Trihalomethanes in global drinking water: Distributions, risk assessments, and attributable disease burden of bladder cancer

This study aimed to assess the global spatiotemporal variations of trihalomethanes (THMs) in drinking water, evaluate their cancer and non-cancer risks, and THM-attributable bladder cancer burden. THM concentrations in drinking water around fifty years on a global scale were integrated. Health risks were assessed using Monte Carlo simulations and attributable bladder cancer burden was estimated by comparative risk assessment methodology. The results showed that global mean THM concentrations in drinking water significantly decreased from 78.37 μg/L (1973–1983) to 51.99 μg/L (1984–2004) and to 21.90 μg/L (after 2004). The lifestage-integrative cancer risk and hazard index of THMs through all exposure pathways were acceptable with the average level of 1.28×10-5 and 7.63×10-2, respectively. The global attributable disability adjusted of life years (DALYs) and the age-standardized DALYs rate (ASDR) dropped by 16% and 56% from 1990–1994 to 2015–2019, respectively. A big decline in the attributable ASDR was observed in the United Kingdom (62%) and the United States (27%), while China experienced a nearly 3-fold increase due to the expanded water supply coverage and increased life expectancy. However, China also benefited from the spread of chlorination, which helped reduce nearly 90% of unsafe-water-caused mortality from 1998 to 2018. Trihalomethanes (THMs) are the most frequently detected disinfection byproducts in chlorinated drinking water around the world and proved significantly associated with the occurrence of bladder cancer. This study analyzed the global spatiotemporal distribution pattern of THMs in drinking water from 1973 to 2021, and first estimated their health impacts including cancer and non-cancer risks and attributable bladder cancer burden. This study confirmed the effectiveness of THM regulations especially in developed countries in the past, but also revealed the discrepancies between developed and developing countries. We identified all potential reasons behind their differences and finally put forward practical improvement suggestions.