He says testing irrigation water is critical. The California Leafy Greens Management Agreement provides guidelines for contaminant levels, based on coliform units (CFUs) per milliliter. A CFU rating of 1 to 234 is acceptable for all kinds of irrigation. With a 235 to 574 rating, water should not come in contact with the edible portion of the plant. “Drip irrigation would be okay,” Anciso said.

At a rating above 575 CFUs, the water is unacceptable for any type of irrigation.

He said pathogens do not move up from roots into other parts of the plant, “based on California studies.”

He also said presence of E. coli is an indication that other pathogens and fecal matter might be present. “Salmonella may not correspond with CFU numbers, however.”

Anciso said manure-based fertilization in organic production should be monitored closely. “Application guidelines are in place and should be followed,” he said. “Follow the pre-harvest time constraints.”

He said pathogens have the potential to “last for years in manure if it’s not properly composted.”

Water used in post harvest operations “must be potable,” Anciso said. Precautions include proper worker hygiene, washing produce, transportation, cooling, processing and maintaining proper temperature differential.

Anciso said chlorine or another sanitizer may be important in packing shed water, not necessarily to clean the produce but to “keep the water clean.”

Suresh Pillai, a Texas A&M microbiology professor and director of the National Center for Electron Beam Research, said a zero contamination level for water or produce is impossible to achieve. “We can’t get samples without organisms,” he said. “Microbes were on the earth billions of years before humans. We now have 6 billion humans on the planet. There are probably that many micro organisms under your big toe.”

He said whether an organism is a pathogen or not “depends on the context. All are opportunists.”

The problem, as Pillai sees it, is lack of an accurate means of assessing food safety. “We have the technology to go millions of miles to the moons of Jupiter and get soil analyses. But we still don’t have an accurate means of checking food safety.”

He said groundwater is not immune from contamination but “it’s unusual to find high concentrations.”

Pillai said testing in the Rio Grande found “fecal matter all across the water. We will find micro organisms if we look for them,” he said. “We need to incorporate practices to limit contamination of produce.”

He said water in packing sheds water may contain viruses that are not controlled by chlorine.

“When, how and for what to sample are big questions,” Pillai said.  And growers and packers should always be skeptical of negative reports.

He said what producers don’t see should concern them. “Interpreting negative results should keep you up at night. With positive results, you can take action.”

 “Growers and packers need a quantitative risk analysis system to help make decisions,” he said. “They need a system to determine risks and if there are hazards or not.”

He said a Quantitative Risk Assessment model identifies “actionable items. Growers can then change those risks, by alternating production practices—changing irrigation methods, for instance.”