Association between Drinking Water Disinfection Byproducts Exposure and Human Bladder Cancer：A Time-updated Meta-analysis of Trihalomethanes

Abstract

Drinking water disinfection byproducts (DBPs) have received widespread attention due to their high concentrations and toxicity. However, the correlation between exposure to disinfection byproducts and bladder cancer in published papers is inconsistent. In this study, a time-updated meta-analysis was conducted, which aimed to elucidate the relationship between the historical exposure time and exposure levels of trihalomethanes (THMs) in drinking water and the associated risk of bladder cancer. A total of 433 relative publications was obtained from databases, however only 16 publications satisfied the inclusive criteria, including 13 case-control studies and 3 cohort studies. The case-control studies encompassed 8,126 bladder cancer cases and 13,843 controls, while the cohort studies included 112,654 cases and 955 bladder cancer patients. In comparison to individuals who have never been exposed to or have only experienced brief exposure to THMs, the odds ratio (OR) for medium-term and long-term exposure of THMs was 1.30 (95% CI = (1.11, 1.53)), and 1.59 (95% CI = (1.40, 1.81)), respectively. This suggests a statistically significant positive correlation between long-term exposure to chlorinated drinking water and an increased risk of bladder cancer. The pooled OR for low and high exposure group was 1.28 (95% CI = (1.06, 1.55)) and 1.45 (95% CI = (1.14, 1.85)), respectively, indicating an increased risk of bladder cancer occurrence compared to the unexposed group. Interestingly, subgroup analysis revealed that high levels of THM exposures of males caused an increased risk of bladder cancer (OR= 1.59, 95% CI = (1.11, 1.53)), while this association was not significant for females (OR = 1.05, 95% CI = (0.61, 1.80)). More importantly, although the case-control studies were consistent with the overall findings, the cohort studies suggest that there is insufficient evidence to establish a definitive causal link between THMs exposure levels and bladder cancer. In general, long-term consumption of chlorinated drinking water was associated with the occurrence of bladder cancer of male rather than female.