United States
Environmental Protection
1=1 m m Agency
EPA/690/R-08/023F
Final
4-30-2008
Provisional Peer Reviewed Toxicity Values for
Vanadium pentoxide
(CASRN 1314-62-1)
Superfund Health Risk Technical Support Center
National Center for Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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Acronyms and Abbreviations
bw
body weight
cc
cubic centimeters
CD
Caesarean Delivered
CERCLA
Comprehensive Environmental Response, Compensation and Liability Act
of 1980
CNS
central nervous system
cu.m
cubic meter
DWEL
Drinking Water Equivalent Level
FEL
frank-effect level
FIFRA
Federal Insecticide, Fungicide, and Rodenticide Act
g
grams
GI
gastrointestinal
HEC
human equivalent concentration
Hgb
hemoglobin
i.m.
intramuscular
i.p.
intraperitoneal
IRIS
Integrated Risk Information System
IUR
inhalation unit risk
i.v.
intravenous
kg
kilogram
L
liter
LEL
lowest-effect level
LOAEL
lowest-observed-adverse-effect level
LOAEL(ADJ)
LOAEL adjusted to continuous exposure duration
LOAEL(HEC)
LOAEL adjusted for dosimetric differences across species to a human
m
meter
MCL
maximum contaminant level
MCLG
maximum contaminant level goal
MF
modifying factor
mg
milligram
mg/kg
milligrams per kilogram
mg/L
milligrams per liter
MRL
minimal risk level
MTD
maximum tolerated dose
MTL
median threshold limit
NAAQS
National Ambient Air Quality Standards
NOAEL
no-ob served-adverse-effect level
NOAEL(ADJ)
NOAEL adjusted to continuous exposure duration
NOAEL(HEC)
NOAEL adjusted for dosimetric differences across species to a human
NOEL
no-ob served-effect level
OSF
oral slope factor
p-IUR
provisional inhalation unit risk
p-OSF
provisional oral slope factor
p-RfC
provisional inhalation reference concentration
p-RfD
provisional oral reference dose
1
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PBPK
physiologically based pharmacokinetic
ppb
parts per billion
ppm
parts per million
PPRTV
Provisional Peer Reviewed Toxicity Value
RBC
red blood cell(s)
RCRA
Resource Conservation and Recovery Act
RDDR
Regional deposited dose ratio (for the indicated lung region)
REL
relative exposure level
RfC
inhalation reference concentration
RfD
oral reference dose
RGDR
Regional gas dose ratio (for the indicated lung region)
s.c.
subcutaneous
SCE
sister chromatid exchange
SDWA
Safe Drinking Water Act
sq.cm.
square centimeters
TSCA
Toxic Substances Control Act
UF
uncertainty factor
Hg
microgram
|j,mol
micromoles
voc
volatile organic compound
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PROVISIONAL PEER REVIEWED TOXICITY VALUES FOR
VANADIUM PENTOXIDE (CASRN 1314-62-1)
Background
On December 5, 2003, the U.S. Environmental Protection Agency's (EPA's) Office of
Superfund Remediation and Technology Innovation (OSRTI) revised its hierarchy of human
health toxicity values for Superfund risk assessments, establishing the following three tiers as the
new hierarchy:
1. EPA's Integrated Risk Information System (IRIS).
2. Provisional Peer-Reviewed Toxicity Values (PPRTV) used in EPA's Superfund
Program.
3. Other (peer-reviewed) toxicity values, including:
~ Minimal Risk Levels produced by the Agency for Toxic Substances and Disease
Registry (ATSDR),
~ California Environmental Protection Agency (CalEPA) values, and
~ EPA Health Effects Assessment Summary Table (HEAST) values.
A PPRTV is defined as a toxicity value derived for use in the Superfund Program when
such a value is not available in EPA's Integrated Risk Information System (IRIS). PPRTVs are
developed according to a Standard Operating Procedure (SOP) and are derived after a review of
the relevant scientific literature using the same methods, sources of data and Agency guidance
for value derivation generally used by the EPA IRIS Program. All provisional toxicity values
receive internal review by two EPA scientists and external peer review by three independently
selected scientific experts. PPRTVs differ from IRIS values in that PPRTVs do not receive the
multi-program consensus review provided for IRIS values. This is because IRIS values are
generally intended to be used in all EPA programs, while PPRTVs are developed specifically for
the Superfund Program.
Because new information becomes available and scientific methods improve over time,
PPRTVs are reviewed on a five-year basis and updated into the active database. Once an IRIS
value for a specific chemical becomes available for Agency review, the analogous PPRTV for
that same chemical is retired. It should also be noted that some PPRTV manuscripts conclude
that a PPRTV cannot be derived based on inadequate data.
