Spatio-temporal distribution and environmental correlates of trihalomethane concentrations in public drinking water supplies in Queensland, Australia: A data linkage study

Prolonged exposure to high concentrations of trihalomethanes (THMs), which are water disinfection by-products, poses a significant human health risk. This study investigated the spatial-temporal distribution of THM concentrations, the exceedance of the Australian drinking water guideline value (250 μg/L), and the environmental factors associated with THM concentrations in public drinking water supplies across Queensland, Australia, to help guide strategies for mitigating THM exposure. We employed a data linkage approach, integrating spatial water quality monitoring data covering 27 local government areas (LGAs) from 2009 to 2020 with environmental data from the Bureau of Meteorology. Key outcomes were THM concentrations and exceedances. Analyses included time-trends, multiple generalised linear models and logistic regression models. The median monthly THM concentration was 78 μg/L [IQR 49, 119 μg/L]. Between 2009 and 2020, the median THM concentration increased from 38 μg/L to 73 μg/L, while the incidence of exceedance increased from 2.3% to 3.0%. THM exceedances were significantly lower in water from treatment plants (AOR = 0.15, 95% CI [0.07, 0.30]), in LGAs within South-East Queensland (AOR = 0.07, 95% CI [0.01, 0.33]), during spring (AOR = 0.39, 95% CI [0.21,0.70]), in advantaged socio-economic areas and major cities. Increase in temperature was associated with greater THM exceedance (AOR = 1.21, 95% CI [1.07,1.37]), but lower during periods of bushfire (exp(β) = 0.85, 95% CI [0.76,0.95]). Rainfall and NDVI were not significantly associated with THM concentration and exceedances. The elevated concentrations and repeated exceedances highlight a persistent challenge coupled with systemic inequities. We recommend consistent THM data collection, monitoring, optimizing treatment and infrastructure upgrades in disadvantaged regions to improve water quality and protect public health.