Human Health Risks Associated With Wastewater Treatment in Arctic Canada

Abstract

This dissertation provides the first estimates of microbial health risks attributable to wastewater treatment systems in Arctic Canada. A participatory quantitative microbial risk assessment was designed to model a range of exposures scenarios and mitigations. In Chapter Two, the state of knowledge on wastewater treatment, exposure pathways, and waterborne disease in Inuit and Arctic communities is reviewed. A conceptual model is developed to guide the risk assessment. Chapter Three describes a screening-level quantitative microbial risk assessment model and estimates the probability of acute gastrointestinal illness (AGI) associated with worst-case exposure scenarios in five Nunavut case study sites. An annual incidence rate of 5.0 cases per person is predicted in Pangnirtung, where a mechanical treatment system discharges to a marine environment at low tide. An incidence rate of 1.2 cases per person is predicted in Naujaat, where an undersized passive system is used, with most cases predicted during spring freshet. These results are considered high and moderate, respectively, in comparison to literature-based estimates of AGI in the region. In Chapter Four, a more in-depth stochastic model is used to characterize risk for inferential Arctic wastewater exposure scenarios and results are compared to a global health guideline (10-3 annual risk of waterborne AGI). The 75th percentile risk level exceeds the guideline in three scenarios: shore recreation near mechanical treatment sites during low tide; consumption of shellfish harvested near mechanical treatment sites during low tide; and wetland travel near passive treatment sites during spring freshet. Rotavirus and Salmonella spp. project the highest risk of the six enteric pathogens included in the model. Two forms of mitigation are also evaluated (improved treatment, behavioural change), and both are shown to potentially reduce risk to varying degrees. These findings suggest that wastewater exposures may be contributing to high AGI rates in some Arctic communities. Passive systems with controlled discharge and risk communication are recommended as the most appropriate wastewater treatment solution. This research has immediate application in Arctic regions and contributes to the broader socio-ecological understanding of water, sanitation, and health.