In all information that I can think of there may be a risk of injury with any
chemical protectant used. Even if there is no known problem at this time, we
may find a problem in the future.
Paint (when cured) works and doesn't seem to have a harmful effect.
Why not just use a longlasting wood like ceder? it weathers beutifully and
if constructed well will last a very long time.
I don't consider myself an expert on preservatives. But this is the personal
rule that I follow with birdhouses.
I have ceder Bluebird houses that have been out in the weather for 6-8 years
and still are going strong, yet others made about the same time have had
parts replaced.

Fred Rutan
BB Trail Coordinator
Kitsap County