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

Authors: HSIN-BAI, YIN - University Of Maryland; GU, GANYU - University Of Maryland; Nou, Xiangwu; Patel, Jitu

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2019
Publication Date: 11/7/2019
Citation: Hsin-Bai, Y., Gu, G., Nou, X., Patel, J.R. 2019. Comparative evaluation of irrigation waters on microbiological safety of spinach in field. Journal of Applied Microbiology. https://doi.org/10.1111/jam.14436.
DOI: https://doi.org/10.1111/jam.14436

Interpretive Summary: Alternative sources of water for irrigation have been considered during water scarcity to maintain agricultural productivity and food security. We investigated the effect of secondary-treated wastewater (STWW) and roof-harvested rainwater (RHW) irrigation on microbiological quality of spinach at the organic farm. Six-week old spinach grown in the field was spray irrigated using STWW, RHW, or ground water (GW, control) once a week for two weeks in the summer and fall seasons. Water, spinach, and soil samples were analyzed for the indicator bacterial populations (total coliforms, fecal coliforms, generic Escherichia coli and enterococci) and the presence of bacterial pathogens (Salmonella, Escherichia coli O157:H7 and L. monocytogenes). For both seasons, there was no significant increase in total coliforms and E. coli populations on STWW or RHW-irrigated spinach as compared to the spinach with GW irrigation. Fecal coliforms were significantly (P < 0.05) increased on GW-irrigated spinach on 0 dpi in the first week of the summer season and at the end of the fall season. Bacterial pathogens were not detected in water, spinach, and soil samples. STWW and RHW containing low indicator bacterial populations seemed adequate as irrigation water without affecting the microbiological safety of spinach. The research benefits farmers in utilizing alternative waters for fresh produce irrigation during water shortage.

Technical Abstract: Secondary-treated wastewater (STWW) and roof-harvested rainwater (RHW) have been considered as potential alternative irrigation water to overcome water scarcity. This study investigated the effect of STWW and RHW irrigation on microbiological quality of spinach in the field. Six-week old spinach grown in the field was spray irrigated using STWW, RHW, or ground water (GW, control) once a week for two weeks in the summer and fall seasons. Four replicate spinach and soil samples from each group were collected weekly pre-irrigation and on 0, 1, 2, and 4 days-post-irrigation (dpi). Water, spinach, and soil samples were analyzed for the indicator bacterial populations (total coliforms, fecal coliforms, generic Escherichia coli and enterococci) and the presence of bacterial pathogens (Salmonella, Escherichia coli O157:H7 and L. monocytogenes). For both seasons, there was no significant increase in total coliforms and E. coli populations on STWW or RHW-irrigated spinach as compared to the spinach with GW irrigation. Fecal coliforms were significantly (P < 0.05) increased on GW-irrigated spinach on 0 dpi in the first week of the summer season and at the end of the fall season due to the higher bacterial populations in GW samples. Bacterial pathogens were not detected in water, spinach, and soil samples. STWW and RHW containing low indicator bacterial populations seemed adequate as irrigation water without affecting the microbiological safety of spinach. However, microbiological quality of alternative waters should be determined prior to their use for irrigation.