Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
United States OSWER 9200.1 -1 1 3
Environmental
Protection Agency
I A \ Compilation and Review of Data on Relative
Bioavailability of Arsenic in Soil
December 2012
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
TABLE OF CONTENTS
LIST OF TABLES iii
LIST OF FIGURES iii
ACRONYMS AND ABBREVIATIONS iv
1.0 INTRODUCTION 1
1.1 Background 1
1.2 Bioavailability -Definitions 1
2.0 KEY AND RELEVANT STUDIES 2
2.1 Methodologies Used in Key and Relevant Studies 3
2.1.1 Single Dose Urinary Excretion Fraction Method 4
2.1.2 Repeated Dose Steady-State Urinary Excretion Fraction Method 5
2.1.3 Single Dose Blood-Time Concentration Curve Method 5
2.2 Key Studies 5
2.2.1 U.S. EPA, 2010 5
2.2.2 Casteel and SRC, 2005 6
2.2.3 Casteel and SRC, 2009a 6
2.2.4 Casteel and SRC, 2009b 6
2.2.5 Casteel and SRC, 2009c 7
2.2.6 Casteel and SRC, 2010a 7
2.2.7 Casteel and SRC, 2010b 7
2.2.8 Casteel and SRC, 2010c 7
2.2.9 Basta et al., 2007; Rodriguez et al., 1999 8
2.2.10 U.S. EPA, 1996 8
2.2.11 Juhasz et al., 2007 9
2.2.12 Roberts et al., 2007 9
2.2.13 U.S. EPA, 2009 9
2.2.14 Roberts et al., 2002 10
2.2.15 Freeman et al., 1995 10
2.2.16 Bradham et al., 2011,2012 11
2.3 Relevant Studies 11
2.3.1 Freeman et al., 1993 11
3.0 LIMITATIONS OF DATA 11
4.0 SUMMARY OF ARSENIC RBA ESTIMATES 13
4.1 Summary of Arsenic RBA Estimates 13
4.2 Factors Influencing RBA Estimates 15
4.2.1 Species Differences 15
4.2.2 Urinary Excretion Fraction (UEF) Method vs. Blood AUC Method 16
4.2.3 Test Material Arsenic Dose and Concentration 17
4.2.4 Explanatory Variables Influencing RBA Estimates in Key Studies 18
4.3 Uncertainties in Use of Compiled RBA Estimates for Prediction of Arsenic RBA 18
5.0 REFERENCES 22
APPENDIX A: Summary Description of Human Arsenic Bioavailability Study (Stanek et al.,
2010) 52
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LIST OF TABLES
Table 1. Confidence in Arsenic RBAEstimates 26
Table 2. Key and Relevant Study Results 29
Table 3. Summary Statistics for RB A (%) Estimates Based on Key Studies 46
Table 4. Weighted RBA Summary Statistics and Confidence Limits 46
Table 5. RBA Estimates for Barber Orchard Soils Administered to Mice, Monkeys, and
Swine 46
Table 6. Comparison Between RBA Estimates Based on Mice and Swine Bioassays 47
Table 7. Comparison Between RBA Estimates Based on UEF and Blood AUC in Monkeys.... 47
LIST OF FIGURES
Figure 1. Distribution of RBA Values for Materials Assayed in Swine, Monkey, and
Mouse 48
Figure 2. Comparison Between Arsenic RBA Estimates from Swine, Monkey, and Mouse
Bioassays of Four Soil Samples from the Barber Orchard Site 49
Figure 3. Comparison Between Arsenic RBA Estimates from Swine or Mouse Bioassays of
11 Test Materials 50
Figure 4. Relationship Between Arsenic RBA Estimates Based on Mouse and Swine
Bioassays Applied to 11 Test Materials 51
in
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ACRONYMS AND ABBREVIATIONS
ABA Absolute bioavailability
AF0 Oral absorption fraction
AM Arithmetic mean
As Arsenic
AUC Area-under-the-curve
bw Body weight
CI Confidence interval
CTE Central tendency estimate
D Dose
FeAs Iron arsenide
ICP-AES Inductively coupled plasma-atomic emission spectrometry
ICP-MS Inductively coupled plasma-mass spectrometry
INAA Instrumental neutron activation analysis
IRIS Integrated Risk Information System
IVBA In vitro bioaccessibility
kg Kilogram
LCL Lower confidence limit
mg Milligram
n Number of data points
NIST National Institute of Standards and Technology
ppm Parts per million
QA Quality assurance
RAGS Risk Assessment Guidance for Superfund
RB A Relative bioavailability
RM Reference material
SD Standard deviation
SE Standard error
SRM Standard reference material
TM Test material
UCL Upper confidence limit
UEF Urinary excretion fraction
ug Microgram
um Micrometer
U.S. EPA United States Environmental Protection Agency
IV
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1.0 INTRODUCTION
1.1 Background
The Risk Assessment Guidance for Superfund (RAGS) Part A (U.S. EPA, 1989),
Framework for Metals Risk Assessment (U.S. EPA, 2007b), and Guidance for Evaluating the
Bioavailability of Metals in Soils for Use in Human Health Risk Assessment (U.S. EPA, 2007c)
discuss using site-specific bioavailability data to make adjustments to exposure estimates or
toxicity values in Superfund site-specific risk assessments when the medium of exposure in the
exposure assessment differs from the medium of exposure associated with the toxicity value
(e.g., cancer slope factor, reference dose value, etc.). In the absence of reliable site-specific data,
the default assumption is that the bioavailability of the contaminant is the same in the exposure
medium at the site (e.g., soil, water, etc.) as in the exposure medium used to derive the toxicity
value. For arsenic, the toxicity values in EPA's Integrated Risk Information System (IRIS) are
based upon exposure to arsenic in water (U.S. EPA, 2012). The default assumption for assessing
risk from arsenic in soil is that the bioavailability of arsenic in soil is the same as the
bioavailability of arsenic dissolved in water. In other words, the relative bioavailability (RBA)
of arsenic (all forms) in soil compared to water-soluble arsenic is assumed to be 1. This
assumption will result in an overestimate of the true risk if the bioavailability of arsenic in soil is
less than that of arsenic in water. The EPA is evaluating the general applicability and potential
uncertainties associated with the assumption that the bioavailability of arsenic in soil is the same
as that of water-soluble arsenic, and is also evaluating and developing laboratory methods for
estimating RBA of soil arsenic. In support of these assessments, EPA is compiling information
on bioassays that have been used to measure RBA of arsenic in soil along with estimates of RBA
that have been derived from these bioassays. This report summarizes RBA estimates compiled
as of September 2011. EPA expects that future data collection efforts will add to this data set
and that the analyses in this report would be periodically updated.
1.2 Bioavailability - Definitions
In this report, the term bioavailability refers to the fraction or percentage of an ingested
dose of arsenic that is absorbed into the systemic circulation. Bioavailability of arsenic in soil
can be expressed either in absolute terms (absolute bioavailability) or in relative terms (relative
bioavailability):
1. Absolute bioavailability (ABA) is defined as the ratio of the amount of arsenic
absorbed to the amount ingested. This ratio is also referred to as the oral absorption
fraction (AF0).
2. Relative bioavailability (RBA) is defined as the ratio of the ABA or AF0 of arsenic
present in the soil (test material, TM) to the absolute bioavailability of arsenic in
some appropriate reference material (RM, Equation 1):
RBA = ^^ Eq. (1)
ABARM M v '
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3. Bioaccessibility refers to the physiological solubility of arsenic in the gastrointestinal
tract (NRC, 2003). Ingested arsenic must become bioaccessible in the gastrointestinal
tract in order to be absorbed. This process may include physical transformation of
arsenic-bearing particles (e.g., break down of the particle to expose arsenic to
gastrointestinal tract fluids), dissolution of arsenic, and chemical transformation of
dissolved arsenic.
For human health risk assessment purposes, relative bioavailability is important because
we are most often interested in knowing the extent to which the absolute bioavailability of a
chemical increases or decreases in different exposure matrices (e.g., food vs. water vs. soil) or
with the physical or chemical form(s) of the chemical to which humans are exposed.
For example, if 100 micrograms (jig) of arsenic dissolved in drinking water were
ingested and a total of 50 |ig were absorbed, the ABA (or AF0) would be 50/100 or 0.50 (50%).
Likewise, if 100 jig of arsenic contained in soil were ingested and 30 jig were absorbed into the
body, the ABA (or AF0) for arsenic in soil would be 30/100 or 0.30 (30%). The RBA for arsenic
in soil, relative to arsenic in water, would be 0.30/0.50 or 0.60 (60%).
The form of arsenic typically used as the reference material in a RBA bioassay is an
arsenic compound dissolved in water or a readily soluble form (e.g., sodium arsenate) that is
expected to completely dissolve when ingested (i.e., 100% bioaccessible).
2.0 KEY AND RELEVANT STUDIES
A search of the literature was conducted to identify studies in which soil arsenic RBA
was estimated from data collected in controlled human clinical studies or from animal bioassays.
Studies that reported only bioaccessibility measurements (e.g., in vitro extraction of soils) or that
attempted to predict arsenic RBA from bioaccessibility measurements were not included in this
data compilation for several reasons. Although there is good evidence to suggest that
bioaccessibility influences and may be an important determinant of RBA, there is no current
consensus on whether or not in vitro bioaccessibility measurements can be used to accurately
predict soil arsenic RBA. EPA has not identified a validated in vitro assay for predicting RBA.
Other on-going efforts by EPA are evaluating methods for predicting arsenic RBA from
bioaccessibility measurements.
Pertinent studies from the published literature were identified by searching bibliographic
databases (i.e., PUBMED, TOXLINE) and other secondary source documents including the cited
references of the retrieved literature. The search period for TOXLINE covered 1980 through
August 2011 and for PUBMED was comprehensive through August 2011. Reference lists from
selected literature were also searched. For additional information or clarification of published
data, study authors were contacted as necessary.
Studies were classified as "key" or "relevant" based on considerations of experimental
design, the number of different test materials analyzed in each animal species, and the source of
test materials. RBA estimates were taken from studies that included a wide variety of bioassay
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protocols that reflect methods currently being used to assess arsenic KB A. Requirements for
inclusion in the analyses were that:
(1) the study was conducted by or for EPA in which EPA developed the KB A estimates
from the raw data using established standard protocols and/or the raw data were
available for Quality Assurance (QA) review by the U.S. EPA Bioavailability
Committee of the Technical Review Workgroup (e.g., EPA swine and mouse
studies); or
(2) the study was conducted by other research groups and results had been subjected to
peer review as a requirement for publication. No attempt was made to reanalyze the
primary data on which each KB A was based (e.g., to verify the KB A value or to apply
the same data reduction methods to the raw data derived from different study
protocols).
Evaluation of multiple test materials in each animal species was considered important for
characterization of uncertainty and variability in KB A estimates. Studies described in this report
assessed KBA of soils that were contaminated in situ. Studies of soils that were spiked with
arsenic in the laboratory (Juhasz et al., 2008; Konstantinos et al., 2008; Nagar et al., 2009) were
not considered based on evidence that KBA of soils spiked with highly bioaccessible sodium
arsenate can change as the soil ages (Juhasz et al., 2008). Studies that assessed absolute
bioavailability and did not report KBA or provide data for calculation of KBA (i.e., Ellickson
et al., 2001) were not considered. As described in Section 2.2 (Key Studies), all "key" studies
were conducted in swine, monkey, or mouse; multiple test materials were analyzed using these
animal models to estimate arsenic KBA. In "key" studies, a total of 103 KBA estimates for
88 unique test materials were obtained in swine (64 KBA estimates), monkeys (24 KBA
estimates), and mice (15 KBA estimates). Among these "key" studies, direct comparisons of
swine, monkey, and mouse KBA estimates are available for only 4 test materials and direct
comparisons of swine and mice KBA estimates are available for 11 test materials. Data obtained
from "key" studies were analyzed to develop summary statistics describing the distribution of
KBA values and to explore sources of variability in the KBA values (i.e., using regression
analysis). As described in Section 2.3 (Relevant Studies), "relevant" studies analyzed a single
test material using a unique animal model (i.e., rabbit). "Relevant" studies provided supportive
data, but were not included in the statistical summary.
A single human experimental study of bioavailability of arsenic soil was reported (Stanek
et al., 2010). This study was not selected for inclusion in this report as a key or relevant study
because of several methodological limitations and uncertainties, which are summarized in
Appendix A.
2.1 Methodologies Used in Key and Relevant Studies
A variety of different in vivo methods have been utilized for estimating soil arsenic KBA.
All of these methods share a common general approach in which biomarkers of arsenic
absorption (blood arsenic concentration or urinary arsenic excretion) were measured following a
single dose or during a period of repeated dosing with arsenic in soil (the test material) and
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Compilation and Review of Data on Relative Unavailability of
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following dosing with sodium arsenate (the reference material). The study protocols differ with
respect to dose (e.g., mg/kg), dosing frequency, the absorption biomarker measured (blood or
urine arsenic), and the computational methods applied to the data for calculating KB A.
In studies that measured urinary arsenic excretion, the absorption dose metric was the
urinary excretion fraction (UEF) which is the amount or rate of arsenic excreted in urine (UAS)
divided by the arsenic dose (DAS, Equation 2).
UEF = Eq. (2)
The KB A was estimated as the ratio of the UEF for arsenic when administered in soil
(test material, TM) to that of the reference material (KM; i.e., sodium arsenate, Equation 3).
= IM E (3)
UEFRM 4 V '
In studies in which animals were dosed one time, the UEF was the cumulative amount of
arsenic excreted during a defined post-dose observation period (e.g., 4 days) divided by the
administered dose. In studies in which doses of arsenic were administered repeatedly to achieve
a quasi-steady state, the UEF was the rate of excretion of arsenic (e.g., jig As/day) divided by the
dosing rate (e.g., jig As/day). In studies in which arsenic was administered at more than one
dose (e.g., 25, 50, or 100 jig As/kg bw/day), the UEF was estimated as the regression slope of
the relationship between urinary arsenic excretion and dose.
In studies that relied on blood arsenic concentration for estimating KB A, the absorption
dose metric was the time-integrated arsenic blood concentration. This was typically measured as
the time-integrated blood concentration of arsenic, referred to in this report and in most of the
literature as the area under the curve (AUC) of the arsenic blood concentration-time profile (e.g.,
estimated using a geometric approximation such as the trapezoid rule). The AUC estimate was
divided by the administered dosage, and the KB A was estimated as the ratio of AUC/dose for the
test and reference materials (Equation 4).
If arsenic was administered at more than one dose (mg/kg), the AUC/dose ratio was
estimated as the regression slope of the relationship between the blood AUC and dose.
Each of these methods is described in greater detail in the sections that follow.
2.1.1 Single Dose Urinary Excretion Fraction Method
In studies conducted using this method, a one-time oral dose of test material or reference
material (sodium arsenate) was administered. Following administration of the arsenic dose,
urine was collected for up to 7 days. Relative bioavailability in test materials was calculated as
the ratio of the UEFs for the test and reference materials, where the UEF was the cumulative
urinary excretion of arsenic divided by the arsenic dose.
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2.1.2 Repeated Dose Steady-State Urinary Excretion Fraction Method
In studies conducted using this method, groups of animals typically were dosed with the
test material or reference material (sodium arsenate) repeatedly for 10-15 days. At various times
during the dosing period, urine samples were collected from each animal and analyzed for
arsenic. The KB A of a test material was calculated as the ratio of the UEFs for the test and
reference materials. In studies in which a single dose level was administered, UEF was
estimated as the cumulative urinary arsenic excretion (e.g., jig As) divided by the dose. In
studies in which arsenic was administered at more than one dose level (e.g., 25, 50, or 100 jig
As/kg bw/day), UEF was calculated by fitting a regression model to the data on dose and urinary
excretion and estimating UEF as the regression slope.
2.1.3 Single Dose Blood-Time Concentration Curve Method
In studies conducted using this method, groups of animals were administered a one-time
oral dose of test material or reference material (sodium arsenate) or an intravenous dose of the
reference material. Test and reference materials were administered at multiple dose levels.
Blood samples were collected at various time points up to 6 days after dosing. For the
calculation of KB A, the time-integrated blood arsenic concentration (AUC) and arsenic dose for
both the test material and reference material were subjected to regression analysis. KB A was
estimated as the ratio of the regression slopes.
2.2 Key Studies
Methods and protocols of key studies are summarized below. Many of these studies
estimated KB A for multiple test materials. Sources of uncertainties that were considered in
assessing confidence in KBA estimates and making statistical inference regarding arsenic KBA
in soils are summarized in Table 1. The identity of the individual test materials, dosing
schedules, and dose levels used to assess KBA for each test material are provided in Table 2.
2.2.1 U.S. EPA, 2010
The KBA of arsenic was estimated for several test materials using the steady-state urinary
excretion fraction method described in U.S. EPA (2010). These studies were sponsored by U.S.
EPA Region 8. Test materials were obtained from various locations throughout the U.S. and
included residential and non-residential soils and mining slag. The concentration of arsenic in
these test materials ranged from 72 to 1050 ppm. All studies were performed using young, intact
male swine (genetically defined Line 26 strain), typically 5 to 7 weeks old, weighing 7 to 12 kg.
Groups of animals (usually 4-5 per dose group) were exposed to 1 to 3 dose levels of test
material or reference material (sodium arsenate) daily for 12-15 days. Test materials were
placed in the center of moistened feed (dough ball) and administered to the animals by hand.
Sodium arsenate (reference material) was administered by gavage or intravenous injection.
