A method for estimating soil ingestion by children

A systematic characterization of soil/dust ingestion for typical subpopulations in China

An accurate assessment of human exposure to pollutants through the ingestion of dust and/or soil particles depends on a thorough understanding their rate of human ingestion. To this end, we investigated the load and size distribution patterns of dust/soil particles on the hands of three typical subpopulations, including preschoolers, college students, and security guards (outdoor workers). The geometric mean diameter of dust/soil particles on hands was observed to be 38.7 ± 11.2, 40.0 ± 12.1, and 36.8 ± 10.4 μm for preschoolers, college students, and security guards, respectively. The particle size distribution differed between subpopulations: Preschoolers were more exposed to fine particles, whereas security guards were exposed to more coarse particles. The geometric means of dust/soil particle loading on the hands were 0.126, 0.0163, and 0.0377 mg/cm2 for preschoolers, college students, and security guards, respectively. Males had statistically higher dust/soil particle loadings on hands than females, notably for preschoolers and college students; preschoolers with frequent hand contact with the bare ground had higher dust/soil particle loadings compared to those of peers in contact with commercial and residential grounds. The mean total dust/soil particle ingestion rate was estimated to be 245, 19.7, and 33.1 mg/day for preschoolers, college students, and security guards, respectively. Our estimates for college students and security guards are close to the consensus central-tendency values recommended by the U.S. EPA's Exposure Factor Handbook for American adults, whereas the estimates for children are much higher than the upper percentile values recommended for American children.

Estimation of Children's Soil and Dust Ingestion Rates and Health Risk at E-Waste Dismantling Area

Due to environmental health concerns, exposure to heavy metals and related adverse effects in electronic waste (e-waste) dismantling areas have attracted considerable interest in the recent years. However, little information is available about the Soil/Dust Ingestion Rates (SIR) of heavy metals for children living in such sites. This study estimated the soil ingestion of 66 children from e-waste disassembly areas by collecting and analyzing selected tracer elements in matched samples of their consumed food, feces, and urine, as well as soil samples from their play areas. The concentrations of tracer elements (including Al, Ba, Ce, Mn, Sc, Ti, Y, and V) in these samples were analyzed. The SIR was estimated to be 148.3 mg/day (median) and 383.3 mg/day (95th percentile) based on the Best Tracer Method (BTM). These values are somewhat higher than those observed in America, Canada, and other parts of China. Health risk assessments showed that Cr presented the greatest carcinogenic risk, at more than 10^-6 in this typical polluted area, while As was second. These findings provide important insights into the exposure risks of heavy metals in e-waste dismantling sites and emphasize the health risk caused by Cr and As.

Soil ingestion among young children in rural Bangladesh

Ingestion of soil and dust is a pathway of children's exposure to several environmental contaminants, including lead, pesticides, and fecal contamination. Empirically based estimates of central tendency for soil consumption by children in high-income countries range from 9 to 135 dry mg/day. Using a Monte Carlo simulation, we modeled the mass of soil directly and indirectly ingested per day by rural Bangladeshi children and identified the parameters that influence the mass ingested. We combined data from observations of direct and indirect ingestion among children with measurements of soil mass on the children's hands, mother's hands, and objects to quantify soil ingestion/day. Estimated geometric mean soil ingestion was 162 dry mg/day for children 3-5 months, 224 dry mg/day for children 6-11 months, 234 dry mg/day for children 12-23 months, 168 dry mg/day for children 24-35 months, and 178 dry mg/day for children 36-47 months old. Across all age groups, children placing their hands in their mouths accounted for 46-78% of total ingestion and mouthing objects contributed 8-12%. Direct ingestion of soil accounted for nearly 40% of soil ingested among children 6-23 months old. Sensitivity analyses identified that the parameters most affecting the estimates were the load of soil on the child's hand, the frequency of hand-to-mouth contacts while not eating, and, for children 6-23 months old, the frequency of direct soil ingestion. In a rural, low-income setting, children's soil consumption was substantially more than the estimates for children in high-income countries. Further characterizing soil ingestion of children in low-income contexts would improve assessments of the risks they face from soil-associated contaminants.

Direct Transfer of Phthalate and Alternative Plasticizers from Indoor Source Products to Dust: Laboratory Measurements and Predictive Modeling

Phthalate and alternative plasticizers are semivolatile organic compounds (SVOCs) and among the most abundant indoor pollutants. Although ingestion of dust is one of the major exposure pathways to them, migration knowledge from source products to indoor dust is still limited. Systematic chamber measurements were conducted to investigate the direct transfer of these SVOCs between source products and dust in contact with the source. Substantial direct source-to-dust transfer of SVOCs was observed for all tests. The concentration of bis(2-ethylhexyl)phthalate in dust was 12 times higher than the pre-experimental level after only two days of source-dust contact. A mechanistic model was developed to predict the direct transfer process, and a reasonable agreement between model predictions and measurements was achieved. The octanol/air partition coefficient (K_oa) of SVOCs, the emission parameter of the source product (y₀), and the characteristics of the dust layer (i.e., porosity and thickness) control the transfer, affecting the SVOC concentration in dust, the kinetics of direct transfer, or both. Dust mass loading has a significant influence on the transfer, while relative humidity only has a limited effect. The findings suggest that minimizing the use of SVOC-containing products and house vacuuming are effective intervention strategies to reduce young children's exposure to SVOCs.

Brominated and organophosphorus flame retardants in body wipes and house dust, and an estimation of house dust hand-loadings in Dutch toddlers

Children generally have higher Flame Retardant (FR) concentrations in serum compared to other age groups. Toddler behavior enhances direct contact with house dust since their frequent presence proximate to the floor, and their mouthing behavior. This study aimed to thoroughly investigate FR levels in body wipes of toddlers 8-18 months old) and in indoor dust using a noninvasive sampling technique. In this cross-sectional study, body wipes from hands, mouth and back, and indoor household dust samples were collected in twenty-one families and analyzed for one brominated- and seven organophosphorus FRs (polybrominated diphenyl ether 209 (BDE209), tris(2-chloroisopropyl) phosphate (TCIPP), tris(chloroethyl) phosphate (TCEP), tris(1,3-dichloroisopropyl) phosphate (TDCIPP), tris(phenyl) phosphate (TPHP), tris(methylphenyl) phosphate (TMPP), resorcinol bis(diphenyl phosphate) and bisphenol A bis(diphenyl phosphate)). Accelerated solvent extraction was used for extraction and the extract was measured with liquid chromatography combined with mass spectrometry. Non-parametric correlation analyses were performed to assess associations. All FRs were detected in body- and indoor dust samples (median range: 1.0ng/hand wipe (BDE209) to 65ng/hand wipe (TCIPP)) and were mostly correlated with each other. We estimated that approximately 260mg dust (range 50-880mg) accumulated on toddler's hands per day. Hand-to-mouth frequency was negatively associated with FR levels in wipes (τ = -0.38, p = 0.04). With increasing age FR concentrations (BDE209, TCEP, TDCIPP, TPHP and TMPP) on hands decreased significantly (p = 0.01-0.03). Girls had significantly less FRs (TCEP, TCIPP, TPHP and TMPP) on the hands (p = 0.01-0.03) than boys. This is to the best of the authors' knowledge the first study in Europe that measured brominated- as well as organophosphorus FRs in several types of body wipes from toddlers and that estimated the amount of house dust that accumulates on toddler's hands.

