No offenses, but I'm gonna put a lot more weight behind a peer reviewed Nature paper, rather than some random podcaster.
The explained their methodology pretty well. They extrapolate the microplastics amount from a small bit of cortical tissue, and compared it to previous results. Yeah there might not be as much in other parts of the brain, but we don't have a reason to think it would be drastically different.
Ironically the reason we can't keep up with car infrastructure is because there's too much of it.
It much more costly to maintain, especially when scaling to more lanes.
Reducing space given to cars and giving more to bikes/buses/trains would make it easier to upkeep our current roads.