Samples of urine were collected from each animal on several different days during the study (the
exact days varied from study to study, with collection periods ranging from 24-48 hours). Urine
samples were prepared for analysis using one of two alternative methods referred to as Phase II
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(acid digestion) and Phase III (acid digestion and ashing). Arsenic in digested urine samples was
measured by hydride generation using atomic absorption spectrometry (limit of detection ~1-
2 |ig/L). Detailed descriptions of the acid digestion and ashing methodologies are provided in
U.S. EPA (2010). The Phase II method yielded a poor recovery of organic metabolites of
arsenic, which could result in underestimates of urinary arsenic. However, comparative studies
using the same test materials showed that the Phase II and Phase III methods yielded essentially
the same RBA estimates. Therefore, RBA estimates using Phase II methods are considered
reliable. For the RBA calculation, regression was used to estimate the slope of the relationship
between urinary arsenic excretion (e.g., jig/day) and arsenic dose (e.g., jig/day) for both the test
and reference materials. The RBA of the test material was calculated as the ratio of the slopes.
A total of 24 test materials were evaluated with RBA estimates ranging from 8 to 61%.
2.2.2 Casteel and SRC, 2005
The RBA of arsenic was estimated for one test material using the steady-state urinary
excretion fraction method described in U.S. EPA (2010). This study was sponsored by U.S. EPA
Region 6. The test material was a soil sample containing 47 ppm arsenic, obtained from a U.S.
Superfund site in Palestine, Texas. The study was conducted using Phase III methodology as
described in U.S. EPA (2010), with groups of 5 intact male swine (genetically defined Line 26
strain) administered 3 dose levels of test material or reference material (sodium arsenate) daily
for 15 days. The estimated RBA of the test material was 15%.
2.2.3 Casteel and SRC, 2009a
The RBA of arsenic was estimated for four test materials using the steady-state urinary
excretion fraction method described in U.S. EPA (2010). This study was sponsored by U.S. EPA
Office of Superfund Remediation and Technology Innovation. The test materials were soil
samples containing 290 to 388 ppm arsenic obtained from a former commercial apple orchard,
the Barber Orchard site located near Waynesville, Haywood County, North Carolina. The study
was conducted using Phase III methodology as described in U.S. EPA (2010), with groups of
4 intact male swine (genetically defined Line 26 strain) administered 2 to 3 dose levels of test
material or reference material (sodium arsenate) daily for 14 days. The RBA of the test materials
ranged from 31 to 53%. Arsenic RBA estimates for these four Barber Orchard test materials
were also obtained in monkeys (U.S. EPA, 2009; see Section 3.2.8).
2.2.4 Casteel and SRC, 2009b
The RBA of arsenic was estimated for one test material using the steady-state urinary
excretion fraction method described in U.S. EPA (2010). This study was sponsored by U.S. EPA
Office of Superfund Remediation and Technology Innovation. The test material was a sample of
National Institute of Standards and Technology (NIST) Standard Reference Material (SRM)
2710. This soil sample, collected in Montana from an area contaminated by mine tailings
deposits, contained 626 ppm arsenic. The study was conducted using Phase III methodology as
described in U.S. EPA (2010), with groups of 4 intact male swine (genetically defined Line 26
strain) administered 3 dose levels of test material or reference material (sodium arsenate) daily
for 14 days. The RBA of the test material was 44%.
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2.2.5 Casteel and SRC, 2009c
The KB A of arsenic was estimated for one test material using the steady-state urinary
excretion fraction method described in U.S. EPA (2010). This study was sponsored by U.S. EPA
Office of Superfund Remediation and Technology Innovation. The test material was a sample of
soil from the Mohr Orchard site located in Region 3, Lehigh County, Pennsylvania. The arsenic
concentration of the Mohr Orchard soil sample was 340ą4.5 mg/kg (meanąSD). The study was
conducted using Phase III methodology as described in U.S. EPA (2010), with groups of 4 intact
male swine (genetically defined Line 26 strain) administered 3 dose levels of test material or
reference material (sodium arsenate) daily for 14 days. The RBA of the test material was 53%.
2.2.6 Casteel and SRC, 2010a
The RBA of arsenic was estimated for two test materials using the steady-state urinary
excretion fraction method described in U.S. EPA (2010). This study was sponsored by U.S. EPA
Office of Superfund Remediation and Technology Innovation. The test materials were samples
of soil from the Iron King Mine - Humboldt Smelter Superfund Site. The soil samples (HSJ583
and IKJ583) were collected from the Chaparral Gulch near a residential area (HSJ583) and a
tailings pile (IKJ583). The mean arsenic concentrations of the soil samples were 200 ppm
(HSJ583, TM1) and 3957 ppm (IKJ583, TM2). The study was conducted using Phase III
methodology as described in U.S. EPA (2010), with groups of 4 intact male swine (genetically
defined Line 26 strain) administered 3 dose levels of test material or reference material (sodium
arsenate) daily for 14 days. The RBA of the test materials were 60% (TM1) and 19% (TM2).
2.2.7 Casteel and SRC, 2010b
The RBA of arsenic was estimated for two test materials (ASARCO and Hawaii) using
the steady-state urinary excretion fraction method described in U.S. EPA (2010). This study was
sponsored by U.S. EPA Office of Superfund Remediation and Technology Innovation. The
ASARCO material was collected from a former smelter site near Tacoma, Washington. Multiple
samples were collected from a stockpile of soil that was removed from residential properties and
composited prior to analysis. The Hawaii material was collected from a garden plot used by
Kea'au Middle School, located in the town of Kea'au on the island of Hawaii. The garden has
high arsenic concentrations attributable to herbicide use between 1920 and 1950 in former sugar
mill plantation lands in the area. The soil samples contained 182 ppm (ASARCO) and 769 ppm
(Hawaii) arsenic. The study was conducted using Phase III methodology as described in U.S.
EPA (2010), with groups of 4 intact male swine (genetically defined Line 26 strain) administered
3 dose levels of test material or reference material (sodium arsenate) daily for 14 days. The RBA
of the test materials were 49% (ASARCO) and 33% (Hawaii).
2.2.8 Casteel and SRC, 2010c
The RBA of arsenic was estimated for one test material using the steady-state urinary
excretion fraction method described in U.S. EPA (2010). This study was sponsored by U.S. EPA
Office of Superfund Remediation and Technology Innovation. The test material was a sample of
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NIST SRM 2710a. This soil sample, obtained in Montana from an area contaminated by mine
tailings deposits, contained 1540 ppm arsenic. The study was conducted using Phase III
methodology as described in U.S. EPA (2010), with groups of 4 intact male swine (genetically
defined Line 26 strain) administered 3 dose levels of test material or reference material (sodium
arsenate) daily for 14 days. The RBA of the test material was 42%.
2.2.9 Basta et al., 2007; Rodriguez et al., 1999
Rodriguez et al. (1999) estimated the RBA of arsenic in several test materials in juvenile
swine using the same steady-state urinary excretion fraction method described in U.S. EPA
(2010). Test materials (soils and slags), with arsenic concentrations ranging from 233 to
17,500 ppm, were collected from mining/smelter sites in the western U.S. Studies were
performed in young, intact male swine (Line 26 strain), weighing 10-12 kg. Test groups of
animals (2-5 per dose group) were administered a single dose level of test material (in a dough
ball) and a control group was administered a reference material (sodium arsenate). The animals
were dosed daily for 15 days, and urine was collected for five 24-hour periods. For the
calculation of RBA, the UEF of arsenic (cumulative urinary excretion/dose) administered in test
material and in reference material (sodium arsenate) was calculated, and the RBA was calculated
as the ratio of the UEF values. The Rodriguez et al. (1999) report did not include standard
deviations (SD), standard errors (SE), or confidence limits (CI) for mean RBA values. Due to
concerns regarding recovery of organoarsenical compounds in urine, Basta et al. (2007) re-
analyzed urine samples from nine test materials reported in Rodriguez et al. (1999) using the
Phase III analytical method (U.S. EPA, 2010). Revised RBA estimates for these nine samples
were reported graphically in Basta et al. (2007); numeric values (mean RBA estimates and
standard deviations) were provided for this report through a personal communication with Dr.
Basta. A total of 14 test materials were evaluated in the Basta et al. (2007) and Rodriguez et al.
(1999) studies, with RBA estimates ranging from 4 to 43%.
2.2.10 U.S. EPA, 1996
In a study sponsored by U.S. EPA Region 10, the RBA of arsenic was estimated for two
test materials (mining soil and slag collected from the Ruston/North Tacoma Superfund site)
using the single dose blood-time concentration curve method. Arsenic concentrations in the test
materials were 1600 ppm for the mining soil and 10,100 ppm for the slag. The study was
conducted in young, female swine (bred from Hampshire sires and Landrace/Large White/Duroc
dams), 6-7 weeks of age, weighing approximately 15 kg. Groups of three animals were
administered a single oral dose of test material as an aqueous suspension or single oral or
intravenous dose of reference material (sodium arsenate); multiple dose levels of test and
reference materials were evaluated. Following administration, blood samples were obtained at
various time points from 15 minutes to 144 hours after dosing. Following acid digestion and
heat treatment, arsenic was measured by hydride generation using atomic absorption
spectrometry (limit of detection = 1 |ig/L). Regression models were fit to the data on time-
integrated blood arsenic concentration (AUC) and dose, and RBA was calculated as the ratio of
slopes for test and reference materials. The study report did not include standard deviations or
standard errors, but reported 95% confidence limits. RBA estimates ranged from 42% (slag) to
78% (soil).
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2.2.11 Juhasz et al., 2007
Juhasz et al. (2007) estimated the KB A of arsenic in several Australian test materials,
with arsenic concentrations ranging from 42 to 1114 ppm, using the single dose blood-time
concentration curve method. Test materials were collected from railway corridors, cattle tick dip
sites, mining sites, and gossans (areas containing naturally elevated concentrations of arsenic).
Groups of 3 female swine (strain: large white; body weight: 20 to 25 kg) were administered
single doses of test materials as soil slurries or sodium arsenate by gavage. Blood samples were
collected at various times up to 26 hours following dosing. Samples were digested by nitric acid
or ammonium hydroxide; arsenic was measured by inductively coupled plasma-mass
spectrometry (ICP-MS; limit of detection not reported). Relative bioavailability of arsenic in test
materials was determined using the ratio of the time-integrated blood arsenic concentration
(AUC) divided by the dose, for the test and reference material. Although Juhasz et al. (2007) did
not report RBA estimates for individual test materials, study authors provided means and
standard deviations for individual test materials in a personal communication (dated June 18,
2008). A total of 12 test materials were evaluated in this study, with RBA estimates ranging
from 7 to 75%.
2.2.12 Roberts et al., 2007
The RBA of arsenic was estimated for several soils (arsenic concentration range: 125 to
1492 ppm) collected from various locations throughout the U.S. (California, Colorado, Florida,
Hawaii. Montana, New York, Washington, and Wisconsin) using the single dose urinary
excretion fraction method. The study was conducted in young adult male cynomolgus monkeys,
weighing 4 to 5 kg. Five animals were administered single doses of test materials (as soil slurry)
or reference material (sodium arsenate) by gavage. Each monkey received the test and reference
material, with dosing of each material separated by at least 3 weeks. Urine and feces were
collected for 4 days after dosing. Urine samples were treated with nitric acid, heat, and hydrogen
peroxide; urin arsenic was measured using inductively coupled plasma-atomic emission
spectrometry (ICP-AES) (limit of detection = 2.3 |ig/L). The relative bioavailability in test
materials was determined using the ratio of the UEF for test and reference materials, where UEF
was the cumulative urinary arsenic (jig) excretion divided by the arsenic dose (jig). A total of
14 test materials were evaluated in this study, with RBA estimates ranging from 5 to 31%.
2.2.13 U.S. EPA, 2009
The RBA of arsenic was estimated for 4 soils collected from the Barber Orchard site near
Waynesville, Haywood County, North Carolina (a former commercial apple orchard, soil arsenic
concentration range: 290 to 388 ppm) using the single dose urinary excretion fraction method.
Single doses of test materials (as soil slurry) or reference material (sodium arsenate) were
administered by gavage to 5 young adult male cynomolgus monkeys, weighing 4 to 5 kg. Each
monkey received the test and reference material, with dosing of each material separated by at
least 3 weeks. Urine and feces were collected for 4 days after dosing. Urine samples were
treated with nitric acid, heat, and hydrogen peroxide; urinary arsenic was measured using ICP-
AES (limit of detection = 0.3 |ig/L). Relative bioavailability in test materials was determined
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using the ratio of the UEF for test and reference materials, where UEF was the cumulative
urinary arsenic (jig) excretion divided by the arsenic dose (|ig). KB A estimates for the Barber
Orchard test materials assayed in this study ranged from 25 to 38%. KB A estimates for these 4
Barber Orchard test materials were also obtained in swine (Casteel and SRC, 2009a; see Section
3.2.3).
2.2.14 Roberts et al., 2002
The RBA of arsenic was estimated for contaminated Florida surface soils (arsenic
concentration range: 101 to 743 ppm) using the single dose urinary excretion fraction method.
The study was conducted using adult male Cebus apella monkeys, weighing 2.5 to 3 kg. Single
doses of test materials (as soil slurry) or reference material (sodium arsenate) were administered
by gavage to 5 animals. Urine and feces were collected for 4 days after dosing. Urine samples
were treated with nitric acid, heat, and hydrogen peroxide; urinary arsenic was measured using
ICP-AES (limit of detection = 2.5 |ig/L). Relative bioavailability in test materials was
determined using the ratio of the UEF for test and reference materials, where UEF was the
cumulative urinary arsenic (jig) excretion divided by the arsenic dose (jig). A total of 5 test
materials were evaluated in this study, with RBA estimates ranging from 1 1 to 25%.
2.2.15 Freeman et al., 1995
Freeman et al. (1995) estimated the RBA of arsenic in a single test material (residential
soil, arsenic concentration: 410 ppm) using both the single dose urinary excretion fraction and
single dose blood-time concentration curve methods in female cynomolgus monkeys (weighing 2
to 3 kg). Three female monkeys were administered single doses of the test material in a capsule
by gavage or reference material (sodium arsenate in solution) by gavage or intravenous injection.
Each monkey received the test and reference material. Urine was collected for 7 days after
dosing, and blood samples were collected at several time points from 15 minutes to 120 hours
after dosing. In this study, the ABA of arsenic was calculated for the test and reference
materials. For this report, RBA was calculated as the ratio of the reported ABA for the test and
reference material.
Freeman et al. (1995) estimated arsenic ABA from both measurements of UEF and time-
integrated arsenic blood concentration (AUC). For each, the ABA was calculated as the ratio of
the biomarker measured following the oral dose to that measured following an intravenous dose
(i.e., 100% absorption, Equations 5 and 6):
ABA = pŦi Eq. (5)
UEFRM,iv
=AUC,oral^AUC^^
DTM,oral DRM,iv
The arsenic RBA calculated based on the UEF data for the individual animals (n=3) was
20. 1% (SD=6.9%), compared to 1 1 .0% (SD=7.7%) based on the blood AUC data. These
estimates are not significantly different (paired t-test, p=0.37).
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2.2.16 Bradham et al., 2011, 2012
The RBA of arsenic was estimated for contaminated surface soils (arsenic concentration
range: 182 to 4495 ppm) using the repeated dose steady state urinary excretion fraction method
(Bradham et al., 2011, 2012). Test materials were obtained from various locations throughout
the U.S. and included agricultural soils and soils impacted by mining and smelting. Four to six
week-old female C57BL/6 mice were fed diets containing the test soil or sodium arsenate. The
test soil and sodium arsenate groups typically consisted of 12 mice that were housed in metabolic
cages containing 3 mice per cage. The test soil was mixed into the powdered AIN-93G purified
rodent diet to achieve a 1% (w/w) soil:diet ratio. Mice received the diets for a period of 10 days
during which urine and feces were collected daily. Arsenic concentrations in diet, soil, urine,
and feces were determined by Instrumental Neutron Activation Analysis (INAA). Daily arsenic
dosages were estimated from measurements of daily diet consumption. Doses ranged from 0.32
to 6.10 mg As/kg bw/day, and soil dose ranged from 1.15 to 1.65 g soil/kg bw/day (over a
10-day period). Arsenic RBA was estimated as the ratio of UEFs for soil arsenic and sodium
arsenate treatment groups, where the UEF was the cumulative urinary arsenic (jig) excretion
divided by the cumulative arsenic dose (jig). A total of 15 test materials were evaluated in these
studies, with RBA estimates ranging from 11 to 52%.
2.3 Relevant Studies
Studies that evaluated soil arsenic RBA bioavailability using a unique animal model (i.e.,
rabbit) were considered to be "relevant" studies in that they provided supportive data but were
not included in the data analysis.
2.3.1 Freeman et al., 1993
Freeman et al. (1993) estimated the RBA of arsenic in a single test material using the
single dose urinary excretion fraction method in New Zealand white rabbits. The arsenic
concentration of the test material (soil contaminated through smelter activities) was 3900 ppm.
Groups of 5 male and 5 female rabbits (9 to 12 weeks old, body weight 2 kg) were administered
single oral doses of test material (formulated in a gelatin capsule) or reference material (sodium
arsenate solution). Urine was collected for 120 hours after dosing. Urine samples were digested
with nitric acid and hydrogen peroxide, and urine arsenic was measured using ICP-MS (limit of
detection = 30 |ig/L). The RBA of the test material was estimated by calculating the ratio of the
UEF values for test and reference materials normalized for dose. This study did not report
standard deviations, standard errors, or confidence limits for the mean RBA values of 48%.
