TABLE OF CONTENTS

5. SOIL INGESTION AND PICA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 5.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 5.2 SOIL INTAKE STUDIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3 5.2.1 Key Studies of Primary Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3 5.2.1.1 Davis et al. , 1990 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3 5.2.1.2 Calabrese et al. , 1997a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5 5.2.1.3 Davis and Mirick, 2006 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7 5.2.2 Relevant Studies of Primary Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8 5.2.2.1 Binder et al. , 1986 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8 5.2.2.2 Clausing et al. , 1987 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10 5.2.2.3 Calabrese et al. , 1989 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11 5.2.2.4 Van Wïjnen et al. , 1990 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13 5.2.2.5 Calabrese et al., 1996 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14 5.2.2.6 Calabrese et al., 1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15 5.2.2.7 Stanek and Calabrese, 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15 5.2.2.8 Stanek et al. , 2001b . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15 5.2.3 Key Studies of Secondary Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-16 5.2.3.1 Stanek and Calabrese, 1995a . . . . . . . . . . . . . . . . . . . . . . . . . 5-16 5.2.3.2 Stanek and Calabrese, 1995b . . . . . . . . . . . . . . . . . . . . . . . . . 5-18 5.2.4 Relevant Studies of Secondary Analysis . . . . . . . . . . . . . . . . . . . . . . . 5-19 5.2.4.1 Thompson and Burmaster, 1991 . . . . . . . . . . . . . . . . . . . . . . 5-19 5.2.4.2 Calabrese and Stanek, 1992a . . . . . . . . . . . . . . . . . . . . . . . . . 5-20 5.2.4.3 Sedman and Mahmood , 1994 . . . . . . . . . . . . . . . . . . . . . . . . 5-21 5.2.4.4 Calabrese and Stanek, 1995 . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22 5.2.4.5 Stanek et al. , 2001a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-23 5.2.4.6 Zartarian et al. , 2005 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24 5.3 PICA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25 5.3.1 Prevalence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25 5.3.1.1 General Pica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25 5.3.1.2 Soil Pica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25 5.3.2 Soil Pica Among Children . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26 5.3.2.1 Calabrese et al. , 1991 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26 5.3.2.2 Calabrese and Stanek, 1992b . . . . . . . . . . . . . . . . . . . . . . . . . 5-27 5.3.2.3 Calabrese and Stanek, 1993 . . . . . . . . . . . . . . . . . . . . . . . . . . 5-27 5.3.2.4 Zartarian et al. , 2005 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29 5.4 RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29 5.5 REFERENCES FOR CHAPTER 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-33LIST OF TABLES Table 5-1. Average Daily Soil Ingestion Values Based on Aluminum, Silicon, and Titanium as Tracer Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-37 Table 5-2. Soil Ingestion Estimates for the Median of Best Four Trace Elements Based on Food/Soil Ratios for 64 Anaconda Children (mg/day) Using Al, Si, Ti, Y, and Zr . . 5-37 Table 5-3. Dust Ingestion Estimates for the Median of Best Four Trace Elements Based on Food/Dust Ratios for 64 Anaconda Children (mg/day) Using Al, Si, Ti, Y, and Zr . . 5-38 Table 5-4. Mean and Median Soil Ingestion (mg/day) by Family Member . . . . . . . . . . . . . . 5-38 Table 5-5. Estimated Daily Soil Ingestion Based on Aluminum, Silicon, and Titanium Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-39 Table 5-6. Calculated Soil Ingestion by Nursery School Children . . . . . . . . . . . . . . . . . . . . 5-40 Table 5-7. Calculated Soil Ingestion by Hospitalized, Bedridden Children . . . . . . . . . . . . . . 5-41

Table 5-8. Mean and Standard Deviation Percentage Recovery of Eight Tracer Elements . . 5-41 Table 5-9. Soil and Dust Ingestion Estimates for Children Ages 1-4 Years . . . . . . . . . . . . . 5-42 Table 5-10. Geometric Mean (GM) and StandardDeviation (GSD) LTM Values for Children at Daycare Centers and Campgrounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-43

Table 5-11. Estimated Geometric Mean Ltm Values of Children Attending Daycare Centers According to Age, Weather Category, and Sampling Period . . . . . . . . . . . . . . . . . . . 5-44 Table 5-12. Distribution of Average (Mean) Daily Soil Ingestion Estimates per Child for 64 Children (mg/day) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-45

Table 5-13. Estimated Distribution of Individual Mean Daily Soil Ingestion Based on Data for 64 Subjects Projected over 365 Days

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-45 Table 5-14. Summary Statistics and Parameters for Distributions of Estimated Soil Ingestion by Tracer Elementa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-46 Table 5-15. Positive/negative Error (Bias) in Soil Ingestion Estimates in the Calabrese et al. (1989) Mass-balance Study: Effect on Mean Soil Ingestion Estimate (Mg/day) a . . . 5-47 Table 5-16. Daily Soil Ingestion Estimation in a Soil-Pica Child by Tracer and by Week (mg/day) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-48Table 5-17. Ratios of Soil, Dust, and Residual Fecal Samples in the Soil Pica Child . . . . . . 5-49 Table 5-18. Daily Variation of Soil Ingestion by Children Displaying Soil Pica in Wong (1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-50 Table 5-19 Key Studies Used to Derive Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . 5-51 Table 5- 20 . Summary of Estimates of Incidental Soil and Dust Ingestion by Children (1-7 years old) from Key Studies (mg/day) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-52 Table 5-21. Summary of Recommended Values for Soil Ingestion . . . . . . . . . . . . . . . . . . . . 5-53

Table 5-22. Confidence in Soil Intake Recommendation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-545-1 

### 5. SOIL INGESTION AND PICA 1 2 

### 5.1 INTRODUCTION 3 4 The ingestion of soil is a potential source of human exposure to toxicants. Some people 5 are surprised to learn that soil ingestion occurs at all, and others are surprised to learn that some 6 people ingest soil intentionally, due to cravings or cultural practices. Children may ingest 7 significant quantities of soil, due to their tendency to play on floors and on the ground outdoors 8 and due to their mouthing behaviors. 9 At this point in time, knowledge of soil ingestion patterns within the United States is 10 somewhat limited. Only a few researchers in the U.S. have attempted to quantify soil ingestion 11 patterns in children, and these researchers have performed studies in only a few locales in the 12 northern parts of the United States. Based on the information that we do have, it appears that 13 children may ingest fairly substantial amounts of soil on a per-kilogram-body-weight basis, and 14 could receive a large proportion of their total exposure to certain toxicants via the soil ingestion 15 route. Thus, understanding soil ingestion patterns is an important part of understanding, and 16 estimating, children’s overall exposures to environmental toxicants. 17 The Centers for Disease Control and Prevention's Agency for Toxic Substances and 18 Disease Registry (ATSDR) held a workshop in June 2000 in which a panel of soil ingestion 19 experts developed definitions for soil ingesti on, soil-pica, and geophagy, to distinguish aspects 20 of soil ingestion patterns that are important from a research perspective (ATSDR 2001): 21 22 Soil ingestion is the consumption of soil. This may be intentional or unintentional, resulting 23 from various behaviors including, but not limite d to, mouthing, contacting dirty hands, eating 24 dropped food, or consuming soil directly. 25 26 Soil ingestion, as defined above, has been documented in U.S. children in several studies 27 that use a "tracer element" methodology. The tracer element methodology attempts to quantify 28 amounts of soil ingested by analyzing samples of soil from childrens' residences, and by 29 analyzing samples of the childrens' excreta (feces , and sometimes also urine). The soil, fecal, 30 and urine samples are analyzed for the presence and quantity of tracer elements - typically, 315-2 aluminum, silicon, titanium, and yttrium, and other elements. Because these metals/metalloids 1 are not metabolized into other substances in the body, their presence in feces and urine can be 2 used to estimate the quantity of soil ingested by mouth. None of the studies attempt to quantify 3 amounts excreted in perspiration, tears, glandular s ecretions, hair or nails. Early versions of this 4 methodology usually did not account for the contribution of tracer elements from non-soil 5 substances (food, medications, and non-food sources such as toothpaste) that children might 6 swallow. Later studies generally account for tracer element contributions from these non-soil 7

sources. 8 Some study authors adjust their soil ingestion estimate results to account for the potential 9 contribution of tracer elements found in household dust as well as soil. Dust is the fine 10 particulate found indoors. It is composed of particles derived from outdoor sources such as soils, 11 smoke, pollen, etc. and indoor sources such as particles associated with construction activities, 12 wood burning, clothes drying, molds, etc. Dust ingestion can occur from inhalation, deposition 13 in the respiratory system and subsequent ingestion. 14 15 Soil-pica is a form of soil ingestion that is characterized by the recurrent ingestion of unusually 16 high amounts of soil (i.e., on the order of 1,000 - 5,000 milligrams per day). The soil ingestion 17 may be intentional or unintentional. 18 19 Soil-pica, as defined above, has been documented in U.S. children with the same tracer 20 element methodology, but to a more limited extent (Calabrese et al., 1991), and documented in 21 Jamaican children (Wong 1988 as reported in Calabrese and Stanek 1993). The existing U.S. 22 studies on soil ingestion, which appear to include some study subjects who exhibited soil-pica 23 behavior, were of short duration, and had relatively small numbers of study participants. These 24 factors combined may obscure the true incidence of soil-pica in the population of U.S. children. 25 Groups at risk of soil-pica behavior include children aged 6 years and younger and individuals 26 who are developmentally delayed. It should be noted that pica behavior is not always associated 27 with developmentally impaired children and that pica behavior is observed in 50% of children 28 between 1 and 3 years of age (Sayetta, 1986). 29 305-3 Geophagy is a form of soil ingestion defined as the intentional ingestion of earths and is usually 1 associated with cultural practices. 2 3 Geophagy is practiced in various places in the United States by members of various 4 cultural groups. It often involves the intentional ingestion of clay materials from 5 uncontaminated sources that are not surface soils (ATSDR 2001, Vermeer and Frate, 1979). 6 However, because geophagy is defined above as the intentional ingestion of clay or earths, and 7 because determining whether a child's soil ingestion is intentional or not is difficult (ATSDR 8 2001), geophagy is not included as a separate concept in the rest of this chapter. 9 The available studies on soil intake are summarized in the following sections. Some of 10 the later studies are re-analyses of data previously published. For this reason, the sections that 11 follow are organized into studies of primary analysis and studies of secondary analysis. Within 12 those two categories, there are studies considered "key" because their experimental design is 13 superior, or they are the only studies with a particular attribute needed for the recommendations. 14 The studies not categorized as "key" are categorized as "relevant" either because they are based 15 on foreign data or because of limitations in the experimental design (e.g., not accounting for 16 tracers found in food and medicines). Recommended soil intake rates are based on the results of 17 key studies and are summarized in the last section, along with additional guidance to risk 18 assessors using soil intake estimates. 19 20 

### 5.2 SOIL INTAKE STUDIES 21 5.2.1 Key Studies of Primary Analysis 22 5.2.1.1 Davis et al. , 1990 23 Davis et al. (1990) used a mass-balance/tracer technique to estimate soil ingestion among 24 children. In this study, 104 children between the ages of 2 and 7 years were randomly selected 25 from a three-city area in southeastern Washington State. The study was conducted over a seven 26 day period, primarily during the summer. Daily soil ingestion was evaluated by analyzing soil 27 and house dust, feces, urine, and duplicate food samples for aluminum, silicon, and titanium. In 28 addition, information on dietary habits and demographics was collected in an attempt to identify 29 behavioral and demographic characteristics that influence soil intake rates among children. The 30 amount of soil ingested on a daily basis was estimated using the following equation: 315-4 (5-2)

