Exposure and carcinogenic risk assessment of trihalomethanes (THMs) for water supply consumers in Addis Ababa, Ethiopia.

BACKGROUND: Trihalomethanes (THMs), a class of DBPs (disinfection byproducts) that includes chloroform, bromodichloromethane (BDCM), chlorodibromomethane (CDBM), and bromoform. To the best of authors' knowledge, no study has addressed the relationship between the concentration of THMs and lifetime cancer risks (LCR) in drinking water supply system in Addis Ababa, Ethiopia. Therefore, this study aimed to determine the lifetime cancer risks of exposure to THMs in Addis Ababa, Ethiopia.

METHOD: A total of 120 duplicate water samples were collected from 21 sampling points in Addis Ababa, Ethiopia. The THMs were separated by a DB-5 capillary column and detected by an electron capture detector (ECD). Cancer and non-cancer risk assessments were performed.

RESULTS: The average total THMs (TTHMs)concentration in Addis Ababa, Ethiopia, was 76.3 μg/L. Chloroform was the most dominant THM species identified. The total cancer risk for males was higher than that for females. The average LCR for TTHMs via ingestion in drinking water in this study was unacceptably high risk 93.4 × 10 - 2 . An average LCR through dermal routes was also of unacceptably high risk 4.3 × 10 - 2 . The LCR by chloroform contributes the highest (72%) of the total risk, followed by BDCM (14%), DBCM (10%) and bromoform (4%).

CONCLUSIONS: The cancer risk of drinking water due to THMs in Addis Ababa was higher than the level recommended by the USEPA. The total LCR from the targeted THMs was higher via the three exposure routes. Males were at higher THM cancer risk than females. The hazard index (HI) indicated that the dermal route caused higher HI values than the ingestion route. It is essential to apply alternatives to chlorine, i.e., chlorine dioxide (ClO2 ), ozone and ultraviolet radiation, in Addis Ababa, Ethiopia. The monitoring and regulation of the THMs is required on a regular basis to analyse the trends and guide the water treatment and distribution system.

AVAILABILITY OF DATA AND MATERIALS: The datasets generated for this analysis are available from the corresponding author upon reasonable request.