Monitoring emissions of harmful fungi in composts/bioaerosols

Compost production is a microbiological process and disturbance of compost windrows during mechanical turning releases bioaerosols composed of high densities of microorganisms in the form of air-borne spores. Bioaerosols are of serious concern for occupational health and safety since they are inhaled by compost operators and are able to travel considerable distances to surrounding inhabitants. The major biological constituents of compost aerosols include actinomycetes, bacteria and fungi. Arguably, the most important component of the fungal constituent of bioaerosols is spores of the genus Aspergillus such as A. fumigatus, A. flavus and A. niger.

Aspergillus species are common soil-borne fungi that are found in abundance in decomposing organic material, such as self-heating compost windrows. Many species are thermotolerant and readily grow at temperatures up to 57oC and certain species such as A. fumigatusand A. niger are able to tolerate temperatures during pasteurisation of up to 63oC. People who handle contaminated compost can develop hypersensitivity to spores of the fungus and may suffer severe allergic reactions upon exposure. Aspergillus species are now widely regarded as one of the most serious air-borne opportunistic pathogens of immunocompromised humans such as AIDS and solid organ transplant patients and are the most common cause of fungal infections requiring hospitalisation. In addition to invasive disease, Aspergillus causes a number of other diseases in man. These include aspergilloma (colonization of pulmonary cavities), sinusitis in normal people, allergic bronchopulmonary and sinus infections, keratitis (which usually leads to blindness) and post-operative infections in immunocompetent patients. Aspergilloma numbers are set to rise dramatically due to the increasing incidence of tuberculosis and such aspergilloma cases are notoriously difficult to treat. Cavities of 2 cm or larger after tuberculosis subsequently develop aspergillomas in 15-20% of patients in the UK. The 5-year survival of patients with aspergillomas is about 40%. Allergic bronchopulmonary aspergillosis occurs in patients with cystic fibrosis and asthmatics (an increasing number) causing pulmonary fibrosis and death usually within 10 years of diagnosis.

The concentrations of Aspergillus spores in bioaerosols are governed by a number of factors including the frequency of windrow turning and temperature profiles within compost piles. Studies suggest that frequent turning of heaps reduces Aspergillus densities by allowing temperatures to rise to levels sufficient to destroy the fungus. Site-specific factors are also likely to play important roles in determining the densities of Aspergillus propagules in compost bioaerosols including feedstock types and layout of the composting site. There are conflicting recommendations for the establishment of safety zones surrounding composting facilities and safe distances have so far been set on an arbitrary basis. Clearly, there is a need for accurate monitoring of Aspergillus at every composting facility and appropriate measures need to be taken to protect personnel during composting operations. At present, monitoring of bioaerosols for fungal contaminants is undertaken on an ad hoc basis and yet both acute and chronic exposure of compost operators to harmful fungi is evident. There is a pressing need for accurate monitoring of harmful fungi in compost bioaerosols and user-friendly techniques need to be developed for rapid ‘on-site’ determination of inoculum loads in bioaerosols.

The aims of our current research are to develop a monoclonal antibody-based lateral flow device (LFD) for the rapid, specific and sensitive detection of Aspergillus species in composts and bioaerosols.