The “Microbial Risk Assessment Guideline:  Pathogenic Microorganisms with Focus on Food and Water” was released by U.S. EPA and the U.S. Department of Agriculture on July 26, 2011. [www.epa.gov/raf/microbial.htm]  The public comment period is open for 60 days.

The Microbial Risk Assessment (“MRA”) Guideline is a resource for evaluating hazards from waterborne pathogens for microbial risk assessors, risk managers, and the regulated community.  But for readers who are familiar with chemical risk assessments, it is critical to note that those protocols do not work for viruses, bacteria, protozoa, fungi and prions.  Why?  One important example is that pathogens may increase or decrease in number in both the environment and in people, with pathogens’ growth following unique patterns.  In contrast, while chemicals may undergo certain transformations, they do not multiply in the environment or in the host.  Another distinctive quality of microbes is that their genomes can mutate quickly within days or weeks – possibly becoming more virulent.  Microbes are a moving target, including their potential secondary transmission.  While diverse, chemicals and their associated toxicities do not change in the same way.  A final difference worth acknowledging is that chemicals can be detected at low concentrations, such as parts per trillion, but research is still needed to develop analytical methods to detect low levels of microbes in water. Although the MRA Guideline focuses on infectious diseases associated with gastrointestinal pathogens transmitted by water and food, the document has utility for a broad variety of scenarios:

  • drinking water
    • inadequate treatment
    • broken water mains
    • aging and cracked pipes
    • small water systems
    • reclaimed water
  • land application of biosolids
  • large animal farms
  • recreational water

Even if you are not a risk assessor, perusing the MRA Guideline is well worth the time.  The assumptions of dose-response relationships, detection methods, and default factors that you are comfortable with in chemical scenarios will be profoundly challenged when evaluating a microbial hazard.

And if you have convinced yourself that you will never need to know about microbes, consider the case of State ex rel. Corday v. Helms, 192 Ohio App. 3d 426, 949 N.E. 2d 522, 2011-Ohio-569, where an apartment owner chose self-help to remedy the malfunction of the on-site sewage treatment plant.  He took untreated sewage from the plant and used it to landscape around the building.  Even more extraordinary, he planned to “‘treat’ some of the sewage by placing it in commercial washing machines, in an attempt to use centripetal force to eliminate pollutants from the water.”  You never know where the next pathogen may come from.