Particle size distributions, size concentration relationships, and adherence to hands of selected geologic media derived from mining, smelting, and quarrying activities

Estimate of the maximum amount of dust adhering to skin and the upper limit of dust-skin adherence factor for young adults: An example from Changchun, China

Contaminants present in dust adhering to the skin can pose a significant risk to human health through dermal absorption and hand-to-mouth contact. The adhesion capacity of dust differs significantly from that of soil due to its physicochemical properties. Therefore, applying the raw soil exposure parameters to estimate the health risks associated with dermal exposure to dust may lead to erroneous conclusions. In this study, we quantified the maximum amount of dust that adhered to the skin (MADmax) and the upper limit of dust-skin adherence factor (DSAFmax) in 26 adults using element markers as a proxy for dust. The volunteers were exposed to dust and rinse water samples were collected from their hands, forearms, lower legs, and feet. We analyzed both the raw dust samples and the rinse water samples for 11 element markers, including Be, V, Cr, Mn, Co, Ni, Cu, Zn, Se, Ba, and Pb. The results showed that the MADmax of indoor dust and outdoor dust increased by 0.08-0.62 mg and 0.33-0.56 mg following a 1 cm2 increase in skin surface area, respectively. Based on best dust element markers, the body part-weighted dust-skin adherences (WDSAFmaxs) of indoor dust and outdoor dust were 0.35 and 0.64 mg/cm2, respectively. A smaller particle size and higher moisture content resulted in a larger DSAFmax. Only when indoor dust concentrations exceed 24.2 mg/m3 or outdoor dust concentrations exceed 44.3 mg/m3, can the WDSAFmax be applied directly in the health risk assessment of dermal exposure to dust. The method from this study can be re-applied in different regions, and the adherence data can help to improve future studies on the health effects of dermal exposure to dust.

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.

Necessity of introducing particle size distribution of hand-adhered soil on the estimation of oral exposure to metals in soil: Comparison with the traditional method

This study aimed to systematically investigate the relationship between children exposure possibility, metal concentration, metal bioaccessibility and soil particle size. fifty Children aged 3-8 years were recruited for the collection of hand-adhered soil, environmental soil, and blood samples. The mass distribution of hand-adhered soil with particle size were analyzed. Based on it, environmental soil samples were divided into five fractions to evaluate the effect of soil particle size on the total contents and bioaccessibilities of toxic metals. Then, a refined soil oral exposure model based on the particle size distribution of hand-adhered soil was established, and the estimation was compared with the typical traditional method. We found that finer particles were preferentially adhered to hand. The highest metal concentrations and bioaccessibilities occurred in the finest fraction, with values decreasing with increasing particle size. The exposure levels using the refined model were 2.0-3.4 times higher than those with the traditional method. In addition, Pb exposure level calculated using the refined model exhibited stronger and more significant correlation with blood Pb than those of the traditional soil. The construction of a refined exposure scenario based on hand-adhered soil could more exactly reflect the real exposure level and the difference among individuals.

Effect of soil particle size and extraction method on the oral bioaccessibility of arsenic

Recent findings indicate that incidental ingestion of soil by humans primarily involves soil particles <150 µm, rather than <250 µm-sized fraction previously used for most oral bioaccessibility and bioavailability studies. It was postulated that a greater soil surface area in the finer fraction (<150 versus <250 µm) might increase oral bioaccessibility of arsenic (As) in soil. Bioaccessibility and concentrations of As were compared in <150 and <250 µm fractions of 18 soil samples from a variety of arsenic-contaminated sites. The two methods used to measure bioaccessibility were compared - EPA Method 1340 and the California Arsenic Bioaccessibility (CAB) method. Arsenic concentrations were nearly the same or higher in the <150 fraction compared with <250 µm. EPA Method 1340 and the CAB method presented significantly different bioaccessibility results, as well as estimated relative oral bioavailability (RBA) based upon algorithms specific to the methods, but there was no marked difference for <150 and <250 µm soil fractions within either method. When compared with RBA determined previously for these soil samples in vivo in non-human primates, EPA Method 1340 was generally more predictive than the CAB method. Data suggest that soil- or site-specific factors control bioaccessibility under either method and that the test method selected is more important than the particle size fraction (<150 or <250) in using these in vitro methods to predict As RBA for use in risk assessment.

