Modeled estimates of soil and dust ingestion rates for children

Innovative non-targeted screening approach using High-resolution mass spectrometry for the screening of organic chemicals and identification of specific tracers of soil and dust exposure in children

Environmental contamination through direct contact, ingestion and inhalation are common routes of children's exposure to chemicals, in which through indoor and outdoor activities associated with common hand-to-mouth, touching objects, and behavioral tendencies, children can be susceptible and vulnerable to organic contaminants in the environment. The objectives of this study were the screening and identification of a wide range of organic contaminants in indoor dust, soil, food, drinking water, and urine matrices (N = 439), prioritizing chemicals to assess children's environmental exposure, and selection of unique tracers of soil and dust ingestion in young children by non-targeted analysis (NTA) using Q-Exactive Orbitrap followed data processing by the Compound Discoverer (v3.3, SP2). Chemical features were first prioritized based on their predominant abundance (peak area>500,000), detection frequency (in >50% of the samples), available information on their uses and potential toxicological effects. Specific tracers of soil and dust exposure in children were selected in this study including Tripropyl citrate and 4-Dodecylbenzenesulfonic acid. The criteria for selection of the tracers were based on their higher abundance, detection frequency, unique functional uses, measurable amounts in urine (suitable biomarker), and with information on gastrointestinal absorption, metabolism, and excretion, and were further confirmed by authentic standards. We are proposing for the first time suitable unique tracers for dust ingestion by children.

Children's lead exposure in the U.S.: Application of a national-scale, probabilistic aggregate model with a focus on residential soil and dust lead (Pb) scenarios

Lead (Pb) exposures from soil and dust ingestion contribute to children's blood lead levels (BLLs) in the United States. The U.S. Environmental Protection Agency (EPA)'s Strategy to Reduce Lead Exposures and Disparities in U.S. Communities and the Federal Action Plan to Reduce Childhood Lead Exposure describe multi-pronged collaborative approaches. These include reducing multi-media lead exposures nationally using analytical tools such as EPA's Stochastic Human Exposure and Dose Simulation model for lead [SHEDS-Pb; formerly known as SHEDS-IEUBK (Integrated Exposure Uptake Biokinetic model)], which was initially developed and applied with a focus on children's drinking water exposures. In this study we applied SHEDS-Pb to determine what residential soil Pb and dust Pb concentrations (individually and their sum) can keep BLLs of potentially exposed young children in the general U.S. population below specified values, considering aggregate exposures from water, soil, dust, food, and air. We considered two age groups (1 to <2 years and 2 to <6 years), two BLL values (5 μg/dL and 3.5 μg/dL), and two population percentiles (95th and 97.5th). Sensitivity analyses were conducted using several alternative model inputs and data sets, yielding 15 scenarios summarized in the paper. Of those scenarios, we focused on ones with the most recent science and available data. Modeled soil Pb concentrations by age group, population percentile and reference BLL scenarios for the focus scenarios ranged from 70 ppm to 220 ppm; and modeled dust Pb concentrations ranged from 110 ppm to 240 ppm. These results are consistent with current soil and dust Pb concentrations in the U.S. general population and are lower than most of the current U.S. Federal standards. Estimated BLLs compared well with measured BLLs from CDC's NHANES 2009-2016 (0-27 % relative error for focus scenarios). This analysis can be used to inform EPA and other federal Pb efforts.

Impact of Airborne Pathogen-Derived Extracellular Vesicles on Macrophages Revealed by Raman Spectroscopy and Multiomics

Long-term exposure to the indoor environment may pose threats to human health due to the presence of pathogenic bacteria and their byproducts. Nanoscale extracellular vesicles (EVs) extensively secreted from pathogenic bacteria can traverse biological barriers and affect physio-pathological processes. However, the potential health impact of EVs from indoor dust and the underlying mechanisms remain largely unexplored. Here, Raman spectroscopy combined with multiomics (genomics and proteomics) was used to address these issues. Genomic analysis revealed that Pseudomonas was an efficient producer of EVs that harbored 68 types of virulence factor-encoding genes. Upon exposing macrophages to environmentally relevant doses of Pseudomonas aeruginosa PAO1-derived EVs, macrophage internalization was observed, and release of inflammatory factors was determined by RT-PCR. Subsequent Raman spectroscopy and unsupervised surprisal analysis of EV-affected macrophages distinguished metabolic alterations, particularly in proteins and lipids. Proteomic analysis further revealed differential expression of proteins in inflammatory and metabolism-related pathways, indicating that EV exposure induced macrophage metabolic reprogramming and inflammation. Collectively, our findings revealed that pathogen-derived EVs in the indoor environments can act as a new mediator for pathogens to exert adverse health effects. Our method of Raman integrated with multiomics offers a complementary approach for rapid and in-depth understanding of EVs' impact.

Strategies for cost-effective remediation of widespread oil-contaminated soils in Kuwait, an environmental legacy of the first Gulf War

The Kuwaiti oil fire during the first Gulf War resulted in the formation of approximately 300 "oil lakes" of varying sizes that covered over 110 km2 of the desert land. This threatens the fragile desert ecosystems and human health. Following the award of over US$2 billion to the State of Kuwait by the United Nations, large-scale remediation of the oil-contaminated soils has now been on the agenda. However, how to implement the remediation program in a cost-effective way represents a major challenge. In this study, cost-effective remediation strategies were developed based on field and laboratory investigations in a typical oil lake area. Overall, most of the lighter petroleum hydrocarbons (PHCs) were lost due to evaporation. Long-chain aliphatic PHCs dominated the PHCs in the investigated oil lake area. This has implications for developing remediation strategies. Toxicity assessment results showed that the majority of soils pose a low environmental risk with a hazard index <1. Therefore, intensive treatment of these PHCs may not be necessary for these soils. Although active treatment methods are needed to remove the contaminants as soon as practical for the relatively small areas of high contamination, more cost-effective passive methods should be considered to minimize the remedial costs for the larger area of the non-hotspot areas. Given the extremely low risk in terms of groundwater contamination by the contaminated soils, it may not be necessary to remove the soils from the contaminated sites. A low-cost capping method should be sufficient to minimize human exposure to the PHC-contaminated soils.

Advancing Methodologies Used in Trace Element-Based Mass Balance Studies to Separately Estimate Soil and Dust Ingestion Rates for Children

Historically, soil ingestion rate estimates were based on trace element-based mass balance (MB) study results. These were used in assessing exposures and health risks for children residing in Superfund or chemically contaminated communities. However, soil and dust can have considerable differences with respect to their sources, chemical, physical, and toxicological characteristics. Unfortunately, the MB approach is incapable of disentangling dust ingestion rates from soil ingestion rates. Alternative methods, such as activity pattern and biokinetic modeling techniques, have also been used to predict soil and dust ingestion rates. The results from these studies differed from those obtained from the MB studies. This research evaluated the MB methodology and formulated a physical model which characterized the environmental and behavioral determinants of soil and dust ingestion exposures by children. This new approach explicitly separates outdoor soil exposures from the indoor tracked-in soil portion of the dust and total dust exposures by utilizing information from five key MB studies along with new information derived from the SHEDS-Soil/Dust time-activity pattern-based modeling runs. Application of this new hybrid methodology showed that the predicted mean soil ingestion rates are 30%-70% less than the "total soil" ingestion rates obtained from the selected MB studies. In contrast, most of the predicted dust ingestion rate estimates were typically greater than the predicted soil ingestion rates. Moreover, the predicted total soil plus dust ingestion rates were found to be mostly higher (by ≤ 60%) than the MB-based "total soil" ingestion rates. Except for one study these results were higher than the results produced by the stand-alone SHEDS-Soil/Dust model runs. Across the MB studies analyzed, predicted outdoor soil ingestion rate contributions to "total soil" ingestion rates varied between 29% and 70% while the tracked-in soil portion of the indoor dust ingestion rates varied between 30% and 71%.

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.

A qualitative characterization of meso-activity factors to estimate soil exposure for agricultural workers

BACKGROUND

Agricultural workers' exposure to soil contaminants is not well characterized. Activity pattern data are a useful exposure assessment tool to estimate extent of soil contact, though existing data do not sufficiently capture the range and magnitude of soil contact in the agricultural context.

OBJECTIVE

We introduce meso-activity, or specific tasks, to improve traditional activity pattern methodology. We propose a conceptual framework to organize the factors that may modify soil exposure and impact soil contact estimates within each meso-activity in agriculture. We build upon models from the US EPA to demonstrate an application of this framework to dose estimation.