The Critical Role of House Dust in Understanding the Hazards Posed by Contaminated Soils

The health risks posed by soil pollutants are generally thought to be due to soilingestion and have often resulted in massive regulatory efforts to remedy such contamination. The contribution of this route to the actual human health hazard has been questioned, however, as soil removal alone seems to have little influence on the body burdens of soil contaminants in exposed individuals. Ongoing research also has repeatedly and substantially reduced the estimates of soilingested daily. Because comparatively little time is spent outdoors by most individuals, exposure to soil brought indoors, present as house dust, is now thought to be nearly as important as the directingestion of soil. Exposure via house dust has not been studied specifically, but several observations suggest that it may be important. Dust is largely composed of fine particles of tracked-in soil. The smaller dust particles cling to surfaces better than soil, and contaminant concentrations are often higher in house dust. Fine particles are likely to be more bioavailable, and degradation is slower indoors. Contaminants thus may be concentrated and more readily available in the areas most frequented. In some studies, contaminant levels in dust are correlated more closely with body burdens of contaminants than other sources, suggesting that this route should be considered when assessing risks from soil. Until more research addressing exposure to dust is conducted, recommendations for assessing potential health risks from this pathway are provided.

A review of soil and dust ingestion studies for children

Soil and dust ingestion by children may be important pathways of exposure to environmental contaminants. Contaminated soil and dust may end up on children's hands and objects, because they play close to the ground. These contaminants can be ingested by children, because they have a tendency to place objects, including their fingers, in their mouths. Assessing exposure through this pathway requires information about the amount of soil and dust ingested by children. Estimates of soil and dust ingestion and information on the prevalence of the behavior have been published in the literature, but research in this area is generally limited. Three methodologies have been used to quantify soil and dust ingestion rates. In this paper, these are referred to as the tracer element method, the biokinetic model comparison method, and the activity pattern method. This paper discusses the information available on the prevalence of soil and dust ingestion behavior, summarizes the three methodologies for quantifying soil and dust ingestion, and discusses their limitations. Soil ingestion data derived from studies that use these methodologies are also summarized. Although they are based on different estimation approaches, the central tendency estimates of soil and dust ingestion derived from the three methodologies are generally comparable.

Soil ingestion rate determination in a rural population of Alberta, Canada practicing a wilderness lifestyle

The inadvertent ingestion of contaminated soil can be a major pathway for chemical exposure to humans. Few studies to date have quantified soil ingestion rates to develop exposure estimates for human health risk assessments (HHRA), and almost all of those were for children in suburban/urban environments. Here we employed a quantitative mass balance tracer approach on a rural population practicing outdoor activities to estimate inadvertent soil ingestion. This study followed 9 subjects over a 13 day period in Cold Lake, Alberta, near the largest in situ thermal heavy oil (bitumen) extraction operation in the world. The mean soil ingestion rate in this study using Al Ce, La, and Si tracers was 32 mg d(-1), with a 90th percentile of 152 mg d(-1) and median soil ingestion rate of 18 mg d(-1). These soil ingestion values are greater than the standard recommended soil ingestion rates for HHRA from Health Canada, and are similar to soil ingestion estimates found in the only other study on a rural population.

General factors of the Korean exposure factors handbook

Risk assessment considers the situations and characteristics of the exposure environment and host. Various physiological variables of the human body reflects the characteristics of the population that can directly influence risk exposure. Therefore, identification of exposure factors based on the Korean population is required for appropriate risk assessment. It is expected that a handbook about general exposure factors will be used by professionals in many fields as well as the risk assessors of the health department. The process of developing the exposure factors handbook for the Korean population will be introduced in this article, with a specific focus on the general exposure factors including life expectancy, body weight, surface area, inhalation rates, amount of water intake, and soil ingestion targeting the Korean population. The researchers used national databases including the Life Table and the 2005 Time Use Survey from the National Statistical Office. The anthropometric study of size in Korea used the resources provided by the Korean Agency for Technology and Standards. In addition, direct measurement and questionnaire surveys of representative samples were performed to calculate the inhalation rate, drinking water intake, and soil ingestion.

Estimating human exposure: improving accuracy with chemical markers

Exposure to chemicals, natural as well as anthropogenic, occurs in the human environment. In the absence of chemical-specific data for the wide variety of exposure scenarios, federal agencies have adopted two approaches to estimating exposures. The first is to set chemical standards for exposures, usually through a single route. These standards are set based on risk assessment principles and economic feasibility. When there are standards, measurement of environmental chemical concentrations can be used to prevent unacceptable levels of exposure. The second approach is to estimate external exposure (typically route-specific) and/or an absorbed dose using a series of assumptions regarding translation of chemical concentrations from one part of the environment to another, human activity patterns, and chemical absorption through various routes into the body. These assumptions have been converted into algorithms that can be used to estimate a human exposure and dosage, typically expressed on body weight basis. These algorithms, designed to avoid underestimations of human exposure, have, in some instances, been incorporated into computer models. Chemical markers, measured either as the parent compound or as metabolites in human populations with known exposure to the parent compound, can be applied to improve the accuracy of these estimates of exposure.

A soil ingestion pilot study of a population following a traditional lifestyle typical of rural or wilderness areas

The relatively few soil ingestion studies underpinning the recommended soil ingestion rates for contaminated site human health risk assessments (HHRAs) that have been conducted to date assessed soil ingestion in children living in urban or suburban areas of the United States, and to a lesser extent, Europe. However, the lifestyle of populations living in North American urban and suburban environments is expected to involve limited direct contact with soil. Conversely, many populations, such as indigenous and Aboriginal peoples residing in rural and wilderness areas of North America and worldwide, participate in activities that increase the frequency of direct contact with soil. Qualitative exposure of Aboriginal populations inhabiting wilderness areas suggest that high levels of soil ingestion may occur that are many times greater than those recommended by regulatory agencies for use in HHRAs. Accordingly, a study of subjects selected from a wilderness community in Canada was conducted using mass balance tracer methods to estimate soil ingestion and the results compared with previous soil ingestion studies and regulatory guidelines for the soil ingestion rates used in HHRA of contaminated sites. A pilot study of 7 subjects living in the Nemiah Valley of British Columbia was conducted over a 3-week period. The mean soil ingestion rate estimated in this study using the 4 elemental tracers with the lowest food-to-soil ratios (i.e., Al, Ce, La, Si), was observed to be approximately 75 mg d(-1) (standard deviation 120 mg d(-1)), the median soil ingestion rate was 50 mg d(-1), and the 90th percentile was 211 mg d(-1). These soil ingestion rate estimates are higher than the soil ingestion estimates currently recommended for HHRAs of adults, and higher than those obtained in most previous studies of adults. However, the estimates are lower than the earlier qualitative assessments of subsistence lifestyles.

