Small-scale risk assessment of transmission of parasites from wastewater treatment plant to downstream vegetable farms

AIM: The aim of the present study was to simultaneously investigate parasitic contamination of treated wastewater and downstream vegetable farms that are irrigated with treated sewage, during a year. BACKGROUND: (Oo) Cysts and eggs of parasites are resistant to most of routine wastewater treatment process. Irrigation of vegetables farms with either treated wastewater or illegally use of raw wastewaters enhances the risk of contamination with enteric pathogens. METHODS: The treated wastewater samples were taken after chlorination from a wastewater treatment plant located at the south of Tehran. In addition, 60 vegetable samples (5 samples from each farm) were collected from the selected downstream farms that routinely used treated wastewater for irrigation of crops. Parasitological tests were performed using Ziehl–Neelsen, conventional lugol’s iodine staining and direct microscopical examination. RESULTS: Parasites including free living larvae, eggs of Toxoascaris leonina, egg of Toxocara sp. Trichuris sp, Trichostrongylus sp and amoeboid trophozoite were seen in 5/12 (41.7%) of vegetable samples gathered during a year. There was no statistically significant correlation between the season and parasitic contamination of the vegetables (P= 1). Furthermore, parasitic contamination was observed in 7/12 (53.8%) of treated wastewater samples. The correlation between season and parasitic contamination of treated wastewater was evaluated that the results showed a higher contamination of treated wastewater in spring and autumn (P<0.05). Fisher’s exact test also showed that there was no significant correlation between parasitic contaminations of vegetable samples and treated wastewater according to seasonal change. CONCLUSION: The results showed parasites in both treated wastewater plant and downstream crops farms that suggests the public health importance of the quality of water resources that routinely used for irrigation of vegetable farms.