Prevention and Mitigation: On-site treatment, in-field die-off and other hazard reduction strategies

Transcription

1 Prevention and Mitigation: On-site treatment, in-field die-off and other hazard reduction strategies Understanding the importance of water quality, the Agricultural Water Rule, and grower options to meet the rule. Channah Rock, PhD PSA Water Summit February 28 th, 2018

2 Why is microbial control important in water? What? Public health protection requires that pathogens in water be removed or inactivated to acceptable levels. Why? Pathogens in water include bacteria, viruses, and protozoan parasites. Pathogenic microorganisms present significant acute risks to the consumer and are the most important concern for production systems.

3 General Monitoring Strategy The more acute the threat, the more strictly it must be monitored and controlled Response Time (corrective actions) Brian Pecson, Trussell Technologies (2015)

4 Normal Distribution of Water Quality Test Results CFU generic E. coli/100 ml Geometric Mean Statistical Threshold Value L. Harris, UC Davis

5 Covered Produce AND Direct Application SURFACE OR GROUND WATER Meets Values? Microbial Water Quality Profile Yes No Maintain Normal Operations Apply Mitigation Strategy or Discontinue Use Monitor Water Quality L. Harris, UC Davis

6 Covered Produce AND Direct Application 1 Four Possible Mitigation Strategies Time Interval Between Irrigation and Harvest 0.5 log reduction per day (<4 day) OR alternative data Time Interval Between Irrigation and End of Storage Commercial Washing Must have supporting data Recordkeeping 2 3 Treat Water Discontinue Use 4 EPA registered pesticide Follow the label Inspect Make changes Retest Goal: Provide same level of public health protection as using irrigation water that met the standard L. Harris, UC Davis

7 Recent Research Objectives Risk-based Approaches for Water Sampling Environmental Impact on Microbial Survival Water Treatment Options Available to Industry

8 Evidence shows that we should pay attention to our water sources as potential vectors for pathogens.

9 Contamination of water with pathogens There s E.coli in the water, but where did it come from? Stormwater, Illegal Discharge or Un-treated Wastewater Recreation Wild or Domestic Animals

10 Irrigation Water Factors Organic Matter Temperature Salinity ph Turbidity

11 Sampling Site Factors Location Main Lateral Pond/Reservoir Size Landscape Features Urban/Rural CAFO/Ranch Land Slope Bridge/Road Canal Width/Depth Lined or Unlined Vegetation

12 Environmental Factors Air Temperature Relative Humidity Solar Radiation Rainfall Duration Rainfall Quantity Rainfall Intensity Bard/ Winterhaven City of Yuma Gila Valley Dome Valley Mohawk Valley Yuma Valley Yuma Mesa

13 Findings Show Historical data from Arizona, California, Nevada, and Oregon Relationships were observed between environmental and physical factors and the occurrence of E. coli in irrigation water Additional factors may have greater influence on water quality Canal maintenance Lined vs. Unlined

14 Main Influential Factors on Irrigation Water Quality Precipitation Temperature EC/Salinity Sediment Bacterial Loading* *E.coli and Salmonella in surface water conveyance systems

15 How can industry use this information to inform practice?

16 Event Tree Scenario & E. coli Exposure

17 Weather Information? Sampling Site Information? Irrigation Water Physical Parameters?

18 Understand Water Distribution Assess Surrounding Land Use Practices Identify Potential Hazards Within Your Watershed

19 What happens to pathogens in the environment?

20 Pathogen Decay in the Environment The environment provides retention time, allowing an additional opportunity for attenuation of microbial contaminants. Survival of microorganism in the environment Temperature Light Oxygen Nutrients Ability of microorganisms to be transported Rainfall and runoff Reduction of bacteria, virus, Giardia, and Cryptosporidium

21 Ag Water Rule Pathogen Die-off 0.5 Log Die-Off Per Day 10,000 3,165 1, Day 0 Day 1 Day 2 Day 3 Day 4

22 Information on Pathogen Die-off Pathogen cell numbers decline over time May decrease with increasing temperatures in irrigation water E. coli O157 up to 8 weeks at 25 degrees C Salmonella spp. > E. coli in surface water International Journal of Food Microbiology 163 (2013)

23 Fitted curves and measured data of the inactivation of faecal coliforms (a) and intestinal Enterococci (b) depending on the exposed sunlight radiation intensity and time of exposure. Water Research 42 (2008)

24 Risk Assessment Assumptions Fraction of E.coli that is transferred to lettuce when irrigated with water inoculated with E.coli (Stine et al. 2005, 2009) Adjusted per capita consumption of lettuce in the United States is 4,416.5 grams Consumption of lettuce occurs one day after irrigation Sprinkler = Furrow = 1.1 x x 10-2 Drip = 8.8 x 10-7

25 Annual Probability of E. coli Infection If a Person Consumes 12.1 Grams Per Day of Fresh Lettuce

26 Relative risk of GI illness in lettuce based on irrigation practice* Irrigation Practice Relative Risk Subsurface Irrigation 9 in 100,000,000 Furrow Irrigation 1.1 in 100,000 Sprinkler Irrigation 1.1 in 1,000 * Assumes 126 E.coli per 100 ml of irrigation water.