METHODS

We conducted in-depth interviews with sixteen fruit and vegetable growers in Maryland to characterize factors that influence soil exposure in agriculture. For illustrative purposes, we demonstrate the application of the framework to translate our qualitative data into quantitative estimates of soil contact using US EPA models for ingestion and dermal exposure.

RESULTS

Growers discussed six tasks, or meso-activities, involving interaction with soil and described ten factors that may impact the frequency, duration and intensity of soil contact. We organized these factors into four categories (i.e., Environmental, Activity, Timing and Receptor; EAT-R) and developed a framework to improve agricultural exposure estimation and guide future research. Using information from the interviews, we estimated average daily doses for several agricultural exposure scenarios. We demonstrated how the integration of EAT-R qualitative factors into quantitative tools for exposure assessment produce more rigorous estimates of exposure that better capture the true variability in agricultural work.

SIGNIFICANCE

Our study demonstrates how a meso-activity-centered framework can be used to refine estimates of exposure for agricultural workers. This framework will support the improvement of indirect exposure assessment tools (e.g., surveys and questionnaires) and inform more comprehensive and appropriate direct observation approaches to derive quantitative estimations of soil exposure.

IMPACT STATEMENT

We propose a novel classification of activity pattern data that links macro and micro-activities through the quantification and characterization of meso-activities and demonstrate how the application of our qualitative framework improves soil exposure estimation for agricultural workers. These methodological advances may inform a more rigorous approach to the evaluation of pesticide and other chemical and biological exposures incurred by persons engaged in the cultivation of agricultural commodities in soil.

Model-based predictions of soil and dust ingestion rates for U.S. adults using the stochastic human exposure and dose simulation soil and dust model

BACKGROUND

Adults can be exposed to chemicals through incidental ingestion of soil and dust, either through hobbies, occupations, or behaviors that increase contact with soil or dust (e.g., cleaning or renovating). However, few data describing these ingestion rates are available.

OBJECTIVE

Our objective was to use the Stochastic Human Exposure and Dose Simulation Soil and Dust (SHEDS-Soil/Dust) model to estimate distributions of soil and dust ingestion rates for adults (≥21 years old) with varying degrees of soil and dust contact.

METHODS

We parameterized SHEDS-Soil/Dust to estimate soil and dust ingestion rates for several categories of adults: adults in the general population; adults with moderate (higher) soil exposure (represented by hobbyists, such as gardeners, with increased soil contact); adults with high soil exposure (represented by occupationally exposed individuals, such as landscapers); and individuals who have high dust exposure (e.g., are in contact with very dusty indoor environments).

RESULTS

Total soil plus dust ingestion for adults in the general population was 7 mg/day. Hobbyists or adults with moderate soil exposure averaged 33 mg/day and occupationally exposed individuals averaged 123 mg/day. Total soil plus dust ingestion for adults in the high dust exposure scenario was 25 mg/day. Results were driven by time spent in contact with soil and, thus, warmer seasons (e.g., summer) were associated with higher ingestion rates than colder seasons (e.g., winter).

SIGNIFICANCE

These results provide modeled estimates of soil and dust ingestion rates for adults for use in decision making using real-world exposure considerations. These modeled estimates suggest that soil and dust ingestion is a potential concern for adults who spend a higher amount of time interacting with either soil or dusty environments.

IMPACT STATEMENT

The parameterization of real-world scenarios within the application of SHEDS-Soil/Dust model to predict soil and dust ingestion rates for adults provides estimates of soil and dust ingestion rates useful for refining population-based risk assessments. These data illuminate drivers of exposure useful for both risk management decisions and designing future studies to improve existing tracer methodologies.

Countrywide Spatial Variation of Potentially Toxic Element Contamination in Soils of Turkey and Assessment of Population Health Risks for Nondietary Ingestion

Countrywide surface soil concentrations of potentially toxic elements (PTEs) in Turkey were reviewed in the Web of Science database. A total of 93 papers were investigated to compose a PTE dataset for determining spatial variations and estimating exposure and health risks. Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were selected as PTEs in surface soil. A compiled PTE concentration dataset was used to estimate chronic toxic risks (CTRs) and carcinogenic risks (CRs) according to the deterministic and probabilistic approaches. While the CTR and CR levels of age and sex groups were estimated using a deterministic approach, population risks were estimated using a probabilistic approach. CTR and CR levels in lower age groups and female sex groups were estimated to be higher than those in higher age groups and associated male sex groups. The average CTR levels of the nondietary ingestion of As-containing soil in <11 year age groups were near/just above the threshold level, while As-associated average CR levels of adults and other age groups were estimated to be in the acceptable risk range (10^-6 < CR < 10^-5) and low priority risk range (10^-5 < CR < 10^-4), respectively. As-, Cr(VI)-, and Pb-associated upper-bound CR levels of the Turkish population were simulated to be 5.14 × 10^-4, 6.23 × 10^-5, and 2.34 × 10^-6, respectively. Health risk models show the significance of As in both chronic toxic and carcinogenic effects.

Exposure Prioritization (Ex Priori): A Screening-Level High-Throughput Chemical Prioritization Tool

To estimate potential chemical risk, tools are needed to prioritize potential exposures for chemicals with minimal data. Consumer product exposures are a key pathway, and variability in consumer use patterns is an important factor. We designed Ex Priori, a flexible dashboard-type screening-level exposure model, to rapidly visualize exposure rankings from consumer product use. Ex Priori is Excel-based. Currently, it is parameterized for seven routes of exposure for 1108 chemicals present in 228 consumer product types. It includes toxicokinetics considerations to estimate body burden. It includes a simple framework for rapid modeling of broad changes in consumer use patterns by product category. Ex Priori rapidly models changes in consumer user patterns during the COVID-19 pandemic and instantly shows resulting changes in chemical exposure rankings by body burden. Sensitivity analysis indicates that the model is sensitive to the air emissions rate of chemicals from products. Ex Priori's simple dashboard facilitates dynamic exploration of the effects of varying consumer product use patterns on prioritization of chemicals based on potential exposures. Ex Priori can be a useful modeling and visualization tool to both novice and experienced exposure modelers and complement more computationally intensive population-based exposure models.

Inadvertently Generated PCBs in Consumer Products: Concentrations, Fate and Transport, and Preliminary Exposure Assessment

Although commercial polychlorinated biphenyl (PCB) production was banned in 1979 under the Toxics Substance Control Act, inadvertent generation of PCBs through a variety of chemical production processes continues to contaminate products and waste streams. In this research, a total of 39 consumer products purchased from local and online retailer stores were analyzed for 209 PCB congeners. Inadvertent PCBs (iPCBs) were detected from seven products, and PCB-11 was the only congener detected in most of the samples, with a maximum concentration exceeding 800 ng/g. Emission of PCB-11 to air was studied from one craft foam sheet product using dynamic microchambers at 40 °C for about 120 days. PCB-11 migration from the product to house dust was also investigated. The IAQX program was then employed to estimate the emissions of PCB-11 from 10 craft foam sheets to indoor air in a 30 m3 room at 0.5 h-1 air change rate for 30 days. The predicted maximum PCB-11 concentration in the room air (156.8 ng/m3) and the measured concentration in dust (20 ng/g) were applied for the preliminary exposure assessment. The generated data from multipathway investigation in this work should be informative for further risk assessment and management for iPCBs.

A mass-balance approach to evaluate arsenic intake and excretion in different populations

Unless a toxicant builds up in a deep compartment, intake by the human body must on average balance the amount that is lost. We apply this idea to assess arsenic (As) exposure misclassification in three previously studied populations in rural Bangladesh (n = 11,224), Navajo Nation in the Southwestern United States (n = 619), and northern Chile (n = 630), under varying assumptions about As sources. Relationships between As intake and excretion were simulated by taking into account additional sources, as well as variability in urine dilution inferred from urinary creatinine. The simulations bring As intake closer to As excretion but also indicate that some exposure misclassification remains. In rural Bangladesh, accounting for intake from more than one well and rice improved the alignment of intake and excretion, especially at low exposure. In Navajo Nation, comparing intake and excretion revealed home dust as an important source. Finally, in northern Chile, while food-frequency questionnaires and urinary As speciation indicate fish and shellfish sources, persistent imbalance of intake and excretion suggests imprecise measures of drinking water arsenic as a major cause of exposure misclassification. The mass-balance approach could prove to be useful for evaluating sources of exposure to toxicants in other settings.

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.

Is hand-to-mouth contact the main pathway of children's soil and dust intake?

