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Ecosystems Research

Research in Action

Quantitative Microbial Risk Assessment Program

Rivers, lakes and coastal waters are favorite vacation spots where people spend time swimming, fishing, boating and relaxing. Recreational water quality can be degraded by sources of fecal pollution such as sewage treatment plant discharges, sewage line leaks, urban and farmland runoff or local wildlife. When water is polluted by these sources, people can become ill from exposure to waterborne pathogens associated with the fecal material.

Recreational water managers conduct routine tests to determine whether bacteria are present in recreational waters as an indicator that contamination by fecal material has occurred. However, these tests cannot tell anything about the source of the fecal material or whether there are disease-causing pathogens also present in the water. This is why researchers are developing quantitative microbial risk assessments, or QMRA.

QMRA is a modeling approach that brings together information from epidemiology studies, dose/response models, and exposure data to predict the probability of human infection due to exposure to waterborne pathogens in recreational water. A key feature of the QMRA approach is that pathogen concentrations can be predicted using standard fecal indicator bacteria tests coupled with information about potential fecal sources that may be impacting a given water body.

EPA scientists are using a QMRA approach in sampling urban and agricultural runoff discharges in streams and other water bodies. Information from this research is expected to improve scientific understanding of relationships between specific disease-producing pathogens and fecal contamination levels at watershed scales. QMRA can also help scientists understand how environmental conditions such as weather or geology affect the transport of pathogens. As part of the QMRA approach, scientists are using DNA techniques, including quantitative real time polymerase chain reaction (Q-PCR), to identify fecal contamination sources in rivers, lakes and other water bodies. These DNA technologies allow scientists to detect waterborne pathogens along with markers that indicate if their origin is animal or human.

Results and Impact
Results from EPA’s QMRA research can be linked with past and present epidemiological studies to help scientists better quantify factors influencing the types and concentrations of waterborne pathogens present in various water bodies. Further, by linking QMRA findings to hydrological models at the watershed scale, EPA scientists are able to predict transport and fate of pathogens in aquatic ecosystems, resulting in useful tools to states and communities for reducing human exposure to disease causing pathogens.

Technical Team: Marirosa Molina (contact), Richard Zepp, Gene Whelan, Kurt Wolfe

Refining model for freshwater baeaches:

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