Bridging the GAPs: Approaches to Treating Water On Farms

Bridging the GAPs

Approaches to Treating Water On Farms

By: John Buchanan, Barbara Chamberlin, Travis Chapin, Faith Critzer, Michelle Danyluk, Laurel Dunn, Chris Gunter, Alexis Hamilton, Lynette Johnston, Troy Peters, Channah Rock, Laura Strawn, Annette Wszelaki

A T T R I B U T I ON

Bridging the GAPs: Approaches to Treating Water On Farms

Copyright © Buchanan, J., Chamberlin, B., Chapin, T., Critzer, F., Danyluk, M., Dunn, L., Gunter, C., Hamilton, A., Johnston, L., Peters, T., Rock, C., Strawn, L., and Wszelaki, A. 2020, Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0). Published by eXtension Foundation.

e-pub: 978-1-7340417-6-7

Publish Date: 9/18/2020

Citations for this publication may be made using the following:

Buchanan, J., Chamberlin, B., Chapin, T., Critzer, F., Danyluk, M., Dunn, L., Gunter, C., Hamilton, A., Johnston, L., Peters, T., Rock, C., Strawn, L., and Wszelaki, A. (2020). Bridging the GAPs: Approaches to Treating Water On Farms (1st ed., 1st rev.). Kansas City: Extension Foundation. ISBN: 978-1-7340417-6-7.

Producer: Ashley S. Griffin Peer Review Coordinator: Heather Martin Technical Implementers: Henrietta Ritchie, Rose Hayden-Smith

Welcome to the Bridging the GAPs: Approaches to Treating Water On Farms, a publication created for the Cooperative Extension Service and published by the Extension Foundation.

This work is supported by the New Technologies for Agriculture Extension (NTAE) grant no. 2019-41595- 30123 from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

For more information please contact: Extension Foundation c/o Bryan Cave LLP One Kansas City Place

1200 Main Street, Suite 3800 Kansas City, MO 64105-2122 https://extension.org

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T A B L E O F CON T E N T S

Attribution............................................................................................................................................................. 2 Table of Contents .................................................................................................................................................. 3 Bridging the GAPs: Approaches to Treating Water On Farms ................................................................................ 4 About Us................................................................................................................................................................ 5 FSMA and Agricultural Water Treatment .............................................................................................................. 8 FSMA Definition and Requirements of Agricultural Water ................................................................................................ 8 Overview of Agricultural Water Treatment...................................................................................................................... 11 Agricultural Water Treatment Tools .................................................................................................................... 16 Commercially Available Agriculture Water Treatment Technologies .............................................................................. 16 Antimicrobial Pesticide Products – Chlorination .............................................................................................................. 17 Antimicrobial Pesticide Products – Chlorine Dioxide ....................................................................................................... 25 Antimicrobial Pesticide Products – Peroxyacetic Acid/Peracetic Acid ............................................................................. 25 Antimicrobial Devices – Ultraviolet light .......................................................................................................................... 26 Antimicrobial Devices – Ozone ......................................................................................................................................... 28 Developing On-Farm Agricultural Water Treatment Programs............................................................................ 31 Importance of SOPs .......................................................................................................................................................... 32 Critical Limits..................................................................................................................................................................... 32 Monitoring ........................................................................................................................................................................ 34 Corrective Actions............................................................................................................................................................. 36 Validation and Verification ............................................................................................................................................... 38 Recordkeeping .................................................................................................................................................................. 42 Implementing Agricultural Water Treatments on the Farm................................................................................. 45 Calcium hypochlorite chlorinator ..................................................................................................................................... 45 Liquid injection: hypochlorite or peroxyacetic acid ......................................................................................................... 47 Ultraviolet light ................................................................................................................................................................. 55 Chemical injection versus treatment with a pesticide device .......................................................................................... 57 Multi-hurdle approach...................................................................................................................................................... 58 Monitoring ........................................................................................................................................................................ 58 Water testing .................................................................................................................................................................... 60 Corrective actions ............................................................................................................................................................. 60 Summary ........................................................................................................................................................................... 61

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B R I D G I NG TH E GA P S : A P P RO A CH E S TO T R E A T I NG WA T E R ON F A RM S

Preventing foodborne illness and the protection of public health is objective 7.1 of the US Department of Agriculture 2018-2022 Strategic Plan. Sanitary irrigation water for produce is mandated by the USDA, including monitoring, treating and verifying compliance. Proper food sanitation is imperative to prevent situations like the Yuma, AZ E. coli outbreak in the spring of 2018 that ultimately resulted in 210 reported illnesses from 36 states, 96 hospitalizations, 27 cases of hemolytic uremic syndrome (HUS) and five deaths. The outbreak was linked to romaine lettuce grown in the Yuma region. In March 2019, FDA published a rule called Standards for the Growing, Harvesting, Packing, and Holding of Produce for Human Consumption; Extension of Compliance Dates for Subpart E, which:

• Extends ALL provisions of Subpart E (Agricultural water) other than sprouts including the safe and sanitary quality, annual inspection, and postharvest water monitoring requirements.

