Microbial Source Tracking Using Digital PCR To Discriminate Sources of Fecal Contamination in Base Flow and Storm Water of Potomac River

Academic Research Topics in Environmental Measurement and Monitoring
Poster Presentation

Prepared by D. Alvi, A. Clare, A. Godrej
Occoquan Watershed Monitoring Laboratory - Virginia Tech Univ., 9408 Prince William St, Manassas, VA, 22033, United States

Contact Information: dongmei@vt.edu; 703-361-5606


Persistent and ongoing problems with fecal contamination of recreational water has led to a ban imposed by to District of Columbia Department of Health on swimming in all rivers and creeks in the District of Columbia, especially contact with water bodies immediately downstream of any combined sewer overflow (CSO) discharge. In this study, we monitored fecal contamination at Potomac River site on the border of Washington DC and Virginia State. The concentrations of Escherichia coli by IDEXX colilert, Bacteroides markers of human- (HF183, BacH) and ruminants- (BacR) specific digital PCR (dPCR) microbial source tracking (MST) were assessed for bi-weekly base flow as well storm events. Quality control procedures such as method detection limit (MDL), precision and accuracy were developed. Sensitivity and specificity of all markers were assessed. Single digit gene copy per chip-reading was achieved. In addition, dPCR TaqMan assay showed consistent resistance to matrix inhibition. At the Potomac monitoring site, the outbreaks were found mostly related to storm event for human related fecal contamination, whilst prominent source of ruminant fecal contamination were observed throughout base flow sampling events. The results in this study demonstrate that dPCR TagMan assay could be a viable tool for MST monitoring projects, not only increasing ability to differentiate fecal contamination sources, also detect low levels of genetic maker concentrations.