Temporal and Spatial Distribution of Disinfection Byproducts in Drinking Water Supplied to the Mega City of Vietnam and Assessment of the Associated Risks

This study investigated the characteristics (levels, profiles, seasonal variations) of disinfection by-products (DBPs) including four trihalomethanes (THMs) and six haloacetic acids (HAAs) in two water supply systems (zones A and B) of Ho Chi Minh City and assessed their human health risk via daily exposure. THMs and HAAs were analyzed simultaneously using GC/MS coupled with a headspace. The results indicated that the levels of total DBPs measured in zone B (419 +/- 223 and 204 +/- 153 mu g/L in dry and rainy seasons, respectively) were significantly higher than those in zone A (101 +/- 49.7 and 48.9 +/- 15.0 mu g/L in dry and rainy seasons, respectively). Significant correlations (p < 0.05) between DBPs indicated similar formation pathways and variations of these DBPs in the pipeline. The findings also showed significant correlations (p < 0.05) of DBPs with not only regular parameters (TOC, UVA(254), residual chlorine, Cl-) but also soluble ions (SO42-, Na+, K+, and Ca2+). THMs were the main contributors to the total DBPs (86.8 +/- 7.4% and 91.4 +/- 10% for zones A and B, respectively). Among four THMs, trichloromethane (TCM) was the predominant compound, accounting for 83.7 +/- 4.8% (zone A) and 91.4 +/- 10.0% (Zone B). For the HAA group, monochloroacetic (MCAA) was the major contributor (86.3 +/- 8.2% and 60.5 +/- 23% for zones A and B, respectively). Non-cancer and cancer risks caused by DBPs for the population using drinking water in Ho Chi Minh City were notably high. The study suggested that water should be pretreated before use in households to eliminate the level of DBPs and reduce their impacts on human health.