Children (n = 240) between the ages of 2 and 17 years were randomly selected from three cities in China. The total amount of soil and dust (SD) on their hands was measured and ranged from 3.50-187.39 mg (median = 19.49 mg). We screened for seven elements (Ce, V, Y, Al, Ba, Sc, and Mn), and Ce levels were used to calculate hand SD by variability and soil elements. The main factors affecting SD amount were location and age group, as identified using a conditional inference tree. Hand SD and the hand SD intake rate were highest in Gansu Province, followed by Guangdong and Hubei provinces, respectively. Hand SD and the hand SD intake rate were highest among children in primary school, followed by kindergarten and secondary school, respectively. The hand SD intake rate of the three typical areas was 11.9 mg/d, which was about 26.6% of the children's soil intake rate (44.8 mg/d), indicating that hand-to-mouth contact is not the main route for children's soil intake in the three areas of China.

Model based prediction of age-specific soil and dust ingestion rates for children

BACKGROUND

Soil and dust ingestion can be a primary route of environmental exposures. Studies have shown that young children are more vulnerable to incidental soil and dust ingestion. However, available data to develop soil and dust ingestion rates for some child-specific age groups are either lacking or uncertain.

OBJECTIVE

Our objective was to use the Stochastic Human Exposure and Dose Simulation Soil and Dust (SHEDS-Soil/Dust) model to estimate distributions of soil and dust ingestion rates for ten age ranges from infancy to late adolescents (birth to 21 years).

METHODS

We developed approaches for modeling age groups previously not studied, including a new exposure scenario for infants to capture exposures to indoor dust via pacifier use and accounting for use of blankets that act as a barrier to soil and dust exposure.

RESULTS

Overall mean soil and dust ingestion rates ranged from ~35 mg/day (infants, 0-<6 m) to ~60 mg/day (toddlers and young children, 6m-<11 yr) and were considerably lower (about 20 mg/day) for teenagers and late adolescents (16-<21 y). The pacifier use scenario contributed about 20 mg/day to the median dust ingestion rate for young infants. Except for the infant age groups, seasonal analysis showed that the modeled estimates of average summer mean daily total soil plus dust ingestion rates were about 50% higher than the values predicted for the winter months. Pacifier use factors and carpet dust loading values were drivers of exposure for infants and younger children. For older children, influential variables included carpet dust loading, soil adherence, and factors that capture the frequency and intensity of hand-to-mouth behaviors.

SIGNIFICANCE

These results provide modeled estimates of children's soil and dust ingestion rates for use in decision making using real-world exposure considerations.

IMPACT STATEMENT

The parameterization of scenarios to capture infant soil and dust ingestion and the application of SHEDS-Soil/Dust to a broader age range of children provides additional estimates of soil and dust ingestion rates that are useful in refining population-based risk assessments. These data illuminate drivers of exposure that are useful to both risk management applications and for designing future studies that improve upon existing tracer methodologies.

Predictive capabilities of in vitro colon bioaccessibility for estimating in vivo relative bioavailability of arsenic from contaminated soils: Arsenic speciation and gut microbiota considerations

Arsenic (As) transformation by human gut microbiota has been evidenced to impact As toxicity and human health. However, little is known about the influence of gut microbiota on As bioavailability from incidental ingestion of soil. In this study, we assessed As relative bioavailability (RBA) using an in vivo mouse model and As bioaccessibility in the colon phase of in vitro assays. Strong in vivo-in vitro correlations (R² = 0.70-0.92, P < 0.05) were observed between soil As RBA (10.2%-57.7%) and colon bioaccessibility (4.8%-49.0%) in 13 As-contaminated soils. Upon in vitro incubation of human colon microbiota, we found a high degree of As transformation and 65.9% of generated As(III) was observed in soil residues. For in vivo mouse assay, DMA(V) accounted for 79.0% of cumulative urinary As excretion. Except for As(V), dominant As species including As(III), DMA(V) and As sulfides were also detected in mouse feces. Gut bacteria (families Rikenellaceae and Marinifilaceae) could be significantly correlated with As intake and excretion in mice (P < 0.05). Our findings provide evidence that gut microbiota can affect transformation, bioavailability, and fate of the orally ingested soil As in human gastrointestinal tract.

Identifying dermal exposure as the dominant pathway of children's exposure to flame retardants in kindergartens

Exploration of multiple sources of brominated (BFRs) and organophosphate flame retardants (OPFRs) for children promotes the understanding of exposure pathways and health risk. 10 BFRs and 9 OPFRs were measured in skin wipes from hands, forehead, and arms of 30 children, and surface wipe samples from sills, toys, desks and floors, and indoor air samples of kindergartens from Xinxiang, China. Higher ∑₉OPFRs concentrations were observed in the forehead (1840 ng/m²), followed by hand (1420 ng/m²) and arm wipes (1130 ng/m²), and the ∑₈BFRs concentrations in forehead, hand and arm wipes were 116, 315 and 165 ng/m², respectively. The total concentration of OPFRs and BFRs in floor wipes (66.1 and 24.5 ng/m²) were lower than those in toy (205 and 535 ng/m²), sill (227 and 30.1 ng/m²) and desk (84.4 and 139 ng/m²) wipes. Concentrations of FRs in forehead wipes were significantly correlated with those in gaseous air (p < 0.05), moderate correlations were found between the hand wipes and surface wipes (p = 0.054). We estimated the daily average dosages (DADs) of children exposure to FRs via multiple pathways. Compared to DADs via inhalation and hand-to-mouth transfer, dermal exposure was determined to be the predominant exposure pathway to ∑₉OPFRs and ∑₈BFRs.

Estimation of Soil and Dust Ingestion Rates from the Stochastic Human Exposure and Dose Simulation Soil and Dust Model for Children in Taiwan

This study focuses on estimating the probabilistic soil and dust ingestion rates for children under 3 years old by the Stochastic Human Exposure and Dose Simulation Soil and Dust (SHEDS-S/D) model developed by the U.S. Environmental Protection Agency. The health risk of children's exposure to heavy metals through soil and dust ingestion and dermal absorption was then assessed in three exposure scenarios. In the exposure scenario of direct contact with soil, the average soil and dust ingestion rates for children aged 24 to 36 months were 90.7 and 29.8 mg day^-1 in the sand and clay groups, respectively. Hand-to-mouth soil ingestion was identified as the main contributor to soil and dust ingestion rates, followed by hand-to-mouth dust ingestion and object-to-mouth dust ingestion. The soil-to-skin adherence factor was the most influential factor increasing the soil and dust ingestion rate based on a sensitivity analysis in the SHEDS-S/D model. Furthermore, the modeled soil and dust ingestion rates based on the SHEDS-S/D model were coincident with results calculated by the tracer element method. Our estimates highlight the soil ingestion rate as the key parameter increasing the risk for children, while a higher frequency of hand washing could potentially reduce the risk.

Digging into Toxoplasma gondii infections via soil: A quantitative microbial risk assessment approach

Soil has been identified as an important source of exposure to a variety of chemical and biological contaminants. Toxoplasma gondii is one of those potential biological contaminants associated with serious health effects in pregnant women and immunocompromised patients. Gardening or consumption of homegrown vegetables may present an important route of T. gondii infection via accidental ingestion of soil. In the Netherlands, there is quantitative information on the risk of T. gondii infection via meat products, but not on the risk of infection through soil. The objective of this study was to develop a quantitative microbial risk assessment (QMRA) model for estimating the risk associated with T. gondii exposure via accidental soil ingestion in the Netherlands. In order to obtain the needed information, a magnetic capture method for detection of T. gondii oocysts in soil samples was developed, and T. gondii DNA was detected using qPCR targeting the 529 bp repeat element. The method was shown to provide 95% probability of detection (95% CI: 88-100%) when at least 34 oocysts are present in 25 g of soil. T. gondii DNA was detected in 5 of 148 soil samples with interpretable results (3%, 95% CI: 1.5-7.7%). Results for 18 samples were not interpretable due to PCR inhibition. The estimated amount of oocysts presented in qPCR positive samples was quantified by a linear model, and the amount varied from 8 to 478 in 25 g of soil. The estimated incidence rate of T. gondii infection from the QMRA model via soil varied from 0.3 to 1.8 per 1000 individuals per day. Several data gaps (e.g., soil contamination/ingestion and oocysts viability) have been identified in this study, the structure of the model can be applied to obtain more accurate estimates of the risk of T. gondii infection via soil when data become available.

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.

