&EPA
TOXICOLOGICAL REVIEW
OF
TRIVALENT CHROMIUM
(CAS No. 16065-83-1)
In Support of Summary Information on the
Integrated Risk Information System (IRIS)
August 1998
U.S. Environmental Protection Agency
Washington, DC
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DISCLAIMER
This document has been reviewed in accordance with U.S. Environmental Protection
Agency policy. Mention of trade names or commercial products does not constitute endorsement
or recommendation for use. This document may undergo revisions in the future. The most up-
to-date version will be available electronically via the IRIS Home Page at
http://www.epa.gov/iris.
11
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CONTENTS—TOXICOLOGICAL REVIEW FOR TRIVALENT CHROMIUM
(CAS No. 16065-83-1)
FOREWORD v
AUTHORS, CONTRIBUTORS, AND REVIEWERS vi
LIST OF ABBREVIATIONS vii
1. INTRODUCTION 1
2. CHEMICAL AND PHYSICAL INFORMATION RELEVANT TO ASSESSMENTS 2
3. TOXICOKINETICS RELEVANT TO ASSESSMENTS 3
3.1. ABSORPTION FACTORS IN HUMANS AND EXPERIMENTAL ANIMALS . . 3
3.1.1. Oral 3
3.1.2. Inhalation 4
3.1.3. Distribution 5
3.1.4. Metabolism 7
3.1.5. The Essentiality of Chromium 7
4. HAZARD IDENTIFICATION 8
4.1. STUDIES IN HUMANS 8
4.1.1. Oral 8
4.1.2. Inhalation 8
4.2. PRECHRONIC AND CHRONIC STUDIES AND CANCER BIOASSAYS IN
ANIMALS—ORAL AND INHALATION 12
4.2.1. Chronic Oral Studies 12
4.2.2. Subchronic Oral Studies 13
4.2.3. Chronic Inhalation Studies 14
4.2.4. Subchronic Inhalation Studies 15
4.3. REPRODUCTIVE/DEVELOPMENTAL STUDIES—ORAL AND INHALATION
17
4.3.1. Oral Studies 17
4.3.2. Inhalation Studies 18
4.4. OTHER STUDIES 19
4.4.1. Contact Dermatitis 19
4.4.2. Toxicant Interactions 19
4.4.3. Genotoxicity 19
4.5. SYNTHESIS AND EVALUATION OF MAJOR NONCANCER EFFECTS AND
MODE OF ACTION (IF KNOWN)—ORAL AND INHALATION 20
4.5.1. Oral Studies 20
4.5.1.1. Human Studies 20
4.5.1.2. Animal Studies 20
iii
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CONTENTS (continued)
4.5.2. Inhalation Studies 21
4.5.2.1. Human Studies 21
4.5.2.2. Animal Studies 21
4.6. WEIGHT-OF-EVIDENCE EVALUATION AND CANCER
CHARACTERIZATION
22
4.7. OTHER HAZARD IDENTIFICATION ISSUES 22
4.7.1. Possible Childhood Susceptibility 22
4.7.2. Possible Sex Differences 22
5. DOSE-RESPONSE ASSESSMENTS 23
5.1. ORAL REFERENCE DOSE (RfD) 23
5.1.1. Choice of Principal Study and Critical Effect
23
5.1.2. Methods of Analysis 23
5.1.3. RfD Derivation 24
5.2. INHALATION REFERENCE CONCENTRATION (RfC) 25
5.3. CANCER ASSESSMENT 26
6. MAJOR CONCLUSIONS IN THE CHARACTERIZATION
OF HAZARD AND DOSE RESPONSE 26
6.1. HUMANHAZARD POTENTIAL 26
6.2. DOSE RESPONSE 27
7. REFERENCES 28
APPENDIX A. EXTERNAL PEER REVIEW-
SUMMARY OF COMMENTS AND DISPOSITION 39
IV
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FOREWORD
The purpose of this Toxicological Review is to provide scientific support and
rationale for the hazard and dose-response assessment in IRIS pertaining to chronic exposure to
trivalent chromium. It is not intended to be a comprehensive treatise on the chemical or
toxicological nature of trivalent chromium (in).
In Section 6, EPA has characterized its overall confidence in the quantitative and
qualitative aspects of hazard and dose response. Matters considered in this characterization
include knowledge gaps, uncertainties, quality of data, and scientific controversies. This
characterization is presented in an effort to make apparent the limitations of the assessment and
to aid and guide the risk assessor in the ensuing steps of the risk assessment process.
For other general information about this assessment or other questions relating to IRIS,
the reader is referred to EPA's Risk Information Hotline at 202-566-1676.
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AUTHORS, CONTRIBUTORS, AND REVIEWERS
Chemical Manager/Author
Peter C. Grevatt, Ph.D., EPA Region 2
Reviewers
This document and summary information on IRIS have received peer review both by EPA
scientists and by independent scientists external to EPA. Subsequent to external review and
incorporation of comments, this assessment has undergone an Agencywide review process
whereby the IRIS Program Manager has achieved a consensus approval among the Office of
Research and Development; Office of Air and Radiation; Office of Prevention, Pesticides, and
Toxic Substances; Office of Solid Waste and Emergency Response; Office of Water; Office of
Policy, Planning, and Evaluation; and the Regional Offices.
Internal EPA Reviewers
Robert Benson, Ph.D., D.A.B.T., Region 8
Charles Hiremath, Ph.D., National Center for Environmental Assessment
Annie Jarabek, National Center for Environmental Assessment
Winona Victery, Ph.D., D.A.B.T., Region 9
External Peer Reviewers
Richard Anderson, Ph.D., U.S. Department of Agriculture
Robert Chapin, Ph.D., National Institute of Environmental Health Sciences
Robert Drew, Ph.D., Consultant in Toxicology
Gunter Obersorster, D.V.M., Ph.D., University of Rochester
Elizabeth T. Snow, Ph.D., New York University Medical Center
Summaries of the external peer reviewers' comments and the disposition of their
recommendations are in Appendix A.
VI
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LIST OF ABBREVIATIONS
BAL bronchoalveolar lavage
BMD benchmark dose
BW body weight
CASRN Chemical Abstracts Service Registry Number
ESADDI estimated safe and adequate daily dietary intake
GIF glucose tolerance factor
IRIS Integrated Risk Information System
MTD maximum tolerated dose
NOAEL no-observed-adverse-effect level
NOEL no-observed-effect level
ppb parts per billion
ppm parts per million
RfC inhalation reference concentration
RfD oral reference dose
vn
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1. INTRODUCTION
This document presents background and justification for the hazard and dose-response
assessment summaries in EPA's Integrated Risk Information System (IRIS). IRIS Summaries
may include an oral reference dose (RfD), inhalation reference concentration (RfC) and a
carcinogenicity assessment.
The RfD and RfC provide quantitative information for noncancer dose-response
assessments. The RfD is based on the assumption that thresholds exist for certain toxic effects
such as cellular necrosis but may not exist for other toxic effects such as some carcinogenic
responses. It is expressed in units of mg/kg-day. In general, the RfD is an estimate (with
uncertainty spanning perhaps an order of magnitude) of a daily exposure to the human population
(including sensitive subgroups) that is likely to be without an appreciable risk of deleterious
effects during a lifetime. The inhalation RfC is analogous to the oral RfD. The inhalation RfC
considers toxic effects for both the respiratory system (portal-of-entry) and for effects peripheral
to the respiratory system (extrarespiratory or systemic effects). It is generally expressed in units
of mg/m3.
The carcinogenicity assessment provides information on the carcinogenic hazard potential
of the substance in question and quantitative estimates of risk from oral exposure and inhalation
exposure. The information includes a weight-of-evidence judgment of the likelihood that the
agent is a human carcinogen and the conditions under which the carcinogenic effects may be
expressed. Quantitative risk estimates are presented in three ways. The slope factor is the result
of application of a low-dose extrapolation procedure and is presented as the risk per mg/kg-day.
The unit risk is the quantitative estimate in terms of either risk per |ig/L drinking water or risk
per |ig/m3 air breathed. Another form in which risk is presented is a drinking water or air
concentration providing cancer risks of 1 in 10,000; 1 in 100,000; or 1 in 1,000,000.
Development of these hazard identifications and dose-response assessments for trivalent
chromium has followed the general guidelines for risk assessment as set forth by the National
Research Council (1983). EPA guidelines that were used in the development of this assessment
may include the following: the Guidelines for Carcinogen Risk Assessment (U.S. EPA, 1986a),
Guidelines for the Health Risk Assessment of Chemical Mixtures (U.S. EPA, 1986b), Guidelines
for Mutagenicity Risk Assessment (U.S. EPA, 1986c), Guidelines for Developmental Toxicity
Risk Assessment (U.S. EPA, 1991), Proposed Guidelines for Neurotoxicity Risk Assessment (U.S.
EPA, 1995a), Proposed Guidelines for Carcinogen Risk Assessment (U.S. EPA, 1996a),
Guidelines for Reproductive Toxicity Risk Assessment (U.S. EPA, 1996b), and Guidelines for
Neurotoxicity Risk Assessment (U.S. EPA, 1998a); Recommendations for and Documentation of
Biological Values for Use in Risk Assessment (U.S. EPA, 1988); (proposed) Interim Policy for
Particle Size and Limit Concentration Issues in Inhalation Toxicity (U.S. EPA, 1994a); Methods
for Derivation of Inhalation Reference Concentrations and Application of Inhalation Dosimetry
(U.S. EPA, 1994b); Peer Review and Peer Involvement at the U.S. Environmental Protection
Agency (U.S. EPA, 1994c); Use of the Benchmark Dose Approach in Health Risk Assessment
(U.S. EPA, 1995b); Science Policy Council Handbook: Peer Review (U.S. EPA, 1998b); and
1
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memorandum from EPA Administrator, Carol Browner, dated March 21, 1995, Subject:
Guidance on Risk Characterization.
Literature search strategies employed for this compound were based on the CASRN and
at least one common name. At a minimum, the following databases were searched: RTECS,
HSDB, TSCATS, CCRIS, GENETOX, EMIC, EMICBACK, DART, ETICBACK, TOXLINE,
CANCERLINE, MEDLINE AND MEDLINE backfiles. Any pertinent scientific information
submitted by the public to the IRIS Submission Desk was also considered in the development of
this document.
2. CHEMICAL AND PHYSICAL INFORMATION RELEVANT TO ASSESSMENTS
Chromium (Cr) is a metallic element belonging to the first transitional series of the
periodic table. Elemental chromium has a CAS Registry Number of 7440-47-3. The three most
stable forms in which chromium occurs in the environment are the 0 (metal and alloys), +3
(trivalent chromium), and +6 (hexavelent chromium) valence states. In the +3 valence state, the
chemistry of chromium is dominated by the formation of stable complexes with both organic and
inorganic ligands (Hartford, 1979). In the +6 valence state, chromium exists as oxo species such
as CrO3 and CrO42" that are strongly oxidizing (Cotton and Wilkinson, 1980).
Chromium in the ambient air occurs from natural sources, industrial and product uses,
and burning of fossil fuels and wood. The most important industrial sources of chromium in the
atmosphere originate from ferrochrome production. Ore refining, chemical and refractory
processing, cement-producing plants, automobile brake lining and catalytic converters for
automobiles, leather tanneries, and chrome pigments also contribute to the atmospheric burden of
chromium (Fishbein, 1981). Chromate chemicals used as mist inhibitors in cooling towers and
the mist formed during chrome plating are probably the primary sources of Cr(VI) emitted as
mists in the atmosphere (Towill et al., 1978).
Scarce information exists in the literature regarding the nature of the chemical species
present in the atmosphere. Under normal conditions, Cr(in) and Cr(0) in the air do not undergo
any reaction (Towill et al., 1978). Cr(VI) in the air eventually reacts with dust particles or other
pollutants to form Cr(ni) (NAS, 1974); however, the exact nature of such atmospheric reactions
has not been studied extensively. Chromium is removed from air by atmospheric fallout and
precipitation (Fishbein, 1981). The atmospheric half-life for the physical removal mechanism
depends on the particle size and particle density of atmospheric chromium. Chromium particles
of small aerodynamic diameter (< 10 |im) may remain airborne for long periods and may be
transported great distances by wind currents and diffusion forces.
Surface runoff, deposition from air, and release of municipal and industrial waste waters
are the sources of chromium in surface waters. The most significant removal mechanism for
Cr(ni) from the aquatic environment is precipitation as Cr2O3- x H2O followed by sedimentation.
Cr(VI), however, can exist in aquatic media as a water-soluble complex anion and may persist in
water for long periods. Cr(VI) is a moderately strong oxidizing agent and will react with organic
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matter or other reducing agents to form Cr(ni). Therefore, in surface water rich in organic
content, Cr(VI) will exhibit a much shorter lifetime (Callahan et al., 1979).
Chromium probably occurs as insoluble Cr2O3- x H2O in soil, given that organic matter in
soil converts soluble chromate to insoluble Cr2O3 (U.S. EPA, 1983). There is no known
chemical process that can cause chromium to be lost from soil. The primary processes by which
chromium is lost from soil are physical. For example, chromium in soil can be transported to the
atmosphere by way of dust or aerosol formation (U.S. EPA, 1983). Chromium is also
transported from soil through runoff. Runoff can remove both chromium ions and bulk
precipitates of chromium. In addition, flooding of soils and the subsequent anaerobic
decomposition of plant matter may increase dissolution of Cr2O3 in soil through complexation
(U.S. EPA, 1983). The water-soluble complexes may cause leaching of chromium from soil.
Page (1981) reported the detection of a small concentration (1 jig/L mean concentration) of
chromium at a frequency of approximately 100% in ground water collected from New Jersey.
The bioconcentration factor (BCF) for Cr(VI) in fish muscle appears to be < 1.0, but
values of 125 and 192 were obtained for oyster and blue mussel, respectively (U.S. EPA, 1980).
For Cr(IU), BCF values of 116, 153, and 86 were obtained with the American oyster, soft shell
clam, and blue mussel, respectively (U.S. EPA, 1983).
3. TOXICOKINETICS RELEVANT TO ASSESSMENTS
3.1. ABSORPTION FACTORS IN HUMANS AND EXPERIMENTAL ANIMALS
3.1.1. Oral
Based on fecal excretion of 51Cr following oral administration of 51CrCl3 to human
patients, Donaldson and Barreras (1966) estimated absorption to be approximately 0.4%. When
51CrCl3 was administered intraduodenally, absorption was not appreciably changed. In rats,
approximately 2% of the intragastric dose of CrCl3 appeared to be absorbed based on fecal
excretion of chromium. Jejunal administration only slightly increased the apparent absorption of
CrCl3 Anderson et al. (1983) confirmed the low absorption of trivalent chromium in humans
following the administration of 200 jig of Cr(UI) trichloride, and they suggested that the
absorption efficiency of trivalent chromium is dependent on dietary intake. Anderson et al.
(1986) reported that at low levels of dietary intake (10 jig) about 2% of trivalent chromium was
absorbed. When intake increases to > 40 jig, the absorption efficiency dropped to approximately
0.5%. Bunker et al. (1984) determined that elderly subjects absorbed less than 3% of trivalent
chromium ingested in the diet.
