Land application of manure and class B biosolids: an occupational and public quantitative microbial risk assessment

Authors: Brooks, John; McLaughlin, Michael; GERBA, CHARLES - University Of Arizona; PEPPER, IAN - University Of Arizona

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/2012
Publication Date: 10/1/2012
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: Occupational exposures to bacterial, viral, or parasitic pathogens is a typical hazard associated with land application of wastes such as municipal biosolids or manure. Typically the regulations and recommendations for either of these are related to protecting the public and reducing nutrient runoff to surface water ways; rarely are pathogen regulations designed to protect the occupationally exposed. To assess this, occupational exposures were simulated during the land application of biosolids and manure involving scenarios ranging from accidental touching of fomites (e.g. truck door handle) to incidental soil ingestion. Risks were relatively high for occupational exposures due to minimal microbial decay following land application and prior to exposure, and exceeded the EPA recommended 1 in 10,000 chance of infection, which is normally reserved for public exposures. Exposures to fomites, in particular, were of greatest risk due to this. Public exposures are typically relegated to exposures following days to months of time between application and exposure and thus risks are typically low; however, risks to waste handlers occur immediately or within days of land application. Biosolids risks were limited to viral risks while manure was associated with bacterial risks. The treatment inherent to biosolids, reduces most bacterial and viral pathogens; however given the presence of even a few human infectious viruses, biosolids can still harbor large risks. Manure is typically not treated, in which case it can harbor large risks associated with the bacterial pathogens. Simple hygienic practices can reduce all risks associated with the occupationally exposed.

Technical Abstract: The land application of municipal Class B biosolids and manure has been a useful implement of these waste residuals. Lands receiving them have often become more fertile, nutritious, and tend to increase crop yields. Their application to non-food crop lands and adherence to rules and regulation timelines tends to shield the public from the microbial risks, but the residual handlers can be exposed to pathogens, without attenuation, resulting from the land application events. This study initiates the first comparison of pathogen risks between manure and municipal biosolids using quantitative microbial risk assessment approaches. This study simulated occupational exposures during working scenarios involving fomite, soil, and aerosol exposures. Overall, the daily risks were greatest from fomite exposures (~10-1), particularly from Campylobacter jejuni, adenovirus, and enteroviruses. All pathogen risks were decreased by microbial decay as demonstrated by simulations involving 1-120 days between fomite or soil contamination and exposure; decreases in risk were typically over six orders of magnitude. Occupational exposures were simulated to occur daily over a period of 255 days per year and therefore annual risks were greater than would be expected for indirect or public exposures. The use of simple hygienic personal protective equipment would serve to limit exposures and thus risk. Since rules and regulations set by the USEPA, USDA, and UKADAS were meant to protect public and future pathogen exposures, the occupationally exposed proved to be the most at risk since exposures typically occur when residual wastes are the most “fresh” and potent.