I was told as a child not to eat berries near roads due to being exposed to exhaust fumes, but never check if there is any science behind it.
These days, tyre microplastics and diesel particulates are still a concern, but there's little hard science around the hazards of eating them in small quantities - there's microplastic in basically everything, to some degree, so you're not making it appreciably worse - and agricultural farm machinery is a worse diesel PM offender by far than a street's worth of modern cars.
One would hope that more expensive chocolate would have a value chain to show that it’s been dried in a proper manner.
Nothing beats random sampling though.