Quantitative Microbial Risk Assessment to Estimate Illness in Freshwater Impacted by Agricultural Animal Sources of Fecal Contamination U.S. Environmental Protection Agency Office of Water December 2010 EPA 822-R-10-005 U.S. Environmental Protection Agency DISCLAIMER Mention of commercial products, trade names, or services in this document or in the references and/or endnotes cited in this document does not convey, and should not be interpreted as conveying, official EPA approval, endorsement, or recommendation. December 2010 ii U.S. Environmental Protection Agency FOREWARD Managing and minimizing the public health threat associated with fecal pollution in recreational water are important aspects of policy development and regulation for the U.S. Environmental Protection Agency (EPA) Office of Water. The Beaches Environmental Assessment and Coastal Health Act of 2000 (BEACH Act) amended the Clean Water Act Sections 104 (v) and 304(a)(9) to require EPA to conduct studies associated with pathogens and human health, and to publish new or revised Recreational Water Quality Criteria (RWQC). To meet these requirements, EPA is conducting a series of studies that will inform the development of new or revised RWQC. This document describes a quantitative microbial risk assessment (QMRA) that was conducted to to estimate illness in freshwater impacted by agricultural animal sources of fecal contamination. This assessment was based on the EPA/International Life Sciences Institute Framework for Microbial Risk Assessment (ILSI, 1996), and the structure follows EPA’s peer-reviewed Microbiological Risk Assessment (MRA) Tools, Methods, and Approaches for Water Media (MRA Tools document), which has been peer-reviewed by renowned microbial risk assessors and the EPA Science Advisory Board. December 2010 iii U.S. Environmental Protection Agency CONTENTS LIST OF TABLES .................................................................................................................................. VII LIST OF FIGURES .................................................................................................................................. IX ACRONYMS AND ABBREVIATIONS ................................................................................................. XI 1. EXECUTIVE SUMMARY ................................................................................................................ 1 1.1. QMRA METHODS ......................................................................................................................... 2 1.1.1. Forward QMRA methods ....................................................................................................... 2 1.1.2. Relative QMRA methods ....................................................................................................... 3 1.2. RESULTS........................................................................................................................................ 3 1.2.1. Risk of illness associated with recreation at a freshwater beach impacted by agricultural animal sources of fecal contamination. ............................................................... 3 1.2.2. Comparison of risks for freshwater beaches impacted by agricultural animal and human sources of fecal contamination ................................................................................... 5 1.3. CONSIDERATIONS ......................................................................................................................... 5 2. PROBLEM FORMULATION .......................................................................................................... 7 2.1. STATEMENT OF CONCERN ............................................................................................................ 7 2.2. PURPOSE AND CONTEXT ............................................................................................................... 7 2.2.1. Purpose ................................................................................................................................... 7 2.2.2. Context for using QMRA to estimate recreational water risks .............................................. 7 2.2.3. Prior use of QMRA to estimate risks associated with waterborne pathogens ...................... 11 2.3. SCOPE AND RISK RANGE ............................................................................................................ 13 2.3.1. Hazards ................................................................................................................................. 13 2.3.2. Reference pathogens ............................................................................................................ 14 2.3.3. Livestock-impacted sites ...................................................................................................... 19 2.3.4. Human-impacted sites .......................................................................................................... 20 2.3.5. Shorebird-impacted sites ...................................................................................................... 21 2.4. POPULATIONS INCLUDED IN THE RISK ASSESSMENT MODEL .................................................... 21 2.5. REFERENCE HEALTH OUTCOMES ............................................................................................... 22 2.6. UNITS OF EXPOSURE AND ROUTE OF CONCERN ......................................................................... 22 2.7. TARGET RISK LEVEL................................................................................................................... 23 2.8. SCENARIOS MODELED ................................................................................................................ 23 2.9. QUESTIONS TO BE ADDRESSED ................................................................................................... 24 2.10. CONCEPTUAL MODELS ............................................................................................................... 24 2.10.1. Top-tier models .................................................................................................................... 24 2.10.2. Sub-tier model: model parameter form and estimation ........................................................ 27 2.10.3. Sub-tier model: animal-impacted water pathogen-loading model ....................................... 28 2.10.4. Sub-tier model: reference pathogen dose-response models ................................................. 31 2.10.5. Sub-tier model: volume of water ingested during recreational activities ............................. 33 2.10.6. Sub-tier model: secondary infections ................................................................................... 34 2.11. SUMMARY OF QMRA METHODS ................................................................................................ 34 December 2010 iv U.S. Environmental Protection Agency 2.11.1. Risk of illness associated with recreation at a beach impacted by agricultural animal sources of fecal contamination ............................................................................................. 35 2.11.2. Comparison of animal-impacted water risks with POTW-impacted water ......................... 36 2.12. ENVIRONMENTAL SAMPLING ...................................................................................................... 38 2.13. TOOLS USED IN THE QMRA ....................................................................................................... 40 2.14. SUMMARY OF ASSUMPTIONS ...................................................................................................... 40 2.15. SOURCES OF VARIABILITY AND UNCERTAINTY ......................................................................... 41 2.15.1. Variability ............................................................................................................................ 42 2.15.2. Sources of uncertainty .......................................................................................................... 43 2.16. FACTORS AND DATA NOT INCLUDED IN THE QMRA ................................................................. 44 2.17. IDENTIFIED GAPS IN THE KNOWLEDGE BASE ............................................................................. 44 3. ANALYSIS ........................................................................................................................................ 46 3.1. EXPOSURE ................................................................................................................................... 46 3.1.1. Prevalence and abundance of reference pathogens in livestock ........................................... 47 3.1.2. Abundance of reference pathogens in disinfected secondary effluent ................................. 51 3.1.3. Abundance of FIB in livestock manures .............................................................................. 52 3.1.4. Ability of livestock-derived reference pathogens to infect humans ..................................... 53 3.1.5. Mobilization of reference pathogens and FIB ...................................................................... 58 3.1.6. Factors used to convert densities of pathogens on land to densities in runoff ..................... 60 3.1.7. Volume of water ingested .................................................................................................... 60 3.1.8. Exposure profile ..................................................................................................................