Agency scientists probed the issue following a public outcry over the use of processed mixed ash from the Edmonton incinerator in construction blocks, and over open storage of the ash on landfill sites in London and Kent.
The investigation looked into all the solid residues produced between 1996 and 2000 by 11 municipal waste incinerators, which dealt with 9% of 28.2 million tonnes of municipal solid waste in 2000/01.
Incinerators produce 'b;ottom ash' (the ash left at the bottom of the incinerator), and air pollution control residues.
The latter are a mixture of fly ash, carbon and lime resulting from a treatment process to clean the gases before they are released into the air, and contain most of the dioxins produced.
Operators’ records show that 2.77 million tonnes of ash was sent out from incinerators, 79% to landfill and the remainder as bulk fill or for use as a secondary aggregate.
Health risks
The agency said that concerns were focussed on the potential of dioxins in ash to harm health, such as causing cancer, particularly as a result of long-term exposure to low-levels.
It found that concentrations of toxic heavy metals and dioxins are generally lower in bottom ash than in air pollution control residues and that both are typical of the levels reported in the rest of Europe.
Bottom ash does not contribute significantly to the public’s exposure to dioxins, more than 90% of which in any event come from food, it concluded.
An experiment on the potential exposure to dioxins in the air of rooms constructed from mixed ash construction blocks indicated these do not release measurable levels of dioxins into the air.
Do-it-yourself work in which these blocks might be drilled would also contribute very little to overall exposure, it found.
Concentrations of fine dusts at landfill sites where the ash was handled were well within the Government air quality objectives.
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