Monday, 28 April 2008

Is industrial scale composting a hazard to public health?

Composting is increasingly being taken up by local councils in the UK in an effort to reduce the amount of material they have to dump in landfill sites. Given that composting generates large quantities of spores, most particularly of the pathogen Aspergillus fumigatus, the question is often asked how close is it safe to site houses, schools and places of work to these facilities.

The Health and Safety Executive in the UK has looked into this in some detail and came up with a detailed review entitled "Occupational and environmental exposure to bioaerosols from composts and potential health effects - A critical review of published data".

One of the most relevant extracts is reproduced here:

Most reported studies have found that people living more than 250 m from composting sites are exposed to microbial emissions that are similar to ‘background’, i.e., are not significantly higher than can occur naturally. However, there are some recordings of high levels. In one study, increased concentrations were detected 500m away from a composting site, with
concentrations of thermophilic actinomycetes reaching 106 cfu/m3 200m away (Neef et al 1999). The predominance of Aspergillus fumigatus in bioaerosol emissions from compost may pose an increased risk of infection to immunocompromised persons, and individual case studies have been reported of allergic bronchopulmonary aspergillosis and invasive aspergillosis associated with the handling of biological waste and composted wood chips respectively (Allmers et al, 2000; Conrad et al, 1992) while allergic diseases such as hypersensitivity pneumonitis have been diagnosed in individual cases associated with compost handling both occupationally (Vinken and Roels, 1984; Weber et al, 1993) and recreationally (Brown et al, 1995). Consequently, persons known to have impaired immunity may be at increased risk of infection if exposed to A fumigatus in compost bioaerosols.
However, to place this in context, a similar risk would occur with exposure to other organic dusts containing Aspergillus fumigatus, such as from other agricultural activities (grain harvesting and handling, also demolition of buildings).

In other words it isn't safe to have a person known to have an impaired immune system or perhaps known to be sensitive to particular aspergillus allergens (and others carried by the bioaerosol) closer than 250-500m from a composting facility BUT the risk is no more than common agricultural and building practices where the earth is disturbed by machinery, gardening, the wind, or is exposed to particular atmospheric conditions.

The key is information and education. These guidelines are useless if ignored, especially when taking on staff to work in one of these facilities or if a vulnerable person is not identified living in the 'at risk' area(s). This is the difficulty - there is a strong danger that the onus will fall onto the effected individuals rather than the companies running the composting facilities.

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