• FDA has stated that the reason for this extension is to allow time “to address questions about the practical implementation of compliance with certain provisions and to consider how we might further reduce the regulatory burden or increase flexibility while continuing to protect public health.”

• Until the process of consideration is finished, the water requirements are the Rule.

A multi-state, interdisciplinary team of public and private sector experts have partnered together to create a curriculum designed to help producers 1) Understand the regulatory requirements for ag water treatment in the Food Safety Modernization Act (FSMA), 2) Find the right water treatment system for their farm, 3) Develop standard operating procedures that will be effective in treating water on their farm and to monitor its implementation, and 4) Ensure that the proper system is implemented correctly and that employees are trained in its use, maintenance and repair. This curriculum, Bridging the GAPS – Approaches for treating water on-farm , is a four-module curriculum designed for a producer audience. The curriculum has been piloted on a limited basis to make initial improvements to improve its effectiveness. It is ready for a broader implementation. Being part of the current New Technologies for Agricultural Extension federal grant will bring the additional resources of the NTAE team to work alongside the Bridging the GAPS team to expand its scope and refine its effectiveness to impact the safety of the national food supply, particularly irrigated produce.

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A B OU T U S

John Buchanan

Dr. Buchanan is an Associate Professor at the University of Tennessee Institute of Agriculture. His work is in the Department of Biosystems Engineering and Soil Science focusing on wastewater management.

Barbara Chamberlin

Dr. Chamberlin is an Extension Instructional Design and Education Media Specialist at New Mexico State University at Las Cruces. She directs research and game development in the Learning Games Lab in the Innovative Media Research and Extension Department.

Travis Chapin

Travis is a former State Specialized Extensio n Agent based at the University of Florida’s Citrus Research and Education Center. His work focused on developing food safety education and outreach for Florida produce growers and processors. He is currently employed with the FDA.

Faith Critzer Dr. Faith Critzer is an Associate Professor and Produce Safety Extension Specialist at the Washington State University in the School of Food Science. Her work is based at the Irrigated Agriculture Research and Extension Center with research and extension responsibilities that focus on planning, implementing, and evaluating a statewide educational program in food safety as it relates to produce from pre-harvest to post- harvest activities.

Michelle Danyluk

Dr. Michelle Danyluk is a Professor and Extension Specialist of Food Safety and Microbiology in the Department of Food Science and Human Nutrition at the University of Florida. Her research and extension efforts focus on the microbial food safety and quality of fruit juices, fresh fruits, vegetables, and nuts.

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Laurel Dunn

Dr. Dunn is an Assistant Professor at the University of Georgia in the Department of Food Science and Technology. Her research focuses on the microbial risks associated with soil amendments and agricultural water, as well as stress response of enteric pathogens on plant tissues.

Chris Gunter

Dr. Gunter is a Professor in the Department of Horticultural Science at North Carolina State University. He is the Vegetable Production Specialist for the commercial vegetable industry in North Carolina, working with commercial vegetable growers to maintain a high quality of life through the use of integrated, economical and environmentally sound production practices.

Alexis Hamilton

Alexis is a Ph.D. student at Washington State University in the Department of Food Science under the direction of Dr. Faith Critzer. Ms. Hamilton’s research is based at the Irrigated Agriculture Research and Extension Center with a focus on fresh produce safety.

Lynette Johnston

Dr. Johnston is an Extension associate at North Carolina State University. She works with produce growers and food processing facilities in training and implementing food safety regulations and standards.

Troy Peters

Dr. Troy Peters is a Professor at Washington State University in the Department of Biological Systems Engineering. His research is in the Land, Air, Water Resources, and Environmental Engineering emphasis area of the department. Dr. Peters’ primary focus is agricultural irrigation.

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Channah Rock

Dr. Rock is a Professor and Extension Specialist at the University of Arizona in the Department of Environmental Science. Her primary research centers around water quality and sustainability, with extension activities focusing on the interaction between the research and the public to promote greater understanding of the issues that affect water quality.

Laura Strawn

Dr. Strawn is an Associate Professor and Extension Specialist of Produce Safety in the Department of Food Science and Technology at Virginia Tech. Her research and extension efforts focus on the microbial safety of fresh fruits and vegetables; specifically, the ecology, evolution and transmission of foodborne pathogens along the produce field to fork continuum.

Annette Wszelaki

Dr. Wszelaki is a Professor in the Department of Plant Sciences at the University of Tennessee. She is the Commercial Vegetable Extension Specialist with statewide responsibilities for developing a comprehensive educational program in vegetable production. The main focuses of her extension program include production and variety recommendations, diversifying production, developing alternative crops, organic and sustainable production, postharvest handling and produce safety.

Coordinators of this Publication

Chris Gunter and Lynette Johnston of North Carolina State University

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F S MA AN D AG R I CU L TU R A L WA T E R T R E A TM E N T

In this module, we will focus on both system evaluation as well as troubleshooting if problems arise. We will cover basic components, methods for monitoring chemicals as well as UV light treatment systems and approaches for correcting issues as they arise. We’ll also discuss a multitiered approach to water treatment and monitoring.