where: 1 S i,e = soil ingested for child ibased on tracer e(g); 2 DWf = feces dry weight (g); 3 DWp = feces dry weight on toilet paper (g); 4 Ef = tracer amount in feces (μg/g); 5 Eu = tracer amount in urine (μg/g); 6 DWfd = food dry weight (g); 7 Efd = tracer amount in food (μg/g); and 8 E soil = tracer concentration in soil (μg/g). 9 10 The soil intake rates were corrected by adding the amount of tracer in vitamins and medications 11 to the amount of tracer in food, and adjusting the food quantities, feces dry weights, and tracer 12 concentrations in urine to account for missing samples. 13 Soil ingestion rates were highly variable, especially those based on titanium. Mean daily 14 soil ingestion estimates were 38.9 mg/day for aluminum, 82.4 mg/day for silicon and 15 245.5 mg/day for titanium (Table 5-1). Median values were 25 mg/day for aluminum, 59 16 mg/day for silicon, and 81 mg/day for titanium. The investigators also evaluated the extent to 17 which differences in tracer concentrations in house dust and yard soil impacted estimated soil 18 ingestion rates. The value used in the denominator of the mass balance equation was 19 recalculated to represent a weighted average of the tracer concentration in yard soil and house 20 dust based on the proportion of time the child spent indoors and outdoors. The adjusted mean 21 soil/dust intake rates were 64.5 mg/day for aluminum, 160.0 mg/day for silicon, and 268.4 22 mg/day for titanium. Adjusted median soil/dust intake rates were: 51.8 mg/day for aluminum, 23 112.4 mg/day for silicon, and 116.6 mg/day for titanium. The investigators also observed that 24 the following demographic characteristics were associated with high soil intake rates: male sex, 25 racial groups other than white, low income, operator/laborer as the principal occupation of the 26 parent, and city of residence. However, none of these factors were predictive of soil intake rates 27 when tested using multiple linear regression. 285-5 The advantages of this study are that soil intake rates were corrected based on the tracer 1 content of foods and medicines and that a relatively large number of children were sampled. 2 Also, demographic and behavioral information was collected for the survey group. However, 3 although a relatively large sample population was surveyed, these children were all from a single 4 area of the U.S. and may not be representative of the U.S. population as a whole. The study was 5 conducted over a one-week period during the summer and may not be representative of long6 term (i.e., annual) patterns of intake. 7 8 5.2.1.2 Calabrese et al. 1997a 9 Calabrese et al. (1997a) estimated soil ingestion rates for children residing on a 10 Superfund site using a mass-balance methodology in which eight tracer elements (i.e., 11 aluminum, barium, manganese, silicon, titanium, vanadium, yttrium, and zirconium) were 12 analyzed. The methodology used in this study is similar to that employed in Calabrese et al. 13 (1989). As in Calabrese et al. (1989), 64 children ages 1-3 years and predominantly from 14 two-parent households were selected for this study. This stratified simple random sample of 15 children was selected from the Anaconda, MT area. Thirty-six of the 64 children were male, and 16 the children ranged in age from 1 to 3 years with approximately an equal number of children in 17 each age group. The study was conducted for seven consecutive days during a two week period 18 in the month of September. Duplicate samples of meals, beverages, and over- the-counter 19 medicines and vitamins were collected over the seven day period, along with fecal samples. In 20 addition, soil and dust samples were collected from the children’s home and play areas. 21 Toothpaste containing nondetectable levels of the tracer elements, with the exception of silica, 22 was provided to all of the children. Infants were provided with baby cornstarch, diaper rash 23 cream, and soap which were found to contain low levels of tracer elements. 24 As in Calabrese et al. (1989), an additional study was conducted in which the identical 25 mass-balance methodology used to estimate soil ingestion rates among children was used on 26 adults in order to validate that soil ingestion could be detected. Known amounts of soil were 27 administered to ten adults (5 males, 5 females) from Western Massachusetts over a period of 28 28 days. Each adult ingested for 7 consecutive days: 1) no soil during Week 1, 2) 20 mg of 29 sterilized soil during Week 2, 3) 100 mg of sterilized soil during Week 3, and 4) 500 mg of 30 sterilized soil during Week 4. Soil samples were previously characterized and were of sufficient 315-6 concentration to be detected in the analysis of fecal samples. Duplicate food and fecal samples 1 were collected every day during each study week and analyzed for the eight tracer elements (Al, 2 Si, Ti, Ce, La, Nd, Y, and Zr). The authors determined that a soil ingestion of 200 to 500 mg/day 3 could be detected in a reliable manner. 4 Calabrese et al. (1997a) estimated soil ingestion by each tracer element using the Best 5 Tracer Method (BTM), which allows for the selection of the most recoverable tracer for a 6 particular group of subjects (Stanek and Calabrese, 1995b). In this case Ba, Mn, and V were 7 dropped as they were found to be poor performing tracers. The median soil ingestion estimates 8 for the four best trace elements based on food/soil ratios for the 64 children using Al, Si, Ti, Y, 9 and Zr were presented (Table 5-2). The best estimate was calculated by taking the median of the 10 best four trace elements. Based on the soil ingestion estimate for the best tracer, the mean soil 11 ingestion rate was 66 mg/day and the median was 20 mg/day. The 95th percentile value was 12 283 mg/day. Using the median of the 4 best tracers, the mean was 7 mg/day and the 95th 13 percentile was 160 mg/day. These results are lower than the soil ingestion estimates obtained by 14 Stanek and Calabrese (1995a). Calabrese et al. (1997a) believe this may be due to the fact that 15 the families of the children who participated in this study were aware that they lived on an EPA 16 Superfund site and this knowledge might have resulted in reduced exposure. There was no 17 statistically significant difference found in soil ingestion estimates by gender or age. There was 18 also no significant difference in soil ingestion by housing or yard characteristics (i.e., porch, 19 deck, door mat, etc.), or between children with or without pets. 20 The median dust ingestion estimates for the f our best tracer elements using Al, Si, Ti, Y, 21 and Zr were also presented (Table 5-3). The estimate is based on food/dust ratios for the 64 22 Anaconda children. The mean dust ingestion rate based on the best tracer was 127 mg/day and 23 the 95th percentile rate was 614 mg/day. 24 The advantages of this study were the use of a longer 7 consecutive day study period 25 rather than two periods of 3 and 4 days (Stanek and Calabrese, 1995a), the use of the BTM, the 26 use of an expanded adult validation study which used 10 volunteers rather than 6 (Calabrese et 27 al. , 1989), and the use of a dietary education program to reduce food tracer input and variability. 28 However, the data presented in this study are from a single 7-day period during September which 29 may not reflect soil ingestion rates for other months or time-periods. In addition, the study 30 displayed a net residual negative error, which may have resulted in underestimated soil ingestion 315-7 rates. The authors believe that this error is not likely to affect the median by more than 40 1 mg/day. 2 3 5.2.1.3 Davis and Mirick, 2006 4 Davis and Mirick (2006) calculated soil ingestion for children and adults in the same 5 family using a mass balance approach. The families in this study were a subset of the 104 6 families who participated in the soil ingestion study by Davis et al. (1990), and the data were 7 collected in 1988, one year prior to the Davis et al. study. Nineteen families were selected for 8 the analyses in this study, and each consisted of a child participant between the age of 3 and 7, a 9 female, and a male parent or guardian living in the same house. Samples were collected for 11 10 consecutive days of all food items consumed, all feces excreted, twice-daily urine, and soil/house 11 dust. Tracer elements for this study included aluminum, silicon and titanium. In addition, 12 parents completed a daily diary of activities for themselves and the participant child for 4 13 consecutive days during the study period. 14 Soil ingestion rates are shown for all three family member participants in Table 5-4. The 15 mean and median estimates for children for all three tracers ranged from 36.7 to 206.9 mg/day 16 and 26.4 to 46.7 mg/day, respectively, and fall within the range of those reported by Davis et al. , 17 1990. Adult soil ingestion estimates ranged from 23.2 to 624.9 mg/day for mean values and 18 from 0 to 259.5 mg/day for median values, and were more variable than for the children in the 19 study regardless of the tracer. The authors believed that this higher variability may have 20 indicated an important occupational contribution of soil ingestion in some, but not all, of the 21 adults. Similar to previous studies, the soil ingestion estimates were the highest for titanium. 22 Although toothpaste is a known source of titanium, the titanium content of the toothpaste used 23 by study participants was not determined. 24 Only three of a number of behaviors examined for their relationship to soil ingestion 25 were found to be associated with increased soil ingestion in this study: 26 27 • reported eating of dirt (for children); 28 • occupational contact with soil (for adults); and 29 • hand washing before meals (for both children and adults). 30 315-8 

### T f F s i,e i,e i i,e 

### = × (5-1) Several typical childhood behaviors, however, including thumb-sucking, furniture licking, and 1 carrying around a blanket or toy were not associated with increased soil ingestion for the 2 participating children. Among both parents and children, neither nail-biting nor eating unwashed 3 fruits or vegetables was correlated with increased soil ingestion. When investigating correlations 4 within the same family, a child’s soil ingestion was not found to be associated with either 5 parent’s soil ingestion, nor did the mother and father’s soil ingestion appear to be correlated. 6 One advantage of this study is that it examines soil ingestion among family members, 7 both children and adults. However, the sample population was small. In addition, the families 8 were a subset of those in a previous study, chosen for their high compliance with the study 9 protocol, and as such may not be representative of the general population. 10 11 5.2.2. Relevant Studies of Primary Analysis 12 5.2.2.1 Binder et al. , 1986 13 Binder et al. (1986) used a tracer technique modified from a method previously used to 14 measure soil ingestion among grazing animals to study the ingestion of soil among children 1 to 15 3 years of age who wore diapers. The children were studied during the summer of 1984 as part 16 of a larger study of residents living near a lead smelter in East Helena, Montana. Soiled diapers 17 were collected over a 3-day period from 65 children (42 males and 23 females), and composited 18 samples of soil were obtained from the children's yards. Both excreta and soil samples were 19 analyzed for aluminum, silicon, and titanium. These elements were found in soil but were 20 thought to be poorly absorbed in the gut and to have been present in the diet only in limited 21 quantities. This made them useful tracers for estimating soil intake. Excreta measurements were 22 obtained for 59 of the children. Soil ingestion by each child was estimated on the basis of each 23 of the three tracer elements using a standard assumed fecal dry weight of 15 g/day, and the 24 following equation: 25 26

