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Food Safety Risk for Leafy Greens and Tomatoes from Small Farm Environments Exposed to Manure Dust, Soil Amendments, Insects and Creek Water

Millner, Patricia
USDA - Agricultural Research Service
Start date
End date
Determine transference prevalence, survival, and quantities of E. coli, Salmonella, and fecal indicator microbes to leafy vegetables and tomatoes relative to proximity to composting and dairy operations, and to irrigation and agricultural sprays with treated and untreated surface waters tomatoes relative to proximity to composting and dairy operations, and to irrigation and agricultural sprays with treated and untreated surface waters.
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Approach: Prevalence and concentrations of viable E. coli, Salmonella, and fecal indicator microbes will be measured prior to application of a common source of thermophilic and vermicomposted and non-composted aged dairy manure to small field and high tunnel plots where leafy greens and tomatoes are grown. Organic spring mix lettuce plants will serve as sentinels during land application and thereafter, several cultivars of tomato will be included in the replicated field and high tunnel plots. Plants will be arrayed on transects 50, 100, and 400 ft from animal and composting operations at BARC. Prevalence/ concentrations of microbes will be measured on plants at each distance from the suspected source and seasonally as well as in the suspected source materials (manure/compost). Particulate depositions onto lettuce and tomatoes will be measured and manure/compost prevalence in samples assessed by non-destructive fluorescence imaging techniques. Survival of microbes on produce will be assessed at seven days prior to harvest. The role of insects in transference of microbes from suspected nearby sources will be evaluated by imposing insect screening to exclude flying insects from plants in comparison with unscreened plants. Insects and dust at suspected sources and on unscreened fresh produce in nearby mini-plots will be captured and assayed for fecal indicators and pathogens and matched by genotype to those from suspected sources. Pathogen survival on leaves and in manure/compost will be evaluated relative to meteorological conditions during exposure periods and the physico-chemical and biological properties of the crop inputs. Creek water will be used directly and also sand filtered and treated treated with UV or chlorine prior to use in drip irrigation and crop protectant sprays. Non-pathogenic E. coli and Salmonella will be spiked into the creek water if none are naturally present. Impacts on survival of these microbes will be measured on spring mix lettuce and tomatoes.
Funding Source
Agricultural Research Service
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Natural Toxins
Viruses and Prions
Bacterial Pathogens
Chemical Contaminants
Escherichia coli