The objective of this study was to examine the influence of soil composition, PAH concentration, and source material type on PAH bioavailability using an approach capable of measuring uptake at low, environmentally relevant PAH concentrations (down to 1 ppm). Contaminated soil samples were constructed using PAHs from three source materials-solvent, soot, and fuel oil-to which 3H-benzo(a)pyrene (3H-BaP; total BaP concentrations of 1, 10, and 100 ppm) was added in a mixture of PAHs. The soils were weathered for 8 weeks using weekly wet-dry cycles. Each soil was administered as a single dose to rats, and blood samples were taken over 6 days. Relative oral bioavailability (RBA) of the BaP from soil was estimated by comparing the area under the curve (AUC) for 3H concentration versus time in blood with the AUC observed from the same PAH mixture dosed in a food matrix. The extent to which BaP RBA was diminished in soil versus food varied among the source materials, but little or no difference was observed among the soil types examined unless carbon amendments were added. These results suggest that the type of PAH source material can have a strong influence on PAH oral bioavailability.

In vitro assessments of 14C-benzo[a]pyrene (BaP) absorption through human epidermis were conducted with the sub-63-μm fraction of four test soils containing different amounts of organic and black carbon. Soils were artificially weathered for eight weeks and applied to epidermis at nominal BaP concentrations of 3 and 10 mg/kg for 8 or 24 h. Experiments were also conducted at 24 h with unweathered soils and with BaP deposited onto skin from acetone at a comparable chemical load. For the weathered soils, absorption was independent of the amount of organic or black carbon, the mass in the receptor fluid was proportional to exposure duration but independent of concentration, and the mass recovered in the skin after washing was proportional to concentration and independent of exposure time. Results from the weathered and unweathered soils were similar except for the mass recovered in the washed skin, which was lower for the weathered soil only at the higher concentration. We hypothesize that chemical concentrations exceeded the BaP sorption capacity accessible within the artificial weathering timeframe for all soils tested, and that BaP mass in the washed skin was dominated by particles that were not removed by washing. Fluxes into and through skin from soils were lower by an order of magnitude than from acetone-deposited BaP.

This article reviews the state of the science regarding oral bioavailability, bioaccessibility, and dermal absorption of carcinogenic polycyclic aromatic hydrocarbons (cPAHs) in soil by humans, and discusses how chemical interactions may control the extent of absorption. Derived from natural and anthropomorphic origins, PAHs occur in a limited number of solid and fluid matrices (i.e., PAH sources) with defined physical characteristics and PAH compositions. Existing studies provide a strong basis for establishing that oral bioavailability of cPAHs from soil is less than from diet, and an assumption of 100% relative bioavailability likely overestimates exposure to cPAHs upon ingestion of PAH-contaminated soil. For both the oral bioavailability and dermal absorption studies, the aggregate data do not provide a broad understanding of how different PAH source materials, PAH concentrations, or soil chemistries influence the absorption of cPAHs from soil. This article summarizes the existing studies, identifies data gaps, and provides recommendations for the direction of future research to support new default or site-specific bioavailability adjustments for use in human health risk assessment.

The Association for Environmental Health and Sciences Foundation has been collecting information on state-by-state petroleum cleanup levels (CULs) for soil since 1990, with the most recent survey in 2012. These data form the basis for this analysis, including a comparison of the CULs to U.S. Environmental Protection Agency (USEPA) regulatory values. The results illustrate the evolving complexity of state regulatory approaches to petroleum mixtures; benzene, toluene, ethylbenzene, and xylenes; and carcinogenic polycyclic aromatic hydrocarbons, as well as the use of multiple exposure scenarios and pathways to regulate petroleum in soil. Different fractionation approaches in use by various states and the USEPA are discussed, their strengths and limitations are reviewed, and their implications for site CULs are evaluated. Because of an increasing array of scenarios and pathways, CUL ranges have widened over time. As the regulatory environment for petroleum releases becomes more complex, it is increasingly important to develop a conceptual site model for fate, transport, land use assumptions, and exposure pathways at petroleum-contaminated sites to enable selection of the most appropriate CULs available.

