Indicator Bacteria-Based Assessment of Microbial Contamination with Wastewater-Agriculture-Health Nexus: Implication for Irrigation Water Safety in Gelan, Ethiopia.

Urban rivers in rapidly urbanizing low-income countries frequently receive untreated wastewater, converting downstream irrigation systems into persistent exposure interfaces within a wastewater-agriculture-health nexus. This study quantified Escherichia coli and total coliform concentrations in irrigation water from 16 sites along the Akaki and Dongora Rivers in Gelan, Ethiopia, over 7 weeks (n = 112) using membrane filtration on CHROMagar™ ECC to assess spatiotemporal fecal contamination loads. Indicator bacteria were detected at all locations, with concentrations routinely surpassing internationally accepted limits for irrigation water by several orders of magnitude. The Escherichia coli concentrations ranged from 1.10 × 105 to 2.82 × 106 CFU/100 mL and total coliforms from 1.13 × 105 to 2.95 × 107 CFU/100 mL, with Akaki River loads substantially higher than the Dongora River (P < .05), suggesting spatial variance from distinct contamination sources. Conceptually, exceedances position the irrigation corridor in a high-risk exposure domain, where regular agricultural activities may enhance occupational and foodborne transmission. While indicator bacteria do not directly quantify pathogen risk, their magnitude indicates elevated public health vulnerability. The site-specific evidence emphasizes the need for risk for health-based monitoring, including continuous microbial surveillance, and farm-level exposure reduction strategies to safeguard livelihood and downstream environmental health.