You never know what parking lot they sat in.... or what a rainstorm could have washed their direction... engine oils, manure from a cattle truck... I would inspect them carefully and think about using the top planks only for smoking wood... Some gravel parking lots are sprayed with pesticides to reduce weeds from germinating....
Picture of NPPO/IPPC Standards
More companies are starting to build one-time-use pallets or using heat treatment rather than Methyl Bromide fumigation.
Pallets now require an IPPC logo which certifies that the pallet was heat-treated or fumigated with Methyl Bromide.
The standard is a 2 letter country code (xx), a unique number (000) assigned by the National Plant Protection Organization (NPPO), HT for Heat Treatment or MB for Methyl Bromide, and DB to signify debarked.
The logo in the first image shows that it was produced in the U.S., the material was provided by 11187 (Unique number assigned to the producer), it was heat treated (HT) and was verified by PRL (Package Research Laboratory)
Picture of Things to consider
The logo in the second images shows that it has also been debarked
This pallet is about as clean as they get. It was heat treated, produced in the U.S. and debarked.
There are some additional codes that can go on pallets but the main one to watch out for is MB. It means it was treated with Methyl Bromide.
If you don't see an IPPC logo then you know not to use it. While a pallet may be perfectly safe without the logo, it could also mean it was treated with chemicals.
Another issue is what has spilled on the pallet. I'd be careful, personally, about oily pallets or ones that have clearly had something spilled on them.
http://www.1001pallets.com/pallet-safety/After reading this stuff, I would NEVER use a pallet to cook food..... Dave