxicity reads like a list of modern ailments. This is
*not* to suggest causality, but rather to highlight the significant
signal/noise problem involved with cadmium symptomology.
Fortunately, cadmium problems are extremely simple to control in
agricultural systems. As long as the soil is even slightly into the
alkaline range, it is quite effectively tied up in the soil.
Bio-availability approaches zero once the pH goes over about 7.
It does not surprise me that el-cheapo zinc sulphate from China is
contaminated with cadmium ... they simply didn't bother to remove what
was already there, which gave them a price advantage. It's the best
example of externalising costs I've seen in awhile.
Bart
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