A number of animal studies confirm that trivalent chromium is poorly absorbed in the
gastrointestinal tract. Visek et al. (1953) estimated that less than 0.5% of ingested CrCl3 was
absorbed through the gastrointestinal tract of the rat. Mertz et al. (1965) estimated that rats
absorbed less than 3% of a single dose of CrCl3 by gavage. MacKenzie et al. (1959) estimated
that less than 3% of a single dose of CrCl3 by stomach tube was absorbed in rats. Ogawa (1976)
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found gastrointestinal absorption of CrCl3 to be less than 3% in rats. Henderson et al. (1979)
determined that hamsters absorbed less than 1.5% of an administered oral dose of trivalent
chromium. Furthermore, Mertz et al. (1965) reported that absorption in rats was independent of
the administered dose and dietary chromium status (deficient or supplemented in chromium) of
the animals. Cr(in) was found to be better absorbed in fasted than in fed rats (MacKenzie et al.,
1959).
3.1.2. Inhalation
A number of factors can influence the absorption of chromium following inhalation,
including the size, oxidation state and solubility of the chromium particles, the activity of
alveolar macrophages, and the interaction of chromium with biomolecules following deposition
in the lung (ATSDR, 1993). Absorption of inhaled chromium compounds following
occupational exposure has been demonstrated by the measurement of chromium in the serum and
urine and hair of workers in the chromium industry (Minoia and Cavalleri, 1988; Randall and
Gibson, 1987; Tossavainen et al., 1980). Cr(ni) is less well absorbed than Cr(VI) due to the
relative inability of Cr(ni) to cross cell membranes. However, workers exposed to Cr(ni)
lignosulfonate dust at 0.005-0.23 mg Cr(in)/m3 had detectable concentrations of chromium in the
urine at the end of the workday (Kiilunen et al., 1983).
Animal studies have shown that trivalent chromium is absorbed very slowly by
inhalation. Baetjer et al. (1959a) administered CrCl3 to guinea pigs intratracheally. Ten minutes
post-treatment, 69% of the administered dose remained in the lungs, while 4% was found in the
blood and tissues. Percentages of administered chromium found in the lungs 24 hours, 30 days,
and 60 days post-treatment were 45%, 30%, and 12%, respectively. These investigators
hypothesized that the slow absorption of trivalent chromium is due to the fact that it forms
insoluble complexes with macromolecules. Furthermore, clearance from the respiratory tract to
the gastrointestinal tract may be a factor when chromium compounds are administered by
inhalation. Visek et al. (1953) found similar results when 51CrCl3 was instilled intratracheally in
guinea pigs. In this study, absorption from the lungs was estimated to be approximately 5%. The
authors suggested that the majority of the CrCl3 was cleared from the lungs by mucociliary action
and passed through the gastrointestinal tract because 55% and 7% of the administered 51Cr had
been recovered from the feces and urine, respectively, within 7 days.
Wada et al. (1983) exposed male Sprague-Dawley strain rats to CrCl3 at an atmospheric
concentration of 14.1 mg/m3 (Cr) and observed that the chromium was associated with both high-
and low-molecular-weight proteins. The chromium that remained in the lungs was associated
with the high-molecular-weight fraction, and this fraction slowly decreased with time following
exposure. The level of chromium associated with the low-molecular-weight fraction remained
constant for the 5 days of observation following treatment; however, chromium associated with
this fraction accumulated with time in the liver. The authors suggested that the low-molecular-
weight protein may be involved in the absorption and transport of chromium following
inhalation.
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Suzuki et al. (1984) exposed rats to potassium dichromate(VI) or Cr(in) trichloride by
inhalation and determined that while lung clearance of both valence states was dependent on
particle size, Cr(VI) was absorbed with threefold greater efficiency than Cr(ni).
3.1.3. Distribution
Much work has been performed on in vivo reduction of Cr(VI) to Cr(in), and some
characterizations can be made. Ingested hexavalent chromium is efficiently reduced to the
trivalent form in the gastrointestinal tract (DeFlora et al., 1987). In the lungs, hexavalent
chromium can be reduced to the trivalent form by ascorbate and glutathione. The reduction by
ascorbate is more rapid than that by glutathione and results in a shorter residence time in the
lungs (Suzuki and Fukuda, 1990). There is no evidence that trivalent chromium is converted to
hexavalent chromium in biological systems (Amdur et al., 1993).
Once absorbed, Cr(in) compounds are cleared rapidly from the blood and more slowly
from the tissues. Hopkins (1965) injected 0.1 jig 51Cr (as chromium chloride)/!OOg
intravenously in male rats. The blood chromium content as a percentage of the blood
concentration decreased from 94% at 30 minutes to 17% in 24 hours and to 5% at 96 hours. Lim
et al. (1983) followed distribution of 51CrCl3 after intravenous administration in six adults.
Within several hours of dosing, > 50% of the chromium in plasma was distributed to the liver,
spleen, and other organs. After 3 months, the liver contained > 50% of the total body burden of
51Cr.
Visek et al. (1953) reported organ distribution of several chromium salts following
intravenous injection in rats. CrCl3 concentrated in the liver, spleen, and bone marrow; once
deposited, it cleared slowly. The liver in the CrCl3-exposed rats was the only organ to clear
significant amounts of chromium over the study period (45 days). In rats receiving
intraperitoneal administration of Cr(ni) nitrate for 30 or 60 days, the highest levels of chromium
were observed in the liver, followed by the kidneys, testes, and brain. Tissue concentration
increased nonlinearly with dose, and concentrations in the kidney increased significantly with
duration (Tandon et al., 1979). Trivalent chromium was detected only in the livers of mice
following administration of 4.8, 6.1, or 12.3 mg Cr(ni)/kg-day as chromium (in) trichloride in
drinking water for 1 year (Maruyama, 1982). Tissue concentrations were 40-90 times below
those reported following administration of hexavalent chromium in this study. MacKenzie et al.
(1958) reported that tissue concentrations of rats given Cr(ni) trichloride were ninefold lower
than those given potassium dichromate in drinking water. Sullivan et al. (1984) treated adult and
neonatal rats with an acute oral dose of radiolabeled Cr(in) trichloride. Seven days following the
dose, neonates and adults retained approximately 35% and 0.2% of the dose in the gut,
respectively. Neonates accumulated 0.12%, 0.05%, and 0.0088% in the kidney, liver, and lung,
while adults accumulated 0.003%, 0.002% and 0.0003% in the kidney, liver and lung,
respectively. Red blood cells were found to accumulate significantly more chromium than white
blood cells following intravenous administration of CrCl3 in the rat (Coogan et al., 1991).
Mice given a single intraperitoneal injection of Cr(ni) trichloride were found to have
retained 87%, 73%, and 45% of the dose on day 3, 7, and 21 post-treatment. The retention of
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chromium was attributed to the formation of trivalent chromium complexes with proteins and
amino acids (Bryson and Goodall, 1983).
Mertz (1969) studied placental transfer of a variety of chemical forms of trivalent
chromium in rats. Male and female rats fed commercial or chromium-depleted yeast diets and
drinking water with or without 2 ppb chromium were mated. Neonates whose dams were fed the
commercial diet contained nearly twice the chromium as neonates of dams fed the chromium-
deficient diet. Exposure of dams to trivalent chromium in drinking water did not increase the
chromium content of the neonates. Neonatal concentrations of chromium were not increased
following administration of CrCl3 intravenously or by gavage before, during, or after mating.
However, administration of chromium in the form of glucose tolerance factor (GIF) by gavage
during gestation resulted in levels in neonates that were 20%-50% of those in the dams.
Danielsson et al. (1982) studied placental transfer of trivalent chromium in mice following
intravenous injection of CrCl3. The highest maternal chromium concentrations were found in the
renal cortex, skeleton, liver, and ovaries. The fetal concentration of chromium was 0.4% and
0.8% of the maternal serum concentration when dams were injected in mid- and late-gestation,
respectively. Chromium accumulated in the fetal skeleton and yolk sac placenta. lijima et al.
(1983) also reported that trivalent chromium crossed the placenta of mice injected
intraperitoneally with CrCl3. Visek et al. (1953) reported that an insignificant amount of 51Cr
crossed the placenta of rats in the 24 hours following intravenous injection regardless of the
chemical form injected, the valence state, the gestational stage, or the size of the litter. In no
instance was the radioactivity measured in the fetuses greater than 0.13% of the dose. Casey and
Hembridge (1984) demonstrated that chromium can be transferred to infants through breast milk.
The breast milk of 45 lactating women was found to have a chromium content averaging 0.3
|ig/L. These concentrations were taken to represent background levels in women whose
chromium exposure occurs primarily through the diet.
Hexavalent chromium readily enters cells through the phosphate and sulfate anion-
exchange carrier pathway, although a portion may remain in plasma for an extended period
(Wiegand et al., 1985). While Cr(ni) compounds are unable to cross the cell membrane by this
pathway (Gray and Sterling, 1950), they may enter cells, but only with very low efficiency
(Lewalter et al., 1985; O'Flaherty, 1996). Hexavalent chromium is reduced to the trivalent form
intracellularly by the action of glutathione (Debetto and Luciani, 1988; Petrilli and De Flora,
1978b). Following reduction to the trivalent form, chromium may interact with cellular
macromolecules, including DNA (Wiegand et al., 1985), or may be slowly released from the cell
(Bishop and Surgenor, 1964).
A physiologically based model for chromium has recently been developed, which
incorporates absorption and disposition schemes for Cr(VI) and Cr(ni) throughout the body
(O'Flaherty, 1996). The model was calibrated on the basis of published oral and intratracheal
kinetic studies using soluble Cr(in) and Cr(VI) in the rat, and it accounts for most of the major
features of chromium kinetics in the rat, including reduction of Cr(VI) to Cr(ni). The model
suggests the following in vivo disposition for chromium. Both Cr(in) and Cr(VI) are poorly
absorbed from the lung and the gastrointestinal tract. Following inhalation exposure, chromium
may be absorbed into the systemic circulation, transferred to the gastrointestinal tract by
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mucociliary action, or remain in the lung. Cr(VI) is reduced to Cr(ni) in all tissues, including the
lung and the gastrointestinal tract. Both Cr(ni) and Cr(VI) are better absorbed from the
gastrointestinal tract in the fasted than in the fed state, and the absorption efficiency of Cr(in)
salts is largely dependent on the nutritional status of the animal as well as the nature of the anion
making up the Cr(ni) salt. The model assumes that reduction of Cr(VI) does not occur in the
plasma. Cr(VI) enters cells by the phosphate and sulfate anion-exchange carrier pathway. Cr(Tfl)
travels in the bloodstream largely bound to amino acids, other organic acids, and plasma proteins
such as globulins. The complexes of Cr(ni) which are bound to lower molecular weight ligands
are most likely to be able to traverse cell membranes (Mertz, 1969). A significant amount of
absorbed chromium is taken up in the bone (Witmer and Harris, 1991; Weber, 1983). Chromium
is also concentrated in tissues of the liver, kidney, and spleen. Once in the cell, Cr(VI) may be
reduced to Cr(in), which may subsequently interact with cellular macromolecules, including
DNA (Wiegand et al., 1985), or may be slowly released from the cell (Bishop and Surgenor,
1964).
The model suggests that the bioaccessibility of chromium to absorption processes may be
the single most important factor determining the toxicity of a specific chromium source
(O'Flaherty, 1996).
Given the rapid reduction of Cr(VI) to Cr(in) in vivo, it is relevant to consider whether
environmental exposures to Cr(VI) or administration of Cr(VI) in controlled animal experiments
is essentially identical to environmental exposures to Cr(ni) or administration of Cr(in) in
controlled experiments. While considerably more data are available for Cr(VI) than for Cr(in), it
appears at present that exposures to Cr(VI) have considerably different outcomes than exposures
to Cr(in). Cr(VI) has been shown to be more lexicologically active than Cr(ni) as it more readily
crosses cell membranes. The Agency has prepared the Toxicological Reviews and IRIS
Summaries for Cr(VI) and Cr(in) from this perspective.
3.1.4. Metabolism
Trivalent chromium potentiates the activity of insulin in vitro and in vitro. In the
biologically active form, chromium occurs in a complex referred to as GTF, tentatively identified
as a chromium-nicotinic acid complex. GTF has been suggested to operate through activation of
membrane phosphotyrosine phosphatase in mammals, although the complete structure of the
complex has not been identified (Mertz, 1993; Davis et al., 1996).
3.1.5. The Essentiality of Chromium
Cr(ni) potentiates insulin action in peripheral tissue and is essential for lipid, protein, and
fat metabolism in animals and humans. Chromium deficiency causes changes in the metabolism
of glucose and lipids and may be associated with maturity-onset diabetes, cardiovascular
diseases, and nervous system disorders (Anderson, 1993, 1995). The National Research Council
(NRC) has identified an estimated safe and adequate daily dietary intake (ESADDI) for
chromium of 50-200 |ig/day (NRC, 1989), corresponding to 0.71-2.9 |ig/kg-day for a 70 kg adult.
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The Food and Drug Administration (FDA) has selected a Reference Daily Intake for chromium
of 120 |ig/d (U.S. DHHS, 1995).
4. HAZARD IDENTIFICATION
Hexavalent chromium is widely considered to have significantly greater toxicity than the
trivalent form. This results in part from the recognition of hexavalent chromium as a known
human carcinogen by the inhalation route of exposure, from the caustic properties of many of the
hexavalent compounds, the greater absorption of the hexavalent species following exposure by
ingestion and inhalation, and the ability of hexavalent chromium to efficiently traverse cell
membranes. However, relatively few studies are available in the literature that directly address
the toxicity of trivalent chromium, particularly by the inhalation route of exposure. This lack of
data results in considerable uncertainty regarding the hazard associated with exposures to
trivalent chromium.
4.1. STUDIES IN HUMANS
4.1.1. Oral
The essential role of trivalent chromium in glucose and lipid metabolism has been widely
studied; however, only one study was located that addressed the oral toxicity of trivalent
chromium in humans. Kusiak et al. (1993) reported increased mortality due to stomach cancer in
gold miners in Ontario, Canada. Exposures to arsenic, chromium, mineral fiber, diesel
emissions, and aluminum powder were considered as possible explanations for the excess
stomach cancer. The authors found that the excess incidence of stomach cancer was best
associated with the time-weighted index of exposure to chromium in miners under the age of 60.
However, a similar association between the index of exposure to chromium and excess stomach
cancer was not seen in older gold miners in this study. Although diet is an important risk factor
in the onset of stomach cancer, the study was unable to consider the role of dietary habits in the
onset of stomach cancer in the study population. While the authors suggest that chromium or a
substance closely associated with chromium may be the causative agent for stomach cancer, the
inability to consider important confounding factors and the absence of a clear pattern of disease
incidence with increasing exposure make this association highly uncertain. The substantial
uncertainties related to the association between chromium exposure and disease incidence and
the significant confounding factors make this study unusable for risk assessment purposes.
4.1.2. Inhalation
Occupational exposure to chromium by inhalation has been studied in the chromate
manufacturing and ferrochromium industries; however, exposures all include mixed exposures to
both Cr(in) and Cr(VI). The Cr(VI) species is widely considered to be the etiologic agent in
reports of excess cancer risk in chromium workers. However, studies are inadequate to rule out a
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contribution by Cr(ni), and Cr(VI) cannot be unequivocally demonstrated to be the etiologic
agent for noncarcinogenic effects following inhalation.
Studies addressing exposures to Cr(in) alone are not available, and the role of Cr(in) in
disease following exposures to mixtures of Cr(ni) and Cr(VI) cannot be determined. Significant
reduction of Cr(VI) to Cr(in) occurs in the lungs, and absorption of Cr(ni) from lung tissue is
known to occur (O'Flaherty, 1996). In order to be comprehensive, a summary of the results of
studies involving mixed exposures to Cr(in) and Cr(VI) is presented below.
A number of epidemiologic studies have considered the association between inhalation of
chromium and noncarcinogenic endpoints, including upper respiratory irritation and atrophy,
lower respiratory effects, and systemic effects.
