Drinking Water Chlorination Byproducts and Cancer Risks in Addis Ababa, Ethiopia
No Thumbnail Available
Date
2023-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
Background: Disinfection byproducts (DBPs) from chlorinated drinking water have been linked to an increased risk of cancer in the bladder, stomach, colon, and rectum. No previous evidence showed the independent trends and prevalence of these cancers in association with DBPs in Ethiopia. Therefore, the study aimed to determine the prevalence and trends of disinfection byproducts related cancers (DBRCs) in Addis Ababa, Ethiopia. Close scrutiny of the published studies showed that this is the first study conducted indicating the association between drinking water source, chlorinated water and colorectal cancer (CRC) in Ethiopia. The present investigation is also the first study in assessing the trihalomethanes level and lifetime cancer risks in the drinking water supply in Addis Ababa, Ethiopia.
Methods: A retrospective record review using the Addis Ababa Cancer Registry (AACR) was conducted in Addis Ababa, Ethiopia. The AACR collects data on cancer cases submitted by three public hospitals and twelve private facilities (the only cancer treatment centers) in Addis Ababa, Ethiopia. Spatial data sets were produced and classified into households receiving chlorinated surface water and unchlorinated groundwater. The Cochran-Armitage trend test was used to evaluate whether there was a disinfection byproduct-related cancers (DBRCs) trend among communities receiving chlorinated water. Negative binomial regression was used to analyze the incidence rate. A facility-based matched case control study was conducted in Tikur Anbessa Specialized Hospital (TASH) involving 224 cases and 448 population controls from June 2020 to May 2021. A multivariable conditional logistic regression was used to identify risk factors of CRC. Stratified analysis was used to detect confounding factors and effect modification.
A cross-sectional study design was used to collect water samples in the water supply networks of Addis Ababa, Ethiopia. One hundred twenty (120) drinking water samples were collected from 21 sampling points in Addis Ababa, Ethiopia. The three sampling areas were Legedadi, Gefersa and groundwater sources. The United States Environmental Protection Agency (USEPA) protocol and practice for sample collection and handling were followed. The trihalomethanes (THMs) were separated by a DB-5 capillary column and detected by GC-ECD (gas chromatography-electron capture detector). Spectrophotometric and Insitu methods were used for physicochemical parameters. Canonical Correspondence for data analysis of trihalomethanes and environmental variables using CANOCO 4.5. Cancer and non-cancer risks of THMs via inhalation, ingestion and dermal contact routes have also determined.
Results: A total of 11,438 cancer cases were registered between 2012 and 2016, and DBRCs accounted for approximately 17%. The majority of the cases were females; 7,706 (67%). The prevalence of DBRCs was found to be higher in communities supplied with chlorinated water. Approximately 56% of colorectal cancer patients and 53% of stomach cancer patients are known to be using chlorinated surface water for drinking regularly. Of 214 colorectal cancer (CRC) cases, 148 (69.2%) used chlorinated water whereas out of 428 controls 161 (37.6%) used chlorinated water. In the final regression model, drinking chlorinated surface water (adjusted matched odds ratio (adjusted mOR) = 2.6;(95% CI: [1.7 ̶ 4.0]), history of swimming (adjusted mOR= 2.4; 95% CI: [1.4 ̶ 4.1]), years at the place of current residence (adjusted mOR=1.5; (95% CI: [1.1 ̶ 2.2]), hot tap water use for showering (adjusted mOR; 3.8= (95% CI: [2.5 ̶ 5.9]) were significantly associated with CRC.
The mean concentration of total trihalomethanes in drinking water in Addis Ababa was 76.3 μg/L. The concentration of chloroform in the drinking water supply in Addis Ababa, Ethiopia, ranged between 4.03-79.4μg/L. The results of the average THM concentration followed the order TCM (Trichloromethane) >BDCM(Bromodichloromethane) > DBCM (Dibromochloromethane) > TBM (Tribromomethane). The mean total THMs in the Gefersa and legedadi water supply systems were 77.4μg/L and 69.66μg/L respectively. The lowest THMs concentration was recorded in the groundwater supply system (15.5μg/L). The residual chlorine, phosphates, UV absorbance at 254 nm, and combined chlorine had positive correlations with THMs formation. However, electron conductivity had negative correlation with THMs formation. The cancer risk study discovered that among the examined routes, ingestion causes the greatest risk. The lifetime cancer risk by chloroform contributes the highest (72%) of the total risk, followed by BDCM (14%), DBCM (10%) and bromoform (4%).
Conclusions: The prevalence of DBRCs in this study was found to be high. The colon cancer trends increased substantially in Addis Ababa, Ethiopia. Drinking chlorinated water for extended years is a significant risk factor for CRC in Addis Ababa, Ethiopia. In addition, hot tap water use for showering, and swimming have higher level total THMs than groundwater supply. The residual chlorine, UV absorbance, phosphate and hardness as calcium, and electron conductivity were found to be the main predictors determining the abundance and distribution of trihalomethanes. The cancer risk study discovered that among the examined routes, ingestion causes the greatest risk. The monitoring and regulation of the THMs is required on a regular basis to analyses trends and guide the water treatment and distribution system.history are risk factors for CRC. Surface water supply networksAnalysis (CCA) or Redundancy Analysis (RDA) was used
Description
Keywords
Chlorination, Cancer risk, Disinfection byproducts, Gas chromatography, Hazard index, Trihalomethanes