Abstracts

Assessment of irrigation water quality for the Quebec horticulture industry

by Divya Gupta




Institution: McGill University
Department:
Year: 2017
Keywords: Bioresource Engineering
Posted: 02/01/2018
Record ID: 2189733
Full text PDF: http://digitool.library.mcgill.ca/thesisfile146995.pdf


Abstract

Ready-to-eat vegetables when irrigated with untreated surface water cause risk of gastrointestinal infection to humans. Greenhouse and field studies were conducted to quantify Escherichia coli in the irrigation water and vegetables irrigated with untreated water. The Quantitative Microbial Risk Assessment (QMRA) model used data from the greenhouse and field studies to estimate the health risk to humans on the consumption of irrigated fresh fruits and vegetables. The field study analyzed pathogenic E. coli in the irrigation water during the May-October growing seasons in 2013 and 2014 from two field sites, St-Remi and Rougemont in Quebec. In Rougemont, the maximum concentration of E. coli was found during the May-June period for both years. Whereas in St-Remi, the maximum E. coli concentration was found during the May-June and the September-October. The greenhouse study was conducted in controlled environmental conditions at the Macdonald campus to confirm the level of contamination that was transferred to fruits and soil over a 30 days' time period. The application of E. coli contaminated irrigation water resulted in the contamination of vegetables and of soil using four different treatments. The highest risk for lettuce was observed in the Sprinkler+Organic treatment, followed by the Sprinkler+Mineral and the Drip+Organic treatments, but risk with the Drip+Mineral treatment was observed only on the 20th day. There was a risk observed in tomatoes only on the 10th day in the Drip+Organic treatment. The QMRA model used data from field experiments and the combined annual disease burden for all the pathogens was found in the range of 10-3 to 10-2 DALYs (Disability Adjusted Life Years) for lettuce and tomatoes. Whereas, the combined gastrointestinal (GI) risk was in the range of 10-2 to 10-1 and 10-3 to 10-1 for lettuce and tomatoes respectively. Comparison of the models used for vegetables, showed that lettuce consumption would result in higher risk because ranges are greater compared to tomato consumption. Another QMRA study was conducted using data from St-Esprit, Quebec, to confirm the quantified gastrointestinal risks when crops were irrigated with untreated surface water. Drip irrigation showed less risk (1.8 X10-8 to 3.9 X10-4 DALYs) than sprinkler irrigation (9.8 X10-8 to 2.1 X10-3 DALYs) across all scenarios. Washing fresh vegetables for 2 min showed the least risk (10-8-10-5 DALYs) as compared to washing vegetables for 3-4 sec (10-8-10-4 DALYs) and to no washing (10-7-10-3 DALYs). Among five vegetables, lettuce showed the highest risk compared to tomatoes, squash (zucchini), cauliflower and broccoli. Therefore, it is recommended to wash fresh vegetables for 2 min prior to consumption; and use drip irrigation and mineral soil to grow the vegetables to be eaten raw. Les lgumes prts consommer, lorsqu'ils sont irrigus avec de l'eau de surface non traite, causent un risque gastro-intestinal pour les humains. Des tudes en serre et sur le terrain ont t menes pour quantifier Escherichia coli dans l'eauAdvisors/Committee Members: Chandra A Madramootoo (Supervisor).