Spatiotemporal lag effects of surface water quality on liver cirrhosis mortality risk in China: a nine-year time-series study of environmental driving mechanism

Surface water is a major source of domestic water supply in China, yet its quality remains uneven despite recent improvements. Chronic exposure to surface-water pollution has been implicated in liver injury, but evidence linking water quality to cirrhosis mortality—particularly accounting for delayed and non-linear effects—remains limited. We investigated the spatiotemporal associations between surface water quality and cirrhosis mortality in China. We conducted a nationwide ecological study integrating surface water monitoring data and cirrhosis mortality data from 2013 to 2021. Distributed lag non-linear models (DLNMs) were applied to assess non-linear and lagged associations (0-2 years) between overall water-quality classes and key pollution indicators, including total phosphorus (TP), chemical oxygen demand, dichromate method (CODCr), and five-day biochemical oxygen demand (BOD5). Analyses were stratified by sex and urban-rural residence. Surface water quality was associated with cirrhosis mortality in a non-linear, delayed, and population-specific manner. Moderate and poor water quality exhibited distinct temporal risk patterns, with sustained exposure to moderate pollution associated with a higher cumulative mortality risk. TP and CODCr showed clear non-linear associations with mortality that intensified at longer lags, whereas BOD5 displayed a U-shaped relationship with relative risks remaining below unity. Stronger and more persistent effects were observed among males and rural residents. Our findings indicate that long-term exposure to moderate surface-water pollution and persistent nutrient and organic contamination contribute to cirrhosis mortality in China. Water-quality management strategies should account for delayed health effects and population vulnerability, with targeted interventions prioritising sustained pollution reduction and protection of high-risk groups.