I was re-reading “The Complete Book of Edible Landscaping” and found this tidbit regarding using plants that have been exposed to lead by being located close to a road:
Fruit and leafy vegetables from plants close to the road should be washed well in acidulated water before cooking or serving. The usual formula is 2-3 tablespoons of vinegar to a quart of water (you can keep a squeeze bottle handy under the sink). Then wash again with fresh water.
I found this post because I am new to foraging herbs and had the same question, but what I wanted to add to the discussion because I saw no mention of it: Sometimes herbicides are sprayed under powerlines… also be aware that winddrift can carry the herbicide over to the other side of the road/nearby areas. Powerline maintenance is usually done every 4 to 5 years. I dont know how long the herbicide lasts on the plants. But if you want to know if your area is sprayed call the power company. I heard of a lady who got very sick from eating blueberries she picked roadside that happened to be in a sprayed area.