Hi Martin,
As I understand it, it is possible to separate the background levels of
freeborn lead from that deposited from human activity based on the 207/208
isotope ratio, and it is this same mathod that is used to calculate modern
polution methods. I'm not sure if this can be identified as specifically the
result of smelting, however I can't think of any other significant
factor/process that would contribute to the made produced levels of lead
pollution for the period.
There have been two study's to calculate lead polution through the ages -
Greenland ice and Swiss bog depositions. It is my understanding that these
showed a high degree of corroboration, so we know that the lead levels
detected, in terms of deposition are reasonably accurate.
I also found an article in French by the same researcher, that says the same
techniques were used to find that 2,000 tons of copper was also being
deposited per annum in the same period (at least, that's what I think it
says).
I will write to the author and clarify the deposition figure, but I'd
suggest that the techniques used are valid and seem to be accepted by most
bodies as being authorative since they form the basis of most studies in
lead polution.
I'm not sure that lack of physical evidence can be used to discredit this
research, as far as I can see an estimate based on the number of known mines
will always dramatically underestimate production, whereas global lead
deposition figures will always be non geographic and include all lead
deposited, not just by smelting or cupilation.
Anyway I've thought of an alternative test for the results.
Would it be possible to go to a point in history we are more certain of and
extimate how much deposition there should have been, perhaps the mid 1700's?
George Chaplin
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