Grow Your Own, Nevada! Summer 2013: Reducing Food Safety Risks in School and Community Gardens


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  • And this week’s report from the CDC provided further evidence that my home garden is the safest source of food for my family. This report examines the links between food commodities and foodborne illness, identifying fresh produce as the most frequent offender… a whopping 46% of all cases! For historical perspective, fresh produce was linked to less than 1% of all foodborne illness in the 1970s, and less than 12% in the 1990s. Why is foodborne illness from produce on the rise?
  • Soil survival of Escherichia coli O157:H7 acquired by a child from garden soil recently fertilized with cattle manureKeywords:bacterial survival;cattle;contamination;enterohaemorrhagic;environmental manure;foodborne pathogenAbstractAims:  This investigation was conducted to determine the survival of a naturally occurring Escherichia coli O157:H7 in garden soil linked to a sporadic case of E. coli O157 infection in Minnesota.Methods and Results:  The presence and viability of E. coli O157:H7 was monitored in manure-contaminated garden soil for several weeks. Bacterial isolates were characterized using PCR and pulsed-field gel electrophoresis (PFGE). Isolates obtained from the patient and the garden plots during this investigation had indistinguishable PFGE patterns and had the same virulence factors (stx1, stx2, eaeA, ehxA). The E. coli O157:H7 levels obtained from the garden plots declined gradually for a period of 2 months, and on day 69 only one garden plot of four had detectable levels of pathogen. All plots were negative on day 92. The rate of decline in the soil samples stored at 4°C was faster compared with soil samples that remained in ambient conditions, and in refrigerated storage E. coli O157:H7 could not be detected after 10 days.Conclusions: E. coli O157:H7 strains can survive on manure-amended soil for more than 2 months, and this survival could be reduced by low temperature.Significance and Impact of the Study:  This is one of the few reports that have investigated the survival of a proven virulent strain in naturally contaminated soil samples. This case stresses the importance of avoiding the use of raw cattle manure to amend soil for cultivation of foods, including soils in residential garden plots.
  • Although it’s a good idea to do it, it’s no guarantee.
  • The way in which you wash your produce may even put you at greater risk of contracting a foodborne illness. Take a sun-warmed tomato from your garden and plunge it under cold running water, and the gases within the tomato tissues contract, creating hydrostatic pressure that pulls in microorganisms. Improper wash-water temperatures have been responsible for numerous outbreaks, including Salmonella in mangoes and tomatoes. Experts recommend that rinse water be as close to the temperature of produce as possible (within 10 degrees Fahrenheit).
  • What are the rules for manure use in non-certified organic or conventional farms? With regards to ensuring food safety, none. Although many states mandate that farmers have a Nutrient Management Plan (to prevent nutrient runoff and subsequent pollution of streams), there are currently no restrictions on timing of raw manure applications for conventional farms. In fact, many conventional farmers lease their land to factory farms for manure disposal. Concentrated animal farm operations (CAFOs) produce well over 1 billiontons of manure each year – it has to go somewhere, and many conventional farms gladly allow the raw manure to be spread on their fields, both for the free fertilizer and the additional money.
  • In fact, many conventional farmers lease their land to factory farms for manure disposal. Concentrated animal farm operations (CAFOs) produce well over 1 billiontons of manure each year – it has to go somewhere, and many conventional farms gladly allow the raw manure to be spread on their fields, both for the free fertilizer and the additional money.
  • Do not use manure from carnivores
  • Why is it important to properly cool vegetables, wash them, and dry them well before storing in your refrigerator? Unlike most human pathogens, soil-inhabiting Listeria can grow in the cold temperatures of a refrigerator, especially under moist conditions (albeit more slowly than on your countertop).
  • Site history:Flood-prone?Animals?Chemical contamination?Heavy metals?Polluted run-off?
  • Grow Your Own, Nevada! Summer 2013: Reducing Food Safety Risks in School and Community Gardens

    1. 1. Reducing Food Safety Risks in School & Community Gardens Heidi Kratsch Grow Your Own, Nevada!
    2. 2. We’ll cover:  Myths  Site selection  Soil  Irrigation  Compost  Garden design  Sanitation  Volunteers
    3. 3. Some facts:  450 outbreaks of foodborne illness in the U.S. due to fruit and vegetable production.  That’s 46% of all cases!  48 million sickened each year.  130,000 hospitalizations and 3,000 deaths.
    4. 4. …and it’s not just large operations  Home, school and community gardens are at risk.  Most illnesses that are linked to home gardens resulted from freshly spread raw manure.
    5. 5. Children are more susceptible than adults
    6. 6. Some of the bad guys  Campylobacter  Cryptosporidia  E. coli  Hepatitis A virus  Listeria  Norovirus  Salmonella  Shigella Hepatitis A virus
    7. 7. Myth 1: Washing or peeling produce is sufficient to remove pathogens.  It’s not!  Prevention of microbial contamination is the most important food safety element.
    8. 8. Bacteria and viruses are not easily washed off of fresh produce.
    9. 9.  Bacteria form sticky biofilms on food surfaces.
    10. 10. Microbes get inside the leaves Saldaña et al. 2011  Rinsing with cold water makes it worse!  Use warm rinse water.  Peel vegetables just before you consume them.
    11. 11. Myth 2: Organic produce is more likely to cause foodborne illness.  Both conventional and organic growers use manure as a fertilizer.  Manure use on certified organic farms is strictly regulated.  There are no rules for use of manure in conventional operations.