Particle transfer and adherence to human skin compared with cotton glove and pre-moistened polyvinyl alcohol exposure sampling substrates

Measurement of skin exposure to particles using interception (e.g., cotton gloves) and removal (e.g., wiping) sampling techniques could be inaccurate because these substrates do not have the same topography and adhesion characteristics as skin. The objective of this study was to compare particle transfer and adherence to cotton gloves, cotton gloves with artificial sebum, and a pre-moistened polyvinyl alcohol (PVA) material with bare human skin (fingertip, palm). Experiments were performed with aluminum oxide powder under standardized conditions for three types of surfaces touched, applied loads, contact times, and powder mass levels. In the final mixed model, the fixed effects of substrate, surface type, applied load, and powder mass and their significant two-way interaction terms explained 71% (transfer) and 74% (adherence) of the observed total variance in measurements. For particle mass transfer, compared with bare skin, bias was -77% (cotton glove with sebum) to +197% (PVA material) and for adherence bias ranged from -40% (cotton glove) to +428% (PVA material), which indicated under- and over-sampling by these substrates, respectively. Dermal exposure assessment would benefit from sampling substrates that better reflect human skin characteristics and more accurately estimate exposures. Mischaracterization of dermal exposure has important implications for exposure and risk assessment.

Soil-skin adherence measures from hand press trials in a Gulf study of exposures

Marine oil spills and the resulting environmental contamination is common along coastal areas; however, information is lacking about the safety of impacted beaches for public use, especially for the most vulnerable population: children. One route of exposure for children at oil impacted beaches is through contact with sands. The purpose of this study was to evaluate beach sand skin adherence for children under the age of seven. Each of 122 children participated in a hand press trial conducted at one of four different U.S. beaches (two in Miami, FL, and two in Galveston, TX USA). During the hand press trials, hand conditions of the children were randomized (dry, wet, or with sunscreen), and soil adherence (mass of sand per palmar surface area of the hand) and the maximum pressure applied (force applied per area of hand) was measured and calculated. Each child was instructed to press their hands on a soil laden tray for 5 s and pressure of contact was measured using a scale. Results (n = 98) showed that the average soil adherence for both palmar hands across the four beaches ranged from 0.200 to 234 mg/cm² with an average of 35.7 mg/cm², with boys (40.4 mg/cm²) showing slightly higher means than girls (31.7 mg/cm²), but these differences were not significant even after adjusting for age. Among the three conditions evaluated, the highest loading was measured for children with wet hands (mean 65.3 mg/cm²), followed by dry hands (mean 24.5 mg/cm²). Sunscreen hands (mean 23.2 mg/cm²) had the lowest loadings. The pressure of contact ranged from 0.180 to 1.69 psi and varied by age groups and by height and weight, where pressure of contact did not have a significant influence on soil adherence. The average adhered sand grain size and average ambient sand grain size both had a statistically significant impact on hand soil adherence. Overall results from this study can be utilized in exposure and risk assessment models to evaluate the possible health impacts from contaminants found in beach sands.

Trace elements in two particle size fractions of urban soils collected from playgrounds in Bratislava (Slovakia)

Today, it is proven that the contaminated urban soils are hazardous for the human health. Soil substrates of playgrounds call for special research as they are places where children are directly exposed to soil contaminants. Therefore, the objective of this work was to measure the pseudo-total contents and bioaccessibility of several metals and metalloids (As, Bi, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Sb, Sn, V, Zn) in two grain sizes (< 150 μm and < 50 μm) of playground soils in Bratislava city (the capital of Slovakia). The content of metal(loid)s in the soils was controlled by a number of factors, with their increased contents (above 75% percentile or higher) at sites influenced by point sources of pollution (industry and agriculture) or at old sites located in the city centre. Cobalt, Cr, Fe, Mn, Ni and V had relatively uniform contents in soils compared to the other elements. As regression modelling with a categorical variable confirmed, the age of urban areas influenced the accumulation of As, Bi, Cd, Cu, Hg, Pb, Sb and Sn in playground soils. Exploratory statistical techniques with compositionally transformed data (principal component analysis, cluster analysis and construction of symmetric coordinates for correlation analysis) divided trace elements into the two main groupings, Co, Cr, Fe, Mn, Ni, V and Bi, Cd, Cu, Hg, Pb, Sb, Sn, Zn. Median concentrations of the elements in smaller soil grains (< 50 μm) were significantly higher than in coarser grains (< 150 μm). Cobalt, Cu, Mn, Pb, Sn and Zn had significantly higher bioaccessible proportions (% of the pseudo-total content) in < 50 μm soil size than in < 150 μm; however, the same order of bioaccessibility was achieved in both grain sizes. The highest bioaccessibility had Cd, Cu, Pb and Zn (~ 40% and more), followed by Co, As, Mn, Sb (18-27%), Hg, Ni, Sn (10-12%) and finally Cr, Fe and V (less than 4%). The hazard index and carcinogenic risk values were higher in < 50 μm than in < 150 μm and significantly decreased in the two soil sizes when the bioaccessibility results were included in the health hazard calculation.