An in vivo pilot study of the oral bioavailability of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in two soils with distinct congener profiles (one dominated by PCDDs, the other by PCDFs) was conducted in rats and juvenile swine. The pilot study revealed potential confounding of relative bioavailability estimates compared to bioavailability in spiked corn oil gavage for tetrachlorodibenzofuran (TCDF) in the rat study due to differential EROD induction between groups receiving soil and those receiving spiked control PCDDs/PCDFs. A follow-up study in rats with the furan-contaminated soil was then conducted with reductions in the spiked control doses to 20%, 50% and 80% of the soil-feed dose in order to bracket hepatic enzyme induction levels in the soil group. When hepatic enzyme induction was matched between the soil and spiked control groups, the apparent relative bioavailability for TCDF was reduced significantly. Overall, after controlling for hepatic enzyme induction, estimates of relative bioavailability in rats and swine differed for the two soils. In the rat study, the relative bioavailability of the two soils were approximately 37% and 60% compared to corn oil administration for the PCDD- and PCDF- dominated soils, respectively, on a TEQ basis. In swine, both soils demonstrated relative bioavailability between 20% and 25% compared to administration in corn oil. These species differences and experimental design issues, such as controlling for differential enzyme induction between corn oil and soil-feed animals in a bioavailability study, are relevant to risk assessment efforts where relative bioavailability inputs are important for theoretical exposure and risk characterization.

Regulatory agencies have relied on dermal absorption data for soluble forms of arsenic as the technical basis for specific absorption values that are used to calculate exposure to arsenic in weathered soil. These evaluations indicate that percutaneous absorption of arsenic from soil ranges from 3.2 to 4.5% of the dermally applied dose, based on studies of arsenic freshly mixed with soil. When this value is incorporated into risk assessments and combined with other assumptions about dermal exposures to soil, the conclusion is often that dermal exposure to arsenic from soil may contribute significantly to overall exposure to arsenic in soil. Prior characterization research has indicated that the solubility of arsenic in soil varies, depending on the provenance of the soil, the source of the arsenic, and the chemical interaction of arsenic with other minerals present within the soil matrix. Weathering produces forms of arsenic that are more tightly bound within the soil and less available for absorption. Our research expands on prior in vivo studies to provide insights into the potential for dermal absorption of arsenic from the more environmentally relevant substrate of soil. Specifically, two soils with very high concentrations of arsenic were evaluated under two levels of skin hydration. One soil, containing 1,400 mg/kg arsenic, was collected adjacent to a pesticide production facility in New York. The other soil, containing 1,230 mg/kg arsenic, was collected from a residential area with a history of application of arsenical pesticides. Although the results of this research are constrained by the small study size dictated by the selection of an animal research model using monkeys, the statistical power was optimized by using a “crossover” study design, wherein each animal could serve as its own comparison control. No other models (animal or in vitro) were deemed adequate for studying the dermal absorption of soil arsenic. Our results show dermal absorption of soluble arsenic in solution to be 4.8% ± 5.5%, which is similar to results reported earlier for arsenic in solution (and used by regulatory agencies in recommendations regarding dermal absorption of arsenic). Conversely, absorption following application of arsenic in the soil matrices resulted in mean estimated arsenic absorption of 0.5% or less for all soils, and all individual estimates were less than 1%. More specifically, following application of arsenic-bearing soils to the abdomens of monkeys, urinary arsenic excretion could not be readily distinguished from background. This was true across all five soil dosing trials, including application of the two soils dry, and three trials with wet soil. These findings are consistent with our understanding of the environmental chemistry of arsenic, wherein arsenic can be present in soils in complexed mineral forms. This research addresses an important component involved in estimating the true contribution of percutaneous exposures to arsenic in soil relative to exposures via ingestion. Our findings suggest that dermal absorption of arsenic 1 ToxSci Advance Access published September 13, 2007

Regulatory agencies have relied on dermal absorption data for soluble forms of arsenic as the technical basis for specific absorption values that are used to calculate exposure to arsenic in weathered soil. These evaluations indicate that percutaneous absorption of arsenic from soil ranges from 3.2 to 4.5% of the dermally applied dose, based on studies of arsenic freshly mixed with soil. When this value is incorporated into risk assessments and combined with other assumptions about dermal exposures to soil, the conclusion is often that dermal exposure to arsenic from soil may contribute significantly to overall exposure to arsenic in soil. Prior characterization research has indicated that the solubility of arsenic in soil varies, depending on the provenance of the soil, the source of the arsenic, and the chemical interaction of arsenic with other minerals present within the soil matrix. Weathering produces forms of arsenic that are more tightly bound within the soil and less available for absorption. Our research expands on prior in vivo studies to provide insights into the potential for dermal absorption of arsenic from the more environmentally relevant substrate of soil. Specifically, two soils with very high concentrations of arsenic were evaluated under two levels of skin hydration. One soil, containing 1400 mg/kg arsenic, was collected adjacent to a pesticide production facility in New York. The other soil, containing 1230 mg/kg arsenic, was collected from a residential area with a history of application of arsenical pesticides. Although the results of this research are constrained by the small study size dictated by the selection of an animal research model using monkeys, the statistical power was optimized by using a "crossover" study design, wherein each animal could serve as its own comparison control. No other models (animal or in vitro) were deemed adequate for studying the dermal absorption of soil arsenic. Our results show dermal absorption of soluble arsenic in solution to be 4.8 +/- 5.5%, which is similar to results reported earlier for arsenic in solution (and used by regulatory agencies in recommendations regarding dermal absorption of arsenic). Conversely, absorption following application of arsenic in the soil matrices resulted in mean estimated arsenic absorption of 0.5% or less for all soils, and all individual estimates were less than 1%. More specifically, following application of arsenic-bearing soils to the abdomens of monkeys, urinary arsenic excretion could not be readily distinguished from background. This was true across all five soil-dosing trials, including application of the two dry soils and three trials with wet soil. These findings are consistent with our understanding of the environmental chemistry of arsenic, wherein arsenic can be present in soils in complexed mineral forms. This research addresses an important component involved in estimating the true contribution of percutaneous exposures to arsenic in soil relative to exposures via ingestion. Our findings suggest that dermal absorption of arsenic from soil is truly negligible, and that EPA's current default assumption of 3% dermal absorption of arsenic from soils results in significant overestimates of exposure.

