Submitted to: Science of the Total Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/30/2014
Publication Date: 6/2/2014
Citation: Corsi, S.R., Borchardt, M.A., Spencer, S.K., Hughes, P.E., Baldwin, A.K. 2014. Human and bovine viruses in the Milwaukee river watershed: hydrologically relevant representation and relations with environmental variables. Science of the Total Environment. 490:849-860. Interpretive Summary: As collectors and conduits of water, rivers are the key landscape feature by which waterborne pathogens become localized and move through the environment. Insofar as people or livestock come in contact with contaminated river water through activities such as drinking, recreation, or crop irrigation, there is the opportunity for infectious disease transmission. We studied three rivers in the Milwaukee River watershed in Wisconsin for the occurrence and variability of human and bovine gastrointestinal viruses. These viruses are released from their hosts to the environment in human fecal wastes and cattle manure. Because water flow and contaminant levels in rivers can be so variable over time, we designed unique automated samplers capable of concentrating viruses over periods of days as river levels and environmental conditions changed over a 17-month period. This approach also allowed us to accurately calculate the quantity of viruses being transported by the rivers, accounting for their different watershed sizes. Among 63 river samples, human and bovine viruses were detected in 49% and 41%, respectively. More samples were positive and virus concentrations were highest when river levels rose from runoff during snowmelt or rainfall. During these runoff events in the Milwaukee River, the largest river in the watershed, 100,000 to 10,000,000 viruses per hour were being transported downstream for every square kilometer of land surface in the watershed. We measured a number of river and weather variables and compared these to virus levels in the rivers. River water flow, precipitation, and season were the variables that predicted human viruses in the rivers; runoff events and season were the two predictor variables when considering both virus types combined, human and bovine. We could not identify variables related to only bovine viruses in the rivers. Understanding the factors that affect virus contamination of rivers should help with watershed management decisions for improving water quality and minimizing opportunities for disease transmission.
Technical Abstract: To examine the occurrence, hydrologic variability, and seasonal variability of human and bovine viruses in surface water, three stream locations were monitored in the Milwaukee River watershed in Wisconsin, USA, from February 2007 through June 2008. Monitoring sites included an urban subwatershed, a rural subwatershed, and the Milwaukee River at the mouth. To collect samples that characterize variability throughout changing hydrologic periods, a process control system was developed for unattended, large-volume (56-2800 L) filtration over extended durations. This system provided flow-weighted mean concentrations during runoff and extended (24-hr) low-flow periods. Human viruses and bovine viruses were detected by real-time qPCR in 49% and 41% of samples (n = 63), respectively. All human viruses analyzed were detected at least once including adenovirus (40% of samples), GI norovirus (10%), enterovirus (8%), rotavirus (6%), GII norovirus (1.6%) and hepatitis A virus (1.6%). Three of seven bovine viruses analyzed were detected including bovine polyomavirus (32%), bovine rotavirus (19%), and bovine viral diarrhea virus type 1 (5%). Human viruses were present in 63% of precipitation and snowmelt runoff samples, and 20% of low-flow samples. Maximum human virus concentrations exceeded 300 genomic copies/L. Bovine viruses were present in 46% of precipitation and snowmelt runoff samples and 14% of low-flow samples. The maximum bovine virus concentration was 11 genomic copies/L. Statistical modeling indicated that stream flow, precipitation, and season explained the variability of human viruses in the watershed, and hydrologic condition (runoff event or low-flow) and season explained the variability of the sum of human and bovine viruses; however, no model was determined that could explain the variability of bovine viruses alone. Understanding the factors that affect virus fate and transport in rivers will aid watershed management for minimizing human exposure and disease transmission.