An epidemiologic study of disinfection by-products and markers of early biologic effect

Disinfection by-products are formed during water treatment when chlorine reacts with organic matter in the source water. Studies have reported an increase in the risk of several cancer sites associated with exposure to drinking water with high levels of disinfection by-products. However, biologic mechanisms explaining this relationship have not been identified. This study will seek to improve the understanding of associations between disinfection by-products and health events by investigating a relationship with markers measured in blood which are suspected of being early effects in the causal pathway towards adverse health events. The study will also determine whether the presence of specific genetic factors associated with how different individuals react to disinfection by-products influence these relationships. Healthy subjects will be recruited in Ontario and Nova Scotia, in municipalities specifically selected to provide variation in disinfection by-product level. Participants will provide a blood sample and home water sample. Disinfection by-products in public water supplies are a potentially important health exposure because of the high rate of exposure to these chemicals in the Canadian population. This study has the potential to increase understanding of health events associated with these exposures and provide guidance with respect to setting appropriate water standards.