SubscribeCentralised composting processes cause the release of micro-organisms into the surrounding atmosphere.
Conditions currently being set in waste management licences specify that facility operators must sample for these micro-organisms around the site.
Some micro-organisms associated with compost production are recognised allergens. Examples include thermophilic actinomycetes and Aspergillus fumigatus, both have been implicated in occupation lung diseases such as Farmers Lung, where gross exposure, typically greater than tens of millions of spores per m3 of air, have triggered the immune response.
One characteristic of the Aspergillus fumigatus biological cycle is its capacity to generate large numbers of spores. In rare instances these spores can cause severe or even fatal infections. Two such case studies have been reported associated with composting.
Typical growth pattern after sampling
Actinomycetes are also found, they are filamentous Gram-positive bacteria that are commonly found coupled with soil and plant materials. Thermophilic actinomycetes, with a growth temperature range of 30 to 60oC, thrive in wet compost that has begun the self-heating process.
They are also recognised respiratory allergens. Actinomycetes produce thousands of very small spores (1-3mm diameter) which easily become airborne in large numbers when heavily colonised material is disturbed. Their size means that they can potentially penetrate deep into human lungs.
Not only is there a moral obligation to monitor compost sites, but it is a requirement of PAS100. The recommended method is fixed point sampling taken at various locations judged to be representative of work activities on site.
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However, there are conflicting views to the range spores can travel. Some argue that a 200m radius of the site should be monitored whilst there is some evidence that spores can be found up to 250m away. Fixed point sampling ensures the airborne particles are deposited directly onto agar plates.
This has the advantage of direct inoculation of the agar on which the biological agent grows, however, they are susceptible to overloading and sampling periods are short for full "loading" of the plate, ranging from approximately 30 minutes for background samples to as short as one minute in highly contaminated environments.
The Microflow 90 air sampler is highly recommended for this application, as it has variable sampling speeds and volumes.
Aspergillus fumigatus
Workers on composting facilities are potentially exposed to considerably higher concentrations of bacteria, including Gram-negative bacteria, actinomycetes, fungi and their associated toxins than are likely to be present in background air away from bioaerosol sources, and that the microbial components of compost bioaerosols have a known potential to cause respiratory ill health.
Conclusion -- Composting on a major scale is a relatively new and rapidly expanding industry in the UK. As yet there is little published evidence of serious/chronic disease in compost workers, although there is evidence of early ill health responses to bioaerosol exposure in compost workers, e.g., raised antibody levels and inflammatory mediators, and evidence of progressive allergic respiratory disease exists in industries such as other waste handling, agriculture and cotton mills, where similar exposure to bioaerosols may exist.
Chronic ill health may not yet have had time to develop.