FSMA Def inition and Requirements of Agr icultural Water

The Produce Safety Rule

America’s food safety net has gotten tighter over the last decade. In 2011 Congress passed the Food Safety Modernization Act (FSMA), which required the Food and Drug Administration (FDA) to be more proactive about maintaining the safety of our food supply. In 2016 the FDA began to enforce the Produce Safety Rule (21 CFR Part 112), a specific set of FSMA rules to help reduce the risk of foodborne illnesses from fresh produce. The Produce Safety Rule requires a set of science-based minimum standards to reduce the risk of microbiological contamination from growing, harvesting, packing, and holding of produce. This is the first time that many fresh produce growers are required to comply with FDA requirements. A major source of potential contamination is the water that fresh produce growers use for everything from irrigation and fertigation to crop sprays and frost protection. Under the Produce Safety Rule, by 2024 many farms will have to meet agricultural water quality requirements that reduce the risk of exposure to human pathogens (with certain farms having earlier deadlines). To help farmers comply with these new regulations, this publication explores farm water treatment methods and products, treatment implementation, and best practices for maintaining safe agricultural water.

Agricultural Production Water

Water used in food production is known to be a potential source of contamination, allowing for widespread contamination throughout growing, harvesting, and handling of fresh produce. Within the Produce Safety Rule, the FDA defines agricultural water in Subpart E as water used in activities on covered produce where water is intended to, or is likely to, contact covered produce or food contact surfaces, including water used in growing activities… and in harvesting, packing, and holding activities (21 CFR 112). Based on FDA’s definition, agricultural water can be divided into two categories according to its intended use: 1) agricultural production water, and 2) harvest/post-harvest water. Agricultural production water is used during growing activities and is either intended to or is likely to contact the edible portion of covered produce during the growing season. Examples of agricultural production water include overhead irrigation, fertigation, crop sprays, and frost protection, to name a few. Agricultural water intended for harvest/postharvest includes water that comes in direct contact with the harvested produce as

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well as food contact surfaces, requiring a higher microbial quality (no detectable E. coli per 100 ml water sample). This publication focuses on the treatment of agricultural production water used during growing activities. In March 2019, FDA published an extension of compliance dates for Subpart E (see Table 1). Within this text, the FDA extended ALL provisions of Subpart E (agricultural water) other than sprouts, including the safe and sanitary quality, annual inspection, and postharvest water monitoring requirements. The reasoning for this extension, as stated by the FDA, is to address questions about the practical implementation of compliance with certain provisions and to consider how we might further reduce the regulatory burden or increase flexibility while continuing to protect public health. Until the process of consideration is complete, the water requirements as written are the rule.

Table 1. Water compliance date extension.

Farm Size*

Compliance Date

Large Farms

January 26, 2022

Small Farms

January 26, 2023

Very Small Farms

January 26, 2024

*In 2011 dollars: Large farms: $500,000+; Small farms: $250,000-499,999; Very small farms: $249,999-25,000

Microbial Risks Associated with Agricultural Production Water

Within the Produce Safety Rule, the FDA states that “all agricultural water must be safe and of adequate sanitary quality for its intended use.” In food production, water can serve as a vector for both human pathogens, as well as plant pathogens in growing operations. Fruit and vegetables that come in contact with contaminated irrigation water can cause illnesses, and plant pathogens can spread via irrigation water leading to plant disease and yield losses. The Produce Safety Rule is focused on reducing the risk of human illnesses via fresh produce rather than plant pathogens. Irrigation water is one of the main sources of pathogenic contamination on produce. Irrigation water is typically sourced from groundwater, surface water, or, in a few cases, municipal sources. Surface waters potentially pose the highest risk, as they are exposed to environmental contamination, followed by groundwater, and municipal water having the least amount of risk. Agricultural production water, particularly surface water including streams, ponds, and lakes, that have been contaminated with feces, has the potential to carry pathogens such as bacteria, viruses, or parasites. The water can serve as a vector or a

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carrier of human pathogens to fresh produce. These pathogens could include enteric organisms such as pathogenic E. coli and Salmonella , as well as Listeria monocytogenes . Sources of pathogens may include direct contact with animals, contaminated water run-off from a nearby animal operation, or wildlife into surface waters. While surface waters are known to be the highest risk of all water sources, growers continue to use surface waters because it is likely the most practical and economical option.

