You can check what levels are allowed for various foods in Europe here which tend to be on the conservative side.

At the moment, research does not seem to be strong. For example, according to the quoted source:

> We systematically reviewed relevant studies published through December 30, 2018 and identified 14 studies on iAs and 37 studies on Pb exposure and their respective associations with ASD. Among them, 8 (53.3%) and 19 (51.3%) studies reported a positive association for iAs and Pb, respectively, and none reported a sole inverse association.

Even though the article says there is "consistent evidence supporting a link between early exposure to the heavy metal and a diagnosis of autism spectrum disorder".