A quest to identify suitable organic tracers for estimating children's dust ingestion rates

Chemical exposure via dust ingestion is of great interest to researchers and regulators because children are exposed to dust through their daily activities, and as a result, to the many chemicals contained within dust. Our goal was to develop a workflow to identify and rank organic chemicals that could be used as tracers to calculate children's dust ingestion rates. We proposed a set of criteria for a chemical to be considered a promising tracer. The best tracers must be (1) ubiquitous in dust, (2) unique to dust, (3) detectable as biomarkers in accessible biological samples, and (4) have available or obtainable ADME information for biomarker-based exposure reconstruction. To identify compounds meeting these four criteria, we developed a workflow that encompasses non-targeted analysis approaches, literature and database searching, and multimedia modeling. We then implemented an ad hoc grading system and ranked candidate chemicals based on fulfillment of our criteria (using one small, publicly available dataset to show proof of concept). Initially, five chemicals (1,3-diphenylguanidine, leucine, piperine, 6:2/8:2 fluorotelomer phosphate diester, 6:2 fluorotelomer phosphate diester) appeared to satisfy many of our criteria. However, a rigorous manual investigation raised many questions about the applicability of these chemicals as tracers. Based on the results of this initial pilot study, no individual compounds can be unequivocally considered suitable tracers for calculating dust ingestion rates. Future work must therefore consider larger datasets, generated from broader measurement studies and literature searches, as well as refinements to selection criteria, to identify robust and defensible tracer compounds.

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.

Addressing uncertainty in mouthing-mediated ingestion of chemicals on indoor surfaces, objects, and dust

In indoor environments, humans ingest chemicals present as surface residues and bound to settled particles (dust), through mouthing hands (hand-to-mouth transfer) and objects (object-to-mouth transfer). Here, we introduce a novel modeling approach in support of systematic investigation into the mouthing-mediated ingestion of chemicals present in indoor environments. This model explicitly considers the indoor dynamics of dust and chemicals, building on mechanistic links with physicochemical properties of chemicals, features of the indoor environment, and human activity patterns. The evaluation of this model demonstrates that it satisfactorily reproduces chemical hand loadings and exposure data reported in the literature. We then use the evaluated model to investigate the response of mouthing-mediated ingestion to chemical partitioning between the gas phase and solid phases, expressed as the octanol-air partition coefficient (K_OA). Assuming a unit emission rate to the indoor environment, we find that low-volatility chemicals (with a K_OA greater than 10⁹) are more efficiently enriched in hand skin, resulting in higher mouthing-mediated ingestion than other compounds. For individuals living in a room with a typical level of dustiness, more than half of the chemical mass found in their hands comes from dust transfer, whereas more than half of the chemical mass ingested is the fraction present as residues on hands. We also use the new model to explore how the mouthing-mediated ingestion of chemicals is dependent on factors describing the indoor environment and human behavior. The model predicts that less frequent cleaning leads to higher accumulation of dust on indoor surfaces, thereby transferring more chemicals to hands and mouth in each contact. Introducing more dust into the room, but maintaining the same cleanup frequency, increases the dustiness of indoor surfaces, which promotes the transfer of relatively volatile chemicals (with a K_OA lower than 10⁹) to hands and mouth but decreases the transfer of chemicals with low volatility. More frequent hand contact with indoor surfaces increases both the hand loading and mouthing-mediated ingestion of chemicals, but the increases are more remarkable for adults than children because the higher surface contact frequency of children "saturates" hand loadings. An increase in handwashing frequency lowers the hand loading and mouthing-mediated ingestion of chemicals and this mitigating process is more prominent for relatively volatile chemicals. The new evaluated modeling approach can facilitate the prediction of mouthing-mediated ingestion for various age groups and the model predictions can be used to aid future fate and (bio)monitoring studies focusing on indoor contamination.

Effect of dietary vitamins in oral bioaccessibility of lead in contaminated soils based on the physiologically based extraction test

To determine the effect of vitamin supplements on the oral bioaccessibility of Pb in soils, Pb bioaccessibility was measured in the presence of 9 vitamins by a physiologically based extraction test. Gastric Pb bioaccessibility (G-BA, 2.6-83.3%) was found to be mostly reduced (1.1-3.1 fold) in the presence of B vitamins, specifically vitamins B1, B6, and B9. In contrast, a significant increase in Pb G-BA was observed with vitamin C and E involved. In the small intestinal phases, Pb bioaccessibility (I-BA) ranged from 0.1% to 16.0%, being 5-50 fold lower than the corresponding G-BA values. Vitamin C supplementation showed a 7-fold increase in Pb I-BA, with a similar increase presented in approximately 30% of samples treated to vitamin B involvement. Lead liberation in gastrointestinal digests was associated with the dissolution of Fe and Mn regulated by vitamins. In conclusion, the addition of B vitamins resulted in the reduction of gastric Pb bioaccessibility, but the bioaccessibility value increased in participation of vitamin C and E. Elevated intestinal bioaccessibility was found especially for vitamin C. This should contribute to more accurate assessment of health risks from contaminated soils. Nutritional management aimed at preventing Pb-induced toxicity can benefit from knowledge of vitamin influence on soil Pb bioaccessibility.

Transient Multimedia Model for Investigating the Influence of Indoor Human Activities on Exposure to SVOCs

Empirical evidence suggests that human occupants indoors, through their presence and activities, can influence the dynamics of semivolatile organic compounds (SVOCs). To better understand these dynamics, a transient multimedia human exposure model was developed (Activity-Based Indoor Chemical Assessment Model (ABICAM)). This model parametrizes mass-balance equations as functions of time-dependent human activities. As a case study, ABICAM simulated exposures of an archetypal adult and toddler over 24 h to diethyl phthalate (DEP), butyl benzyl phthalate (BBzP), and di-2-ethylhexyl phthalate (DEHP) that span a wide range of gas-particle partitioning tendencies. Under baseline (no activities beyond respiration), the toddler's time-average internal doses were three to four times higher than the adult's, due to differences in physical human attributes (e.g., inhalation rate). When time-dependent activities were considered, interindividual (e.g., adult vs toddler) variability was accentuated by up to a factor of 3 for BBzP. Activities with the greatest influence on time-average internal dose were showering (-71% for BBzP), cooking (+27% for DEHP), and sleeping (-26% for DEHP). Overall, the results support the hypotheses that (1) transient indoor activities can give rise to intraindividual variability in estimated internal doses of SVOCs, and (2) interindividual variability in such exposure can result from differences in activity patterns and physical human attributes, according to a compound's physical-chemical properties.

Aggregate and cumulative chronic risk assessment for pyrethroids in the French adult population

Pyrethroids are commonly used as insecticides in households, in agriculture or in veterinary and medicinal products. This study aimed to assess cumulative aggregate exposure to cyfluthrin, cypermethrin, deltamethrin and permethrin in adults in France and the associated health risk, and to identify major contributions of exposure sources and routes. External chronic exposures were estimated from dietary and several environmental sources for the oral, inhalation and dermal routes. Internal concentrations of five associated metabolites were simulated with a physiologically-based pharmacokinetic model. The predicted urinary concentrations were in same order of magnitude as those of the French ENNS biomonitoring survey. Dietary exposure, especially from cereals and animal products, was the major source of exposure. For the 1% of adults most highly exposed, dermal exposure to permethrin through medicinal and veterinary products was an important source of exposure. Considering alterations of motor, sensory and autonomic division, all individual margins of exposure were higher than 100, suggesting that no neurotoxic risk associated with the cumulative aggregate exposure to these four pyrethroids is expected for the French adult population.

Development of General Exposure Factors for Risk Assessment in Korean Children

There has been an increasing need for the risk assessment of external environmental hazards in children because they are more sensitive to hazardous chemical exposure than adults. Therefore, the development of general exposure factors is required for appropriate risk assessment in Korean children. This study aimed to determine the general exposure factors among Korean children aged ≤18 years. We developed the recommended exposure factors across five categories: physiological variables, inhalation rates, food and drinking water intake, time-activity patterns, and soil and dust ingestion. National databases were used, and direct measurements and questionnaire surveys of representative samples were performed to calculate the inhalation rate, water intake, and soil ingestion rate. With regard to the time-activity patterns, the daily inhalation rates ranged from 9.49 m3/day for children aged 0-2 years to 14.98 m3/day for those aged 16-18 years. This study found that Korean children spent an average of 22.64 h indoors, 0.63 h outdoors, and 0.73 h in-transit on weekdays. The general exposure factors of Korean children were studied for the first time, and these results could be used to assess children's exposure and risk. They also suggest the differences compared with the results of international results.