Evaluating Water Quality: Use of Microbial Water Quality Profiles, Microbial Water Criteria, and Corrective Measures

Because of known microbial hazards, water used for growing purposes that meets FDA’s definition of agricultural water includes specific requirements to reduce the risk of contamination. These requirements include maintenance and assessment of water sources and distribution systems, as well as the development of a microbial water quality profile by enumerating the indicator organism, E. coli . For agricultural production water from a surface or ground water source, the Produce Safety Rule establishes water quality criteria where each source of production water must be tested to evaluate whether its water quality profile meets the following criteria: 1. A geometric mean of 126 or less colony forming units (CFU) of generic E. coli per 100 mL of water, 2. A statistical threshold value (STV) of 410 CFU or less of generic E. coli per 100 mL of water. Water testing can provide information to help reduce the microbial risks to the grower’s commodity. By testing their water, growers may understand the long-term quality of a water source. This information can then be applied to better determine appropriate uses for each water source. Most importantly, by understanding the microbial quality of water, growers will know when to apply corrective measures if the microbial water quality profile exceeds numerical criteria as required by the Produce Safety Rule. The number of tests will depend on the water source. Table 2 lists the required testing for each water source.

Table 2. Testing Requirements for Water Sources

Source

Testing Requirement*

Public Water Supply

Copy of test results or current certificates of compliance

4 or more times during the growing season or over the period of a year 1 or more samples rolled into profile every year after initial year

Ground

20 or more times over a period of 2 to 4 years 5 or more samples rolled into profile every year after initial survey

Surface

*With appropriate documentation, there is no requirement to test water that meets the requirements for public water supplies. *Profile samples must be representative of use and must be collected as close in time as practicable to, but before, harvest.

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In terms of assessing water quality, as FDA reconsiders the requirements in Subpart E, growers who are currently testing their water should continue to do so. If not testing, growers may consider initiating a testing program to better understand their water quality, and if not already doing so, should follow Good Agricultural Practices (GAPs) to protect and maintain quality. As written in the rule, growers should identify and reduce risks by developing water management strategies, such as a water system survey. This helps to prioritize those areas of concern within the system that could pose a threat to pathogenic contamination.

Corrective Measures

If a grower meets the above criteria, the water can be used as intended for growing purposes. However, if the water does not meet the criteria or exceeds the threshold, the grower can apply the following corrective measures, according to the Produce Safety Rule: 1. Stop using the water and re-inspect the water distribution system for potential sources of hazards. Once corrective actions are applied and verified to reduce the risk of microbial contamination, the water can be used.

2. Apply a time interval for microbial die-off between the last application and harvest, or between harvest and the end of storage and/or removal during activities, such as commercial washing.

3.

Treat the water.

According to the FDA, treating the water may be a viable corrective measure to lower the risk of pathogenic contamination.

Overview of Agr icultural Water Treatment

Why treat agricultural water?

There are multiple reasons why growers may treat irrigation water. Particularly in greenhouse operations, treatment of water may be implemented to prevent biofilm formation. A biofilm is an aggregate or community of bacteria, algae, or a mixture of both, that attaches to a surface and produces an extracellular polymeric substance commonly known as slime. Biofilms can persist in irrigation lines feeding off nutrients meant for plants, thus causing nutritional deficiencies for proper plant growth. Furthermore, biofilms can clog irrigation lines and emitters, impacting pressure and continuous flow. In addition to preventing biofilm formation, treatment of irrigation water may be implemented to improve the microbial quality of the water. Irrigation water can serve as a vector for plant pathogens, as well as human pathogens. While plant pathogens can directly impact plant health, irrigation water is a major source of concern for spreading human pathogens, such as E. coli O157:H7, Salmonella, or Listeria monocytogenes. In addition, treatment of irrigation water may be applied to minimize effects of seasonal variability and unexpected events, such as heavy rainfall. Treatment could also be implemented due to limited or infrequent use of a particular surface water.

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For some growers, microbial testing may not be a suitable option due to land leasing or rotation, and treatment of irrigation water may be a more feasible option. The Produce Safety Rule does not require testing of surface waters or a grower to maintain a microbial water quality profile if a water treatment is applied that is intended to lower the risk of microbial conta mination of food safety concerns. However, it’s important to understand that the Produce Safety Rule provides a set of minimum food safety standards. Most buyer requirements or third-party certifications require growers to test irrigation water; buyer requirements may also include treatment of irrigation water for food safety. Testing will likely be included in implementing a treatment system providing validation and verification that a treatment is effective.

Identify all true statements regarding agricultural water, as defined by the FDA within the Produce Safety Rule (21 CFR Part 112).

o Agricultural water includes water used in activities on covered produce that is intended or likely to contact produce that is intended to, or likely to contact covered produce or food contact surfaces. o Irrigation water can serve as a vector for pathogens, such as E. coli O157:H7 and Salmonella, that may cause foodborne illnesses. Surface waters pose the highest risk of contamination of foodborne pathogens, as compared to ground or municipal water. o The Produce Safety Rule establishes microbial water quality criteria where each source of agricultural water must be tested for E. coli, unless a treatment is applied to the water that is intended to lower the risk of microbial contamination of food safety concerns.

o Treatment of agricultural water is an example of a corrective measure to apply, if the grower does not meet the E. coli threshold as established by the FDA.

o Buyers may require growers to treat their irrigation water for microbial contamination of food safety concerns.

