Agriculture Water Treatment – Southwest Region

Growers are faced with a myriad of options related to water treatment and/or sanitization with very little guidance on the requirements needed for successful implementation of the treatment option. With limited guidance, water treatment decisions are likely to be unsuccessful and expend both excess time and money without the ultimate outcome of reduction in generic E. coli, Total Coliform bacteria, and potential pathogen loading within a water source and thus little to no reduction in microbiological risk. Additionally, there may be regional and site-specific considerations important for effective water treatment. Grower guidance is needed on water treatment best management practices and monitoring strategies to ensure adequate treatment, attainment of regulatory limits, and ultimately the protection of public health. Research will focus on comparative evaluation of three agricultural water treatment options (PAA, Calcium Hypochlorite, and UV Light) in four produce growing regions of the Southwest (AZ and TX). The overall goal of this proposal is to develop scientific data, which allow produce growers to better manage their use of agriculture water treatments.

Recent metrics changes to the Arizona and California Leafy Greens Marketing Agreement(s) (LGMA) now require growers utilizing surface water for overhead irrigation, to treat their water within 21 days of harvest. For many producers, this is the first time that water quality data may indicate the need for antimicrobial treatment of agricultural water as a corrective action before irrigation can be applied safely. Exacerbating these challenges, growers are faced with a myriad of options related to antimicrobial water treatment with very little guidance on the most appropriate treatment option for their ranch, or the requirements needed for successful implementation. With limited guidance, water treatment decisions are likely to be unsuccessful and expend both excess time and money without the ultimate outcome of eliminating generic E. coli (non-detect per 100mL), and reducing Total Coliform bacteria (< 99 MPN/100mL). Unsuccessful treatments will likely lead to little or no reduction in potential pathogen loading in an agricultural water source and thus little to no reduction in microbiological risk. CPS-funded studies conducted by Dr. Rock characterizing microbial quality of water used to irrigate fresh produce in the Southwest found that foodborne pathogens are present in surface waters (Rock and Gerba, 2014) and that treatment options can be highly variable (Rock, 2019). Grower guidance is needed on antimicrobial agricultural water treatment options available to industry and monitoring strategies to ensure successful treatment and ultimately the protection of public health. Over the course of one growing season, the research team will evaluate the efficacy of three antimicrobial treatments (Peroxyacetic Acid - PAA, Calcium Hypochlorite, and Ultra Violet Light) across four produce growing regions of the Southwest; Yuma, AZ; Maricopa, AZ; Edinburg, TX; and Uvalde, TX. The overall goal of this proposal is to develop scientific data, which will allow produce growers to better manage their use of antimicrobial agriculture water treatments in the Southwest.

1. Determine reductions of pertinent foodborne bacterial pathogens (Shiga-toxigenic Escherichia coli), non-pathogenic indicators, E. coli and Total Coliform bacteria in surface water samples from four major growing regions in Arizona (2) and Texas (2), which will establish robust inactivation data for target treatments (calcium hypochlorite, peroxyacetic acid (PAA), and UV light). This will result in documented scientific-data, which growers can use as justification for validity of their antimicrobial treatment. 

2. Conduct in-field evaluation of the most appropriate treatment dose per chemistry with grower collaborators. This will effectively allow the research team to study treatment systems when utilized for commercial scale production and document key criteria which must be monitored and documented when designing, implementing, and managing effective antimicrobial water treatment systems on-farm. 

3. Concurrently with Objective 2, evaluate the accuracy of commercially available and emerging test strips/kits and on-farm cloud-based data monitoring systems for quantifying the effectiveness of antimicrobial water treatments as well as a range of physical and chemical parameters. 

4. Evaluate the short- and medium-term impacts on soil/plant microbial communities in response to antimicrobial water treatment as well as define a metric of soil health.

• Data indicate that agricultural water treatment systems are highly dynamic. It is important to note that system “stabilization” is highly variable beyond pressurization of the distribution system, and that sanitizers/devices do not kill microbes instantaneously. These are two key considerations for industry. 

• In the bench-top log reduction evaluations, 32°C resulted in greater log reductions than 12°C. This may be important for specific growing regions and/or times of year when industry can expect more or less variability in their agricultural water treatment success. 

• Breakthrough of microbial targets was detected on all sanitizers/devices evaluated at the first and last sprinkler heads during treatment over time in 1-acre research plots. This is an important finding as we assess how agricultural water treatment systems are regulated and monitored. 

• The impact of sample volume increasingly has become important over the course of recent agriculture water treatment studies, including this study. While non-detect for total coliform bacteria or generic E. coli in 100ml is the goal, this does not necessarily indicate a non-detect in larger water volumes, on product, or in soil. A true quantitative microbial risk assessment is needed to better determine the detection limits and equivalent sample volume required to assess the risk of contaminating produce with irrigation water and risk to consumers by eating that product. 

• It should be noted that microbiome differences were detected on plant tissue and root zone for PAA and chlorine. This was not seen in top soils evaluated by the same methodologies. PAA treatment results in a more significant impact on microbiome than chlorine, indicating a potential prolonged effect or susceptibility of bacterial populations in the microbiome to residual PAA. 

• It is important that growers assess when source water conditions may vary and result in significant impact to risk reduction (treatment). Of particular concern are increased turbidity, rainfall, run-off, canal maintenance activities, or any activity that may disturb sediments in the canal upstream. 

• It is evident that all chemistries/devices can be successful if implemented properly, however it is important to note that none of the treatments evaluated were effective 100% of the time. Therefore, it is recommended that agricultural water treatment should be viewed as a risk reduction practice rather than a risk elimination practice and should be part of an overall layer approach to food safety.