High Andean rivers in Ecuador as critical pathways for carcinogenic exposure

A critical environmental problem persists in Andean rivers due to pollution that threatens human health. This study evaluated the water quality of 22 high-Andean rivers in Ecuador and assessed non-carcinogenic and carcinogenic health risks considering seasonality (dry and rainy periods), water use, and age groups. A total of 29 physicochemical and microbiological parameters were analyzed using the CCME Water Quality Index (WQI), the Heavy Metal Pollution Index (HPI), and the Heavy Metal Evaluation Index (HEI). Human health risks were estimated for oral ingestion and dermal contact pathways through the hazard quotient (HQ), hazard index (HI), and cancer risk (CR). Results indicate that total petroleum hydrocarbons (TPH), fecal coliforms (FC), and aluminum exceeded national and international limits in 100% of the rivers, followed by iron (73%), turbidity (62%), cadmium (52%), and lead, which exceeded limits only during the dry period. The CCME WQI classified 100% of rivers as marginal and poor during the dry season, whereas in the rainy season, 92% were suitable for recreational use and only 4% were rated fair for human consumption. Average HPI and HEI values suggest no overall heavy-metal toxicity risk; however, seasonal variability significantly affects water quality and may generate critical conditions in specific river reaches. Non-carcinogenic risk (HI > 1) was identified in 46% of rivers, with metal contributions ranked Cd > As > Hg > Pb > Cr(VI), disproportionately affecting children (HI > 1.5), while recreational use remained safe. Cancer risk associated with Cd exceeded acceptable thresholds in all rivers, particularly during the dry season and for children, whereas Cr(VI) and As posed only localized risks. Multivariate analysis highlighted elevated health risks, especially for children, underscoring the need for water-management strategies tailored to use, age group, and seasonal conditions.