Sources of variability in collection and preparation of paint and lead-coating samples

Chronic exposure of children to lead (Pb) can result in permanent physiolog ical impairment. Since surfaces coated with lead-containing paints and varn ishes are potential sources of exposure, it is extremely important that rel iable methods for sampling and analysis be available. The sources of variab ility in the collection and preparation of samples were investigated to imp rove the performance and comparability of methods and to ensure that data g enerated will be adequate for its intended use. Paint samples of varying si zes (areas and masses) were collected at different locations across a varie ty of surfaces including metal, plaster, concrete, and wood. A variety of g rinding techniques were compared. Manual mortar and pestle grinding for at least 1.5 min and mechanized grinding techniques were found to generate sim ilar homogenous particle size distributions required for aliquots as small as 0.10 g. When 342 samples were evaluated for sample weight loss during mo rtar and pestle grinding, 4% had 20% or greater loss with a high of 41%. Ho mogenization and sub-sampling steps were found to be the principal sources of variability related to the size of the sample collected. Analysis of sam ples from different locations on apparently identical surfaces were found t o vary by more than a factor of two both in Pb concentration (mg cm(-2) or %) and areal coating density (g cm(-2)). Analyses of substrates were perfor med to determine the Pb remaining after coating removal. Levels as high as 1% Pb were found in some substrate samples, corresponding to more than 35 m g cm(-2) Pb. In conclusion, these sources of variability must be considered in development and/or application of any sampling and analysis methodologi es.