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Research clears bulb onions of E. coli risk

Sean Ellis

Capital Press

Oregon State University researchers in Ontario have found that bulb onions pose no risk of E. coli contamination from irrigation water regardless of how they are irrigated and regarless of how much bacteria is present in the water.

ONTARIO, Ore. — Research conducted at Oregon State University’s Malheur County experiment station has shown that E. coli contamination is not a risk in furrow- or drip-irrigated bulb onions.

The research began last year after the U.S. Food and Drug Administration released a proposed produce safety rule that would limit the amount of generic E. coli bacteria that can be present in irrigation water.

This year’s trial is much larger and researchers expect it will confirm last year’s findings, which showed bulb onions pose no risk of E. coli contamination, regardless of how they are irrigated and regardless of the water quality.

Researchers even enriched some of the water with extremely high levels of generic E. coli by using runoff water from a pasture. Still, there was no trace of bacteria when the onions were ready for packing.

“By the time we packed them out, the numbers were all zero,” said Clint Shock, director of the Malheur experiment station.

There were traces of E. coli present on the outside of some onion bulbs when they were pulled out of the soil and left on the ground to dry. But after they were cured in the field — all bulb onions in this area go through that process — and ready for packing, no E. coli was present on any of the onions.

“The results of last year showed that the bacteria died off really rapidly after they were lifted, and cured in the field,” Shock said. “And we didn’t have any generic E. coli at all on any of the onions when we packed them out.”

E. coli levels for soils and onions were recorded during growing, harvesting and processing conditions. At no time was E. coli ever detected inside of any of the onions.

Water doesn’t meet regulations

The FDA’s proposed produce safety rule, which covers any produce that could be consumed raw, would require farmers to test their irrigation water weekly and stop using it if generic E. coli bacteria levels exceed a certain standard.

Shock said onions are highly susceptible to even small amounts of water stress and a brief interruption in irrigation could cause huge losses in yields and size.

“The financial penalty of delaying irrigation is extreme,” he said.

Most onions in the Eastern Oregon-Idaho onion growing region are irrigated with water from irrigation ditches and would not meet the FDA’s proposed bacteria standard.

“The tests show that in general onions are a safe crop, so all of these additional measures that may be required … would result in a tremendous cost to the industry without providing any health safety benefits,” said OSU researcher Stuart Reitz.

Following a loud outcry from some farm groups and members of congress, FDA announced in December it would revise the proposed rule.

An FDA spokeswoman told Capital Press the agency plans to issue the revised rules by the end of this summer.

Shock said the station’s research has shown that “the potential cost in monitoring and everything else to North American onion growers is very high and the potential benefits to public health are extremely low.”

According to OSU research assistant Rocco Roncarati, the test onions are being watered four different ways.

Some are furrow irrigated with ditch water, others are furrow irrigated with ditch water intentionally enhanced with extremely high amounts of bacteria, some are drip irrigated with ditch water and some are drip irrigated with clean well water with no bacteria.

The same amounts of E. coli were present on onions when they were lifted from the soil regardless of the water source.

Shock said the fact that bacteria was found on onions at harvest whether or not they were irrigated with water with no bacteria is a strong indication that bird and rodent droppings contributed to E. coli in the field.

E. coli on the onions’ surface was reduced and eventually eliminated by in-field drying and harvesting, which removes loose skins and dirt.

In case the part of FDA’s proposed rule regarding irrigation water isn’t changed,

Solutions sought

OSU researchers are also looking at possible remediation strategies.

One includes injecting a chemical such as chlorine dioxide through drip tape. Growers who are drip-irrigating their onions are already using this chemical to kill algae to keep the drip lines clean.

“We would try to apply it in a strategy that would also indirectly wipe out all the E. coli,” Shock said.

But about half of onions in the region are furrow irrigated and that process, even if it works, wouldn’t help them.

OSU’s research appears to confirm what the industry’s own experience has shown for years.

Kay Riley, manager of Snake River Produce in Nyssa, said his company has been required by a customer to test for E. coli and salmonella for several years.

“We’ve never had a positive sample,” Riley said. “It’s great to have Clint’s research to verify what we’ve known for years. Even though irrigation water may not meet the (proposed) standards, we know there is nothing in the onions.”

FDA’s proposed rule also would require onion growers to switch from the wooden crates they have used for decades to plastic ones.

Shock and Reitz have conducted research that shows that conversion would be extremely expensive and unnecessary.

OSU researchers sterilized new plastic crates with bleach and filled them with onions. Old, wooden boxes that have been used for two decades were filled with onions without being cleaned.

The result: No traces of E. coli bacteria on onions in the wooden boxes and a couple in the plastic crates that Shock said could be chalked up to chance.

The Eastern Oregon-Idaho onion industry has about 1 million wooden boxes and replacing them with plastic crates would cost about $200 million, Reitz said.

Besides the cost of the more expensive plastic crates, storage buildings would have to be reconfigured because the crates are smaller and require more air circulation.

Riley said the wooden bins hold about 1,600 pounds of onions and cost $55 new, while the plastic ones hold about 900 pounds and cost $150.

“There is absolutely no reason we should have to use plastic bins,” he said. “It’s insane to even consider such a thing.”

Shock, Reitz, Roncarati and OSU students are looking at several ways to address the issues involved with the FDA’s proposed rule.

Roncarati was part of a group of OSU seniors in Corvallis last year who studied the possibility of using a filtration pond to filter out pathogens before pumping the water onto onion fields.

The idea was viable technically but “economically it wasn’t so feasible because the pond we needed would be over an acre in surface and it would be really expensive to excavate the soil and fill it with the right materials,” he said.

OSU researches are taking a serious look at this and other ideas students are coming up with, Reitz said.

“We had several student groups that really came up with some intriguing and potentially practical solutions to these types of issues,” he said.

Rep. Greg Walden, R-Ore., told the Capital Press via email that the research being conducted at the Malheur County experiment station proved invaluable in helping persuade FDA to take another look at its proposed rule.

Without it, “I could not have convinced the FDA to pull back on their burdensome, one-size-fits-all water quality rules for onions and other crops,” he said. The research “produced hard science that convinced the agency that the rules they drafted just didn’t work for farmers or consumers.”


A 28-page report on Oregon State University’s research on the possibility of onions being contaminated with E. coli bacteria from irrigation water can be found online at www.cropinfo.net. Click on “Onions” on the left side of the page and then on “Preliminary studies on E. coli and onion.”


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