Modeling brominated trihalomethane compounds and carcinogenic risk from drinking water

One of the most important human health concerns in the effort to provide a safe drinking water supply is risk tradeoffs because efforts to reduce one risk from drinking water may introduce either intentionally or unintentionally a different risk. A primary example of this type of risk tradeoff involves the chlorination of drinking water, accordingly and because of their potential carcinogenic effects special attention is paid in this study to concentrations of the most prevalent volatile trihalomethane by-products (THM): chloroform (CHCl3), bromodichloromethane (CHBr2Cl) and bromoform (CHBr3). Two major issues are considered in this study:;First, during the last twenty years, only aromatic or UV absorbent carbon was considered as THM formation precursors in drinking water. The second issue refers to exposure assessment; specifically when assessing human exposure to THM the major issue is estimating the concentration of THM in water. In earlier studies, considerable exposure misclassification was likely to occur when exposures were estimated by sampling at the treatment plant because both the time and location of sampling are important given the large variability in the concentration of THM temporally and spatially. The goal of this research is to formulate mechanistic-based regression models, that estimate concentrations of THM in both the water treatment plant and distribution system, and to delineate more clearly the spatial and daily variations in disinfection by-product levels from drinking water. A second goal of this study is to assess the impact of human health risks from exposures to THM, i.e.: liver and kidney and intestine cancer risks as a function of drinking water distance traveled in the distribution system and bromide level in raw water. Organic carbon to organic nitrogen ratio is used to assess natural organic material precursor. Br/Cl2 and ammonium are used as THM formation potential (THMFP) precursors. Traveled distance and water temperature are used in the model to reduce the error on THM prediction at any point in the distribution system. Finally, the 24 hours daily change of temperature is probably the reason for THM daily variation in drinking water.;Cumulative risks from these compounds and the relative risk increase in the distribution system at Beaumont are 2 to 3 times higher than the one from Ontario. This may due to the differences in bromide level, water temperature and total organic carbon (TOC) content of raw water. CHCl2Br in drinking water showed that the magnitude of estimated risk from showering was the same magnitude, as the one estimated from oral consumption. Human cancer risk increases as we go further from the treatment plant. Finally, we further conclude that if sampling were to take place at a time other than 2-PM an under estimation of the estimated risks would occur.