3.0 LIMITATIONS OF DATA
The data used to estimate RBA for arsenic in soil materials have the following limitations
and uncertainties for making generic prediction of soil arsenic RBA in humans.
Extrapolation of results to humans: The swine and monkey models have been utilized to
predict human RBA of arsenic for site risk assessment because the gastric physiology of both
animal species is similar to that of humans (U.S. EPA, 2007a) and because of a prior history of
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using these models for assessing KB A of other inorganic contaminants (e.g., lead; U.S. EPA,
2007a) and gastrointestinal absorption of drugs (Chiou and Buehler, 2002; Roberts et al., 2007).
Although estimates of KB A of arsenic in soil materials in animal models have not been
quantitatively compared to estimates made in humans for the same material, this report shows
that RBA estimates obtained from swine, monkey, and mouse for the same test materials are
sufficiently similar to suggest that large differences in RBA across mammalian species are
unlikely. This increases confidence in extrapolating RBA estimates obtained from these assays
to humans.
Comparability of estimates from swine, monkey, and mouse assays: When applied to
the same test materials, the swine, monkey, and mouse assays yielded remarkably similar RBA
estimates for some materials and widely different estimates for other materials (see Section
4.2.1). However, collectively, the differences in the RBA estimates were relatively small. The
absolute difference in the RBA estimates (e.g., RBAswine - RBAmouse, RBAsw;ne - RBAmonkey)
ranged from <1 to 28%, and the average difference was 12%. This magnitude of difference is
relatively small in the context of risk assessment, where uncertainties in other parameters in risk
calculations can exceed several orders of magnitude. Therefore, from the perspective of use of
the assays to support risk assessment, the swine, monkey, and mouse assays appear to yield
essentially equivalent information about arsenic RBA.
The reason why the same test materials give different outcomes in the three animal
models are discussed in Section 4.4.1.
Single dose vs. steady-state models: Animal models that estimate RBA with steady state
dosing have some useful advantages over single dose assays.
(1) Steady state models more closely mimic the status of the human receptor who
receives continuous daily exposure to soil.
(2) At steady state, urinary excretion of arsenic will be relatively constant over time, and
as a result, urinary arsenic excretion rate and UEF can be estimated by averaging
multiple estimates obtained from several urine samples collected over time. By
contrast, in a single dose study, UEF must be estimated as the cumulative urinary
arsenic excretion. This requires absolute accuracy in sampling urine at each interval
of the post-dosing observation period.
(3) Random errors in urine sampling (e.g., completeness of collection) would be expected
to have a larger impact on estimates of the cumulative arsenic excretion than on
average steady state arsenic excretion.
Single vs. multiple dose level models: Assays that estimate RBA at multiple arsenic dose
levels have some useful advantages over single dose level assays.
(1) Potential dependence of UEF on arsenic dose level can be detected and accounted for
in the data reduction and estimate of RBA. Thus far, dose dependence of arsenic
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UEF has not been demonstrated in swine or monkeys, at least not with the range of
arsenic doses examined in reported studies (Roberts et al., 2007; U.S. EPA, 2010).
(2) In multiple dose level studies, UEF can be estimated from regression models of the
relationship between excretion and dose (i.e. change in urinary arsenic
excretion/change in dose level) This provides a statistical alternative to discrete
estimates of UEF based on results obtained at a single dose level.
Test material dose levels: Ideally, animal bioassays should administer test material doses
(i.e., mg soil/kg bw/day) that are similar to those expected in the human receptor population.
This would reduce uncertainty related to possible dependences of arsenic KB A on test material
dose. However, the design of animal KB A assays, particularly detection limits for blood and
urinary arsenic and the wide variation in the arsenic concentrations of test materials, has placed
constraints on experimental control of both the arsenic dose and test material dose used in each
assay. The doses (single doses were administered) of test material in key studies ranged from
approximately 0.4 to 3528 mg soil/kg bw in swine, 490 to 2970 mg soil/kg bw in monkeys and
1150 to 1650 mg soil/kg bw in mice. These ranges include values that are substantially higher
than typical daily soil ingestion rates in children or adults (U.S. EPA, 2008). The implication of
these high test material doses in extrapolating RBA estimates from animals to humans (e.g.,
effect of the test material dose on RBA) has not been thoroughly investigated.
4.0 SUMMARY OF ARSENIC RBA ESTIMATES
4.1 Summary of Arsenic RBA Estimates
Relative bioavailability estimates for individual test materials evaluated in "key" and
"relevant" studies are summarized in Table 2. Summary statistics for RBA estimates from "key"
studies are provided in Table 3. "Key" studies consist of 64 RBA estimates based on bioassays
in juvenile swine (Basta et al., 2007; Casteel and SRC, 2005, 2009a,b,c, 2010a,b,c; Juhasz et al.,
2007; Rodriguez et al., 1999; U.S. EPA, 1996, 2010), 24 RBA estimates based on bioassays in
monkeys (Freeman et al., 1995; Roberts et al., 2002, 2007; U.S. EPA, 2009), and 15 RBA
estimates based on bioassays in mice (Bradham et al., 2011, 2012). Eleven test materials were
evaluated in both swine and mice, and 4 test materials (Barber Orchard soils) were evaluated in
swine, monkeys, and mice. Test materials assessed in "key" studies come from sites impacted
by various arsenic sources: mining/smelting (n=57); agriculture, including orchards and livestock
dipping sites (n=12); other chemical manufacturing/processes, mainly pesticide manufacture
(n=9); railway corridors (n=6); and miscellaneous or uncharacterized sites such as volcanic soils
(n=l). In developing summary statistics shown in Table 3, two approaches were used:
(1) RBA estimates for materials tested in more than one assay were treated either as
independent estimates (where RBA is represented in sample statistics), or
(2) as repeated measurements of the same sample (where the average value for all assays
of the same test material is represented in the sample statistics).
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The two approaches yield essentially the same values for the summary statistics (n=103 or n=88,
see Table 3). For the entire data set (n=103), KB A estimates ranged from 4.1 to 78%, with an
arithmetic mean of 31% (ą16, SD, 5th-95th percentile range: 7-57%).
Summary statistics shown in Table 3 give equal weight to each of the KB A estimates in
the key study data set. However, each RBA estimate represents a mean value for a group of
animals, and each mean has an associated uncertainty given by the standard error and confidence
limits. If each RBA estimate were to be weighted according to its associated confidence, the
resulting distribution of RBA estimates would be a more accurate reflection of the confidence in
each RBA estimate. Monte Carlo simulation was used to derive an uncertainty-weighted
estimate of the mean and selected percentiles and to derive confidence limits for these empirical
parameters. Monte Carlo analysis was conducted as follows.
(1) For each test material, a mean RBA and standard error (SE) were identified.
(2) A distribution for the mean RBA for each test material was defined as
TRUNCATED NORMAL (mean, SE, 0, 100)
where 0 and 100 were the truncation limits and represent the minimum and maximum
values possible for RBA, respectively, and SE is the standard error. If the standard
deviation (SD) was reported but not a SE, the SE was estimated as SD/n°5, where n was
the number of animals represented in the mean. If confidence limits were available but
not standard errors, the standard error was estimated assuming the standard normal
distribution of error and the appropriate value for Z value for the standard normal
distribution (i.e., 1.96 for 95% confidence limits). For 95% upper and lower confidence
limits (UCL, LCL), the corresponding SE was calculated as follows (Equation 7).
95%UCL-95%LCL _ , ,
SE = Eq. (7)
2-1.96 M V '
(3) Each iteration of the Monte Carlo simulation consisted of a random selection from the
distribution of means from each and every test material (i.e., sampling without
replacement). Iteration yielded 10,000 sets of RBA estimates (one per test material).
(4) The mean and 5th, 50th and 95th percentile RBA values were calculated for each
iteration of the Monte Carlo, yielding 10,000 realizations of each parameter.
(5) The 2.5th percentile and 97.5th percentile values were calculated from the 10,000
values for each parameter. These were used to represent the 95% confidence
intervals on the mean 5th, 50th, and 95th percentile RBA values.
Results of the Monte Carlo analysis are shown in Table 4. The uncertainty-weighted
estimates from the Monte Carlo simulation are very similar to the unweighted estimates (see
Table 3). For example, the weighted estimate of the 50th percentile (n=103) is 28.5%
(unweighted = 29.1%), and the confidence interval is 26-31%. The weighted estimate of the 95th
percentile RBA is 58.1% (compared to 56.8% for the unweighted estimate), and the confidence
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interval is 53-64%. Truncation of the distributions used in the Monte Carlo analysis had a
negligible effect on the weighted parameter estimates and confidence limits. Only one RBA
estimate, the Tacoma, WA sample (U.S. EPA, 1996), which had an RBA of 78% (ą14 SE) in
swine, would have been affected by truncation. A random draw from this distribution would be
expected to yield values 2 SE above the mean (106%) at a frequency of approximately 2.5%.
However, this had a minimal effect on the weighted estimates and confidence limits for the full
data set.
4.2 Factors Influencing RBA Estimates
RBA estimates showed a wide range (i.e., 4.1 to 78%). Variability in RBA estimates
may be due to several factors, including differences between animal species, experimental
methods and methods of data reduction, arsenic source, arsenic soil concentration and dose, soil
characteristics, and arsenic mineralogy. Not all of these factors could be assessed with the
available data.
4.2.1 Species Differences
Comparisons of RBA estimates assayed in swine, monkeys, and mice show that arsenic
RBA estimates for materials assayed in swine and mice tended to be higher than estimates for
test materials assayed in monkeys (see Table 3, Figure 1). The mean RBA estimates for test
materials assayed in swine and mice are 34.5% (95% CI: 30.2-38.8, n=64) and 33.5% (95% CI:
27.1-39.8, n=15), respectively, compared to 19.2% (95% CI: 15.8-22.6, n=24) in monkeys.
Data from two different species of monkey, cynomolgus (Freeman et al., 1995; Roberts et al.,
2007) and C. apella (Roberts et al., 2002), are represented in the data set. These data were
combined in the summary statistics reported above because comparison of RBA estimates from
cynomolgus and C. apella bioassays did not show significant differences. The mean RBA values
were 19.9% (ą9.2 SD, n=19) for cynomolgus and 16.7 (ą5.1 SD, n=5) for C. apella. However,
these estimates correspond to different test materials assayed in the two species. Available data
do not allow comparisons of RBA estimates for the same test materials assayed in different
monkey species to determine if different species actually yield different RBA values. Given the
lack of information on which to distinguish RBA estimates from cynomolgus and C. apella,
RBA estimates from both monkeys species were combined for comparison of RBA estimates
from swine, monkey, and mouse assays (described below).
Differences between RBA estimates from swine, monkey, and mouse assays may also be
attributable to:
(1) species difference in RBA;
(2) differences in assay protocols;
(3) differences in data reduction methods used to calculate RBA;
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Compilation and Review of Data on Relative Unavailability of
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(4) differences in methods used to measure arsenic concentration in soils and biological
samples, and
(5) differences in the test materials assayed.
Theoretically, direct comparison of results from different bioassays when applied to the
same test materials would provide a test of whether or not differences can be attributed to the test
materials, rather than to the bioassay protocols and/or species. Thus far, such direct comparisons
between swine, monkey, and mouse assays are available for only 4 test materials, all of which
were obtained from the same site (Barber Orchard, Region 4). These data are shown in Table 5
and Figure 2. The sample size (n=4) is too small to make meaningful statistical comparisons.
However, based on the 95% confidence limits, the uncertainty bounds on estimates obtained
from the three assays show substantial overlap. Furthermore, the 95% confidence limits on the
group mean KB A (n=4) also overlap substantially (see Figure 2). Therefore, if these four soil
samples were used in a risk assessment to represent the RBA for the Barber Orchard site (it is not
unusual to base site-wide RBA estimates on a few samples of in vivo RBA estimates), the site-
wide RBA estimates from the swine, monkey, and mouse assays would be statistically
indistinguishable.
A larger set of comparisons are available for swine and mouse RBA estimates. The data
set includes 2 standard reference materials (NIST 2710 and 2710a), the 4 Barber Orchard
samples, and 5 soil samples from 4 other sites (see Table 6). Collectively, these comparisons
show that the assays yielded similar results for 5 of the materials (95% confidence limits
overlap) and dissimilar estimates for 6 of the materials (see Figure 3). In all of the latter cases,
the RBA from the mouse bioassay was less than the RBA from the swine assay. Figure 4 shows
a scatter plot of RBA estimates in swine and mice for these 11 test materials. The data tend to
cluster around the line of identity; however, the linear regression model showed a relatively
weak association between the RBA estimates obtained in swine and mice (R2=0.35, p=0.053).
Although different RBA values were obtained from the swine and mouse assays for some test
materials, the differences were relatively small. The absolute difference in the RBA estimates
(RBAswine - RBAmouse) ranged from <1% (NIST 2710 and 2710a) to 28% (Barber Orchard MS-5),
and the average difference was 12%. For the 4 Barber Orchard soils, the absolute difference
between swine and monkey RBA values (RBAswine - RBAmonkey) ranged from 2% (Barber
Orchard MS-1) to 28% (Barber Orchard MS-8), and the average difference was 8%; and the
absolute difference between monkey and mouse (RBAmouse - RBAmonkey) ranged from 7% (Barber
Orchard MS-1 and MS 4) to 17% (Barber Orchard MS-5), and the average difference was 10%.
4.2.2 Urinary Excretion Fraction (UEF) Method vs. Blood AUC Method
In theory, we expect RBA estimates based on blood AUC measurements to be equivalent
to RBA estimates based on urinary excretion measurements. The underlying assumption for
both methods is that arsenic absorbed from the test and reference materials have the same
toxicokinetics; and therefore, for both test and reference material, the same fraction of the
absorbed dose is expected to appear in blood or urine.
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The only direct comparison of the two methods is from Freeman et al. (1995). This study
used blood AUC and UEF to estimate arsenic ABA for an oral dose of sodium arsenate and
arsenic in soil, using the same three monkeys. These data allow calculation of the KB A for each
monkey, for each method, and for the same test material (see Table 7). The RBA estimates
based on the two methods were not significantly different based on paired t-test (p=0.37) or
unpaired t-test (p=0.20). As there is no evidence to suggest that the blood AUC method and
UEF method would yield different estimates of RBA, and there is no theoretical argument for a
difference, RBA estimates obtained from the UEF method and blood AUC method are combined
in summary statistics of RBA estimates for the entire data set (see Table 3).
4.2.3 Test Material Arsenic Dose and Concentration
Doses of arsenic varied with test material and study. In general, arsenic doses
administered to monkeys were higher than those administered to swine, although the range of
doses evaluated in each species overlapped. The range of arsenic doses evaluated in swine was
approximately 1.5 to 1540 jig As/kg bw/day, in monkeys approximately 120 to 1330 jig As/kg
bw (single dose), and in mice approximately 320-6100 jig As/kg bw/day. It is not possible to
evaluate potential effects of arsenic dose on RBA because of the different dosing protocols used
in the various studies. In some protocols, repeated doses of arsenic were administered at
multiple dose levels, and RBA was derived from the composite data (e.g., Casteel and SRC,
2009a,b,c, 2010a,b,c), whereas other protocols administered repeated doses of arsenic at the
same dose level (e.g., Basta et al., 2007; Bradham et al., 2011, 2012; Casteel and SRC,
2009a,b,c, 2010a,b,c; Rodriguez et al., 1999) or administered a single dose of arsenic (e.g.,
Freeman et al., 1995; Juhasz et al., 2007; Roberts et al., 2002, 2007; U.S. EPA, 1996, 2009).
Doses used in these different protocols are not directly comparable. In studies conducted in
swine, arsenic urinary excretion rate (jig As/day) was a linear function of arsenic dose for both
sodium arsenate (dose range <310 jig As/kg bw/day) and test material arsenic (dose range <1540
jig As/kg bw/day). This observation suggests that arsenic absorption (based on UEF) was not
strongly dependent on arsenic dose (Casteel and SRC, 2009a,b,c, 2010a,b,c; U.S. EPA, 2010).
In studies conducted in cynomolgus monkeys, the arsenic UEF was shown to be independent of
dose (administered as a single gavage dose) over the dose range 250-1000 |ig/kg (Roberts et al.,
2007). In mice, arsenic UEF was shown to be independent of dose over a dose range of 580-
2600 |ig As/kg bw/day (Bradham et al., 2011, 2012).
Arsenic levels in the test materials assayed in swine ranged from 42 to 17,500 mg/kg, in
monkeys from 101 to 1492 mg/kg, and in mice from 182 to 4495 mg/kg. The wide range of
arsenic concentrations resulted in a similarly wide range of soil doses given to the animals (e.g.,
lower soil arsenic concentrations required larger doses of soil to be administered to achieve the
same arsenic dose). The soil doses ranged from approximately 0.4 to 3528 mg soil/kg bw/day in
swine, 490 to 2970 mg soil/kg (single dose) in monkeys, and 1150 to 1650 mg soil/kg bw/day in
mice. A direct evaluation of the influence of soil dose on arsenic RBA cannot be made from
these data because of the differences in dosing regimens used in the various bioassays.
