Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 19, 2012
Publication Date: November 1, 2012
Citation: Brooks, J.P., McLaughlin, M.R., Gerba, C.P., Pepper, I.L. 2012. Land application of manure and class B biosolids: an occupational and public quantitative microbial risk assessment. Journal of Environmental Quality. 41:2009-2023. Interpretive Summary: The land application of wastes, such as wastewater treatment plant biosolids and manures, has been practiced for years and serves as a method to dispose and treat these wastes. The presence of bacterial, viral, and parasitic pathogens in these wastes can further complicate issues and reduce public confidence in their disposal. Typically the concern and hence the regulations governing their land application and use have revolved around controlling nutrient runoff and public contact with these microbial pathogens. The recent foodborne outbreaks involving bacterial and viral pathogens has brought into question the use of these wastes and potential for public exposures. To properly assess the use of these wastes a quantitative microbial risk assessment was conducted comparing the use of manure and municipal biosolids using current pathogen data and simulating potential public exposures following a variety of exposures ranging from fresh food crop consumption to aerosol exposures. A comparison of the risks demonstrated that public health risks are relatively low during non-intentional exposures such as fresh food crop or aerosol exposures and fall below the USEPA recommended annual 1 per 10,000 risk of infection. Only exposures in which intentional consumption of soil contaminated with fecal matter yielded risks which were greater. Risks were far below occupational exposures for the most part and demonstrated that risks between the two types of wastes were similar. Infectious risks from biosolids were greater from viral pathogens, while bacterial pathogens presented the greatest risks from manure. This study demonstrated that given typical conditions, the risk of infection from land application and use of either of these types of wastes are acceptable given time between application and exposures.
Technical Abstract: Public exposures to pathogens can vary from contact with fomites to foodborne exposures. Regulations and recommendations for land application of manure or Class B biosolids are designed to limit public exposures to pathogens in each residual waste. Lands receiving these residuals are more fertile and tend to yield greater crop yield, therefore their use is warranted by the farmer. This study initiates the first comparison of pathogen risks between manure and municipal biosolids using quantitative microbial risk assessment approaches designed to determine potential “downstream” public risks. This study simulated public exposures during various scenarios involving soil, crop, and aerosol exposures. Overall, the greatest risks were from intentional consumption of soil contaminated with residual pathogens, with exposures yielding risks approaching ~10-1, particularly from Campylobacter jejuni, adenovirus, and enteroviruses. All pathogen risks were decreased by microbial decay as demonstrated by simulations involving 1 day to 38 months between soil contamination and exposure; decreases in risk were typically over six orders of magnitude. Incidental ingestion of soil or crops yielded risks near 10-1, assuming that the contamination occurred within 7 days of consumption; however, risks were reduced with pathogen attenuation over time. If regulations and recommendations of a minimal of 4 months were simulated, nearly all risks were reduced to non-significant levels, even assuming daily produce consumption. Soil attenuation and dilution appeared to have the most effect on risk, as pathogen levels decreased significantly with these parameters. In contrast, risks may be great in situations in which recent contamination or regrowth events occur. Comparison of risks between the two types of residuals demonstrated that despite the untreated nature of manure, the risks are comparable to a treated product such as municipal biosolids. Risks between the two were parsed into pathogen groups with the greatest bacterial risks belonging to manure, while viral risks were exclusive to biosolids. Residual treatment and soil attenuation and dilution will further serve to reduce all risks. The pathogen levels presently found in both residual types are such that any further treatments may not significantly decrease risk, particularly if current regulations are followed properly.