Endotoxin emissions from commercial composting activities

Lead Research Organisation: University of the West of England
Department Name: Faculty of Health and Life Sciences

Abstract

Bioaerosols are airborne particles of microbial, plant or animal origin and may be thought of as 'organic dust'. There is a growing recognition amongst scientists that there are potential health risks associated with inhalation of bioaerosols. These health risks include infections and irritations of the respiratory system. There is evidence that bioaerosols are generated at some waste facilities and therefore scientific research is needed to find the best way of managing these facilities to minimise health risks to the people who work there and also people living nearby. This project aims to develop new knowledge of a specific bioaerosol component of concern known as endotoxin. Endotoxin is a constituent of many bacteria found in compost and is known to cause adverse health effects including respiratory disease and lung damage if inhaled. However, the extent of the risk to the public from endotoxin released from composting facilities is unknown. This project aims to find out how much endotoxin is released from composting facilities, how far it will travel and whether the concentrations found in air from composting facilities could potentially affect the health of people living close to these facilities.

Publications

10 25 50
 
Description Objective 1 Examine the emissions of endotoxins from static windrow compost piles and from compost processing activities, such as shredding, turning and screening. Achievement & significance. The release and dispersal of endotoxin from composting operations has been quantified for the first time. Replicated and repeated sampling provided a measure of the variability of airborne endotoxin concentrations at such sites. Endotoxin was not detected in upwind samples but was detected consistently in on site samples confirming composting as a source. Concentrations were significantly higher during composting activities compared to periods of no activity. Downwind measurements showed a pattern of peaks and troughs suggesting complex dispersal dynamics. The highest concentrations were detected at 280 m from site boundary. Detection of elevated concentrations so far from the site boundary was unexpected but it was not possible to confirm that composting was its source. These findings contribute significantly to understanding of endotoxin dynamics and provide an important basis for future health impact assessments. Objective achieved.
Objective 2 Compare the measured emissions of endotoxins to emissions of fungi (Aspergillus fumigatus) and bacteria (actinomycetes) sampled simultaneously with the endotoxins. Achievement & significance. As with endotoxin, site activities significantly elevated the concentrations of culturable bioaerosols (compared to upwind samples). Bioaerosol concentrations decreased to 80 m followed by a second peak at 100-150 m (similar to endotoxin). Secondary peaks have not previously been reported in the literature. Unlike the endotoxin results there was no tertiary peak at 280 m suggesting either a secondary source of endotoxin or different dispersal behaviour. Replicated and repeated sampling has provided scientifically rigorous validation of previously reported dispersal patterns for culturable bioaerosols and contributes significantly to the evidence base from which regulatory risk assessment and compliance decisions are taken. Objective achieved.
Objective 3 Capture the particle size of bioaerosols emitted from the composting facility. Achievement & significance. Culture dependent tests using membranes filters suggested a significant proportion of airborne A. fumigatus cells were individual spores. For actinomycetes and gram negative bacteria culture-dependent tests proved inconclusive. Observation of filters by SEM confirmed that the majority of bioaerosols were present as individual cells with a small fraction present as aggregates. Measurements made with an ultra-fine particle counter indicated a relationship between sub-micron particles and endotoxin. These exploratory findings have important implications for dispersal behaviour, its simulation, and inhalability. The determination of the physical nature of endotoxin (and related toxin) particles emitted from composting and other waste management activities is a future research priority. Objective achieved.
Objective 4 Predict the concentrations of fungi, bacteria and endotoxins around the facility using a dispersion model. Achievement & significance. Atmospheric Dispersion Modelling Software (ADMS 4) was utilised to determine endotoxin and Aspergillus concentrations in the vicinity of a composting facility. Numerous uncertainties and assumptions were identified. Recommendations from this element of the project will reduce the number and magnitude of modelling uncertainties and ultimately improve the accuracy of future environmental risk assessment studies. The dispersion modelling contour plots (based on three meteorological scenarios using 24-hour and long term average times) indicated that a 50 EU/m3 endotoxin contour would lie just outside the site boundary (maximum impact distance beyond the site boundary of ~10m) while a 1000 cfu/m3 Aspergillus contour would substantially exceed the 250m risk assessment threshold (maximum impact distance beyond the site boundary of 697-1060m). This suggests that the 250m risk assessment threshold is conservative for endotoxins but not stringent enough for Aspergillus. Objective achieved.
Objective 5 To relate the concentrations and particle sizes of endotoxins, bacteria and fungi measured to possible human health impacts in an in vitro model. Achievement & significance. Inhalation of endotoxin has important health implications and we have set up an in vitro cell-based assay to investigate the inflammatory potential of the endotoxin extracted from the sampling filters in this study. We have utilised human monocyte (MM6) and lung epithelial (D562) cell lines to investigate the inflammatory potential of the endotoxin detected. Endotoxin extracted from the filters was found to stimulate both cell lines to produce significant amounts of pro-inflammatory cytokines. Endotoxin levels below 50EU/m3 did not induce a significant inflammatory response as measured by the release of Interleukin-6 (IL-6) or interleukin-8 (IL-8) from the cells and this value might be used as a tentative limit for airborne endotoxin at these sites. Interestingly, on a weight basis, we found that endotoxin extracted from the composting source has a greater inflammatory cytokine inducing effect than commercial E. coli endotoxin. This was particularly significant for the airway epithelial cells. This raises the possibility that endotoxin in these bioaerosols is intrinsically more reactive with such cells or that endotoxin in association with particles has greater inflammatory potential. Objective achieved.
Exploitation Route The findings have contributed to the evidence base used by the Environment Agency to inform their regulatory decision making.
Sectors Environment

 
Description The findings of this research have informed Environment Agency thinking and policy on the regulation of bioaerosols emissions from industrial facilities, including the rationale for the development of the recently published Technical Guidance Note M9 Environmental Monitoring of bioaerosols at regulated facilities.
First Year Of Impact 2017
Sector Environment
Impact Types Policy & public services

 
Description Environment Agency engagement
Geographic Reach National 
Policy Influence Type Citation in other policy documents
Impact Contribution to Environment Agency technical guidance document and to staff training
 
Description Defra waste evidence portfolio
Amount £168,000 (GBP)
Funding ID WR1121 
Organisation Department For Environment, Food And Rural Affairs (DEFRA) 
Sector Public
Country United Kingdom
Start 01/2011 
End 12/2013
 
Description Environmental Microbiology and Human Health
Amount £572,000 (GBP)
Funding ID NE/M011631/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 06/2015 
End 12/2018
 
Description Composting industry talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Talk sparked questions and discussion afterwards

None known
Year(s) Of Engagement Activity 2010