Intra- and Interlaboratory Evaluation of an Assay of Soil Arsenic Relative Bioavailability in Mice

Hand-to-mouth activity in children can be an important route for ingestion of soil and dust contaminated with inorganic arsenic. Estimating the relative bioavailability of arsenic present in these media is a critical element in assessing the risks associated with aggregate exposure to this toxic metalloid during their early life. Here, we evaluated the performance of a mouse assay for arsenic bioavailability in two laboratories using a suite of 10 soils. This approach allowed us to examine both intralaboratory and interlaboratory variations in assay performance. Use of a single vendor for preparation of all amended test diets and of a single laboratory for arsenic analysis of samples generated in the participating laboratories minimized contributions of these potential sources of variability in assay performance. Intralaboratory assay data showed that food and water intake and cumulative urine and feces production remained stable over several years. The stability of these measurements accounted for the reproducibility of estimates of arsenic bioavailability obtained from repeated intralaboratory assays using sodium arsenate or soils as the test material. Interlaboratory comparisons found that estimates of variables used to evaluate assay performance (recovery and urinary excretion factor) were similar in the two laboratories. For all soils, estimates of arsenic relative bioavailability obtained in the two laboratories were highly correlated (r² = 0.94 and slope = 0.9) in a linear regression model. Overall, these findings show that this mouse assay for arsenic bioavailability provides reproducible estimates using a variety of test soils. This robust model may be adaptable for use in other laboratory settings.

Combining data from heterogeneous surveys for aggregate exposure: Application to children exposure to lead in France

To assess human health risks related to the environment, it is necessary to aggregate exposure from multiple sources. The objective of this paper was to propose a relevant approach to combine data from heterogeneous populations and methodologies. Five different methods based on Monte-Carlo simulations were tested and compared. Differences were: taking into account or not stratification variable, timeline to assign exposure factors and concentration and way to account for concentration correlations. The methods were applied to estimate lead exposure from food, dust, soil, air, and tap water or French children aged between six months and three years old. Comparing results' uncertainty, it is recommended to 1) select a reference population representative of the target population, 2) select stratification variables to combine surveys, and 3) simulate a new population by randomly sampling individuals in the reference population and simultaneously assigning human exposure factors and environmental concentrations from other surveys in integrating correlations (MC1S). No difference was observed when taking into account correlations using vectors of determinist data from one survey or rank of correlations with the Iman-Conover method. Regardless the methods used to combine data, dust was the main exposure source, followed by soil and in a less extent by food. Exposures from air and tap water were found to be insignificant for most children.

Urinary phthalate metabolites among children in Saudi Arabia: Occurrences, risks, and their association with oxidative stress markers

Phthalates have been used as plasticizers in numerous consumer applications and therefore, their metabolites have been detected in human urine worldwide. Despite concerns regarding their potential adverse health effects, few exposure assessments have been conducted among young populations in Middle Eastern countries. In this study, children (n = 109, aged 3-9 years) were recruited from four elementary schools in Riyadh, Saudi Arabia, in 2017, and major phthalate metabolites were measured in their urine. Their parents were asked to complete a questionnaire on their behalf to assess potential exposure sources of phthalates. In addition to 18 phthalate metabolites, malondialdehyde (MDA) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were measured in urine samples by LC/MS/MS. Among the children of Saudi Arabia, urinary levels of monoisobutyl phthalate (MiBP) and monobutyl phthalate (MnBP) were higher than those reported previously in children worldwide. Monoethyl phthalate (MEP) was also detected at high levels. Several phthalate metabolites showed significant associations with the levels of MDA or 8-OHdG. Hazard quotients (HQs) derived for certain phthalates were greater than one. In particular, the HQs for di(2-ethylhexyl) phthalate (DEHP) were greater than one in 34% of the participating children. Levels of monocyclohexyl phthalate (MCHP), monoisodecyl phthalate (MiDP), mono(2-ethylhexyl) phthalate (MEHP), and mono[2-(carboxymethyl)hexyl] phthalate (MCMHP) in the urine samples were positively associated with the consumption frequency of certain foods. Very high levels of exposure to phthalates, along with positive associations with oxidative stress markers, outline the importance of follow-up investigations for identification of phthalate exposure sources and potential health implications among the young population of Saudi Arabia.

Phthalates and organophosphates in settled dust and HVAC filter dust of U.S. low-income homes: Association with season, building characteristics, and childhood asthma

Phthalates and organophosphates are ubiquitous indoor semi-volatile organic contaminants (SVOCs) that have been widely used as plasticizers and flame retardants in consumer products. Although many studies have assessed their levels in house dust, only a few used dust samples captured by filters of building heating, ventilation, and air conditioning (HVAC) systems. HVAC filters collect particles from large volumes of air over a long period of time (potentially known) and thus provide a spatially and temporally integrated concentration. This study measured concentrations of phthalates and organophosphates in HVAC filter dust and settled floor dust collected from low-income homes in Texas, United States, in both the summer and winter seasons. The most frequently detected compounds were benzyl butyl phthalate (BBzP), di-(2-ethylhexyl) phthalate (DEHP), di-n-octyl phthalate (DnOP), tris (1-chloro-2-propyl) phosphate (TCIPP), triphenyl phosphate (TPHP), and tris (1,3-dichloroisopropyl) phosphate (TDCIPP). The median level of TCIPP in settled dust was 3- to 180-times higher than levels reported in other studies of residential homes. Significantly higher concentrations were observed in HVAC filter dust as compared to settled dust for most of the frequently detected compounds in both seasons, except for several phthalates in the winter. SVOC concentrations in settled dust in winter were generally higher than in summer, while different seasonality patterns were found for HVAC filter dust. Settled dust samples from homes with vinyl flooring contained significantly higher levels of BBzP and DEHP as compared to homes with other types of floor material. The concentration of DEHP and TDCIPP in settled dust also significantly associated with the presence of carpet in homes. Cleaning activities to remove dust from furniture actually increased the levels of certain compounds in HVAC filter dust, while frequent vacuuming of carpet helped to decrease the concentrations of some compounds in settled dust. Additionally, the size and age of a given house also correlated with the levels of some pollutants in dust. A statistically significant association between DEHP concentration in HVAC filter dust in summer and the severity of asthma in children was observed. These results suggest that HVAC filter dust represents a useful sampling medium to monitor indoor SVOC concentrations with high sensitivity; in contrast, when using settled dust, in addition to consideration of seasonal influences, it is critical to know the sampling location because the type and level of SVOCs may be related to local materials used there.

Children Are Exposed to Fecal Contamination via Multiple Interconnected Pathways: A Network Model for Exposure Assessment

In recent decades, quantitative microbial risk assessment (QMRA) has been widely used to assess exposure to fecal microbes and associated health risks. In this study, a multipathway exposure assessment model was developed to evaluate exposure to fecal microbes for children under 5 in highly contaminated urban environments. Children had contact with various environmental compartments. The contamination levels of these compartments were estimated from fecal indicator counts in the environmental samples. Structured observations of child behavior (including activities, locations, and time) were used to model behavioral sequences as a dynamic network. The exposure model combines behavior sequences with environmental contamination, using additional exposure factors when needed, to estimate the number of fecal microbes transferred from environmental sources to human oral ingestion. As fecal exposure in a highly contaminated urban environment consists of contributions from multiple pathways, it is imperative to study their relative importance. The model helps us better understand the characteristics of the exposure pathways that may be driven by variation in contamination and by variable behavior, like hygiene and high-risk activities. Importantly, the model also allows prediction of the quantitative effects of an intervention-the expected reduction in exposure due to infrastructural or behavioral changes-by means of scenario studies. Based on experience with this exposure model, we make specific recommendations for additional studies of child behavior and exposure factors in order to fill critical information gaps and improve the model structure and assumptions.

Introducing relative potency quotient approach associated with probabilistic cumulative risk assessment to derive soil standards for pesticide mixtures

Children can be exposed to organophosphate and carbamate mixtures, which pose additive health effects via soil exposure. However, only 23 countries have soil standard values for organophosphate and carbamate pesticides, and most regulatory jurisdictions do not consider the cumulative exposure. This study derived proposed soil standards for organophosphates and carbamates by introducing the relative potency quotient approach (RPQ). The probabilistic cumulative risk assessment was also applied to evaluate current soil standards of pesticide mixtures. The U.S. Environmental Protection Agency (EPA) have soil standards of 19 organophosphates and five carbamates. However, these standards cannot protect population health via chronic exposure in conservative and semi-conservative scenarios based on the probabilistic risk assessment because the U.S.EPA simplified the regulatory process for the cumulative exposure to pesticide mixtures and omitted the soil allocation factor, which should be set for aggregate exposure. The analysis of proposed soil standards developed by the RPQ approach indicates that some human behavior variables, such as soil intake rate and exposure duration, have stronger impacts on the proposed soil standards than human biometric variables like body weight. This study may be helpful to develop regulatory standards and a framework for pesticide mixtures having additive health effects.

