Spatial/temporal distribution and multi-pathway cancer risk assessment of trihalomethanes in low TOC and high bromide groundwater

Abstract

This study aims (1) to determine the seasonal and spatial distribution of THMs formed in chlorinated groundwater containing low levels of organic matter (0.4–0.8 mg L⁻¹) and low to high levels of bromine (40–380 μg L⁻¹), and (2) to evaluate the multi-route cancer risks associated with them. The study was conducted in Kayseri (Turkey), where drinking water is supplied from groundwater after chlorination only. THM formation in 50 water samples from 18 storage tanks and 32 distribution points was investigated to evaluate the spatial and temporal changes in THM concentrations for 12 months. The lifetime cancer risk associated with exposure to THMs through multiple pathways (i.e., oral ingestion, dermal absorption, and inhalation) was estimated for males and females. For a 12 month sampling period, the minimum and maximum THM concentrations varied from 2 μg L⁻¹ to 17 μg L⁻¹ and from 2 μg L⁻¹ to 29 μg L⁻¹ in storage tanks and distribution points, respectively. The ranges of median concentrations of THM were 5 μg L⁻¹ to 9 μg L⁻¹ in storage tanks and 5 μg L⁻¹ to 12 μg L⁻¹ in distribution points. In all samples dibromochloromethane was the dominant species, followed by bromoform, chloroform, and bromodichloromethane. The average values of total cancer risk associated with exposure to THMs via oral ingestion, dermal absorption, and inhalation for females and males were 1.31 × 10⁻⁵ and 1.25 × 10⁻⁵ in storage tanks, and 1.46 × 10⁻⁵ and 1.39 × 10⁻⁵ in distribution points, respectively. Although THM concentrations were very low, cancer risk values are 1.0 × 10⁻⁶ < CR < 1.0 × 10⁻⁴, which are higher than the negligible risk level (1.0 × 10⁻⁶).