The level chosen seems like a reasonable level to put up a flag. 200ppm is a level where an active gardener could cause excess exposure by growing leafy vegeta

The level chosen seems like a reasonable level to put up a flag. 200ppm is a level where an active gardener could cause excess exposure by growing leafy vegetables-- so that being the point where you warn people there's a potential problem and they should consider where to plant and what to grow. If you told me my soil lead content was 200ppm, I would change my gardening practices and-- even though it may be a little overprotective-- cover contaminated soils where my kids play most. (Now, if you told me that only 1/8th of homes would be affected if you set the level to 250ppm, maybe I'd say 250ppm would be a more appropriate level to balance the number of people warned; but if it's not a huge increment in the number warned, 200ppm seems appropriate-- that is, the tradeoff isn't just between direct harms and direct benefits but also, as grandparent seems to state, in helping people judge relative levels of risk accurately).