However, a strong dependence of RBA on soil dose would be expected to also result in a
dependence on soil arsenic concentration since these two variables would be strongly negatively
correlated if soil dose was adjusted to achieve a fixed range of soil arsenic doses. Simple
regression analysis of these data indicated a relatively small influence (<14%) of arsenic level on
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KB A, with values for R2 of 0.10 (p=0.01, n=64) for test materials assayed in swine, 0.14
(p=0.07, n=24) for test materials assayed in monkeys, 0.03 (p=0.51, n=15) for test materials
assayed in mice, and 0.06 (p=0.01, n=1036) for swine, monkey, and mice combined.
4.2.4 Explanatory Variables Influencing RBA Estimates in Key Studies
Multivariate regression analyses were conducted using factors found to be significant
variables in simple regression analyses (species, iron arsenide [FeAs] sulfate content of arsenic-
bearing particles, and arsenic levels in test materials) as explanatory variables. These analyses
were restricted to data from swine and monkey studies for which data on arsenic mineralogy
were available. Content of FeAs sulfate was examined because it has been shown to be an
influential variable on RBA in monkeys (Roberts et al., 2007). The R2 for the model that
included all three variables was 0.38 (p=0.006, n=29); however, only species (i.e., monkey or
swine) was significant (p=0.02). When the analysis was restricted to monkeys, the dominant
influential variable was relative mass of the FeAs sulfate phase of arsenic-bearing particles (R2=
0.70, p=0.015, n=10), as reported in Roberts et al. (2007). When the analysis was restricted to
swine none of the variables (i.e., arsenic level, FeAs sulfate) were found to be significant
predictors of RBA (R2= 0.05, p=0.68, n=19).
Based on these analyses, the dominant influential variable on RBA in this data set
appears to be species (i.e., whether the test material was assayed in monkeys or swine) and for
test materials assayed in monkeys, the relative mass of the FeAs sulfate phase of arsenic-bearing
particles. As previously noted, an explanation for the difference between RBA estimates from
monkey and swine assays is not apparent from these analyses.
Other factors, not explored in this analysis, may contribute to the unexplained variability
in the arsenic RBA estimates. Approximately 62% of the RBA estimates are based on an R2
value of 0.38 for the model that included species, FeAs sulfate content of arsenic-bearing
particles, and arsenic levels in test materials. Likely candidates are arsenic mineralogy (chemical
composition and morphology of the arsenic-bearing particles) and soil characteristics, which
together may determine arsenic bioaccessibility and/or absorption of bioaccessible arsenic.
4.3 Uncertainties in Use of Compiled RBA Estimates for Prediction of Arsenic RBA
Table 1 summarizes sources of uncertainties to be considered in assessing confidence in
RBA estimates and making statistical inference regarding arsenic RBA in soils. These include
the following.
Adequacy of Approach:
o Confidence in predictions of arsenic RBA in humans based on animal bioassays has
not been assessed. This would require measuring RBA of the same soils in both
humans and animal models.
o When applied to the same test materials (see results for Barber Orchard soil samples
in Table 5), the swine, monkey, and mouse assays yielded remarkably similar RBA
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estimates for some materials and widely different estimates for other materials.
However, collectively, the differences in the KB A estimates were relatively small.
The average absolute difference in the RBA estimates for assays conducted on the
same test materials ranged from <1 to 28%, and the average differences were 8, 12,
and 10% for RBAswine - RBAmonkey, RBAswine - RBAmouse, and RBAmouse - RBAmonkey,
respectively. When the three assays were applied to multiple samples from the same
site (i.e., 4 samples from the Barber Orchard site), 95% confidence limits on the site-
wide mean RBA values overlapped substantially, suggesting that for these samples,
assays in the 3 species provided site-wide estimates of RBA that were statistically
indistinguishable. The reason why the same test materials give different RBA
outcomes for some of the Barber Orchard samples tested in the three animal models is
not apparent from available data and could be related to one or more factors (as
described in Section 4.7.1):
(1) animal species differences in arsenic absorption;
(2) differences in assay protocols;
(3) differences in data reduction methods used to calculate RBA; and
(4) differences in methods used to measure arsenic concentration in soils and
biological samples.
o Experimental protocols of RBA bioassays differ (e.g., multiple dose levels vs. single
dose level, repeated dosing vs. single dose), and each protocol may have different
sources and magnitudes of measurement error.
o The arsenic dose range for test materials administered in the bioassays includes
values that are substantially higher than typical daily soil ingestion rates in children or
adults. The implication of these high test material doses in extrapolating RBA
estimates from animal bioassays to humans (e.g., the effect of test material dose on
RBA) has not been thoroughly investigated; however, based on measurements of
urinary arsenic, the absorption fraction does not appear to be strongly dependent on
dose.
Representativeness: The RBA estimates considered in this analysis are derived from an
opportunistic sample of soils and do not represent a statistical sample of soils in any
geographic region (e.g., U.S.) or source of arsenic contamination. The samples were
collected because of regulatory interest in specific sites. Although the data set includes
samples from sites impacted by various sources of arsenic contamination (e.g.,
mining/smelting, agricultural, chemical/pesticide manufacturing facilities, and railway
corridors), the dominant arsenic sources in the data set are mining and smelting (54 of
88 test materials). The absence of a statistical sampling design limits confidence in
statistical inference based on the data set. For example, sample statistics such as the
mean and standard deviation, even for specific categories of arsenic contamination,
mineralogy, or soil characteristics, cannot be assumed to represent these categories in
19
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
general. Nevertheless, the data set does describe the distribution of RBA values that have
been encountered in soils from various sites of regulatory interest. The empirical
distribution of RBA values in this data set suggests that values for arsenic RBA
exceeding 60% are relatively uncommon (i.e., less than 5% of the estimates exceed 60%
RBA). Based on this experience, it is reasonable to expect that future RBA estimates
exceeding 60% would also be uncommon if samples were to be drawn from a collection
of similar types of sites and soils. This prediction could be further evaluated with
additional data collection efforts and may be of value for informing assumptions about
soil arsenic RBA at sites where RBA estimates have not yet been made (e.g., screening
level assessments).
Variability of Test Material RBA Estimates: Multivariate regression models used to
explore the contribution of bioassay and soil variables to variability in RBA estimates
yielded R2 values <38%. Therefore, these models could explain no more than 38% of the
variability observed in the RBA estimates, most of which was attributed to bioassay
species. The relatively low explanatory power of the models explored in this analysis
precludes their use in making predictions about RBA of arsenic in soil. It is likely that
more informative regression models (or other variance models) could be developed that
account for test material variables not considered in this analysis (e.g., arsenic
mineralogy and soil characteristics). These variables are currently being explored as part
of on-going EPA research. In addition to variables related to the soil test materials, other
variables are likely to have contributed to the unexplained variability in the RBA
estimates. These include the bioassay methods (e.g., dosing regimens), biomarkers used
to estimate absorption (e.g., urine and blood), methods used to measure arsenic in soil
and in biological samples, measurement error (e.g., doses administered, urinary arsenic
excretion, and blood arsenic concentrations), and differences in data reduction methods.
It is expected that differences in experimental design and protocol, data reduction
methods, and measurement error contribute to variability in the RBA estimates. The
above variables may explain differences in RBA estimates for some test materials that
have been assayed in swine, monkey, and mouse. This complicates analyses of the
impacts of other variables (e.g., arsenic mineralogy and soil characteristics) on RBA.
Interindividual Variability in RBA: The RBA estimates for each test material represent
mean values derived from experiments made on groups of animals. Estimates of
interindividual variability in RBA were not possible for all studies and study designs.
Interindividual variability in UEF for the test and reference material groups were
accounted for in the calculation of group mean RBA estimates in the swine and mouse
studies; however, the statistical design of the studies does not yield an estimate of
interindividual variability in RBA, although it does provide an estimate of uncertainty in
the RBA represented by the confidence limits. The monkey studies used a repeated
measures design in which each animal received the soil and reference materials. This
design allowed estimation of a group mean and standard deviation for RBA for each
study, representing the interindividual variability in the RBA for each test material.
Coefficients of variation (SD/mean) for the 20 RBA estimates derived from monkey
bioassays ranged from 0.11 to 0.80 (mean 0.38 ą 0.17 SD). This outcome suggests that
interindividual variability in RBA in monkeys that received the same test material varies
20
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
across test materials and/or studies. Numerous other factors may contribute to
interindividual variability in arsenic KB A, including diet, nutrition, and age. Since these
variables were controlled in the animal bioassays, interindividual variability observed in
the animal bioassays is presumably dominated by contributions from the test material and
physiological variables that affect bioaccessibility and absorption of arsenic. However,
in human populations, interindividual variability in diet/nutrition, disease states, and
other factors may also contribute to variability in KB A.
Intraindividual Variability in RBA: This analysis did not attempt to estimate
intraindividual variability in RBA. The RBA studies compiled in this review did not
provide data on intraindividual variability, which would have required repeated
measurements of RBA in the same animals. As noted above, the controlled conditions of
the bioassays would have eliminated variables that may contribute to intraindividual
variability in RBA estimates in humans. Variables that may contribute to intraindividual
variability in arsenic RBA include age, diet/nutrition, disease states, etc.
Relevance of Soil Arsenic Concentrations Tested: Arsenic RBA was not significantly
correlated with arsenic concentration (<100 to 17,500 mg kg"1). Nevertheless, RBA
estimates at sites that have arsenic concentrations well below or above the risk-based
decision level may not influence cleanup decisions.
Data Collection Period and Relevance of Soil Aging to Arsenic RBA: RBA estimates
in this report cannot represent temporal changes in soil characteristics (e.g., changes in
soil composition or arsenic speciation) at the sites that might alter RBA. Bioavailability
of arsenic in soil may change over time. Although direct evidence for this for in situ
contaminated soils is not available, studies of laboratory-contaminated soils suggest that
changes over time in certain soils can be substantial. Juhasz et al. (2008) found that RBA
decreased from 100 to 25% in 3 months and then remained constant for the next 9 months
following addition of sodium arsenate to a soil containing a high iron content (99,671 mg
Fe/kg soil). Arsenic RBA remained approximately 100% in a similarly spiked soil that
contained lower iron content (7980 mg/kg). The predominant arsenic phase in the high
iron content soil was associated with iron oxides. Although this study was limited to
soils spiked in the laboratory with sodium arsenate, it suggests the possibility that arsenic
RBA may change over time and that the magnitude of the change may depend on soil
characteristics. Studies in which arsenic RBA is measured repeatedly over time, in a
variety of soils, would be needed to determine the relevance of this observation to
arsenic-contaminated sites. On-going EPA research is attempting to evaluate the long-
term stability of arsenic bioaccessibility of soils contaminated in situ.
Extrapolation to Humans: Studies comparing arsenic RBA in humans and animals for
the same soils are not available and are not likely to be undertaken. This limitation
introduces uncertainty into predictions of arsenic RBA in humans based on results from
animal bioassay studies; however, it should not preclude making extrapolations of animal
bioassay data to humans. EPA currently recommends use of a swine RBA assay (or an
in vitro bioaccessibility (IVBA) assay that was validated with a swine assay) for
predicting site-specific lead RBA in human health risk assessments (U.S. EPA,
21
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
2007a,b,c). As noted previously, when applied to the same test materials, RBA estimates
based on the swine, monkey, and mouse assays yielded remarkably similar RBA
estimates for some materials and collectively, the differences in the RBA estimates were
relatively small. The similarity of RBA estimates based on assays in three mammalian
species increases confidence in extrapolation of these results to humans.
Quality Assurance: For some studies, information on quality assurance/quality control
was limited or absent.
5.0 REFERENCES
Basta, N.T., Foster, J.N., Dayton, E.A., Rodriguez, R.R., and Casteel, S.W. (2007) The effect of
dosing vehicle on arsenic bioaccessibility in smelter-contaminated soils. J. Environ. Sci. Heath
Part A 42: 1275-1281.
Bradham, K.D., Scheckel. K.G., Nelson, C.M., Seales, P.E., Lee, G.E., Hughes, M.F., Miller,
B.W., Yeow, A., Gilmore, T., Harper, S., Thomas, DJ. (2011) Relative Bioavailability and
Bioaccessibility and Speciation of Arsenic in Contaminated Soils. Environ. Health Perspect.
119(11): 1629-1634.
Bradham et al. (2012) Assessing performance of the mouse assay of bioavailability of arsenic.
(manuscript in preparation)
Casteel and SRC. (2005) Relative Bioavailability of Arsenic and Vanadium in Soil from a
Superfund Site in Palestine, Texas. Prepared by University of Missouri, Columbia and SRC.
Prepared for U.S. Environmental Protection Agency, Office of Superfund Remediation
Technology Innovation. Prepared by University of Missouri, Columbia and SRC.
Casteel and SRC. (2009a) Relative Bioavailability of Arsenic in Barber Orchard Soils. Prepared
for U.S. Environmental Protection Agency, Office of Superfund Remediation Technology
Innovation. Prepared by University of Missouri, Columbia and SRC.
Casteel and SRC. (2009b) Relative Bioavailability of Arsenic in NIST SRM 2710 (Montana
Soil). Prepared for U.S. Environmental Protection Agency, Office of Superfund Remediation
Technology Innovation. Prepared by University of Missouri, Columbia and SRC.
Casteel and SRC. (2009c) Relative Bioavailability of Arsenic in a Mohr Orchard Soil. Prepared
for U.S. Environmental Protection Agency, Office of Superfund Remediation Technology
Innovation. Prepared by University of Missouri, Columbia and SRC.
Casteel and SRC. (2010a) Relative Bioavailability of Arsenic in an Iron King Soil. Prepared for
U.S. Environmental Protection Agency, Office of Superfund Remediation Technology
Innovation. Prepared by University of Missouri, Columbia and SRC.
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Casteel and SRC. (201 Ob) Relative Bioavailability of Arsenic in an ASARCO and Hawaiian soil.
Prepared for U.S. Environmental Protection Agency, Office of Superfund Remediation
Technology Innovation. Prepared by University of Missouri, Columbia and SRC.
Casteel and SRC. (2010c) Relative Bioavailability of Arsenic in NIST SRM 2710a (Montana
Soil). Prepared for U.S. Environmental Protection Agency, Office of Superfund Remediation
Technology Innovation. Prepared by University of Missouri, Columbia and SRC.
Chiou, W.L. and Buehler, P.W. (2002) Comparison of oral absorption and bioavailability of
drugs between monkey and human. Pharm. Res. 19(6): 868-874.
Ellickson, K.M., Meeker, R.J., Gallo, M.A., Buckley, B.T., Lioy, P.J. (2001) Oral bioavailability
of lead and arsenic from a NIST standard reference soil material. Arch. Environ. Contam.
Toxicol. 40(1): 128-135.
Freeman, G.B., Johnson, J.D., Killinger, J.M., Liao, S.C., Davis, A.O., Ruby, M.V., Chaney,
R.L., Lovre, S.C., and Bergstrom, P.D. (1993) Bioavailability of arsenic in soil impacted by
smelter activities following oral administration in rabbits. Fundam. Appl. Toxicol. 21(1): 83-88.
Freeman, G.B., Schoof, R.A., Ruby, M.V., Davis, A.O., Dill, J.A., Liao, S.C., Lapin, C.A., and
Bergstrom, P.D. (1995) Bioavailability of arsenic in soil and house dust impacted by smelter
activities following oral administration in cynomolgus monkeys. Fundam. Appl. Toxicol. 28(2):
215-222.
Juhasz, A.L., Smith, E., Weber, J., Rees, M., Rofe, A., Kuchel, T., Sansom, L., andNaidu, R.
(2007) Comparison of in vivo and in vitro methodologies for the assessment of arsenic
bioavailability in contaminated soils. Chemosphere 69(6): 961-966.
Juhasz, A.L., Smith, E., Weber, J., Naidu, R., Rees, M., Rofe, A., Kuchel, T., and Sansom, L.
(2008) Effect of aging on in vivo arsenic bioavailability in two dissimilar soils. Chemosphere
71(10): 2180-2186.
Konstantinos, C.M., Makris, S.Q., Nagar, R., Sarkar, D., Datta, R., and Sylvia, L. (2008) In vitro
model improves the prediction of soil arsenic bioavailability: Worst-case scenario. Environ. Sci.
Technol. 42: 6278-6284.
Nagar, R., Sarkar, D., Konstantinos C.M., Datta, R., and Sylvia, V.L. (2009) Bioavailability and
bioaccessibility of arsenic in a soil amended with drinking-water treatment residuals. Arch.
Environ. Contam. Toxicol. 57: 755-766.
NRC (National Research Council). 2003. Bioavailability of Contaminants in Soils and
Sediments: Processes, Tools, and Applications. National Academies Press: Washington, DC.
http://www.nap.edu/openbook/0309086256/html/.
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Roberts, S.M., Weimar, W.R., Vinson, J.R., Munson, J.W., and Bergeron, RJ. (2002)
Measurement of arsenic bioavailability in soil using a primate model. Toxicol. Sci. 67(2): 303-
310.
Roberts, S.M., Munson, J.W., Lowney, Y.W., and Ruby, M.V. (2007) Relative oral
bioavailability of arsenic from contaminated soils measured in the cynomolgus monkey. Toxicol.
Sci. 95(1): 281-288. (Erratum for Table 3 of the report, correcting the columns headings for the
NYPF samples, was provided as a personal communication from the co-authors S. Roberts and
Y. Lowney on 09/24/2010.)
Rodriguez, R.R., Basta, N.T., Casteel, S.W., and Pace, L.W. (1999) An in vitro gastrointestinal
method to estimate bioavailable arsenic in contained soils and solid media. Environ. Sci.
Technol. 33(4): 642-649.
