Pallets are either heat-treated (heated to a high temperature in kilns to seal the wood) or treated with methyl bromide — a toxic pesticide that has been linked to human health problems and ozone layer depletion. ... Avoid unmarked pallets or those stamped with an “MB” for methyl bromide.

Are pallets treated for outdoor use?

While most wooden pallets are designed to be stored outside when in use for commercial shipping, chances are they are NOT treated to the standards you'll need for long-term outdoor exposure. Chances are they will not stand up to wear by climate and weather without some additional treatment.

Is it OK to burn pallets?

Pallets, lumber, and other cut and dried scrap wood are indeed good to burn (as long as you are completely sure they were not treated with any chemicals such as arsenic or methyl bromide, which are very hazardous when burned). ... Old shipping pallets pose a few risks despite being dried and milled.