A recent study from Australia suggests that plastics may have something to do with autism.
https://theconversation.com/do-plastics-cause-autism-heres-what-the-latest-study-really-says-236401
Over the years there have been many suggested causes from vaccines to Glysophate to Tylenol(paracetamol).
A few years ago Forbes ran an interesting article on weird causes:
https://www.forbes.com/sites/emilywillingham/2013/09/04/10-weirdest-things-linked-to-autism/
Please form your own opinion, but please accept many people accept that autism is genetic in origin.