Seed saving from plants growing in questionable areas

I haven't been able to find any info on this by means of a cursory google search so I thought I'd see what the census is. There are some wild edibles growing on a piece of my property that is a bit questionable (close to the road, in the leech field of our septic system). Our pond is the lowest point in about a mile around others' property as well. I've been thinking of attempting a "native edible garden patch" and I wanted to know if I saved seeds from plants I thought questionable if anything would pass to the seeds.

The seeds will be fine. I would grow the plants somewhere else. Growing plants of any kind in or near human waste is not recommended. The seeds will be fine however. Your greatest threat from fruits and vegetables is on the exterior of the plant. The viruses, bacteria, fungus and nematodes that infect plants do not infect us and vice versa...as a general rule. So bacteria such as e. coli, while it might be found on the exterior of the plant, would not be on the interior and not infect the seeds of the plant.

Close to the road might mean years and years of lead from exhaust. Unless it's a new road.
I'm not 100% convinced that growing on or near a leach field is necessarily a bad thing as long as the leach field is working properly, doesn't have wet soggy areas and you don't grow things with root systems that'll infest the pipes. I might pause too at things that grow on the ground, like pumpkins or cucumbers. But then I've never worried about filling garden trenches with cow manure or doing more than washing off the occasional bird dropping on the tomatoes. Heaven knows what rodents are running around out there at night either.

You also need to check the propagation methods of each plant.

Some reproduce best from cuttings or rhizome transfers.

Often wild plants do not respond well to attempts at cultivation so do not be surprised if it is not an easy go.