Meta-analysis of mass-balance studies of soil ingestion in children

Ingestion of soil by young children may be an important source of exposure to environmental contaminants. Estimates of soil ingestion have been made by several studies using trace elements in a mass-balance approach, but differ substantially between studies and trace elements. We conduct a meta-analysis of four major mass-balance soil ingestion studies conducted on children between one and seven in the summer/fall in the northern United States. The analysis takes advantage of primary data from all studies, and provides a more complete description of soil ingestion among children. The meta-analysis uses data based on the two most reliable trace elements, Al and Si, that have passed a screening to identify and exclude measures with a high likelihood of bias. Details are described in a companion paper. The best linear unbiased predictor is used in a mixed model to estimate soil ingestion for study subjects. Overall, 11% of subject-periods are identified as outliers and excluded from the analysis. An analysis on 216 children based on Al and Si as tracer elements indicates that the mean (median) soil ingestion is 26 mg/day (33 mg/day), with the 95th percentile estimated as 79 mg/day. This systematic approach provides more reliable estimates than individual study results. There is some evidence that soil ingestion increases with a child's age, but insufficient data to distinguish soil ingestion by gender.

Modeled estimates of soil and dust ingestion rates for children

Daily soil/dust ingestion rates typically used in exposure and risk assessments are based on tracer element studies, which have a number of limitations and do not separate contributions from soil and dust. This article presents an alternate approach of modeling soil and dust ingestion via hand and object mouthing of children, using EPA's SHEDS model. Results for children 3 to <6 years old show that mean and 95th percentile total ingestion of soil and dust values are 68 and 224 mg/day, respectively; mean from soil ingestion, hand-to-mouth dust ingestion, and object-to-mouth dust ingestion are 41 mg/day, 20 mg/day, and 7 mg/day, respectively. In general, hand-to-mouth soil ingestion was the most important pathway, followed by hand-to-mouth dust ingestion, then object-to-mouth dust ingestion. The variability results are most sensitive to inputs on surface loadings, soil-skin adherence, hand mouthing frequency, and hand washing frequency. The predicted total soil and dust ingestion fits a lognormal distribution with geometric mean = 35.7 and geometric standard deviation = 3.3. There are two uncertainty distributions, one below the 20th percentile and the other above. Modeled uncertainties ranged within a factor of 3-30. Mean modeled estimates for soil and dust ingestion are consistent with past information but lower than the central values recommended in the 2008 EPA Child-Specific Exposure Factors Handbook. This new modeling approach, which predicts soil and dust ingestion by pathway, source type, population group, geographic location, and other factors, offers a better characterization of exposures relevant to health risk assessments as compared to using a single value.

Mass balance soil ingestion estimating methods and their application to inhabitants of rural and wilderness areas: a critical review

Quantitative soil ingestion studies employing a mass balance tracer approach have been used to provide a defensible means to estimate soil ingestion for human health risk assessments. Past studies have focused on soil ingestion in populations living in urban/suburban environments. There is a paucity of reliable quantitative soil ingestion data to support human health risk assessments of other lifestyles that may be predisposed to ingesting soil, such as agricultural workers or indigenous populations following traditional lifestyles. The results of a preliminary analysis of sampling and analytical variability that would result from assessing activities typical of populations in rural or wilderness areas and conducted over wide areas show that approximately 225 subject days would be required to detect a difference of 20mg/d in soil ingestion. Given the typically small populations in these areas, future soil ingestion studies should be focused on specific activities with a high potential for soil ingestion.

Estimating consumer exposure to PFOS and PFOA

Perfluorinated compounds have been used for more than 50 years as process aids, surfactants, and for surface protection. This study is a comprehensive assessment of consumer exposure to perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) from a variety of environmental and product-related sources. To identify relevant pathways leading to consumer exposure to PFOS and PFOA a scenario-based approach has been applied. Scenarios represent realistic situations where age- and gender-specific exposure occurs in the everyday life of consumers. We find that North American and European consumers are likely to experience ubiquitous and long-term uptake doses of PFOS and PFOA in the range of 3 to 220 ng per kg body weight per day (ng/kg(bw)/day) and 1 to 130 ng/kg(bw)/day, respectively. The greatest portion of the chronic exposure to PFOS and PFOA is likely to result from the intake of contaminated foods, including drinking water. Consumer products cause a minor portion of the consumer exposure to PFOS and PFOA. Of these, it is mainly impregnation sprays, treated carpets in homes, and coated food contact materials that may lead to consumer exposure to PFOS and PFOA. Children tend to experience higher total uptake doses (on a body weight basis) than teenagers and adults because of higher relative uptake via food consumption and hand-to-mouth transfer of chemical from treated carpets and ingestion of dust. The uptake estimates based on scenarios are within the range of values derived from blood serum data by applying a one-compartment pharmacokinetic model.

Air quality and deposition of trace elements in Didouche Mourad, Algeria

Total suspended particulate matter and deposition fluxes of particles were investigated in the town of Didouche Mourad which is located 13 km north of Constantine. Samples of air particulate matter were collected at one site located in the heart of the town and situated 3 km north of a cement plant. Samples were collected from 2 November 2002 to 28 April 2003 every 3 days using a high volume air sampler. Sampling intervals were 24 h in all cases. During the same period, samples of dust fallout were collected at the same site. Samples were collected at 30-day intervals. Lead, chromium, manganese, nickel, copper, cobalt and cadmium deposition fluxes were measured and both the soluble and insoluble fractions were determined. Furthermore, the information gathered by this study was correlated with the corresponding hourly weather data provided by a weather station installed at the study station. The possible sources for dust and trace metals were analyzed by comparing average contributions of wind aspects to the concentrations and depositions of mass and chemical species with the average frequencies of wind direction. The mean concentration was 300 microg/m3. The average dust deposition rate through the period of study was 221 mg/(m2.day). Results indicate that anthropogenic sources contribute greatly to trace elements. An exposure assessment to the heavy metals taking into account the inhalation route and soil dust ingestion was carried out and allowed direct comparison of trace metal intakes via these routes.

