A couple of thoughts:
Plant matter gets burned on allotments to get rid of diseased material and to kill pests which would survive composting.
The discussion has considered burning of wood and the likelihood of accumulation of pah, however most of the material being burned will be last years growth which is at most a year old. I'd have thought that this was different to bringing wood on to site to burn.
As the volume of ash will be small, if its well spread any contaminants will be dispersed - unless there is a regular spot used for fires which would then be a hot spot.
Brassicas (cabbage family) have been touted as useful as bioacumulators of metal in soil - they also have woody stems and are likely to be burned. Is this a mechanism for building up metals in the soil if repeated over many cycles?
Chimney soot is also used as a soil improver and to help the soil warm up in the spring, as surface cover, this practice would have significantly raised levels of contaminants I'm sure.
Testing we've done on allotments has only shown elevated levels on areas repeatedly used for fires.
Anyway I'd better go to my allotment I've a box of matches in my pocket and heap of stuff drying out nicely with all this sun...
Neil Scott
Senior Scientific Officer
Eastleigh Borough Council
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