All of the above statements are true.

o

Factors to consider when choosing a water treatment method

When choosing a water treatment, a grower must consider various factors in order to find one that works in his or her situation. Each farm or operation will have specific needs and constraints that will drive the best option that works in each situation. The following considers several factors:

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1. Environmental Protection Agency (EPA) regulations

For water treatment, either by chemical (such as chlorine or peroxyacetic acid, for example) or device (such as filtration or UV light), EPA approval will be required to assure safe-handling and efficacy of the intended use. EPA requires that any chemical that claims to reduce or kill organisms must be registered and approved for use; a manufacturer of a pesticide device must have an EPA establishment number. Financial investment Growers must consider the cost of set-up, continued use, and maintenance. Microbial water testing will also be required to prove efficacy and verify the system is working as intended to reduce the risk of pathogen contamination. Management of system According to the Produce Safety Rule, once a treatment is in place, growers will be required to monitor and verify the effectiveness of treatment. As mentioned, this will include microbial testing as well as routine monitoring to assure the system’s parts are working correctly. Application method Various application methods exist depending on the type of treatment that is chosen. For chemical treatments, this could include injectors through the use of pumps or using a venturi system. Other methods, such as devices, could include filtration, UV light, or ozonator units. Source of water The efficacy of treatment often depends on the source, i.e., the amount of organic matter and initial microorganism levels. For example, some surface waters may have higher amounts of organic matter (soil, plant debris, etc.) and microorganism levels where treatments may not be effective. The use of UV light, for example, with high solids content in water may not be effective without the use of a prior filtration step. Infrastructure Choosing an appropriate method, one has to account for the equipment required to implement a system. For example, the availability and storage of chlorine gas must be considered in such a treatment. Additional piping or pumps may be needed as well. Crop sensitivity The use of chemicals for irrigation water treatment can impact the quality of both the soil, as well as the crop. For example, while research is limited, continued use of chlorine can damage sensitive crops and the continuous use of residual chlorine in water may impact crop yield and leave behind the build-up of toxic halogen compounds.

2.

3.

4.

5.

6.

7.

8.

Worker Safety It is important for growers to be aware of worker safety and hazards that are associated with use of

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the chemical or device. The product label and instructions must include information on safe handling and the potential risk to human health.

9.

Environmental considerations Growers must consider EPA and/or local environmental considerations, particularly for use of a chemical treatment. Key concerns are the consistent use of a chemical and its effect on soil and water conditions that may impact the surrounding ecological habitat.

Which factor do you consider the most burdensome for growers when implementing a water treatment system? Why? Environmental Protection Agency (EPA) regulations, Financial investment, Management of system, Application method, Source of water, Infrastructure, Crop sensitivity, Worker safety, or Environmental considerations.

Types of Irrigation Water Treatment and EPA Regulation

Microbial treatment of irrigation water can be classified into two categories: chemical and physical treatments. Chemical treatment involves the use of antimicrobial pesticides which are defined by the EPA as a substance or a mix of substances formulated to destroy, repel, prevent, or mitigate a pest. In case of treating agricultural water, the target pests are microorganisms. Physical treatments, known as pesticide devices, work by physical means, such as electricity, light, or mechanics. They do not contain any substances or mix of substances to destroy, prevent, or reduce a pest. For most antimicrobial pesticides, and many devices, the EPA oversees or regulates the approval of these treatments. The Federal Fungicide, Insecticide, and Rodenticide Act (FIFRA) governs the registration, distribution, sale, and use of pesticides in the United States. The EPA reviews the product label as part of the registration process for pesticides. This label on a product and the instructions are a key part of pesticide regulation. The label provides critical instructions on how to safely handle and use the product to avoid adverse health effects and harm to the environment. This label must include the EPA registration number and specific instructions for treating irrigation water, such as concentration and contact time. Some states may also have registration and environmental requirements. For example, the commercial product Sanidate, which is a formulation of hydrogen peroxide and acetic acid, has restrictions on use in California, while most other states have less strict requirements. While the EPA label provides information on the target organism for intended use, there is no EPA-approved chemical treatment for irrigation water to reduce microbiological indicators, such as E. coli or enteric pathogens. The target organism for EPA approval is most likely a plant pathogen. Certain registered antimicrobial products are labeled for use in the treatment of irrigation water systems or irrigation ponds to control plant bacteria or algae growth. Independent studies may be performed by academia or industry to

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demonstrate efficacy against foodborne pathogens and indicator organisms within the label. Many registered antimicrobial products are labeled as antimicrobial washes for use during postharvest fruit and vegetable washing. Because these products are not labeled for EPA use for irrigation water, they cannot be used to treat irrigation water that is applied prior to harvest. Pesticide devices or non-chemical treatments, are also regulated by the EPA, but do not require EPA registration. While they do not requi re federal registration, devices are regulated in that “false or misleading claims” cannot be made about their effectiveness. A manufacturer of a pesticide device that is regulated will have an EPA establishment number even though the device itself is not registered. Pesticide devices must meet the EPA definition as follows: an instrument or contrivance other than a firearm (or medical device) that is used to destroy, trap, repel, or mitigate (lessen the severity of) any pest such as insects, weeds, rodents, birds, mold/mildew, bacteria, and viruses.