27 When die-off isn t enough

28 Why would a grower want to treat irrigation water? Water quality exceeds the generic E.coli standard set by FSMA Buyer requirements More stringent Positive for pathogens (E.coli O157H7, Salmonella, Listeria) Marketing/Brand protection Proactive Historical

29 Commonly Used Water Treatment Methods Physical Heat Sterilization Ultra Violet Light (UV) Filtration (Membrane, or other media) Biological Sand Filtration (biofilms) Constructed Wetlands Chemical Peroxyacetic Acid (PAA) Chlorine / Chlorine Dioxide /ewater Sodium or Calcium Hypochlorite Copper / Silver Ionization Ozone Bromine

30 Important Considerations for Treatment Effectiveness Source Water Quality Turbidity/Organic Matter ph Alkalinity Microbial loading On-site Monitoring/Dosing Equipment Scale Is it mobile? Volume of Water (million gallons vs. acre feet) Energy Requirements

31 Organic Matter Contact Time Factor Issue/Problem Solution Organic matter load in the water can affect disinfection efficiency. Higher organic matter levels consume more disinfectant and therefore, in order to reach a particular concentration, addition of more disinfectant is needed. The duration of time allowed for contact and reaction between the disinfectant and the microorganisms is extremely important. Preliminary water filtration may substantially decrease organic matter load, thus reducing the amount of chlorine/paa needed for effective disinfection. At longer contact times lower concentrations of disinfectant can be used and vice versa. Water ph Temperature Turbidity Free chlorine in water exists in 3 forms: Cl2 (dissolved gas), HOCl (Hypochlorous acid), OCl- (hypochlorite). Disinfection can be more effective in higher temperature, although too high temperature can also reduce the efficiency of disinfection. Turbid water that contains suspended particles allows bacteria to "hide" in between the particles, thus evading contact with the disinfectant. The relative proportions of these three forms are determined by the water ph. HOCl is 100 times more effective than OCl- therefore water ph should be monitored. Temperatures should be monitored so adequate disinfectant dosing can be conducted. A decrease of 10 degrees Celsius can reduce efficiency of disinfection by up to 50-60%. Filtering the water prior to disinfection can increase the ability to adequately treat the water with the disinfectant.

32 Important Considerations for Successful Implementation Will it work? Pathogen loading Contact time Dosing requirement Capital Equipment Cost O&M Costs Worker Safety Ease of Use Figure 1. Pump station showing the metering / injection pump and injection port used to add Safe Zone PW3300 to the supply line of a center pivot irrigation system during a 2016 pilot study. Ozone > ewater > Chlorine Dioxide > PAA > Sodium Hypochlorite

33 Example: Chemical Disinfection Disinfectants/Sanitizers do not kill pathogens instantaneously on contact. The rate of inactivation depends on 5 factors: 1. The Pathogen 2. Chemical Concentration, C (mg/l) 3. Contact Time, T (minutes) 4. Temperature of water 5. ph of water

34 CT Tables How do we know if the calculated CT value is good enough? EPA has published CT tables for different pathogens and disinfectants The tabulated values in the CT tables are also dependent on temperature and ph

35 Disinfection Table from the U.S. EPA with CT Values* for 3-log 10 Inactivation of Giardia cysts with Free Chlorine Chlorine Concentration (mg/l) Temperature = 20 C ph <= <= (*min-mg/l) adapted from USEPA, 2003

36 Rules of Thumb Chemical disinfection is often more effective with decreasing ph, Figure 4. Hanna Combo ph/ec/tds/temperature tester (left) and HACH HQ40d Multi-Parameter Meter (right). with increasing temperature, and may be easier to meet CT in summer than winter.

37 Verification of Proper Concentration (PPM) Jay Sughroue, BioSafe Systems

38 What grower tools are available?

39 Industry Applications Risk assessments of irrigation water can provide protection to produce and human health. On Farm Readiness Review (OFRR) Cooperative Extension Service Industry Organizations Water Treatment Manufacturers USDA NIFA - CONSERVEwaterforfood.org

40 Ag Water App & Resources Ag Water app is available on any Wi-Fi enabled mobile device including tablets, ipads, mobile phones and computers Webpage: Android Google Play Store Apple App Store Related Resources: Online MWQP Calculator: Downloadable Excel Spreadsheet with MWQP Calculator:

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42 Acknowledgements - Arizona LGMA & Yuma Safe Produce Council - L. Harris, UC Davis - Natalie Brassill, Jessica Dery & Dametreea Carr, University of Arizona - J. Waite-Cuisic, Oregon State - T. Suslow, UC Davis - M. Danyluk, University of Florida - C. Gerba, K. Bright, A. Tamimi, University of Arizona