where: 27 Ti,e = estimated soil ingestion for child i based on elemente(g/day); 285-9 f i,e = concentration of element ein fecal sample of child i (mg/g); 1 Fi = fecal dry weight (g/day); and 2 S i,e = concentration of element ein child i 's yard soil (mg/g). 3 4 The analysis assumed that (1) the tracer elements were neither lost nor introduced during sample 5 processing; (2) the soil ingested by children originates primarily from their own yards; and (3) 6 that absorption of the tracer elements by children occurred in only small amounts. The study did 7 not distinguish between ingestion of soil and housedust, nor did it account for the presence of the 8 tracer elements in ingested foods or medicines. 9 The arithmetic mean quantity of soil ingested by the children in the Binder et al. 10 (1986) study was estimated to be 181 mg/day (range 25 to 1,324) based on the aluminum tracer; 11 184 mg/day (range 31 to 799) based on the silicon tracer; and 1,834 mg/day (range 4 to 17,076) 12 based on the titanium tracer (Table 5-5). The overall mean soil ingestion estimate, based on the 13 minimum of the three individual tracer estimates for each child, was 108 mg/day (range 4 to 14 708). The median values were 121 mg/day, 136 mg/day, and 618 mg/day for aluminum, silicon, 15 and titanium, respectively. The 95th percentile values for aluminum, silicon, and titanium were 16 584 mg/day, 578 mg/day, and 9,590 mg/day, respectively. The 95th percentile value based on 17 the minimum of the three individual tracer estimates for each child was 386 mg/day. 18 The authors were not able to explain the difference between the results for titanium and 19 for the other two elements, but they speculated that unrecognized sources of titanium in the diet 20 or in the laboratory processing of stool samples may have accounted for the increased levels. 21 The frequency distribution graph of soil ingestion estimates based on titanium shows that a 22 group of 21 children had particularly high titanium values (i.e., >1,000 mg/day). The remainder 23 of the children showed titanium ingestion estimates at lower levels, with a distribution more 24 comparable to that of the other elements. 25 The advantages of this study are that a relatively large number of children were studied 26 and tracer elements were used to estimate soil ingestion. However, the children studied may not 27 be representative of the U.S. population, and the study did not account for tracers ingested via 28 foods or medicines. Also, the use of an assumed fecal weight instead of actual fecal weights 29 may have biased the results of this study. Finally, because of the short-term nature of the survey, 30 soil intake estimates may not be entirely representative of long-term behavior, especially at the 31 upper end of the distribution of intake. 325-10 5.2.2.2 Clausing et al. , 1987 1 Clausing et al. (1987) conducted a soil ingestion study with Dutch children using a tracer 2 element methodology similar to that of Binder et al. (1986). Aluminum, titanium, and 3 acid-insoluble residue (AIR) contents were determined for fecal samples from children aged 2 to 4 4 years attending a nursery school and for sample s of playground dirt at that school. Twenty5 seven daily fecal samples were obtained over a 5-day period for the 18 children examined. 6 Using the average soil concentrations present at the school, and assuming a standard fecal dry 7 weight of 10 g/day, soil ingestion was estimated for each tracer. Eight daily fecal samples were 8 also collected from six hospitalized, bedridden children. These children served as a control 9 group, representing children who had very limited access to soil. 10 The average quantity of soil ingested by the school children in this study was as follows: 11 230 mg/day (range 23 to 979 mg/day) for aluminum; 129 mg/day (range 48 to 362 mg/day) for 12 AIR; and 1,430 mg/day (range 64 to 11,620 mg/day) for titanium (Table 5-6). As in the Binder 13 et al. (1986) study, a fraction of the children (6/19) showed titanium values well above 14 1,000 mg/day, with most of the remaining children showing substantially lower values. Based 15 on the Limiting Tracer Method (LTM), mean soil intake was estimated to be 105 mg/day with a 16 population standard deviation of 67 mg/day (range 23 to 362 mg/day). Use of the LTM assumed 17 that "the maximum amount of soil ingested corresponded with the lowest estimate from the three 18 tracers" (Clausing et al. , 1987). Geometric mean soil intake was estimated to be 90 mg/day on 19 the assumption that the maximum amount of soil ingested cannot be higher than the lowest 20 estimate for the individual tracers. 21 Mean (arithmetic) soil intake for the hospitalized children was estimated to be 56 mg/day 22 based on aluminum (Table 5-7). For titanium, three of the children had estimates well in excess 23 of 1,000 mg/day, with the remaining three children in the range of 28 to 58 mg/day. Using the 24 LTM method, the mean soil ingestion rate was estimated to be 49 mg/day with a population 25 standard deviation of 22 mg/day (range 26 to 84 mg/day). The geometric mean soil intake rate 26 was 45 mg/day. The data on hospitalized children suggest a major nonsoil source of titanium for 27 some children and may suggest a background nonsoil source of aluminum. However, conditions 28 specific to hospitalization (e.g., medications) were not considered. AIR measurements were not 29 reported for the hospitalized children. Assuming that the tracer-based soil ingestion rates 30 observed in hospitalized children actually represent background tracer intake from dietary and 315-11 other nonsoil sources, mean soil ingestion by nursery school children was estimated to be 1 56 mg/day, based on the LTM (i.e., 105 mg/day for nursery school children minus 49 mg/day for 2 hospitalized children). 3 The advantages of this study are that the investigators evaluated soil ingestion among two 4 populations of children that had differences in access to soil and corrected soil intake rates based 5 on background estimates derived from the hospitalized group. However, a smaller number of 6 children were used in this study than in the Binder et al. (1986) study and these children may not 7 be representative of the U.S. population. Tracer elements in foods or medicines were not 8 evaluated. Also, intake rates derived from this study may not be representative of soil intake 9 over the long-term because of the short-term nature of the study. In addition, one of the factors 10 that could affect soil intake rates is hygiene (e.g., hand washing frequency). Hygienic practices 11 can vary across countries and cultures and may be more stringently emphasized in a more 12 structured environment such as that found in child care centers in The Netherlands and other 13 European countries, compared to child care centers in the U.S. 14 15 5.2.2.3 Calabrese et al. , 1989 16 Calabrese et al. (1989) studied soil ingestion among children using the basic tracer design 17 developed by Binder et al. (1986). However, in contrast to the Binder study, eight tracer 18 elements—aluminum, barium, manganese, silicon, titanium, vanadium, yttrium, and 19 zirconium— were analyzed instead of only three (aluminum, silicon, and titanium). Sixty-four 20 children between the ages of 1 and 4 years old were included in the study. These children were 21 all selected from the greater Amherst, MA area and were predominantly from two-parent 22 households where the parents were highly educated. The Calabrese et al. (1989) study was 23 conducted over a period of eight days to two weeks and included the use of a mass-balance 24 methodology in which duplicate samples of food, beverages, medicines, and vitamins were 25 collected and analyzed in addition to soil and dust samples collected from the child’s home and 26 play area. Fecal and urine samples were also collected and analyzed for tracer elements. 27 In order to validate the mass-balance methodology used to estimate soil ingestion rates 28 among the children and to determine which tracer elements provided the most reliable data on 29 soil ingestion, known amounts of soil (300 mg over 3 days and 1,500 mg over 3 days) containing 30 eight tracers were administered to six adult volunteers (three males and three females). Soil, 315-12 feces, and samples of food were analyzed for tracer elements to calculate recovery rates of tracer 1 elements in soil. From this investigation the authors confirmed that the tracer methodology 2 could adequately detect tracer elements in feces at the levels expected for the study of soil intake 3 rates in children. Aluminum, silicon, and yttrium exhibited the lowest standard deviation of 4 recovery and were therefore identified as the most reliable of the eight tracer elements analyzed; 5 the percentage of recovery of these three tracers was closest to 100%. The recovery of these 6 three tracers ranged from 120 to 153 percent when 300 mg of soil had been ingested over a 7 three-day period and from 88 to 94 percent when 1,500 mg soil had been ingested over a three8 day period (Table 5-8). 9 Using the three most reliable tracer elements, the mean soil intake rate for children, 10 adjusted to account for the amount of tracer found in food and medicines, was estimated to be 11 153 mg/day based on aluminum, 154 mg/day based on silicon, and 85 mg/day based on yttrium 12 (Table 5-5). Median intake rates were somewhat lower (29 mg/day for aluminum, 40 mg/day for 13 silicon, and 9 mg/day for yttrium). Upper (95 th) percentile values were 223 mg/day for 14 aluminum, 276 mg/day for silicon, and 106 mg/day for yttrium. Similar results were observed 15 when soil and dust ingestion was combined (Table 5-9). Intake of soil and dust was estimated 16 using a weighted ingestion for one child in the study ranged from approximately 10 to 17 14 grams/day during the second week of observation. Average soil ingestion for this child was 18 5 to 7 mg/day, based on the entire study period. 19 In a subsequent paper (Calabrese and Stanek, 1992a), the authors used statistical 20 modeling to revise these soil ingestion estimates downward, based on a more accurate 21 representation of the amount of outdoor soil in indoor dust (31.3%). These new analyses 22 indicate that the estimates of median outdoor soil ingestion presented in the previous study 23 should be reduced by 35%. These revised soil ingestion estimates are reduced from 29 to19 24 mg/d based on aluminum, 40 to 26 mg/d based on silicon, and 9 to 6 mg/d based on yttrium. 25 However, this adjustment was not used in subsequent analyses by Stanek and Calabrese. 26 The advantage of this study is that intake rates were corrected for tracer concentrations 27 in foods and medicines . Also, intake was observed over a longer time period in this study than 28 in earlier studies and the number of tracers used was larger than for other studies. A relatively 29 large population was studied, but it may not be entirely representative of the U.S. population 305-13 because it was selected from a single location. The results presented in Calabrese et al. 1989 1 have been superseded by more refined analyses of the same data. 2 3 5.2.2.4 Van Wïjnen et al. , 1990 4 In a study by Van Wïjnen et al. (1990), soil ingestion among Dutch children ranging in 5 age from 1 to 5 years was evaluated using a tracer element methodology similar to that used by 6 Clausing et al. (1987). Van Wïjnen et al. (1990) measured three tracers (i.e., titanium, 7 aluminum, and acid insoluble residue (AIR)) in soil and feces and estimated soil ingestion based 8 on the LTM. An average daily feces dry weight of 15 g was assumed. A total of 292 children 9 attending daycare centers were sampled during the first of two sampling periods and 187 10 children were sampled in the second sampling period; 162 of these children were sampled during 11 both periods (i.e., at the beginning and near the end of the summer of 1986). A total of 78 12 children were sampled at campgrounds, and 15 hospitalized children were sampled. The mean 13 values for these groups were: 162 mg/day for children in daycare centers, 213 mg/day for 14 campers and 93 mg/day for hospitalized children. 15 The authors also reported geometric mean LTM values because soil intake rates were 16 found to be skewed and the log transformed data were approximately normally distributed. 17 Geometric mean LTM values were estimated to be 111 mg/day for children in daycare centers, 18 174 mg/day for children vacationing at campgrounds (Table 5-10) and 74 mg/day for 19 hospitalized children (70-120 mg/day based on the 95 percent confidence limits of the mean). 20 AIR was the limiting tracer in about 80 percent of the samples. Among children attending 21 daycare centers, soil intake was also found to be higher when the weather was good (i.e., <2 22 days/week precipitation) than when the weather was bad (i.e., >4 days/week precipitation (Table 23 5-11). The authors suggest that the mean LTM value for hospitalized infants represents 24 background intake of tracers and should be used to correct the soil intake rates based on LTM 25 values for other sampling groups. Using mean values, corrected soil intake rates were 69 mg/day 26 (162 mg/day minus 93 mg/day) for daycare children and 120 mg/day (213 mg/day minus 93 27 mg/day) for campers. Corrected geometric mean soil intake was estimated to range from 0 to 90 28 mg/day with a 90th percentile value of 190 mg/day for the various age categories within the 29 daycare group and 30 to 200 mg/day with a 90th percentile value of 300 mg/day for the various 30 age categories within the camping group. 315-14 The advantage of this study is that soil intake was estimated for three different 1 populations of children; one expected to have high intake, one expected to have "typical" intake, 2 and one expected to have low or background-level intake. Van Wïjnen et al. (1990) used the 3 background tracer measurements to correct soil intake rates for the other two populations. The 4 major limitation of this study is that tracer concentrations in food and medicine were not 5 evaluated. Also, the population of children studied was relatively large, but may not be 6 representative of the U.S. population. This study was conducted over a relatively short time 7 period. Thus, estimated intake rates may not reflect long-term patterns, especially at the high8 end of the distribution. Another limitation of this study is that values were not reported element9 by-element, which would be the preferred way of reporting. In addition, one of the factors that 10 could affect soil intake rates is hygiene (e.g., hand washing frequency). Hygienic practices can 11 vary across countries and cultures. 12 13 5.2.2.5 Calabrese et al. 1996 14 Calabrese et al. , 1996 examined the hypothesis that one cause of the variation between 15 tracers seen in soil ingestion studies could be related to differences in soil tracer concentrations 16 by particle size. In this study, the soil that was used by Calabrese et al. 1997a from Anaconda, 17 Montana was reanalyzed for the tracer concentration after it had been sieved to a particle size of 18 <250 μm in diameter (<2 mm soil particle size in the original study). The smaller particle size 19 was examined based on the assumption that children and adults principally ingest soil of small 20 particle size adhering to fingertips and under fingernails. For five of the tracers used in the 21 original study (Al, Si, Ti, Y, and Zr), soil concentration was not changed by particle size. 22 However, the soil concentrations of three tracers (La, Ce, and Nd) were increased two- to 23 fourfold at the smaller soil particle size. Soil ingestion estimates for these three tracers were 24 decreased by approximately 60% at the 95th percentile. 25 The importance of this study is that it provides further insights regarding the selection of 26 tracers for soil ingestion studies. 27 28 5.2.2.6 Calabrese et al. 1999 29 Calabrese et al. 1999 extends the findings from Calabrese et al. 1996 by quantifying trace 30 element concentrations in soil based on sieving to particle sizes of 100 to 250 μm and to particle 315-15 sizes of 53 to < 100 μm. This study used the data from soil concentrations from the Anaconda, 1 Montana site reported by Calabrese et al. 1997. Results of the study indicated that soil 2 concentrations of Al, Si, and Ti do not increase at the two finer particle size ranges measured. 3 However, soil concentrations of Ce, La, and Nd increased by a factor of 2.5 to 4.0 in the 100-250 4 μm particle size range when compared with the 0 to 2 μm particle size range. There was not a 5 significant increase in concentration in the 53 to 100 μm particle size range. 6 The importance of this study is that it provides further insights regarding the selection of 7 tracers for soil ingestion studies. 8 9 5.2.2.7 Stanek and Calabrese 2000 10 In Stanek and Calabrese, 2000, the authors reanalyzed the soil ingestion data from the 11 Anaconda study. The authors assumed a lognormal distribution for the soil ingestion estimates 12 in the Anaconda study to predict average soil ingestion for children over a longer time period. 13 Using best linear unbiased predictors, the authors predicted 95 thpercentile soil ingestion values 14 over time periods of 7 days, 30 days, 90 days, and 365 days. The 95 thpercentile soil ingestion 15 values were predicted to be 133 mg/day over 7 days, 112 mg/day over 30 days, 108 mg/day over 16 90 days, and 106 mg/day over 365 days. Based on this analysis, estimates of the distribution of 17 longer term average soil ingestion are expected to be narrower, with the 95 thpercentile estimates 18 being as much as 25% lower (Stanek and Calabrese, 2000). 19 20 5.2.2.8 Stanek et al. 2001b 21 Stanek et al. (2001b) developed best linear unbiased predictors to reduce the biasing 22 effect of short-term soil ingestion estimates. This study estimated long-term average soil 23 ingestion distribution using daily soil ingestion estimates from children who participated in the 24 Anaconda, MT study. In this long-term (annual) distribution, the soil ingestion estimates were: 25 mean 31, median 24, 75 thpercentile 42, 90 thpercentile 75, and 95 thpercentile 91 mg/day. A 26 limitation of this analysis is that the distribution of long-term soil ingestion uses the median soil 27 ingestion estimate on a day, rather than the average of the tracer element estimate. 28 29 5.2.3 Key Studies of Secondary Analysis 30 5.2.3.1 Stanek and Calabrese, 1995a 315-16 Stanek and Calabrese (1995a) presented a methodology which links the physical passage 1 of food and fecal samples to construct daily soil ingestion estimates from daily food and fecal 2 trace-element concentrations. Soil ingestion data for children obtained from the Amherst study 3 (Calabrese et al., 1989) were reanalyzed by Stanek and Calabrese (1995a). In the Amherst 4 study, soil ingestion measurements were made over a period of 2 weeks for a non-random 5 sample of sixty-four children (ages of 1-4 years old) living adjacent to a university in western 6 Massachusetts. During each week, duplicate food samples were collected for 3 consecutive days 7 and fecal samples were collected for 4 consecutive days for each subject. The total amount of 8 each of eight trace elements present in the food and fecal samples was measured. The eight trace 9 elements are aluminum, barium, manganese, silicon, titanium, vanadium, yttrium, and zirconium. 10 The authors expressed the amount of trace element in food input or fecal output as a "soil 11 equivalent," which was defined as the amount of the element in average daily food intake (or 12 average daily fecal output) divided by the concentration of the element in soil. A lag period of 13 28 hours between food intake and fecal output was assumed for all respondents. Day 1 for the 14 food sample corresponded to the 24 hour period from midnight on Sunday to midnight on 15 Monday of a study week; day 1 of the fecal sample corresponded to the 24 hour period from 16 noon on Monday to noon on Tuesday. Based on these definitions, the food soil equivalent was 17 subtracted from the fecal soil equivalent to obtain an estimate of soil ingestion for a trace 18 element. A daily overall ingestion estimate was constructed for each child as the median of trace 19 element values remaining after tracers falling outside of a defined range around the overall 20 median were excluded. Additionally, estimates of the distribution of soil ingestion projected 21 over a period of 365 days were derived by fitting log-normal distributions to the overall daily 22 soil ingestion estimates. 23 Table 5-12 presents the estimates of mean daily soil ingestion intake per child (mg/day) 24 for the 64 study participants. (The authors also presented estimates of the median values of daily 25 intake for each child. For most risk assessment purposes the child mean values, which are 26 proportional to the cumulative soil intake by the child, are needed instead of the median values.) 27 The approach adopted in this paper led to changes in ingestion estimates from those presented in 28 Calabrese et al. (1989). 29 Specifically, among elements that may be more useful for estimation of ingestion, the 30 mean estimates decreased for Al (153 mg/d to 122 mg/d) and Si ( 154 mg/d to 139 mg/d), but 315-17 increased for Ti (218 mg/d to 271 mg/d) and Y (85 mg/d to 165 mg/d). The overall mean 1 estimate from this reanalysis was 179 mg/d. Table 5-13 presents the empirical distribution of the 2 the “overall” mean daily soil ingestion estimates for the 8-day study period (not based on 3 lognormal modeling). The estimated intake based on the overall estimates is 45 mg/day or less 4 for 50 percent of the children and 208 mg/day or less for 95 percent of the children. The upper 5 percentile values for most of the individual trace elements are somewhat higher. Next, estimates 6 of the respondents soil intake averaged over a period of 365 days were presented based upon the 7 lognormal models fit to the daily ingestion estimates (Table 5-13). The estimated median value 8 of the 64 respondents' daily soil ingestion averaged over a year is 75 mg/day, while the 9 95th percentile is 1,751 mg/day. 10 A strength of this study is that it attempts to make full use of the collected data through 11 estimation of daily ingestion rates for children. The screening of data to remove less consistent 12 tracer estimates, and the aggregation of the remaining values, may introduce error to the 13 analysis. Individual daily estimates of ingestion will be subject to larger errors than are weekly 14 average values, particularly since the assumption of a constant lag time between food intake and 15 fecal output may be not be correct for many subj ect days. The aggregation approach used to 16 arrive at the overall ingestion estimates rests on the assumption that the mean ingestion estimates 17 across acceptable tracers provides the most reliable ingestion estimates. The validity of this 18 assumption depends on the particular set of tracers used in the study, and is not fully assessed. 19 In developing the 365-day soil ingestion estimates, data that were obtained over a short 20 period of time (as is the case with all available soil ingestion studies) were extrapolated over a 21 year. The 2-week study period may not reflect variability in tracer element ingestion over a year. 22 While Stanek and Calabrese (1995a) attempt to address this through lognormal modeling of the 23 long term intake, new uncertainties are introduced through the parametric modeling of the 24 limited subject day data. Also, the sample population size of the original study was small and 25 site limited, and, therefore, is not representative of the U.S. population. Study mean estimates of 26 soil ingestion, such as the study mean estimates presented in Table 5-12, are substantially more 27 reliable than any available distributional estimates. 28 29 5.2.3.2 Stanek and Calabrese, 1995b 305-18 Stanek and Calabrese (1995b) recalculated ingestion rates that were estimated in three 1 previous mass-balance studies (Calabrese et al. , 1989 and Davis et al. , 1990 for children's soil 2 ingestion, and Calabrese et al. , 1990 for adult soil ingestion) using the Best Tracer Method 3 (BTM). This method allows for the selection of the most recoverable tracer for a particular 4 subject or group of subjects. The selection process involves ordering trace elements for each 5 subject based on food/soil (F/S) ratios. These ratios are estimated by dividing the total amount 6 of the tracer in food by the tracer concentration in soil. The F/S ratio is small when the tracer 7 concentration in food is almost zero when compared to the tracer concentration in soil. A small 8 F/S ratio is desirable because it lessens the impact of transit time error (the error that occurs 9 when fecal output does not reflect food ingestion, dueto fluctuation in gastrointestinal transit 10 time) in the soil ingestion calculation. Because the recoverability of tracers can vary within any 11 group of individuals, the BTM uses a ranking scheme of F/S ratios to determine the best tracers 12 for use in the ingestion rate calculation. To reduce biases that may occur as a result of sources of 13 fecal tracers other than food or soil, the medianof soil ingestion estimates based on the four 14 lowest F/S ratios was used to represent soil ingestion among individuals. 15 For children, the authors used data on 8 tracers from Calabrese et al., 1989 and data on 3 16 tracers from Davis et al. (1990) to estimate soil ingestion rates. The median of the soil ingestion 17 estimates from the lowest four F/S ratios from the Calabrese et al. (1989) study most often 18 included Al, Si, Ti, Y, and Zr. Based on the median of soil ingestion estimates from the best 19 four tracers, the mean soil ingestion rate was 132 mg/day and the median was 33 mg/day. The 20 95th percentile value was 154 mg/day. These estimates are based on data for 128 subject weeks 21 for the 64 children in the Calabrese et al. (1989) study. For the 101 children in the Davis et al. 22 (1990) study, the mean soil ingestion rate was 69 mg/day and the median soil ingestion rate was 23 44 mg/day. The 95th percentile estimate was 246 mg/day. These data are based on the three 24 tracers (i.e., Al, Si, and Ti) from the Davis et al. (1990) study. When the Calabrese et al. (1989) 25 and Davis et al. (1990) studies were combined, soil ingestion for children was estimated to be 26 104 mg/day (mean); 37 mg/day (median); and 217 mg/day (95th percentile), using the BTM. 27 When the adult data from the Calabrese et al. (1990) study were reevaluated, soil 28 ingestion rates were estimated to be 64 mg/day (mean); 87 mg/day (median); and 142 mg/day 29 (95th percentile), using the BTM. 305-19 This study provides a reevaluation of previ ous studies. Its advantages are that it 1 combines data from two studies for children, one from Washington and one from Massachusetts, 2 which increases the number of observations. It also corrects for biases associated with the 3 differences in tracer metabolism. The limitations associated with the data used in this study are 4 the same as the limitations described in the summaries of the Calabrese et al. (1989), Davis et al. 5 (1990) and Calabrese et al. (1990) studies. 6 7 5.2.4. Relevant Studies of Secondary Analysis 8 5.2.4.1 Thompson and Burmaster, 1991 9 Thompson and Burmaster (1991) developed parameterized distributions of soil ingestion 10 rates for children based on a reanalysis of the key study data collected by Binder et al. (1986). 11 In the original Binder et al. (1986) study, an assumed fecal weight of 15 g/day was used. 12 Thompson and Burmaster reestimated the soil ingestion rates from the Binder et al. (1986) study 13 using the actual stool weights of the study partic ipants instead of the assumed stool weights. 14 Because the actual stool weights averaged only 7.5 g/day, the soil ingestion estimates presented 15 by Thompson and Burmaster (1991) are approximately one-half of those reported by Binder et 16 al. (1986). Table 5-11 presents the distribution of estimated soil ingestion rates calculated by 17 Thompson and Burmaster (1991) based on the three tracers elements (i.e., aluminum, silicon, 18 and titanium), and on the arithmetic average of soil ingestion based on aluminum and silicon. 19 The mean soil intake rates were 97 mg/day for aluminum, 85 mg/day for silicon, and 1,004 20 mg/day for titanium. The 90th percentile estimates were 197 mg/day for aluminum, 166 mg/day 21 for silicon, and 2,105 mg/day for titanium. Based on the arithmetic average of aluminum and 22 silicon for each child, mean soil intake was estimated to be 91 mg/day and 90th percentile intake 23 was estimated to be 143 mg/day. 24 Thompson and Burmaster (1991) tested the hypothesis that soil ingestion rates based on 25 the adjusted Binder et al. (1986) data for aluminum, silicon and the average of these two tracers 26 were lognormally distributed. The distribution of soil intake based on titanium was not tested for 27 lognormality because titanium may be present in food in high concentrations and the Binder et 28 al. (1986) study did not correct for food sources of titanium. Although visual inspection of the 29 distributions for aluminum, silicon, and the average of these tracers all indicated that they may 30 be lognormally distributed, statistical tests indicated that only silicon and the average of the 315-20 silicon and aluminum tracers were lognormally distributed. Soil intake rates based on aluminum 1 were not lognormally distributed. Table 5- 14 also presents the lognormal distribution 2 parameters and underlying normal distribution parameters (i.e., the natural logarithms of the 3 data) for aluminum, silicon, and the average of these two tracers. According to the authors, “the 4 parameters estimated from the underlying normal distribution are much more reliable and 5 robust” (Thompson and Burmaster, 1991). 6 The advantages of this study are that it provides percentile data and defines the shape of 7 soil intake distributions. However, the number of data points used to fit the distribution was 8 limited. In addition, the study did not generate “new” data. Instead, it provided a reanalysis of 9 previously-reported data using actual fecal weights. This analysis is based on a study that did 10 not correct for tracer intake from food or medicine and the results may not be representative of 11 long-term intake rates because the data were derived from a short-term study. 12 13 5.2.4.2 Calabrese and Stanek 1992a 14 Calabrese and Stanek 1992a estimated the amount of outdoor soil in indoor dust using 15 statistical modeling. The model used data from 60 homes who participated in the Calabrese et 16 al. 1989 study. Scatter plots of each tracer concentration in soil versus dust for the subject 17 population were developed. Correlation analysis of the scatter plots was performed and an 18 estimate of the proportion of outdoor soil in indoor dust was developed using a model based on 19 the soil and dust data from Calabrese et al. 1989. The scatter plots show little evidence of a 20 consistent relationship between outdoor soil and indoor dust concentrations. The model uses 21 several simplifying assumptions. First, it assumes that the amount of dust produced every day 22 from both indoor and outdoor sources in a house is constant for all houses. Second, the model 23 assumes that the proportion of indoor dust due to outdoor soil is constant for all houses. Third, it 24 assumes that the concentration of the tracer element in dust produced from indoor sources is 25 constant for all houses. Using these assumptions, the model predicts that 31.3% of indoor dust 26 comes from outdoor soil. This model was then used to adjust the soil ingestion estimates from 27 Calabrese et al. 1989. In 1989, Calabrese assumed that all the excess fecal tracers were of soil 28 origin. Stanek and Calabrese 1992a reported that 50% of the excess fecal tracers were from 29 indoor origin. Taking that 50% multiplied by 31.3% results in 15%; which added to the 50% 305-21 indicates that approximately 65% of the total residual excess fecal tracer were of soil origin 1 (Calabrese and Stanek 1992a). 2 This study provides a refinement to the calculations from Calabrese et al. 1989. 3 However, several assumptions were made to estimate the total residual excess fecal tracer that 4 comes from soil. The validity of these assumptions cannot be evaluated. Subsequent papers by 5 Stanek and Calabrese did not make use of this adjustment. 6 7 5.2.4.3 Sedman and Mahmood , 1994 8 Sedman and Mahmood (1994) used the results of two previous children’s tracer studies 9 (Calabrese et al. 1989; Davis et al. 1990) to determine estimates of average daily soil ingestion 10 in young children and for over a lifetime. In the two studies, the intake and excretion of a 11 variety of tracers were monitored, and concentrations of tracers in soil adjacent to the children’s 12 dwellings were determined. The authors determined soil ingestion in these children using a mass 13 balance approach, dividing the excess tracer intake (i.e., quantity of tracer recovered in the feces 14 in excess of the measured intake) by the average concentration of tracer in soil samples from 15 each child's dwelling. They adjusted the mean estimates of soil ingestion in children for each 16 tracer (Y) from both studies to reflect that of a 2-year old child using the following equation: 17 18 19 

