In article ,
Stewart Robert Hinsley wrote:

As you say it's the dose that makes the poison. But, I think you'll find
that most Welsh soils don't have significantly raised levels of heavy
metals, and that no-one grows food on the spoil heaps of Parys Mountain.

I should be surprised at the former, if you use the chalk and clay
areas of the south east as a baseline. Rock (often granite) dust
contains a lot of different heavy metals, and is fairly widely used
as a fertiliser. But I agree that the use of much tanalised ash
could raise the content to spoil heap levels.

According to Wikipedia the lethal dose of tanalised wood ash is 20g
(about a teaspoonful).

Hmm. Methinks you place too much trust in Wikipedia. 20 grams being
a teaspoonful implies a specific density of 4!

I can believe 20 grams, because a lethal dose of arsenic can be as
low as 125 milligrams. But that is more than a teaspoonful of even
compacted ash, and MUCH more of uncompacted ash.

Some plants concentrate heavy metals.

Yes. But, if any of the common food plants concentrated things like
arsenic to any great extent, don't you think that it would be a
known problem?

Maybe the concentration is diluted to a safe level by harvest, but using
tanalised wood ash as a fertiliser is an unnecessary risk. I wouldn't do
it, anymore than I would eat a random umbellifer from a hedgerow.

I agree with that. My point is that you don't have any evidence
either way - and nor do I - so you are basing that entirely on
estimates of the potential consequences.

If we still had a semi-independent scientific civil service or even
a university system with independent funding, this would doubtless
have been investigated and we would have some facts to go on. But
we no longer have either :-(


Regards,
Nick Maclaren.