this study was conducted to develop a method that would accurately assess children 's exposure to lead in schools in philadelphia , pennsylvania . 
 we examined three wipe sample protocols : one included accessible surfaces such as desktops and windowsills , the second included inaccessible surfaces such as the top of filing cabinets and light fixtures , and the third included hand wipes of the study participants . 
 surface wipes were collected at 10 locations from accessible and inaccessible classroom surfaces ( n = 11 at each location ) and from the palms of student subjects in the same locations ( n = 168 ) . 
 we found a significant difference in lead dust concentrations determined by the three protocols ( f = 4.619 ; 2,27 degrees of freedom ; p = 0.019 ) . 
 lead dust concentrations were significantly elevated at the inaccessible surfaces yet they were uniformly low on the accessible surfaces and the children 's palms . 
 these findings were consistent with observed changes in blood lead levels of study participants : after 6 months of exposure to the study locations , 156 of 168 children experienced no change in blood lead level , whereas 12 experienced only a minimal change of 1 - 2 microg / dl . the mere presence of lead in inaccessible dust in the school environment does not automatically constitute a health hazard because there may not be a completed exposure pathway.imagesfigure 1figure 2