### Y i 

### = − × 

### xe yr 0 112

. (5-3)

where: 20 Yi= adjusted mean soil ingestion (mg/day) 21

x = a constant 22 yr = average age (2 years) 23 24 The average ages of children in the two previous studies were 2.4 years in Calabrese 25 et al. (1989) and 4.7 years in Davis et al. (1990). The mean of the adjusted levels of soil 26 ingestion for a two year old child was 220 mg/kg for the Calabrese et al. (1989) study and 170 27 mg/kg for the Davis et al. (1990) study. From the adjusted soil ingestion estimates, based on a 28 normal distribution of means, the mean estimate for a 2-year old child was 195 mg/day and the 29 overall mean of soil ingestion and the standard error of the mean was 53 mg/day. Based on 30 uncertainties associated with the method employed, Sedman and Mahmood (1994) 315-22 recommended a conservative estimate of soil ingestion in young children of 250 mg/day. Based 1 on the 250 mg/day ingestion rate in a 2-year old child, an average daily soil ingestion over a 2 lifetime was estimated to be 70 mg/day. The lifetime estimates were derived using the equation 3 presented above that describes changes in soil ingestion with age. 4 5 5.2.4.4 Calabrese and Stanek, 1995 6 Calabrese and Stanek (1995) explored sources and magnitude of positive and negative 7 errors in soil ingestion estimates for children on a subject-week and trace element basis. 8 Calabrese and Stanek (1995) identified possible sources of positive errors to be: 9 