Bloomfield and Blum (1928) examined 23 men from six chromium plating plants in the
United States. Fourteen of these workers typically spent 2-7 hours/day over vats of chromic acid,
which generated airborne hexavalent chromium ranging from 0.12-5.6 mg/m3. These men
experienced nasal tissue damage, including perforated septum (2), ulcerated septum (3), chrome
holes (6), nosebleed (9), and inflamed mucosa (9). In general, the nine remaining workers
examined, who were not directly exposed to chromium vapors, had only inflamed mucosae. The
authors concluded that chromic acid at concentrations greater than 0.1 mg/m3 is likely to cause
nasal tissue injury. However, while no concentrations lower than 0.12 mg/m3 were observed,
injury to nasal tissue caused by lower concentrations could not be ruled out.
Machle and Gregorius (1948) reported an incidence of nasal septal perforation of 43.5%
in 354 employees who worked in a chromate-producing plant that manufactured sodium
chromate and bichromate. At the time of the study, airborne chromate concentrations ranged
from 0.1 to 2.8 mg/m3. The plant had been in operation for at least 17 years, and some
employees probably worked in the plant when reverberatory furnaces, a prominent source of high
chromate exposure, were used.
Mancuso (1951) reported on physical examinations of a random sample of 97 workers
from a chromate-chemical plant. The results indicated that 61 of the 97 workers (63%) had
septal perforation. The data suggested to the author that Cr(in) may be partly responsible for the
perforations; however, there were insufficient data to make an unequivocal conclusion.
The U.S. Public Health Service conducted a study of workers in seven
chromate-producing plants in the early 1950s. Of 897 chromate industry workers in the study,
57% were found to have a nasal septum perforation. Perforated septum was observed even in
workers employed fewer than 6 months. The study indicated that exposure to chromate results in
severe nasal tissue destruction, but exposure levels were not measured; hence, the data are of
limited usefulness for risk assessment purposes (Federal Security Agency, 1953).
Vigliani and Zurlo (1955) reported nasal septal perforation in workers exposed to
chromic acid and chromates in concentrations of 0.11 -0.15 mg/m3. The lengths of exposure were
not known. Hanslian et al. (1967) reported on otolaryngologic examinations of 77 persons
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exposed to chromic acid aerosol during chrome plating. Of those, 19% were observed to have
septal perforation and 48% to have nasal mucosal irritation. The workers averaged 6.6 years of
exposure to an airborne chromium concentration of 0.4 mg/m3. In 14 persons, papillomas of the
oral cavity and larynx were found. The diagnosis of papilloma was confirmed by histologic
examination. There were no signs of atypical growth or malignant degeneration.
Kleinfeld and Russo (1965) reported some degree of nasal septal ulceration in seven of
nine workers in a chrome-plating plant, with four of seven demonstrating frank perforations.
Analyses of air samples showed chromium concentrations of 0.18-1.4 mg/m3. Data regarding the
length of exposure and exposure concentration for individual workers were not available.
Gomes (1972) examined 303 employees who worked in 81 electroplating operations in
Sao Paulo, Brazil. Over two-thirds of the workers had mucous membrane or cutaneous lesions,
with many of them having ulcerated or perforated nasal septa. The duration of exposure was not
stated, but the author mentioned that the harmful effects were noted in under 1 year. A direct
correlation between workers exposed to a given airborne concentration of Cr(VI) and the
development of harmful effects could not be made.
Cohen and Kramkowski (1973) and Cohen et al. (1974) examined 37 workers (7 male
and 30 female) employed in the nickel-chrome department of an electroplating plant in
comparison with 21 workers (15 male and 6 female) in other areas of the plant not significantly
exposed to chromic acid. Smoking demographic data was not provided. Environmental air
samples were collected from breathing zones of several workers in the exposed and control
groups to determine concentrations of total chrome and Cr(VI). Brief medical histories were
confined to the ear, nose, throat, and cutaneous structures. Within 1 year of employment, 12
workers experienced nasal ulceration or perforation. Nasal ulcers and perforations were
associated with total chromium concentrations of 1.4 to 49.3 |ig/m3, averaging 7.1 |ig/m3, and
Cr(VI) concentrations of 0.09 to 9.1 |ig/m3, averaging 2.9 |ig/m3. Ninety-five percent of the 37
workers studied exhibited pathologic changes in nasal mucosa in a concentration-duration
response. More than half of the workers employed less than 1 year had nasal pathology that was
more severe than simple redness of the nasal mucosa. Almost all the workers (35 of 37)
employed longer than 1 year had nasal tissue damage. The authors noted the lack of good
industrial hygiene practices, implicating direct contact, such as touching of the nose with
chromium-contaminated hands, as a potentially important route of exposure.
Lucas and Kramkowski (1975) conducted a health hazard evaluation of 11 employees in
the "hard" chrome area of an industrial plating facility. The average age of the employees was 39
years, and the average duration of employment in the hard chrome area was 7.5 years. Medical
examinations were conducted to evaluate the presence of dermatitis, chrome holes, old chrome
hole scars, ulcerated nasal septum, infection of the mucosa, nasal redness, perforated nasal
septum, reddened throat, conjunctivitis, and wheezing. Environmental air samples were
collected from the breathing zone on all workers in the hard chrome area to determine the
concentrations of hexavalent chromium. Cr(VI) concentrations ranged from 1 to 20 |ig/m3,
averaging 4 |ig/m3. However, the authors attributed the nasal pathology primarily to direct
contact. Clinical observations included injection of the nasal mucosa in five workers, ulcerated
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nasal septum in two workers, atrophic scarring indicative of the presence of past ulceration in
two workers, and complete perforation of the nasal septum in four workers. Poor hygiene
practices, including touching the nose with the hand, were noted at the plant and represented a
confounding factor in the etiology of the nasal lesions.
Market and Lucas (1973) conducted a health hazard evaluation of 32 workers at a "cold
dip" chrome plating plant who were employed in the chrome department or who regularly spent a
portion of their workday in that area. Twenty of the employees worked in the chrome area of the
plant for more than 5 years. A total of 16 personal and 7 general air samples were taken to
determine the concentrations of Cr(VI). Maximum airborne Cr(VI) concentration was 3 |ig/m3.
No workers were found to have ulcerated nasal mucosa or perforated nasal septa. Half of the 32
employees had varying degrees of mucosal irritation. The authors did not consider this to be
significant, because the survey was carried out at the peak of the 1972-1973 influenza epidemic.
Lindberg and Hedenstierna (1983) compared lung function, the condition of the nasal
septum, and subjective symptoms related to respiratory health (data obtained by questionnaire) in
unexposed controls (119) and workers (43) exposed to chromic acid in chrome plating
operations. Workers were further divided into low (< 2 jig Cr[VI]/m3) and high (> 2 jig
Cr[VI]/m3) exposure groups. Complaints of diffuse nasal symptoms ("constantly running nose,"
"stuffy nose," or "a lot to blow out") were registered by 4/19 workers in the low group and half
of the 24 workers in the high group. The authors reported reddening of the nasal mucosa at 1 to
2 |ig/m3 and nasal irritation (chronic and nasal septal ulceration and perforation) in two-thirds of
the subjects at concentrations from 2 to 20 |ig/m3. All workers with nasal ulceration had been
exposed to chrome acid mist, which contained Cr(VI) at 20 |ig/m3, or greater near the baths. For
pulmonary function measurements, changes in vital capacity and forced expiratory volume at 1
second (FEY^ were seen from Cr(VI) exposures greater than 2 |ig/m3. Examination of the nasal
septum revealed that damage was significantly greater in exposed workers than in unexposed
controls and appeared to be somewhat more severe in the high group than in the low group.
There was a tendency for lung function parameters to return to normal over a 2-day weekend.
In the United States, 97 workers in chromate-producing plants had a higher incidence of
severely red throats and pneumonia, but they did not show any increase in the incidence of other
respiratory diseases when compared with control groups. Although bilateral hilar enlargement
was observed, there was no evidence of excessive pulmonary fibrosis in these workers (Federal
Security Agency, 1953). The various lung changes described in these workers may represent a
nonspecific reaction to irritating material or a specific reaction to chromium compounds. Many
of the conditions mentioned occur widely in the general population (NAS, 1974).
Lindberg and Vesterberg (1983b) studied urinary excretion of proteins in 24 currently
employed chrome platers and 27 former chrome platers. Results were compared with those for a
group of 37 referents. Exposures for current workers were determined using personal samplers
and were found to range from 2 to 20 |ig/m3, with an average level of 6 |ig/m3. Exposures of
former platers were thought to be higher than those for the current workers. The duration of
exposure ranged from < 1 to 26 years. Cr(VI) exposure was found to result in renal effects in a
dose-dependent fashion (based on elevated excretion of p-2-microglobulin as an indicator of
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nephrotoxicity) in current workers exposed to 4 to 20 |ig/m3 Cr(VI) over 8-hour shifts. The
effect may be reversible since former chrome platers did not have an elevated concentration of
either B-2-microglobulin or albumin in their urine. Most of the currently exposed workers were
also observed to have irritation symptoms of the airways, including ulcerated nasal septum and
complete perforations. Severe objective and subjective levels for the airway effects occurred at
no-observed-adverse-effect levels (NOAELs) for renal toxicity.
In another study, Saner et al. (1984) did not find increased urinary p-2-microglobulin
levels in tannery workers in comparison with referent control workers. However, comparison of
urinary chromium concentrations of the tannery workers in this study versus the chrome platers
in the Lindberg and Vesterberg (1983a,b) study suggests that the latter had distinctly higher
chromium exposures.
Exposure to vapors of chromium salts has been suspected as a cause of asthma, coughing,
wheezing, and other respiratory distress in ferrochromium workers (Langard, 1980). Novey et al.
(1983) identified chromium-specific antibodies in a 32-year-old white male worker who
experienced a productive cough, wheezing, and dyspnea within 2 weeks of beginning a new job
electroplating with chromium. Laboratory testing of this individual was performed with placebo
and nickel and chromium solutions vaporized by heat. The nickel and chromium solutions
precipitated asthmatic symptoms identical to those experienced on the job. The authors
concluded that the affected individual developed an acquired sensitivity to chromium and nickel
vapors.
Actual Cr(in) and Cr(VI) exposure levels in many of the studies attributing respiratory
effects to chromium were unknown. In addition, data on other confounding factors such as
smoking were frequently unavailable. These caveats significantly complicate determination of
the potential health effects associated with exposure to chromium.
Various other disease states have been attributed to chromium, but in most cases, the
etiologic relation to chromium is doubtful because of the presence of other chemicals (NAS,
1974). These studies, reviewed by the U.S. EPA (1984), will not be reviewed here.
4.2. PRECHRONIC AND CHRONIC STUDIES AND CANCER BIOASSAYS IN
ANIMALS—ORAL AND INHALATION
4.2.1. Chronic Oral Studies
Two oral chronic rodent bioassays of Cr(in) were located in the literature. Ivankovic and
Preussman (1975) fed 60 male and female rats (per dose group) 0%, 1%, 2%, or 5% Cr2O3, baked
in bread, 5 days/week for 600 feeding days (120 weeks). The primary purpose of this study was
to assess the carcinogenic potential of Cr2O3. The authors estimated, based on measures of food
consumption and body weight (bw), that rats consumed 360 g/kg bw, 720 g/kg bw, and 1,800
g/kg bw of total Cr2O3 over the duration of the study in the 1%, 2%, and 5% Cr2O3 feeding
groups, respectively. The animals were maintained on control diets following termination of the
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exposure until they became moribund or died. No adverse effects were noted at any feeding
level. The highest dose level (5%), which represented a total Cr2O3 consumption for 600 days of
feeding of 1,800 g/kg bw, corresponds to a total Cr(Tfl) intake of 1,232 g/kg or 1,467 mg/kg-day,
expanding exposure over 840 days (600 days at 5 days/week =120 weeks or 840 days). The lack
of toxicity given the high concentrations of trivalent chromium used in the dose groups may
reflect the poor absorption of trivalent chromium by the oral route of exposure (Visek et al.,
1953; Mertz et al., 1965; MacKenzie et al., 1959; Ogawa, 1976; Henderson et al., 1979). Cr(IH)
has been found to be better absorbed in fasted than in fed rats (MacKenzie et al., 1959). The use
of baked bread as a vehicle for dosing may have further reduced the absorption of chromium in
the Ivankovic and Preussman (1975) study.
Schroeder et al. (1965) exposed 54 male and 54 female Swiss mice to drinking water that
contained 5 ppm chromium (as chromium acetate) for life (0.46 mg Cr(ni)/kg/day). No increase
in the incidence of tumors was seen in the treated animals with respect to controls. Similar
results were obtained by Schroeder et al. (1965) for Long-Evans rats. The dose of trivalent
chromium used in this study was 2,000- to 10,000-fold lower than the dose in the Ivankovic and
Preussman (1975) study, and most likely did not approach the maximum tolerated dose (MTD).
The Schroeder et al. (1965) study is considered to be an inadequate test of carcinogenicity.
4.2.2. Subchronic Oral Studies
Several subchronic studies regarding oral exposure to trivalent chromium were located in
the literature. Akatsuka and Fairhall (1934) fed cats 50-100 mg of Cr(IH)/day for 1-3 months.
No effects on weights or gross or microscopic pathology of major organs were noted. This study
cannot be used for quantitative risk assessment since the dose and duration of exposure were not
defined precisely.
MacKenzie et al. (1958) provided rats with 25 ppm Cr(in) in drinking water for 12
months and noted no change in body weight, macroscopic or microscopic pathology, or clinical
chemistry variables. The MacKenzie et al. (1958) study suggests a no-observed-effect level
(NOEL) at 25 ppm CrCl3, equivalent to 8.2 ppm trivalent chromium. Assuming that an average
rat weighs 0.35 kg and consumes 0.035 L water/day, 8.2 ppm is adjusted to 0.82 mg trivalent
chromium/kg bw/day.
Ivankovic and Preussman (1975) fed rats baked bread containing up to 5% chromic oxide
(Cr2O3) for 90 days. The only effects observed were reductions in the absolute weights of the
livers and spleens of animals in the high-dose group, which does not necessarily represent an
adverse effect. This study suggests a NOAEL of 5% Cr2O3 (50,000 ppm), although no clear
adverse effects were observed at any dose used in the study. The authors calculated, based on
measured food consumption and body weight, that male rats in the 5% feeding group consumed
180 g/kg Cr2O3 total over the 88-day experimental period. This corresponds to 1,399 mg/kg-day
Cr(HI).
Anderson et al. (1997) fed Sprague-Dawley rats 0-100 mg/kg Cr(HI) chloride or Cr(HI)
tripicolinate (trivalent chromium coordinated with 2-carboxypyridine) in the diet for 24 weeks.
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No statistical differences in body weight or blood variables were noted among the groups
examined at 11, 17, or 24 weeks. Histological examination of the animals in the high-dose
groups did not reveal any detectable differences. Animals fed chromium picolinate were found
to have liver and kidney chromium concentrations two- to threefold greater than those fed
chromium chloride, demonstrating the higher absorption of chromium tripicolinate. No toxicity
was observed in any of the dose groups in this study.
4.2.3. Chronic Inhalation Studies
Several animal studies have been performed to assess the carcinogenic potential of Cr(in)
in the respiratory tract. Only one study was located that utilized an exposure route similar to that
expected for humans (inhalation of chromium dusts) (Baetjer et al., 1959b).
