ADHD is irreversible, it's not something that can be reversed or goes away on its own.

There is literature on a link between fetal heavy metal exposure and ADHD development.

I can't find anything on neurotoxins "mimicking" ADHD.

Again, by the very biological definition of what happens in a brain on ADHD, this is not reversible. It's chronic.

Sources:

1: https://my.clevelandclinic.org/health/diseases/neurotoxicity

2: https://pubmed.ncbi.nlm.nih.gov/36972880/