Soil, Hand, and Body Adherence Measures across Four Beach Areas: Potential Influence on Exposure to Oil Spill Chemicals

Skin adherence (SA) of soil affects exposure from soil contaminants through dermal routes via loading on the skin and through ingestion routes through hand to mouth activities. The objectives of this study were to evaluate the relationships between adherence versus child-specific and environmental factors. Two sets of soil-to-skin adherence were evaluated. The first was based on loading on hands following hand presses (Hand SA). The second was based on body rinses following one hour of play activities on the beach (Body SA). Results for 98-119 children conducted at four beach sites show that mean Hand SA was 35.7 mg/cm2 (std. dev. 41.8 mg/cm2), while Body SA based on full coverage was 352.3 mg/cm2 (std. dev. 250.4 mg/cm2). Statistically significant differences in Body SA were observed between male (419.2 mg/cm2) and female (300.4 mg/cm2) children (p < 0.05). No significant difference by sex was found for Hand SA. Other statistically different observations were that Hand SA (p < 0.05), but not Body SA, differed across the four beaches (p < 0.05). For Hand SA, this difference was associated soil size variability across the beaches. Hand and Body SA values measured during this study are recommended for use in risk assessments that evaluate beach exposures to oil spill chemicals for young children.

Objective ranges of soil-to-dust transfer coefficients for lead-impacted sites

Residential yard soil and indoor dust datasets from eight communities near historical mining, smelting, and refining operations were used to quantify soil track-in, an important factor in evaluating indoor exposures to soil metals and to set residential soil cleanup levels. Regression analyses were used to derive slopes that represent mass soil-to-dust transfer coefficients or MSDs. Lead concentration data were available for all datasets. Arsenic data were available for six of the eight datasets. Cadmium and zinc data were available for one dataset, allowing limited comparison of MSDs for lead with other metals. Covariates that could indicate potential indoor sources of metals, such as house age and indoor heating source, were examined by multivariate regression analysis when available (three datasets). Covariates that could affect soil track-in, such as the amount of bare soil in the yard or having pets, were examined by stratified linear regression analysis when available (two datasets). Most of the R-squared values for lead, cadmium and zinc indicate a good to moderate fit (≥0.25), but for arsenic most indicate a poor fit (<0.25). Significant MSDs for models with a good to moderate fit range from 0.14 to 0.47 for lead, and 0.12 to 0.43 for the other metals (arsenic, cadmium, and zinc). The treatment of outliers was a significant methodological factor affecting the slope of the regressions. Substantial variability is expected among soils at residences due to both physical characteristics of each property and the ways in which residents interact with their home. Survey data providing information on various factors affecting soil track-in help to refine MSD estimates. For three of the datasets, covariate data were available that improved model fit by multivariate or stratified regression analysis for lead. When multivariate or stratified regression analyses were performed, the estimated MSD varied as little as <1% to as great as 200% depending on the dataset, but all estimates were below 0.4. Notably, the MSDs were lowest for the three datasets with the highest soil lead concentrations, i.e., those with average soil lead concentrations greater than 300 mg/kg after outlier removal. For five of the six datasets that had both arsenic and lead sampled, arsenic MSDs were much less than the lead MSDs; however, only two of the sites' arsenic models had significant MSDs and adequate fit. Cadmium and zinc were only included in one dataset, limiting our ability to draw any conclusions from comparison to those MSDs. The results of our study are consistent with prior studies suggesting that MSDs for metals without internal sources are 0.3-0.4, and application of MSDs in that range will provide more reliable exposure estimates than the 0.7 default value used by the United States Environmental Protection Agency in the Integrated Exposure Uptake Biokinetic (IEUBK) Model.

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.