### C Ingestion of high levels of tracers before the start of the study and low ingestion 10 during the study period may result in over estimation of soil ingestion; and 11 

### C Ingestion of element tracers from a non-food or non-soil source during the study 12 period. 13 Possible sources of negative bias identified by Calabrese and Stanek (1995) are the following: 14 

### C Ingestion of tracers in food, but the tracers are not captured in the fecal sample either 15 due to slow lag time or not having a fecal sample available on the final study day; and 16 

### C Sample measurement errors which result in diminished detection of fecal tracers, but 17 not in soil tracer levels. 18 The authors developed an approach that attempted to reduce the magnitude of error in the 19 individual trace element ingestion estimates. Results from a previous study conducted by 20 Calabrese et al. (1989) were used to quantify these errors based on the following criteria: (1) a 21 lag period of 28 hours was assumed for the passage of tracers ingested in food to the feces (this 22 value was applied to all subject-day estimates); (2) a daily soil ingestion rate was estimated for 23 each tracer for each 24-hr day a fecal sample was obtained; (3) the median tracer-based soil 24 ingestion rate for each subject-day was determined; and (4) negative errors due to missing fecal 25 samples at the end of the study period were also determined. Also, upper- and lower-bound 26 estimates were determined based on criteria formed using an assumption of the magnitude of the 27 relative standard deviation(RSD) presented inanother study conducted by Stanek and Calabrese 28 (1995a). Daily soil ingestion rates for tracers that fell beyond the upper and lower ranges were 29 excluded from subsequent calculations, and the median soil ingestion rates of the remaining 30 tracer elements were considered the best estimate for that particular day. The magnitude of 315-23 positive or negative error for a specific tracer per day was derived by determining the difference 1 between the value for the tracer and the median value. 2 Table 5-16 presents the estimated magnitude of positive and negative error for six tracer 3 elements in the children's study (conducted by Calabrese et al. , 1989). The original mean soil 4 ingestion rates ranged from a low of 21 mg/day based on zirconium to a high of 459 mg/day 5 based on titanium (Table 5-15). The adjusted mean soil ingestion rate after correcting for 6 negative and positive errors ranged from 97 mg/day based on yttrium to 208 mg/day based on 7 titanium (Table 5-16). Calabrese and Stanek (1995) concluded that correcting for errors at the 8 individual level for each tracer element provides more reliable estimates of soil ingestion. 9 This study is valuable in providing additional understanding of the nature of potential 10 errors in trace element specific estimates of soil ingestion. However, the operational definition 11 used for estimating the error in a trace element estimate was the observed difference of that 12 tracer from a median tracer value. The authors did not specifically identify sources of error or 13 seek direct evidence that individual tracers were indeed in error. Corrections to individual tracer 14 means were made according to how different values for that tracer were from the median values. 15 This approach is based on the hypothesis that the median tracer value is the most accurate 16 estimate of soil ingestion, and the validity of this assumption depends on the specific set of 17 tracers used in the study and need not be correct. The approach used for the estimation of daily 18 tracer intake is the same as in Stanek and Calabrese (1995a), and some limitations of that 19 approach are mentioned in the review of that study. 20 21 5.2.4.5 Stanek et al. , 2001a 22 In order to identify and evaluate biasing factors for soil ingestion estimates, the authors 23 developed a simulation model based on data from previous soil ingestion studies. The soil 24 ingestion data used in this model were taken from Calabrese et al. , 1989 (the Amherst study); 25 Davis et al. , 1990; Calabrese et al. , 1997a (the Anaconda study) and Calabrese et al. , 1997b, and 26 relied only on the aluminum and silicon trace element estimates provided in these studies. 27 Of the biasing factors explored, the impact of study duration was the most striking, with a 28 positive bias of more than 100% for 95 thpercentile estimates in a 4-day mass balance study. A 29 smaller bias was observed for the impact of absorption of trace elements from food. Although 30 the trace elements selected for use in mass balance studies are believed to have low absorption, 315-24 whatever amount is not accounted for will result in an underestimation of the soil ingestion 1 distribution. In these simulations, the absorption of trace elements from food of up to 30% was 2 shown to negatively bias the estimated soil ingestion distribution by less than 20 mg/day. No 3 biasing effect was found for misidentifying play areas for soil sampling (i.e., ingested soil from a 4 yard other than the subject’s yard). 5 6 5.2.4.6 Zartarian et al. , 2005 7 Zartarian et al. (2005) conducted an analysis of soil ingestion rates from several studies 8 in the literature to be used as input for the Stochastic Human Exposure and Dose Simulation 9 (SHEDS) model which was used in the EPA report entitled A Probabilistic Exposure Assessment 10 for Children Who Contact CCA-Treated Playsets and Decks(U.S. EPA 2005). 11 Soil ingestion rate estimates were derived for the SHEDS-Wood model (this refers to the 12 application of the SHEDS model to wood preservative exposure scenarios) using data from 13 Calabrese’s Amherst and Anaconda studies. Data statistics from both of these studies were used 14 to fit distributions of soil/dust ingestion rates. The statistical distributions generated for 15 variability and uncertainty distributions relied upon two tracers only, Al and Si, in estimating the 16 parameters of the lognormal variability and uncertainty distributions. Using Monte-Carlo 17 sampling, values from the fitted distribution were sampled. The sampled values were separated 18 into those values under 500 mg/day and values that exceeded 500 mg/day. The model assumes 19 that soil ingestion values that exceed 500 mg/day are representative of pica behavior. The soil 20 ingestion rate distribution for non-pica behavior children developed for the SHEDS model has a 21 mean of 61, standard deviation 81, median 30, 25 th percentile 12, 75 th percentile 73, 95 th 22 percentile 236, and 99 th percentile 402 (mg/day). This distribution was simulated using only the 23 results generated below 500 mg/day. For children exhibiting pica behavior the summary 24 statistics are: mean 962 mg/day, standard deviation 758, median 735, 25 th percentile 590, 75 th 25 percentile 1046, 95 th percentile 2130, 99 th percentile 3852 mg/day. 26 The strength of this analysis is that it provides variability and uncertainty distributions. It 27 also provides estimates for pica behavior. A limitation of this analysis is that pica children and 28 incidental ingestion were simulated separately. The distribution for incidental soil ingestion 29 does not take into account that for long-term behavior, children are expected to have days where 30 they may ingest unusually high levels of soil. 315-25 1 

### 5.3 PICA 2 5.3.1. Prevalence 3 5.3.1.1 General Pica 4 Feldman (1986) defines pica as “the repeated eating of non-nutritive substances” . 5 Numerous articles have been published that report on the incidence of pica among various 6 populations. However, most of these papers describe pica for substances other than soil 7 including sand, clay, paint, plaster, hair, string, cloth, glass, matches, paper, feces, and various 8 other items. These papers indicate that pica behavior occurs in approximately half of all 9 children between the ages of 1 and 3 years (Sayetta, 1986). The incidence of behavior 10 ingesting non-nutritive substances in children has been shown to differ for different 11 subpopulations. The incidence rate appears to be higher for black children than for white 12 children. Approximately 30 percent of black children aged 1 to 6 years are reported to have 13 pica behavior, compared with 10 to 18 percent of white children in the same age group (Danford, 14 1982). There do not appear to be any sex differences in the incidence rates for males or females 15 (Kaplan and Sadock, 1985). Lourie et al. (1963) states that the incidence of pica is higher 16 among children in lower socioeconomic groups (i.e., 50 to 60 percent) than in higher income 17 families (i.e., about 30 percent). Pica behavior appears to be more common in rural areas 18 (Vermeer and Frate, 1979). A higher rate of pica has also been reported for pregnant women and 19 individuals with poor nutritional status (Danford, 1982). In general, pica behavior is more 20 frequent and more severe in mentally retarded children than in children in the general population 21 (Behrman and Vaughan 1983, Danford 1982, Forfar and Arneil 1984, Illingworth 1983, Sayetta 22 1986). 23 24 5.3.1.2 Soil Pica 25 It should be noted that the pica statistics cited above apply to the incidence of general 26 pica and not soilpica. A soil pica workshop conducted by ATSDR defined soil pica as the 27 recurrent ingestion of unusually high amounts of soil (i.e., 1,000 - 5,000 mg/day)(ATSDR, 28 2001). Information on the incidence of soil pica is limited, but it appears that soil pica is less 29 common than general pica. In addition, parental observations regarding children who are likely 30 to be high soil ingesters have been found to be inaccurate (Calabrese et al. , 1997b). A study by 315-26 Vermeer and Frate (1979) showed that the incidence of geophagia (i.e., intentional earth-eating) 1 was about 16 percent among children from a rural black community in Mississippi. However, 2 geophagy was described as a cultural practice among the community surveyed and may not be 3 representative of the general population. Average daily consumption of soil was estimated to be 4 50 g/day. Bruhn and Pangborn (1971) reported the incidence of pica for “dirt” to be 19 percent 5 in children, 14 percent in pregnant women, and 3 percent in nonpregnant women. However, 6 “dirt” was not clearly defined. The Bruhn and Pangborn (1971) study was conducted among 91 7 non-black, low income families of migrant agricultural workers in California. Based on the data 8 from the five key tracer studies (Binder et al. , 1986; Clausing et al., 1987; Van Wïjnen et al. , 9 1990; Davis et al. , 1990; and Calabrese et al. , 1989) only one child out of the more than 600 10 children involved in all of these studies ingested an amount of soil significantly greater than the 11 range for other children. Although these studies did not include data for all populations and 12 were representative of short-term ingestions only, it can be assumed that the incidence rate of the 13 recurrent ingestion of unusually high amounts of soil in the general population is low. 14 However, it is incumbent upon the user to use the appropriate value for their specific study 15 population. 16 17 5.3.2. Soil Pica Among Children 18 Information on the amount of soil ingested by children with pica behavior is limited. 19 However, some evidence suggests that a rate on the order of 10 g/day may not be unreasonable. 20 21 5.3.2.1. Calabrese et al. , 1991 22 Calabrese et al. (1991) estimated that upper range soil ingestion values may range from 23 approximately 5 to 7 g/day. This estimate was based on observation of one pica child among the 24 64 children who participated in the study. In the study, a 3.5-year-old female exhibited extremely 25 high soil ingestion behavior during one of the two weeks of observation. Intake ranged from 74 26 to 2200 mg/day during the first week of observation and from 10,100 to 13,600 mg/day during 27 the second week of observation (Table 5-16). These results are based on mass-balance analyses 28 for seven tracer elements (aluminum, barium, manganese, silicon, titanium, vanadium, and 29 yttrium) of the eight used. Intake rates based on zirconium were significantly lower. In a 305-27 subsequent paper, the authors indicated that this may have resulted from sample loss due to GI 1 absorption (Stanek and Calabrese, 1994). 2 3 5.3.2.2. Calabrese and Stanek, 1992b 4 Using a methodology that compared differential element ratios, Calabrese and Stanek 5 (1992b) quantitatively distinguished outdoor soil ingestion from indoor dust ingestion in a soil 6 pica child. This study was based on a previous mass-balance study (Calabrese et al. , 1991) in 7 which a 3.5-year-old child ingested 10 to 13 grams of soil per day during the second week of a 2- 8 week soil ingestion study. 9 Table 5-17 presents tracer ratios of soil, dust, and residual fecal samples in the soil pica 10 child. The authors reported that there was a maximum total of 28 pairs of tracer ratios based on 11 eight tracers. However, only 19 pairs of tracer ratios were available for quantitative evaluation, 12 as shown in Table 5-17. Of these 19 pairs, nine fecal tracer ratios fell between the limits for soil 13 and dust (Table 5-17). For these nine tracer soils, an interpolation was performed to estimate the 14 relative contribution of soil and dust to the residual fecal tracer ratio; this analysis indicates that 15 from 71 to 99% of the tracer originated from soil. All of the other 10 fecal tracer ratios that fell 16 outside the soil and dust limits were indicative of 100% soil origin. Therefore, the authors 17 conclude that the predominant proportion of the fecal tracers originated from outdoor soil and 18 not indoor dust. 19 20 5.3.2.3. Calabrese and Stanek, 1993 21 Calabrese and Stanek (1993) reviewed a study by Wong (1988) that attempted to estimate 22 the amount of soil ingested by two groups of children. Wong studied a total of 52 children in two 23 government institutions in Jamaica. The younger group (from the Glenhope Place of Safety) 24 contained 24 children with an average age of 3.1 years (range of 0.3 to 7.6 years). The older 25 group (from the Reddies Place of Safety) contained 28 children with an average age of 7.2 years 26 (range of 1.8 to 14 years). Fecal samples were obtained from the subject children and the 27 amount of silicon in dry feces was measured to estimate soil ingestion. 28 An unspecified number of daily fecal samples were collected from a hospital control 29 group of 30 children with an average age of 4.8 years (range of 0.3 to 12 years). Dry feces were 30 observed to contain 1.45% silicon, or 14.5 mg Si per gram of dry feces. This quantity was used 315-28 as a baseline representing the background level of silicon ingestion from dietary sources. 1 Observed quantities of silicon greater than 1.45% were interpreted as originating from soil 2 ingestion. 3 The amount of soil ingested was calculated using the formula of Binder et al. (1986). One 4 fecal sample was collected each month from each subject over the four-month study period. 5 For the 28 children in the older group, soil ingestion was estimated to be 58 mg/day, 6 based on the mean minus one outlier, and 1520 mg/day, based on the mean of all the children. 7 The outlier was a child with an estimated average soil ingestion rate of 41 g/day over the 4 8 months. Of the 28 children in the group, 7 had an average soil ingestion greater than 100 mg/day, 9 4 had an average soil ingestion greater than 200 mg/day, and 1 had an average soil ingestion 10 greater than 300 mg/day; 8 children showed no indication of soil ingestion. 11 Estimates of soil ingestion were higher in the younger group of children. The mean soil 12 ingestion of all the children was 470 ± 370 mg/day. Due to some sample losses, of the 24 13 children studied, only 15 had samples for each of the 4 months of the study. Of the 24 children in 14 the group, 14 had an average soil ingestion less than 100 mg/day, 10 had an average soil 15 ingestion greater than 100 mg/day, 5 had an average soil ingestion greater than 600 mg/day, and 16 4 had an average soil ingestion greater than 1000 mg/day; 5 children showed no indication of 17 soil ingestion. 18 Over the entire 4-month study period, 9 of 84 samples (or 10.5%) yielded soil ingestion 19 estimates in excess of 1 g/day, indicating pica behavior. Of the 52 children studied, 6 displayed 20 soil pica behavior. The estimated soil ingestion for each of these subjects is shown in Table 5-18. 21 For the younger group of children, 5 of 24 (or 20.8%) displayed pica behavior on at least one 22 occasion. A high degree of daily variability in soil ingestion was observed among the six pica 23 children; three (#11, 12, and 22) showed pica behavior on only 1 of 4 days. The other three (#14, 24 18, and 27) showed pica behavior on 2, 3, and 4 days, respectively. Subject #27 consumed the 25 most soil (3.7 to 60.6 g/day); however, it was indicated that this child was mentally retarded, 26 whereas the other pica children were considered to have normal mental capabilities. 27 Sources of uncertainty or error in this study include differences between the hospital 28 study group (the background control) and the two study groups, lack of information on the intake 29 of silicon for the children in the study, use of a single fecal sample, and loss of fecal samples. 30 The use of a single soil tracer may also introduce error because there may be other sources of the 315-29 tracer in the children’s environment. For example, some toothpastes have extremely high silica 1 concentrations, and children may ingest significant quantities of toothpaste. Tracers may also be 2 found in indoor dust that children could ingest. However, despite these uncertainties, the results 3 are important in that they indicate that soil pica is not a rare occurrence in younger children. 4 5 5.3.2.4. Zartarian et al. 2005 6 Zartarian et al. (2005) conducted an analysis of soil ingestion rates from several studies 7 in the literature to be used as input for the Stochastic Human Exposure and Dose Simulation 8 (SHEDS-Wood) model which was used in the EPA report entitled A Probabilistic Exposure 9 Assessment for Children Who Contact CCA-Treated Playsets and Decks(U.S. EPA 2005). 10 Soil ingestion rate estimates were derived for the SHEDS-Wood model using data from 11 Calabrese’s Amherst and Anaconda studies. Data statistics from both of these studies were used 12 to fit distributions of soil/dust ingestion rate s. Zartarian et al. (2005) derived a soil pica 13 distribution by sampling from the fitted lognormal distribution and retaining values above 500 14 mg/day. The mean and 95 thpercentile values for this population was estimated to be 963 mg/day 15 and 2170 mg/day, respectively. The distribution is presented in Table 5-20. 16 17 

