Hi Neil
Thanks for your email, you raise some interesting points.
I have tested 9 allotments in my borough. All were previously fields, then allotments, so no industrial use. Benzo(a)pyrene ranged from 0.1 - 26.3mg/kg, and we did not sample from any "burning hotspots".
If only allotment holders just burned the previous year's plant growth! Anything from old compost bags, treated wood, plant pots, polystyrene trays goes onto the bonfire.
Also, not everyone burns and uses ash. Those who do, do so out of habit and have done so for years, so the PAH levels vary considerably from plot to plot.
My thinking is, why would you want to spread sooty potentially carcinogenic waste on the soil you choose to use to dig in and grow something you eat? Spreading it in a Swedish forest in one thing, but having the soot in contact with your veg, and the dust in your lungs and on your skin?
- if it's for the P, K, N use fertilizer, compost, manure or commercial potash from marine deposits, as the quantities of these in your ash will be minimal
- if it's to dispose of waste, compost or mulch instead
- if it's to adjust the pH, use lime or ericaceous compost
- if it's to deter slugs, use hair, crushed egg-shells etc
And what is the impact of ash on soil organisms? I imagine a soil that has compost instead of ash to be healthier.
I suppose this practice is similar to views on smoking. The "My granddad smoked for 70 years, and it didn't do him any harm" mentality. But most people have an allotment for a healthier lifestyle choice, and spreading ash just seems contradictory to this.
And one final thought... if I find BaP at 20mg/kg in your allotment plot where you have been spreading ash for years, would you be the Class A person under Part 2A? Hmmm...
Regards
Christopher Taylor
Enforcement Officer
Regulatory Services
Brent Council
Tel: 020 8937 5159
www.brent.gov.uk
-----Original Message-----
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Neil Scott
Sent: 22 April 2015 08:57
To: [log in to unmask]
Subject: Re: Wood ash vs coal ash and IBA/FBA and all that
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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