Determination of hand soil loading, soil transfer, and particle size variations after hand-pressing and hand-mouthing activities

Hand-pressing trials and hand-to-mouth soil transfer experiments were conducted to better understand soil loadings, soil transfer ratios for three mouthing activities, and variations in particle size distributions under various conditions. Results indicated that sand caused higher soil loadings on the hand than clay. When the moisture level of clay soil exceeded its liquid limit, soil loadings also increased. Greater pressing pressures also led to larger clay loadings. Clay with a moisture content close to its plastic limit caused the smallest soil loadings due to strong soil cohesion. Particle sizes of the transferred clay were larger than that of the original clay, indicating that hand-pressing and the pressure exerted may have enhanced clay particles of larger sizes adhering onto the hand. Nevertheless, the sizes of most particles that adhered to the hand were still smaller than 150 μm. Higher pressing pressures and greater moisture contents resulted in larger soil loadings on the hand, and transfer ratios became smaller. Transfer ratios from palm-licking with clay particles were smaller than those from finger-mouthing, which may have been due to finer particles that more readily adhered to the skin of the palm and that were transferred from the hand to the mouth with greater difficulty.

Lead and Arsenic Bioaccessibility and Speciation as a Function of Soil Particle Size

Bioavailability research of soil metals has advanced considerably from default values to validated in vitro bioaccessibility (IVBA) assays for site-specific risk assessment. Previously, USEPA determined that the soil-size fraction representative of dermal adherence and consequent soil ingestion was <250 μm. This size fraction was widely used in testing efforts for both in vivo and in vitro experiments. However, recent studies indicate the <150-μm size fraction better represents the particle size that adheres to skin for potential ingestion. At issue is the relevance of validated in vivo and in vitro methods developed with <250 μm moving to the <150-μm fraction. The objectives of this study were to investigate <250-μm versus <150-μm particle size and particle size groups for evaluating lead (Pb) and arsenic (As) IVBA and speciation. Soils with different properties were homogenized, oven dried, and sieved: <250 to > 150, <150 to >75, <75 to >38, and <38 μm. Sieved versus ground subsamples of <250-μm and <150-μm bulk soils were also used for IVBA and synchrotron-based Pb and As speciation. Although we observed an increase in total and IVBA-extractable Pb and As with decreased soil particle size, changes in %IVBA of Pb and As (dependent on the ratio extractable:total) remained consistent in all of the tested soils. No significant changes in Pb and As speciation were observed across the soil fractions. The results suggest that using the more relevant <150-μm fraction will not undermine currently validated IVBA protocols in future bioavailability studies.

Connecting the Dots: Linking Environmental Justice Indicators to Daily Dose Model Estimates

Many different quantitative techniques have been developed to either assess Environmental Justice (EJ) issues or estimate exposure and dose for risk assessment. However, very few approaches have been applied to link EJ factors to exposure dose estimate and identify potential impacts of EJ factors on dose-related variables. The purpose of this study is to identify quantitative approaches that incorporate conventional risk assessment (RA) dose modeling and cumulative risk assessment (CRA) considerations of disproportionate environmental exposure. We apply the Average Daily Dose (ADD) model, which has been commonly used in RA, to better understand impacts of EJ indicators upon exposure dose estimates and dose-related variables, termed the Environmental-Justice-Average-Daily-Dose (EJ-ADD) approach. On the U.S. nationwide census tract-level, we defined and quantified two EJ indicators (poverty and race/ethnicity) using an EJ scoring method to examine their relation to census tract-level multi-chemical exposure dose estimates. Pollutant doses for each tract were calculated using the ADD model, and EJ scores were assigned to each tract based on poverty- or race-related population percentages. Single- and multiple-chemical ADD values were matched to the tract-level EJ scores to analyze disproportionate dose relationships and contributing EJ factors. We found that when both EJ indicators were examined simultaneously, ADD for all pollutants generally increased with larger EJ scores. To demonstrate the utility of using EJ-ADD on the local scale, we approximated ADD levels of lead via soil/dust ingestion for simulated communities with different EJ-related scenarios. The local-level simulation indicates a substantial difference in exposure-dose levels between wealthy and EJ communities. The application of the EJ-ADD approach can link EJ factors to exposure dose estimate and identify potential EJ impacts on dose-related variables.

