Modelling health risks of urine-derived fertiliser application in urban green areas using quantitative microbial risk assessment

A comparative risk scenario analysis was conducted using quantitative microbial risk assessment for urine-derived fertiliser (UDF) use, considering membrane filtration and urine storage as treatment options. The risk scenarios examined included accidental ingestion through unwashed, uncooked home-grown crops; occupational exposure of workers handling and mixing UDF; and recreational exposure of toddlers playing in green areas where the fertiliser had been recently applied. The primary source of contamination originates from fecal displacement into urine during source separation in the toilet. Campylobacter jejuni and rotavirus were selected as reference pathogens. As no guidelines currently specify benchmarks for urine reuse, the annual infection risk and the DALY were estimated and evaluated against existing wastewater reuse benchmarks. The analysis shows that membrane treatment can greatly reduce health risks associated with UDF use: the risk was sufficiently low to meet annual, and DALY targets for bacterial and viral risks. The results also indicate that inactivation of both bacteria and viruses through urine storage is unlikely to meet safety targets without extended storage durations. The infection risks were higher during accidental ingestion of urine fertiliser on food crops compared to indirect exposure due to occupational and recreational activities. Nevertheless, the residual risk is sufficiently low to be effectively managed with additional, simple mitigation measures communicated through user guidance on product labels. In conclusion, membrane treatment technology could mitigate exposure to microbial hazards potentially present in UDF and may be satisfactory to reassure health regulators of its safety, thereby supporting progress toward sustainability goals.