Occurrence and transport of waterborne viruses in surface water in Michigan and associated public health risks

• Main Author: Fong, Theng Theng
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01.01.2009
• Subjects: Health risk assessment; Public health; Surface water; United States > US; Michigan
• ISBN: 9781109237412; 1109237413

Enteric viruses are excreted in high concentrations by humans and are frequently detected in fecally-contaminated surface water. Enteric viruses, such as adenoviruses and enteroviruses, are capable of causing a wide spectrum of diseases and are the main cause of water-transmitted gastrointestinal diseases in swimmers. The overall objective of this study was to develop an understanding of and quantify human health risks associated with the presence of viral pathogens, particularly human adenoviruses (HAdVs), contracted during recreational activities at beaches affected by sewage inputs in the lower Grand River, Michigan. In this research, it is hypothesized that human adenoviruses are present in high concentrations in sewage and rivers receiving sewage effluents because wastewater treatments do not efficiently remove these viruses and the risks for virus exposure at Great Lakes beaches are elevated above an acceptable risk for recreational waters during the swimming season. Adenovirus distribution and loading in sewage contaminated water were evaluated by determining concentrations of HAdVs in the lower Grand River during dry weather and after combined sewer overflow (CSO) events. Human adenoviruses were detected from 6/20 river water samples collected during dry weather with concentrations ranging between 8 × 101 and 6.6 × 104 viruses/L (average: 7.8 x 103 viruses/L). Concentration of HAdVs in samples collected after CSO events ranged between 6 × 104 and 1.3 × 10 6 viruses/L (average: 5.4 × 105 viruses/L). As a part of exposure assessment and to model virus transport and inactivation after CSO events, a dual tracer study was conducted on a 40-km reach of the lower Grand River in Grand Rapids. From the tracer study, it was concluded that bacteriophage P22 is a suitable tracer for the complex surface water system with inactivation rates between 0.27 and 0.57 day-1. A model for estimating virus transport and attenuation after discharge was developed based on data from the tracer study. With the field survey data and virus transport model, a quantitative microbial risk assessment was performed to evaluate the probability of infection or gastrointestinal disease resulting from incidental ingestion of contaminated recreational water at Lake Michigan beaches that receive input from the lower Grand River. Monte Carlo simulations were used to characterize uncertainty associated with different discharge scenarios. Uncertainty analysis showed that river discharge and concentration of viruses in CSO discharge were the main contributing factors to differences in risk and duration of elevated risk. The duration of CSO discharge was identified as the key factor determining the duration of Beach closure after a CSO event. Risk analysis showed that even in the best case scenario (i.e. with the lowest CSO virus concentration and CSO discharge volume), the gastrointestinal illness risk from viruses for swimming in Lake Michigan beaches after a CSO event in the lower Grand River in Grand Rapids is 2.4 × 10-1 , which is higher than EPA tolerable level for fresh recreational water of 8 × 10-3. The high risk associated with recreating in water receiving CSO discharge determined from this study emphasizes the importance of proper wastewater treatment and retention.