Timber offcuts, sawdust and ash from burnt timber can contain high concentrations of arsenic, a toxic chemical that cannot be broken down.
Timber may be treated with chemical solutions to prolong its life, particularly when used for outdoor and building purposes. It is difficult to identify whether timber has been treated or not.
In New Zealand the following chemicals may have been used to preserve timber:
Find out more by watching: Learn why you shouldn't put timber off-cuts into your green wheelie bin(external link).