Stanek, E.J., Calabrese, E.J., Barnes, R.M., Danku, J.M.C., Zhou, Y., Kostecki, P.T., Zillioux, E.
(2010) Bioavailability of arsenic in soil: Pilot study results and design considerations. Hum.
Exper. Toxicol. 29(11): 945-960.
U.S. EPA (U.S. Environmental Protection Agency). (1989) Risk Assessment Guidance for
Superfund (RAGS). Volume I. Human Health Evaluation Manual (Part A). U.S. Environmental
Protection Agency, Office of Emergency and Remedial Response: Washington, DC.
EPA/540/1-89/002. December. Available online at:
http://www.epa.gov/swerrims/riskassessment/ragsa/pdf/rags-vol l-pta_complete.pdf
U.S. EPA (U.S. Environmental Protection Agency). (1996) Bioavailability of Arsenic and Lead
in Environmental Substrates. U.S. Environmental Protection Agency, Region 10: Seattle, WA.
EPA910/R-96-002. February. Available online at:
http://yosemite.epa.gov/rlO/OMP.NSF/webpage/Bioavailability+of+Arsenic+and+Lead+in+Env
ironmental+Substrates/$FILE/bio-arsenic.pdf
U.S. EPA (U.S. Environmental Protection Agency). (2007a) Estimation of Relative
Bioavailability of Lead in Soil and Soil-Like Materials by In Vivo and In Vitro Methods. U.S.
Environmental Protection Agency, Office of Solid Waste and Emergency Response:
Washington, DC. OSWER 9285.7-77. Available online at:
http://www.epa.gov/superfund/health/contaminants/bioavailability/lead_tsd_main.pdf.
U.S. EPA (U.S. Environmental Protection Agency). (2007b) Framework for Metals Risk
Assessment. U.S. Environmental Protection Agency, Office of the Science Advisor: Washington,
DC. EPA 120/R-07/001. March. Available online at:
http://www.epa.gov/raf/metalsframework/pdfs/metals-risk-assessment-fmal.pdf.
U.S. EPA (U.S. Environmental Protection Agency). (2007c) Guidance for Evaluating the Oral
Bioavailability of Metals in Soils for Use in Human Health Risk Assessment. U.S.
Environmental Protection Agency, Office of Solid Waste and Emergency Response:
Washington, DC. OSWER 9285.7-80. May. Available online at:
http://www.epa.gov/superfund/heal th/contaminants/bioavailability/bio_guidance.pdf.
24
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
U.S. EPA (U.S. Environmental Protection Agency). (2008) Child-Specific Exposure Factors
Handbook. U.S. Environmental Protection Agency, National Center for Environmental
Assessment, Office of Research and Development: Washington, DC. EPA/600/R-06/096F.
Available online at: http://ofmpub.epa.gov/eims/eimscomm.getfile?p_download_id=484738.
U.S. EPA (U.S. Environmental Protection Agency). (2009) Relative Bioavailability of Arsenic
from Soil Barber Orchard Superfund Site Waynesville, North Carolina. Prepared for U.S.
Environmental Protection Agency, Region 4 by Center for Environmental & Human Toxicology,
University of Florida, (available through U.S. EPA Region 4 Administrative Record Index for
the Barber Orchard (Explanation of Significant Differences) NCSDN0406989).
U.S. EPA (U.S. Environmental Protection Agency). (2010) Relative Bioavailability of Arsenic in
Soils at 11 Superfund Sites Using an In Vivo Juvenile Swine Method. U.S. Environmental
Protection Agency. Available online at:
http://epa.gov/superfund/bioavailability/pdfs/as_in_vivo_rba_main.pdf.
U.S. EPA (U.S. Environmental Protection Agency). (2012) Arsenic, inorganic. Integrated Risk
Information System (IRIS). U.S. Environmental Protection Agency, National Center for
Environmental Assessment: Washington, DC. Available online at:
http://www.epa.gov/ncea/iris/subst/0278.htm.
25
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 1. Confidence in Arsenic RBA Estimates
General Assessment Factors
Rationale
Rating
Soundness
Adequacy of Approach
Bias
Methodologies included several limitations:
(1) Estimates of RBA of arsenic in soil materials in humans have not been reported. The
monkey and swine models have been utilized for predicting RBA of arsenic in humans
because the gastric physiology of both animal species share many similarities to that of
humans and because of a prior history of use of the models for assessing RBA of other
inorganic contaminants (e.g., lead) and gastrointestinal absorption of drugs. Estimates of
RBA of arsenic in soil materials in animal models cannot be quantitatively compared to
estimates made in humans, as estimates in humans are not available for these test materials.
(2) Reported estimates of RBA for arsenic in soil materials obtained from monkey assays are
significantly lower than reported estimates obtained from swine or mouse assays. The
mechanism for the different outcomes from the two assays is not apparent and could be
related to several factors (e.g., species differences, protocol differences, test material
differences).
(3) Experimental protocols utilizing a steady-state design with multiple dose levels may
introduce less error than experimental protocols using a steady-state design with a single
dose level or a single dose (i.e., non steady-state) design.
(4) Variations in the design of animal RBA assays, in particular, different detection limits for
blood and urinary arsenic and wide variations in arsenic concentrations of test materials, has
placed constraints on experimental control of both the arsenic dose and test material dose
used in each assay. Therefore, the dose range for test materials administered in the animal
bioassays includes values that are substantially higher than typical daily soil ingestion rates
in children or adults. The implication of these high test material doses in extrapolating RBA
estimates from monkey and swine assays to humans has not been thoroughly investigated
(e.g., effect of test material dose on RBA).
Numerous sources of measurement error exist. Studies utilizing multiple dose levels and dosing
regimens to achieve steady-state are more likely to have less measurement error in the critical
parameter (i.e., UEF). The upper bound estimate may be biased by sample selection bias
(samples dominated by mining/smelter sources).
Medium
26
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 1.
Confidence in Arsenic RBA Estimates
General Assessment Factors
Rationale
Rating
Applicability and Utility
Default Value of Interest
Representativeness
Currency
Data Collection Period
All "key" and "relevant" studies focus on the relative bioavailability of arsenic.
The RBA estimates considered in this analysis do not represent a statistical sample of soils in any
geographic region (e.g., U.S.). Although not a statistical sample of soils, nearly all samples were
collected at hazardous waste sites. These included test materials collected from mining and/or
smelter operations, pesticides (orchards), and manufacturing/electrical waste. Therefore, the
samples may provide adequate representation of soils at sites of the highest regulatory interest or
concern.
Test materials assayed reflect recent conditions (samples collected over <10-15 years).
Test materials assayed represent a cross-sectional sample of soils. However, RBA estimates of
those test materials cannot assess temporal change in soil characteristics (e.g., changes in soil
composition or arsenic speciation) at the sites and potential related changes in RBA estimates of
those materials.
Medium
Clarity and Completeness
Accessibility
Reproducibility
Quality Assurance
Variability
Observations for individual data on which RBA estimates were based are available in the
published literature or online.
Reproducibility has not been evaluated across methodologies.
For some studies, information on quality assurance/quality control was limited or absent.
Low
and Uncertainty
Variability in Estimates
Minimal Uncertainty
Evaluation
The sample of test materials is not a statistical sample of soils. Therefore, variability in arsenic
RBA for soils in general or for any subset of characteristics of the test materials (e.g., arsenic
mineralogy, soil characteristics) cannot be inferred from the variability represented in the data
set.
Estimates of the mean and percentiles for RB As of test material sample are reasonably certain;
however, the representativeness of the sample for making statistical inference about arsenic RBA
estimates for soils in general, or about soils at specific sites is uncertain.
Low
and Review
Peer Review
The animal bioassays used in all studies either appeared in peer reviewed journals or the study
was conducted by or for EPA in which EPA developed the RBA estimates from the raw data
using established standard protocols and/or the raw data were available for QA review by the
U.S. EPA Bioavailability Committee of the Technical Review Workgroup (e.g., EPA swine
studies); or, the study was conducted by other research groups and results had been subjected to
peer review as a requirement for publication.
Medium
27
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 1. Confidence in Arsenic RBA Estimates
General Assessment Factors
Number and Agreement of Studies
Rationale
Application of similar assay methodologies produced highly variable estimates of arsenic RBA.
However, these differences may reflect differences in test material characteristics, differences in
assay protocols, or differences in species (monkeys, swine, mouse). Direct comparisons of
swine, monkey, and mouse RBA estimates are available for only 4 test materials and direct
comparisons of swine and mouse RBA estimates are available for 1 1 test materials. Based on
this limited comparison, the magnitude of difference between RBA estimates derived from swine,
monkey, and mouse assays is relatively small in the context of risk assessment, where
uncertainties in other parameters in risk calculations can exceed several orders of magnitude.
Therefore, from the perspective of use of the assays to support risk assessment, the swine,
monkey, and mouse assays appear to yield essentially equivalent information about arsenic RBA.
Overall Rating
Rating
Medium
Medium
28
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Key Studies
Source: Bingham Creek Channel
soil (sieved to <250 um)
Type: Mining/smelting
As concentration: 149 mg/kg soil
Source: Murray smelter slag
(sieved to <250 um)
Type: Mining/smelting
As concentration: 695 mg/kg soil
Source: Butte soil, composite
soil waste rock dumps
(sieved to <250 um)
Type: Mining/smelting
As concentration: 234 mg/kg soil
Source: Midvale slag, composite
sample Midvale smelter slag pile
(sieved to <250 urn)
Type: Mining/smelting
As concentration: 591 mg/kg soil
Source: California Gulch Phase I
residential soil, composite
residential soil, Leadville, CO
(sieved to <250 um)
Type: Mining/smelting
As concentration: 203 mg/kg soil
Source: California Gulch Fe/Mn
PbO, composite soil, Leadville,
CO (sieved to <250 um)
Type: Mining/smelting
As concentration: 110 mg/kg soil
Source: Palmerton Location 2,
composite soil, Palmerton, PA
(sieved to <250 um)
Type: Mining/smelting
As concentration: 110 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 5, 20, or 50 ug As/kg bw/day;
5 animals/group
Test material dose: 15.8 ug As/kg bw/day (106.0 mg soil/kg
bw/day); 5 animals/group
Steady-state urinary excretion fraction method
Reference material dose: 5, 20, or 50 ug As/kg bw/day;
5 males/group
Test material dose: 13.4 ug As/kg bw/day (19.2 mg soil/kg
bw/day); 5 animals/group
Steady-state urinary excretion fraction method
Reference material dose: 5, 20, or 50 ug As/kg bw/day;
5 animals/group
Test material dose: 6.3 ug As/kg bw/day (26.2 mg soil/kg
bw/day); 5 animals/group
Steady-state urinary excretion fraction method
Reference material dose: 5, 20, or 50 ug As/kg bw/day;
5 animals/group
Test material dose: 16.8 ug As/kg bw/day (28.5 mg soil/kg
bw/day); 5 animals/group
Steady-state urinary excretion fraction method
Reference material dose: 5, 20, or 50 ug As/kg bw/day;
5 animals/group
Test material dose: 6.1 ug As/kg bw/day (30.0 mg soil/kg
bw/day); 5 animals/group
Steady-state urinary excretion fraction method
Reference material dose: 5, 20, or 50 ug As/kg bw/day;
5 animals/group
Test material dose: 5.7 ug As/kg bw/day (52.1 mg soil/kg
bw/day); 5 animals/group
Steady-state urinary excretion fraction method
Reference material dose: 5, 20, or 50 ug As/kg bw/day;
5 animals/group
Test material dose: 7.7 ug As/kg bw/day (70.0 mg soil/kg
bw/day); 5 animals/group
39ą8
MeanąSE
55ą10
MeanąSE
9ą3
MeanąSE
23ą4
MeanąSE
8ą3
MeanąSE
57ą12
MeanąSE
49ą10
MeanąSE
U.S. EPA, 2010
U.S. EPA, 2010
U.S. EPA, 2010
U.S. EPA, 2010
U.S. EPA, 2010
U.S. EPA, 2010
U.S. EPA, 2010
29
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Source: Palmerton Location 4,
composite soil, Palmerton, PA
(sieved to <250 um)
Type: Mining/smelting
As concentration: 134 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 5, 20, or 50 ug As/kg bw/day;
5 animals/group
Test material dose: 14.0 ug As/kg bw/day (104.7 mg soil/kg
bw/day); 5 animals/group
61ą11
MeanąSE
U.S. EPA, 2010
Source: California Gulch AV
slag, Leadville, CO
(sieved to <250 um)
Type: Mining/smelting
As concentration: 1050 mg/kg
soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 5, 20, or 50 ug As/kg bw/day;
2 animals/group
Test material dose: 22.3 ug As/kg bw/day (21.2 mg soil/kg
bw/day); 2 animals/group
18ą2
MeanąSE
U.S. EPA, 2010
Source: Murray Smelter Soil,
composite
(sieved to <250 um)
Type: Mining/smelting
As concentration: 310 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 5, 20, or 50 ug As/kg bw/day;
5 animals/group
Test material dose: 65.4 ug As/kg bw/day (211.0 mg soil/kg
bw/day); 5 animals/group
33ą5
MeanąSE
U.S. EPA, 2010
Source: Clark Fork Tailings, MT
(sieved to <250 um)
Type: Mining/smelting
As concentration: 181 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 20 or 50 ug As/kg bw/day;
4 animals/group
Test material dose: 10.0 or 25 ug As/kg bw/day (55.2 or
138.1 mg soil/kg bw/day); 4 animals/group
51ą6
MeanąSE
U.S. EPA, 2010
Source: Sample TM1 Vasquez
Boulevard and 1-70, composite
residential, Denver CO
(sieved to <250 um)
Type: Mining/smelting
As concentration: 312 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 50 or 125 ug As/kg bw/day;
4 animals/group
Test material dose: 37.0 or 92.5 ug As/kg bw/day (59.2 or
148.1 mg soil/kg bw/day); 4 animals/group
40ą4
MeanąSE
U.S. EPA, 2010
Source: Sample TM2 Vasquez
Boulevard and 1-70, composite
residential, Denver CO
(sieved to <250 um)