    12. 12. Concentrated Animal Feeding Operations (CAFOs)
    13. 13. Organic rules for manure use  The National Organic Program (NOP) specifies that if manure is not composted, it must be tilled into the soil: ◦ at least 120 days before the harvest of a food crop that comes in contact with soil (like leafy greens), ◦ or at least 90 days before the harvest of a crop that does not come into contact with the soil (like corn).
    14. 14. Use manure safely  Compost your manure.  Make sure your compost reaches at least 131 degrees, or  Amend with manure in the fall BEFORE you intend to plant.
    15. 15. Myth 3: Bacteria are killed by pesticides.  Pesticides sprayed on food crops do not kill bacteria.  Spraying pesticides can actually cause microbial contamination.  Some pesticide formulations actually support the growth of bacteria in the pesticide holding tanks.
    16. 16. Safe pesticide use  Read the label to make sure it’s labeled for use on crop plants.  Use potable water to mix.  Have well water tested for microbes.  Mix only the amount of pesticide that you need for a single application.  Avoid pesticide use in school gardens.
    17. 17. Myth 4: I don’t apply manure to my garden or have pets, so I don’t have to worry about pathogens.  What about rabbits, squirrels, birds, moles, voles, mar mots...?  Many pathogenic organisms are native to soils (ex. Listeria).  Improperly brewed compost teas are a potential source of pathogens.
    18. 18. Handwashing You need:  Potable running water.  Soap.  Single-use towels.  Hand sanitizer if soap not available.  Disposable gloves is also an option.
    19. 19. Handwashing rules for the garden  Scrub nails and fingertips with a brush.  Wet hands with clean running water and apply soap.  Scrub the backs, between fingers and under nails.  Rinse well and dry with a single-use towel.
    20. 20. Myth 5: Since I am growing my own food, I don’t need to wash or refrigerate it after harvesting.  Most foods are safer if they are washed, dried and stored in the refrigerator. ◦ Exceptions: tomatoes, potatoes, berries - wash them right before you consume them.  For produce that contacts the ground as it grows (ex. cantaloupes) ◦ Wash with a vegetable brush (to remove dirt stuck in their netted skins) and dry completely before refrigerating.
    21. 21. Prevent Listeria outbreaks!
    22. 22. Site selection
    23. 23. Minimize site risk  Industrial sites or neighborhoods pose a risk.  Best to establish a long-term arrangement with the landowner.  Need good community support for garden longevity.
    24. 24. Urban soils carry greater risk  Test soils for the presence of heavy metals (lead, arsenic).  Copper and zinc are not a risk to you but levels may be too high for plant growth.
    25. 25. Water Quality  Water is the mostly likely vehicle to put pathogens in contact with produce.  Best source is municipal.  Use drip irrigation to minimize contact with edible parts.
    26. 26. Water quality of other sources  Have water tested for coliform and generic E. coli (indicator of fecal contamination).  Consider contamination from domestic waste, nitrates, petroleum residues, heavy metals.  Avoid unregulated sources for school and community gardens.
    27. 27. What about rainwater?  Fine for watering ornamental plants, but…  Test for E. coli if it is used on edible plants.  Roof run-off: ◦ Climate ◦ Age of roof ◦ Materials (metal?) ◦ Air quality ◦ Slope of roof ◦ Temperature
    28. 28. Gardens and allergens  Some gardeners (or children!) have serious food allergies  Avoid planting (or bringing into the garden) common allergens: ◦ Peanuts or peanut butter ◦ Soybeans, soy milk, tofu products ◦ Corn ◦ Wheat ◦ Tree nuts
    29. 29. Safe composting  Turn pile once per week (but not more than every three days).  Internal temperature of compost pile over 130 degrees Fahrenheit for 5 days to kill (most) pathogens.  Use of composted manure NOT recommended for school gardens.
    30. 30. Pile heats up Temperature peaks Pile shrinks 160 F Turn the pile
    31. 31. Use a compost thermometer
    32. 32. Making compost safe for pets and children  Do not leave food scraps lying on top of the pile.  Tremorgenic mycotoxin is produced by a mold that causes tremors.  Pesticides are not reliably degraded by the composting process.
    33. 33. Fence off composting areas
    34. 34. Safe compost location?
    35. 35. What about compost tea?
    36. 36.  Compost tea is not the dark-colored solution that leaks from the bottom of the compost pile (do not spray this on food crops!)  Compost tea is the extract of compost made suspending compost in a barrel of water (aerated or unaerated) for a short period of time (up to a week). What is compost tea?
    37. 37.  Use only potable water.  Sanitize all equipment.  Use only compost that has maintained a temp of 131 F for 3 days (hot composting method).  Must be used within 24 hours of making it.  Avoid additives (esp. simple sugars like molasses). If you decide to make compost tea:
    38. 38. Worm composting and kids
    39. 39. Gardens and animals
    40. 40. Sanitation and tools  Wear gloves when harvesting.  Wash hands before and after harvesting.  Tools should be sanitized before and after use. ◦ No more than 1 T. bleach to one gallon water.
    41. 41. Other garden activities
    42. 42. Volunteer management  Develop safety rules.  Provide an orientation.  Make it easy to follow the rules.  Set a good example!  Post signs. CLEAN HANDS. CLEAN WATER. CLEAN SOIL. CLEAN SURFACES.