Lead is used as a stabilizer in some plastics.
As the plastic decays (weathering, mechanical wear, oxidation), the lead can be released onto the surface as a fine dust.
Usually this isn't a problem, but in some situations you can get lead dust levels that exceed regulatory maximums. One example _may_ be plastic mini-blinds, which have lots of surface area, and sit in sunny windows getting lots of daylight exposure.
Here is a discussion on lead in plastic toys. I won't say that it isn't biased; the company makes wood toys, but it provides decent background on the topic.
http://www.turnertoys.com/pvc3Stabilizers.htm -Jon