Chemical mixtures: evaluation of risk for child-specific exposures in a multi-stressor environment

Evaluating the health impact from exposure to chemical mixtures is multifaceted. One component is exposure. Exposure, and consequently risk assessment for mixtures and chemicals in general, are often viewed in terms of a given exposure to a given population at a given location over a given time period. However, environmental exposures are present throughout human lifetime. As a result, an evaluation of risk must include the distinctive characteristics related to chemical exposures which will impact risk depending upon the particular life stage where exposure occurs. Risks to offspring may be associated with unique exposures in utero, during infancy, childhood, or adolescent periods. For example, exposure of infants to anthropogenic chemicals via breast milk may be of concern. The Agency for Toxic Substances and Disease Registry's (ATSDR's) approach to evaluating risks associated with exposure to mixtures of chemicals is presented. In addition to the breast milk issues, indoor exposure to combined air pollutants, drinking water contaminants, and soil and dust contaminants are discussed. The difference between a mixture's risk evaluation for children and adults is in the distinct exposure scenarios resulting from variations in behavior, physiology, and/or pharmacokinetics between adults and children rather than in the method for the specific mixtures evaluation per se.

Bioavailability of PCDD/F from contaminated soil in young Goettingen minipigs

For the general population the intake of food of animal origin is the main route of human exposure to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F). Besides this the ingestion of contaminated soil might be an important exposure path for small children. For risk assessment the knowledge of the bioavailable fraction of soil bound contaminants is important. In a balance study with young Goettingen minipigs the oral bioavailability of PCDD/F from contaminated soil was estimated by determination of the retention of PCDD/F from soil in different organs and tissues. Relative bioavailability was estimated by comparing the retention from soil to the retention of PCDD/F in organs and tissues after oral administration of a PCDD/F mixture extracted from the same soil by solvent. The soil had a PCDD/F-contamination of 5.3 microg I-TEq/kg and originated from a former arable land that had been treated with sludge from the port of Hamburg some years ago. Two groups of each four animals were exposed daily for 28 days via their diet either to 0.5 g soil per kg body weight and day (2.63 ng I-TEq/(kg(bw).d)) or to a daily dose of 1.58 ng I-TEq/(kg(bw).d) given to the diet by solvent. Five unexposed animals were used as a control group. Liver, adipose tissue, muscle, brain and blood were analyzed for their PCDD/F content. Accumulation of PCDD/F from soil or solvent in comparison to control animals was only observed for congeners with 2378-chlorosubstitution and predominantly took place in the liver. Bioavailability of 2378-chlorosubstituted congeners was in the range of 0.64%-21.9% (mean: 10.1%) from soil and 2.8%-59.8% (mean: 31.5%) when administered by solvent. The soil matrix reduced the bioavailability by about 70%. Expressed as I-TEq only 13.8% of the PCDD/F contamination were bioavailable from soil. The relative bioavailability of 2378-chlorosubstituted congeners from soil in relation to administration by solvent was in the range of 2%-42.2% (mean: 28.4%). When not considering the bioavailability, the risk by oral uptake of PCDD/F contaminated soil might be overestimated.

What are the sources of exposure to eight frequently used phthalic acid esters in Europeans?

Phthalic acid esters (phthalates) are used as plasticizers in numerous consumer products, commodities, and building materials. Consequently, phthalates are found in human residential and occupational environments in high concentrations, both in air and in dust. Phthalates are also ubiquitous food and environmental contaminants. An increasing number of studies sampling human urine reveal the ubiquitous phthalate exposure of consumers in industrialized countries. At the same time, recent toxicological studies have demonstrated the potential of the most important phthalates to disturb the human hormonal system and human sexual development and reproduction. Additionally, phthalates are suspected to trigger asthma and dermal diseases in children. To find the important sources of phthalates in Europeans, a scenario-based approach is applied here. Scenarios representing realistic exposure situations are generated to calculate the age-specific range in daily consumer exposure to eight phthalates. The scenarios demonstrate that exposure of infant and adult consumers is caused by different sources in many cases. Infant consumers experience significantly higher daily exposure to phthalates in relation to their body weight than older consumers. The use of consumer products and different indoor sources dominate the exposure to dimethyl, diethyl, benzylbutyl, diisononyl, and diisodecyl phthalates, whereas food has a major influence on the exposure to diisobutyl, dibutyl, and di-2-ethylhexyl phthalates. The scenario-based approach chosen in the present study provides a link between the knowledge on emission sources of phthalates and the concentrations of phthalate metabolites found in human urine.

Identifying soil cleanup criteria for dioxins in urban residential soils: how have 20 years of research and risk assessment experience affected the analysis?

This article reviews the scientific evidence and methodologies that have been used to assess the risks posed by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and presents a probabilistic analysis for identifying virtually safe concentrations of TCDD toxicity equivalents (TEQ) in residential soils. Updated data distributions that consider state-of-the-science cancer and noncancer toxicity criteria, child soil ingestion and dermal uptake, bioavailability in soil, and residential exposure duration are incorporated. The probabilistic analysis shows that the most sensitive determinants of dose and risk are childhood soil ingestion, exposure duration, and the selected TCDD cancer potency factor. It also shows that the cancer risk at 1 per 100,000 predicted more conservative (lower) soil criteria values than did the noncancer hazard (e.g., developmental and reproductive effects). In this analysis, acceptable or tolerable soil dioxin concentrations (TCDD TEQ) ranged from 0.4 to 5.5 ppb at the 95th percentile for cancer potency factors from 9600 to 156,000 (mg/kg/d)(-1) with site-specific adjustments not included. Various possible soil guidelines based on cancer and noncancer risks are presented and discussed. In the main, the current toxicology, epidemiology, and exposure assessment data indicate that the historical 1 ppb TEQ soil guidance value remains a reasonable screening value for most residential sites. This analysis provides risk managers with a thorough and transparent methodology, as well as a comprehensive information base, for making informed decisions about selecting soil cleanup values for PCDD/Fs in urban residential settings.

Soil ingestion in children and adults in the same family

Ingestion of soil may be a potentially important pathway of exposure to environmental pollutants. Although several studies have estimated soil ingestion in children, data on ingestion in adults are sparse. The purposes of this study were to estimate soil ingestion in children aged 3 to 8 years and their parents, identify factors associated with increased ingestion, and compare ingestion rates within the same family. Food/liquid, excreta, and soil/dust samples were collected for the mother, father, and participant child for 11 consecutive days in 19 families. Soil ingestion was estimated using a mass balance approach. Soil ingestion levels in children were similar to those reported previously, whereas adult estimates were somewhat higher than previous estimates. Children's eating of dirt and parents' occupational contact with soil were associated with increased ingestion. Within families, soil ingestion levels in children and adults were not correlated, although this analysis was based on fewer than 19 participant families. Children's mean soil ingestion rates ranged from 37 to 207 mg/day depending on the tracer, with the highest values based on titanium as a tracer. Adult mean soil ingestion rates ranged from 23 to 625 mg/day depending on the tracer, with the highest value based on titanium as a tracer. Soil ingestion rate estimates were more variable in adults than in children.