Three strains of mice (strain A, Swiss, and C57BL) were exposed to chromium-
containing dust (Baetjer et al., 1959b). These strains have, respectively, high, medium, and low
spontaneous lung tumor incidences. The dust was similar to that found in the chromium
chemical manufacturing industry, containing 13.7% Cr(VI) oxide (CrO3) and 6.9% Cr(ni) oxide
(Cr2O3), along with other metal oxides. In addition, potassium dichromate (K2Cr2O7) was added
at a level of 1%. The animals were exposed to the dust-laden atmosphere containing between 0.5
and 1 mg total chromium 4 hours/day, 5 days/week for an average of 39.7 weeks (range of 16 to
58 weeks). At death or termination of exposure, the lungs were examined by means of a low-
power microscope, and abnormal tissues were submitted for histologic confirmation of tumors.
The incidence of lung tumors was not different in exposed mice of any strain as compared
with approximately equal numbers of the appropriate controls of unexposed mice of the same
age. There was also no difference in those strains having high spontaneous tumor incidence with
regard to the average number of tumors per mouse or the percent of mice with multiple tumors.
The lung tumors present in both control and treated animals were adenomas, which appeared to
be histologically similar; however, in exposed animals, the adenomas developed slightly earlier
in the strain A mice. Three additional small groups of mice (two groups of 10 Swiss female mice
and one group of 9 female strain A mice) were exposed to high concentrations of chromium dust
(7.8 to 13 mg Cr/m3) in a nose-only chamber 0.5 hours/day, 5 days/week for 43, 52, and 20
weeks, respectively. No increase in the incidence of lung tumors was observed. It is unclear
from the report whether the MTD was achieved by the dosing regimen used in these studies.
Data on lung chromium content presented in the report indicated levels that were considerably
lower than those observed in humans exposed occupationally. Ambiguity regarding the MTD
and the variation in exposure periods used complicates the interpretation of the results.
Several studies assessed the carcinogenic potential of Cr(in) in the respiratory tract
following exposure by intratracheal introduction, intrapleural injection, or intrabronchial
implantation (Baetjer et al., 1959b; Hueper and Payne, 1962; Levy and Venitt, 1975; Levy and
Martin, 1983). These studies did not report an increased incidence of tumors following exposure
to trivalent chromium.
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Baetjer et al. (1959b) suspended a chromium dust, similar in composition to that used in
the inhalation studies, in olive oil, and zinc chromate and barium chromate in saline prior to
intratracheal introduction into strain A, Swiss, and C57BL mice and mixed-breed rats (Wistar
and McCollum stocks). The mice each received five to six installations of 0.01 to 0.05 mg
chromium at 4- to 6-week intervals, while the rats received 15 introductions at the same dose at
2-week intervals. The total duration of the studies was between 32 and 52 weeks. The mice
treated with chromium had a tumor incidence similar to age-matched controls, and the rats in
both the treated and control groups had no benign or malignant tumors.
Hueper and Payne (1962) noted that no implantation site tumors were observed in 42 rats
during a 24-month period following eight intrapleural implantations of 25 mg trivalent chromium
acetate in gelatin over a 13-month period.
The National Institute for Occupational Safety and Health (NIOSH, 1975) criteria
document on hexavalent chromium described a written communication (Levy and Venitt, 1975)
reporting the results of a study performed at the Chester Beatty Research Institute in London.
Random-bred Parton Wistar rats of both sexes received a pellet in the left inferior bronchiolus
via tracheotomy under anesthesia. The rats were kept for 2 years. One hundred rats were used in
the test group. The pellets that were implanted contained 2 mg ground chromite ore suspended
50/50 (weight/weight) in cholesterol. Negative control groups received either blank metal pellets
or pellets and vehicle. Positive control groups received 3-methylcholanthrene. The lungs of all
rats either dying during the study or killed at its termination were examined both macroscopically
and microscopically. No bronchial carcinomas of the left lung were observed in the chromite ore
test group.
Levy and Martin (1983) conducted an extensive investigation of 21 chromium-containing
test materials in Wistar rats by intrabronchial implantation of a stainless steel wire mesh pellet
containing 2 mg test material suspended in 2 mg cholesterol. The rats were allowed to live for 2
years, after which the study was terminated. No bronchial carcinomas were observed in the
group receiving high silica chrome ore (HI).
4.2.4. Subchronic Inhalation Studies
Data from subchronic animal studies identify the respiratory tract as the primary target of
chromium toxicity following inhalation. Johansson et al. (1986) exposed rabbits to aerosols of
hexavalent (0.9 mg/m3 Na2CrO4) or trivalent (0.6 mg/m3 Cr(NO3)3) chromium for 5 days/week, 6
hours/day for 4 to 6 weeks. The number of macrophages obtained from the lungs of the rabbits
exposed to Cr(VI) was significantly increased. While the numbers of macrophages from rabbits
exposed to Cr(UI) were not increased, striking morphologic changes were observed, including
round dark chromium-rich inclusions in the cytoplasm, an increased number of cells with a
smooth inactive cell surface, enlarged Golgi apparatus, and a tendency toward elongated cell
shape. The macrophages from rabbits exposed to Cr(VI) showed less marked morphologic
changes than those exposed to Cr(UI).
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Johansson et al. (1980) exposed groups of four rabbits to chromium dust at
concentrations of 3.1 mg/m3 and 0.6 mg/m3 for 5 days/week, 6 hours/day for 4 weeks.
Macrophages collected from rabbits exposed to the higher concentration of chromium
phagocytized significantly more chromium particles than the controls, although the number of
nonviable macrophages was less than 3%.
Akatsuka and Fairhall (1934) exposed two cats to chromium carbonate dust at a level that
varied from 3.3-83 mg/m3 (average = 58.3 mg/m3) for 86 sessions. Each session varied from
10-60 minutes, averaging 28 minutes for one cat and 57 minutes for the other. No effects in
terms of gross or microscopic pathology were observed upon termination of the experiment.
Examination of control animals, if there were any, was not reported.
Glaser et al. (1985) exposed 5-week-old male Wistar rats to aerosols of sodium
dichromate at concentrations ranging from 0.025 to 0.2 mg Cr(VI)/m3 22 hour/day in subacute
(28 days) or subchronic (90 days) protocols. Subacute and subchronic exposures to Cr(VI)
aerosol concentrations resulted in a positive correlation between exposure dose and significant
effects on alveolar macrophages and immunologic function. Inhaled chromium was found to
preferentially accumulate in the lung following exposure to chromate aerosols. Lung and spleen
weights were significantly increased after both subacute and subchronic inhalation of chromate
aerosols at concentrations greater than 0.025 mg/m3. Serum contents of triglycerides and
phospholipids differed significantly from controls (p < 0.05) in rats exposed sub chronically to 0.2
mg/m3 chromate. Inhalation of Cr(VI) aerosols stimulated the humoral immune system.
Differences in the mean total serum immunoglobulin were significant at exposures above 0.025
mg/m3, while exposures to aerosol concentrations greater than 0.1 mg/m3 resulted in depression
of the immune system stimulation. The primary antibody response to the B-cell-dependent
antigen sheep red blood cell was elevated in a chromium-time and dose-dependent manner. The
immune-stimulating effect of subchronic exposure to an aerosol with 0.05 mg/m3 chromium was
not reversed after 2 months of fresh air regeneration. The spleen T-lymphocyte subpopulation
was also stimulated by subchronic exposure to 0.2 mg/m3 chromium. Bronchoalveolar lavage
(BAL) cell counts were significantly decreased following subchronic exposure to levels above
0.025 mg/m3 chromium. The number of lymphocytes and granulocytes showed a slight but
significant increase in the lavage fluids of the subacute and subchronically exposed groups. At
subacute exposure concentrations up to 0.05 mg/m3, the phagocytic activity of the alveolar
macrophages increased; however, subchronic exposure at 0.2 mg/m3 decreased this function
significantly. Following subacute exposure to 0.2 mg/m3 chromium, reductions in macrophage
cell counts and phagocytic activities correlate with an observed lower clearance of inhaled iron
oxide.
Glaser et al. (1990) exposed 8-week-old male Wistar rats to sodium dichromate at 0.05,
0.1, 0.2, and 0.4 mg Cr(VI)/m3 22 hours/day, 7 days/week for 30-90 days. Chromium-induced
effects were observed to occur in a strong dose-dependent manner. The authors observed
obstructive respiratory dyspnea and reduced body weight following subacute exposure at the
higher dose levels. The mean white blood cell count was increased at all doses (p < 0.05) and
was related to significant dose-dependent leukocytosis following subacute exposures. Mean lung
weights were significantly increased at exposure levels of 0.1 mg/m3 following both the subacute
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and subchronic exposures. Accumulation of macrophages was seen in all of the exposure groups
and was postulated to be a chromium-specific irritation effect that accounted for the observed
increases in lung weights.
Focal inflammation was observed in the upper airways following the subchronic
exposure. BAL analyses provided more detailed information on the nature of the dichromate-
induced irritation effect. BAL albumin was increased following the subacute exposure and was
taken to indicate exudation into the alveolar region as an early irritation effect. The mean protein
content of the cell-free lavage fluid was significantly increased in a dose-dependent fashion after
the subacute and subchronic exposures. However, protein levels returned to control levels
following a recovery period. Cytosolic lactate dehydrogenase and the number of mononuclear
macrophages were also elevated following the subacute and subchronic exposures, particularly at
the highest dose levels. The enzyme activity and number of macrophages returned to the control
level following the recovery period. The authors concluded that chromium inhalation induced
pneumocyte toxicity and suggested that inflammation is essential for the induction of most
chromium inhalation effects and may influence the carcinogen!city of Cr(VI) compounds (Glaser
etal., 1990).
Lee et al. (1988) exposed groups of 30 male and 30 female rats to 0.5 mg/m3 or 25 mg/m3
CrO2 (IV) for 6 hours/day, 5 days/week for 2 years. Dust-laden alveolar macrophages with slight
type II pneumocyte hyperplasia were noted following exposure at 0.5 mg/m3. Inhaled particles
were deposited mainly in the alveoli adjacent to the alveolar ducts, and the dust particles
appeared as dense particles and were phagocytized by intra-alveolar macrophages. Exposure at
25 mg/m3 overwhelmed the lung clearance mechanisms and resulted in significant increases in
dust-laden macrophages, bronchioloalveolar cell hyperplasia with foamy macrophage response,
and cholesterol granuloma in females in comparison with males. Two female rats developed
well-differentiated cystic keratinizing squamous cell carcinomas with no tumor metastasis. The
tumors were not characterized as neoplastic lesions.
4.3. REPRODUCTIVE/DEVELOPMENTAL STUDIES—ORAL AND INHALATION
4.3.1. Oral Studies
No studies were located on reproductive or developmental effects in humans following
exposure to Cr(in) compounds. Male and female rats treated with 1,806 mg Cr(ni) kg/day as
Cr(ni) oxide 5 days/week for 60 days before gestation and throughout the gestation period had
normal fertility, gestational length, and litter size (Ivankovic and Preussman, 1975).
Zahid et al. (1990) fed BALB/c albino Swiss mice trivalent (chromium sulfate) and
hexavalent (potassium dichromate) chromium at concentrations of 100, 200, and 400 ppm for 35
days in the diet. The authors stated that the exposure groups included seven animals per group,
and an additional seven animals were used as controls, although the report presents conflicting
summaries of the actual group sizes throughout the report. Following the treatment, the authors
examined the testes and epididymis of the animals. The epididymis was weighed and minced
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suspended in buffered formalin. Sperm counts were then subsequently determined and sperm
were examined for morphological abnormalities. Testes were fixed with Bouin's fluid for 1
week and were subsequently sectioned to 0.6 micron thickness and stained with haematoxylin
and eosin for histologic examination. Ten sections were chosen randomly from the anterior,
middle, and posterior parts of each testis and studied. One seminiferous tubule was chosen and
examined to determine the cellular stages of spermatogenesis and the number of degenerated
tubules. Statistical analyses of the data were conducted using the t-test between means and the
2x2 contingency Chi-square test between percentages. The authors reported deleterious effects
on the male mouse testes, including ambiguous levels of degeneration in the outermost cellular
layers of the seminiferous tubules, reduced (or absence of) spermatogonia per tubule,
accumulation of germ cells in the resting spermatocytes stage, reduced sperm count in the
epididymis, and increased percentage of morphologically abnormal sperm at all chromium
sulfate dose levels. The authors concluded that the small but significant increase of hexavalent
chromium in the testes of fed animals induced significant degeneration.
Serious questions have been raised regarding the design and conduct of this study (Finley
et al., 1993; NTP, 1996a,b, 1997). The methods utilized by Zahid et al. (1990) are considered to
be insufficient to identify spermatogonia, likely generated nonreproducible counts of epididymal
sperm, and resulted in the biologically implausible conclusion of reduction in spermatogonia
numbers concurrent with unchanged spermatocyte and spermatid numbers. Additional questions
have been raised with regard to uncertainties regarding the actual groupings of animals used and
the statistical analysis of the data (Finley et al., 1993).
Elbetieha and Al-Hamood (1997) examined fertility following chromium chloride
exposures in mice. Sexually mature male and female mice were exposed to 1,000, 2,000, or
5,000 mg/L chromium chloride in drinking water for 12 weeks. The effects of the exposures on
fertility were examined at 140 days. No mortality or clinical signs of toxicity were reported in
any group of male or female mice exposed at any concentration in the experiment. The authors
reported a number of effects, although in many cases the results were not strongly dose-
dependent. The authors reported exposure of male mice to 5,000 ppm trivalent chromium
compounds for 12 weeks had adverse impacts on male fertility. Testes weights were increased in
the males exposed in the 2,000 and 5,000 mg/L dose groups, while seminal vesicle and preputial
gland weights were reduced in the 5,000 mg/L exposed males. The number of implantation sites
and viable fetuses were significantly reduced in females exposed to 2,000 and 5,000 mg/L
chromium chloride. The authors did not report the amount of water ingested by the animals,
other than to note that water ingestion was reduced in animals exposed to chromium. While the
results of this study suggest the potential presence of reproductive effects, the lack of dose
dependence in reported effects and the absence of data indicating actual exposures to the animals
preclude the use of these data in risk assessment.
4.3.2. Inhalation Studies
No studies were located on reproductive or developmental effects in humans following
exposure to Cr(in) compounds. No histopathologic abnormalities were observed in the testes of
rats exposed to 0.1 mg total chromium (as a 3:2 mixture of Cr(VI) trioxide and Cr(ni) oxide) for
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18 months (Glaser et al., 1986, 1988). No additional data regarding the teratogenicity of inhaled
trivalent chromium could not be located in the available literature.
4.4. OTHER STUDIES
4.4.1. Contact Dermatitis
Dermal exposure to chromium has been demonstrated to produce irritant and allergic
contact dermatitis (Bruynzeel et al., 1988; Polak, 1983; Cronin, 1980; Hunter, 1974). Primary
irritant dermatitis is related to the direct cytotoxic properties of chromium, while allergic contact
dermatitis is an inflammatory response mediated by the immune system. Allergic contact
dermatitis is a cell-mediated immune response that occurs in a two-step process. In the first step
(induction), chromium is absorbed into the skin and triggers an immune response (sensitization).
Sensitized individuals will illicit an allergic dermatitis response when exposed to chromium
above a threshold level (Polak, 1983). Induction is generally considered to be irreversible.
Chromium allergic dermatitis is characterized by symptoms of erythema, swelling, papules, small
vesicles, dryness, scaling, and fissuring (Adams, 1990; MacKie, 1981).