A number of studies have found that gastrointestinal absorption of arsenic from soil is limited, indicating that a relative oral bioavailability (RBA) adjustment is warranted when calculating risks from exposure to arsenic-contaminated soil. However, few studies of arsenic bioavailability from soil have been conducted in animal models with phylogenetic similarity to humans, such as nonhuman primates. We report here the results of a study in which the RBA of arsenic in soil from a variety of types of contaminated sites was measured in male cynomolgus monkeys. A single oral dose of each contaminated soil was administered to five adult male cynomolgus monkeys by gavage, and the extent of oral absorption was evaluated through measurement of arsenic recovery in urine and feces. Urinary recovery of arsenic following doses of contaminated soil was compared with urinary recovery following oral administration of sodium arsenate in water in order to determine the RBA of each soil. RBA of arsenic in 14 soil samples from 12 different sites ranged from 0.05 to 0.31 (5-31%), with most RBA values in the 0.1-0.2 (10-20%) range. The RBA values were found to be inversely related to the amount of arsenic present with iron sulfate. No other significant correlations were observed between RBA and arsenic mineralogic phases in the test soils. The lack of clear relationships between arsenic mineralogy and RBA measured in vivo suggests that gastrointestinal absorption of arsenic from soil may be more complex than originally thought, and subject to factors other than simple dissolution behavior.

This research compares the As and Cr chemistry of dislodgeable residues from chromated copper arsenate (CCA)-treated wood collected by two different techniques (directly from the board surface either by rubbing with a soft bristle brush or by rinsing from human hands after contact with CCA-treated wood) and demonstrates that these materials are equivalent in terms of both the chemical form and bonding of As and Cr and in terms of the As leaching behavior. This finding links the extensive chemical characterization and bioavailability testing that has been done previously on the brush-removed residue to a material that is derived from human skin contact with CCA-treated wood. Additionally, this research characterizes the arsenic present in biological fluids (sweat and simulated gastric fluid) following contact with these residues. The data demonstrate that in biological fluids the arsenic is present primarily as free arsenate ions. Arsenic-containing soils were also extracted into human sweat to evaluate the potential for arsenic dissolution from soils at the skin surface. For soils from field sites, only a small fraction of the total arsenic is soluble in sweat. Based on comparisons to reference materials that have been used for in vivo dermal absorption studies, these findings suggest that the actual relative bioavailability via dermal absorption of As from CCA residues and soil may be well below the current default value of 3% used by U.S. EPA.

P-604 Abstract: Between July 2002 and May 2005, the U.S. Strategic Environmental Research and Development Program sponsored research focused on understanding the bioavailability of metals in soils. The broad goals of this effort were to better understand what metals drive remedial decisions at metals-impacted sites, evaluate the relative bioavailability of these metals in soil to human and ecological receptors, and to assess the potential for developing simple bench-top (in vitro) methods that might be predictive of the results observed in animals (in vivo). This presentation will provide a brief overview of the full breadth of the research that was undertaken, and more detailed information regarding the study design and findings regarding the relative oral bioavailability, as measured in the cynomolgus monkey, and dermal absorption of arsenic from soils, as measured in the Rhesus monkey. Additionally, discussion of current progress toward developing in vitro methods for estimating the relative oral bioavailability arsenic from soil will be provided. This emerging research indicates that soil-related factors impose significant controls on the availability for arsenic to be absorbed under physiologic conditions, and that existing benchtop (in vitro) methods for assessing the bioaccessibility of other metals from soil may not be appropriate for evaluating the bioaccessibility of arsenic from soil.

