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Land application of manure and Class B biosolids: An occupational and public quantitative microbial risk assessment

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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. Th is 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 10−1. Recent contamination and high exposures doses increased most risks. Campylobacter jejuni 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 10−4 when using a 4-mo harvest delay for crop consumption. Occupational, more direct risks were greater than indirect public risks, which oft en occur aft er time and dilution have reduced pathogen loads to tolerable levels. Comparison of risks by pathogen group confi rmed 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 Cryptosporidium and Listeria 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 nearinsignifi cant levels. Th at being said, limited data sets, dose exposures, site-specifi c inactivation rates, pathogen spikes, environmental change, regrowth, and wildlife will increase risk and uncertainty and remain areas poorly understood. L
John P. Brooks , Michael R. McLaughlin , Charles P. Gerba , Ian L. Pepper
USDA Scientist Submission
Journal of Environmental Quality 2012 v.41
Journal Articles, USDA Authors, Peer-Reviewed
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