Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : The Effect of treated wastewater irrigation on fecal indicator bacteria and microbial pathogens in soil and crops

Auteur : Orlofsky, Ezra

Etablissement de soutenance : Ben-Gurion University of the Negev

Grade : Doctor of Philosophy (PhD) 2015

Résumé partiel
Contamination of edible crops with human pathogens results in significant morbidity and mortality worldwide. With growing water scarcity the risk of produce contamination is likely to rise due to increased use of treated wastewater (TWW) for irrigation practices. Fecal pathogens have been implicated in numerous disease outbreaks, as well as chronic gastrointestinal illness, in people who consume various raw crops such as basil, lettuce or tomatoes. To date, the most common water monitoring practice for fecal contamination in irrigation water relies on culturing fecal indicator bacteria such as Escherichia coli. However, numerous studies have recently raised concerns that fecal indicators do not always correlate with levels of disease-causing fecal pathogens in water sources, including treated effluents. The inability of indicators to accurately predict whether fecal pathogens are present or absent in treated wastewater and the irrigated crops themselves warrants further research that could provide improved produce safety monitoring guidelines to insure that the use of reused wastewater in irrigation is a sustainable and safe practice in arid climates. The aim of my study was to examine the correlation between fecal indicators and a wide range of fecal pathogens possibly found in irrigation wastewater, the irrigated soil and the cultivated plants. Due to the noted lack of field studies that were performed for this purpose, I conducted field experiments aimed to compare secondary and tertiary TWW with potable water for irrigation of tomatoes. Human pathogens including a suite of obligate and opportunistic bacterial pathogens (Campylobacter, Pseudomonas, Salmonella, Shigella, Staphylococcus), protozoa (Cryptosporidium and Giardia), and viruses (Adenovirus and Enterovirus) were monitored in two field trials using a combination of microscopic, cultivationbased, and molecular techniques. A wide set of fecal indicator bacteria (FIB) including total and fecal coliforms, E. coli and Enterococci were monitored throughout the two growing seasons. Results from the field trials showed that FIB contamination was not statistically different on tomatoes irrigated with TWW or potable water. In fact, indicator bacteria testing did not predict the presence of pathogens in any of the matrices tested. Indicator bacteria were detected in water, soil and on tomato surfaces from all irrigation treatment schemes, and were positively correlated with duration of time in the field (p < 0.05). Pathogen contamination (Cryptosporidium) was only detected in secondary TWW (3/14 samples).

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