In recent years, regulatory and public attention has become focused on the potential risks associated with exposure to chromated copper arsenate (CCA)-treated wood – the most widely used wood treatment product in the United States. CCA has been used to treat lumber for over 60 years (1), mainly because of the extended lifetime of CCA-treated wood as compared to untreated wood (2-5) and the higher costs of non-wood alternatives. Since the late 1980s, U.S. production of CCA-treated wood has averaged approximately 5 x 10 ft/y (6) and by 1996, sales of treated wood products reached over $3.9 billion (1). Although in January 2004 a voluntary ban on CCA for residential use went into effect, it is estimated that 300,000 metric tons of As have been used in CCA production since 1975 with most of that product still remaining in use today (7). Because of the potential toxicity of the metal constituents of CCA, attention has become focused on the potential risks from this exposure source, and in particular, the exposure of children to arsenic from CCAtreated wood used in decks and play sets. As a result, the U.S. EPA Office of Pesticide Programs (OPP) is currently preparing a human health risk assessment for direct-contact exposures to CCA-treated wood. Using the assumptions proposed in its initial 2001 exposure evaluation methodology, the U.S. EPA suggested that the major routes of arsenic exposure to younger children, 1 to 6 years, from CCA products would be through contact with wood residues, with roughly 50% coming through dermal absorption of arsenic and 46% coming through incidental ingestion. The dermal absorption estimate was calculated by assuming that 6.4% of a dermally applied arsenic dose would be absorbed. The remaining 4% of the exposure was estimated to come from exposure to arsenic containing soils.

Current knowledge of percutaneous absorption of arsenic is based on studies of rhesus monkeys using soluble arsenic in aqueous solution, and soluble arsenic mixed with soil (Wester et al., 1993). These studies produced mean dermal absorption rates in the range of 2.0-6.4% of the applied dose. Subsequently, questions arose as to whether these results represent arsenic absorption from environmental media. Factors such as chemical interactions, the presence of other metals, and the effects of weathering on environmental media all can affect the nature of arsenic and its potential for percutaneous absorption. Therefore, research specific to more relevant matrices is important. The focus of this effort is to outline study design considerations, including particle size, application rates, means of ensuring skin contact and appropriate statistical evaluation of the data. Appropriate reference groups are also important. The potential for background exposure to arsenic in the diet possibly obscuring a signal from a dermally applied dose of arsenic will also be addressed. We conclude that there are likely to be many site-or sample-specific factors that will control the absorption of arsenic, and matrix-specific analyses may be required to understand the degree of percutaneous absorption.

: The research conducted under this project is designed to yield a database that establishes whether site- or soil-specific factors affect the bioavailability of target metals from soils. Where the database (from in vivo research) identifies that these types of factors are operating, an additional goal of the research has been to develop simple extraction tests that are inexpensive to perform and that are predictive of metals bioavailability from soil. These tools can then be available to U.S. Department of Defense (DoD) personnel for site-specific evaluation of metals bioavailability from soil at field sites and will result in more accurate exposure and risk estimates that are still protective of human health and the environment. Exposure pathways and receptors of concern were established to target the in vivo research, and focused on three distinct areas: oral bioavailability to humans, dermal bioavailability to humans, and oral bioavailability to wildlife. The project was designed in this manner, because each of these receptor/pathway combinations requires a different approach, due to the differences in the mechanism of absorption and/or differences in risk assessment methods. The research was undertaken in three phases. First, research was conducted to understand which metals are risk drivers at DoD sites. Second, in vivo testing was conducted on soils to understand whether there are site- or soil-specific parameters that control absorption, and if so, to generate a database of information upon which to base development and validation of in vitro approaches to assessing bioavailability. The third phase, conducted once the in vivo data were compiled, involved determining whether in vitro methods for approximating bioavailability can be supported.

In preparation for a study of the relative oral bioavailability of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in soils (typically containing less than 1 ppb 2,3,7,8-tetrachlo-rodibenzo-p-dioxin [TCDD] toxic equivalents [TEQ]), the background concentrations of PCDD/Fs and selected polychlorinated biphenyls (PCBs) were measured in liver and adipose tissue from female Sprague-Dawley rats and juvenile swine after 30 d of ingesting laboratory chow. The measured concentrations of TCDD and other PCDD/Fs in rat livers were severalfold less than previously reported in the literature for control (unexposed) laboratory rodents. The concentrations of PCDD/Fs and selected PCBs in livers of swine were three- to fourfold lower than those reported for rats. The lower concentrations found in this study compared to previous findings may be due to inadvertent laboratory contamination in previous studies or to declining levels of PCDD/Fs in laboratory feed, which parallel the declines in emissions, general environmental levels, and human food and tissue levels of PCDD/Fs.

