I was just wondering the same thing. I have a small garden of ig food going -- has not had a good 36 hours the lawn guys weed whacked my taller collards down and Bob ate 1/2 of my seedlings the next day -- and I have a small row of radish going.
Bob has had some over the years with no ill effects but they were mixed in with many other greens. The larger leaves have "fuzz" on them and I don't know how that goes down.
Ig-den cites Radish as having a 1.2 Ca/P ratio USDA search shows that raw radish is rather high in potassium 233mg per 100 gram sample.
No mention of greens nor of goitogens and oxilates that I recognize.