Chromium is one of the most common contact sensitizers in males in industrialized
countries (Fowler, 1990; Cronin, 1980) and is associated with occupational exposures to
numerous materials and processes, including chrome plating baths, chrome colors and dyes,
cement, tanning agents, wood preservatives, anticorrosive agents, welding fumes, lubricating oils
and greases, cleaning materials, and textiles and furs (Burrows and Adams, 1990; Polak et al.,
1973). Solubility and pH appear to be the primary determinants of the capacity of individual
chromium compounds to elicit an allergic response (Fregert, 1981; Polak et al., 1973). The low
solubility Cr(in) compounds are much less efficient contact allergens than Cr(VI) (Spruit and van
Neer, 1966). While chromium compounds have been found to elicit an allergic response in
occupational settings, this endpoint is not considered suitable for the development of a noncancer
dose-response assessment.
4.4.2. Toxicant Interactions
Ascorbic, picolinic, and nicotinic acids have all been demonstrated to facilitate the
absorption of Cr(ffl) through the intestinal wall (Anderson, 1997; ATSDR, 1993).
4.4.3. Genotoxicity
Trivalent chromium has been demonstrated to decrease the fidelity of DNA synthesis
(Snow and Xu, 1991; Snow, 1994). Trivalent chromium chloride has been shown to produce
genotoxic DNA adducts that inhibit DNA replication and are mutagenic (Snow, 1994). In
general, trivalent chromium was not mutagenic in bacterial assays when tested with or without a
mammalian activation system (Venitt and Levy, 1974; Petrilli and DeFlora, 1977, 1978a,b). In
one study, trivalent chromium was mutagenic in Baccillus subtilis, but this activity was low
compared with compounds of hexavalent chromium (Nakamuro et al., 1978).
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There is conflicting information with regard to the ability of trivalent chromium to
interact with DNA. Compounds of trivalent chromium were found to be clastogenic in BALB/c
cells as CrCl3 (Raffetto, 1977); CHO cells as CrCl3, Cr(NO3)3, KCr(SO4)2, or Cr(CH3COO)3
(Levis and Majone, 1979); Don Chinese hamster cells as hydrated CrCl3 (Ohno et al., 1982); and
cultured human leukocytes as Cr(CH3COO)3 (Nakamuro et al., 1978). However, compounds of
Cr(ni) were not clastogenic in mouse FM3A cells as Cr2(SO4)3 (Umeda and Nishimura, 1979),
cultured human leukocytes as CrCl3 or Cr(NO3)3 (Nakamuro et al., 1978), or Don Chinese
hamster cells as Cr2(SO4)3 (Ohno et al., 1982).
Cr(ni) picolinate was shown to produce chromosome damage 3- to 18-fold above the
control levels following soluble doses of 0.05, 0.1, 0.5, and 1.0 mM over a 24-hour treatment.
The chromosome damage was inferred to result from the picolinate ligand following the
demonstration of clastogenicity in the absence of Cr(in) (Stearns et al., 1995).
4.5. SYNTHESIS AND EVALUATION OF MAJOR NONCANCER EFFECTS AND
MODE OF ACTION (IF KNOWN)—ORAL AND INHALATION
4.5.1. Oral Studies
4.5.1.1. Human Studies
No human studies addressing noncarcinogenic effects of trivalent chromium were located
in the available literature.
4.5.1.2. Animal Studies
Two oral chronic rodent bioassays of Cr(in) were located in the literature. Ivankovic and
Preussman (1975) fed male and female rats up to 5% Cr2O3 baked in bread 5 days/week for 120
weeks. No adverse effects were noted at any feeding level. Schroeder et al. (1965) exposed mice
and rats to drinking water containing 5 ppm Cr(ni) for life. No increase in the incidence of
tumors was seen in the treated animals with respect to controls.
Anderson et al. (1997) evaluated the subchronic toxicity of Sprague-Dawley rats fed 0-
100 mg/kg Cr(ni) chloride or Cr(ni) tripicolinate in the diet for 24 weeks. No statistical
differences in body weight or blood variables were noted among the groups examined at 11, 17,
or 24 weeks. Histologic examination of the animals in the high-dose groups did not reveal any
detectable differences. No toxicity was observed in any of the dose groups in this study.
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4.5.2. Inhalation Studies
4.5.2.1. Human Studies
All of the available studies of occupational exposures include mixed exposures to both
Cr(ni) and Cr(VI). The Cr(VI) species has been suggested as the likely etiologic agent in reports
of excess cancer risk in chromium workers; however, Cr(VI) cannot be unequivocally
demonstrated to be the etiologic agent for noncarcinogenic effects following inhalation. While
data addressing exposures to Cr(ni) alone are not available, significant reduction of Cr(VI) to
Cr(ni) occurs in the lungs, and absorption of Cr(in) from lung tissue is known to occur (ATSDR,
1993; O'Flaherty, 1996). The following discussion presents results of studies involving mixed
exposures to Cr(ni) and Cr(VI).
4.5.2.1.1. Respiratory tract effects. Three studies on chrome platers seem to provide some
quantitative information on upper respiratory irritation after exposure to Cr(VI) as chromic acid.
Cohen et al. (1974) reported that nasal ulcers and perforations were associated with total
chromium concentrations of 1.4 to 43.9 |ig/m3, averaging 7.1 |ig/m3, and Cr(VI) concentrations
of 0.09 to 9.1 |ig/m3, averaging 2.9 |ig/m3. The authors implicated direct contact, such as
touching of the nose with chromium-contaminated hands, as a potentially important route of
exposure. Lucas and Kramkowski (1975) reported similar results following worker exposure to
Cr(VI) concentrations ranging from 1 to 20 |ig/m3, averaging 4 |ig/m3. Lindberg and
Hedenstierna (1983) also found similar effects on nasal pathology and subjective symptoms.
They reported reddening of the nasal mucosa at 1 to 2 |ig/m3, and nasal irritation (chronic and
nasal septal ulceration and perforation) in two-thirds of the subjects at concentrations from 2 to
20 |ig/m3. Changes in vital capacity and forced expiratory volume were reported following
Cr(VI) exposures greater than 2 |ig/m3.
4.5.2.1.2. Renal effects. Cr(VI) exposure as low as 4 to 6 |ig/m3 has been reported to result in
elevated excretion of p-2-microglobulin (Lindberg and Vesterberg, 1983b). The effect may be
reversible since former chrome platers did not have an elevated concentration of either
P-2-microglobulin or albumin in their urine.
In conclusion, effects on the airways and kidney have been observed in chrome platers
exposed subchronically to chromic acid mist containing chromium in air at concentrations
greater than 1 jig/m3. Such effects include reddening of nasal mucosa, nasal irritation
(ulceration, perforation), changes in pulmonary function, and renal proteinuria. Few of the
available studies, however, provide quantitative concentration-response data on chromium health
effects.
4.5.2.2. Animal Studies
In the only study specifically addressing noncarcinogenic effects by inhalation of Cr(in),
Johansson et al. (1986) exposed rabbits to aerosols of trivalent chromium (Cr(NO3)3) at
concentrations of 0.6 and 0.9 mg/m3 for 6 hours/day, 5 days/week for 4-6 weeks. Striking
morphologic changes were observed, including round dark chromium-rich inclusions in the
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cytoplasm, an increased number of cells with a smooth inactive cell surface, enlarged Golgi
apparatus, and a tendency toward elongated cell shape.
Johansson et al. (1980) exposed rabbits to chromium dust at 3.1 mg/m3 and 0.6 mg/m3 for
5 days/week, 6 hours/day for 4 weeks. Alveolar macrophages harvested from the exposed
animals phagocytized significantly more chromium particles than those harvested from controls,
although the number of nonviable macrophages was within the normal range (less than 3%)
(Johansson et al., 1980).
4.6. WEIGHT-OF-EVIDENCE EVALUATION AND CANCER CHARACTERIZATION
Applying the criteria for evaluating the overall weight of evidence for carcinogen!city to
humans outlined in EPA's Guidelines for Carcinogen Risk Assessment (U.S. EPA, 1986a),
trivalent chromium is most appropriately designated a Group D-Not classified as to its human
cartinogenicity. Using the Proposed Guidelines for Carcinogen Risk Assessment (U.S. EPA,
1996a), there are inadequate data to determine the potential carcinogenicity of trivalent
chromium. The classification of hexavalent chromium as a known human carcinogen raises a
concern for the carcinogenic potential of trivalent chromium. The inability to elucidate the
contribution of trivalent chromium to cancer incidence following exposures to total chromium
mixtures in these studies precludes a separate determination of whether trivalent chromium
alone has carcinogenic potential. Data from oral and inhalation exposures of animals to trivalent
chromium are inadequate to determine the carcinogenicity of trivalent chromium. The
International Agency for Research on Cancer (IARC, 1990) concluded that animal data are
inadequate for the evaluation of the carcinogenicity of Cr(IJJ) compounds. Furthermore,
although there is sufficient evidence of respiratory carcinogenicity associated with exposure to
chromium, the relative contributions of Cr(IJJ), Cr(VI), metallic chromium, or soluble versus
insoluble chromium to carcinogenicity cannot be elucidated.
4.7. OTHER HAZARD IDENTIFICATION ISSUES
4.7.1. Possible Childhood Susceptibility
A number of factors may differentially affect the response of children to toxicants such as
Cr(JJI). These factors include diet, physical environment, as well as maturation of physiological
and biochemical processes. At present, there is too little information to make any statements
about how these factors may specifically affect the toxicological responses of Cr(JJI) in children,
be they cancer or noncancer.
4.7.2. Possible Sex Differences
At present, there is too little information to make any statements about the extent to
which men differ from women in susceptibility to Cr(JJI) toxicity.
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5. DOSE-RESPONSE ASSESSMENTS
5.1. ORAL REFERENCE DOSE (RfD)
The RfD is based on the assumption that thresholds exist for certain toxic effects such as
cellular necrosis, but may not exist for other toxic effects such as carcinogenicity. In general, the
RfD is an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily exposure
to the human population (including sensitive subgroups) that is likely to be without an
appreciable risk of deleterious effects during a lifetime. Please refer to the Oral RfD Background
Document (on IRIS) for an elaboration of these concepts.
5.1.1. Choice of Principal Study and Critical Effect
Relatively few studies were located in the literature that addressed the oral toxicity of
Cr(ni). Ivankovic and Preussman (1975) fed rats baked bread containing up to 5% chromic
oxide (Cr2O3) for 840 days. No effects due to Cr2O3 treatment were observed at any dose level.
Ivankovic and Preussman (1975) also fed rats baked bread containing up to 5% Cr2O3 for 90
days. The only effects observed were reductions in the absolute weights of the livers and spleens
of animals in the high-dose group. The absence of toxicity of trivalent chromium following these
extraordinarily high doses likely reflect the low oral bioavailability of dietary Cr2O3.
In a subchronic study, Anderson et al. (1997) evaluated the toxicity of 0-100 mg/kg
Cr(ni) chloride and Cr(in) tripicolinate fed to Sprague-Dawley rats in the diet. Both of these
forms of chromium have considerably higher bioavailability than that of Cr2O3. Histologic
examination of the animals in the high-dose groups did not reveal any detectable differences with
controls, and no toxicity was observed in any of the dose groups in this study. Dose levels in this
study were considerably lower than those used by Ivankovic and Preussman (1975).
Elbetieha and Al-Hamood (1997) examined fertility following chromium chloride
exposures in sexually mature mice at concentrations of 1,000, 2,000, or 5,000 mg/L chromium
chloride in drinking water for 12 weeks. No mortality or clinical signs of toxicity were reported
in any group of male or female mice exposed at any concentration in the experiment. The
authors reported a number of effects on male fertility, although in many cases the results were not
strongly dose dependent. The authors also reported a reduced number of implantation sites and
viable fetuses in exposed females. The authors did not report the amount of water ingested by
the animals, other than to note that water ingestion was reduced in animals exposed to chromium.
While this study suggests the potential presence of reproductive effects, the lack of dose
dependence in reported effects and the absence of data indicating actual exposures to the animals
preclude the use of these data in risk assessment.
The Ivankovic and Preussman (1975) studies are considered to be most appropriate for
development of the RfD.
5.1.2. Methods of Analysis
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Ivankovic and Preussman (1975) fed groups of 60 male and 60 female rats chromic oxide
(Cr2O3) baked in bread at dietary levels of 0%, 1%, 2%, or 5%, 5 days/week for 600 feedings
(840 total days). Body weight and food consumption were monitored. The average total
amounts of ingested Cr2O3 were given as 360, 720, and 1,800 g/kg bw for the 1%, 2%, and 5%
treatment groups, respectively. The animals were maintained on control diets following
termination of exposure until they became moribund or died. All major organs were examined
histologically. Other toxicologic parameters were not mentioned explicitly but may have
included some or all of those described for the accompanying subchronic study (see below). No
effects due to Cr2O3 treatment were observed at any dose level.
Ivankovic and Preussman (1975) also treated rats (both sexes, 12-19 rats/group) at dietary
levels of 0%, 2%, or 5% Cr2O3 in bread, 5 days/week for 90 days. Food consumption and body
weight were monitored. Toxicologic parameters included serum protein, bilirubin, hematology,
urinalysis, organ weights, and histopathology. With the exception of reductions (12%-37%) in
the absolute weights of the livers and spleens of animals in the high-dose group, no effects could
be detected that could be attributed to the Cr2O3 treatment.
5.1.3. RfD Derivation
No effects were reported at any dose level in Ivankovic and Preussman (1975) chronic
study. The highest dose group (receiving 5% Cr2O3 in the diet for 600 feedings) can be
considered a NOAEL for the study and was selected for derivation of the reference dose. The 5%
dose group received an equivalent of 1,800 g/kg body weight. Adjustment of this dose level
based on the amount of ingested Cr(ni) (0.6849 Cr/g Cr2O3) and the feeding schedule (600
feeding days * 5 days/7 days) yields an adjusted NOAEL of 1,468 mg/kg-d. The lack of toxicity
given the high concentrations of trivalent chromium used in the dose groups may reflect the poor
absorption of trivalent chromium by the oral route of exposure (Visek et al., 1953; Mertz et
al.,1965; MacKenzie et al., 1959; Ogawa, 1976; Henderson et al., 1979). Cr(HI) has been found
to be better absorbed in fasted than in fed rats (MacKenzie et al., 1959). The use of baked bread
as a vehicle for dosing may have further reduced the absorption of chromium in the Ivankovic
and Preussman (1975) study.
The adjusted NOAEL is further modified by two 10-fold uncertainty factors to account
for the expected interspecies and interhuman variability in lieu of specific data. An additional
10-fold modifying factor is applied to reflect database deficiencies, including the lack of a study
in a nonrodent mammal, lack of unequivocal data evaluating reproductive impacts, and the
concern regarding potential reproductive effects raised by the study of Elbetieha and Al-Hamood
(1997). The following additional uncertainties relate to the NOAEL derived from the Ivankovic
and Preussman (1975) study: (1) the effects observed in the 90-day study were not explicitly
addressed in the 2-year study; (2) the effect of the vehicle (baked bread) on absorption of
chromium is uncertain, and the relevance of this dosing regimen to exposures in the environment
is unclear; and (3) animals were allowed to die naturally after exposure stopped (2 years) and
only then was histology performed. Application of the 100-fold uncertainty factor and 10-fold
modifying factor to the adjusted NOAEL of 1,468 mg/kg-d gives the reference dose of 1.5
mg/kg-d.
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5.2. INHALATION REFERENCE CONCENTRATION (RfC)
The inhalation RfC is based on the assumption that thresholds exist for certain toxic
effects such as cellular necrosis but may not exist for other toxic effects such as carcinogenicity.
