Farm Progress

Thirty-three people from five states were infected and nearly half of those were hospitalized in late 2012 after consuming spinach and bagged spring mix salads contaminated with E. coli.Preventive efforts are under way to reduce the occurrence of similar situations.Irrigation water is one of many potential avenues how food can become contaminated.

May 15, 2013

5 Min Read

Thirty-three people from five states were infected and nearly half of those were hospitalized in late 2012 after consuming spinach and bagged spring mix salads contaminated with E. coli.

The contaminated salads originated from a plant in Massachusetts.

There were nine outbreaks of foodborne illnesses in the U.S. last year, and one of five outbreaks associated with soil-grown produce, according to the U.S. Centers for Disease Control and Prevention (CDC). Preventive efforts are under way to reduce the occurrence of similar situations.

“If you’re going to grow products that will be consumed by humans you need to have a food safety program,” said JV Farms food safety director Fatima Corona.

“Food safety covers three types of contamination – physical, chemical, and biological. But the most severe would be biological because that could really make people sick.”

JV Farms manages about 8,000 acres in the Yuma area and produces a large portion of the lettuce crop grown there.

About 90 percent of the nation’s leafy green vegetables available during the winter come from Yuma, says Kurt Nolte, University of Arizona (UA) Yuma County Cooperative Extension director.

Microorganisms of greatest concern include Salmonella, Listeria, enterococci, norovirus, and pathogenic forms of Escherichia coli, commonly called E. coli, says Channah Rock, assistant professor and water quality specialist in the UA Department of Soil, Water and Environmental Science.

The Yuma County Cooperative Extension and the Department of Soil, Water and Environmental Science are part of the UA College of Agriculture and Life Sciences, and often coordinate efforts to assist with community and industry issues.

Rock’s graduate student Natalie Brassill is studying to detect E. coli most effectively in the water used to irrigate crops in three regions in California and southwestern Arizona.

Generic E. coli (E. coli that will not cause sickness) is commonly used as an indicator of water quality. Brassill’s project includes reviewing three Environmental Protection Agency (EPA)-approved methods for detection to figure out which method works best given different environmental conditions.

There can potentially be variations in the results of all three methods depending on the temperature or when there is higher salinity in the water, including after a local rain, Brassill says.

Each method can indicate the presence or absence of E. coli. Brassill is deciphering if and when these methods give a false indication of E. coli.

Growers periodically collect samples of irrigation water for lab testing of E. coli and other potential pathogens.

While no laws exist regarding levels of E. coli in irrigation water, the EPA’s legally unenforceable ‘guideline’ is the same as the one for bathing water. Bathing water must contain no more than 126 counts of E. coli per 100 milliliters of water – roughly equivalent to half a cup of water.

Irrigation water is one of many potential avenues how food can become contaminated. Produce must be protected at various points along the “farm to fork continuum,” Rock says.

Contamination in the field

Rock said produce can become tainted with pathogens while in the field, during processing, in transport to market, and other ways. Yet from her perspective, contamination most likely will “come from things that are happening in the field.”

Corona stressed the importance of observing farm fields from the moment crops are planted.

“Continuously, what we do is monitor our ranches,” Corona said.

She and others will install safety fences, monitor water samples, and even place ‘enforcers’ outside portable bathroom units to ensure that produce pickers wash their hands before going back into the field.

Rock noted that efforts like these have helped.

“In about the last five years the industry has changed due to different outbreaks, and they have stepped up to the plate to take over some new initiatives that will help in the long run,” Rock said.

For example, some Yuma growers have volunteered to test their operations through the Arizona Leafy Green Marketing Agreement (ALGMA), which involves having a third party perform an audit to evaluate food safety measures.

Third-party audits include checking the cleanliness of surfaces which produce touches, evaluating standard operating procedures, confirming that composted organic fertilizers are applied within the proper time frame, and assessing irrigation water quality.

These audits can be particularly helpful for producers of raw vegetables.

“If you cook a vegetable, you’re killing some of the bacteria that could potentially be on the vegetable,” Brassill said.

Fresh lettuce and other raw vegetables do not typically pass through a cooking process, even though they might be rinsed with water.

While there is no legal standard for E. coli in irrigation water, the standard for E. coli in drinking water is a zero count per 100 milliliters. Brassill believes it is only a matter of time before an enforceable standard is released for irrigation water as part of the Food and Drug Administration’s proposed Food Safety Modernization Act.

If signed into law, a portion of this act will include new science-based regulations for the safe growing, harvesting, packing, and holding of produce. There is current open discussion concerning the proposed regulations, which show similarity to guidelines already found in the (ALGMA).

Among the rules that will be presented in the new federally proposed regulations, Rock said the one on E. coli counts in irrigation water is sure to be included.

Brassill’s research showed significant variation of E. coli counts depending on which of the three methods used. Although detection of E. coli is not uncommon in irrigation water, Brassill’s research shows that two of those three methods are more reliable for E. coli detection.

This new finding can provide growers more dependable information when testing irrigation water quality.

In addition, Rock and Brassill are working with other UA researchers to publish a risk assessment to allow growers to better understand the potential risks associated with E. coli contaminationbased on subsurface, furrow, and sprinkler irrigation methods.

As CDC data demonstrate, outbreaks of foodborne illness can have a deadly and far-reaching impact. And as food safety continues to be a hot topic of discussion, Rock and Brassill’s study, and others like it, will continue to make important discoveries to help protect growers and consumers alike.

For more information, contact Rock at (520) 381-2258 or [email protected].

Todd McOmber is a University of Arizona graduate student.


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