A GUIDE TO INTERPRETING SOIL INGESTION STUDIES .2. QUALITATIVE AND QUANTITATIVE EVIDENCE OF SOIL INGESTION

Four major studies have attempted to qualitatively and quantitatively assess the extent of soil ingestion in children using the soil tracer methodology. The validity of the estimates of soil ingestion in each study was reevaluated in light of the inherent strengths and limitations of study design and/or execution, as well as via a novel methodology for estimating the soil recovery variance for each tracer, which then led to the estimation of soil ingestion detection limits for each tracer for studies performing mass-balance analyses. Based on these analyses it is concluded that the Binder et al. (1986, Arch. Environ. Health 41, 341-345) and Van Wijnen et al. (1990, Environ. Res. 51, 147-162) studies provide no convincing evidence to support qualitative and quantitative estimates of soil ingestion due to inherent limitations in their respective study designs. The Davis et al. (1990, Arch. Environ. Health 45, 112-122) and Calabrese et al. (1989, Regul. Toxicol. Pharmacol. 10, 123) studies displayed convincing qualitative evidence of soil ingestion. However, the results indicate that the median soil ingestion estimates of Davis et al. were less reliable than those of Calabrese et al. The range of detection limits vary according to the tracer and the assumption of acceptable precision in recovery estimation. The minimum detection level of soil ingestion in children in the Calabrese et al. study, with a variance in recovery of 100% ±20%, was 21 mg/day based on Zr. These findings are of particular regulatory significance since they provide: (1) a method of assessing the level of detection inherent in soil ingestion studies, (2) a reevaluation of the major soil ingestion studies in light of new methodology, and (3) guidance for future studies so that detection capacity can now be included in the presentation of study findings. © 1991.