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Sharon Walker

Interim Dean, Bourns College of Engineering
John Babbage Chair in Environmental Engineering
Professor of Chemical and Environmental Engineering
Sharon Walker
Improving Wastewater Management Policies
Each year, contaminated irrigation sources contribute to countless food-related bacterial outbreaks, often leading to serious sickness or death. Walker’s lab analyzes every stage of the food production and distribution process, paying particular attention to the growth, harvesting, rinsing, packaging, and retail practices associated with the produce that ultimately ends up on our tables. Her lab’s findings enable the USDA to better regulate land management policies, as well as specific harvesting and handling procedures that contribute to contamination.

Areas of Expertise

Select Honors and Distinctions

  • Chancellor’s Award for Excellence in Undergraduate Research and Creative Achievement 2011
  • NSF Career Award 2010–2015
  • Fulbright Fellowship 2009-2010
  • John Babbage Chair in Environmental Engineering 2005–present
  • Woman of Distinction, Girl Scouts of San Gorgonio Award 2008
  • UC Regents Faculty Fellowship 2005, 2007
  • UC Faculty Senate Research Award 2005, 2008


Q: Why is your research important?
Each year, food-related bacterial outbreaks endanger the lives of countless individuals, often resulting in serious illness or death. In 2011, the Center for Disease Control estimates 128,000 people were hospitalized and 3,000 people died from foodborne diseases. Contaminated irrigation, caused by contact with wild and domestic animal feces, is a major cause of bacterial outbreaks in our produce. My lab seeks to identify and eradicate the sources of contaminated irrigation at every stage of the produce production process.

Q: What has your research revealed about how produce comes to be contaminated?
It is estimated that 0.1% of the crop contributes to 99% of the resulting foodborne outbreaks. It is important to note that contamination may occur at almost any step from farm to table, depending on the source of the contamination and the pathogen’s mode of transmission. However, all of the transmission modes intersect at one critical step—the initial stage of adhesion, which can occur during the growth, harvesting, rinsing, packaging, or retail processes. The contamination is then spread within the rinse waters and through processing equipment. Therefore, understanding the initial stage is critical to preventing the spread of contamination following the harvest.

Q: What are some possible implications of your findings?
The attachment of E. coli to the leaf surfaces is dictated by the water chemistry of the irrigation sources. However, preliminary data suggests that simply rinsing the leaves with deionized water (as may be done in a processing plant) does not significantly remove the pathogen from the leaves—this indicates that additional disinfection treatments are required. Future work will investigate the impact of various commercial disinfection treatments, such as bleach, on the plants. The treatments will be rigorously tested under relevant processing conditions (such as high mass loading of spinach), and the findings of these tests will be used to inform necessary changes in the industry. Ideally, this research will help to improve and better regulate production and transport procedures, thereby drastically reducing the number of bacterial outbreaks caused by unclean produce making it to the market.

Q: What is the goal of your research?
Our goal is to inform stakeholders on how pathogens get from the farm, through the harvesting and production processes, to the consumer. Specifically, we hope to provide a scientific basis upon which irrigation, harvesting and handling procedures are regulated.

Q: How is your research being used?
Food safety is still a relatively new area of study for my research group, and the project is still in its infancy at this time. However, in the past we collaborated with the USDA to analyze how bacterial pathogens from cows, horses, sheep, pigs, humans, and wild birds behave in the environment. We were able to show conclusively that pathogens transport differently into groundwater depending on the source of the manure or compost. We also demonstrated that the presence of manure creates a very different cellular environment than the idealized conditions studied previously. The combination of these findings have led to the USDA taking a closer look at land management policies, specifically, the allowable distances between septic tanks or concentrated animal operations and wells.

Q: What advice do you have for students graduating in the next five years?
I regularly point out to my students that it is their generation that will have to face the long-term challenges of managing water in an equitable and efficient manner. We have to balance the essential agricultural needs with those of communities and businesses. Our well-being depends on this delicate balance being achieved. We can’t just think like engineers, policy makers, biologists, etc. We have focus on the convergence of our disciplines if we are to be successful in this.

Sharon Walker “We hope to provide a scientific basis upon which irrigation, harvesting and handling procedures are regulated.”

—Sharon Walker
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