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Distinguishing outdoor soil ingestion from indoor dust ingestion in a soil pica child
REGULATORY
TOXICOLOGY
AND PHARMACOLOGY
l&83-85
(1992)
Distinguishing Outdoor Soil Ingestion from Indoor Dust Ingestion in a Soil Pica Child EDWARDJ.CALABRESE'ANDEDWARDS.STANEK School of Public Health, University of Massachusetts, Amherst, Massachusetts 01003
Received June 27, 1991
This paper represents the first quantitative attempt to distinguish the amount of outdoor soil ingestion from indoor dust ingestion in a soil pica child. Based on a methodology using a comparison of differential element ratios it is estimated that the predominant proportion of the fecal tracers were from outdoor soil and not indoor dust origin. The methodology employed can be utilized on a broader scale to assessthe relative amounts of soil and dust consumed by individuals. 0 1992 Acackmic Press. Inc.
INTRODUCTION Calabrese et al. (199 1) have recently reported the case of a 3 f-year-old child who displayed soil pica behavior. This child ingested lo- 13 g of soil per day over the second week of a 2-week soil ingestion study. This paper extends this earlier report by providing a methodology for differentiating the amount of outdoor soil from indoor dust ingested for this particular soil pica child. METHODOLOGY A detailed description of the methodology and results of the soil ingestion study was published previously (Calabrese et al., 1989) and should be referred to. This massbalance study utilized a soil tracer methodology with eight different tracers (Al, Ba, Mn, Si, Ti, V, Y, and Zr). The strategy for distinguishing indoor dust From outdoor soil in ingested soil is based on element concentration ratios. For illustration, let C(s) denote the concentration of an element in outdoor soil, C(d) denote the concentration of an element in indoor dust, and Y denote the total residual amount of an element in urine and feces (after subtracting food) for a subject for a day. Then define the quantities. ’ To whom correspondence should be addressed. 83 0273-2300192 $3.00 Copyright 0 1992 by Academic R-w, Inc. M rights afrepmduction in any form reserved.
84
CALABRESE
AND
STANEK
s = C(s) for element A C(s) for element 3 D = C(d) for element A C(d) for element B and R _ Y for element A Y for element B ’ For example, if element A was four times more plentiful in outdoor soil than element B, but both elements were equally plentiful in indoor dust, then D = 1 and S = 4. We would expect R to fall between 1 and 4, since the residual for each element must be composed of a combination of outdoor soil and indoor dust. In practice, the observed value of R may be larger than 4 or less than 1 due to the imperfect mismatch of collected food ingestion with collected fecal output. RESULTS Table 1 presents the results for the tracer ratio comparisons for the soil pica child during Week 2 of the study. There was a maximum total of 28 pairs of tracer ratios based on the eight tracers. Of the 28 tracer ratio pairs 19 ratios for the residual fecal sample were available for quantitative evaluation. Of these 19, 9 fecal tracer ratios
TABLE RATIOS
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
Mn/Ti Ba/Ti Si/Ti V/Ti Ai/Ti Y/Ti Mn/Y BaJY Si/Y V/Y Al/Y Mn/Al Ba/Al Si/Al V/Al SifV Mu/ii Ba/Si Mu/Be
OF SOIL, DUST,
AND RESIDUAL
1
FECAL SAMPLES IN THE SOIL F?CA CHILD
Soil
Fecal
Dust
Estimated % of residual fecal tracers of soil origin as predicted by specific tracer ratios
208.368 187.448 148.117 14.603 18.410 8.577 24.293 21.854 17.268 1.702 2.146 11.318 10.182 8.045 0.793 10.143 1.407 1.266 1.112
215.241 206.191 136.662 10.261 21.087 9.621 22.373 21.432 14.205 1.067 2.192 10.207 9.778 6.48 1 0.487 13.318 1.575 1.509 1.044
260.126 115.837 7.490 17.887 13.326 5.669 45.882 20.432 1.321 3.155 2.351 19.520 8.692 0.562 1.342 0.419 34.732 15.466 2.246
87 100 92 100 100 100 100 71 81 100 88 100 73 81 100 100 99 83 loo
A SOIL PICA CHILD
85
