PCBs are persistent environmental contaminants, but are low on the toxicity list. To get it into your bloodstream effectively, you would probably require a suppository. BTW, the Italian word for those is "innuendo."
Since you're warning them, one of the idiots not knowing any better just might decide to screw with you. Perhaps a "safe" demonstration might be in order? Seriously. Every shop has one of those.....At work if I am in a 480 cabinet and some one is nearby I tell them not to lick anything if I have to grab a tool or something. They think its funny but sometimes I wonder if one of them will one of these days the stuff they pull?...