Seawater intrusion in the coastal regions: effects on DBPs speciation and risks

Seawater intrusion changes the chemical composition of fresh water in coastal groundwater and surface water sources, leading to the formation of additional brominated and iodinated disinfection byproducts (DBPs) in drinking water. In this study, impact of seawater intrusion on trihalomethanes (THMs) and haloacetic acids (HAAs) concentrations was assessed through mixing 0.0 to 2.0% seawater (SW) to groundwater (GW). Human exposure and risks were predicted for selected DBPs, which were then used to estimate the loss of disability-adjusted life years (DALY). The initial concentrations of bromide and iodide ions in GW without seawater were 42.5 µg/L and non-detectable (ND), respectively. For 2.0% SW, the concentrations were increased up to 1100 and 2.1 µg/L respectively. For 0.0% SW, averages of regulated THMs, HAAs and iodinated THMs (I-THMs) were 30.4, 27.9 and 0.13 µg/L respectively while these concentrations were 106.3, 72.9 and 1.6 µg/L in the samples with 2.0% SW respectively. From 0.0% to 2.0% SW, bromoform (TBM) and iodoform levels were increased up to 94.3 and 1.02 µg/L respectively. For HAAs, tribromoacetic acid was increased from 2.0 to 43.7 µg/L. The overall cancer risk from selected DBPs was 3.09 × 10⁻⁵ for 0.0% SW, while at 1.0% and 2.0% SW, the risks were 4.88 × 10⁻⁵ and 4.11 × 10⁻⁵ respectively. The loss of DALY was increased for up to 1.0%SW (77.30 at 0.0%SW and 122.0 at 1.0%SW), which was decreased to 102.8 at 2.0%SW. Future study is warranted to better control emerging DBPs in the coastal regions.