A Systematic Review of Irrigation Water Quality, Vegetable Contamination, and Food Safety Concerns in Peri-Urban Addis Ababa, Ethiopia

Urban and peri-urban agriculture (UPA) plays a vital role in enhancing food security, employment, and livelihoods in Addis Ababa and its surrounding areas. However, the widespread use of untreated or poorly treated wastewater for vegetable irrigation poses significant environmental and public health challenges. To better understand these risks, a systematic review was conducted to examine the interlinked issues of irrigation water quality, vegetable contamination, and food safety in urban and peri-urban Addis Ababa. A comprehensive literature search was conducted across multiple electronic databases, including PubMed, Scopus, African Journals Online (AJOL), and Google Scholar, and supplemented with grey literature, institutional reports, and government documents. Guided by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), the search yielded 404 records; 55 studies met the inclusion criteria for qualitative and quantitative synthesis, providing a robust evidence base for examining contamination patterns, environmental drivers, and associated health risks. The review and empirical findings reveal a highly interconnected contamination continuum, where pollutants from municipal wastewater, industrial effluents, and urban runoff accumulate in soils and are subsequently bioaccumulated in vegetables. Heavy metals in soils followed the order Mn > Ni > Pb > Cu > Zn, often exceeding WHO, USEPA, and EU permissible limits. Leafy vegetables, particularly lettuce and cabbage, exhibited the highest bioaccumulation, notably for Ni and Pb (BCF > 1). In addition, microbial pathogens – including E. coli, faecal coliforms, and parasites such as Ascaris and Giardia – and pesticide residues were detected at levels surpassing international safety standards. Contamination displayed spatial and seasonal variability, with hotspots in Akaki-Kality and Bole Bulbula linked to industrial proximity, wastewater irrigation, and intensive farming practices. The findings indicate that children are particularly vulnerable to non-carcinogenic risks from Pb and Ni, while chronic exposure may result in organ damage, neurological disorders, and reproductive effects. Overall, the results highlight the dual nature of contamination – immediate microbial hazards alongside long-term heavy metal accumulation – and underscore the urgent need for integrated water management, regulatory oversight, and sustainable peri-urban agriculture interventions to safeguard food safety and public health in rapidly urbanizing contexts.