METHODOLOGY TO ESTIMATE THE AMOUNT AND PARTICLE-SIZE OF SOIL INGESTEDBY CHILDREN - IMPLICATIONS FOR EXPOSURE ASSESSMENT AT WASTE SITES

Despite considerable efforts to improve the design of soil ingestion s tudies, substantial variability in daily soil ingestion rates based on different tracer estimates exists in the same subjects, The present s tudy assessed the hypothesis that one of the unexplored causes of this intertracer variation in soil ingestion estimation was related to dif ferences in soil tracer concentration by particle size. The study anal yzed the tracer concentration in soil for children in the Anaconda, Mo ntana soil ingestion study for the particle size fraction less than 25 0 mu m in diameter. Soil ingestion estimates for these children were r ecalculated based on the new soil concentration values and compared to previous findings (E. J. Calabrese, E. J. Stanek, P, Pekow, and R.M. Barnes, submitted, 1996) when the soil concentrations were determined for soil particle size diameter of <2 mm. The results indicated that f ive tracers (Al, Si, Ti, Y, and Zr) did not have their soil concentrat ions changed by particle size. However, for three tracers (La, Ce, and Nd) the concentration increased by two- to fourfold with the smaller particle size. Recalculation of soil ingestion estimates indicates tha t the soil ingestion estimates of the five tracers not varying by part icle size did not change while those of the remaining three tracers we re decreased by approximately 60%, The revised calculations provide a substantial improvement in intertracer estimates of soil ingestion and suggest that the children ingested soil of small particle size, These findings are of significance since they (1) identify an important pot ential cause of intertracer variability in soil ingestion estimates, ( 2) establish a new criterion for soil tracer selection, and (3) develo p a method for not only providing improved soil ingestion estimates bu t also determining the particle size of the ingested soil, These findi ngs offer important potential applications for risk assessment practic es at contaminated sites since soil ingestion is frequently the domina nt route of estimated contaminant exposure in children. (C) 1996 Acade mic Press, Inc.