### 5.4 RECOMMENDATIONS 18 The key studies described in this section were used to recommend values for soil intake 19 among children. The list of these studies is provided in Table 5-19. Estimates of the amount of 20 soil ingested by children based on the key studies are summarized in Table 5-20 and the 21 recommended values are presented in Table 5-21. The mean values ranged from 38 mg/day to 22 193 mg/day with a weighted average of 90 mg/day for soil ingestion and 106 mg/day when it 23 was considered that a portion of the soil ingested comes from dust. These estimates are based 24 on weighted averages using aluminum and silicon as tracers, except for Calabrese et al. (1997), 25 which uses the best tracer methodology. These tracer elements were considered the most 26 reliable based on a review of the current literature. Results obtained using titanium as a tracer 27 were not considered in the derivation of the recommendations because titanium exhibits greater 28 variability compared to other tracers. Results using titanium are consistently higher than other 29 tracers. This may indicate that there are other non-food and non-soil sources of titanium being 30 ingested. For example, titanium is used in paper coatings and as paper fillers and in paints, 315-30 lacquers, and enamels (IPCS, 1982). Ingestion of these non-food items has not been 1 investigated. 2 Most of the studies used in this chapter did not categorize soil intake by the age groups 3 recommended in EPA 2005. Therefore, the recommended values in Table 5-21 apply to 4 children from age 1 to 7 years. At this time, the raw data from these studies are not available. 5 Data are particularly lacking for children < 1 year of age. Van Wijnen et al. (1990) (Table 5-10) 6 derived soil ingestion estimates for various age categories. Although Van Wijnen et al. (1990) 7 was not considered a key study because the presence of tracers in food and medicines was not 8 taken into consideration and the study may not representative of U.S. children, it showed that 9 children 4 to < 5 years of age had median soil ingestion rates up to 1.8 times higher than children 10 <1 year of age. However, one needs to consider that infants may spend most of their time indoors 11 and dust concentration may be more appropriate for calculating ingestion rates for this group. 12 Using dust concentrations for estimating intake rates generally results in higher ingestion rates. 13 Dust samples were not collected by Van Wijnen et al. (1990). 14 There are a number of limitations with the data presented in Table 5-20. A number of 15 studies have indicated that aluminum and silicon can be absorbed in small amounts from the 16 digestive tract in adults (Davis and Mirick 2006). Therefore, these soil ingestion values may be 17 biased low. It is also worth noting that even though there are five key studies presented in Table 18 5-20, they represent only four populations (i.e, Amherst, Anaconda, Tri-city area in southeastern 19 Washington, and a subset of the Tri-city area study) adding up to 241 children. Other studies are 20 reanalyses of these populations. Therefore, in some instances the same population is counted 21 more than once in the weighted averages presented in Table 5-20. In addition, since the children 22 were studied for short periods of time and the prevalence of pica behavior is not known, 23 excluding children with pica behavior from the calculations may underestimate long-term soil 24 intake rates. It is plausible that many children may exhibit some pica behavior if studied for 25 longer periods of time. Since young children may spend a significant number of hours indoors, 26 it may not be appropriate to assume that all the soil ingested came from outdoor exposure. 27 Therefore, the recommended soil ingestion values are based on soil and dust estimates. 28 Rounding up to the nearest hundred, 100 mg/day is the best estimate of the mean soil 29 ingestion for children under 7 years of age.Over the period of study, 95th percentile values 30 ranged from 217 mg/day to 449mg/day with an average of 236 mg/day for soil ingestion and 449 315-31 mg/day when both soil and dust are considered. Rounding to the nearest hundred, the 1 recommended 95th percentile soil ingestion rate for children is 400 mg/day based on soil 2 and dust ingestion.A distribution of soil ingestion values is presented in Table 5-20. However, 3 since the children were studied for a short period of time and usually during the summer months, 4 these values are not estimates of usual intake. 5 Data on soil ingestion rates for children who exhibit pica behavior (i.e., ingest unusually 6 high amounts of soil on a recurrent basis) are also limited. In conducting a risk assessment for 7 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD), U.S. EPA (1984) used 5 g/day to represent the soil 8 intake rate for pica children. The Centers for Disease Control (CDC) also investigated the 9 potential for exposure to 2,3,7,8-TCDD via soil ingestion. CDC used a value of 10 g/day to 10 represent the amount of soil that a child with pica behavior might ingest (Kimbrough et al. , 11 1984). These values are consistent with those observed by Calabrese et al. (1991). An ingestion 12 rate of 10 g/day is a reasonable value for use in acute exposure assessments, based on the 13 available information. This value is based on only one pica child observed in the Calabrese et al. 14 (1989) study where the intake ranged from 10-14 grams/day during the second week of 15 observation. In addition, a statistical designation is not assigned to this value. 16 These recommendations are based on studies that used different survey designs and 17 populations. For example, in some studies soil ingestion estimates were adjusted to account for 18 the contribution of house dust to this estimate. Other studies used best tracer methodology while 19 others relied on estimates from specific tracers. Despite these differences, the mean and upper20 percentile estimates reported for these studies are relatively consistent. The confidence rating 21 for soil intake recommendations is presented in Table 5-22. It is important to understand, 22 however, the various uncertainties associated with these values. First, individuals were not 23 studied for sufficient periods of time to get a good estimate of the usual intake. Therefore, the 24 values presented in this section may not be representative of long-term exposures. Second, the 25 experimental error in measuring soil ingestion values for individual children is also a source of 26 uncertainty. For example, incomplete sample collection of both input (i.e., food and non food 27 sources) and output (i.e., urine and feces) is a limitation for some of the studies conducted. In 28 addition, an individual's soil ingestion value may be artificially high or low depending on the 29 extent to which a mismatch between input and output occurs due to individual variation in the 30 gastrointestinal transit time. Third, the degree to which the tracer elements used in these studies 315-32 are absorbed in the human body is uncertain. Accuracy of the soil ingestion estimates depends 1 on how good this assumption is. Fourth, there is uncertainty with regard to the homogeneity of 2 soil samples and the accuracy of parents’ knowledge about their child’s playing areas. Fifth, all 3 the soil ingestion studies presented in this section with the exception of Calabrese et al. (1989) 4 were conducted during the summer when soil contact is more likely. 5 Although the recommendations presented in this section are derived from studies which 6 were mostly conducted in the summer, exposure during the winter months, when the ground is 7 frozen or snow covered in many regions of the United States, should not be considered as zero. 8 Exposure during these months, although lower than in the summer months, would not be zero 9 because some portion of house dust comes from outdoor soil. 10 11 12 135-33 5.5 REFERENCES FOR CHAPTER 5 1 2 ATSDR (2001) Summary report for the ATSDR soil-pica workshop. ATSDR, Atlanta, GA. March 20, 2001. 3 Available on line at: http://www.atsdr.cdc.gov/NEWS/soilpica.html. 4 5 Binder, S.; Sokal, D.; Maughan, D. ( 1986) Estimating soil ingestion: the use of tracer elements in estimating the 6 amount of soil ingested by young children. Arch. Environ. Health. 41(6):341-345. 7 8 Behrman, L.E.; Vaughan, V.C., III. (1983) Textbook of Pediatrics. Philadelphia, PA: W.B. Saunders Company. 9 10 Bruhn, C.M.; Pangborn, R.M. (1971) Reported incidence of pica among migrant families. J. of the Am. Diet. 11 Assoc. 58:417-420. 12 13 Calabrese, E.J.; Pastides, H.; Barnes , R.; Edwards, C.; Kostecki, P.T.; et al. (1989) How much soil do young 14 children ingest: an epidemiologic study. In: Petroleum Contaminated Soils, Lewis Publishers, Chelsea, MI. 15 pp. 363-397. 16 17 Calabrese, E.J.; Stanek, E.J.; Gilbert, C.E.; and Barnes, R. (1990) Preliminary adult soil ingestion estimates: Results 18 of a pilot study. Regul. Toxicol. Pharmacol. 12:88-95. 19 20 Calabrese, E.J.; Stanek, E.J.; Gilbert, C.E. (1991) Evidence of soil-pica behavior and quantification of soil ingested. 21 Hum. Exp. Toxicol. 10:245-249. 22 23 Calabrese, E.J.; Stanek, E.J. (1992) What proportion of hous ehold dust is derived from outdoor soil? J. Soil Contam. 24 1(3): 253-263. 25 26 Calabrese, E.J.; Stanek, E.J. (1992) Distinguishing outdoor soil ingestion from indoor dust ingestion in a soil pica 27 child. Regul. Toxicol. Pharmacol. 15:83-85. 28 29 Calabrese, E.J.; Stanek, E.J. (1993) Soil pica: not a rare event. J. Environ. Sci. Health. A28(2):373-384. 30 31 Calabrese, E.J.; Stanek, E.J. (1995) Resolving intertracer inconsistencies in soil ingestion estimation. Environ. 32 Health Perspect. 103(5):454-456. 33 34 Calabrese, E.J.; Stanek, E.J.; Barnes, R.M. (1996) Methodology to estimate the amount and particle size of soil 35 ingested by children: Implications for exposure assessment at waste sites. Regul. Toxicol. Pharmacol. 24: 36 264-268. 375-34 Calabrese, E.J.; Stanek, E.J.; Pekow, P.; Barnes, R.M. (1997a) Soil ingestion estimates for children residing on a 1 Superfund site. Ecotoxicology and Environmental Safety. 36:258-268. 2 3 Calabrese, E.J.; Stanek, E.J.; Barnes, R.M. (1997b) Soil ingestion rates in children identified by parental 4 observation as likely high soil ingesters. J. Soil Contam. 6(3): 271-279. 5 6 Clausing, P.; Brunekreef, B.; Van Wijnen, J.H. (1987) A method for estimating soil ingestion by children. Int. 7 Arch. Occup. Environ. Health (W. Germany) 59(1):73-82. 8 9 Danford, D.C. (1982) Pica and nutrition. Annual Review of Nutrition. 2:303-322. 10 11 Davis, S.; Waller, P.; Buschbon, R.; Ball ou, J.; White, P. (1990) Quantitative estimates of soil ingestion in normal 12 children between the ages of 2 and 7 years: population based estimates using aluminum, silicon, and titanium 13 as soil tracer elements. Arch. Environ. Hlth. 45:112-122. 14 15 Davis, S. and Mirick, D. (2006) Soil ingestion in children and adults in the same family. Journal of Exposure 16 Analysis and Environmental Epidemiology. 16:63-75. 17 18 Feldman, M.D. (1986) Pica: current perspectives. Psychosomatics (USA) 27(7):519-523. 19 20 Forfar, J.O.; Arneil, G.C., eds. (1984) Textbook of Paediatrics. 3rd ed. London: Churchill Livingstone. 21 22 Illingworth, R.S. (1983) The normal child. New York: Churchill Livingstone. 23 24 IPCS (1982). Environmental health criteria 24: Titanium. International Programme on Chemical Safety. Published 25 under the joint sponsorship of the United NationsEnvironment Programme, the International Labour 26 Organisation, and the World Health Organization. Available on-line at 27 http://www.inchem.org/documents/ehc/ehc/ehc24.htm#SectionNumber:3.1 28 29 Kaplan, H.I.; Sadock, B.J. (1985) Comprehensive textbook of psychiatry/IV. Baltimore, MD: Williams and 30 Wilkins. 31 32 Kimbrough, R.; Falk, H.; Stemr, P.; Fries, G. (1984) Health implications of 2,3,7,8-tetrachlorodibenzo-p-dioxin 33 (TCDD) contamination of residential soil. J. Toxicol. Environ. Health 14:47-93. 34 35 Lourie, R.S.; Layman, E.M.; Millican, F.K. (1963) Why children eat things that are not food. Children 10:143-146. 36 37 Sayetta, R.B. (1986) Pica: An overview. American Family Physician 33(5):181-185. 385-35 1 Sedman, R.; Mahmood, R.S. (1994) Soil ingestion by children and adults reconsidered using the results of recent 2 tracer studies. Air and Waste, 44:141-144. 3 4 Stanek, E.J.; Calabrese, E.J. (1994) Bias and the detection limit model for soil ingestion. J. Soil Contam. 3(2): 183- 5 189. 6 7 Stanek, E.J.; Calabrese, E.J. (1995a) Daily estimates of soil ingestion in children. Environ. Health Perspect. 8 103(3):276-285. 9 10 Stanek, E.J.; Calabrese, E.J. (1995b) Soil ingestion estimates for use in site evaluations based on the best tracer 11 method. Human and Ecological Risk Assessment. 1:133-156. 12 13 Stanek, E.J.; Calabrese, E.J.; Barnes, R. (1999) Soil inge stion estimates for children in Anaconda using trace element 14 concentrations in different particle size fractions. Human Ecol. Risk Assessment 5(3): 547-558. 15 16 Stanek, E.J.; Calabrese, E.J. (2000) Daily soil ingestion estimates for children at a Superfund site. Risk Analysis 17 20(5): 627-635. 18 19 Stanek, E.J.; Calabrese, E.J.; Zorn, M. (2001a) Biasing f actors for simple soil ingestion estimates in mass balance 20 studies of soil ingestion. Human and Ecological Risk Assessment. 7(2): 329-355. 21 22 Stanek, E.J.; Calabrese, E.J.; Zorn, M. (2001b) Soil ingestion distributions for Monte Carlo risk assessment in 23 children. Human and Ecological Risk Assessment. 7(2): 357-368. 24 25 Thompson, K.M.; Burmaster, D.E. (1991)Parametric distributions for soil ingestion by children. Risk Analysis. 26 11:339-342. 27 28 U.S. EPA. (1984) Risk analysis of TCDD contaminated soil. Washington, DC: U.S. Environmental Protection 29 Agency, Office of Health and Environmental Assessment. EPA 600/8-84-031. 30 31 U.S. EPA. (2005) Guidance on selecting age groupsfor monitoring and assessing childhood exposures to 32 environmental contaminants. Risk Assessment Forum, Office of Research and Development, Washington, 33 DC. EPA/630/P-03/003F. 34 35 Van Wijnen, J.H.; Clausing, P.; Brunekreff, B. (1990) Estimated soil ingestion by children. Environ. Res. 51:147- 36 162. 37 385-36 Vermeer, D.E.; Frate, D.A. (1979) Geophagia in rural Mississippi: environmental and cultural contexts and 1 nutritional implications. Am. J. Clin. Nutr. 32:2129-2135. 2 3 Wong, M.S. (1988) The Role of Environmental and Host Behavioural Factors in Determining Exposure to Infection 4 with Ascaris lumbricoldes and Trichuris trichlura. Ph .D. Thesis, Faculty of Natural Sciences, University of 5 the West Indies. 1988. 6 7 Zartarian, V.G., J. Xue, H. A. Ozkaynak, W. Dang, G. Glen, L. Smith, and C. Stallings. (2005). A probabilistic 8 exposure assessment for children who contact CCA-treated playsets and decks using the stochastic human 9 exposure and dose simulation model for the wood pres ervative scenario (SHEDS-WOOD), Final Report. U.S. 10 Environmental Protection Agency, Washington, DC, EPA/600/X-05/009. 11 125-37 Table 5-1. Average Daily Soil Ingestion Values Based on Aluminum, Silicon, and Titanium as Tracer Elements a