In the fall of 2000, 34 groundwater samples were collected from beneath an active pesticide reformulating and packaging facility in coastal northeastern Florida to measure the enantiomer fractions ...

AbstractThis article presents a review of in situ technologies for the remediation of soils contaminated with lead, zinc, and/or cadmium. The objective of this review is to assess the developmental status of the available in situ technologies and provide a general summary of typical applications and limitations of these technologies. The literature review identified seven in situ remediation technologies—solidification/stabilization, vitrification, electrokinetic remediation, soil flushing, phytoextraction, phytostabilization, and chemical stabilization. These technologies were considered for their ability to meet a specific set of remediation objectives under a range of conditions. Each of these technologies has both strengths and weaknesses for addressing particular remedial situations discussed in the article for each of the technologies. A general summary of which technologies are most applicable to common remedial scenarios is also provided. © 2004 Wiley Periodicals, Inc.

ABSTRACT This study was undertaken to establish which metals are most likely to drive the risk-based remedial decision-making process at those U.S. Department of Defense (DoD) sites that are affected by metals in site soils. Our approach combined queries of various databases, interviews with U.S. Environmental Protection Agency (USEPA) experts in each Region, and communication with database administrators and DoD personnel. The databases that were used were comprehensive for DoD sites, yet sometimes contained inaccuracies. Metal concentration data for various DoD facilities were screened against established regulatory criteria for both human health and ecological endpoints. Results from this analysis were compared against the information gleaned from the interviews. This preliminary analysis indicates that the five metals that most frequently exceeded risk-based screening criteria for potential human health concerns at DoD sites, in descending order of frequency, are lead, arsenic, cadmium, chromium, and antimony. The metals that most frequently exceeded ecological screening criteria, in order, are lead, cadmium, mercury, zinc, arsenic, chromium, and selenium. Although the majority of USEPA personnel interviewed indicated that human health risk, rather than ecological endpoints, generally drives remedial decision-making, the data indicated that ecological screening thresholds were exceeded more often than human health standards.

The abiotic tools that are available, or under development, for evaluating the oral and dermal bioavailability of contaminants from soils are described in this article. These tools generally rely on one of two approaches: (1) characterizing the form of the contaminant and the chemical binding of the contaminant to the soil matrix, and (2) chemical extractions intended to evaluate the fraction of the chemical that would be liberated in biological fluids (gastrointestinal fluid or sweat). For the purpose of human health risk assessment, abiotic methods to estimate the bioavailability of inorganic contaminants in soil are considered generally to be "screening" level tools at this time. Development work for physiologically based extraction tests (PBETs) is ongoing for many inorganic contaminants, and these methods hold great promise for eventual use in making quantitative bioavailability adjustments in risk assessment. The availability of abiotic tools to evaluate the bioavailability of organic contaminants from soils lags behind that for metals, due to the difficulty in conducting in vivo bioavailability studies with organic compounds and their complex interactions with soil. However, considerable research is being conducted in this field, and new assessment tools are being validated for use in human health risk assessment.

This study was conducted to evaluate the dermal absorption of arsenic from residues present on the surface of wood preserved with chromated copper arsenate (CCA). The research reported herein used methods parallel to those of earlier research on the dermal absorption of radiolabeled arsenic (R. C. Wester et al., 1993, Fund. Appl. Toxicol. 20, 336-340), with modifications to allow use of environmental matrices that are not radiolabeled. These modifications include the surface area of application and dietary intake of arsenic, thus maximizing the potential for detection of dermally absorbed arsenic in exposed animals above diet-associated background levels of exposure. Two forms of arsenic were administered in this work. The first, arsenic in solution, was applied to the skin of monkeys to calibrate the model against prior absorption research and to serve as the basis of comparison for absorption of arsenic from CCA-treated wood residues. The second substrate was residue that resides on the surface of CCA-treated wood. Results from this research indicate that this study methodology can be used to evaluate dermally absorbed arsenic without the use of a radiolabel. Urinary excretion of arsenic above background levels can be measured following application of soluble arsenic, and absorption rates (0.6-4.4% absorption) are consistent with prior research using the more sensitive, radiolabeled technique. Additionally, the results show that arsenic is poorly absorbed from CCA-treated wood residues (i.e., does not result in urinary arsenic excretion above background levels).