(i.e., Mn/Ti, Si/Ti, Ba/Y, SifY, Al/Y, BafAi, Si/Al, MnjSi, Ba/Si) fell within the boundaries for soil and dust. The remaining 10 fecal tracer ratios (Ba/Ti, V/Ti, Al/Ti, Y/Ti, Ma/Y, V/Y, Mn/Al, V/Al, Sip, Mn/Ba) fell outside of the boundaries for soil and dust. Whenever a value fell outside of the boundaries the source of the residual tracers was concluded to be 100% from the source it was most similar to. For example, tracer ratio No. 16 for Si/V (Table 1) was judged to indicate that 100% of the residual fecal soil tracers for this ratio were from soil. For tracer ratios where the values were between the boundaries an interpolation was performed to estimate the relative contribution of soil and dust to the residual fecal tracer ratio. The results indicate that all 10 of the ratios that exceeded the boundary did so on the soil side. These 10 ratios were interpreted as indicating that 100% of the fecal tracer ratios were from soil origin. The nine residual fecal samples within the boundaries revealed that a high percentage (i.e., 7 l-99%) of the residual fecal tracers were estimated to be of soil origin. DISCUSSION The results of this study indicate an extremely high agreement among the available 19 ratio pairs concerning the source of the residual fecal tracer ratios. All ratio pairs indicate that either all or a predominant proportion of the residual fecal tracers were from soil and not of dust origin. This study represents the tirst time that origins of the fecal tracers used in soil ingestion studies have been distinguished by the most likely source. The results presented here are so striking so as to leave little uncertainty over the relative contribution of soil to dust ingestion in this child during Week 2 of the soil ingestion study. The findings also illustrate the strength of the soil tracer ratio analysis when applied to the issue of soil pica. This approach is now being applied to the remaining 127 person weeks of the UMass soil ingestion data base which will be published in a subsequent report. REFERENCES CALABRESE, hSZTITY,
E. J., BARNES, R., STANEK, E. J., PASTIDE, II., GILBERT, C. E., VENEMAN, P., WANG, X., A., AND KOSTECKI, P. T. (1989). How much soil do young children ingest: An epidemiologic
study. Regul. Toxicol. Pharmacol. 10, 123-l 31. E. J., STANEK, E. J., AND GILBERT, C. E. ( 199 1). Evidence of soil-pica behavior and quantification of soil ingested. Hum. Exp. Toxicol. 10,245-249.
CALABRESE,
TOXICOLOGY
AND PHARMACOLOGY
l&83-85
(1992)
Distinguishing Outdoor Soil Ingestion from Indoor Dust Ingestion in a Soil Pica Child EDWARDJ.CALABRESE'ANDEDWARDS.STANEK School of Public Health, University of Massachusetts, Amherst, Massachusetts 01003
Received June 27, 1991
This paper represents the first quantitative attempt to distinguish the amount of outdoor soil ingestion from indoor dust ingestion in a soil pica child. Based on a methodology using a comparison of differential element ratios it is estimated that the predominant proportion of the fecal tracers were from outdoor soil and not indoor dust origin. The methodology employed can be utilized on a broader scale to assessthe relative amounts of soil and dust consumed by individuals. 0 1992 Acackmic Press. Inc.
INTRODUCTION Calabrese et al. (199 1) have recently reported the case of a 3 f-year-old child who displayed soil pica behavior. This child ingested lo- 13 g of soil per day over the second week of a 2-week soil ingestion study. This paper extends this earlier report by providing a methodology for differentiating the amount of outdoor soil from indoor dust ingested for this particular soil pica child. METHODOLOGY A detailed description of the methodology and results of the soil ingestion study was published previously (Calabrese et al., 1989) and should be referred to. This massbalance study utilized a soil tracer methodology with eight different tracers (Al, Ba, Mn, Si, Ti, V, Y, and Zr). The strategy for distinguishing indoor dust From outdoor soil in ingested soil is based on element concentration ratios. For illustration, let C(s) denote the concentration of an element in outdoor soil, C(d) denote the concentration of an element in indoor dust, and Y denote the total residual amount of an element in urine and feces (after subtracting food) for a subject for a day. Then define the quantities. ’ To whom correspondence should be addressed. 83 0273-2300192 $3.00 Copyright 0 1992 by Academic R-w, Inc. M rights afrepmduction in any form reserved.
