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Water Quality Introduction Agricultural Water Postharvest & Processing Water Sponsored by: USDA-CSREES CSREES Project Number 00-51110-9722 National Integrated Food Safety Initiative

Acknowledgements Some of the information and slides used in preparing this presentation were provided by: FDA, “Improving the Quality and Safety of  Fresh Fruits and Vegetables: Training Curriculum.” (draft) Trevor Suslow, Univ. Calif., Davis

Introduction Water destined for agricultural production can easily get contaminated with human and/or animal feces by direct or indirect routes It is important to keep animals and children out of fields and processing facilities and to provide workers with properly constructed restrooms or sanitary mobile units

Introduction Anytime water comes in contact with fresh produce, its quality determines the potential for pathogen contamination since water may be a carrier of a number of types of microorganisms: Escherichia coli, Salmonella spp., Vibrio cholerae, Shigella spp, Cryptosporidium parvum, Giardia lamblia, Cyclospora cayetanensis, Toxisplasma gondii, the Norwalk virus and hepatitis A

I. Agricultural Water Usually, water for agricultural uses comes from: Surface sources such as rivers, streams, irrigation ditches and canals Reservoirs (open or capped) Municipal water systems

Ground water may be contaminated by a variety of biological and chemical hazards, which include: Bacteria and viruses Domestic waste Nitrate nitrogen Synthetic organic chemicals Heavy metals Petroleum residues Combustion products from roadways

Microbiological Testing  Microbiological testing is used in the verification steps of a safety assurance program.  It is important to document the frequency and results of each water test for comparison purposes.  These records would become very  important in the event of a microbiological outbreak investigation.

Water Source Will Determine the Possible Frequency of Testing

Water Sample Collection A sterile sample bottle preferably provided by a testing laboratory should be used for sample collection If the water is collected from a tap, the water should be allowed to flow for 1-3 minutes before the sample is taken The sample should be delivered to the laboratory as soon as possible and no more than 30 hrs after its collection Samples should be kept cool during transportation.

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Sources of Water to Monitor. Dump or soak tanks. Washing lines.

Sources of Water to Monitor. Hydrocoolers. Infiltration into the commodity?

Sources of Water to Monitor. Top ice & liquid-ice injecting. Ice makers. Melting ice is messy.

The Problem with Water Handling Systems … Produce from the field usually harbors many pathogens (including dirty and decaying fruit). Postharvest handling of fruits & vegetables often includes the use of flumes, dump tanks, spray washers, or hydrocoolers. Pathogens can quickly accumulate in these water sources and contaminate healthy fruit.

Agents used to sanitize fruits and vegetables: Chlorine Chlorine dioxide (‘Sanova’, ‘Oxine’, etc.) Bromine & iodine Hydrogen peroxide Peroxyacetic acid (‘Tsunami’) Electrolyzed water Ozone UV-C illumination

Common Water Sanitizers Chlorine is by far the most widely used in fruit & vegetable packinghouses Peroxyacetic acid commonly used in fresh-cut operations Less affected by organic load Ozone and UV used to some extent in fresh-cut operations More effective treating a stream of clear water

Benefits of Chlorination Relatively inexpensive (Cl2 least expensive) Can effectively reduce pathogen inoculum in dump tanks, hydrocoolers, etc. Reduces the transfer of decay organisms to healthy fruit. Can kill some existing pathogens on fruit surfaces.

Sources of Chlorine Sodium hypochlorite (NaOCl) Liquid (5.25, 12.75, or 15%) Calcium hypochlorite [Ca(OCl)2] Solid (65 or 68%) Chlorine gas (Cl2) Gas cylinders Chlorine dioxide (ClO2) Generated on-site from sodium chlorite + acid

Factors Affecting Chlorine’s Effectiveness Water pH (ClO2 least affected) Chlorine concentration Contact time Organic matter in the water Water temperature Type & growth stage of pathogen

Water pH Hypochlorite and Cl2 form hypochlorous acid (HOCl). Hypochlorous acid is what kills pathogens.

High pH At high pH, hypochlorous acid converts to hypochlorite ion (OCl-). Hypochlorite ion is relatively ineffective against pathogens.

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Low pH At low pH, hypochlorous acid is quickly lost. Increased corrosiveness to equipment. Unpleasant working conditions due to increased chlorine odor. Recommended pH is between 6.5 & 7.5.

Chlorine Concentration Relatively low chlorine concentrations (< 40 ppm) can kill pathogens. Higher concentrations are commonly used to compensate for various losses. Recommendation: 100 to 150 ppm free chlorine.

Contact Time Higher chlorine concentrations kill microbes faster (e.g. < 1 min). Lower chlorine concentrations require longer exposure time. More resistant microbes or stages of growth may require longer exposure times to kill.

Organic Matter in the Water Organic matter reacts with chlorine and quickly reduces the amount of chlorine available to kill microbes. However, this chlorine may still be measured by total chlorine testing kits.

Water Temperature At higher temperatures, available chlorine kills microbes faster. Higher temperatures also causes more rapid loss of chlorine activity. In practice, water temperature is usually optimized for reasons other than optimized chlorine effectiveness (e.g. rapid cooling).

Type and Growth Stage of Microbe Bacteria, and germinating fungal spores and mycelia are relatively easy to kill with chlorine. Quiescent spores are much more resistant to chlorine. Microbes inside fruits and vegetables are protected and will not be killed.

Chlorine Recommendations Maintain free chlorine levels between 100 to 150 parts per million. Maintain pH between 6.5 and 7.5. Drain tanks often (e.g., daily) and refill with clean water. Use self-cleaning screens in dump tanks to remove large debris and organic matter.

Maintaining Adequate Chlorination Manual monitoring and addition of chlorine. Requires frequent monitoring of chlorine concentrations and pH. Automated chlorine dispensing. Timed release or based on measured chlorine concentrations or ORP. With or without automatic pH adjustments.

Chlorine Test Kits Use kits that measure free chlorine levels Total chlorine kits can measure both free and bound chlorine. If sample dilution is required, dilute with distilled water.

Chlorine Recommendations Check free chlorine levels often or use automated systems. Use all chemicals according to their labels. Consult local regulations for disposal of chlorinated water.

Summary Maintain water free of decay causing organisms. Use potable water & change daily. Wash particularly dirty commodities prior to hydrocooling. Use self-cleaning screens at pump intakes to remove larger debris. Design water handling equipment for easy cleaning. Use an approved sanitizer.

Thank you!