Soil-to-skin adherence during different activities for children in Taiwan

Children may be exposed to environmental contaminants through incidental ingestion of soil resulting from hand-to-mouth contact. We measured soil adherence to the skin among 86 children from four kindergartens and one elementary school in Taiwan. Rinse water samples were collected from the hands, forearms, feet and lower legs of children after they had engaged in assigned activity groups (pre-activity, indirect contact and direct contact) from two different soil textures groups: sand and clay. We found that the soil loadings significantly differed between the different soil textures, body parts, activities, and clothing groups. Measured soil loadings for hands of pre-activity, indirect contact activity, and direct contact activity groups were 0.0069, 0.0307 and 0.153 mg cm^-2, respectively, for the group playing on sand and 0.0061, 0.0116 and 0.0942 mg cm^-2, respectively, for the group playing on clay. To facilitate the use of soil adherence data in exposure assessments, we provided a new and simple way to group activities based on the intensity of children's interactions with soil. The adherence data from this study can help enhance existing information based on soil-to-skin adherence factors used to assess children's exposure to soil contaminants during their play activities.

High time-resolution simulation of E. coli on hands reveals large variation in microbial exposures amongst Vietnamese farmers using human excreta for agriculture

Infectious disease transmission is frequently mediated by the environment, where people's movements through and interactions with the environment dictate risks of infection and/or illness. Capturing these interactions, and quantifying their importance, offers important insights into effective interventions. In this study, we capture high time-resolution activity data for twenty-five Vietnamese farmers during collection and land application of human excreta for agriculture. Although human excreta use improves productivity, the use increases risks of enteric infections for both farmers and end users. In our study, the activity data are integrated with environmental microbial sampling data into a stochastic-mechanistic simulation of E. coli contamination on hands and E. coli ingested. Results from the study include frequent and variable contact rates for farmers' hands (from 34 to 1344 objects contacted per hour per hand), including highly variable hand-to-mouth contact rates (from 0 to 9 contacts per hour per hand). The frequency of hand-to-mouth contacts was substantially lower than the widely-used frequency previously reported for U.S. Office Workers. Environmental microbial contamination data highlighted ubiquitous E. coli contamination in the environment, including excreta, hands, toilet pit, handheld tools, soils, surfaces, and water. Results from the simulation suggest dynamic changes in E. coli contamination on hands, and wide variation in hand contamination and E. coli ingested amongst the farmers studied. Sensitivity analysis suggests that E. coli contamination on hands and ingested doses are most influenced by contamination of handheld tools, excreta, and the toilet pit as well as by frequency of hand-to-mouth contacts. The study findings are especially relevant given the context: no farmers reported adequate storage time of human excreta, and personal protective mask availability did not prevent hand-to-mouth contacts. Integrating high time-resolution activity data into exposure assessments highlights variation in exposures amongst farmers, and offers greater insight into effective interventions and their potential impacts.

A soil ingestion pilot study for teenage children in China

Soil ingestion by people is an important route of exposure to environmental contaminants. Studies on soil ingestion using tracer mass-balance method are mainly for young children and adults, scarcely for teenagers. In such case, the soil ingestion rate for teenagers recommended by regulators is generally identical to that of adults based on one activity pattern modeling study. However, teenagers are expected to have different soil ingestion exposure via ingestion pathway due to different activity patterns and exposure scenarios. We conducted a pilot study on soil ingestion in 30 teenage children aged 12.0-16.5 years from Hubei Province of China, using the best tracer method, with the results compared with previous soil ingestion studies. The estimated mean and median soil ingestion rates for teenagers in this study based on the best five tracers (Al, Ce, Sc, V, and Y) were 45.2 mg d^-1 and 44.8 mg d^-1 respectively, with the 95% confidence interval of the mean value ranging from 28.0 mg d^-1 to 50.9 mg d^-1. These soil ingestion rate estimates were slightly higher than the recommended values for adults by U.S. EPA, but lower than those for Chinese younger children observed in the other similar study. The result in this study is important to access the health risk resulting from exposure to toxic substances in soil via direct soil ingestion pathway by teenagers in China as well as other countries.

Daily Intake Estimation for Young Children's Ingestion of Residential Dust and Soils Contaminated with Chlorpyrifos and Cypermethrin in Taiwan

We estimated the daily intakes of chlorpyrifos and cypermethrin via ingestion of indoor dust and outdoor soils using the Stochastic Human Exposure and Dose Simulation Model on a probabilistic approach for Taiwanese young children. Variables for the estimation, such as concentration, ingestion rate, and body weight, were adopted from previous studies. Monte Carlo simulation was performed with 1,000,000 iterations to simulate a single daily intake, which was shown in terms of percentage of the Acceptable Daily Intake (ADI) of either insecticide. The daily intakes are minimal with a 99% probability, but go up steeply at the 99.9th percentile (13.1% and 20.0% of the ADIs of chlorpyrifos and cypermethrin, respectively). The sensitivity analysis indicates that concentration is the most determinant variable for daily intake estimation, suggesting that high intakes may occur when insecticide concentrations are elevated. Compared to the data of daily intakes via dietary ingestion of vegetables derived from a previous study, the estimated non-dietary intakes are negligible until reaching the highest percentile. Consequently, the non-dietary ingestion exposure to either insecticide is commonly low for young children in Taiwan’s homes, unless high contamination (e.g., indoor insecticide application) occurs in the environment. Care has to be taken to avoid high contamination indoors.

The influence of physicochemical parameters on bioaccessibility-adjusted hazard quotients for copper, lead and zinc in different grain size fractions of urban street dusts and soils

When the hazard quotient for ingestion (HQI) of a trace element in soil and dust particles is adjusted for the element's bioaccessibility, the HQI is typically reduced as compared to its calculation using pseudo-total element concentration. However, those studies have mostly used bulk particles (<2 mm or <250 µm), and the reduction in HQI when expressed as bioaccessible metal may not be similar among particle size fractions, the possibility probed by the present study of street dusts and soils collected in Tehran. The highest Cu, Pb and Zn near-total concentrations occurred in the finest particles of dusts and soils. Bioaccessible concentrations of Cu, Pb and Zn in the particles (mg kg^-1) were obtained using simple bioaccessibility extraction test (SBET). The bioaccessibility (%) did not vary much among near-total concentrations. In the bulk (<250 µm) sample, the bioaccessible concentration of Cu and Pb increased as the pH of sample increased, while Zn bioaccessibility (%) in the bulk particles was influenced by organic matter and cation exchange capacity. X-ray diffraction identified sulfide and sulfate minerals in all of the size-fractionated particles, which are insoluble to slightly soluble in acidic conditions and included most of the Cu and Pb in the samples. The only Zn-bearing mineral identified was hemimorphite, which would be highly soluble in the SBET conditions. The calculated HQI suggested potential non-carcinogenic health risk to children and adults from ingestions of soils and dusts regardless of particle size consideration, in the order of Zn > Pb ≥ Cu. The HQI calculated from near-total metal was not much different for particle size classes relative to bulk particles; however, the bioaccessibility percent-adjusted HQI for Pb was higher for the smaller particles than the bulk. This work is novel in its approach to compare HQI for a bulk sample of particles with its composite particle size fractions.

Per- and Polyfluoroalkyl Substances (PFASs) in Indoor Air and Dust from Homes and Various Microenvironments in China: Implications for Human Exposure

A newly developed solid-phase extraction cartridge composed of mixed sorbents was optimized for collection of both neutral and ionizable per- and polyfluoroalkyl substances (PFASs) in indoor air. Eighty-one indoor air samples and 29 indoor dust samples were collected from rooms of homes and hotels, textile shops, and cinemas in Tianjin, China. Fluorotelomer alcohols (FTOHs) were the predominant PFASs found in air (250-82 300 pg/m³) and hotel dust (24.8-678 ng/g). Polyfluoroalkyl phosphoric acid diesters were found at lower levels of nd-125 pg/m³ in air and 0.32-183 ng/g in dust. Perfluoroalkyl carboxylic acids (PFCAs) were dominant ionizable PFASs in air samples (121-20 600 pg/m³) with C4-C7 PFCAs contributing to 54% ± 17% of the profiles, suggesting an ongoing shift to short-chain PFASs. Long-chain PFCAs (C > 7) were strongly correlated and the intermediate metabolite of FTOHs, fluorotelomer unsaturated carboxylic acids, occurred in all the air samples at concentrations up to 413 pg/m³, suggesting the transformation of precursors such as FTOHs in indoor environment. Daily intake of ∑PFASs via air inhalation and dust ingestion was estimated at 1.04-14.1 ng/kg bw/d and 0.10-8.17 ng/kg bw/d, respectively, demonstrating that inhalation of air with fine suspended particles was a more important direct exposure pathway than dust ingestion for PFASs to adults.

