Comparative evaluation of irrigation waters on microbiological safety of spinach in field

Effect of ground water (GW), secondary-treated wastewater (STWW) and roof-harvested rainwater (RHW) irrigation on microbiological quality of spinach in field was investigated.

Spinach grown at the Fulton farm (Chambersburg, PA) was spray-irrigated with GW, STWW or RHW once a week for 2 weeks in summer and fall seasons. Four replicate spinach and soil samples collected from two plots for each group were analysed for indicator and pathogenic bacteria on 0, 1, 2 and 4 days postirrigation (dpi). While total coliforms remained unchanged on spinach regardless of the treatment waters and growing seasons, populations of faecal coliform significantly decreased on RHW- and STWW-irrigated spinach as compared to spinach irrigated with GW at 4 dpi of each week in fall. Irrigation with STWW that contained Escherichia coli population <1·0 log CFU per 100 ml resulted in the lowest E. coli recovery on spinach in fall. Bacterial pathogens were not detected in any sample.

The transference of indicator micro-organisms from irrigation waters to plants was influenced by the type of water and growing season.

Alternative water sources such as STWW and RHW containing low indicator bacterial populations may be suitable for spinach irrigation in the mid-Atlantic region. However, microbiological quality of these waters must be determined prior to their use for irrigation.