Mutagens in contaminated soil: a review

The intentional and accidental discharges of toxic pollutants into the lithosphere results in soil contamination. In some cases (e.g., wood preserving wastes, coal-tar, airborne combustion by-products), the contaminated soil constitutes a genotoxic hazard. This work is a comprehensive review of published information on soil mutagenicity. In total, 1312 assessments of genotoxic activity from 118 works were examined. The majority of the assessments (37.6%) employed the Salmonella mutagenicity test with strains TA98 and/or TA100. An additional 37.6% of the assessments employed a variety of plant species (e.g., Tradescantia clone 4430, Vicia faba, Zea mays, Allium cepa) to assess mutagenic activity. The compiled data on Salmonella mutagenicity indicates significant differences (p<0.0001) in mean potency (revertents per gram dry weight) between industrial, urban, and rural/agricultural sites. Additional analyses showed significant empirical relationships between S9-activated TA98 mutagenicity and soil polycyclic aromatic hydrocarbon (PAH) concentration (r2=0.19 to 0.25, p<0.0001), and between direct-acting TA98 mutagenicity and soil dinitropyrene (DNP) concentration (r2=0.87, p<0.0001). The plant assay data revealed excellent response ranges and significant differences between heavily contaminated, industrial, rural/agricultural, and reference sites, for the anaphase aberration in Allium cepa (direct soil contact) and the waxy locus mutation assay in Zea mays (direct soil contact). The Tradescantia assays appeared to be less responsive, particularly for exposures to aqueous soil leachates. Additional data analyses showed empirical relationships between anaphase aberrations in Allium, or mutations in Arabidopsis, and the 137Cs contamination of soils. Induction of micronuclei in Tradescantia is significantly related to the soil concentration of several metals (e.g., Sb, Cu, Cr, As, Pb, Cd, Ni, Zn). Review of published remediation exercises showed effective removal of genotoxic petrochemical wastes within one year. Remediation of more refractory genotoxic material (e.g., explosives, creosote) frequently showed increases in mutagenic hazard that remained for extended periods. Despite substantial contamination and mutagenic hazards, the risk of adverse effect (e.g., mutation, cancer) in humans or terrestrial biota is difficult to quantify.

Soils: their implications to human health

This paper reviews how the health of humans is affected by the world's soils, an association that to date has been under appreciated and under reported. Soils significantly influence a variety of functions (e.g. as a plant growth medium; its importance on the cycling of water; as a foundation for buildings) that sustains the human population. Through ingestion (either deliberate or involuntary), inhalation and dermal absorption, the mineral, chemical and biological components of soils can either be directly beneficial or detrimental to human health. Specific examples include: geohelminth infection and the supply of mineral nutrients and potentially harmful elements (PHEs) via soil ingestion; cancers caused by the inhalation of fibrous minerals or Rn gas derived from the radioactive decay of U and Th in soil minerals; and tetanus, hookworm disease and podoconiosis caused by skin contact and dermal absorption of appropriate soil constituents. Human health can also be influenced in more indirect ways as soils interact with the atmosphere, biosphere and hydrosphere. Examples include: the volatilisation of persistent organic pollutants (POPs) from soils and their subsequent global redistribution that has health implications to the Aboriginal people of the Arctic; the frequent detrimental chemical and biological quality of drinking and recreational waters that are influenced by processes of soil erosion, surface runoff, interflow and leaching; and the transfer of mineral nutrients and PHEs from soils into the plants and animals that constitute the human food chain. The scale and magnitude of soil/health interactions are variable, but at times a considerable number of people can be affected as demonstrated by the extent of hookworm infection or the number of people at risk because they live in an I-deficient environment. Nevertheless, it can often be difficult to establish definite links between soils and human health. This, together with the emergence of new risks, knowledge, or discoveries, means that there is considerable scope for research in the future. Such investigations should involve a multidisciplinary approach that both acquires knowledge and ensures its dissemination to people in an understandable way. This requires an infrastructure and finance that governments need to be responsive to.

Reducing uncertainty in the derivation and application of health guidance values in public health practice. Dioxin as a case study

We were requested by the U.S. Environmental Protection Agency (EPA) to clarify the relationships among the minimal risk level (MRL), action level, and environmental media evaluation guide (EMEG) for dioxin established by the Agency for Toxic Substances and Disease Registry (ATSDR). In response we developed a document entitled "Dioxin and Dioxin-Like Compounds in Soil, Part I: ATSDR Interim Policy Guideline"; and a supporting document entitled "Dioxin and Dioxin-Like Compounds in Soil, Part II: Technical Support Document". In these documents, we evaluated the key assumptions underlying the development and use of the ATSDR action level, MRL, and EMEG for dioxin. We described the chronology of events outlining these different health guidance values for dioxin and identified the areas of uncertainty surrounding these values. Four scientific assumptions were found to have had a great impact on this process; these were: (1) the specific uncertainty factors used, (2) the toxicity equivalent (TEQ) approach, (3) the fractional exposure from different pathways, and (4) the use of body burdens in the absence of exposure data. This information was subsequently used to develop a framework for reducing the uncertainties in public health risk assessment associated with exposure to other chemical contaminants in the environment. Within this framework are a number of future directions for reducing uncertainty, including physiologically based pharmacokinetic modeling (PBPK), benchmark dose modeling (BMD), functional toxicology, and the assessment of chemical mixture interactions.

High concentrations of heavy metals in neighborhoods near ore smelters in northern Mexico

In developing countries, rapid industrialization without environmental controls has resulted in heavy metal contamination of communities. We hypothesized that residential neighborhoods located near ore industries in three northern Mexican cities would be heavily polluted with multiple contaminants (arsenic, cadmium, and lead) and that these sites would be point sources for the heavy metals. To evaluate these hypotheses, we obtained samples of roadside surface dust from residential neighborhoods within 2 m of metal smelters [Torreón (n = 19)] and Chihuahua (n = 19)] and a metal refinery [Monterrey (n = 23)]. Heavy metal concentrations in dust were mapped with respect to distance from the industrial sites. Correlation between dust metal concentration and distance was estimated with least-squares regression using log-transformed data. Median dust arsenic, cadmium, and lead concentrations were 32, 10, and 277 microg/g, respectively, in Chihuahua; 42, 2, and 467 microg/g, respectively, in Monterrey, and 113, 112, and 2,448 microg/g, respectively, in Torreón. Dust concentrations of all heavy metals were significantly higher around the active smelter in Torreón, where more than 90% of samples exceeded Superfund cleanup goals. At all sites, dust concentrations were inversely related to distance from the industrial source, implicating these industries as the likely source of the contamination. We concluded that residential neighborhoods around metal smelting and refining sites in these three cities are contaminated by heavy metals at concentrations likely to pose a health threat to people living nearby. Evaluations of human exposure near these sites should be conducted. Because multiple heavy metal pollutants may exist near smelter sites, researchers should avoid attributing toxicity to one heavy metal unless others have been measured and shown not to coexist.

