Food Safety Implications of Preharvest Water Use in Hydroponic and Soil-Based Production of Fresh Produce

Abstract

Fresh produce is frequently associated with foodborne outbreaks and recalls, as these products are highly susceptible to microbial contamination from the environment and poor handling practices. At the preharvest level, numerous contamination routes may compromise the safety of fresh produce, including agricultural water. Agricultural water is a well-documented route of preharvest contamination, and outbreaks involving pathogens such as Escherichia coli and Salmonella have been linked to contaminated irrigation water. To prevent food safety issues associated with fresh produce, the Food and Drug Administration(FDA) established the Produce Safety Rule (PSR) in 2016. Following the implementation of the PSR, significant research efforts have been made nationwide to characterize risks associated with agricultural water. However, most studies have focused on large fresh produce-growing regions (e.g., the Southwest and Northeast U.S.), leaving critical knowledge gaps in understudied regions, such as the Southeastern U.S., particularly in Alabama. In Alabama, more than 2,000 small farms operate with limited regulatory oversight due to exemptions under the PSR, which could represent food safety risks to consumers, especially given the state’s historical challenges with surface and groundwater quality. In contrast, Georgia (particularly the southwestern region) has a larger commercial produce industry and has received greater research attention. To address regional disparities in data and oversight, this dissertation presents findings from two longitudinal studies evaluating the prevalence and diversity of two foodborne pathogens (Salmonella and pathogenic E. coli) in PSR-covered farms in Georgia and exempt farms in Alabama. Machine learning models (e.g., random forest) were developed to predict pathogen prevalence. Overall, findings from the two studies indicate that pathogen presence is not strictly associated with farm size or PSR compliance status. The frequent detection of enteric pathogens in both Georgia and Alabama highlights the influence of local agricultural practices on water quality. In addition, to address knowledge gaps regarding food safety needs among produce growers in Alabama, a two-phase exploratory study was conducted. Phase 1 involved a needs assessment survey, and phase 2 focused on developing an extension program centered on technical support for agricultural water quality and risk mitigation. Findings from phase 1 suggest that specialty crop growers in Alabama are interested in learning about food safety plan writing, cleaning and sanitizing, and postharvest handling. Based on the results from phase 2, produce growers benefited from the extension program, as prior to this, only 40% had tested their water sources. Moreover, it was identified that fecal indicator bacteria were prevalent in surface and groundwater sources. In parallel, this dissertation examines the behavior of Salmonella in hydroponic production systems, prompted by recent outbreaks and recalls associated with hydroponically grown produce. While most existing research has focused on lettuce, this study evaluates the survival of Salmonella in herbs (basil, cilantro, and arugula) grown under Nutrient Film Technique (NFT) systems. Results show that Salmonella can survive in nutrient solutions for up to 35 days, and sporadic contamination in the system can lead to the presence of the pathogen in edible tissue. The insights this hydroponic study contributes to the growing body of knowledge regarding Salmonella in Controlled Environment Agriculture. Collectively, this research advances our understanding of the implications of preharvest agricultural water quality in diverse farming contexts. Here, we provided practical information to improve the microbial safety of fresh produce grown in the Southeastern U.S. Lastly, this information will guide Alabama food safety educators in establishing produce safety programming, prioritizing the current needs.