Reusable plastic containers used by farmers to ship fresh produce from farms to grocery stores have gained wide usage in the last decade, effectively replacing corrugated boxes with a more environmentally friendly alternative.
But two studies — one in Canada and one in the U.S. — have found serious problems with the general sanitation and cleanliness of those containers, raising concerns about possible food safety risks. They say the containers — which some retailers now require growers to use — could transfer pathogens from contaminated produce onto clean produce when not sanitized thoroughly.
First, in 2013 and again this year, Canadian researchers found evidence of fecal bacteria left over in containers said to have been sanitized. University of Guelph food science professor Keith Warriner, Ph.D., found contamination of innocuous strains of coliform E. coli on containers, suggesting that the company’s sanitation process was inadequate, he said.
Judging the cleanliness of the containers using U.K. food safety standards of food surfaces, Warriner determined that 43 percent of containers failed sanitary standards when inspected this year.
Now, in California, a soon-to-be-published companion study found similar results. University of California Davis extension research specialist Trevor Suslow, Ph.D., found that a “significant number” of produce containers exceeded reasonable expectations for cleanliness and failed to meet expected microbiological standards for surface sanitation.
Over a six-day period, Suslow’s team inspected produce containers after they had been sanitized but before they had been given to growers to pack for shipments. The system is arranged so that growers rent out the containers from the manufacturer and empty containers are sent back to the manufacturer to undergo a sanitation process before being packed with produce once again.
But Suslow and Warriner want to raise awareness in the produce industry that these sanitation processes might not be getting the job done.
“Although we’re aware there’s a cleaning and sanitizing process, it appears to be inconsistent and we found a number of indicators of uncleanliness in our study,” Suslow told Food Safety News.
After swabbing container surfaces for bacterial indicators of uncleanliness, Suslow found 38 percent of samples to carry 100,000 bacterial cells, while eight percent had more than one million. That, he said, wasn’t acceptable.
One problem with the containers is that they have hinges and other pinch-points where food can get caught and stay trapped for a long time. The studies found numerous instances of mold and spoilage in containers that had undergone the sanitization process.
While no cases of illness have been directly connected to produce containers, Suslow said that it would be very difficult to trace an illness back to something as unsuspecting as a plastic container.
“Taking a systems approach to produce safety, while there may be no recognized outbreaks linked to containers, we see a lot of sporadic illnesses where you never learn the cause,” he said.
Warriner said that his study also found a noticeable increase in broken containers between the first and second years of his study. Unfortunately, he said, growers are sometimes in a position where they’re eager to take any available container, as it’s the only way they can ship out product.
In the Canadian study, Warriner found that the company providing containers to growers in Canada did not have a washing facility in the country. As a result, the containers were supposed to be shipped back to Chicago to undergo cleaning after delivery.
In the case of the unclean containers returning to Canada, Warriner could only speculate as to what was occurring:
“There’s one of three things going on,” he said. “One, they’re going to Chicago but not being sanitized; two, they’re not going to Chicago; or three, they’re going to Chicago, being sanitized, and somehow meeting the cleanliness standards of the company.”
For now, the companies have no cleanliness standards on public record, Warriner said.
Warriner also questioned the silence of retailers on the topic.
“What’s interesting is that although retailers have very strong scrutiny about food products, they haven’t really paid attention to the food safety concern here,” he said.
Another problem Warriner found: sticker labels from previous produce shipments would often remain stuck inside the containers. In one case, a label for products grown in Mexico made its way to a farm in Canada.
With two independent studies raising such similar concerns about reusable containers, Suslow said that he hopes the container manufacturers will recalculate their cleaning and sanitization processes. In the meantime, growers and handlers should implement their own procedures for cleaning the containers, he said, and possibly testing the containers with rapid bacterial swabs themselves.
Suslow said that because it’s impossible to completely control for contamination when growing produce in an open environment, fresh produce shouldn’t come into direct contact with reusable containers.
“Contamination of these containers is something you should be able to control, and if you can’t, you have to start looking for other options,” he said.
Photo of soiled plant material inside a reusable produce container courtesy of Trevor Suslow.