The potential health risks of stored urine used as fertilizer – what evidence do we have?

ABSTRACT To supplement chemical fertilizers with more sustainable nutrient sources, innovative wastewater separation technologies have been developed to recover nutrients from human urine to derive fertilizers. However, microbial health risks associated with wastewater reuse and urine source separation remain a concern when integrating these technologies into existing sanitation systems. Pathogens, particularly those originating from faecal cross-contamination during source separation, can cause severe acute gastrointestinal disease. Following PRISMA guidelines, this systematic review examines microbial hazards of health relevance in human urine and identifies gaps in understanding pathogen inactivation during storage. Thirty-five empirical studies were reviewed, including investigations of bacterial species (20), viral agents (11), and antimicrobial resistance genes (11). Findings reveal that the range of microbial health risks associated with urine has expanded since source separation was introduced in the 1990s. Key knowledge gaps include uncertainties in pathogen concentrations at the source, the efficacy and stability of urea hydrolysis as a single treatment method, and the use of surrogate pathogens to represent inactivation dynamics in hydrolyzed urine. Addressing these uncertainties will strengthen quantitative microbial risk assessments and support regulatory confidence in the safe agricultural application of urine-derived fertilizers.