84
CALABRESE
AND
STANEK
s = C(s) for element A C(s) for element 3 D = C(d) for element A C(d) for element B and R _ Y for element A Y for element B ’ For example, if element A was four times more plentiful in outdoor soil than element B, but both elements were equally plentiful in indoor dust, then D = 1 and S = 4. We would expect R to fall between 1 and 4, since the residual for each element must be composed of a combination of outdoor soil and indoor dust. In practice, the observed value of R may be larger than 4 or less than 1 due to the imperfect mismatch of collected food ingestion with collected fecal output. RESULTS Table 1 presents the results for the tracer ratio comparisons for the soil pica child during Week 2 of the study. There was a maximum total of 28 pairs of tracer ratios based on the eight tracers. Of the 28 tracer ratio pairs 19 ratios for the residual fecal sample were available for quantitative evaluation. Of these 19, 9 fecal tracer ratios
TABLE RATIOS
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
Mn/Ti Ba/Ti Si/Ti V/Ti Ai/Ti Y/Ti Mn/Y BaJY Si/Y V/Y Al/Y Mn/Al Ba/Al Si/Al V/Al SifV Mu/ii Ba/Si Mu/Be
OF SOIL, DUST,
AND RESIDUAL
1
FECAL SAMPLES IN THE SOIL F?CA CHILD
Soil
Fecal
Dust
Estimated % of residual fecal tracers of soil origin as predicted by specific tracer ratios
208.368 187.448 148.117 14.603 18.410 8.577 24.293 21.854 17.268 1.702 2.146 11.318 10.182 8.045 0.793 10.143 1.407 1.266 1.112
215.241 206.191 136.662 10.261 21.087 9.621 22.373 21.432 14.205 1.067 2.192 10.207 9.778 6.48 1 0.487 13.318 1.575 1.509 1.044
260.126 115.837 7.490 17.887 13.326 5.669 45.882 20.432 1.321 3.155 2.351 19.520 8.692 0.562 1.342 0.419 34.732 15.466 2.246
87 100 92 100 100 100 100 71 81 100 88 100 73 81 100 100 99 83 loo
A SOIL PICA CHILD
85
(i.e., Mn/Ti, Si/Ti, Ba/Y, SifY, Al/Y, BafAi, Si/Al, MnjSi, Ba/Si) fell within the boundaries for soil and dust. The remaining 10 fecal tracer ratios (Ba/Ti, V/Ti, Al/Ti, Y/Ti, Ma/Y, V/Y, Mn/Al, V/Al, Sip, Mn/Ba) fell outside of the boundaries for soil and dust. Whenever a value fell outside of the boundaries the source of the residual tracers was concluded to be 100% from the source it was most similar to. For example, tracer ratio No. 16 for Si/V (Table 1) was judged to indicate that 100% of the residual fecal soil tracers for this ratio were from soil. For tracer ratios where the values were between the boundaries an interpolation was performed to estimate the relative contribution of soil and dust to the residual fecal tracer ratio. The results indicate that all 10 of the ratios that exceeded the boundary did so on the soil side. These 10 ratios were interpreted as indicating that 100% of the fecal tracer ratios were from soil origin. The nine residual fecal samples within the boundaries revealed that a high percentage (i.e., 7 l-99%) of the residual fecal tracers were estimated to be of soil origin. DISCUSSION The results of this study indicate an extremely high agreement among the available 19 ratio pairs concerning the source of the residual fecal tracer ratios. All ratio pairs indicate that either all or a predominant proportion of the residual fecal tracers were from soil and not of dust origin. This study represents the tirst time that origins of the fecal tracers used in soil ingestion studies have been distinguished by the most likely source. The results presented here are so striking so as to leave little uncertainty over the relative contribution of soil to dust ingestion in this child during Week 2 of the soil ingestion study. The findings also illustrate the strength of the soil tracer ratio analysis when applied to the issue of soil pica. This approach is now being applied to the remaining 127 person weeks of the UMass soil ingestion data base which will be published in a subsequent report. REFERENCES CALABRESE, hSZTITY,
E. J., BARNES, R., STANEK, E. J., PASTIDE, II., GILBERT, C. E., VENEMAN, P., WANG, X., A., AND KOSTECKI, P. T. (1989). How much soil do young children ingest: An epidemiologic
study. Regul. Toxicol. Pharmacol. 10, 123-l 31. E. J., STANEK, E. J., AND GILBERT, C. E. ( 199 1). Evidence of soil-pica behavior and quantification of soil ingested. Hum. Exp. Toxicol. 10,245-249.
CALABRESE,