Element Mean (mg/d) Median (mg/d) Standard Error of the Mean

(mg/d) Range (mg/d) b Aluminum 38.9 25.3 14.4 279.0 to 904.5 Silicon 82.4 59.4 12.2 -404.0 to 534.6 Titanium 245.5 81.3 119.7 -5,820.8 to 6,182.2 Minimum 38.9 25.3 12.2 -5,820.8 Maximum 245.5 81.3 119.7 6,182.2

aExcludes three children who did not provide any samples (N=101).

bNegative values occurred as a result of correction for nonsoil sources of the tracer elements.

Source: Adapted from Davis et al. (1990).

Table 5-2. Soil Ingestion Estimates for the Median of Best Four Trace Elements Based on Food/Soil Ratios for 64 Anaconda Children (mg/day) Using Al, Si, Ti, Y, and Zr

Category Soil Ingestion (mg/day) a Min P5 P10 P25 P50 P75 P90 P95 Max Mea

n SD

Median of best 4 -101.3 -91.0 -53.8 -38.0 -2.4 26.8 73.1 159.8 380.2 6.8 74.5

Best tracer -53.4 -24.4 -14.4 2.2 20. 1 68.9 223.6 282.4 609.9 65.5 120.3 2nd best -115.9 -62.1 -48.6 -26.6 1.5 38.4 119.5 262.3 928.5 33.2 144.8 3rd best -170.5 -88.9 -67.0 -52.0 -18. 8 25.6 154.7 376.1 1293.5 31.2 199.6 4th best -298.3 -171.0 -131.9 -74.7 - 29.3 0.2 74.8 116.8 139.1 -34.6 79.7

aNegative values occurred as a result of calculating child-specific estimates for multiple days. For example, negative estimates of soil ingestion occurred when an individual child had low, but positive, soil ingestion, but the standard deviation was large. Source: Calabrese et al. (1997).5-38 Table 5-3. Dust Ingestion Estimates for the Median of Best Four Trace Elements Based on Food/Dust Ratios for 64 Anaconda Children (mg/day) Using Al, Si, Ti, Y, and Zr

Category Soil Ingestion (mg/day) a Min P5 P10 P25 P50 P75 P90 P95 Max Mean SD Median of best 4 -261.5 -186.2 -152.7 -69.5 -5.5 62. 8 209.2 353.0 683.9 16.5 160.9

Best tracer -377.0 -193.8 -91.0 -20.8 26.8 198.1 558.6 613.6 1499.4 127.2 299.1 2nd best -239.8 -147.2 -137.1 -59.1 7.6 153.1 356.4 409.5 1685.1 82.7 283.6 3rd best -375.7 -247.5 -203.1 -81.7 -14. 4 49.4 406.5 500.5 913.2 25.5 235.9 4th best -542.7 -365.6 -277.7 -161.5 -55. 1 52.4 277.3 248.8 6120.5 81.8 840.3

aNegative values occurred as a result of calculating child-specific estimates for multiple days. For example, negative estimates of dust ingestion occurred when an individual child had low, but positive, dust ingestion, but the standard deviation was large. Source: Calabrese et al. (1997).

Table 5-4. Mean and Median Soil Ingestion (mg/day) by Family Member

Participant Tracer Element Estimated Soil Ingestiona (mg/day) Mean Median Std Maximum Childb Aluminum 36.7 33.3 35.4 107.9 Silicon 38.1 26.4 31.4 95.0 Titanium 206.9 46.7 277.5 808.3 Source: Davis and Mirick 2006

a For some study participants, estimated soil ingestion resulted in a negative value. These estimates have been set to 0 mg/day for tabulation and analysis.

bResults based on 12 children with complete food, excreta, and soil data.5-39 Table 5-5. Estimated Daily Soil Ingestion Based on Aluminum, Silicon, and Titanium Concentrations

Estimation

Method Mean (mg/day) Median (mg/day) Standard Deviation (mg/day) Range (mg/day) 95th Percentile (mg/day) Geometric Mean (mg/day) Aluminum 181 121 203 25-1,324 584 128 Silicon 184 136 175 31-799 578 130 Titanium 1,834 618 3,091 4-17,076 9,590 401 Minimum 108 88 121 4-708 386 65 Source: Binder et al. (1986).5-40 Table 5-6. Calculated Soil Ingestion by Nursery School Children

Child Sample Number Soil Ingestion as Calculated from Ti (mg/day) Soil Ingestion as Calculated from Al (mg/day) Soil Ingestion as Calculated from AIR (mg/day) Limiting Tracer (mg/day) 1 L3 L14 L25 103 154 130 300 211 23 107 172

- 103 154 23 2 L5 L13 L27 131 184 142 - 103 81 71 82 84 71 82 81 3 L2 L17 124 670 42 566 84 174 42 174 4 L4 L11 246 2,990 62 65 145 139 62 65 5 L8 L21 293 313 -

- 108 152 108 152 6 L12 L16 1,110 176 693

- 362 145 362 145 7 L18 L22 11,620 11,320 - 77 120

- 120 77 8 9 10 11 12 13 14 15 16 17 18 L1 L6 L7 L9 L10 L15 L19 L20 L23 L24 L26 3,060 624 600 133 354 2,400

124 269 1,130

64 184 82 979 200

- 195

- 71 212 51 566 56 96 111 124 95 106 48 93 274 84

-

- 82 111 124 95 106 48 71 212 51 64 56 Arithmetic Mean 1,431 232 129 105

Source: Adapted from Clausing et al. (1987).5-41 Table 5-7. Calculated Soil Ingestion by Hospitalized, Bedridden Children

Child Sample Soil Ingestion as Calculated from Ti (mg/day) Soil Ingestion as Calculated from Al (mg/day) Limiting Tracer (mg/day) 1 G5 G6 3,290 4,790 57 71 57 71 2 G1 28 26 26 3 G2 G8 6,570 2,480 94 57 84 57 4 G3 28 77 28 5 G4 1,100 30 30 6 G7 58 38 38 Arithmetic Mean 2,293 56 49

Source: Adapted from Clausing et al. (1987).

