The effect of waste water reuse in irrigation on the contamination level of food crops by Giardia cysts and Ascaris eggs

In Marrakech, raw sewage has been used for farming purposes for several decades for many types of crops. This study aimed to determine the contamination level of Giardia cysts and Ascaris eggs for crops designated for human consumption. Collected crops in irrigated fields were turnip, marrow, squash, potatoes, pepper and eggplant. Field trials were also carried out on four crops, coriander, carrots, mint and radish, using three water types for irrigation: i.e. raw waste water, treated waste water (sedimentation and 16 days retention) and fresh water. Giardia cysts were detected at a level of 5.1 cysts/kg in potatoes, while Ascaris eggs were observed in numbers varying between 0.18 eggs/kg in potatoes and 0.27 eggs/kg in turnip. Field trials confirmed that irrigation of crops by raw waste water leads to contamination. Giardia and Ascaris were isolated in coriander at concentrations of 254 cysts/kg and 2.7 eggs/kg, respectively; mint was also highly contaminated with numbers reaching 96 cysts/kg and 4.63 eggs/kg. Carrots and radish were contaminated and respective numbers observed for Giardia were 155 and 59.1 cysts/kg; Ascaris was discovered in numbers of 0.7 and 1.64 eggs/kg, respectively. However, cultures irrigated with treated waste water and fresh water were free from contamination. Cysts and eggs on coriander persisted for a maximum of 8 days. (C) 1999 Elsevier Science B.V. All rights reserved.