However, according to Solid Residues from Municipal Waste Incinerators in England and Wales, published by the Environment Agency, the Government should consider the need for guidance on acceptable contaminant levels in construction materials in terms of impacts on health and the environment. The study of the use and constituents of incinerator ash between 1996 and 2000 was carried out as a result of public concern over possible health risks related to dioxins in construction blocks.

The 11 municipal waste incinerators in England dealt with 8% of the 27.6 million tonnes of municipal solid waste produced in the country in 1999/2000 – that’s 2.21 million tonnes, and 9% of the 28.2 million tonnes – that’s 2.54 million tonnes – produced over 2000/01, says the Environment Agency. There are no municipal waste incinerators in Wales.

Incinerators produce two types of solid residues: bottom ash and air pollution control residues, the latter being a mixture of fly ash, carbon and lime, and containing most of the dioxins produced. The Agency also found that concentrations of heavy metals are generally lower in bottom ash, and are on a par with levels in the rest of Europe.

Dioxin levels in bottom ash – whichever method of storage or disposal is used – does not contribute significantly to the public’s exposure to dioxins, and is at a level similar to urban soils and other commonly used secondary aggregates. This includes those people who breathe the air in rooms constructed from mixed ash construction blocks, indicating that the blocks do not release measurable levels of dioxins into the air. Even drilling into the blocks during DIY work still contributes very little to typical overall exposure to dioxins – although undue exposure to any dust from DIY work should be avoided, says the Agency.

A total of 2.78 million tonnes of bottom ash were produced throughout the five years and were sent to 42 destinations. Of this, 79% went to landfill, and 21% to ash processors to make into bulk fill, such as for the construction of embankments, or as substitute aggregate. The resulting fine dust at landfills was found to be well within Government recommended air quality targets, said the Agency.

The use of processed bottom ash in engineering applications is in its infancy in the UK, although its use is well established in The Netherlands, Denmark, France and Germany, says the Environment Agency.

Edmonton incinerator was designed differently from other incinerators, in that it mixed the bottom and fly ash together. However, this practice ended in August 2000. The majority of the mixed bottom ash was sent to regulated landfill sites, although some was used in engineering and about 15,000 tonnes were used to manufacture construction blocks. These blocks could have been used for a variety of different construction types, but, if used for housing, could have been incorporated in around 3,400 houses.

With regards to air pollution control residues, 314,000 tonnes were produced over the five years and sent to landfill sites or waste treatment plants. The Environment Agency was able to trace records for 308,000 tonnes of the total, with the difference between the two figures thought to be accounted for by the use of different weighing systems.

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