Environmental arsenic exposure of children around a former copper smelter site

Arsenic residues in the communities surrounding former smelters remain a public health concern, especially for infants and children. To evaluate environmental exposure among these children, a population-based cross-sectional study was conducted in the vicinity of a former copper smelter in Anaconda, Montana. A total of 414 children less than 72 months old were recruited. First morning voided urine samples and environmental samples were collected for arsenic measurements. The geometric mean of speciated urinary arsenic was 8.6 microg/liter (GSD = 1.7, N = 289). Average arsenic levels of different types of soil ranged from 121 to 236 microg/g and were significantly related to proximity and wind direction to the smelter site. The same significant relationship was observed for interior dust arsenic. Speciated urinary arsenic was found to be significantly related to soil arsenic in bare areas in residential yards (P < 0.0005). In general, elevated excretion of arsenic was demonstrable and warranted parents' attention to reduce exposure of their children to environmental arsenic.

Probabilistic prediction of exposures to arsenic contaminated residential soil

Probabilistic modelling using Monte Carlo simulation has been proposed as a more scientifically valid method of estimating soil contaminant exposures than conservative deterministic methods currently used by regulatory agencies. A retrospective application of probabilistic modelling to an exposure scenario involving arsenic-contaminated residential soil near the former ASARCO smelter near Tacoma, Washington is presented. The population of interest is children, aged 2-6 years, living within one-half mile (0.3 km) of the smelter site. Models that predict urinary arsenic levels based on unintentional soil ingestion and inhalation exposure pathways are used. Distributions of exposure variables are based on site-specific data and previous exposure studies. Simulated urinary arsenic levels are compared with data from two biomonitoring studies performed during the late 1980s. Arsenic distributions produced by simulation and biomonitoring are significantly different, and likely contributors to this difference are discussed. However the probabilistic model provides closer estimations of urinary arsenic levels than conservative deterministic models similar to those used by regulatory agencies, and provides useful information regarding parameter uncertainty. Soil ingestion rate was a driving variable in the probabilistic models. Further quantification of soil ingestion rates is warranted.

Resolving intertracer inconsistencies in soil ingestion estimation

In this article we explore sources and magnitude of positive and negative error in soil ingestion estimates for children on a subject-week and trace element basis. Errors varied among trace elements. Yttrium and zirconium displayed predominantly negative error; titanium and vanadium usually displayed positive error. These factors lead to underestimation of soil ingestion estimates by yttrium and zirconium and a large overestimation by vanadium. The most reliable tracers for soil ingestion estimates were aluminum, silicon, and yttrium. However, the most reliable trace element for a specific subject-day (or week) would be the element with the least error during that time period. The present analysis replaces our previous recommendations that zirconium and titanium are the most reliable trace elements in estimating soil ingestion by children. This report identifies limitations in applying the biostatistical model based on data for adults to data for children. The adult-based model used data less susceptible to negative bias and more susceptible to source error (positive bias) for titanium and vanadium than the data for children. These factors contributed significantly to inconsistencies in model predictions of soil ingestion rates for children. Correction for error at the subject-day level provides a foundation for generation of subject-specific daily soil ingestion distributions and for linking behavior to soil ingestion.

Parameter values to model the soil ingestion pathway

Soil ingestion is an important exposure pathway for contaminants that are not otherwise very mobile in the environment. Health of both humans and animals can be affected. This paper summarizes the literature and recommends models and probabilistic parameter values for risk assessment applications. Models of the pathway require estimates of the amounts of soil ingested, the concentration of contaminants relative to the original soil, and the bioavailability in the gut of the contaminants ingested with soil. Using a lead-contaminated sandbox as an example, the modelling recommendations suggest that a child typically may consume 50 mg d(-1) of the sandbox soil, the soil ingested will have a tenfold higher lead concentration than the original soil, and the lead will be as bioavailable as if ingested as inorganic lead in water.

Recommended distributions for exposure factors frequently used in health risk assessment

Although there has been nearly complete agreement in the scientific community that Monte Carlo techniques represent a significant improvement in the exposure assessment process, virtually all state and federal risk assessments still rely on the traditional point estimate approach. One of the rate-determining steps to a timely implementation of Monte Carlo techniques to regulatory decision making is the development of "standard" data distributions that are considered applicable to any setting. For many exposure variables, there is no need to wait any longer to adopt Monte Carlo techniques into regulatory policy since there is a wealth of data from which a robust distribution can be developed and ample evidence to indicate that the variable is not significantly influenced by site-specific conditions. In this paper, we propose several distributions that can be considered standard and customary for most settings. Age-specific distributions for soil ingestion rates, inhalation rates, body weights, skin surface area, tapwater and fish consumption, residential occupancy and occupational tenure, and soil-on-skin adherence were developed. For each distribution offered in this paper, we discuss the adequacy of the database, derivation of the distribution, and applicability of the distribution to various settings and conditions.

The benefits of probabilistic exposure assessment: three case studies involving contaminated air, water, and soil

Probabilistic risk assessments are enjoying increasing popularity as a tool to characterize the health hazards associated with exposure to chemicals in the environment. Because probabilistic analyses provide much more information to the risk manager than standard "point" risk estimates, this approach has generally been heralded as one which could significantly improve the conduct of health risk assessments. The primary obstacles to replacing point estimates with probabilistic techniques include a general lack of familiarity with the approach and a lack of regulatory policy and guidance. This paper discusses some of the advantages and disadvantages of the point estimate vs. probabilistic approach. Three case studies are presented which contrast and compare the results of each. The first addresses the risks associated with household exposure to volatile chemicals in tapwater. The second evaluates airborne dioxin emissions which can enter the food-chain. The third illustrates how to derive health-based cleanup levels for dioxin in soil. It is shown that, based on the results of Monte Carlo analyses of probability density functions (PDFs), the point estimate approach required by most regulatory agencies will nearly always overpredict the risk for the 95th percentile person by a factor of up to 5. When the assessment requires consideration of 10 or more exposure variables, the point estimate approach will often predict risks representative of the 99.9th percentile person rather than the 50th or 95th percentile person. This paper recommends a number of data distributions for various exposure variables that we believe are now sufficiently well understood to be used with confidence in most exposure assessments. A list of exposure variables that may require additional research before adequate data distributions can be developed are also discussed.

Evaluation of methods for monitoring the potential exposure of small children to pesticides in the residential environment

A nine-home pilot study was conducted to evaluate monitoring methods in the field that may be used to assess the potential exposures of children aged 6 months to 5 years to pesticides found in the home environment. Several methods, some of which were newly developed in this study, were tested for measuring pesticide residues in indoor air, carpet dust, outdoor soil, and on the children's hands. Information was also collected on household characteristics, pesticides used and stored at the residence, and children's activities. Pesticides were detected at all nine study homes. With the exception of one home, at least one pesticide was detected in all matrices sampled at each house. Of the 30 target pesticides, 23 were detected during the study. The most frequently detected pesticides were chlordane, chlorpyrifos, dieldrin, hepatachlor, and pentachlorophenol. The greatest number of pesticides and highest concentrations were found in carpet dust. The results of these investigations will be discussed in terms of performance of the methods and the distribution of pesticides across the various media sampled.

