Summary of Awards to Date

Evaluation of risk-based water quality sampling strategies for the fresh produce industry


Jan. 1, 2014 - Dec. 31, 2015

Award Number


Funding Agency

Center for Produce Safety

Amount Awarded



Channah Rock, Ph.D.
University of Arizona


Charles P. Gerba


Layperson's Summary

The goal of this project is to develop a risk-based approach for sampling of irrigation waters used for produce production to minimize the risk of crop contamination by foodborne bacteria. Irrigation water has been implicated in a number of outbreaks associated with fresh produce. Currently, there are no scientific methods for determining where and how often water quality sampling should take place in constructed irrigation system’s typical of Arizona and Southern California. We propose to use a risk assessment considering factors which are known to influence contamination of surface waters including rainfall, watershed characteristics (landscape features, urban development, etc), the type of produce, and the irrigation method (e.g. spray vs. flood) to develop recommendations for risk-based sampling strategies for growers. Additionally, since rainfall plays a significant role in surface water quality a user friendly application, for use with mobile phones or other hardware, will be developed to aid in determining the need for risk-based sampling based on downloadable local weather information. This study will offer recommendations towards risk-based sampling strategies (frequency, timing, location, volume) for E.coli indicator bacteria in irrigation waters that provide the greatest risk reduction to produce.

Technical Abstract

Irrigation water has been implicated in a number of outbreaks associated with fresh produce. General guidelines for water quality sampling for indicator bacteria (Escherichia coli) and sampling frequency have recently been proposed by the Food and Drug Administration (Federal Register, 2013), however, it is not apparent if they are based on site specific conditions with quantifiable benefits related to risk reduction. The goals of this research are to assess and quantify factors which 1) determine variability of generic (indicator) E.coli, pathogenic E.coli (Shiga toxin producing stains – STEC), and Salmonella occurrence in irrigation water over time, based on historic data and data collected as part of this study, at specific locations in Arizona/Southern California. This data will be used to assess the impact of risk events such as rainfall, water quality factors including temperature and turbidity, canal size, and watershed characteristics (potential sources of fecal contamination), on the occurrence of these organisms. 2) Assess the impact of occurrence, duration and intensity of rainfall events on E coli/Salmonella in irrigation waters with the goal to determine how long after a specific rainfall event the irrigation water quality will be impacted. 3) Use an exposure scenario risk based model for E.coli/Salmonella in irrigation waters to quantify the risks of infection with different sampling frequencies of irrigation waters based on environmental factors (e.g. rainfall), irrigation methods, and type of produce. 4) Develop a cell-phone/computer application (app) that can be used for guidance for frequency of sampling after high risk (rainfall) events.