Effect of Irrigation with Untreated Municipal Wastewater of Hamadan on the Abundance of Enteric Coliforms in Soil and Vegetables’ Tissue

The study of population and survival of enteric bacteria in vegetables is very important in order to keep health and to inhibit epidemic diseases. The aims of this study were assessment of coliforms in soil and in tissues of the vegetables irrigated with untreated municipal wastewater in Hamadan, Iran. Samples of aerial parts of the vegetables and the soil around the roots were taken monthly from May to September, 2011. The abundance of E. coli, the lactose positive and negative coliforms in soil were 5.32, 5.81 and 5.39 log CFU g-1 respectively. The difference between the numbers of the lactose positive and negative coliforms in the soils irrigated with the untreated wastewater and their numbers in the control (Hydare) soil was not significant (p>0.05) in June and July. But their numbers were significantly (p<0.05) lower in the control soil in September. The means of E. coli, and the lactose positive and negative coliforms in the tissues of vegetables were 0.3, 3.97, 3.72 log CFU g-1 respectively. The E. coli was not detected in the vegetables in most cases. Irrigation with the untreated municipal wastewater had a significant effect (p<0.001) on the abundance of the lactose negative coliforms in the tissues of vegetables. The highest abundance of lactose negative coliforms was found in the Farhangian vegetables (4.58 log CFU g-1) and the lowest abundance of the lactose negative coliforms was found in the Hydare vegetables (1.08 log CFU g-1). The numbers of the lactose positive and negative coliforms in the vegetables did not have significant correlations with their numbers in the soils but they had high significant correlations with their abundances in the irrigation waters (p<0.001).