Wood has natural antimicrobial chemicals, while plastic is easier to clean, according to Gerba. New plastic is less likely to trap bacteria, but once it has nicks and scratches, Gerba said plastic can becomes a host.
"I read all the literature, and I think it's a toss-up," said Gerba.
Trevor Suslow, a research specialist in food safety at the University of California, Davis, said he's not surprised by the high-stakes back and forth between the plastic and wooden pallet industry.
"It's a big market. No wonder they fight about it," Suslow said.
However, as the worries for contaminating produce go, Suslow said pallets have worked well enough that they do not cause a great deal of worry.
"In the hierarchy of things to worry about, it's not on the top of the list, because the product is not loaded directly on the pallet," Suslow said.
Indeed, according to Moore and Scholnick, the FDA only regulates three aspects of the pallet industry and two of the regulations have to do with permitting food items on pallets -- pallets coming into the country must be either heat treated, or treated with methyl bromide to remove pests, only stainless steel pallets can be used in a produce cooling technique called hydrocooling and no raw materials, especially meats, can directly touch a pallet.
"In just about all cases, pallet is a secondary packaging," Moore said.