Wastewater reuse in agriculture: A review of soil and crops parasitic contamination, associated health risks and mitigation approach

Background: Wastewater reuse in agriculture can potentially result in adverse health implications including parasitic diseases spread. Trichuris, Ascaris, and Giardia are major pathogenic parasites of concern associated with this practice. This review investigated their occurrence in wastewater, and environmental components reached through wastewater application, including irrigated soil and grown crops. Exposure pathways and evidence for health risks were also explored. Methods: Several databases (Google Scholar, PubMed, Science Direct, Scopus, Web of Science, and ResearchGate) and other sites were searched for published literature up to 2021. The searched keywords include wastewater reuse, soil-transmitted helminths (STHs), Ascaris, Trichuris, Giardia, crop contamination, soil contamination, health risk, epidemiological studies, exposure pathways, and risk mitigation. Overall, 160 papers have been yielded. After screening for relevance, 60 studies were considered for inclusion. Results: Giardia, Ascaris, and Trichuris were frequently detected in wastewater with up to 5 × 10^5 cysts/L and 5.73 × 10^3 eggs/L. Concentrations of 750 eggs/100 g and 2.8 × 10^4 cysts/100 g were reported in wastewater irrigated soil. Ascaris was reported in irrigated crops with up to 70 eggs/kg versus 6.6 × 10^3 cysts/kg for Giardia, depending on the type of crops. Epidemiological studies provided evidence supporting the increase of ascariasis, trichuriasis, and giardiasis diseases related to the exposure to wastewater irrigated soil and crops. Conclusion: The findings suggest that wastewater reuse in agriculture leads to contamination of soil, and crops with pathogenic parasites, increasing health risks in the exposed groups. To remedy this issue, protection measures, including a multi-barrier approach, can be applied to mitigate the health risks engendered by wastewater reuse for irrigation.