The EPA oversees or regulates the approval of antimicrobial pesticides, and many devices. Following the label assures compliance with the law regarding safe use, avoiding adverse health effects to humans and the environment.

True False

• •

Summary

While treating irrigation water is not a requirement under the FSMA Produce Safety Rule, it may serve as an effective preventive strategy and risk reduction measure to lower microbial contamination in water. This treatment can be implemented using either an EPA-regulated chemical or device as a corrective measure for production agriculture water. These treatments must be used in accordance with the EPA label and instructions. While there is no EPA-approved chemical treatment of production agricultural water for reducing microorganisms of food safety concerns, current studies may exist for setting limits for control of foodborne pathogens or indicators (E. coli).

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AG R I CU L TU R A L WA T E R T R E A TM E N T TOO L S

This chapter aims to introduce the methods for treating agricultural water for fruit and vegetable growers. It includes antimicrobial chemical options and antimicrobial devices that are available to treat water. The knowledge of how these chemicals and devices function, as well as the advantages and disadvantages of each.

There are various methods for treating agricultural water, including antimicrobial chemistries (chlorine for example) or antimicrobial devices (UV light for example). It is important to remember that there is no “one size fits all” selection. This section provides information regarding the most common methods used to provide reduction of microorganisms along with advantages and disadvantages of each method.

Commercial ly Avai lable Agr iculture Water Treatment Technologies

In general, there are two types of irrigation treatment methods: chemical and device treatments. Chemical treatments include the use of antimicrobial pesticide products that are required to be registered by the EPA.

Antimicrobial Pesticide Product – contains a substance or mixture of substances that is intended to destroy, repel, prevent, or mitigate (lessen the severity of) a pest. This includes substances that attract pests to lessen their impact, for example by attracting pests to a trap. Pesticide products must be registered by the EPA unless they qualify for an exemption. Pesticide Device – works by physical means (such as electricity, light or mechanics) and does not contain a substance or mixture of substances to perform its intended pesticidal purpose. EPA registration is required; however, these devices are regulated in that “false or misleading claims” cannot be made about the effectiveness of devices. If a manufacturer is making claims about a device, they should have scientific data to back up the claims. Some devices are not regulated. For example, any device that depends more upon the performance of the user than the performance of the device itself to be effective (such as a fly swatter) is not regulated. Also, traps for vertebrate animals are not regulated.

What type of irrigation water treatment system(s) do you use or are you familiar with?

Select your response to the poll question and click Submit below

• Antimicrobial pesticide (examples include chlorine, chlorine dioxide, peroxyacetic acid) • Antimicrobial device (examples include UV light, ozone) • I’m not familiar with any.

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Critical Selection and Evaluation Criteria of Treatment Methods

While various treatment methods exist, ultimately, the grower has to make a decision as to the technology that is best for their operation. The following list includes several factors and questions to consider when evaluating disinfection technologies.

Disinfection Volume: The volume of irrigation water as well as flow rate will be important in validating the system is actually effective in lowering the microbial load. Factors to consider include:

• Irrigation volume: Does the irrigation system apply acre-inches or acre-feet of water? Two inches per week over 10 acres is 543,000 gallons per week (one acre-inch is 27,156 gallons). If you are going to apply 20 ppm of Active Ingredient chlorine, you have to add 133 pounds of Ca(OCl)2 per week. This will certainly factor in for system cost and infrastructure. • Irrigation Flow Rate: What is the flow rate of the irrigation system? For example, if it applies water at 200 gallons per minute, your injection system needs to add Ca(OCl)2 at approximately 23 grams per minute. Contact time: This refers to the amount of time the disinfectant needs to contact the target microorganism to inactivate it. Contact time can be the time the water is exposed to UV, or how long water and chlorine are in the irrigation distribution pipe before the water contacts the crop.

Interaction with Amendments: If using Fertigation or Chemigation, will the disinfectant react with the fertilizer or pesticide?

Worker Safety and Protection: Disinfectants can be hazardous to humans. Therefore, worker safety should be a key consideration. A grower should consider the degree of worker competence available to operate the equipment and the type of training required.

Antimicrobial Pesticide Products – Chlor ination

While the addition of chlorine has been shown and widely used as an effective solution to orifice or emitter clogging due to bacterial growth, it can also increase the microbial quality of agricultural production water by potentially reducing the levels of bacterial pathogens of human concern and indicator organisms, such as generic E. coli. The use of chlorine is a very common disinfectant that is widely used across the food industry. It is relatively inexpensive, effective against a broad spectrum of microorganisms, and available in several forms. This includes liquids (sodium hypochlorite), powders (calcium hypochlorite), and gas (chlorine gas). Regardless of delivery, the active form of chlorine that kills or inactivates microorganisms is hypochlorous acid. This chemical is formed when chlorine reacts with water.

