Can I use old decking boards to create animal houses?

I've used old decking boards to make a hedgehog house without any problems. Wood for external use was tanalised with an arsenic compound some years ago (I seem to remember it was banned in the mid-noughties), so anything that dates from after that time should be absolutely fine (even stuff that pre-dates it is probably going to be ok for a hedgehog house, but maybe not a bird box as the birds peck away at the entrance). The potential for arsenic compounds are why you shouldn't burn old tanalised timber