Mouthing activity data for children age 3 to <6 years old and fraction of hand area mouthed for children age <6 years old in Taiwan

Non-dietary ingestion is an important exposure pathway for children owing to their frequent hand-to-mouth and object-to-mouth activities involving soil and dust contacts. We used videotaping and the computer-based translating methods to quantify the mouthing activity information for 24 children ages 3 to <6 years old living in Taiwan. We also reviewed the entire mouthing activity data collected during the project to determine the lesser studied information on hand surface areas mouthed by children ages <6 years old. The median indoor hand-to-mouth and object-to-mouth frequencies were found to be 10 and 4.3 contacts/h, respectively. Hand-to-mouth and object-to-mouth contact frequencies used in exposure assessments for children ages 3 to <6 years old in this study were similar to the recommended values reported in United States. Exposure Factors Handbook for comparable age US children. The average fractions of the hand area mouthed for children 6 to <12 months, 1 to <2 years, 2 to <3 years, and 3 to <6 years old were 0.12, 0.12, 0.13, and 0.09, respectively. The fraction of hand area mouthed by children was found to be significantly and negatively correlated with their age. About half of the total hand-to-mouth contact events involved immersion of part of a hand or a finger into the mouth. The findings from this study extend the available mouthing activity information for 3 to <6 years old children and also provide new data for an Asian country, allowing comparison of results with western values collected mostly in the United States.

Estimation of the daily soil/dust (SD) ingestion rate of children from Gansu Province, China via hand-to-mouth contact using tracer elements

A total of 60 children (31 males and 29 females) between the ages of 3 and 12 years were randomly selected from Lanzhou City in Gansu Province, northwest China. Hand (soil/dust) SD samples from these children were collected using hand wipes. We determined the approximate amounts of hand SD and the concentrations of three tracer soil elements (Ce, Y, and V) in these samples. The approximate amounts of hand SD ranged from 42.28 to 173.76 mg, with a median value of 85.42 mg. In addition, the mean amounts of hand SD estimated using the concentrations of Ce, Y, and V in the samples were 4.63, 3.43, and 3.42 mg, respectively. The amount of hand SD varied greatly among the age groups: primary school children had more hand SD than kindergarten children, males had more hand SD than females, and children from rural areas had more hand SD than those from urban areas. The rates of daily ingestion of hand SD for kindergarten and primary school children were estimated to be 7.73 and 6.61 mg/day, respectively.

Indoor residential exposure to semivolatile organic compounds in France

Multiple chemicals are emitted in residential accommodation. Aggregate Daily Doses (ADD) (ng/kg-bw/d) were estimated for 32 semivolatile organic compounds (SVOCs) of different chemical families that are frequently detected in French dwellings in both air and settled dust. Daily doses were determined using steady-state models for the population, categorized into 11 age groups covering birth to age 30. Three routes of exposure were taken into account: dust ingestion, inhalation (gaseous and particulate phases) and dermal contact with the gaseous phase of air. Contamination levels were preferentially retrieved from large, nationwide representative datasets. A two-dimensional probabilistic approach was used to assess parametric uncertainty and identify the most influential factors. For children aged 2 to 3years, ADD estimates spanned orders of magnitude, with median values ranging from 8.7pg/kg-bw/d for 2,2',3,4,4'-pentabromodiphenylether (BDE 85) to 1.3μg/kg-bw/d for di-isobutyl phthalate (DiBP). Inhalation, ingestion and dermal pathway contributed at varying levels, and depending on compound, air was the dominant medium for 28 of the 32 compounds (either by inhalation or dermal contact). Indoor exposure estimate variance was mainly driven by indoor contamination variability, and secondarily by uncertainty in physical and chemical parameters. These findings lend support to the call for cumulative risk assessment of indoor SVOCs.

Children's Lead Exposure: A Multimedia Modeling Analysis to Guide Public Health Decision-Making

BACKGROUND

Drinking water and other sources for lead are the subject of public health concerns around the Flint, Michigan, drinking water and East Chicago, Indiana, lead in soil crises. In 2015, the U.S. Environmental Protection Agency (EPA)'s National Drinking Water Advisory Council (NDWAC) recommended establishment of a "health-based, household action level" for lead in drinking water based on children's exposure.

OBJECTIVES

The primary objective was to develop a coupled exposure-dose modeling approach that can be used to determine what drinking water lead concentrations keep children's blood lead levels (BLLs) below specified values, considering exposures from water, soil, dust, food, and air. Related objectives were to evaluate the coupled model estimates using real-world blood lead data, to quantify relative contributions by the various media, and to identify key model inputs.

METHODS

A modeling approach using the EPA's Stochastic Human Exposure and Dose Simulation (SHEDS)-Multimedia and Integrated Exposure Uptake and Biokinetic (IEUBK) models was developed using available data. This analysis for the U.S. population of young children probabilistically simulated multimedia exposures and estimated relative contributions of media to BLLs across all population percentiles for several age groups.

RESULTS

Modeled BLLs compared well with nationally representative BLLs (0-23% relative error). Analyses revealed relative importance of soil and dust ingestion exposure pathways and associated Pb intake rates; water ingestion was also a main pathway, especially for infants.

CONCLUSIONS

This methodology advances scientific understanding of the relationship between lead concentrations in drinking water and BLLs in children. It can guide national health-based benchmarks for lead and related community public health decisions. https://doi.org/10.1289/EHP1605.

Estimates of Soil Ingestion in a Population of Chinese Children

BACKGROUND

China's soil pollution poses serious health risks. However, data regarding the soil ingestion rate (SIR) of the Chinese population, which is critical to assessing associated health risks, are lacking.

OBJECTIVES

We estimated soil ingestion of 177 Chinese children from Guangdong, Hubei, and Gansu Provinces.

METHODS

We conducted this investigation by employing a tracer mass-balance method. We collected a duplicate of all food consumed and all feces and urine excreted on 1 d (n=153) and over 3 consecutive d (n=24), as well as soil samples from play areas and drinking-water samples. We analyzed concentrations of the tracer elements Al, Ba, Ce, Mn, Sc, Ti, V, and Y in these samples using ICP-AES and ICP-MS and estimated the SIR for each subject.

RESULTS

The estimated SIR data based on each tracer element were characterized by a skewed distribution, as well as higher inter-tracer and inter-subject variation, with several outliers. After removing the outliers, daily SIR median (range) values in milligrams per day were Al, 27.8 (−42.0 to 257.3); Ba, 36.5 (−230.3 to 412.7); Ce, 35.3 (−21.2 to 225.8); Mn, 146.6 (−1259.4 to 1827.7); Sc, 54.8 (−4.5 to 292.0); Ti, 36.7 (−233.7 to 687.0); V, 92.1 (10.4 to 308.0); and Y, 59.1 (−18.4 to 283.0). Daily SIR median/95th percentile (range) values based on the best tracer method (BTM) were 51.7/216.6 (−9.5 to 297.6) mg/d.

CONCLUSIONS

Based on the BTM, recommended SIR values for the general population of Chinese children (2.5 to 12 years old) are 52 mg/d for the central tendency and 217 mg/d for the upper percentile. We did not differentiate between outside soil and indoor dust. Considering the lower concentration of tracer elements in indoor dust than outside soil, actual soil and dust ingestion rates could be higher. https://doi.org/10.1289/EHP930.

