I've been looking for a house to buy in a new area, and it's amazing how many homes have shored up their surroundings with aresenic/copper/chromium treated pine. In the area and price range I want, about one in three homes has extensive use of treated pine.
These houses have treated pine retaining walls; treated pine garden edging; treated pine decks; treated pine swing-sets; and/or treated pine pool surrounds. Some have all of the above. Our house had treated pine decking when we moved in. We thought nothing of it when we bought.
Is treated pine a factor in increasing autism rates? I don't know.
All I know is something causes autism.