The kiln drying process heats the wood up(cooking it) so it removes the majority of the moisture and phenol oils that are present in the wood.
For those of us that breed rats for feeders we want our rats to be big, healthy and well fed so they recover quickly and produce nice large litters of healthy babies. So if there was a health risk that would jeopardize this we wouldn't be using pine shavings as bedding.
BTW there are also phenol oils in aspen!