Type: Mining/smelting
As concentration: 983 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 50 or 125 ug As/kg bw/day;
4 animals/group
Test material dose: 33.9 or 84.7 ug As/kg bw/day (17.2 or
43.1 mg soil/kg bw/day); 4 animals/group
42ą4
MeanąSE
U.S. EPA, 2010
30
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Source: Sample TM3 Vasquez
Boulevard and 1-70, composite
residential, Denver CO
(sieved to <250 um)
Type: Mining/smelting
As concentration: 390 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 50 or 125 ug As/kg bw/day;
4 animals/group
Test material dose: 27.5 or 68.7 ug As/kg bw/day (35.2 or
88.0 mg soil/kg bw/day); 4 animals/group
37ą3
MeanąSE
U.S. EPA, 2010
Source: Sample TM4 Vasquez
Boulevard and 1-70, composite
residential, Denver, CO
(sieved to <250 um)
Type: Mining/smelting
As concentration: 813 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 50 or 125 ug As/kg bw/day;
4 animals/group
Test material dose: 37.4 or 93.5 ug As/kg bw/day (22.9 or
57.5 mg soil/kg bw/day); 4 animals/group
24ą2
MeanąSE
U.S. EPA, 2010
Source: Sample TM5 Vasquez
Boulevard and 1-70, composite
residential, Denver, CO
(sieved to <250 um)
Type: Mining/smelting
As concentration: 368 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 50 or 125 ug As/kg bw/day;
4 animals/group
Test material dose: 41.1 or 102.7 ug As/kg bw/day (55.8 or
139.5 mg soil/kg bw/day); 4 animals/group
21ą2
MeanąSE
U.S. EPA, 2010
Source: Sample TM6 Vasquez
Boulevard and 1-70, composite
residential, Denver, CO
(sieved to <250 um)
Type: Mining/smelting
As concentration: 516 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 50 or 125 ug As/kg bw/day;
4 animals/group
Test material dose: 32.4 or 81.0 ug As/kg bw/day (31.4 or
78.5 mg soil/kg bw/day); 4 animals/group
24ą3
MeanąSE
U.S. EPA, 2010
Source: Butte TM1, composite
waste rock dumps (U.S. EPA
Sample #8-37926)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 234 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 34, 59, or 94 ug As/kg bw/day;
4 animals/group
Test material dose: 30.4, 60.5, or 92.0 ug As/kg bw/day
(130.0, 258.5, or 393.2 mg soil/kg bw/day);
4 animals/group
18ą3
MeanąSE
U.S. EPA, 2010
Source: Butte TM2, composite
(U.S. EPA Sample #BPSOU-
0501-ASBIO)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 367 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 34, 59, or 94 ug As/kg bw/day;
4 animals/dose
Test material dose: 25.7, 62.5, or 92.6 ug As/kg bw/day
(70.0, 170.3, or 252.3 mg soil/kg bw/day); 4 animals/dose
24ą2
MeanąSE
U.S. EPA, 2010
31
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Source: Aberjona River sediment
composite TM1
(fine sieved, but no information
was reported on size)
Type: Mining/smelting
As concentration: 676 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 30, 60, or 90 ug As/kg bw/day;
4 animals/dose
Test material dose: 18.3, 40.2, or 46.9 ug As/kg bw/day
(27.1, 59.5, or73.3 mg soil/kg bw/day); 4 animals/dose
38ą2
MeanąSE
U.S. EPA, 2010
Source: Aberjona River sediment
composite TM2
(fine sieved, but no information
was reported on size)
Type: Mining/smelting
As concentration: 313 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 30, 60, or 90 ug As/kg bw/day;
4 animals/group
Test material dose: 18.8, 35.9, or 61.9 ug As/kg bw/day
(60.1, 114.7, or 197.8 mg soil/kg bw/day); 4 animals/group
52ą2
MeanąSE
U.S. EPA, 2010
Source: Soil sample (TM1)
American Canal, El Paso
County, TX (sieved to <250 urn)
Type: Mining/smelting
As concentration: 74 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 25 or 50 ug As/kg bw/day;
5 animals/group
Test material dose: 40, 80, or 160 ug As/kg bw/day (540.5,
1081.1, or2162.2 mg soil/kg bw/day); 5 animals/group
44ą3
MeanąSE
U.S. EPA, 2010
Source: Soil sample (TM2)
American Canal, El Paso
County, TX (sieved to <250 urn)
Type: Mining/smelting
As concentration: 73 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 25 or 50 ug As/kg bw/day;
5 animals/group
Test material dose: 40, 80, or 160 ug As/kg bw/day (547.9,
1095.9, or 2191.8 mg soil/kg bw/day); 5 animals/group
37ą3
MeanąSE
U.S. EPA, 2010
Source: Utility pole soil, Conley,
GA (sieved to <250 urn)
Type: Pesticide application
As concentration: 320 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 30 or 60 ug As/kg bw/day;
5 animals/group
Test material dose: 46.5 or 91.0 ug As/kg bw/day (145.3 or
284.4 mg soil/kg bw/day); 5 animals/group
47ą3
MeanąSE
U.S. EPA, 2010
Source: Soil, Superfund site,
Palestine, TX
(sieved to <250 um)
Type: Mining/smelting
As concentration: 47 mg/kg soil
Swine (Line 26,
male, immature, 5-6
weeks old, 7-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: 30, 60, or 121 ug As/kg bw/day;
5 animals/group
Test material dose: 42.6, 84.8, or 165.8 ug As/kg bw/day
(906.4, 1804.3, or 3527.7 mg soil/kg bw/day);
5 animals/group
MeanąSE
Casteel and SRC,
2005
32
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Source: Barber Orchard NC,
sample MS-1
(sieved to <250 um)
Type: Agriculture
As concentration: 290 mg/kg soil
Swine (Line 26,
male, immature, 6-7
weeks old)
Steady-state urinary excretion fraction method
Reference material dose: 32.0, 55.7, or 125.2 ug As/kg
bw/day; 4 animals/group
Test material dose: 72.9 or 145.7 ug As/kg bw/day (251.0
or 502.4 mg soil/kg bw/day); 4 animals/group
31ą4.0
MeanąSE
Casteel and SRC,
2009a
Source: Barber Orchard NC,
sample MS-4
(sieved to <250 um)
Type: Agriculture
As concentration: 388 mg.kg soil
Swine (Line 26,
male, immature, 6-7
weeks old)
Steady-state urinary excretion fraction method
Reference material dose: 25.4, 53.6, or 104.6 ug As/kg
bw/day; 4 animals/group
Test material dose: 52.6, 77.3, or 144.4 ug As/kg bw/day
(135.6, 199.2, or 372.2 mg soil/kg bw/day);
4 animals/group
41ą1.8
MeanąSE
Casteel and SRC,
2009a
Source: Barber Orchard NC,
sample MS-5
(sieved to <250 um)
Type: Agriculture
As concentration: 382 mg/kg soil
Swine (Line 26,
male, immature, 6-7
weeks old)
Steady-state urinary excretion fraction method
Reference material dose: 29.7 or 57.3 ug As/kg bw/day;
4 animals/group
Test material dose: 46.0, 71.0, or 138.9 ug As/kg bw/day
(120.4, 185.8, or 363.6 mg soil/kg bw/day);
4 animals/group
49ą4.7
MeanąSE
Casteel and SRC,
2009a
Source: Barber Orchard NC,
sample MS-8
(sieved to <250 um)
Type: Agriculture
As concentration: 364 mg/kg soil
Swine (Line 26,
male, immature, 6-7
weeks old)
Steady-state urinary excretion fraction method
Reference material dose: 25.4, 53.6, or 104.6 ug As/kg
bw/day; 4 animals/group
Test material dose: 44.6, 72.0, or 155.0 ug As/kg bw/day
(122.5, 197.8, or 425.8 mg soil/kg bw/day);
4 animals/group
53ą2.3
MeanąSE
Casteel and SRC,
2009a
Source: NIST SRM 2710
(sieved to 74 um)
Type: Mining/smelting
As concentration: 626ą38 mg/kg
soil
Swine (Line 26,
male, immature, 6-7
weeks old, -9-10
kg)
Steady-state urinary excretion fraction method
Reference material dose: 24.1, 47.5, or 95.9 ug As/kg
bw/day; 4 animals/group
Test material dose: 58.2 or 114.5 ug As/kg bw/day (93.0 or
182.9 mg soil/kg bw/day); 4 animals/group
44ą2.3
MeanąSE
Casteel and SRC,
2009b
Source: Mohr Orchard PA
sample
(sieved to <250 um)
Type: Agriculture
As concentration: 340 mg/kg soil
Swine (Line 26,
male, immature, 6-7
weeks old, -9-10
kg)
Steady-state urinary excretion fraction method
Reference material dose: 29, 62, or 130 ug As/kg bw/day;
4 animals/group
Test material dose: 52, 72, or 153 ug As/kg bw/day (153,
212, or 450 mg soil/kg bw/day); 4 animals/group
53 (51-57;
90% CI)
Casteel and SRC,
2009c
33
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Source: Iron King, AZ soil
sample TM1 (sieved to <250
urn)
Type: Mining/smelting
As concentration: 200ą5.3
mg/kg soil
Swine (Line 26,
male, immature, 6-7
weeks old, -9-10
kg)
Steady-state urinary excretion fraction method
Reference material dose: 25, 50, or 100 ug As/kg bw/day;
4 animals/group
Test material dose: 40, 60, or 120 ug As/kg bw/day (200,
300, or 600 mg soil/kg bw/day); 4 animals/group
60ą2.7
MeanąSE
Casteel and SRC,
2010a
Source: Iron King, AZ soil
sample TM2 (sieved to <250
urn)
Type: Mining/smelting
As concentration: 3957ą332.7
mg/kg soil
Swine (Line 26,
male, immature, 6-7
weeks old, -9-10
kg)
Steady-state urinary excretion fraction method
Reference material dose: 25, 50, or 100 ug As/kg bw/day;
4 animals/group
Test material dose: 116, 175, or 349 ug As/kg bw/day (29,
44, or 88 mg soil/kg bw/day); 4 animals/group
19ą1.0
MeanąSE
Casteel and SRC,
2010a
Source: ASARCO soil sample
(sieved to <250 um)
Type: Mining/smelting
As concentration: 181.9ą6.3
mg/kg soil
Swine (Line 26,
male, immature, 6-7
weeks old, -9-10
kg)
Steady-state urinary excretion fraction method
Reference material dose: 25, 50, or 100 ug As/kg bw/day;
4 animals/group
Test material dose: 40, 60, or 120 ug As/kg bw/day (220,
330, or 660 mg soil/kg bw/day); 4 animals/group
49ą2.5
MeanąSE
Casteel and SRC,
2010b
Source: Hawaiian soil sample
(sieved to <250 um)
Type: Agriculture
As concentration: 768.85ą32.3
mg/kg soil
Swine (Line 26,
male, immature, 6-7
weeks old, -9-10
kg)
Steady-state urinary excretion fraction method
Reference material dose: 25, 50, or 100 ug As/kg bw/day;
4 animals/group
Test material dose: 40, 60, 120 ug As/kg bw/day (80, 120,
or 240 mg soil/kg bw/day); 4 animals/group
33ą1.7
MeanąSE
Casteel and SRC,
2010b
Source: NIST SRM 2710a
(sieved to <74 um)
Type: Mining/smelting
As concentration: 1540ą100
mg/kg soil
Swine (Line 26,
male, immature, 6-7
weeks old, -9-10
kg)
Steady-state urinary excretion fraction method
Reference material dose: 26, 52, or 105 ug As/kg bw/day;
4 animals/group
Test material dose: 41, 62, or 121 ug As/kg bw/day (27, 40,
or 79 mg soil/kg bw/day); 4 animals/group
42ą1.4
MeanąSE
Casteel and SRC,
2010c
Source: Mining smelter soil
(sample #1)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 11,300 mg/kg
soil
Swine (Line 26,
male, 10-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: not reported; 5 animals/group
Test material dose: 70.6 ug As/kg/day (6.25 mg
soil/kg/day); 5 animals/group
8.6ą6.9
MeanąSD
Bastaetal.,2007
34
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Source: Mining smelter soil
(sample #2)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 17,500 mg/kg
soil
Swine (Line 26,
male, 10-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: not reported; 5 animals/group
Test material dose: 109 ug As/kg bw/day (6.25 mg soil/kg
bw/day); 5 animals/group
4.1ą2.1
MeanąSD
Bastaetal.,2007
Source: Mining smelter soil
(sample #3)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 13,500 mg/kg
soil
Swine (Line 26,
male, 10-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: not reported; 4 animals/group
Test material dose: 84.4 ug As/kg bw/day (6.25 mg soil/kg
bw/day); 4 animals/group
7.9ą4.3
MeanąSD
Bastaetal.,2007
Source: Mining smelter soil
(sample #4)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 11,500 mg/kg
soil
Swine (Line 26,
male, 10-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: not reported; 5 animals/group
Test material dose: 71.9 ug As/kg bw/day (6.25 mg soil/kg
bw/day); 5 animals/group
22.8ą4.6
MeanąSD
Bastaetal.,2007
Source: Mining smelter soil
(sample #6)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 405 mg/kg soil
Swine (Line 26,
male, 10-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: not reported; 2 animals/group
Test material dose: 2.5 ug As/kg bw/day (6.25 mg soil/kg
bw/day); 2 animals/group
38.7ą15.3
MeanąSD
Bastaetal.,2007
Source: Mining smelter soil
(sample #7)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 450 mg/kg soil
Swine (Line 26,
male, 10-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: not reported; 4 animals/group
Test material dose: 2.8 ug As/kg bw/day (6.25 mg soil/kg
bw/day); 4 animals/group
43.0ą23.8
MeanąSD
Bastaetal.,2007
Source: Mining smelter soil
(sample #8)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 1180 mg/kg
soil
Swine (Line 26,
male, 10-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: not reported; 4 animals/group
Test material dose: 7.4 ug As/kg bw/day (6.25 mg soil/kg
bw/day); 4 animals/group
39.1ą15.5
MeanąSD
Bastaetal.,2007
35
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Source: Mining smelter soil
(sample #9)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 5020 mg/kg
soil
Swine (Line 26,
male, 10-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: not reported; 5 animals/group
Test material dose: 31.4 ug As/kg bw/day (6.25 mg
soil/kg/day); 5 animals/group
32.9ą7.4
MeanąSD
Bastaetal.,2007
Source: Mining smelter soil
(sample #10)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 4650 mg/kg
soil
Swine (Line 26,
male, 10-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: not reported; 4 animals/group
Test material dose: 29.1 ug As/kg bw/day (6.25 mg soil/kg
bw/day); 4 animals/group
21.9ą5.6
MeanąSD
Bastaetal.,2007
Source: Mining smelter soil
(sample #11)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 331 mg/kg soil
Swine (Line 26,
male, 10-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: not reported; 5 animals/group
Test material dose: 2.2 ug As/kg bw/day (6.25 mg soil/kg
bw/day); 5 animals/group
6.2
Mean (SE or
SDnot
reported)
Rodriguez et al..
1999
Source: Mining smelter soil
(sample #12)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 233 mg/kg soil
Swine (Line 26,
male, 10-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: not reported; 5 animals/group
Test material dose: 1.5 ug As/kg bw/day (6.25 mg soil/kg
bw/day); 5 animals/group
42.8
Mean (SE or
SDnot
reported)
Rodriguez et al..
1999
Source: Mining smelter soil
(sample #13)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 799 mg/kg soil
Swine (Line 26,
male, 10-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: not reported; 5 animals/group
Test material dose: 5.0 ug As/kg bw/day (6.25 mg soil/kg
bw/day); 5 animals/group
29.1
Mean (SE or
SDnot
reported)
Rodriguez et al..
1999
Source: Mining smelter soil
(sample #14)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 1460 mg/kg
soil
Swine (Line 26,
male, 10-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: not reported; 5 animals/group
Test material dose: 9.1 ug As/kg bw/day (6.25 mg soil/kg
bw/day); 5 animals/group
18.7
Mean (SE or
SDnot
reported)
Rodriguez et al..