A proposed approach to regulating contaminated soil: identify safe concentrations for seven of the most frequently encountered exposure scenarios

Since 1980, more than 10,000 sites in the United States have been shown to contain soil which has elevated concentrations of various xenobiotics. Since that time, guidelines for deciding whether the level of contamination is worthy of concern have been proposed or promulgated by dozens of local, state, and federal regulatory agencies. Unfortunately, there has been little consistency in the guidelines suggested for each soil contaminant. For example, (a) the basis or rationale for some of the cleanup levels is unclear, (b) approaches to setting cleanup levels vary between states and agencies, (c) cleanup objectives often vary among agencies within the same state, and (d) the cleanup levels are usually set in a scientifically haphazard manner. This paper proposes that the most cost-effective and efficient way to quickly regulate contaminated soil is to establish "safe" concentrations for each chemical for the seven most common exposure scenarios. These exposure scenarios include (1) residential, (2) industrial, (3) agricultural, (4) recreational, (5) groundwater, (6) wildlife and aquatic species, and (7) runoff/erosion of particulates to waterways. The scientific approach and rationale for calculating the cleanup criteria are illustrated by evaluating dioxin and benzene, toluene, and xylene (BTX). The methods suggested here indicate that levels of dioxin of 25 and 50 ppb in residential and industrial soils, respectively, should be acceptable. The predominant concern for the agricultural and recreational scenarios is the runoff of particulates to waterways. For BTX, benzene will dictate the degree of cleanup and the primary hazard at most residential sites will be the inhalation of vapors. Benzene concentrations of 2.5, 14, and 250 ppm should be acceptable for residential, industrial, and recreational soils, respectively. Depending on the depth to groundwater and aquifer use, protection of groundwater may be the driving concern for establishing BTX cleanup levels and must be determined using site-specific factors.

Recent developments on the hazards posed by 2,3,7,8-tetrachlorodibenzo-p-dioxin in soil: implications for setting risk-based cleanup levels at residential and industrial sites

Since the publication of the Times Beach risk assessment in 1984, which suggested that residential soils were of concern when the level of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was in excess of 1 ppb, there has been continued interest in this topic. Studies conducted within the past 5 yr on the environmental and toxicological behavior of TCDD, as well as refinement of parameters regarding human exposure, indicate that previous assessments of the risk to humans posed by TCDD-contaminated soil were overestimated. In this paper, recent information drawn from nearly 100 recently published articles regarding the histopathology interpretation of the Kociba bioassay, environmental fate and half-life of TCDD in soil, and estimates of human exposure via soil ingestion, dermal contact, inhalation, surface runoff, and the consumption of fish were incorporated into a risk assessment. Cleanup levels for TCDD in residential and industrial soils were calculated based on most likely exposure scenarios. Probability distributions of key exposure parameters were incorporated into a Monte Carlo uncertainty analysis to predict the range and probability of TCDD uptake and corresponding cleanup levels in soil. This analysis demonstrated that the most significant route of human exposure to TCDD is through dermal contact with soil, followed by soil ingestion, fish consumption, and inhalation of airborne particulates. At residential sites, soils containing 20 parts per billion (ppb) of TCDD were found to pose a lifetime cancer risk no greater than 1 in 100,000 (10(-5) risk) under typical exposure conditions. Based on the Monte Carlo analysis, soil concentrations for the 75th and 95th percentile person were 12 and 7 ppb (10(-5) risk), respectively. In industrial soils, TCDD concentrations ranged between 131 and 582 ppb (10(-5) risk), depending on the amount of time spent outdoors under typical exposure conditions. Industrial soil concentrations of approximately 93 and 46 ppb (10(-5) risk) were calculated for the 75th and 95th percentile worker, respectively, engaged in outdoor activities. The range of TCDD concentrations in industrial soils was not reduced significantly when the consumption of fish from a neighboring waterway by off-site receptors was considered. While cleanup levels for TCDD should be derived on a site-specific basis, this analysis indicated that soil cleanup standards can be generally higher than those implemented over the past 8 yr.

A guide to interpreting soil ingestion studies. II. Qualitative and quantitative evidence of soil ingestion

Four major studies have attempted to qualitatively and quantitatively assess the extent of soil ingestion in children using the soil tracer methodology. The validity of the estimates of soil ingestion in each study was reevaluated in light of the inherent strengths and limitations of study design and/or execution, as well as via a novel methodology for estimating the soil recovery variance for each tracer, which then led to the estimation of soil ingestion detection limits for each tracer for studies performing mass-balance analyses. Based on these analyses it is concluded that the Binder et al. (1986, Arch. Environ. Health 41, 341-345) and Van Wijnen et al. (1990, Environ. Res. 51, 147-162) studies provide no convincing evidence to support qualitative and quantitative estimates of soil ingestion due to inherent limitations in their respective study designs. The Davis et al. (1990, Arch. Environ. Health 45, 112-122) and Calabrese et al. (1989, Regul. Toxicol. Pharmacol. 10, 123) studies displayed convincing qualitative evidence of soil ingestion. However, the results indicate that the median soil ingestion estimates of Davis et al. were less reliable than those of Calabrese et al. The range of detection limits vary according to the tracer and the assumption of acceptable precision in recovery estimation. The minimum detection level of soil ingestion in children in the Calabrese et al. study, with a variance in recovery of 100% +/- 20%, was 21 mg/day based on Zr.(ABSTRACT TRUNCATED AT 250 WORDS)

A guide to interpreting soil ingestion studies. I. Development of a model to estimate the soil ingestion detection level of soil ingestion studies

This paper provides a model with which to predict soil ingestion recovery values in soil ingestion studies either retrospectively or prospectively. The predictive equations generated from the model can be used to estimate minimum soil ingestion detection levels from soil ingestion studies which use mass-balance methods. The model is derived from data assessing soil recovery efficiencies in adults using eight different predictive tracer elements. The results constitute a methodology for determining minimum detection levels of soil ingestion and hence have important regulatory significance.

