| Microbial Risk Assessment Framework for Exposure to Amended Sludge Projects Joseph N.S. Eisenberg,1 Kelly Moore,2 Jeffery A. Soller,3 Don Eisenberg,4 and John M. Colford Jr.2 1Department of Epidemiology, University of Michigan, Ann Arbor, Michigan, USA; 2School of Public Health, University of California Berkeley, Berkeley, California, USA; 3Soller Environmental, Berkeley, California, USA; 4EOA Inc, Oakland, California, USA Abstract
Background: Although the U.S. Environmental Protection Agency has a long history of using risk-based approaches for regulatory purposes, pollutant limits for pathogens in biosolids are not currently based on quantitative risk assessments. Objectives: We developed and demonstrated a risk-based methodology for assessing the risk to human health from exposure to pathogens via biosolids. Materials: Four models were developed, incorporating direct ingestion, groundwater, and aerosol exposure pathways. Three sources of environmental data were used to estimate risk: pathogen monitoring of sludge, efficacy of sludge treatment, and pathogen monitoring of biosolids. Results: Risk estimates were obtainable even for Class A biosolids, where posttreatment monitoring data are below detectable levels, demonstrating that risk assessments for biosolids exposure are practical. Model analyses suggest that: a) a two-digester design decreases the probability of risks > 10–4 compared with one-digester designs, b) risks associated with exposures to groundwater and aerosol pathways were, in general, lower than exposures to the direct ingestion pathway, and c) secondary transmission can be an important factor in risk estimation. Conclusions: The risk-based approach presented here provides a tool to a) help biosolids producers interpret the results of biosolids monitoring data in terms of its health implications, b) help treatment plant engineers evaluate the risk-based benefits of operational changes to existing or projected treatment processes, and c) help environmental managers evaluate potential capital improvements and/or land application site placement issues. Regulation of pathogens can now be based on human health risk in a manner parallel to other water-related risks. Key words: environment, microbial, risk assessment, sludge. Environ Health Perspect 116:727–733 (2008) . doi:10.1289/ehp.10994 available via http://dx.doi.org/ [Online 13 March 2008]
Address correspondence to J.N.S. Eisenberg, University of Michigan, School of Public Health, Department of Epidemiology, 109 Observatory, Ann Arbor, MI 48109 USA. Telephone: (734) 615-1625. Fax: (734) 998-6837. Email: jnse@umich.edu Supplemental Material is available online at http://www.ehponline.org/members/2008/10994/suppl.pdf We thank the members of the project's Health Advisory Committee, P. Berger, W. Jakubowski, G. Kester, S. Pillai, and R. Spear, as well as the members of the Project Subcommittee, C. Lue-Hing, S. Munger, T. Murphy, S. Sedita, J.E. Smith, and G. Tchobanoglous, for their insightful comments throughout this project. In particular, we thank G. Kester and B. Percha for their extensive editorial comments. The research on which this manuscript is based was funded, in part, by the U.S. Environmental Protection Agency (Cooperative Agreement No. CR-825237) through the Water Environment Research Foundation (WERF) (Fund No. 98-REM-01) . The authors declare they have no competing financial interests. Received 18 October 2007 ; accepted 13 March 2008.
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