Pathogen Monitoring and Quantitative Microbial Risk Assessment of Secondary Water in Cache Valley, UT

Diminished water supplies have resulted in an increased use of secondary water for irrigation, including the use of treated municipal wastewater. Treatment plant effluent, secondary water systems and irrigated vegetable crops in Cache Valley, UT were tested for the presence of bacterial, protozoan, and viral pathogens by culture based and quantitative polymerase chain reaction (qPCR) based methods. Culture based results indicate the secondary water quality decreases after release from the wastewater treatment plant, and in some case of some irrigation plots exceeds the FDA Food Safety Modernization Act guidelines for agriculture water quality (410 CFU/100 mL). Furthermore, qPCR analysis of residential and farm secondary waterlines, and irrigated vegetables reveals the presence of viruses (norovirus and human adenovirus), protozoans (giardia spp.) and bacteria (E. coli, salmonella spp., and enterococcus faecalis). Mean qPCR results for samples collected from Hyrum, UT secondary waterlines are the following: norovirus (0.0017 average gene copy/mL), human adenovirus (0.046 average gene copy/mL), giardia spp. (0.098 average gene copy/mL), E. coli (0.51 average gene copy/mL), salmonella spp. (0.49 average gene copy/mL), and enterococcus faecalis (1.3 average gene copy/mL). A preliminary quantitative microbial risk assessment from exposure to waterborne pathogens of irrigated vegetables, direct consumption, bioaerosol inhalation, and accidental ingestion scenarios were calculated with culture and qPCR results.