In general, the RfC is an estimate (with uncertainty spanning perhaps an order of magnitude) of a
daily exposure to the human population (including sensitive subgroups) that is likely to be
without an appreciable risk of deleterious effects during a lifetime.
Studies of occupational exposure to chromium by inhalation all involve mixed exposures
to both Cr(ni) and Cr(VI). While data addressing exposures to Cr(in) alone are not available,
significant reduction of Cr(VI) to Cr(in) occurs in the lungs, and absorption of Cr(ni) from lung
tissue is known to occur (O'Flaherty, 1996). Cr(VI) cannot be unequivocally demonstrated to be
the sole etiologic agent for noncarcinogenic effects following inhalation.
Three studies on chrome platers reported upper respiratory irritation after exposure to
Cr(VI) as chromic acid. In the study of Cohen et al. (1974), nasal ulcers and perforations were
associated with total chromium concentrations of 1.4 to 43.9 |ig/m3, averaging 7.1 |ig/m3.
Ninety-five percent of the 37 workers studied exhibited pathologic changes in nasal mucosa in a
concentration-duration response. More than half of the workers employed less than 1 year had
nasal pathology that was more severe than simple redness of the nasal mucosa. Almost all
workers (35 of 37) employed longer than 1 year had nasal tissue damage. The authors implicated
direct contact, such as touching of the nose with chromium-contaminated hands, as a potentially
important route of exposure. Lucas and Kramkowski (1975) revealed similar results. Lindberg
and Hedenstierna (1983) also found similar effects on nasal pathology and subjective symptoms.
All workers with nasal ulceration had been exposed to chrome acid mist, which contained Cr(VI)
at 20 |ig/m3, or greater near the baths. Changes in vital capacity and forced expiratory volume
were seen following Cr(VI) exposures greater than 2 |ig/m3.
Only one animal study addressed exposure to Cr(ni) by inhalation. Johansson et al.
(1986) reported the results of a subchronic study in which rabbits were exposed to aerosols of
trivalent chromium (Cr(NO3)3) at concentrations of 0.6 and 0.9 mg/m3 for 6 hours/day, 5
days/week for 4-6 weeks. Striking morphologic changes were observed, including round dark
chromium-rich inclusions in the cytoplasm, an increased number of cells with a smooth inactive
cell surface, enlarged Golgi apparatus, and a tendency toward elongated cell shape. This study
utilized small groups and focused on endpoints that are not considered to be appropriate for
development of an RfC for Cr(IU).
Data are considered to be inadequate for development of an RfC due to the lack of a
relevant toxicity study addressing respiratory effects of Cr(IU). The currently available data are
inadequate to elucidate the contribution of trivalent chromium to respiratory effects observed
following occupational exposures to mixtures of trivalent and hexavalent chromium. The one
animal study that evaluated the toxicity of trivalent chromium by the inhalation route of exposure
(Johansson et al., 1986) utilized only one exposure concentration and did not identify a lowest-
observed-adverse-effect level. As a result, this study is considered inadequate to support the
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development of an RfC for trivalent chromium, and an RfC for trivalent chromium cannot be
developed at this time.
5.3. CANCER ASSESSMENT
Occupational exposure to airborne chromium has been studied in the chromate
manufacturing and ferrochromium industries; in all cases exposures all include mixed exposures
to both Cr(ni) and Cr(VI). Data addressing exposures to Cr(in) alone are not available. Cr(VI)
has been classified as a known human carcinogen, and the contribution of Cr(ni) to the observed
lung cancer in these populations cannot be elucidated from these studies. Animal data are
inadequate for the evaluation of the carcinogenicity of Cr(in) compounds. The two oral studies
located in the available literature (Schroeder et al., 1965; Ivankovic and Preussman, 1975)
reported negative results for rats and mice. Several animal studies have been performed to assess
the carcinogenic potential of Cr(in) by inhalation. These studies have not found an increased
incidence of lung tumors following exposure either by natural routes, intrapleural injection or
intrabronchial implantation (Baetjer et al., 1959b; Hueper and Payne, 1962; Levy and Venitt,
1975; Levy and Martin, 1983). For the reasons stated above, a quantitative dose-response
assessment has not been generated for Cr(in).
6. MAJOR CONCLUSIONS IN THE CHARACTERIZATION
OF HAZARD AND DOSE RESPONSE
6.1. HUMAN HAZARD POTENTIAL
Chromium is a naturally occurring element that may exist in several chemical forms and
valence states in the environment. The most commonly occurring valence states are chromium
metal (0), trivalent chromium (in), and hexavalent chromium (VI). Cr(in) potentiates the action
of insulin in peripheral tissue and is essential for animals and humans. Adults in the United
States are estimated to ingest approximately 60 |ig/day of chromium from food (ATSDR, 1993).
NRC has identified an ESADDI for chromium of 50-200 |ig/d (NRC, 1989),
corresponding to 0.71-2.9 jig/kg/day for a 70 kg adult. FDA has selected a Reference Daily
Intake for chromium of 120 |ig/d (U.S. DHHS, 1995).
The bioavailability of chromium may be the single most important factor determining the
toxicity of a specific chromium source (O'Flaherty, 1996). Ingested hexavalent chromium is
efficiently reduced to the trivalent form in the gastrointestinal tract. Gastrointestinal absorption
of Cr(VI) occurs with greater efficiency than absorption of Cr(ni), and absorption of ingested
trivalent chromium is estimated to be less than 3%. Trivalent chromium is absorbed very slowly
by inhalation. Following inhalation exposure, chromium may be absorbed into the systemic
circulation, transferred to the gastrointestinal tract by mucociliary action, or remain in the lung.
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A significant amount of absorbed chromium is taken up in the bone, liver, kidney, and
spleen. Hexavalent chromium readily crosses cell membranes through the phosphate and sulfate
anion-exchange carrier pathway. Cr(ni) compounds may cross cell membranes, but only with
very low efficiency. There is conflicting information regarding the ability of trivalent chromium
to interact with DNA. In general, trivalent chromium was not mutagenic in bacterial assays when
tested with or without a mammalian activation system.
Occupational exposure to trivalent chromium and other chromium compounds by
inhalation has been studied in the chromate manufacturing and ferrochromium industries;
however, all studies include mixed exposures to both Cr(in) and Cr(VI). While the Cr(VI)
species is the likely etiologic agent in reports of excess cancer risk in chromium workers, studies
are inadequate to rule out a contribution of Cr(ni) to chromium carcinogen!city, and data
addressing exposures to Cr(in) alone are not available.
Relatively few studies were located in the literature that addressed the oral or inhalation
toxicity of Cr(in). No effects other than reductions of the absolute weights of livers and spleens
of rats have been observed following oral exposure to Cr(Tfl). While striking morphologic
changes occurred in the macrophages of rabbits exposed to Cr(in) aerosols in the one inhalation
study of Cr(in) in animals, the database is inadequate to support development of an RfC for
Cr(HI).
Chromium is one of the most common contact sensitizers in industrialized countries, and
allergic contact dermatitis is associated with occupational exposures to numerous materials and
processes, including chrome plating baths, chrome colors and dyes, cement, leather tanning
agents, and wood preservatives.
6.2. DOSE RESPONSE
Studies of inhalation of mixtures of trivalent and hexavalent chromium in occupational
populations support the classification of Cr(VI) as a known human carcinogen but provide
inadequate data for evaluation of carcinogenicity of Cr(Tfl) compounds.
The database on noncarcinogenic effects of Cr(ni) is also lacking. Relatively few studies
were located in the literature that addressed the oral toxicity of Cr(in). Of these, the Ivankovic
and Preussman (1975) study was judged to be the only study suitable for development of an RfD
for Cr(in). The confidence in the RfD developed using the Ivankovic and Preussman (1975)
study is low. The primary purpose of the Ivankovic and Preussman (1975) study was to assess
the carcinogenic potential of Cr2O3. The confidence in the principal study is considered low
because of the lack of explicit detail on study protocol and results. No effects due to Cr2O3
treatment were observed at any dose level in this study. No macroscopic or histologic signs of
toxicity were noted in the 2-year study, although the effects observed in the 90-day study were
not explicitly addressed. Animals in this study were allowed to die naturally after exposure
stopped (2 years) and only then was histology performed. Data on potential reproductive and
developmental effects of Cr(in) are lacking. A modifying factor of 10 was applied to the
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adjusted NOAEL to account for the potential reproductive toxicity identified by the study of
Elbetieha and Al-Hamood (1997) and the absence of a credible study addressing reproductive
endpoints. The adjusted NOAEL is further modified by two 10-fold uncertainty factors to
account for the expected interspecies and interhuman variability in lieu of specific data. Only
one study was located that specifically addressed noncarcinogenic effects of Cr(in) by the
inhalation route of exposure (Johansson, 1986). While this study reported striking morphologic
changes in the macrophages of rabbits exposed to Cr(UI) aerosols, the database is inadequate to
support development of an RfC for Cr(UI). Nasal septum irritation, atrophy, and perforations
have been widely reported following mixed exposures to hexavalent and trivalent chromium in
the occupational setting. The available studies are inadequate to determine whether trivalent
chromium contributed to the observed effects.
7. REFERENCES
Adachi, S. (1987) Effect of chromium compounds on the respiratory system. Part 5. Long term
inhalation of chromic acid mist in electroplating by C57BL female mice and recapitulation on
our experimental studies. Jpn J Ind Health 29:17-33.
Adachi, S; Yoshimura, H; Katyama, H; et al. (1986) Effects of chromium compounds on the
respiratory system. Part 4. Long term inhalation of chromic acid mist in electroplating to ICR
female mice. Jpn J Ind Health 28:283-287.
Adams, RM. (1990) In: Occupational skin disease, 2nd ed. Adams, RM, ed. Philadelphia: W.B.
Saunders, pp. 26-31.
Agency for Toxic Substances and Disease Registry (ATSDR) Public Health Service, U.S.
Department of Health and Human Services. (1993) Toxicological profile for chromium. TP-
92/08. Atlanta, GA.
Akatsuka, K; Fairhall, J. (1934) The toxicology of chromium. J Ind Hyg 16:1-24.
Amdur, MO; Doull, J; Klaassen, CD. (1993) Casarett and Doull's Toxicology. New York:
McGrawHill.
Anderson, RA; Polansky, MM; Bryden, NA; et al. (1983) Effects of chromium supplementation
on urinary Cr excretion of human subjects and correlation of Cr excretion with selected clinical
parameters. J Nutr 113:276-281.
Anderson, RA. (1986) Chromium metabolism and its role in disease processes in man. Clin
Physiol Biochem 4:31-41.
Anderson, RA. (1993) Recent advances in the clinical and biochemical effects of chromium
deficiency. Prog Clin Biol Res 380:221-234.
28
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Anderson, RA. (1995) Chromium and parenteral nutrition. Nutrition 11(1 suppl.):83-86.
Anderson, RA; Bryden, NA; Polansky, MM. (1997) Lack of toxicity of chromium chloride and
chromium picolinate in rats. J Am Coll Nutr 16(3):273-279.
Baetjer, AM; Damron, C; Budacz, V. (1959a) The distribution and retention of chromium in men
and animals. Arch Ind Health 20:136-150.
Baetjer, AM; Lowney, JF; Steffee, H; et al. (1959b) Effect of chromium on incidence of lung
tumors in mice and rats. Arch Ind Health 20:124-135.
Bishop, C; Surgenor, M, eds. (1964) The red blood cell: a comprehensive treatise. New York:
Academic Press.
Bloomfield, JJ; Blum, W. (1928) Health hazards in chromium plating. Public Health Rep 43:
2330-2351.
Bruynzeel, DP; Hennipman, G; van Ketel, WG. (1988) Irritant contact dermatitis and chromium-
passivated metal. Contact Derm 19:175-179.
Bryson, WG; Goodall, CM. (1983) Differential toxicity and clearance kinetics of chromium (HI)
or (VI) in mice. Carcinogenesis 4:1535-1539.
Bunker, VW; Lawson, MS; Delves, HT. (1984) The uptake and excretion of chromium by the
elderly. Am J Clin Nutr 39:797-802.
Burrows, D; Adams, RM. (1990) In: Occupational skin disease, 2nd ed. Adams, RM, ed.
Philadelphia: W.B. Saunders, pp. 349-386.
Callahan, MA; Slimak, MW; Gabel, NW; et al. (1979) Water-related environmental fate of 129
priority pollutants. Vol. I. Office of Water Planning and Standards, Office of Water and Waste
Management, U.S. Environmental Protection Agency, Washington, DC. EPA UO/4-79-029a.
Casey, CE; Hembridge, KM. (1984) Chromium in human milk from American mothers. Br J
Nutr 52:73-77.
Cohen, SR; Kramkowski, RS. (1973) Health hazard evaluation determination, report no.
72-118-104. National Institute for Occupational Safety and Health, U.S. Department of Health,
Education, and Welfare, Cincinnati, OH.
Cohen, SR; Davis, DM; Kramkowski, RS. (1974) Clinical manifestations of chronic acid
toxicity—nasal lesions in electroplate workers. Cutis 13:558-568.
Coogan, TP; Squibb, KS; Mot, J; et al. (1991) Distribution of chromium within cells of the
blood. Toxicol Appl Pharmacol 108:157-166.
29
-------
Cotton, FA; Wilkinson, G. (1980) Advanced organic chemistry. A comprehensive text, 4th ed.
New York: John Wiley and Sons, Inc., pp. 719-736.
Cronin, E. (1980) Contact dermatitis. New York: Churchill Livingstone, pp. 287-390.
Danielsson, BRF; Hassoun, E; Dencker, L. (1982) Embryotoxicity of chromium: distribution in
pregnant mice and effects on embryonic cells in vitro. Arch Toxicol 51:233-245.
Davis, CM; Sumrall, KH; Vincent, JB. (1996) A biologically active form of chromium may
activate a membrane phosphotyrosine phosphatase (FTP). Biochemistry 35:12963-12969.
Debetto, P; Luciani, S. (1988) Toxic effect of chromium on cellular metabolism. Sci Total
Environ 71:365-377.
DeFlora, S; Badolati, GS; Serra, D; et al. (1987) Orcadian reduction of chromium in the gastric
environment. MutatRes 192:169-174.
Donaldson, RM; Barreras, RF. (1966) Intestinal absorption of trace quantities of chromium. J
Lab ClinMed 68:484-493.
Elbetieha, A; Al-Hamood, MH. (1997) Long-term exposure of male and female mice to trivalent
and hexavalent chromium compounds: effect on fertility. Toxicology 116:39-47.
Federal Security Agency. (1953) Health of workers in chromate producing industry. A study.
U.S. Public Health Service publication no. 192. Washington, DC: U.S. Government Printing
Office. 131 pp.
Finley, BL; Johnson, EM; Holson, JF. (1993) Comment on "comparative effects of trivalent and
hexavalent chromium on spermatogenesis of the mouse." Toxicol Environ Chem 39:133-137.
Fishbein, L. (1981) Sources, transport and alterations of metal compounds: an overview. I.
Arsenic, beryllium, cadmium, chromium, and nickel. Environ Health Perspect 40:43-64.
Fowler, J. (1990) Allergic contact dermatitis to metals. Am J Contact Derm l(4):212-223.
Fregert, S. (1981) Chromium valencies and cement dermatitis. Br J Dermatol 105
(suppl. 21):7-9.
Glaser, U; Hochrainer, D; Kloppel, H; et al. (1985) Low level chromium (VI) inhalation effects
on alveolar macrophages and immune functions in Wistar rats. Arch Toxicol 57: 250-256.
