Agricultural Water Safety

The year 2018 was a hard time for romaine lettuce. Two massive, multistate E. coli outbreaks associated with leafy greens occurred (even extending into Canada), sickening hundreds of people and killing at least five. But as the outbreaks wound down, the culprit appeared even more difficult to control than leafy greens: It was a matter of contaminated agricultural water. And while the puzzle of making agricultural water safe has challenged food safety experts for a long time, the 2018 outbreaks introduced the question to the general public, many of whom now joined in asking, “How do we ensure the water used to irrigate fresh fruit and vegetables is safe?”

“Both the spring and fall outbreaks were devastating to the leafy greens industries,” says Jennifer McEntire, PhD, vice president of food safety and technology for United Fresh Produce Association in Washington, D.C. “In both cases, it appears that there is an environmental source of the pathogen. This is a new type of challenge in that it’s not about preventing an occurrence at a single point in time—it requires a revaluation of the system. Agricultural water has always been recognized as a risk and has always been managed.”

Luke LaBorde, PhD, professor of food science at Penn State’s College of Agricultural Sciences, concurs, underlining that the safety of agricultural water has always been notoriously hard to control.

“Especially,” he tells Food Quality & Safety, “if you’re using surface water from streams and irrigation ditches and things like that—it can change very suddenly. It can take some contamination upstream, what they call ‘point contamination,’ and spread it over wide distances, sometimes unexpectedly. In the case of the romaine outbreaks in Yuma, Arizona, it’s thought that there were irrigation ditches used for their produce farms that ran adjacent to animal-holding facilities. Now, we’ve known for a long time that that’s not a good idea. But still it happens.”

This contradiction is at the crux of agricultural water safety, Dr. LaBorde says. Though many farms know what approach they should be taking, they can be limited in their ability to implement them by financial concerns and other challenges like a lack of control over how neighboring farms handle waste.

“It’s tough, because people are slow to change their whole operation,” he says. “There are all sorts of things people can do, like keeping the animal facilities farther away and watching for drainage and run-off, but if it’s not your property, it’s kind of hard to control what other people do.”

Yet Rebecca Ozeran and Brooke Latack, livestock advisors at University of California Cooperative Extension, note that industry has hardly been inactive on the issue of agricultural water safety—particularly not the leafy greens industry.

“The food safety community has long been aware of the risks of water contamination, and water quality has not been ignored in food safety practices,” Ozeran and Latack jointly explained in an email to Food Quality & Safety. “Most leafy greens growers in the U.S. (producing about 95 percent of our lettuce) are already certified by the Leafy Greens Marketing Agreement, which […] regularly audits food safety practices at all certified operations. But there are inherent risks of contamination from eating any food produced in an open system. It is not feasible to grow all our crops in sterile, enclosed environments. Although operations can and do follow many practices to reduce the risks of food contamination and foodborne illness, the risks will never completely disappear. Even the best possible regulations and management will never achieve permanent zero percent contamination.”

Sampling Falls Short

The overarching problem, says Dr. LaBorde, is that regardless of regulation, some producers will inevitably end up facing situations they couldn’t have predicted. Existing regulations demand sampling and provide metrics for microorganisms, particularly (the largely harmless) generic E. coli, a good indicator of fecal contamination that can signal pathogenic E. coli or Salmonella. Even when sampling water according to regulations, a facility may miss pathogens.