Viral, bacterial, and protozoan pathogens and fecal markers in wells supplying groundwater to public water systems in Minnesota, USA

Drinking water supply wells can be contaminated by a broad range of waterborne pathogens. However, groundwater assessments frequently measure microbial indicators or a single pathogen type, which provides a limited characterization of potential health risk. This study assessed contamination of wells...

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Bibliographic Details
Published in:Water research (Oxford) 2020-07, Vol.178, p.115814-115814, Article 115814
Main Authors: Stokdyk, Joel P., Firnstahl, Aaron D., Walsh, James F., Spencer, Susan K., de Lambert, Jane R., Anderson, Anita C., Rezania, Lih-In W., Kieke, Burney A., Borchardt, Mark A.
Format: Article
Language:English
Subjects:
Animals
Cryptosporidiosis
Cryptosporidium
Environmental Monitoring
Feces
Groundwater
HF183 Bacteroides
Humans
Microbial indicators
Minnesota
Pathogen-indicator ratios
Pathogens
Pepper mild mottle virus
Water Microbiology
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Summary:Drinking water supply wells can be contaminated by a broad range of waterborne pathogens. However, groundwater assessments frequently measure microbial indicators or a single pathogen type, which provides a limited characterization of potential health risk. This study assessed contamination of wells by testing for viral, bacterial, and protozoan pathogens and fecal markers. Wells supplying groundwater to community and noncommunity public water systems in Minnesota, USA (n = 145) were sampled every other month over one or two years and tested using 23 qPCR assays. Eighteen genetic targets were detected at least once, and microbiological contamination was widespread (96% of 145 wells, 58% of 964 samples). The sewage-associated microbial indicators HF183 and pepper mild mottle virus were detected frequently. Human or zoonotic pathogens were detected in 70% of wells and 21% of samples by qPCR, with Salmonella and Cryptosporidium detected more often than viruses. Samples positive by qPCR for adenovirus (HAdV), enterovirus, or Salmonella were analyzed by culture and for genotype or serotype. qPCR-positive Giardia and Cryptosporidium samples were analyzed by immunofluorescent assay (IFA), and IFA and qPCR concentrations were correlated. Comparisons of indicator and pathogen occurrence at the time of sampling showed that total coliforms, HF183, and Bacteroidales-like HumM2 had high specificity and negative predictive values but generally low sensitivity and positive predictive values. Pathogen-HF183 ratios in sewage have been used to estimate health risks from HF183 concentrations in surface water, but in our groundwater samples Cryptosporidium oocyst:HF183 and HAdV:HF183 ratios were approximately 10,000 times higher than ratios reported for sewage. qPCR measurements provided a robust characterization of microbiological water quality, but interpretation of qPCR data in a regulatory context is challenging because few studies link qPCR measurements to health risk. [Display omitted] •Repeated well testing for 23 gene targets identified widespread contamination.•Bacteria and protozoa were detected more frequently than viruses.•Pathogens were detected in 70% of 145 wells and 21% of 964 samples.•HF183 and pepper mild mottle virus poorly predicted pathogen presence in wells.•Pathogen-indicator ratios in well water were much higher than ratios for sewage.
ISSN:0043-1354
1879-2448
DOI:10.1016/j.watres.2020.115814