All that I know:
Pallets for export/import are required to be treated (against wood boring insects)
Some pallets may have been used to transport tins and packs of noxious product. Pallets are recycled in transport- who knows where they’ve been .Just avoid clearly stained, dirty ones.
Allow to stand out in rain for a rinse.
No known issues during my use of palletwood have been attributed to contamination from this source.
Blue pallets are the property of CHEP* and ‘should not’ be re-purposed. IE you cannot legally be in possession of them without a rental contract, only made with major shippers.
*https://www.chep.com/uk/en/consumer-goods/platforms/pallets/wooden-uk-pallet