Table 5-8. Mean and Standard Deviation Percentage Recovery of Eight Tracer Elements

Tracer Element 300 mg Soil Ingested 1,500 mg Soil Ingested

Mean SD Mean SD

Al 152.8 107.5 93.5 15.5 Ba 2304.3 4533.0 149.8 69.5 Mn 1177.2 1341.0 248.3 183.6 Si 139.3 149.6 91.8 16.6 Ti 251.5 316.0 286.3 380.0 V 345.0 247.0 147.6 66.8 Y 120.5 42.4 87.5 12.6 Zr 80.6 43.7 54.6 33.4 Source: Adapted from Calabrese et al. (1989).5-42 Table 5-9. Soil and Dust Ingestion Estimates for Children Ages 1-4 Years

Tracer Element N Intake (mg/day) a

Mean Median SD 95th Percentile Maximum Aluminum soil dust soil/dust combined Silicon soil dust soil/dust combined Yttrium soil dust soil/dust combined Titanium soil dust soil/dust combined 64 64 64

64 64 64

62 64 62

64 64 64 153 317 154

154 964 483

85 62 65

218 163 170 29 31 30

40 49 49

9 15 11

55 28 30 852 1,272 629

693 6,848 3,105

890 687 717

1,150 659 691 223 506 478

276 692 653

106 169 159

1,432 1,266 1,059 6,837 8,462 4,929

5,549 54,870 24,900

6,736 5,096 5,269

6,707 3,354 3,597

aCorrected for Tracer Concentrations in Foods

Source: Adapted from Calabrese et al. (1989).5-43 Table 5-10. Geometric Mean (GM) and Standard Deviation (GSD) LTM Values for Children at Daycare Centers and Campgrounds

Age (yrs) Sex Daycare Centers Campgrounds

n GM LTM (mg/day) GSD LTM (mg/day) n GM LTM (mg/day) GSD LTM (mg/day) birth to <1 Girls Boys 3 1 81 75 1.09

- -

- -

- -

- 1 to <2 Girls Boys 20 17 124 114 1.87 1.47 3 5 207 312 1.99 2.58 2 to <3 Girls Boys 34 17 118 96 1.74 1.53 4 8 367 232 2.44 2.15 3 to <4 Girls Boys 26 29 111 110 1.57 1.32 6 8 164 148 1.27 1.42 4 to <5 Girls Boys 1 4 180 99 - 1.62 19 18 164 136 1.48 1.30 3 to <5 c Girls Boys 27 33 146 105 1.57 1.47 25 26 164 142 1.38 1.36 All girls All boys Total 86 72 162 a 117 104 111 1.70 1.46 1.60 36 42 78 b 179 169 174 1.67 1.79 1.73

aAge and/or sex not registered for eight children.

bAge not registered for seven children.

cThis age category is calculated from the previous two rows of data in order to conform to the standardized age categories used in this Handbook. Source: Adapted from Van Wijnen et al. (1990).5-44 Table 5-11. Estimated Geometric Mean Limiting Tracer Method (LTM) Values of Children Attending Daycare Centers According to Age, Weather Category, and Sampling Period

Weather Category Age (years) First Sampling Period Second Sampling Period

n Estimated Geometric Mean LTM Value

(mg/day) n Estimated Geometric Mean LTM Value

(mg/day) Bad (>4 days/week precipitation) <1 1 to <2 2 to <3 4 to <5 3 18 33 5 94 103 109 124 3 33 48 6 67 80 91 109 Reasonable (2-3 days/week precipitation) <1 1 to <2 2 to <3 3 to <4 4 to <5 3 to <5 a 1 10 13 19 1 20 61 96 99 94 61 92 Good (<2 days/week precipitation) <1 1 to <2 2 to <3 3 to <4 4 to <5 3 to <5 a 4 42 65 67 10 77 102 229 166 138 132 137

aThis age category is calculated from the available data inorder to conform to the standardized age categories used in this Handbook. Value is a weighted mean of the previous two rows.

Source: Van Wijnen et al. (1990).5-45 Table 5-12. Distribution of Average (Mean) Daily Soil Ingestion Estimates per Child for 64 Children a(mg/day)

Type of Estimate Number of

Samples Overall (64) A1 (64) Ba (33) Mn (19) Si (63) Ti (56) V (52) Y (61) Zr (62) Mean 179 122 655 1,053 139 271 112 165 23 25th Percentile 10 10 28 35 5 8800 50th Percentile 45 19 65 121 32 31 47 15 15 75th Percentile 88 73 260 319 94 93 177 47 41 90th Percentile 186 131 470 478 206 154 340 105 87 95th Percentile 208 254 518 17,374 224 279 398 144 117 Maximum 7,703 4,692 17,991 17,374 4,975 12,055 845 8,976 208

aFor each child, estimates of soil ingestion were formed on days 4-8 and the mean of these estimates was then evaluated for each child. The values in the column “overall” correspond to percentiles of the distribution of these means over the 64 children. When specific trace elements were not excluded via the relative standard deviation criteria, estimates of soil ingestion based on the specific trace element were formed for 108 days for each subject. The mean soil ingestion estimate was ag ain evaluated. The distribution of these means for specific trace elements is shown.

Source: Stanek and Calabrese (1995a).

Table 5-13. Estimated Distribution of Individual Mean Daily Soil Ingestion Based on Data for 64 Subjects Projected over 365 Days a

Range 50th Percentile (median) 90th Percentile 95th Percentile 1 - 2,268 mg/db 75 mg/d 1,190 mg/d 1,751 mg/d

a Based on fitting a log-normal distribution to model daily soil ingestion values.

bSubject with pica excluded.

Source: Stanek and Calabrese (1995a).5-46 Table 5-14. Summary Statistics and Parameters for Dist ributions of Estimated Soil Ingestion by Tracer Elementa

Soil Intake (mg/day) A1 Si Ti Mean a

Mean Min 10th 20th 30th 40th Med 60th 70th 80th 90th Max 97 11 21 33 39 43 45 55 73 104 197 1,201 85 10 19 23 36 52 60 65 79 106 166 642 1,004 1 3 22 47 172 293 475 724 1,071 2,105 14,061 91 13 22 34 43 49 59 69 92 100 143 921 Lognormal Distribution Parameters Median Standard Deviation Arithmetic Mean 45 169

97 60 95 85 --

--

-- 59 126

91 Underlying Normal Distribution Parameters Mean Standard Deviation 4.06 0.88 4.07 0.85 --

-- 4.13 0.80

a Using Binder et al. (1986) data with actual fecal weights.

b Mean = arithmetic average of soil ingestion based on aluminum and silicon.

Source: Thompson and Burmaster (1991).5-47 Table 5-15. Positive/negative Error (Bias) inSoil Ingestion Estimates in the Calabrese et al. (1989) Massbalance Study: Effect on Mean Soil Ingestion Estimate (Mg/day) a

Tracer Negative Error

Lack of Fecal Sample on Final Study Day Other Causes b Total Negative

Error Total Positive

Error Net Error Original Mean Adjusted Mean Aluminum Silicon Titanium Vanadium Yttrium Zirconium 14 15 82 66 8 6 11 6 187 55 26 91 25 21 269 121 34 97 43 41 282 432 22 5 +18 +20 +13 +311 -12 -92 153 154 218 459 85 21 136 133 208 148 97 113

aHow to read table: for example, aluminum as a soil tracer displayed both negative and positive error. The cumulative total negative error is estimated to bias the mean estimate by 25 mg/day downward. However, aluminum has positive error biasing the original meanupward by 43 mg/day. The net bias in the original mean was 18 mg/day positive bias. Thus, the original 156 mg/day mean for aluminum should be corrected downward to 136 mg/day.

bValues indicate impact on mean of 128-subject-weeks in milligrams of soil ingested per day.

Source: Calabrese and Stanek (1995).5-48 Table 5-16. Daily Soil Ingestion Estimation in a Soil-Pica Child by Tracer and by Week (mg/day)

Tracer element Estimated Soil Ingestion (mg/day) Week 1 Week 2 Al Ba Mn Si Ti V Y Zr 74 458 2,221

142 1,543 1,269

147

86 13,600 12,088 12,341 10,955 11,870 10,071 13,325

2,695 Source: Calabrese et al. (1991).5-49 Table 5-17. Ratios of Soil, Dust, and Residual Fecal Samples in the Soil Pica Child

Tracer Pairs Ratio Estimated Residual Fecal Tracers of Soil Origin as Predicted by Specific Tracer Ratios (%) Soil Fecal Dust 1. Mn/Ti 2. Ba/Ti 3. Si/Ti 4. V/Ti 5. Ai/Ti 6. Y/Ti 7. Mn/Y 8. Ba/Y 9. Si/Y 10. V/Y 11. Al/Y 12. Mn/Al 13. Ba/Al 14. Si/Al 15. V/Al 16. Si/V 17. Mn/Si 18. Ba/Si 19. Mn/Ba 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 6.481 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 83 100 Source: Calabrese and Stanek (1992).5-50 Table 5-18. Daily Variation of Soil Ingestion by Children Displaying Soil Pica in Wong (1988)

Child subject number Month Estimated soil ingestion (mg/day) Glenhope Place of Safety 11 1 55 2 1,447 3 22 4 40 12 1 0 2 0 3 7,924 4 192 14 1 1,016 2 464 3 2,690 4 898 18 1 30 2 10,343 3 4,222 4 1,404 22 1 0 2 -- 3 5,341 4 0 Reddies Place of Safety 27 1 48,314 2 60,692 3 51,422 4 3,782

Source: Calabrese and Stanek (1993).5-51 Table 5-19 Key Studies Used to Derive Recommendations

Key Studies Sample Size Comments Davis et al. 1990 Stanek and Calabrese, 1995a Stanek and Calabrese, 1995b

Calabrese et al. 1997a Davis and Mirick 2006 101 64

162

64 12 Primary analysis Secondary analysis. This paper is a refinement of the data collected by Calabrese et al. 1989 Secondary analysis. This paper is a refinement of the data collected by Calabrese et al. 1989 and Davis et al. 1990 using the best tracer methodology. Primary analysis Primary Analysis5-52Table 5- 20 . Summary of Estimates of Incidental Soil and DustIngestion by Children (1-7 years old) from Key Studies (mg/day)aSample Size Age(yr)Source Mean P25 P50 P75 P90 P95 Reference101 2-7 Soil 61 42 Daviset al.1990Soil and Dust 112 8264 1-4 Soil 131 8 31 84 169 239 Stanek andCalabrese1995a162 1-7 Soil 104 10 37 80 156 217 Stanek andCalabrese1995b64b1-3Soil 66 2 20 69 224 283 Calabreseet al.1997aDust Onlyc127 - 27 198 559 614Soil and Dustd97 24 134 392 44912 3-7 Soil 38Davis andMirick 2006WeightedAverage1-7 Soil 90 8 35 78 174 236Soil and Dust 106 60 134 392 449aUsing the average of Al and Si as tracers (except otherwise specified under note “b”)bUsing the best tracer methodcCalculated assuming all the ingestion originated from dust.dCalculated by averaging the “soil” and “dust only” rows.5-53 Table 5-21. Summary of Recommended Values for Soil Ingestion Population Mean 95 thpercentile

Children (1-7 years old) Incidental Ingestion Pica Incidental Ingestion Pica

100 mg/day 10 g/day 400 mg/day --

Note: See Section 5.4 for discussion of these values.5-54 Table 5-22. Confidence in Soil Intake Recommendation Considerations Rationale Rating Study Elements C Level of peer review All key studies are from peer review literature. High C Accessibility Papers are widely available from peer review journals. However, raw data were not available to do age specific analysis Medium

C Reproducibility Methodology used was presented, but results are difficult to reproduce. Medium

C Focus on factor of interest The focus of the studies was on estimating soil intake rate by children. High

C Data pertinent to U.S. Studies used children from specific areas of the U.S. Medium C Primary data All the studies were based on primary data. High C Currency Studies were conducted after 1980. Soil ingestion behaviors are not expected to change with time. High

C Adequacy of data collection period Children were not studied long enough to fully characterize day to day variability. Most of the studies were conducted during the summer months. Medium

C Validity of approach The basic approach is the only practical way to study soil intake, but refinements are needed in tracer selection and matching input with outputs. The more recent studies corrected the data for sources of the tracers in food. There are, however, some concerns about absorption of the tracers into the body and lag time between input and output. Medium

C Study size The sample sizes used in the key studies were adequate for some age groups, but not representative of the U.S. Data are lacking for the very young children and children older than 7 years old. Medium

C Representativeness of the

population The study population may not be representative of the U.S. in terms of race, socio-economics, and geographical location; Studies focused on specific areas. Low

C Characterization of variability Day-to-day variability was not very well characterized. Low C Lack of bias in study design (high

rating is desirable) The selection of the population studied may introduce some bias in the results (i.e ., children near a smelter site, volunteers in nursery school). Low

C Measurement error Errors may result due to problems with absorption of the tracers in the body and mismatching inputs and outputs. Low

Other ElementsTable 5-22. Confidence in Soil Intake Recommendation Considerations Rationale Rating

5-55 C Number of studies There are 5 key studies. However, only four of those are original data. Medium

C Agreement between researchers Despite the variability, there is general agreement among researchers on central estimates of daily intake for children. Medium

Overall Rating Studies were well designed; results were fairly consistent; sample size was adequate for some age groups; accuracy of methodology is uncertain; variability cannot be characterized due to limitations in data collection period. Data at the upper end are highly uncertain. Distributions provided may not be representative of long-term behavior. Medium(for children - long-term central estimate) Low(for upper percentile and distributions of long-term behavior)