Glaser, U; Hochrainer, D; Kloppel, H; et al. (1986) Carcinogenicity of sodium dichromate and
chromium (VI/III) oxide aerosols inhaled by male Wistar rats. Toxicology 42:219-232.
30
-------
Glaser, U; Hochrainer, D; Oldiges, H. (1988) Investigations of the lung carcinogenic potentials
of sodium dichromate and Cr(VI/ni) oxide aerosols in Wistar rats. Environ Hyg 1:111-116.
Glaser, U; Hochrainer, D; Steinhoff, D. (1990) Investigation of irritating properties of inhaled
Cr(VI) with possible influence on its carcinogenic action. In: Environmental hygiene n.
Seemayer, NO; Hadnagy, W, eds. Berlin/New York: Springer-Verlag.
Gomes, ER. (1972) Incidence of chromium-induced lesions among electroplating workers in
Brazil. IndMed 41:21-25.
Gray, SJ; Sterling, K. (1950) The tagging of red cells and plasma proteins with radioactive
chromium. J Clin Invest 29:1604-1613.
Hanslian, L; Nauratli, J; Jurak, J; et al. (1967) Upper respiratory tract lesions from chromic acid
aerosols. Pracovni Lekar 19:294-298. (Czech., English abstr.)
Hartford, WH. (1979) Chromium compounds. In: Kirk-Othmer encyclopedia of chemical
technology, 3rd ed., vol. 6. Grayson, M; Eckroth, O, eds. New York: John Wiley and Sons, Inc.,
pp. 82-120.
Henderson, RF; Rebar, AH; Pickrell, JA; et al. (1979) Early damage indicators in the lung. in.
Biochemical and cytological response of the lung to inhaled metal salts. Toxicol Appl Pharmacol
50:123-136.
Hopkins, LL, Jr. (1965) Distribution in the rat of physiological amounts of injected Cr 51(ni) with
time. Am JPhysiol 209:731-735.
Hueper, WC; Payne, WW. (1962) Experimental studies in metal carcinogenesis—Chromium,
nickel, iron, arsenic. Arch Environ Health 5:445-462.
Hunter, D. (1974) The diseases of occupations, 5th ed. Boston: Little, Brown.
lijima, S; Matsumoto, N; Lu, C. (1983) Transfer of chromic chloride to embryonic mice and
changes in the embryonic mouse neuroepithelium. Toxicology 26:257-265.
International Agency for Research on Cancer (IARC). (1990) IARC monographs on the
evaluation of the carcinogenic risk of chemicals to humans. Vol. 49. Some metals and metallic
compounds. Lyon, France: World Health Organization.
Ivankovic, S; Preussman, R. (1975) Absence of toxic and carcinogenic effects after
administrations of high doses of chronic oxide pigment in subacute and long term feeding
experiments in rats. Food Cosmet Toxicol 13:347-351.
31
-------
Johansson, A; Lundborg, M; Hellstrom, P; et al. (1980) Effect of iron, cobalt, and chromium dust
on rabbit alveolar macrophages: a comparison with the effects of nickel dust. Environ Res
21:165-176.
Johansson, A; Wirenik, A; Jarstrand, C; et al. (1986) Rabbit alveolar macrophages after
inhalation of hexa- and trivalent chromium. Environ Res 39:372-385.
Kiilunen, M; Kivisto, H; Ala-Laurila, P. (1983) Exceptional pharmacokinetics of trivalent
chromium: tissue levels and treatment by exchange transfusion. Br J Ind Med 37:114-120.
Kleinfeld, M; Russo, A. (1965) Ulcerations of the nasal septum due to inhalation of chromic acid
mist. Ind Med Surg 34:242-243.
Kusiak, RA; Ritchie, AC; Springer, J; et al. (1993) Mortality from stomach cancer in Ontario
miners. Br J Med 50:117-126.
Langard, S. (1980) A survey of respiratory symptoms and lung function in ferrochromium and
ferrosilicon workers. International Archives of Occupational and Environmental Health. 46:1-9.
Lee, KP; Ulrich, CE; Geil, RG; et al. (1988) Effects of inhaled chromium dioxide dust on rats
exposed for two years. Fund Appl Toxicol 10:125-145.
Levis, AG; Majone, F. (1979) Cytotoxic and clastogenic effects of soluble chromium compounds
on mammalian cell cultures. Br J Cancer 40:523-533.
Levy, LS; Venitt, S. (1975) Carcinogenic and mutagenic activity of chromium-containing
materials. Br J Cancer 32:254-255.
Levy, LS; Martin, PA. (1983) The effects of a range of chromium-containing materials on rat
lung. Dye Color Manufacturers Association.
Lewalter, J; Korallus, U; Harzdorf C; et al. (1985) Chromium bond detection in isolated
erythrocytes: a new principle of biological monitoring of exposure to hexavalent chromium. Int
Arch Occup Environ Health 55:305-318.
Lim, TH; Sargent, T, IE; Kusubov, N. (1983) Kinetics of trace element chromium (in) in the
human body. Am J Physiol 244:445-454.
Lindberg, E; Hedenstierna, G. (1983) Chrome plating: symptoms, finding in the upper airways,
and effects on lung functions. Arch Environ Health 38(6):367-374.
Lindberg, E; Vesterberg, O. (1983a) Monitoring exposure to chromic acid in chromeplating by
measuring chromium in urine. Scand J Work Environ Health 9:333-340.
32
-------
Lindberg, E; Vesterberg, O. (1983b) Urinary excretion of proteins in chromeplaters,
exchromeplaters and referents. Scand J Work Environ Health 9:505-510.
Lucas, JB; Kramkowski, RS. (1975) Health hazard evaluation determination report no. 74-87-
221. Health Hazard Evaluation Branch, U.S. Department of Health, Education, and Welfare.
National Institute for Occupational Safety and Health, Cincinnati, OH.
Machle, W; Gregorius, F. (1948) Cancer of the respiratory system in the United States
chromate-producing industry. Public Health Rep 63(35): 1114-1127.
MacKenzie, RD; Byerrum, RU; Decker, CF; et al. (1958) Chronic toxicity studies, n. Hexavalent
and trivalent chromium administered in drinking water to rats. Am Med Assoc Arch Ind Health
18:232-234.
MacKenzie, RD; Anwar, RA; Byerrum, RU; et al. (1959) Absorption and distribution of 51Cr in
the albino rat. Arch Biochem Biophys 79:200-205.
MacKie, RM. (1981) Clinical dermatology. New York, Toronto: Oxford University Press.
Mancuso, TF; Hueper, WC. (1951) Occupational cancer and other health hazards in a chromate
plant: A medical appraisal. I: Lung cancer in chromate workers. Ind Med Surg 20:358-363.
Market, HL, Jr; Lucas, JB. (1973) Health hazard evaluation determination report no. 72-106.
Health Hazard Evaluation Branch, U.S. Department of Health, Education, and Welfare. National
Institute for Occupational Safety and Health, Division of Technical Services, Hazard Evaluation
Services Branch, Cincinnati, OH.
Maruyama, Y. (1982) The health effect of mice given oral administration of trivalent and
hexavalent chromium over a long term. Acta Scholae Medicinalis Universitatis in Gifu 31:24-46.
(as reported in ATSDR, 1993)
Mertz, W. (1969) Chromium occurrence and function in biological systems. Physiol Rev 49:163-
239.
Mertz, W. (1993) Chromium in human nutrition: a review. J Nutr 123:626-633.
Mertz, W; Roginski, EE; Reba, RC. (1965) Biological activity and fate of trace quantities of
intravenous chromium (IE) in the rat. Am J Physiol 209:489-494.
Minoia, C; Cavalleri, A. (1988) Chromium in the urine, serum and red blood cells in the
biological monitoring of workers exposed to different chromium valency states. Sci Total
Environ 71:213-221.
Nakamuro, K; Yoshikawa, K; Sayato, Y; et al. (1978) Comparative studies of chromosomal
aberration and mutagenicity of trivalent and hexavalent chromium. MutatRes 58:175-181.
33
-------
National Academy of Sciences (NAS). (1974) Medical and biological effects of environmental
pollutants: chromium. Washington, DC: National Academy Press.
National Institute for Occupational Safety and Health (NIOSH). (1975) Criteria for a
recommended standard—occupational exposure to chromium (VI). U.S. Department of Health,
Education, and Welfare, Washington, DC.
National Research Council. (1989) Recommended dietary allowances. 10th ed. Washington, DC:
National Academy of Sciences, pp. 241-243.
National Toxicology Program (NTP), Public Health Service, U.S. Department of Health and
Human Services. (1996a) Final report. Potassium dichromate (hexavalent): the effects of
potassium dichromate on Sprague-Dawley rats when administered in the diet. December 13,
1996. Available from: National Institute of Environmental Health Sciences, Research Triangle
Park, NC.
NTP, Public Health Service, U.S. Department of Health and Human Services. (1996b) Final
report. Potassium dichromate (hexavalent): the effects of potassium dichromate in BALB/c mice
when administered in the diet. November 27, 1996. Available from National Institute of
Environmental Health Sciences, Research Triangle Park, NC.
NTP, Public Health Service, U.S. Department of Health and Human Services. (1997) Final
report. Potassium dichromate (hexavalent): reproductive assessment by continuous breeding
when administered to BALB/c mice in the diet. February 18, 1997. Available from: National
Institute of Environmental Health Sciences, Research Triangle Park, NC.
Nettesheim, P; Hanna, MG, Jr.; Doherty, DG; et al. (1971) Effect of calcium chromate dust,
influenza virus, and 100 R wholebody X-radiation on lung tumor incidence in mice. J Natl
Cancer Inst 47:1129-1144.
Novey, HS; Habib, M; Wells, IO. (1983) Asthma and IgE antibodies induced by chromium and
nickel salts. J Allergy Clin Immunol 72(4):407-412.
O'Flaherty, EJ. (1996) A physiologically-based model of chromium kinetics in the rat. Toxicol
Appl Pharmacol 138:54-64.
Ogawa, E. (1976) Experimental study on absorption, distribution and excretion of trivalent and
hexavalent chromes. Jap J Pharmacol 26:92.
Ohno, H; Hanaoka, F; Yanada, M. (1982) Inducibility of sister-chromatid exchanges by heavy
metal ions. MutatRes 104:141-145.
Page, GW. (1981) Comparison of ground water and surface water for patterns and levels of
contaminants by toxic substances. Environ Sci Technol 15:1475-1481.
34
-------
Petrilli, FL; DeFlora, S. (1977) Toxicity and mutagenicity of hexavalent chromium on
Salmonella typhimurium. Appl Environ Microbiol 33:805-809.
Petrilli, F; DeFlora, S. (1978a) Oxidation of inactive trivalent chromium to the mutagenic
hexavalent form. Mutat Res 58:167-178.
Petrilli, FL; DeFlora, S. (1978b) Metabolic deactivation of hexavalent chromium mutagenicity.
Mutat Res 54:139-147.
Polak, L. (1983) Immunology of chromium. In: Chromium: metabolism and toxicity. Burrows,
D, ed. Boca Raton, FL: CRC Press, pp. 51-135.
Polak, L; Turk, JL; Frey, FR. (1973) Studies on contact hypersensitivity to chromium
compounds. Prog Allergy 17:145-219.
Raffetto, G. (1977) Direct interaction with cellular targets as the mechanism for chromium
carcinogenesis. Tumorigenesis 63:503-512.
Randall, JA; Gibson, RS. (1987) Serum and urine chromium as indices of chromium status in
tannery workers. Proc Soc Exp Biol Med 185:16-23.
Saner, G; Yuzbasiyan, V; Cigdem, S. (1984) Hair chromium concentration and chromium
excretion in tannery workers. Br J Ind Med 41:263-266.
Schroeder, HA; Balassa, JJ; Vinton, WH, Jr. (1965) Chromium, cadmium and lead in rats:
effects on lifespan, tumors, and tissue levels. J Nutr 86:51-66.
Snow, ET. (1994) Effects of chromium on DNA replication in vitro. Environ Health Perspect
102(suppl. 3):41-44.
Snow, ET; Xu, L-S. (1991) Chromium(ni) bound to DNA templates enhances DNA polymerase
processivity during replication in vitro. Biochemistry 30:11238-11245.
Spruit, D; vanNeer, FCJ. (1966) Penetration rate of Cr(IH) and Cr(VI). Dermatological 132:179-
182.
Stearns, DM; Wise, JP, Sr; Patierno, SR; et al. (1995) Chromium(IU) picolinate produces
chromosome damage in Chinese hamster ovary cells. FASEB J 9:1643-1648.
Sullivan, MF; Miller, BM; Goebel, JC. (1984) Gastrointestinal absorption of metals (51Cr, 65Zn,
95mTc, 109Cd, 113Sn, 147Pm and 238Pu) by rats and swine. Environ Res 35:439-453.
Suzuki, Y; Homma, K; Minami, M; et al. (1984) Distribution of chromium in rats exposed to
hexavalent chromium and trivalent chromium aerosols. Ind Health 22:261-267.
35
-------
Suzuki, Y; Fukuda, K. (1990) Reduction of hexavalent chromium by ascorbic acid and
glutathione with special reference to the rat lung. Arch Toxicol 64:169-176.
Tandon, SK; Behari, JR; Kachru, DN. (1979) Distribution of chromium in poisoned rats.
Toxicology 13:29-34.
Tossavainen A; Nurminen, P; Mutanen, P. (1980) Application of mathematical modeling for
assessing the biological half-times of chromium and nickel in field studies. Br J Ind Med 37:285-
291.
Towill, LE; Shriner, CR; Drury, JS; et al. (1978) Reviews of the environmental effects of
pollutants, ni. Chromium. Prepared by the Health Effects Research Laboratory, Office of
Research and Development, U.S. Environmental Protection Agency, Cincinnati, OH. Report No.
ORNL/EIS-80. EPA 600/1-78-023. NTIS PB 282796.
Umeda, M; Nishimura, M. (1979) Inducibility of chromosomal aberrations by metal compounds
in cultured mammalian cells. MutatRes 67:221-229.
U.S. Department of Health and Human Services, Food and Drug Administration. (1995, Dec. 28)
Food labeling: reference daily intakes, final rule. Federal Register 60(249):67164-67175.
U.S. EPA. (1980) Ambient water quality criteria for chromium. Environmental Criteria and
Assessment Office, Cincinnati, OH. EPA/440/5-80-035. NTIS P8 81-117467.
U.S. EPA. (1983) Health assessment document for chromium. Prepared by the Environmental
Criteria and Assessment Office, Research Triangle Park, NC. External review draft.
EPA/600/8-83-014A. NITS PB 83-252205.
U.S. EPA. (1984) Health assessment document for chromium. Environmental Criteria and
Assessment Office Research Triangle Park, NC. EPA/600/8-83-014F. NTIS PB 85-115905.
U.S. EPA. (1986a) Guidelines for carcinogen risk assessment. Federal Register 51(185):33992-
34003.
U.S. EPA. (1986b) Guidelines for the health risk assessment of chemical mixtures. Federal
Register 51(185):34014-34025.
U.S. EPA. (1986c) Guidelines for mutagenicity risk assessment. Federal Register 51(185):34006-
34012.
U.S. EPA. (1988) Recommendations for and documentation of biological values for use in risk
assessment. Environmental Criteria and Assessment Office, Cincinnati, OH. EPA/600/6-87/008,
NTIS PB88-179874/AS, February 1988.
36
-------
U.S. EPA. (1991) Guidelines for developmental toxicity risk assessment. Federal Register
56(234):63798-63826.
