Integrated Assessment of Physicochemical Instability, Pharmaceutical Persistence, Microbial Contamination, and Antimicrobial Resistance In an Urban Water System in Zimbabwe

Urban water security in the Global South is increasingly governed by the coupled degradation of aging infrastructure and the persistence of complex chemical stressors. This study presents a longitudinal, systems-level assessment (2020–2024) of the Harare metropolitan water continuum, conceptualizing the system as an active evolutionary reactor rather than a passive conveyance network. A three-stage analytical framework was applied, beginning with Stage I (2020) detection of the persistent antibiotics sulfamethoxazole and trimethoprim at the Lake Chivero water–sediment interface using a solid-phase extraction method developed by our group. This baseline was integrated with a Stage II (2021) spatial assessment of physicochemical instability across treat-ment and distribution infrastructure, followed by Stage III (2024) validation of pharmaceutical and agrochemical persistence using an optimized liquid–liquid extraction approach. Sulfamethoxazole and trimethoprim were identified using high-performance liquid chromatography (HPLC), while atrazine was confirmed by gas chromatography–mass spectrometry (GC–MS). These qualitative analyses demonstrated incomplete interruption of antibiotic transfer from wastewater effluent into Lake Chivero, which functions as a primary environmental reservoir for chemical and biological selection. The additional identification of atrazine established the presence of a non-antibiotic co-selective stressor within the same matrices. Distribution-system instability, marked by collapse of the free residual chlorine barrier under elevated ammonia loading, coincided with microbial recovery at distal consumer endpoints. Antimicrobial susceptibility testing of source-interface isolates revealed reduced susceptibility to the detected antibiotics, linking chronic sub-therapeutic exposure to environmentally relevant resistance phenotypes. Viewed through a One Health lens, these findings underscore the need for integrated water management strategies that extend beyond centralized treatment to encompass wastewater control, source-water protection, and distribution-system stability.