Age-Specific Monte Carlo Simulation-Based Microbial Risk Assessment of Drinking Water Contamination in Islamabad:...

Microbial contamination of drinking water poses a significant public health concern, yet age-specific risks in Islamabad, Pakistan, remain poorly characterized. This study applied a Monte Carlo simulation-based quantitative microbial risk assessment to estimate the annual probability of infection (P_(a)inf) and disease burden (DB) associated with indicator organisms Escherichia coli (E. coli) and total coliforms across four age groups and one overall population category at three microbiologically contaminated drinking-water locations in Islamabad. Hydrochemical analysis, including principal component analysis, was conducted to characterize groundwater chemistry and explore links between physicochemical conditions and contamination vulnerability. Estimated risks were evaluated against U.S. EPA and WHO health-based benchmarks, and sensitivity analysis was used to identify the main drivers of DB. The results showed that estimated P(a)inf exceeded the U.S. EPA benchmark (1E-4 pppy) and DB exceeded the WHO benchmark (1E-6 DALYs pppy) across all modeled age groups at the three microbiologically contaminated drinking-water locations. Risk estimates were highest among middle-aged adults and elderly individuals and lowest among children, primarily due to differences in assumed drinking-water intake volumes. The total coliforms-associated risks were generally higher than those associated with E. coli. Sensitivity analysis identified exposure concentration as the dominant contributor to DB variability, accounting for 73%-75% of total variance. Some microbiologically unsafe locations showed hydrochemical characteristics associated with higher mineralization, including elevated EC, TDS, and HCO₃ ^- concentrations; however, these associations represent statistical patterns rather than evidence of direct causal relationships between hydrochemical conditions and microbial contamination. These findings suggest that routinely measured physicochemical parameters may serve as practical screening indicators for identifying contamination-prone zones and support targeted drinking water monitoring and intervention in Islamabad.