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What is an indicator organism?

Because enteric pathogens, such as Salmonella and E. coli O157:H7, are both difficult and expensive to reliably detect, it is often not practical to test for pathogens. Indicator organisms have been historically used to assess the microbiological quality of water and foods. Generic (or non-pathogenic) E. coli occur naturally in large numbers in the intestines (i.e., enteric) and feces of humans, mammals, and warm- blooded animals. The presence of E. coli in water directly indicates fecal contamination by animals or humans, and indirectly, the potential presence of enteric pathogens, such as bacteria, viruses, or parasites.

Chlorine chemistry and its mode of action

When chlorine is dissolved in water, the chlorine molecules combine with water in a reaction called hydrolysis, forming hypochlorous acid (HOCl) and hydrochloric acid (HCl-). Cl2 + H2O → HOCl + H+ + Cl-

Depending on the pH, hypochlorous acid can further dissociate into hypochlorite ions (OCl-).

HOCl → H+ + OCl-

Hypochlorous acid (HOCl) and hypochlorite (OCl- ) are together referred to as “free available chlorine” or “free chlorine”. These molecules coexist in an equilibrium relationship that is influenced by pH and temperature. Other factors will impact chlorine’s effectiveness including chlorine concentration, contact time, and organic matter in the water.

Chlorine’s Mode of Action

As previously stated, when chlorine is dissolved in water, it forms hypochlorous acid (HOCl) and hypochlorite (-OCl), both strong oxidizing agents reacting with various biological molecules including proteins, amino acids, peptides, lipids, and DNA as mechanisms for cell destruction. Hypochlorous acid is 40 to 80 times more effective at killing microorganisms than hypochlorite. The mechanism of germicidal activity is based on the ability of HOCl to penetrate the membrane of microbial cells (Figure 1). The neutral charge of hypochlorous acid, along with the negatively charged bacterial cell walls, allows HOCl to more easily penetrate into bacteria, oxidizing cellular structures both outside and inside the cell. Once inside the cell, the natural pH of the cell causes HOCl to dissociate and oxidize various components within the cell – such as the mitochondrion, which is the powerhouse of the cell.

Hypochlorite (-OCl) has a reduced germicidal effect on cells due to its negative charge and its inability to pass through the cell wall, exerting oxidizing action only from the outside of the cell.

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Figure 1- Illustration of chlorine's mode of action on a bacterial cell

Once inside the cell, the oxidation damages important cellular components such as the mitochondrion, which is the powerhouse of the cell. Just a few “hits” of HOCl will inactivate the cell. While -OCl has a negative charge and is repelled by the cell membrane, hypochlorite will oxidize components of the cell wall. This creates significant damage, but it takes many more “hits” before the sufficient damage is done that would inactivate the cell.

Importance of pH

Hypochlorous acid is a weak acid (pKa = 7.5) in aqueous solution and is dissociated readily to -OCl and H+ depending on the pH. At a pH of 7.5, half of the chlorine present is in the form of HOCl and half in the form of -OCl. As shown in Figure 2, with an example of 5 ppm chlorine, at a pH of 7.5, the amount of HOCl, the most active form of chlorine, is at 2.5 ppm; the lower the pH, the higher the concentration of HOCl. Chlorine solutions with pH above 8 are relatively ineffective against pathogens because most of the chlorine is in the ion form. As the pH rises above 7, available chlorine drops rapidly. Additionally, chlorine gas predominates once you get to pH below 4.0, which will not readily stay in solution and can be corrosive to equipment surfaces and materials.

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Figure 2 - pH impact on HOCl concentrations (Adapted from: https://journals.flvc.org/edis/article/view/108301/103581)

As for irrigation water, it’s important to understand that the source of the water can directly impact its pH. For example, the geology from which the water passed through or passed over influences pH as ions from the rocks and soil dissolve into the water. Geology high in carbonates tends to produce waters with higher pH; geology high in iron and/or sulfur tends to produce waters with lower pH. In the water treatment industry, it is very common to adjust the pH before adding chlorine. With an understanding of the water source and its pH, growers can determine the amount of additives needed. It is best to take water samples (of a known volume) and add the pH adjustment in small increments. With each increment, measure (and write down) how that addition changed the pH. For high pH values, acid may be added such as sodium bisulfate (NaHSO4), muriatic acid (HCl), or citric acid, for example. For low pH water sources, a base (high pH) solution can be added, such as sodium carbonate (soda ash – Na2CO3) or sodium hydroxide (lye – NaOH). For pH control, it is important to note chlorine and acids/bases are not compatible; addition of the acid or base should be injected separately from the chlorine.

Based on Figure 2, at what pH is chlorine most effective? Are there any drawbacks at this pH?

