Soil ingestion estimates for children in Anaconda using trace element concentrations in different particle size fractions

This investigation assessed the effect of soil particle size on soil ingest ion estimates of children residing at a superfund site. Earlier research in dicated that wide intertracer variability in soil ingestion estimates are b ased on soil concentrations with a soil particle size of 0 to 2 mu m was ma rkedly reduced when the estimates were based on soil tracer concentrations for a soil particle size of 0-250 mu m. The reduced intertracer variation w as principally attributed to changes in soil concentrations of only three o f the soil tracers (i.e., Ce, La, Nd) which became concentrated in the fine r particle size by approximately 2.5 to 4.0-fold. It was hypothesized that the intertracer agreement in soil ingestion estima tes may continue to improve if the estimates are based on concentrations of tracers at finer particle sizes assuming that children ingest finer partic les and that the above three tracers would continue to be further concentra ted in the finer sized soil particles. The principal findings indicate: 1. The soil concentrations of Al, Si, and Ti do not increase at the two fin er particle size ranges measured. 2. The soil concentrations of Ce, La, and Nd increased by a factor 2.5 to 4 .0 in the 100 to 250 mu m particle size range when compared with the 0 to 2 mu m particle size range. No further substantial increase in concentration was observed in the 53 to 100 mu m particle size range. 3. The soil ingestion estimates are consistently and markedly changed only between the estimates based in 0 to 2 mu m and 100 to 250 mu m for Ce, La, and Nd. These changes reduced the intertracer variability in estimating soi l ingestion, suggesting that the children eat finer soil particle sizes. 4. Because the particle sizes for all tracers (except Zr) were only modestl y affected at the 55 to 100 mu m range, it was not possible to confidently resolve the particle size of soil ingested by the children. 5. Residual intertracer variability in soil ingestion estimates based on Ce , La, Nd are likely to be significantly affected by non-food, non-soil sour ces of these tracers (i.e., source error). 6. Soil ingestion estimates of this study will be more reliable when derive d from the finer-sized particles.