Land Application of Manure and Class B Biosolids: An Occupational and Public Quantitative Microbial Risk Assessment

Abstract

Land application is a practical use of municipal Class B biosolids and manure that also promotes soil fertility and productivity. To date, no study exists comparing biosolids to manure microbial risks. This study used quantitative microbial risk assessment to estimate pathogen risks from occupational and public exposures during scenarios involving fomite, soil, crop, and aerosol exposures. Greatest one-time risks were from direct consumption of contaminated soil or exposure to fomites, with one-time risks greater than 10. Recent contamination and high exposures doses increased most risks. and enteric viruses provided the greatest single risks for most scenarios, particularly in the short term. All pathogen risks were decreased with time, 1 d to14 mo between land application and exposure; decreases in risk were typically over six orders of magnitude beyond 30 d. Nearly all risks were reduced to below 10 when using a 4-mo harvest delay for crop consumption. Occupational, more direct risks were greater than indirect public risks, which often occur after time and dilution have reduced pathogen loads to tolerable levels. Comparison of risks by pathogen group confirmed greater bacterial risks from manure, whereas viral risks were exclusive to biosolids. A direct comparison of the two residual types showed that biosolids use had greater risk because of the high infectivity of viruses, whereas the presence of environmentally recalcitrant pathogens such as and maintained manure risk. Direct comparisons of shared pathogens resulted in greater manure risks. Overall, it appears that in the short term, risks were high for both types of residuals, but given treatment, attenuation, and dilution, risks can be reduced to near-insignificant levels. That being said, limited data sets, dose exposures, site-specific inactivation rates, pathogen spikes, environmental change, regrowth, and wildlife will increase risk and uncertainty and remain areas poorly understood.

Estimation of Infectious Risks in Residential Populations Exposed to Airborne Pathogens During Center Pivot Irrigation of Dairy Wastewaters

“…Some recently published risk analyses addressing biosolids land application scenarios have utilized this approach. 4,61,71 Similar to the approach used in this paper, QMRA has been used to understand human health effects from exposures to biosolids and related pathogens released during land application. 26,71,74 Regardless of the context in which these exposures were being assessed, there is much uncertainty associated with inhalation of airborne pathogens and their ability to cause infection after subsequent ingestion.…”

Anaerobic Membrane Bioreactor Effluent Reuse: A Review of Microbial Safety Concerns

“…Class B biosolids in the United States differ from Class A biosolids in that they contain detectable levels of human pathogens and are restricted by specific preventative practices during the process of land application. Pathogen levels in Class B biosolids can be highly variable due to the lack of stringent regulations regarding indicator bacteria concentrations (fecal coliform < 2 × 10 6 CFU per gram), resulting in potentially high short-term microbial risks [96]. Anaerobic digestion of both agricultural and municipal sludge has long been established as an effective method for reducing pathogenic risk arising from sludge disposal and land application [97,98].…”

Salmonella and Tomatoes

“…Rain-induced runoff and subsequent contamination of irrigation water or groundwater is a fairly well-known mechanism for horizontal and vertical bacterial and viral transport (Curriero et al, 2001;Brooks et al, 2012). However, aerosolization of foodborne pathogens via this route has been largely ignored.…”

“…The presence of high organic matter fecal wastes would most likely decrease aerosolization, given the binding properties of some fecal materials (Chetochine et al, 2006). The amount of agitation needed to aerosolize deposited fecal material would most likely exceed that provided by rain; additionally, the heavier the rainfall (with higher energy), may serve to scrub the air, actually suppressing aerosolization (Cevallos-Cevallos et al, 2012b) and enhancing horizontal runoff (Brooks et al, 2012). To date no other studies have been conducted regarding this method of aerosolization of foodborne pathogens, particularly using fecal material in the field or controlled greenhouse experiments.…”

“…To consider these as sources, one has to assume that these operations are near fresh food crop operations; the 2006 spinach E. coli O157:H7 outbreak was in part due to the proximity of an animal-feeding operation to the spinach operation . For the most part, fresh or minimally treated manure/municipal biosolids are not used near or on fresh food crop lands (Brooks et al, 2012). This is in part due to design and regulations, but with more urban sprawl and less land available to dispose the millions of tons of manure/biosolids, the eventuality suggests that land application of waste residuals will take place near fresh food crop operations.…”