DH's supervisor at work is a Ph.D. chemist. Said Ph.D. chemist and his wife are organic gardeners, right down to the free-range (daylight only) chickens and the feral rabbit around whom they've built a safe surround because of raccoons. They live in Davis, Sunset Zone 15 (significantly warmer summers and less winter rain than here).
You could've knocked me over with less than a chicken feather
the day that DH came home last fall and said, "John and [DW] harvested their potatoes over the weekend."
"Oh, good for them! Did they use a hand fork, or ...?"
"John said he just knocked the tires over and had his little girl [daughter] hand him the potatoes. He put 'em into a couple of buckets."
Oooooh kaaaay. Here we have a Ph.D. chemist, certainly aware of the potential for toxic leaching (however much that potential might or might not be), growing his own spuds in tires and having his 6-year-old daughter messing around in the growing medium to hand him the spuds. Sounds like a fun time!
I realize that a scientist would call this "anecdotal" evidence, but I do find it "indicative" as well.
Sunset Zone 17, USDA Zone 9