Evaluation of Potential Exposure to Metals in Laundered Shop Towels

We reported in 2003 that exposure to metals on laundered shop towels (LSTs) could exceed toxicity criteria. New data from LSTs used by workers in North America document the continued presence of metals in freshly laundered towels. We assessed potential exposure to metals based on concentrations of metals on the LSTs, estimates of LST usage by employees, and the transfer of metals from LST-to-hand, hand-to-mouth, and LST-to-lip, under average- or high-exposure scenarios. Exposure estimates were compared to toxicity criteria. Under an average-exposure scenario (excluding metals' data outliers), exceedances of the California Environmental Protection Agency, U.S. Environmental Protection Agency, and the Agency for Toxic Substances and Disease Registry toxicity criteria may occur for aluminum, cadmium, cobalt, copper, iron, and lead. Calculated intakes for these metals were up to more than 400-fold higher (lead) than their respective toxicity criterion. For the high-exposure scenario, additional exceedances may occur, and high-exposure intakes were up to 1,170-fold higher (lead) than their respective toxicity criterion. A sensitivity analysis indicated that alternate plausible assumptions could increase or decrease the magnitude of exceedances, but were unlikely to eliminate certain exceedances, particularly for lead.

Modeling particulate matter emissions during mineral loading process under weak wind simulation

The quantification of particulate matter emissions from mineral handling is an important problem for the quantification of global emissions on industrial sites. Mineral particulate matter emissions could adversely impact environmental quality in mining regions, transport regions, and even on a global scale. Mineral loading is an important process contributing to mineral particulate matter emissions, especially under weak wind conditions. Mathematical models are effective ways to evaluate particulate matter emissions during the mineral loading process. The currently used empirical models based on the form of a power function do not predict particulate matter emissions accurately under weak wind conditions. At low particulate matter emissions, the models overestimated, and at high particulate matter emissions, the models underestimated emission factors. We conducted wind tunnel experiments to evaluate the particulate matter emission factors for the mineral loading process. A new approach based on the mathematical form of a logistical function was developed and tested. It provided a realistic depiction of the particulate matter emissions during the mineral loading process, accounting for fractions of fine mineral particles, dropping height, and wind velocity.

Selective soil particle adherence to hands: implications for understanding oral exposure to soil contaminants

Over the last 30 years, there has been extensive research designed to quantify the extent of oral bioavailability and bioaccessibility of organic and inorganic contaminants in soil. One aspect of this research is the soil particle size selected to represent environmental exposures, which may affect study results and comparability across studies. Different research groups have studied soil particle sizes ranging from <45 μm to <2000 μm. This article reviews the historical and technical considerations that pertain to the selection of an appropriate particle size fraction for evaluating the relative oral bioavailability of chemicals from soil, which include (1) how the resultant data will be used in human health risk assessment, (2) soil fractions historically used in oral bioavailability studies, (3) studies of soil adherence to human hands, (4) the distribution of contaminants in soils as a function of particle size, and (5) the effect of differential bioavailability as a function of soil particle size and geochemical matrix. These factors are first discussed from a general perspective, applicable to all contaminants in soil, and then more specifically for polycyclic aromatic hydrocarbons (PAHs) in soil. Based on this review, a specific soil particle size of <150 μm is recommended for future studies on the oral bioavailability and bioaccessibility of PAHs in soil.

A review on the importance of metals and metalloids in atmospheric dust and aerosol from mining operations

Contaminants can be transported rapidly and over relatively long distances by atmospheric dust and aerosol relative to other media such as water, soil and biota; yet few studies have explicitly evaluated the environmental implications of this pathway, making it a fundamental but understudied transport mechanism. Although there are numerous natural and anthropogenic activities that can increase dust and aerosol emissions and contaminant levels in the environment, mining operations are notable with respect to the quantity of particulates generated, the global extent of area impacted, and the toxicity of contaminants associated with the emissions. Here we review (i) the environmental fate and transport of metals and metalloids in dust and aerosol from mining operations, (ii) current methodologies used to assess contaminant concentrations and particulate emissions, and (iii) the potential health and environmental risks associated with airborne contaminants from mining operations. The review evaluates future research priorities based on the available literature and suggest that there is a particular need to measure and understand the generation, fate and transport of airborne particulates from mining operations, specifically the finer particle fraction. More generally, our findings suggest that mining operations play an important but underappreciated role in the generation of contaminated atmospheric dust and aerosol and the transport of metal and metalloid contaminants, and highlight the need for further research in this area. The role of mining activities in the fate and transport of environmental contaminants may become increasingly important in the coming decades, as climate change and land use are projected to intensify, both of which can substantially increase the potential for dust emissions and transport.