Determining Chlorine Addition: Chlorine Demand and Chlorine Residual

Chlorine is a strong oxidizer and will react with both organic and inorganic matter. The demand by organic and inorganic matter is known as chlorine demand. Chlorine demand is defined as the difference between the amount of chlorine added and the residual chlorine available (Figure 3). Examples of inorganic

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compounds could include iron, manganese, nitrite; nitrogen-based compounds, such as ammonia may also be found due to decaying plant material.

An understanding of chlorine demand is just as important as the pH of the water source. As chlorine is added to irrigation water, initially, a portion of the added chlorine is consumed as it reacts with minerals and organic compounds, including bacteria. It is desirable to add sufficient chlorine so that there is a residual, thus overloading chlorine (to a small extent). This extra chlorine provides downstream protection and can help prevent or reduce the likelihood of biofilms that may form in the water distribution system.

Figure 3 - Comparison of the different forms of Chlorine (Source: Faith Critzer, Washington State University).

The total residual chlorine is the remaining chlorine that has disinfectant properties. The residual chlorine is divided into two groups: 1) combined residual chlorine; and 2) free residual chlorine (Figure 3). Combined residual chlorine is chlorine that has reacted with ammonia to form monochloramine, dichloramine, and trichloramine. These chloramines are poor disinfectants because they take an extremely long time to kill microorganisms (over 30 minutes). Free residual chlorine or free available chlorine is the sum of HOCl and - OCl. Free residual chlorine is available downstream of the injection point, after the initial binding of chlorine molecules to organic, inorganic, and ammonium compounds. The chlorine dose will include the demand as well as the desired residual. An additional decision that needs to be made is the quantity of the residual. Depending on the situation, a residual of 10 ppm may be desirable. Too high of a chlorine residual may damage the soil health and the crop.

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Figure 4 - This picture shows an injection system using a peristaltic pump. In order to determine the mass of chlorine being added, the user will need to know the flow rate of the irrigation system, the injection rate of the peristaltic pump, and the chlorine concentrate tank below the pump. (Photo Credit: Faith Critzer, Washington State University.)

Measuring Chlorine

Most chlorine test kits available on the market will measure total chlorine (HOCl + OCl- + chloramines), free available chlorine (HOCl + OCl-), or only hypochlorous acid (HOCl). Recall that HOCl is the most active form of chlorine and is highly influenced by pH of the water. Overall, there are three types of chlorine measurement devices, including 1) pH and ion specific test strips; 2) colorimeters (titration, spectrophotometric, direct read); and 3) electrodes (ion specific).

Test Strips

Test strips are widely available and are the least expensive option for measuring chlorine concentration. They are user-friendly as operators dip the strip in a water sample for a prescribed length of time, hold for a few seconds, and compare to a color chart for an estimate or range of concentration. It is important to understand what form of chlorine you are testing and be able to test the desired chlorine concentration. In addition, users will need to consider the test strips’ expiration dates. It is important to note that there is variation in methods and procedures used to perform the tests with these strips from brand to brand. Also, there is variability in the color spectrum used to gauge the results of the test.

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Colorimeters

These kits can be more precise and accurate; however, they can be cumbersome to use. A sample must be taken and mixed with a packet to create a color change. The less expensive kits use a color chart to determine the results and the more expensive kits have a meter that provides a read out of the chlorine content.

Electrodes

This method includes an ion selective probe or amperometric device. This measures the movement of electrons due to oxidation and reduction of chlorine compounds. While ion selective probes can be very handy for quick measurements, periodic calibration is required using standards and they can be fouled by compounds in the water. Cleaning and preventive maintenance is required.

Chlorine Dosage

The dosage required to eliminate pathogens is a function of both chlorine concentration and contact time. Disinfection is not an instantaneous process and the chlorine must come in contact with the microorganisms. The greater the concentration, the more likely a chlorine molecule will come into contact with a microbe; increasing the contact time also increases the likelihood a chlorine molecule will come into contact with microorganisms. In regards to treatment of agricultural water, the contact time is the duration the water is in the pipeline after the chlorine is injected. The longer the contact time, the lower the concentration of chlorine needed to kill the microorganisms. Municipal water and wastewater disinfection allows for 20 minutes of contact time, which means a lower chlorine concentration. A typical irrigation system may be designed to have a water velocity between two and five feet per second. If our irrigation mainline is 1,000 feet long, then our contact time within the mainline will be between 200 and 500 seconds (three to eight minutes). Dosage or Ct is concentration (C) multiplied by time (t). For example, 50 mg/L with a 10 minute contact time is 500 mg min/L. This assumes that the water will be in the pipeline for 10 minutes. However, if the water is only in the pipeline for three minutes after the chlorine injection, then we need 167 mg/L of chlorine to get the same dosage. That is, 167 mg/L multiplied by 3 = 501 mg min/L.

Temperature

Temperature is another factor that impacts the efficacy of chlorine disinfection. Room temperature (or about 70oF) is standard when measuring chemical activity. Warmer temperatures increase activity and cooler temperatures decrease activity. In general, every 18oF drop in water temperature will double the required contact time. As temperatures drop, chemical reactions take longer, thus more time is needed to ensure the disinfection process takes place.

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