U.S. EPA. (1994a) Interim policy for particle size and limit concentration issues in inhalation
toxicology: notice of availability. Federal Register 59(206):53799.
U.S. EPA. (1994b) Methods for derivation of inhalation reference concentrations and application
of inhalation dosimetry. Office of Health and Environmental Assessment, Environmental Criteria
and Assessment Office, Research Triangle Park, NC. EPA/600/8-90/066F.
U.S. EPA. (1994c) Peer review and peer involvement at the U.S. Environmental Protection
Agency. Signed by the U.S. EPA Administrator Carol M. Browner, dated June 7, 1994.
U.S. EPA. (1995a) Proposed guidelines for neurotoxicity risk assessment. Federal Register
60(192):52032-52056.
U.S. EPA. (1995b) Use of the benchmark dose approach in health risk assessment. Office of
Research and Development, Washington, DC. EPA/630/R-94/007.
U.S. EPA. (1996a) Proposed guidelines for carcinogen risk assessment. Federal Register
61(79):17960-18011.
U.S. EPA. (1996b) Reproductive toxicity risk assessment guidelines. Federal Register
61(212):56274-56322.
U.S. EPA. (1998) Science policy council handbook: peer review. Prepared by the Office of
Science Policy, Office of Research and Development, Washington, DC. EPA/100/B-98-001.
Venitt, S; Levy, LS. (1974) Mutagenicity of chromates in bacteria and its relevance to chromate
carcinogenesis. Nature 250:493-495.
Vigliani, EC; Zurlo, N. (1955) Efahrung der Clinica del Lavoro mit einigen maximalen
Arbitsplatzkonzentrationen (MAK) von Industriegiften. Arch Gewerbepath Gewerbhyg
13:528-534. (Ger.)
Visek, WJ; Whitney, IB; Kuhn, USG, HI; et al. (1953) Metabolism of CR-51 by animals as
influenced by chemical state. Proc Soc Exp Biol Med 84:610-615.
Wada, O; Manabe, S; Yamaguchi, N; et al. (1983) Low-molecular -weight, chromium-binding
substance in rat lungs and its possible role in chromium movement. Indust Health 21:35-41.
Weber, H. (1983) Long-term study of the distribution of soluble chromate-51 in the rat after a
single intratracheal administration. J Toxicol Environ Health 11, 749-764.
37
-------
Wiegand, HJ; Ottenwalder, H; Bolt, HM. (1985) Fast uptake kinetics in vitro of 51Cr(VI) by red
blood cells of man and rat. Arch Toxicol 57:31-34.
Witmer, CM; Harris, R. (1991) Chromium content of bone after oral and intraperitoneal (IP)
administration of chromium (VI) to rats. Toxicologist 11:41. (Abstract)
Zahid, ZR; Al-Hakkak, ZS; Kadhim, AHH; et al. (1990) Comparative effects of trivalent and
hexavalent chromium on spermatogenesis of the mouse. Toxicol Environ Chem 25:131-136.
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APPENDIX A. EXTERNAL PEER REVIEW-
SUMMARY OF COMMENTS AND DISPOSITION
The support document and IRIS summary for trivalent chromium have undergone both
internal peer review performed by scientists within EPA and a more formal external peer review
performed by scientists in accordance with EPA guidance on peer review. Comments made by
the internal reviewers were addressed prior to submitting the documents for external peer review
and are not part of this appendix. The external peer reviewers were tasked with providing written
answers to general questions on the overall assessment and on chemical-specific questions in
areas of scientific controversy or uncertainty. A summary of significant comments made by the
external reviewers and EPA's response to these comments follows.
Comments on General Questions
1. Are you aware of any other data/studies that are relevant (i.e., useful for the hazard
identification or dose-response assessment) for the assessment of the adverse health effects,
both cancer andnoncancer, of this chemical?
A. Comment: A new report has been found showing significant embryotoxic and fetotoxic
damage due to exposure of rats and mice to high doses of Cr(VI) or Cr(in) in drinking water. I
don't feel confident rederiving an RfD based on these data, and the doses are clearly very high.
However, derivation of an RfD based on an observed toxicological effect appears to be
preferable to an RfD based on a NOAEL.
Response to Comment: The report has been added to the reproductive/developmental
studies section of the toxicological review document. The study reports on a variety of
embryotoxic and fetotoxic endpoints; however, many of the observed effects did not occur in a
clear dose-dependent fashion. Further, the authors did not indicate the amount of water ingested
by the animals and only stated that water ingestion was reduced in the treatment groups relative
to the controls. This omission precludes determination of the actual doses experienced by the
treated animals. This study is not considered to be sufficient for development of the RfD for
Cr(HI).
B. Comment: The study by Baetjer et al. (1959b) needs some more discussion regarding the
question as to whether the MTD has been achieved in this particular study. From the published
paper there is no indication that, indeed, the animals had been sufficiently dosed, and it is
therefore questionable whether this study should be labeled an adequate carcinogenicity study.
Response to Comment: The discussion has been added to the text.
C. Comment: The documents correctly state that Cr(VI) gets transformed to Cr(in) in vivo, but
they skirt the issue of whether or not a Cr(VI) study is really a study of in vivo exposure to
Cr(HI).
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Response to Comment: Given the rapid reduction of Cr(VI) to Cr(ni) in vitro, it is
relevant to consider whether environmental exposures to Cr(VI) or administration of Cr(VI) in
controlled animal experiments is essentially identical to environmental exposures to Cr(in) or
administration of Cr(in) in controlled experiments. While considerably more data are available
for Cr(VI) than for Cr(in), it appears at present that exposures to Cr(VI) have considerably
different outcomes than exposures to Cr(in). The Agency has prepared the Toxicological
Reviews and IRIS files for Cr(VI) and Cr(in) from this perspective.
2. For the RfD andRfC, has the most appropriate critical effect been chosen (i.e., that adverse
effect appearing first in a dose-response continuum)? For the cancer assessment, are the
tumors observed biologically significant? Relevant to human health? Points relevant to this
determination include whether or not the choice follows from the dose-response assessment,
whether the effect is considered adverse, and if the effect (including tumors observed in the
cancer assessment) and the species in which it is observed is a valid model for humans.
A. Comment: I believe the Agency is a bit conservative regarding the confidence of the RfD.
The Ivankovic and Preussman (1975) study appears to be done according to acceptable practices
at the time. I also take issue with the modifying factors. The Agency used a modifying factor of
10 to reflect uncertainty in the database. I disagree with the speculation that the NOAEL could
be a LOAEL. The fact that uptake is low and variable does not justify such a high uncertainty
factor, and the fact that the animals died naturally if anything would tend to increase disease
incidence rates. I believe a threefold modifying factor is sufficient. I would also note that the
authors arbitrarily dropped the RfD by an additional 1/3 by rounding down from 1.468 to 1. A
more realistic estimate might be 1,468/300 = 5 mg/kg-day.
Response to Comment: In order to be conservative regarding the limited database on
Cr(ni), the Agency supports the use of a 10-fold modifying factor to reflect uncertainty in the
database, including uncertainty resulting from the deficiencies in the database addressing
potential reproductive and developmental effects. The speculation that the NOAEL could be a
LOAEL has been removed from the document. The RfD has been rounded to 1.5.
B. Comment: In consideration of uncertainties surrounding the critical study for the RfD, such
as the appropriateness of the method of administration (in baked bread, which might be expected
to have a lesser bioavailability than if administered in feed or water), the use/application of a
modifying factor of 3 (reducing the RfD to about 0.3 mg/kg-day) seems appropriate.
Response to Comment: The derivation of the RfD using the data of Ivankovic and
Preussman (1975) incorporated a 10-fold uncertainty factor to account for uncertainties in the
study, including the likely low absorption of chromium from the baked bread. The Agency
considers the current uncertainty factors to be sufficient for development of the RfD.
3. Have the noncancer and cancer assessments been based on the most appropriate studies?
These studies should present the critical effect/cancer (tumors or appropriate precursor) in
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the clearest dose-response relationship. If not, what other study (or studies) should be
chosen and why?
A. Comment: The RfC should be for total chromium since it is not clear that soluble chromium
species make up all of the hexavalent chromium species in the mixture, nor that insoluble
chromium species consist solely of trivalent species. Furthermore, the data suggest that there
might be a positive interaction between the two forms of chromium and that the risk for exposure
to a mixture is not the sum (or average) of the risks from either species. However, the available
data do not provide any evidence that trivalent chromium alone is toxic by inhalation. The data
are inconclusive with regard to inhalation exposure to trivalent chromium.
Response to Comment: Considerable data are available regarding the effects of
inhalation of hexavalent chromium in the form of chromic acid mists and hexavalent chromium
particulates. The limited data available for trivalent chromium suggest that this compound may
behave essentially as a nuisance dust upon inhalation. The Agency considers the data to be
insufficient to support the application of the RfCs derived for hexavalent chromium to the
trivalent species.
4. Studies included in the RfD and RfC under the heading "Supporting/Additional Studies " are
meant to lend scientific justification for the designation of critical effect by including any
relevant pathogenesis in humans, any applicable mechanistic information, any evidence
corroborative of the critical effect, or to establish the comprehensiveness of the database
with respect to various endpoints (such as reproductive/developmental toxicity studies).
Should other studies be included under the "Supporting/Additional" category? Should some
studies be removed?
A. Comment: Some of the statements related to the genotoxic effects of trivalent chromium are
either inaccurate or misleading.
Response to Comment: The recommended modifications to this section have been made.
B. Comment: The new data on reproductive toxicity of chromium in the drinking water needs
to be carefully compared to the NTP study in which rats and mice were fed potassium chromate
in the diet. The form of chromium and route of exposure are clearly of paramount importance.
Response to Comment: A discussion comparing and contrasting the results of the NTP
studies and the new report has been added to the reproductive/developmental studies section of
the Toxicological Review document. The report of Elbetieha and Al-Hamood (1997) raises the
possibility of reproductive effects at very high doses, but the observed endpoints do not show a
clear dose response, and the authors did not provide the data on drinking water ingestion required
to determine the doses experienced by the treatment groups. This study is not considered
sufficient for development of the RfD.
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5. For the noncancer assessments, are there other data that should be considered in developing
the uncertainty factors or the modifying factor? Do you consider that the data support the
use of different (default) values than those proposed?
A. Comment: The appropriate data have been considered in developing the uncertainty factors
and the modifying factor.
6. Do the confidence statements andweight-of-evidence statements present a clear rationale
and accurately reflect the utility of the studies chosen, the relevancy of the effects (cancer
and noncancer) to humans, and the comprehensiveness of the database? Do these statements
make sufficiently apparent all the underlying assumptions and limitations of these
assessments? If not, what needs to be added?
A. Comment: The evidence for the role or lack of role of trivalent chromium in human cancer
is not convincingly presented. In particular the lack of effect of feeding rats chromium-laden
bread is not balanced by any demonstration of chromium uptake in the animals.
Response to Comment: The Toxicological Review document concludes that there are
inadequate data to determine the potential carcinogenicity of trivalent chromium. This should
not be construed as a conclusion that trivalent chromium is not carcinogenic.
Comments on Chemical-Specific Questions
1. Are the conclusions ofZahid et al. (1990) regarding potential reproductive toxicity ofCr(III)
in any way countered by the results of the NTP study?
A. Comment: If NTP was not able to reproduce Zahid's results, I do not believe Zahid's results
should be considered.
B. Comment: The Zahid et al. studies are supported, but in a more realistic fashion by the
studies of Juniad and Kanojia.
Response to Comments: The studies of Zahid et al. (1990) and Juniad et al. and Kanojia
et al. (1996) did not involve common endpoints. The NTP study was unable to repeat the
findings of Zahid et al. The results of Juniad and Kanojia provide evidence of reproductive and
fetotoxic effects of Cr(VI) at high doses but do not support the findings of Zahid et al. regarding
toxicity of Cr(IH).
C. Comment: Additional description should be provided regarding the report of Zahid et al. in
relation to the NTP study.
Response to Comment: Additional description has been added.
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2. Are there any studies available which could be used to develop an RfCfor trivalent
chromium?
A. Comment: I agree with the document that there are no adequate data for Cr(ni).
B. Comment: I agree with EPA's assessment that there are no suitable data sets to use in
calculating an RfC for airborne Cr(in).
Response to Comments: An RfC for airborne Cr(in) has not been developed.
3. The principal study (Mancuso, 1975) and the follow-up study (Mancuso, 1997) show the best
dose-response relationship for total chromium, but animal data only support a conclusion of
carcinogenicity ofhexavalent chromium. Should the potency estimate address total
chromium or hexavalent chromium?
A. Comment: Mancuso alleges that his data support a conclusion that both Cr(in) and Cr(VI)
are carcinogens. His data set is very small, and in my view, it lacks the power to distinguish
between Cr(VI) and total chromium. The animal data present a convincing story that Cr(ni) is
not carcinogenic. Hence, I believe the potency estimates should address only hexavalent
chromium. EPA should be more explicit as to why they discount Mancuso's allegation.
Response to Comment: Additional commentary has been added to the section addressing
the conclusion that only Cr(VI) is known to be carcinogenic by the inhalation route of exposure.
B. Comment: The potency estimate should be based on total chromium but should note that the
exposure is mixed (and give the relative proportions of Cr(in) and Cr(VI) to which the workers
were exposed). Although it is probably true that the carcinogenicity is due to the hexavalent
chromium, the finding that trivalent chromium can be taken up by the aveolar macrophages could
imply that the carcinogenic process may be modulated by the presence of trivalent chromium.
Response to Comment: The Agency acknowledges that the cohort was occupationally
exposed to mixtures of trivalent and hexavalent chromium, and agrees that it is probably true that
the carcinogenicity is due to the hexavalent chromium. The ratio of trivalent and hexavalent
chromium in the mixture have been provided. However, the Agency considers the data on
carcinogenicity of trivalent chromium to be insufficient to support a conclusion that trivalent
chromium contributed to the cancer observed in the cohort. The Agency concluded that Cr(VI) is
known to be carcinogenic in humans and that data are insufficient to form a conclusion regarding
the potential carcinogenicity of trivalent chromium.
C. Comment: It is obvious that based on the human data hexavalent chromium is a Group A
carcinogen. However, because of the insufficient data, a contribution of the trivalent chromium
cannot be ruled out since the workers are always exposed to a mixture of both chromium types.
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Response to Comment: The Toxicological Review document concludes that there are
insufficient data to determine whether trivalent chromium is a carcinogen. This conclusion
should not be misconstrued as ruling out a role for trivalent chromium in carcinogenicity.
4. There is a Canadian study that relates stomach cancer to gold mining follow ing exposures to
chromium. Does this study justify/support determination of an oral factor for chromium?
A. Comment: No.
Response to Comment: The Canadian study has not been used to develop an oral slope
factor for chromium.
REFERENCES
Junaid, M; Murthy, RC; Saxena, DK. (1996) Embryotoxicity of orally administered chromium in
mice: Exposure during the period of organogenesis. Toxicol Lett 84:143-148.
Kanojia, RK; Junaid, M; Murthy, RC. (1996) Chromium induced teratogenicity in female rat.
Toxicol Lett 89:207-213.
Mancuso, TF. (1975) International Conference on Heavy Metals in the Environment, Toronto, CN,
Oct. 27-31.
Mancuso, TF. (1997) Chromium as an industrial carcinogen: Part 1. Am J Ind Med 31:129-139.
Zahid, ZR; Al-Hakkak, ZS; Kadhim, AHH; et al. (1990) Comparative effects of trivalent and
hexavalent chromium on spermatogenesis of the mouse. Toxicol Environ Chem 25:131-136.
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