1999
36
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Source: Mining smelter soil
(sample #15)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 401 mg/kg soil
Swine (Line 26,
male, 10-12 kg)
Steady-state urinary excretion fraction method
Reference material dose: not reported; 5 animals/group
Test material dose: 2.5 ug As/kg bw/day (6.25 mg soil/kg
bw/day); 5 animals/group
36.5
Mean (SE or
SDnot
reported)
Rodriguez et al.,
1999
Source: Smelter composite soil
Ruston/North Tacoma Superfund
site (no information available on
particle size of test material)
Type: Mining/smelting
As concentration: 1600 mg/kg
soil
Swine (sires:
Hampshire hybrid;
dams: crossbred
Landrace/Large
White/Duroc,
immature, -6-7
weeks old, -15 kg)
Single dose blood-time concentration curve method
Reference material dose: 10, 110, or 310 ug As/kg bw;
3 animals/group
Test material dose: 40, 100, 160, or 240 ug As/kg bw (25,
62.5, 100, or 150 mg soil/kg bw); 3 animals/group
78
Mean (SE or
SDnot
reported)
U.S. EPA, 1996
Source: Smelter composite slag
Ruston/North Tacoma Superfund
site (no information available on
particle size of test material)
Type: Mining/smelting
As concentration: 10,100 mg/kg
soil
Swine (sires:
Hampshire hybrid;
dams: crossbred
Landrace/Large
White/Duroc,
immature, -6-7
weeks old, -15 kg)
Single dose blood-time concentration curve method
Reference material dose: 10, 110, or 310 ug As/kg bw;
3 animals/group
Test material dose: 610, 1010, or 1540 ug As/kg bw (60.4,
100, or 152.5 mg soil/kg bw); 3 animals/group
42
Mean (SE or
SDnot
reported)
U.S. EPA, 1996
Source: Australian railway
corridor soil (sample #2)
(sieved to <250 um)
Type: Railway corridor
As concentration: 267 mg/kg soil
Swine (large white,
female, 20-25 kg)
Single dose blood-time concentration curve method
Reference material dose: 100 ug As/kg bw;
3 animals/group
Test material dose: 119 to 297 ug As/kg bw (0.4 to 1.1 mg
soil/kg bw); 3 animals/group
67.4ą32.2
MeanąSD
Juhasz et al., 2007
Source: Australian railway
corridor soil (sample #4)
(sieved to <250 um)
Type: Railway corridor
As concentration: 42 mg/kg soil
Swine (large white,
female, 20-25 kg)
Single dose blood-time concentration curve method
Reference material dose: 100 ug As/kg bw;
3 animals/group
Test material dose: 19 to 47 ug As/kg bw (0.4 to 1.1 mg
soil/kg bw); 3 animals/group
41.6ą11.5
MeanąSD
Juhasz et al., 2007
Source: Australian railway
corridor soil (sample #5)
(sieved to <250 um)
Type: Railway corridor
As concentration: 1114 mg/kg
soil
Swine (large white,
female, 20-25 kg)
Single dose blood-time concentration curve method
Reference material dose: 100 ug As/kg bw;
3 animals/group
Test material dose: 495 to 1238 ug As/kg bw (0.4 to 1.1 mg
soil/kg bw); 3 animals/group
20.0ą16.5
MeanąSD
Juhasz et al., 2007
37
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Source: Australian railway
corridor soil (sample #10)
(sieved to <250 um)
Type: Railway corridor
As concentration: 257 mg/kg soil
Swine (large white,
female, 20-25 kg)
Single dose blood-time concentration curve method
Reference material dose: 100 ug As/kg bw;
3 animals/group
Test material dose: 114 to 285 ug As/kg bw (0.4 to 1.1 mg
soil/kg bw); 3 animals/group
11.2ą4.7
MeanąSD
Juhasz et al., 2007
Source: Australian railway
corridor soil (sample #16)
(sieved to <250 um)
Type: Railway corridor
As concentration: 751 mg/kg soil
Swine (large white,
female, 20-25 kg)
Single dose blood-time concentration curve method
Reference material dose: 100 ug As/kg bw;
3 animals/group
Test material dose: 334 to 834 ug As/kg bw (0.4 to 1.1 mg
soil/kg bw); 3 animals/group
22.5ą3.8
MeanąSD
Juhasz et al., 2007
Source: Australian railway
corridor soil (sample #18)
(sieved to <250 um)
Type: Railway corridor
As concentration: 91 mg/kg soil
Swine (large white,
female, 20-25 kg)
Single dose blood-time concentration curve method
Reference material dose: 100 ug As/kg bw;
3 animals/group
Test material dose: 40 to 101 ug As/kg bw (0.4 to 1.1 mg
soil/kg bw); 3 animals/group
74.7ą11.2
MeanąSD
Juhasz et al., 2007
Source: Australian cattle tick dip
soil (sample #24)
(sieved to <250 um)
Type: Agriculture
As concentration: 713 mg/kg soil
Swine (large white,
female, 20-25 kg)
Single dose blood-time concentration curve method
Reference material dose: 100 ug As/kg bw;
3 animals/group
Test material dose: 317 to 792 ug As/kg bw (0.4 to 1.1 mg
soil/kg bw); 3 animals/group
33.0ą17.0
MeanąSD
Juhasz et al., 2007
Source: Australian cattle tick dip
soil (sample #27)
(sieved to <250 um)
Type: Agriculture
As concentration: 228 mg/kg soil
Swine (large white,
female, 20-25 kg)
Single dose blood-time concentration curve method
Reference material dose: 100 ug As/kg bw;
3 animals/group
Test material dose: 100 to 250 ug As/kg bw (0.4 to 1.1 mg
soil/kg bw); 3 animals/group
49.9ą11.0
MeanąSD
Juhasz et al., 2007
Source: Australian mine site
(sample #33)
Type: Mining/smelting
(sieved to <250 um)
As concentration: 807 mg/kg soil
Swine (large white,
female, 20-25 kg)
Single dose blood-time concentration curve method
Reference material dose: 100 ug As/kg bw;
3 animals/group
Test material dose: 359 to 897 ug As/kg bw (0.4 to 1.1 mg
soil/kg bw); 3 animals/group
40.8ą7.4
MeanąSD
Juhasz et al., 2007
Source: Australian mine site
(sample #34)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 577 mg/kg soil
Swine (large white,
female, 20-25 kg)
Single dose blood-time concentration curve method
Reference material dose: 100 ug As/kg bw;
3 animals/group
Test material dose: 248 to 619 ug As/kg bw (0.4 to 1.1 mg
soil/kg bw); 3 animals/group
6.9ą5.0
MeanąSD
Juhasz et al., 2007
38
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Source: Australian gossan soil
(sample #44)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 190 mg/kg soil
Swine (large white,
female, 20-25 kg)
Single dose blood-time concentration curve method
Reference material dose: 100 ug As/kg bw;
3 animals/group
Test material dose: 84 to 211 ug As/kg bw (0.4 to 1.1 mg
soil/kg bw); 3 animals/group
16.4ą9.1
MeanąSD
Juhasz et al., 2007
Source: Australian gossan soil
(sample #45)
(sieved to <250 um)
Type: Mining/smelting
As concentration: 88 mg/kg soil
Swine (large white,
female, 20-25 kg)
Single dose blood-time concentration curve method
Reference material dose: 100 ug As/kg bw;
3 animals/group
Test material dose: 39 to 98 ug As/kg bw (0.4 to 1.1 mg
soil/kg bw); 3 animals/group
12.1ą8.5
MeanąSD
Juhasz et al., 2007
Source: Montana smelter soil
(sieved to <250 um)
Type: Mining/smelting
As concentration: 650 mg/kg soil
Cynomolgus
monkeys (male, 4-5
kg)
Single dose urinary excretion fraction method
Reference material dose: 250, 500, or 1000 ug As/kg bw;
5 animals/group
Test material dose: 650 ug As/kg bw (1000 mg soil/kg bw);
5 animals/group
13ą5
MeanąSD
Roberts et al., 2007
Source: Wisconsin smelter soil
(sieved to <250 um)
Type: Mining/smelting
As concentration: 1412 mg/kg
soil
Cynomolgus
monkeys (male, 4-5
kg)
Single dose urinary excretion fraction method
Reference material dose: 250, 500, or 1000 ug As/kg bw;
5 animals/group
Test material dose: 1330 ug As/kg bw (942 mg soil/kg bw);
5 animals/group
13ą7
MeanąSD
Roberts et al., 2007
Source: Florida cattle dip site
(sieved to <250 um)
Type: Agriculture
As concentration: 189 mg/kg soil
Cynomolgus
monkeys (male, 4-5
kg)
Single dose urinary excretion fraction method
Reference material dose: 250, 500, or 1000 ug As/kg bw;
5 animals/group
Test material dose: 180 ug As/kg bw (952 mg soil/kg bw);
5 animals/group
31ą4
MeanąSD
Roberts et al., 2007
Source: California mine tailings
(sieved to <250 um)
Type: Mining/smelting
As concentration: 300 mg/kg soil
Cynomolgus
monkeys (male, 4-5
kg)
Single dose urinary excretion fraction method
Reference material dose: 250, 500, or 1000 ug As/kg bw;
5 animals/group
Test material dose: 300 ug As/kg bw (1000 mg soil/kg bw);
5 animals/group
19ą2
MeanąSD
Roberts et al., 2007
Source: Washington orchard soil
(sieved to <250 um)
Type: Agriculture
As concentration: 301 mg/kg soil
Cynomolgus
monkeys (male, 4-5
kg)
Single dose urinary excretion fraction method
Reference material dose: 250, 500, or 1000 ug As/kg bw;
5 animals/group
Test material dose: 300 ug As/kg bw (997 mg soil/kg bw);
5 animals/group
24ą9
MeanąSD
Roberts et al., 2007
39
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Source: New York orchard soil
(sieved to <250 um)
Type: Agriculture
As concentration: 125 mg/kg soil
Cynomolgus
monkeys (male, 4-5
kg)
Single dose urinary excretion fraction method
Reference material dose: 250, 500, or 1000 ug As/kg bw;
5 animals/group
Test material dose: 120 ug As/kg bw (960 mg soil/kg bw);
5 animals/group
15ą8
MeanąSD
Roberts et al., 2007
Source: Colorado smelter soil
(sieved to <250 um)
Type: Mining/smelting
As concentration: 394 mg/kg soil
Cynomolgus
monkeys (male, 4-5
kg)
Single dose urinary excretion fraction method
Reference material dose: 250, 500, or 1000 ug As/kg bw;
5 animals/group
Test material dose: 400 ug As/kg bw (1015 mg soil/kg bw);
5 animals/group
18ą6
MeanąSD
Roberts et al., 2007
Source: Colorado smelter
(sieved to <250 um)
Type: Mining/smelting
As concentration: 1230 mg/kg
soil
Cynomolgus
monkeys (male, 4-5
kg)
Single dose urinary excretion fraction method
Reference material dose: 250, 500, or 1000 ug As/kg bw;
5 animals/group
Test material dose: 1000 ug As/kg bw (813 mg soil/kg bw);
5 animals/group
17ą8
MeanąSD
Roberts et al., 2007
Source: Colorado smelter soil
(sieved to <250 um)
Type: Mining/smelting
As concentration: 1492 mg/kg
soil
Cynomolgus
monkeys (male, 4-5
kg)
Single dose urinary excretion fraction method
Reference material dose: 250, 500, or 1000 ug As/kg bw;
5 animals/group
Test material dose: 1000 ug As/kg bw (670 mg soil/kg bw);
5 animals/group
5ą4
MeanąSD
Roberts et al., 2007
Source: Florida chemical plant
soil (sieved to <250 um)
Type: Chemical manufacturing
As concentration: 268 mg/kg soil
Cynomolgus
monkeys (male, 4-5
kg)
Single dose urinary excretion fraction method
Reference material dose: 250, 500, or 1000 ug As/kg bw;
5 animals/group
Test material dose: 340 ug As/kg bw (1269 mg soil/kg bw);
5 animals/group
7ą3
MeanąSD
Roberts et al., 2007
Source: New York pesticide
facility soil #1
(sieved to <250 um)
Type: Chemical manufacturing
As concentration: 1000 mg/kg
soil3
Cynomolgus
monkeys (male, 4-5
kg)
Single dose urinary excretion fraction method
Reference material dose: 250, 500, or 1000 ug As/kg bw;
5 animals/group
Test material dose: 990 ug As/kg bw (2920 mg soil/kg bw);
5 animals/group
19ą5
MeanąSD
Roberts et al., 2007
Source: New York pesticide
facility soil #2
(sieved to <250 um)
Type: Chemical manufacturing
As concentration: 339 mg/kg
soil3
Cynomolgus
monkeys (male, 4-5
kg)
Single dose urinary excretion fraction method
Reference material dose: 250, 500, or 1000 ug As/kg bw;
5 animals/group
Test material dose: 300 ug As/kg bw (549 mg soil/kg bw);
5 animals/group
28ą10
MeanąSD
Roberts et al., 2007
40
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Source: New York pesticide
facility soil #3
(sieved to <250 um)
Type: Chemical manufacturing
As concentration: 546 mg/kg
soil3
Cynomolgus
monkeys (male, 4-5
kg)
Single dose urinary excretion fraction method
Reference material dose: 250, 500, or 1000 ug As/kg bw;
5 animals/group
Test material dose: 490 ug As/kg bw (490 mg soil/kg bw);
5 animals/group
20ą10
MeanąSD
Roberts et al., 2007
Source: Hawaiian volcanic soil
(sieved to <250 um)
Type: Volcanic
As concentration: 724 mg/kg soil
Cynomolgus
monkeys (male, 4-5
kg)
Single dose urinary excretion fraction method
Reference material dose: 250, 500, or 1000 ug As/kg bw;
5 animals/group
Test material dose: 730 ug As/kg bw (1008 mg soil/kg bw);
5 animals/group
5ą1
MeanąSD
Roberts et al., 2007
Source: Barber Orchard NC,
sample MS-1
(sieved to <250 um)
Type: Agriculture
As concentration: 290 mg/kg soil
Cynomolgus
monkeys (adult
male, 4-5 kg)
Single dose urinary excretion fraction method
Reference material dose: 300 and 500 ug As/kg bw;
5 animals/group
Test material dose: 290 ug As/kg bw (1000 mg soil/kg bw);
5 animals/group
33ą5
MeanąSE
U.S. EPA, 2009
Source: Barber Orchard NC,
sample MS -4
(sieved to <250 um)
Type: Agriculture
As concentration: 388 mg/kg soil
Cynomolgus
monkeys (adult
male, 4-5 kg)
Single dose urinary excretion fraction method
Reference material dose: 300 and 500 ug As/kg bw;
5 animals/group
Test material dose: 388 ug As/kg bw (1000 mg soil/kg bw);
5 animals/group
28ą3
MeanąSE
U.S. EPA, 2009
Source: Barber Orchard NC,
sample MS -5
(sieved to <250 um)
Type: Agriculture
As concentration: 382 mg/kg soil
Cynomolgus
monkeys (adult
male, 4-5 kg)
Single dose urinary excretion fraction method
Reference material dose: 300 and 500 ug As/kg bw;
5 animals/group
Test material dose: 382 ug As/kg bw (1000 mg soil/kg bw);
5 animals/group
38ą7
MeanąSE
U.S. EPA, 2009
Source: Barber Orchard NC,
sample MS -8
(sieved to <250 um)
Type: Agriculture
As concentration: 364 mg/kg soil
Cynomolgus
monkeys (adult
male, 4-5 kg)
Single dose urinary excretion fraction method
Reference material dose: 300 and 500 ug As/kg bw;
5 animals/group
Test material dose: 364 ug As/kg bw (1000 mg soil/kg bw);
5 animals/group
25ą5
MeanąSE
U.S. EPA, 2009
Source: Florida electrical
substation soil
(sieved to <250 um)
Type: Other manufacturing
As concentration: 312 mg/kg soil
Cebus apella
monkeys (adult
male, 2.5-3. Okg)
Single dose urinary excretion fraction method
Reference material dose: 1000 ug As/kg bw;
5 animals/group
Test material dose: 500 ug As/kg bw (1602 mg soil/kg bw);
5 animals/group
14.6ą5.1
MeanąSD
Roberts et al., 2002
41
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Source: Cattle dip site soil
(sieved to <250 um)
Type: Agriculture
As concentration: 189 mg/kg soil
Cebus apella
monkeys (adult
male, 2.5-3.Okg)
Single dose urinary excretion fraction method
Reference material dose: 1000 ug As/kg bw;
5 animals/group
Test material dose: 500 ug As/kg bw (2646 mg soil/kg bw);
5 animals/group
24.7ą3.2
MeanąSD
Roberts et al., 2002
Source: Florida pesticide site #1
soil
(sieved to <250 um)
Type: Chemical manufacturing
As concentration: 743 mg/kg soil
Cebus apella
monkeys (adult
male, 2.5-3.Okg)
Single dose urinary excretion fraction method
Reference material dose: 1000 ug As/kg bw;
5 animals/group
Test material dose: 1000 ug As/kg bw (1346 mg soil/kg
bw); 5 animals/group
10.7ą4.9
MeanąSD
Roberts et al., 2002
Source: Wood preservative site
#2 soil
(sieved to <250 um)
Type: Chemical manufacturing
As concentration: 101 mg/kg soil
Cebus apella
monkeys (adult
male, 2.5-3.Okg)
Single dose urinary excretion fraction method
Reference material dose: 1000 ug As/kg bw;
5 animals/group
Test material dose: 300 ug As/kg bw (2970 mg soil/kg bw);
5 animals/group
16.3ą6.5
MeanąSD
Roberts et al., 2002
Source: Pesticide site soil
(sieved to <250 um)
Type: Chemical manufacturing
As concentration: 329 mg/kg soil
Cebus apella
monkeys (adult
male, 2.5-3.Okg)
Single dose urinary excretion fraction method
Reference material dose: 1000 ug As/kg bw;
5 animals/group
Test material dose: 500 ug As/kg bw (1520 mg soil/kg bw);
5 animals/group
17.0ą10.0
MeanąSD
Roberts et al., 2002
Source: Composite residential
soil, Anaconada, MT
(sieved to <250 um)
Type: Mining/smelting
As concentration: 410 mg/kg soil
Cynomolgus
monkeys (adult
female, 2-3 kg)
Single dose urinary excretion fraction method
Reference material dose: 620 ug As/kg bw;
3 animals/group
Test material dose: 620 ug As/kg bw (1500 mg soil/kg bw);
3 animals/group
20.1
Mean (SE or
SDnot
reported)
Freeman etal.,
1995
Source: NIST SRM 2710
(sieved to 74 um)
Type: Mining/smelting
As concentration: 601 mg/kg soil
(INAA)
C57BL/6 mice
(female, 6 weeks,
15-20 g)
Steady-state urinary excretion fraction method
Reference material dose: 820-1160 ug As/kg bw/day
Test material dose: 650-1020 ug As/kg bw/day (1150-1420
mg soil/kg bw/day)
42.9
(40.5-45.4)
Mean (95% CI)
Bradhametal.,
2011,2012
Source: NIST SRM 27lOa
(sieved to <74 um)
Type: Mining/smelting
As concentration: 1513 mg/kg
soil (INAA)
C57BL/6 mice
(female, 6 weeks,
15-20 g)
Steady-state urinary excretion fraction method
Reference material dose: 820-1160 ug As/kg bw/day
Test material dose: 580-2360 ug As/kg bw/day (1460-1490
mg soil/kg bw/day)
42.1
(39.8-44.4)
Mean (95% CI)
Bradhametal.
2011,2012
42
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Source: Iron King, AZ soil
sample TM1 (sieved to <250
urn)
Type: Mining/smelting
As concentration: 280 mg/kg soil
(INAA)
C57BL/6 mice
(female, 6 weeks,
15-20 g)
Steady-state urinary excretion fraction method
Reference material dose: 820-1160 ug As/kg bw/day
Test material dose: 390 ug As/kg bw/day (1490 mg soil/kg
bw/day)
39.9
(36.2-43.8)
Mean (95% CI)
Bradhametal.
2011,2012
Source: Iron King, AZ soil
sample TM2 (sieved to <250
urn)
Type: Mining/smelting
As concentration: 4495 mg/kg
soil (INAA)
C57BL/6 mice
(female, 6 weeks,
15-20 g)
Steady-state urinary excretion fraction method
Reference material dose: 820-1160 ug As/kg bw/day
Test material dose: 6100 ug As/kg bw/day (1430 mg soil/kg
bw/day)
14.5
(11.2-17.8)
Mean (95% CI)
Bradhametal.
2011,2012
Source: ASARCO soil sample
(sieved to <250 um)
Type: Mining/smelting
As concentration: 182 mg/kg soil
(INAA)
C57BL/6 mice
(female, 6 weeks,
15-20 g)
Steady-state urinary excretion fraction method
Reference material dose: 820-1160 ug As/kg bw/day
Test material dose: 320 ug As/kg bw/day (1460 mg soil/kg
bw/day)
26.7
(22.8-30.7)
Mean (95% CI)
Bradhametal.
2011,2012
Source: Sample TM2 Vasquez
Boulevard and 1-70, composite
residential, Denver CO
(sieved to <250 um)
Type: Mining/smelting
As concentration: 990 mg/kg soil
(INAA)
C57BL/6 mice
(female, 6 weeks,
15-20 g)
Steady-state urinary excretion fraction method
Reference material dose: 820-1160 ug As/kg bw/day
Test material dose: 1580 ug As/kg bw/day (1450 mg soil/kg
bw/day)
48.7
(43.4-54.2)
Mean (95% CI)
Bradhametal.
2011,2012
Source: Sample TM4 Vasquez
Boulevard and 1-70, composite
residential, Denver, CO
(sieved to <250 um)
Type: Mining/smelting
As concentration: 829 mg/kg soil
(INAA)
C57BL/6 mice
(female, 6 weeks,
15-20 g)
Steady-state urinary excretion fraction method
Reference material dose: 820-1160 ug As/kg bw/day
Test material dose: 1190 ug As/kg bw/day (1400 mg soil/kg
bw/day)
49.7
(45.0-54.5)
Mean (95% CI)
Bradhametal.
