Environmental Exposure to Waterborne Pollutants and Colorectal Cancer Risk in Lebanon

Colorectal cancer (CRC) has a complex etiology involving genetic, lifestyle, and environmental factors. This study investigates the association between exposure to water contaminants and the risk of developing CRC in Lebanon. Population Attributable Fraction (PAF) was calculated using exposure prevalence from environmental reports and water quality assessments. Relative risks (RR) were obtained from multiple meta-analyses and epidemiological studies to quantify the contribution of five water contaminants to CRC incidence: nitrates, mercury, arsenic, trihalomethanes (THMs), and microbial pollutants (<i>E. coli</i>). A synthetic cohort was simulated using national exposure data and probabilistic techniques, employing multivariate logistic regression models to ensure precise CRC risk and controlling for lifestyle covariates. Adjusted PAF values were calculated using regression data to determine the proportion of CRC cases attributable to each water contaminant. THMs and <i>E. coli</i> showed the strongest association with CRC, with adjusted PAF values of 25.76% and 23.65%, respectively. Exposure to nitrates, arsenic, and mercury contributed less to CRC risk (1.02%, 0.52% and 2.20%, respectively). Multivariate regression confirmed that THMs and <i>E. coli</i> remained the strongest independent predictors of CRC risk (OR = 1.37, <i>p</i> = 0.001) and (OR = 1.79, <i>p</i> < 0.0001) among water contaminants, respectively. Our model-based approach carries limitations due to reliance on indirect exposure and risk estimates, which may introduce uncertainty stemming from data gaps and underlying assumptions. This study highlights the importance of water quality management in CRC prevention as exposure to drinking water contaminants contributes meaningfully to disease burden.