A review of models for near-field exposure pathways of chemicals in consumer products

Exposure to chemicals in consumer products has been gaining increasing attention, with multiple studies showing that near-field exposures from products is high compared to far-field exposures. Regarding the numerous chemical-product combinations, there is a need for an overarching review of models able to quantify the multiple transfers of chemicals from products used near-field to humans. The present review therefore aims at an in-depth overview of modeling approaches for near-field chemical release and human exposure pathways associated with consumer products. It focuses on lower-tier, mechanistic models suitable for life cycle assessments (LCA), chemical alternative assessment (CAA) and high-throughput screening risk assessment (HTS). Chemicals in a product enter the near-field via a defined "compartment of entry", are transformed or transferred to adjacent compartments, and eventually end in a "human receptor compartment". We first focus on models of physical mass transfers from the product to 'near-field' compartments. For transfers of chemicals from article interior, adequate modeling of in-article diffusion and of partitioning between article surface and air/skin/food is key. Modeling volatilization and subsequent transfer to the outdoor is crucial for transfers of chemicals used in the inner space of appliances, on object surfaces or directly emitted to indoor air. For transfers from skin surface, models need to reflect the competition between dermal permeation, volatilization and fraction washed-off. We then focus on transfers from the 'near-field' to 'human' compartments, defined as respiratory tract, gastrointestinal tract and epidermis, for which good estimates of air concentrations, non-dietary ingestion parameters and skin permeation are essential, respectively. We critically characterize for each exposure pathway the ability of models to estimate near-field transfers and to best inform LCA, CAA and HTS, summarizing the main characteristics of the potentially best-suited models. This review identifies large knowledge gaps for several near-field pathways and suggests research needs and future directions.

Soil ingestion rates for children under 3 years old in Taiwan

Soil and dust ingestion rates by children are among the most critical exposure factors in determining risks to children from exposures to environmental contaminants in soil and dust. We believe this is the first published soil ingestion study for children in Taiwan using tracer element methodology. In this study, 66 children under 3 years of age were enrolled from Taiwan. Three days of fecal samples and a 24-h duplicate food sample were collected. The soil and household dust samples were also collected from children's homes. Soil ingestion rates were estimated based on silicon (Si) and titanium (Ti). The average soil ingestion rates were 9.6±19.2 mg/day based on Si as a tracer. The estimated soil ingestion rates based on Si did not have statistically significant differences by children's age and gender, although the average soil ingestion rates clearly increased as a function of children's age category. The estimated soil ingestion rates based on Si was significantly and positively correlated with the sum of indoor and outdoor hand-to-mouth frequency rates. The average soil ingestion rates based on Si were generally lower than the results from previous studies for the US children. Ti may not be a suitable tracer for estimating soil ingestion rates in Taiwan because the Ti dioxide is a common additive in food. To the best of our knowledge, this is the first study that investigated the correlations between soil ingestion rates and mouthing behaviors in Taiwan or other parts of Asia. It is also the first study that could compare available soil ingestion data from different countries and/or different cultures. The hand-to-mouth frequency and health habits are important to estimate the soil ingestion exposure for children. The results in this study are particularly important when assessing children's exposure and potential health risk from nearby contaminated soils in Taiwan.

Environmental and dietary exposure of young children to inorganic trace elements

Children are exposed to toxic metals and metalloids via their diet and environment. Our objective was to assess the aggregate chronic exposure of children aged 3-6years, living in France, to As, Cd, Cr, Cu, Mn, Pb, Sb, Sr, and V present in diet, tap water, air, soil and floor dust in the years 2007-2009. Dietary data came from the French Total Diet Study, while concentrations in residential tap water, soil and indoor floor dust came from the 'Plomb-Habitat' nationwide representative survey on children's lead exposure at home. Indoor air concentrations were assumed to be equal to outdoor air concentrations, which were retrieved from regulatory measurements networks. Human exposure factors were retrieved from literature. Data were combined with Monte Carlo simulations. Median exposures were 1.7, 0.3, 10.2, 34.1, 60.3, 0.7, 0.1, 44.3, 1.5 and 95th percentiles were 4.4, 0.5, 15.8, 61.3, 98.3, 2.5, 0.1, 111.1, 2.9μg/kgbw/d for As, Cd, Cr, Cu, Mn, Pb, Sb, Sr, and V respectively. Dietary exposures dominate aggregate exposures, with the notable exception of Pb - for which soils and indoor floor dust ingestion contribute most at the 95th percentile. The strengths of this study are that it aggregates exposures that are often estimated separately, and uses a large amount of representative data. This assessment is limited to main diet and residential exposure, and does not take into account the relative bioavailability of compounds. These results could be used to help target prevention strategies.

DDT, DDD, and DDE in soil of Xiangfen County, China: Residues, sources, spatial distribution, and health risks

We collected and analyzed 128 surface soil samples from Xiangfen County for dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethane (DDD), and dichlorodiphenyldichloroethylene (DDE). Total DDT concentrations (DDTs; sum of p,p'-DDD, p,p'-DDE, and p,p'-DDT) ranged from ND to 427.81 ng g(-1) (dry weight, dw), with a mean of 40.26 ng g(-1) (dw). Among the three compounds, p,p'-DDD was the most dominant. The DDTs in Xiangfen County soils mainly originated from historical DDT use, but there were also new inputs likely related to dicofol use. The DDTs in Xiangfen County soils were mainly degraded under anaerobic conditions, and direct degradation to DDD was the main degradation route. Regions with relatively high concentrations of DDTs were mainly located in North and South Xiangfen County. In these regions, many soil samples contained p,p'-DDT as the predominant pollutant, suggestive of extensive new inputs of DDT. A health risk assessment revealed that there are no serious long-term health impacts of exposure to DDTs in soil, for adults or children.

Estimating Children's Soil/Dust Ingestion Rates through Retrospective Analyses of Blood Lead Biomonitoring from the Bunker Hill Superfund Site in Idaho

BACKGROUND

Soil/dust ingestion rates are important variables in assessing children's health risks in contaminated environments. Current estimates are based largely on soil tracer methodology, which is limited by analytical uncertainty, small sample size, and short study duration.

OBJECTIVES

The objective was to estimate site-specific soil/dust ingestion rates through reevaluation of the lead absorption dose-response relationship using new bioavailability data from the Bunker Hill Mining and Metallurgical Complex Superfund Site (BHSS) in Idaho, USA.

METHODS

The U.S. Environmental Protection Agency (EPA) in vitro bioavailability methodology was applied to archived BHSS soil and dust samples. Using age-specific biokinetic slope factors, we related bioavailable lead from these sources to children's blood lead levels (BLLs) monitored during cleanup from 1988 through 2002. Quantitative regression analyses and exposure assessment guidance were used to develop candidate soil/dust source partition scenarios estimating lead intake, allowing estimation of age-specific soil/dust ingestion rates. These ingestion rate and bioavailability estimates were simultaneously applied to the U.S. EPA Integrated Exposure Uptake Biokinetic Model for Lead in Children to determine those combinations best approximating observed BLLs.

RESULTS

Absolute soil and house dust bioavailability averaged 33% (SD ± 4%) and 28% (SD ± 6%), respectively. Estimated BHSS age-specific soil/dust ingestion rates are 86-94 mg/day for 6-month- to 2-year-old children and 51-67 mg/day for 2- to 9-year-old children.

CONCLUSIONS

Soil/dust ingestion rate estimates for 1- to 9-year-old children at the BHSS are lower than those commonly used in human health risk assessment. A substantial component of children's exposure comes from sources beyond the immediate home environment.

CITATION

von Lindern I, Spalinger S, Stifelman ML, Stanek LW, Bartrem C. 2016. Estimating children's soil/dust ingestion rates through retrospective analyses of blood lead biomonitoring from the Bunker Hill Superfund Site in Idaho. Environ Health Perspect 124:1462-1470; http://dx.doi.org/10.1289/ehp.1510144.

Estimated lead (Pb) exposures for a population of urban community gardeners

Urban community gardens provide affordable, locally grown, healthy foods and many other benefits. However, urban garden soils can contain lead (Pb) that may pose risks to human health. To help evaluate these risks, we measured Pb concentrations in soil, vegetables, and chicken eggs from New York City community gardens, and we asked gardeners about vegetable consumption and time spent in the garden. We then estimated Pb intakes deterministically and probabilistically for adult gardeners, children who spend time in the garden, and adult (non-gardener) household members. Most central tendency Pb intakes were below provisional total tolerable intake (PTTI) levels. High contact intakes generally exceeded PTTIs. Probabilistic estimates showed approximately 40 % of children and 10 % of gardeners exceeding PTTIs. Children's exposure came primarily from dust ingestion and exposure to higher Pb soil between beds. Gardeners' Pb intakes were comparable to children's (in µg/day) but were dominated by vegetable consumption. Adult household members ate less garden-grown produce than gardeners and had the lowest Pb intakes. Our results suggest that healthy gardening practices to reduce Pb exposure in urban community gardens should focus on encouraging cultivation of lower Pb vegetables (i.e., fruits) for adult gardeners and on covering higher Pb non-bed soils accessible to young children. However, the common practice of replacement of root-zone bed soil with clean soil (e.g., in raised beds) has many benefits and should also continue to be encouraged.