My personal experience as a landlord: kids putting their mouths on rails and banisters that are at the level of their mouths. Vivid memories of kids standing around just hanging out on the deck (pre-Internet obviously) with their mouth on the rail. "Does eating a couple flakes lower your IQ in a measurable way? Seems very unlikely." Like asking about the effect of a little second-hand smoke. Probably not a measurable effect, but many people would not be consoled by the inability of the data to register an effect.