2011,2012
Source: Sample TM5 Vasquez
Boulevard and 1-70, composite
residential, Denver, CO
(sieved to <250 um)
Type: Mining/smelting
As concentration: 379 mg/kg soil
(INAA)
C57BL/6 mice
(female, 6 weeks,
15-20 g)
Steady-state urinary excretion fraction method
Reference material dose: 820-1160 ug As/kg bw/day
Test material dose: 520 ug As/kg bw/day (1580 mg soil/kg
bw/day)
51.6
(47.0-56.3)
Mean (95% CI)
Bradhametal.
2011,2012
43
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Species
Method/Dose
RBA (%)
Reference
Source: Midvale slag, composite
sample Midvale smelter slag pile
(sieved to <250 um)
Type: Mining/smelting
As concentration: 837 mg/kg soil
(INAA)
C57BL/6 mice
(female, 6 weeks,
15-20 g)
Steady-state urinary excretion fraction method
Reference material dose: 820-1160 ug As/kg bw/day
Test material dose: 1040 ug As/kg bw/day (1650 mg soil/kg
bw/day)
11.2
(10.6-11.8)
Mean (95% CI)
Bradhametal.
2011,2012
Source: Hawaiian soil sample
(sieved to <250 um)
Type: Agriculture
As concentration: 769 mg/kg soil
(INAA)
C57BL/6 mice
(female, 6 weeks,
15-20 g)
Steady-state urinary excretion fraction method
Reference material dose: 820-1160 ug As/kg bw/day
Test material dose: 1100 ug As/kg bw/day (1500 mg soil/kg
bw/day)
24.0
(20.9-27.2)
Mean (95% CI)
Bradhametal.
2011,2012
Source: Barber Orchard NC,
sample MS-1
(sieved to <250 um)
Type: Agriculture
As concentration: 322 mg/kg soil
(INAA)
C57BL/6 mice
(female, 6 weeks,
15-20 g)
Steady-state urinary excretion fraction method
Reference material dose: 820-1160 ug As/kg bw/day
Test material dose: 470 ug As/kg bw/day (1470 mg soil/kg
bw/day)
26.3
(23.4-29.4)
Mean (95% CI)
Bradhametal.
2011,2012
Source: Barber Orchard NC,
sample MS-4
(sieved to <250 um)
Type: Agriculture
As concentration: 387 mg/kg soil
(INAA)
C57BL/6 mice
(female, 6 weeks,
15-20 g)
Steady-state urinary excretion fraction method
Reference material dose: 820-1160 ug As/kg bw/day
Test material dose: 600 ug As/kg bw/day (1480 mg soil/kg
bw/day)
35.2
(30.9-39.6)
Mean (95% CI)
Bradhametal.
2011,2012
Source: Barber Orchard NC,
sample MS-5
(sieved to <250 um)
Type: Agriculture
As concentration: 467 mg/kg soil
(INAA)
C57BL/6 mice
(female, 6 weeks,
15-20 g)
Steady-state urinary excretion fraction method
Reference material dose: 820-1160 ug As/kg bw/day
Test material dose: 630 ug As/kg bw/day (1370 mg soil/kg
bw/day)
20.9
(15.9-26.0)
Mean (95% CI)
Bradhametal.
2011,2012
Source: Barber Orchard NC,
sample MS-8
(sieved to <250 um)
Type: Agriculture
As concentration: 396 mg/kg soil
(INAA)
C57BL/6 mice
(female, 6 weeks,
15-20 g)
Steady-state urinary excretion fraction method
Reference material dose: 820-1160 ug As/kg bw/day
Test material dose: 640 ug As/kg bw/day (1510 mg soil/kg
bw/day)
35.0
(31.2-38.9)
Mean (95% CI)
Bradhametal.
2011,2012
44
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 2. Key and Relevant Study Results
Test Material
Source: Mohr Orchard PA
sample
(sieved to <250 um)
Type: Agriculture
As concentration: 340 mg/kg soil
(INAA)
Species
C57BL/6 mice
(female, 6 weeks,
15-20 g)
Method/Dose
Steady-state urinary excretion fraction method
Reference material dose: 820-1160 ug As/kg bw/day
Test material dose: 500 ug As/kg bw/day (1440 mg soil/kg
bw/day)
RBA (%)
33.2
(27.7-38.7)
Mean (95% CI)
Reference
Bradhametal.,
2011,2012
Relevant Studies
Source: Residential soil,
Anaconda, MT
(test material particle size
19 um)
Type: Mining/smelting
As concentration: 3900 mg/kg
soil
Rabbit (New
Zealand white
rabbits male and
female; 9-12 weeks
old, ~2 kg)
Single dose urinary excretion fraction method
Reference material dose: 1950 ug As/kg bw;
5 animals/sex/group
Test material dose: 780, 1970, or 3900 ug As/kg bw (200,
500, or 1000 mg soil/kg bw); 5 animals/sex/group
48.2
Mean (SE or
SDnot
reported)
Freeman etal.,
1993
a Arsenic concentrations based on personal communication from the co-authors S. Roberts and Y. Lowney (09/24/2010) which corrects an error in column headings in Table 3 of
Roberts et al. (2007); reported values: NYPF1=339 ppm, NYPF2=546 ppm, and NYPF3=1000 ppm)
45
-------
Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 3. Summary Statistics for RBA (%) Estimates Based on Key Studies
Parameter
Nc
AM
SD
SE
95LCLd
95UCLd
MIN
5th %
10th %
25th %
50th %
75th %
90th %
95th %
MAX
SKEW
KURT
Swine
64
34.5
17.5
2.2
30.2
38.8
4.1
7.9
9.7
20.8
37.0
44.8
54.4
60.9
78.0
0.21
-0.42
Monkeys
24
19.2
8.6
1.7
15.8
22.6
5.0
5.3
8.1
14.2
18.5
24.8
30.1
32.7
38.0
0.29
-0.21
Mice
15
33.5
12.6
3.3
27.1
39.8
11.2
13.5
17.0
25.2
35.0
42.5
49.3
50.2
51.6
-0.24
-0.92
All
Species"
103
30.8
16.4
1.6
27.6
34.0
4.1
7.1
10.8
18.0
29.1
42.0
51.5
56.8
78.0
0.47
-0.23
All
Speciesb
88
29.9
16.8
1.8
26.4
33.4
4.1
6.9
8.9
16.9
28.3
42.0
50.3
56.3
78.0
0.55
-0.14
a Each RBA estimate for materials evaluated in more than one assay is given equal weight.
b RBA estimates for materials evaluated in more than on assay are represented by the average of values from all assays. These
include the following test materials: Barber Orchard MS-1, -4, -5, and -8 (swine, monkey, and mouse); and Iron King TM1 and
TM2, Ruston/ASARCO, Hawaii, Mohr Orchard, NIST 2710 and NIST 2710A (swine and mouse).
0 Number of RBA estimates.
0 Number of RBA estimates.
d Assumes central limit and Z= 1.96 for standard normal
AM, arithmetic mean; KURT, kurtosis; LCL, lower confidence limit on the mean; MAX, maximum; MIN, minimum; SD,
standard deviation; SE, standard error; UCL, upper confidence limit on the mean; 5th %, 5th percentile
Table 4. Weighted RBA Summary Statistics and Confidence Limits3
Parameter
AM
5th %
50th %
95th %
CTE
30.8
6.6
28.5
58.1
95% LCL
29.8
5.1
26.2
53.3
95% UCL
31.7
8.3
31.0
64.0
a Weighted for uncertainty (SE of mean, based on Monte Carlo analysis of all RBA estimates from swine, monkey, and mouse
studies [n=103]).
AM, arithmetic mean; CTE, central tendency estimate; LCL, lower confidence limit; UCL, upper confidence limit
Table 5. RBA Estimates for Barber Orchard Soils Administered to Mice, Monkeys, and
Swine
Species
Mice
Monkey
Swine
RBA % (95% Confidence Limits)
MS-1 (290 ppm)a
26 (23-29)
33 (23-43)b
31 (24-40)
MS-4 (388 ppm)a
35(31-40)
28 (22-34)b
41 (37-44)
MS-5 (382 ppm)a
21 (16-26)
38 (24-52)b
49 (40-59)
MS-8 (364 ppm)a
35(31-39)
25 (15-35)b
53 (48-57)
1 Test material number (As concentration): arsenic concentration measured on sieved (250 um) fractions.
3 Estimated as SE x 1.96 (Z=1.96 for standard normal), where SE values were reported in U.S. EPA, 2009.
46
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Table 6. Comparison Between RBA Estimates Based on Mice and Swine Bioassays
Test Materials
Iron King HSJ-583
Iron King IKJ-583
Ruston ASARCO
Hawaii
Barber Orchard MS- 1
Barber Orchard MS-4
Barber Orchard MS-5
Barber Orchard MS-8
Mohr Orchard
NIST2710
NIST2710A
RBA % (95% Confidence Limits)
Mice
40 (36^4)
14(11-18)
27(23-31)
24 (21-27)
26 (23-29)
35(31-40)
21 (16-26)
35(31-39)
33 (28-39)
43 (40^5)
42 (40^4)
Swine
60 (55-66)a
19 (17-20)
49 (44-54)a
33 (30-36)3
31(24-10)
41 (37-14)
49 (40-59)3
53 (48-57)a
53 (50-57)3
44 (40-49)
42 (39-45)
a Confidence limits do not overlap.
Table 7. Comparison Between RBA Estimates Based on UEF and Blood AUC in Monkeys
Monkey Number
30-544
20-784
30-537
Mean
SD
RBA based on UEF
27.7
18.6
14.1
20.1
6.9
RBA based on Blood AUC
6.1
6.9
19.9
11.0
7.7
Based on Freeman et al. (1995). RBA estimates based on the two methods are not significantly different based on paired t-test
(p=0.37) or unpaired t-test (p=0.20).
AUC, area under the blood concentration - time curve; UEF, urinary excretion fraction
47
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
A 0
Materials
DON
Number of Test
0 -fc. O> 0
^
0.
J
1
1
n
I
I
n
T
Swine
D Monkey
n Mouse
JIM
i i i i i i i i i i i i i i
^v ^v ^v ^v >^S ^S >^S
RBA(%)
I
i i i
s? <^
s*
Figure 1. Distribution of RBA Values for Materials Assayed in Swine, Monkey, and
Mouse.
The mean RBA value for test materials assayed in monkeys is 19.2% (95% CI: 15.8-22.6,
n=24); the mean for test materials assayed in swine is 34.5% (95% CI: 30.2-38.8, n=64); the
mean for test materials assayed in mice is 33.5% (95% CI: 27.1-39.8, n=15).
48
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
/u
60 -
50 -
g40-
DO
cr 30 -
20 -
10 -
t
^
<
[ I
>
0 I
MS1
A Monkey
t
<
r_..4._..
I
L
Mouse
^
<
L
i
ŧ
MS4 MS5
I^Swine
J
>
.__ Ŧ,Ŧ*Ŧ*Ŧ
1
_j__
"** "*"*""""*
A
' T
ŧ^^^^^^^^^^
k
j
MS 8
^
L
<
ŧ j
I
>
Site
Figure 2. Comparison Between Arsenic RBA Estimates from Swine, Monkey, and Mouse
Bioassays of Four Soil Samples from the Barber Orchard Site.
Shown are mean and 95% confidence limits. The values shown for "site" are the means for all
four soil samples.
49
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
OU J-- -,-:--.-
vn J
' U f
on 1 '
OU i ;
i -.
50 -I
<^ 40 h*L iff,
DO !
o: j :
i
H n J -.-..-,-,..- .^.. - .-,,..
1 U i
i
0 ~'
N2710 N2710P
I,.
v IK
M
.
-
^
1 IK2
ouse
>
BO1
\
BO4
*Swin
'- '"A
^
1
T
BO5
j
x
\
BOS
I
T.
<
>
MO
!
:
f;
j '-. T
-
:
:
RA HI
Figure 3. Comparison Between Arsenic RBA Estimates from Swine or Mouse Bioassays of
11 Test Materials.
Shown are mean and 95% confidence limits. The values shown for "site" are the means for all
four soil samples.
BO, Barber Orchard; HI, Hawaii; IK, Iron King; MO, Mohr Orchard; N, NIST; RA, Ruston-
ASARCO
50
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
100
80
0
40 60
Swine RBA(%)
80
100
Figure 4. Relationship Between Arsenic RBA Estimates Based on Mouse and Swine
Bioassays Applied to 11 Test Materials.
Error bars for mice are 95% confidence limits. Solid line is the linear regression model
(R2=0.35, p=0.053).The mouse and swine RBA estimates are not significantly correlated
(Pearson r=0.60, p=0.053; Spearman r=0.42, p=0.19).
51
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
APPENDIX A: Summary Description of Human Arsenic
Bioavailability Study (Stanek et al., 2010)
52
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
A single human experimental study of bioavailability of arsenic in soil was reported
(Stanek et al., 2010). This study was not used selected for inclusion in this report as a key or
relevant study because of several methodological limitations and uncertainties, which are briefly
summarized below. Stanek et al. (2010) utilized a mass balance approach to estimate absolute
bioavailability of arsenic in food and soil in a small group of human subjects (n=13 subjects
including 7 females and 6 males, age 26-53 years). The study consisted of two phases
conducted approximately 2-3 years apart, with partial overlap of subjects in both phases. Phase
1 of the study estimated absolute bioavailability of arsenic in food and included 11 subjects
(6 females and 5 males, age 26-53 years). Daily complete urine and fecal samples, and duplicate
diet samples were collected from each subject for a period of 7 consecutive days. For each
subject, for each day, absolute bioavailability of ingested arsenic was calculated as follows
(Equation A-l):
"" "" Eq.(A-l)
Asfood
where ABA is absolute bioavailability and Asf00d and Asfecai are the rate of intake of arsenic in
food and rate of excretion of arsenic in feces (jig/day), respectively.
Phase 2 estimated the absolute bioavailability of arsenic in soil and included 11 subjects,
9 of whom participated in Phase 1. Subjects were asked to avoid eating seafood, rice,
mushrooms, spinach, or grape juice (foods typically having high levels of arsenic) for 4 days
preceding the 7-day observation period. On day 2 of the observation period, each subject
ingested a gelatin capsule containing 111.7 jig As in 0.636 g of soil. The soil was obtained from
a cattle dip site (see Roberts et al., 2007). Absolute bioavailability of arsenic in soil was
calculated as follows (Equation A-2):
_ Asfecal-Asfood-(l-ABAfood)
Assoil
The above calculation utilizes the estimate of the absolute bioavailability of arsenic in
food to calculate the amount of fecal arsenic attributable to food in Phase 2. The difference
between total fecal arsenic and fecal arsenic attributed to food was attributed to the soil dose.
Bioavailable arsenic from the soil dose was calculated as the difference between the soil arsenic
dose and fecal arsenic attributed to the soil dose.
Stanek et al. (2010) reported estimates of 87.5% (95% CI: 81.2, 93.8) and 89.7% (95%
CI: 83.4, 96.0) for absolute arsenic bioavailability in food, based on Phase 1 and Phase 2
respectively. The estimate for absolute bioavailability of arsenic in soil was 48.7% (95% CI:
36.2, 61.3). The estimate for bioavailability of arsenic from soil relative to food was 54.5%
(48.7%/89.7%).
Several important uncertainties attend these above estimates of bioavailability, which
precluded the using the estimates in the calculation of soil RBA for the upper bound estimate for
soil RBA:
53
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Compilation and Review of Data on Relative Unavailability of
Arsenic in Soil
Stanek et al. (2010) does not provide an estimate of the KB A for arsenic in soil relative to
that of a completely bioaccessible form of arsenic (e.g., to sodium arsenate). The ratio of
the absolute bioavailability of arsenic in soil to that of arsenic in food, reported in Stanek
et al. (2010), is not directly comparable to KB As based on key studies described in this
report (e.g., soil KBA relative to sodium arsenate).
The two study phases were separated by -2.5 years and, although there was substantial
overlap among subjects in both phases, individual subjects could not serve as their own
measures for absolute bioavailability of dietary arsenic in the calculation of absolute
bioavailability of soil arsenic.
Sample collection (duplicate diets, feces, and urine) appears to have been unsupervised
and was performed by individual subjects outside of a clinical research center where
adherence to sampling protocols could have been assured.
No attempt was made to control dietary arsenic intake, other than the 4-day voluntary
"arsenic suppression" diet that preceded Phase 2. As a result, intra- and inter-subject
variability in dietary intakes was substantial (e.g., maximum/minimum arsenic intake
ratio in Phase 1 ranged from 6 to 84). This magnitude of variability in dietary arsenic
intakes during the study is likely to have contributed substantial dietary noise to the
estimation the fraction of fecal arsenic attributed to the soil dose in Phase 2.
The recovery of arsenic from a duplicate diet spiked with a known amount of soil arsenic
was reported to have been 78.9% and no explanation is given for the low recovery. The
resulting uncertainty in the dietary and soil arsenic doses contributes to uncertainty in the
corresponding bioavailability estimates for food and soil. The magnitude of the error in
the bioavailability estimates attributable to error in the arsenic dose estimates depends on
whether or not the low arsenic recovery represents arsenic in soil, and/or arsenic in food,
and/or arsenic in soil added to food. Therefore, without an understanding of the recovery
problem, or of the reproducibility of recovery, the magnitude of the error cannot be
reliably determined. Based on data reported in the Appendix to Stanek et al. (2010), the
estimates of soil KBA may have ranged from 40 to 60%, depending on the assignment of
the recovery error to food, soil, or both media.
54
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