Lead and arsenic enrichment across soil particle size fractions relevant to exposure assessment

• Lead and arsenic enrichment in the <150 versus <250 μm fraction was generally low • Enrichment was lowest at concentrations above background (e.g., 50-400 mg/kg lead) • Sieving to <250 or <150 μm is unlikely to alter residential soil cleanup decisions Soil lead exposure assessment is based on concentrations in fine particle fractions most likely to be ingested after adhering to children's hands or other objects. The <250 micron (μm) particle size fraction is often used for residential lead soil assessment and bioavailability studies that guide subsequent decisions regarding the scope of soil remediation at contaminated sites. Recent studies suggest use of a finer fraction (<150 μm) may be more representative of exposures, but data documenting a difference in lead concentrations between these two size fractions are limited. Site investigations may require analysis of hundreds of samples. Screening these samples to <150 μm requires significantly more sample mass and laboratory processing time and space. Due to these sampling and analysis limitations, it is important to understand whether analysis of the finer fraction yields significantly different results compared with the <250 μm fraction. To assess the potential for lead enrichment in the <150 μm fraction relative to the <250 μm fraction, lead concentrations in both fractions were compared. Enrichment at <150 μm was statistically significant but relatively low, particularly at concentrations relevant for human exposure assessment. Arsenic enrichment was also evaluated in this study. The results of this and the few other comparable studies indicate that reliance on the <250 μm versus <150 μm sieve size is unlikely to significantly alter site assessments. This finding should be considered in determining the need to use the <150 μm fraction or in assessing the accuracy of prior data based on the <250 μm fraction.