Defra publishes latest study on bioaerosols

The Defra commissioned report, entitled Defra Project WR 1121 Bioaerosols and odour emissions from composting facilities, aimed to provide evidence on bioaerosol production, dispersion and potential exposure from composting facilities to support future developments of policy and regulation at biowaste sites.

Bioaerosols are a collection of biological particles including bacteria and fungi made airborne. In composting, this occurs through process operations such as shredding, screening and turning which the report said significantly increased emissions.

The study, which took place between 2011 and 2013 and cost 490,453, found that within its limited dataset there was no consistent relationship between bioaerosols concentration and odour at composting facilities.

Methods

Four composting sites with different tonnage throughputs were monitored as part of the study. Bioaerosol measurements were taken on a minimum of three and a maximum of six occasions over a 12 month period. The use of different sites allowed a comparison to be drawn between bioaerosol concentrations at open windrow sites versus a fully contained site.

The study claims that bioaerosol concentrations at the enclosed site were generally lower than at the open windrow sites. There was no evidence of a seasonal pattern in bioaerosol concentrations at any of the sites however there were variations between sampling days. The causes of these variations have not been identified.

The report states: The findings of this research have implications for the current standard monitoring protocol which should be reviewed accordingly. The findings of this multi-site survey accord with existing regulatory policy. They are also supportive of the concept of using enclosed facilities to mitigate bioaerosol emissions.

However, it added that more research is needed to determine the cause of bioaerosol peaks and to improve exposure assessments.

Additionally, the study found that the site which handled the greatest tonnage of waste had the greatest impact on bioaerosol concentrations at less than 250m downwind of the source.

Explaining the impacts of this finding, the report states: This tentatively supports the concept of applying greater regulatory scrutiny to large sites. However this conclusion should be applied with caution and due consideration of the possible effect of other factors. There may be other variables in addition to tonnage which contribute to higher bioaerosol concentrations at Site A.

Health impact

The report recommends that the Agency retains its precautionary approach until such time as evidence for a health-based threshold value is available. While it is understood that exposure to bioaerosols has the potential to be harmful to human health, at present there is limited data to understand their full affects.

The Agencys current position statement is that a higher level of regulatory scrutiny where there are sensitive receptors within 250m of composting operations. This is backed up by the study which confirmed that bioaerosols decline rapidly between the point of emission and 250m from the source.

The outputs from this study have the potential to inform the design of bioaerosol exposure assessment for use in future small area health studies. The aim of such studies would be to examine health outcomes in relation to composting site proximity and estimated bioaerosol exposure using national routine data such as hospital admissions, birth registrations and, potentially, general practice data. The outputs from the current Defra study would be a key resource in developing an exposure assessment protocol to provide better estimates of community exposures than distance from site at composting sites.