Wood is natural and does not give of any toxins... i don't mean to be rude or smart but... for the person who does not appreciate the beauty and practicality of real wood... pvc is the way to go...
...what about the chemicals used to treat/impregnate the timber, or the stain/varnish? .........or we could say, "save a tree, use PVC" - wood is o.k. for those who're prepared to mind it, for those who're prepared to live with the colour of it, for those who're prepared to re-finish it every X no of years. I could even suggest that timber frames are, in fact, a cold bridge..........but I won't