Assessment of the human health risks posed by exposure to chromium-contaminated soils

Millions of tons of chromite-ore processing residue have been used as fill in various locations in northern New Jersey and elsewhere in the United States. The primary toxicants in the residue are trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)]. The hazard posed by Cr(III) is negligible due to its low acute and chronic toxicity. In contrast, Cr(VI) is a human carcinogen following inhalation of high concentrations. It can also cause allergic contact dermatitis. This evaluation addresses a residential site where the arithmetic mean (x) and geometric mean (gm) concentrations of Cr(III) in soil were 2879 and 1212 mg/kg (ppm). The mean and geometric mean concentrations of Cr(VI) were 180 and 4 mg/kg, respectively. The uptake (absorbed dose) of Cr(III) via soil ingestion, consumption of homegrown vegetables, and ingestion of inspired particles was determined. The uptake of Cr(VI) via dermal absorption from contact with surface soil and building wall surfaces, as well as inhalation, was also evaluated. The techniques used in this assessment are applicable for evaluating the human health risks posed by any residential site having contaminated soil. The potential for both sensitized and unsensitized persons to develop allergic contact dermatitis due to exposure to soil contaminated at these levels was found to be negligible. The estimated average daily dose (ADD) via ingestion and dermal absorption for the maximally exposed individual (MEI) was about 1500- and 40-fold below the EPA reference dose (RfD) for Cr(III) and Cr(VI), respectively. It was shown that for residential sites, the most important route of exposure to Cr(III) was incidental soil ingestion. Although not relevant to these sites specifically, if garden vegetables could be successfully grown in these soils, then they would probably be the predominant source of uptake of Cr(III). Since inhalation of Cr(VI)-contaminated dust (but not ingestion or dermal contact) poses a cancer hazard, the doses and associated risks were assessed. The estimated cancer risks for the MEI and most likely exposed individual (MLEI) were approximately 5 x 10(-9) and 2 x 10(-9), respectively. These levels of risk have always been considered well below those that warrant regulatory concern. For persons living on residential properties, the cancer risk due to inhaling suspended particles is likely to be less than 1 in 1,000,000 if Cr(VI) levels in soil are less than 180 mg/kg (ppm). Based on this analysis, the levels of Cr(III) and Cr(VI) at this and similar sites do not pose a health hazard following acute or chronic exposure.

Human exposures from dioxin in soil--a meeting report

A 1984 risk assessment identified 1 part per billion (ppb) of dioxin in soil as a "level of concern" at Times Beach, Mo. The authors of the assessment had to rely on many assumptions in their analysis, but since that time, a number of investigators have obtained data that bear directly on estimating exposures from substances in soil. Partly because of the assumptions and partly because of the site-specific nature of their analysis, the authors of the Times Beach risk assessment cautioned against the adoption of 1 ppb as a delineator between acceptable and nonacceptable levels of contamination. Those cautions have been more frequently ignored than honored, and 1 ppb has become a de facto standard. In November 1989, the Center for Risk Management at Resources for the Future hosted 50 experts at a workshop that heard and discussed published and new research about exposure estimates and measures. The 1984 assessment identified soil ingestion by toddlers as the single most important source of exposure to dioxin in soil; it assumed that toddlers ingested 10 g soil daily. Research discussed at the workshop shows that the average child ingests about 0.04 g soil daily, but that 1 of 320 studied children ingested 5 g. These findings leave open the risk management decision about whether acceptable exposure levels should be established to protect the average child or the extreme child. Furthermore, the absence of children from commercial and industrial sites led to suggestions that higher concentrations of dioxin are acceptable in soil at such sites. Some workshop participants objected to those suggestions because of the difficulty of assuring that such sites would not revert to residential use in the future. Whether deed restrictions are sufficient to prevent such reversions was seen as an important research topic. Workshop participants repeatedly discussed the importance of site-specific data in estimating exposures: Measured half-lives of dioxin in different soils range from 18 mo to greater than 100 yr; bioavailability from various soils differs by at least 20-fold; and the amounts of soil ingested by grazing cattle can differ 20-fold depending on conditions. Workshop participants agreed upon some suggestions for research and generally favored the development of guidelines for exposure assessment that would allow consideration of site-specific information. Furthermore, they generally agreed that no single concentration should be taken as a level of concern. Instead, levels should be established that consider the planned uses of the sites.

Preliminary adult soil ingestion estimates: results of a pilot study

Six adults were evaluated for the extent to which they ingest soil. This study was originally part of a large childhood soil ingestion study and was used to validate part of the analytical methodology used in that larger study. The adult study followed the soil tracer methodology of the children's study. The principal findings of the adult study revealed that the four most reliable tracer elements based on recovery studies in a mass balance assessment [aluminum (Al), silicon (Si), yttrium (Y), and zirconium (Zr)] yielded the following mean daily adult soil ingestion estimations: Al (77 mg), Si (5 mg), Y (53 mg), and Zr (22 mg). The median daily soil ingestion estimations based on these same tracer elements were: Al (57 mg), Si (1 mg), Y (65 mg), and Zr (-4 mg). These findings represent the first published quantitative estimates of soil ingestion by adults.

Assessing the contribution from lead in mining wastes to blood lead

Lead has been recognized for years as an environmental pollutant of concern for young children. Nonetheless, many children in the United States still experience high body burdens of lead. Reducing exposure to lead must include an assessment of all potential sources of lead and a definition of routes of exposure. In this paper, the relationships between soil lead and blood lead concentrations in residents in communities with high soil lead concentrations resulting from past mining and ore processing (milling) activities are compared to those derived from studies in urban communities or communities with operating smelters. The impact of mine waste-derived lead in soil (usually in the form of lead sulfide) on blood lead is less than that for lead in soil derived from smelter, vehicle, or paint sources. Possible reasons for a reduced impact of lead sulfide on blood lead in children in mining communities include the following: lead from mining sources contributes less to lead in the immediate environment of children than lead from other sources; mine wastes typically are of larger particle size, which decreases the bioavailability of lead in the gastrointestinal tract; and lead sulfide is absorbed less in the gastrointestinal tract compared to other lead species. A reduced impact of mine waste-derived lead on blood lead may be important from a regulatory point of view. Expensive cleanup actions for lead-contaminated soils in mining communities based on acceptable soil lead concentrations derived from smelter or urban communities may be questionable in terms of reducing blood lead in children.

Quantitative estimates of soil ingestion in normal children between the ages of 2 and 7 years: population-based estimates using aluminum, silicon, and titanium as soil tracer elements

This investigation was undertaken to provide quantitative estimates of soil ingestion in young children on a population basis, and to identify demographic and behavioral characteristics that influence the amount of soil ingested. A total of 104 children between the ages of 2 and 7 yr were selected randomly from the population of a three-city area in southeastern Washington State. Using aluminum, silicon, and titanium as tracer elements, a mass-balance approach was employed to assess daily soil ingestion. A duplicate of all food items consumed, all feces, and some urine excreted were collected on 4 consecutive d, along with soil and house dust samples from each child's home. Samples were analyzed by x-ray fluorescence spectrometry. After adjustment of the soil ingestion estimates to account for missing food, excreta samples, and nonfood items consumed, the average daily values based on the three tracer elements were: aluminum, 38.9 mg/d (median = 25.3 mg/d); silicon, 82.4 mg/d (median = 59.4 mg/d); and titanium, 245.5 mg/d (median = 81.3 mg/d). No consistent pattern emerged regarding a demographic or behavioral profile that was predictive of soil ingestion. This work demonstrates (a) the feasibility of conducting large-scale studies to determine soil intake levels in human populations, (b) provides estimates of soil ingestion in small children based on a random population sample, and (c) suggests several possibilities for additional research initiatives in this area.