Occurrence, formation, and human health risk assessment of trihalomethanes in source, treated, and supply water of Dhaka, Bangladesh

Chlorination is one of the most functional and cost-effective techniques for water treatment against microbial growth. Trihalomethanes (THMs) are the predominant class of disinfection by-products formed during chlorination. Present study assessed concentrations of the THMs in the source, treated, and supply tap water of Dhaka, Bangladesh. Liquid-liquid extraction and gas chromatography-electron capture detector (GC-ECD) were used to extract and analyze the THMs, respectively. Trichloromethane (TCM), Bromodichloromethane (BDCM), and Dibromochloromethane (DBCM) were obtained from a water treatment plant (WTP), whereas only TCM and BDCM were found in the tap water samples. The Total THM (TTHM) concentration observed at the WTP was 27.33 ± 2.67 μg/L and that of the tap water samples ranged from 0.18-2.07 μg/L. TTHM value strongly correlated with TCM of the water sample (Pearson Coefficient=0.957). Health risk assessments were obtained for THMs in oral, dermal, and inhalation pathways. Total hazard index of WTP samples was 0.1435 and 0.1677 for male and female consumers, respectively. A moderate cancer risk (10-5) was found for TCM through oral exposure. Female consumers are more prone to carcinogenic health effects (11.8% higher) than males. This study provides a comprehensive insight into the total trihalomethane levels in the water supply of Dhaka City.