Disclaimers
Users of this document should first check to see if any IRIS values exist for the chemical
of concern before proceeding to use a PPRTV. If no IRIS value is available, staff in the regional
Superfund and RCRA program offices are advised to carefully review the information provided
in this document to ensure that the PPRTVs used are appropriate for the types of exposures and
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circumstances at the Superfund site or RCRA facility in question. PPRTVs are periodically
updated; therefore, users should ensure that the values contained in the PPRTV are current at the
time of use.
It is important to remember that a provisional value alone tells very little about the
adverse effects of a chemical or the quality of evidence on which the value is based. Therefore,
users are strongly encouraged to read the entire PPRTV manuscript and understand the strengths
and limitations of the derived provisional values. PPRTVs are developed by the EPA Office of
Research and Development's National Center for Environmental Assessment, Superfund Health
Risk Technical Support Center for OSRTI. Other EPA programs or external parties who may
choose of their own initiative to use these PPRTVs are advised that Superfund resources will not
generally be used to respond to challenges of PPRTVs used in a context outside of the Superfund
Program.
Questions Regarding PPRTVs
Questions regarding the contents of the PPRTVs and their appropriate use (e.g., on
chemicals not covered, or whether chemicals have pending IRIS toxicity values) may be directed
to the EPA Office of Research and Development's National Center for Environmental
Assessment, Superfund Health Risk Technical Support Center (513-569-7300), or OSRTI.
Vanadium is a group Vb transition metal, which exists in several oxidation states from -2
to +5. Vanadium is commonly found in ores, tars, coals and oils and is used as an alloy in steel
(WHO, 1988). Vanadium pentoxide (V2O5) (Figure 1) is the most common form of vanadium
used commercially. Occupational exposure to vanadium pentoxide is primarily by inhalation of
dust generated during vanadium processing and fuel-oil ash during cleaning of oil-burning
boilers and furnaces.
The U.S. Environmental Protection Agency's (EPA) Integrated Risk Information System
(IRIS) (U.S. EPA, 2007) lists a chronic reference dose (RfD) of 9E-03 mg/kg-day for vanadium
pentoxide based on a 2.5-year dietary no-observed-adverse-effect level (NOAEL) of 17.85 ppm
vanadium pentoxide (equivalent to 0.89 mg vanadium pentoxide/kg-day) for decreased hair
cystine content reported in an unpublished study by Stokinger et al. (1953) (verification date
02/26/1986). IRIS does not list a chronic inhalation reference concentration (RfC) or cancer
assessment for vanadium pentoxide, and currently contains no files for vanadium or other
vanadium compounds (U.S. EPA, 2007). The Health Effects Assessment Summary Table
(HEAST) (U.S. EPA, 1997) lists a subchronic RfD of 9E-03 mg/kg-day for vanadium pentoxide,
INTRODUCTION
o
o
Figure 1. Vanadium pentoxide structure
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derived by adopting the chronic RfD from IRIS as the subchronic RfD (U.S. EPA, 1997). The
Drinking Water Standards and Health Advisories list (U.S. EPA, 2004) does not report an RfD or
carcinogenicity assessment for vanadium or vanadium compounds. The CARA list (U.S. EPA,
1991, 1994a) includes a Health and Environmental Effects Profile (HEEP) for Vanadium
Pentoxide (U.S. EPA, 1985) that declined to derive toxicity values for vanadium pentoxide due
to the weak database and a Health Effects Assessment (HEA) for Vanadium and Compounds
(U.S. EPA, 1987) that derived the same RfD for vanadium pentoxide as that presented on IRIS.
The Agency for Toxic Substance and Disease Registry (ATSDR, 1992) derived an
intermediate-duration oral minimal risk level (MRL) for vanadium of 3E-03 mg/kg-day (3xl0"3
mg V/kg-day) based on NOAELs of 0.3 mg/kg-day for renal and respiratory effects (renal
hemorrhagic foci and pulmonary vascular infiltration) seen at higher doses (0.57 mg/kg-day) in a
3-month study in rats exposed to sodium metavanadate in drinking water (Domingo et al., 1985).
ATSDR (1992) did not derive a chronic oral MRL for vanadium due to lack of quantitative
chronic exposure data. ATSDR (1992) did not consider data from the studies by Stokinger et al.
(1953) useful for derivation of a chronic oral MRL, because data were "not available to
determine the most sensitive end point." IARC (2006) has classified vanadium pentoxide as a 2B
carcinogen (possible human carcinogen). Vanadium exists in several different valence states, all
of which are not equivalent toxicologically (IPCS, 2001). Therefore, the vanadium pentoxide
assessment should not be applied to other vanadium compounds.
Literature searches for studies relevant to the derivation of provisional toxicity values for
vanadium pentoxide (CASRN 1314-62-1) were conducted from 1986 to April 2007 in
TOXLINE (supplemented with BIOSIS and NTIS updates), MEDLINE, TSCATS, RTECS,
CCRIS, DART, EMIC/EMICBACK, HSDB, GENETOX and CANCERLIT, and Current
Contents. The Environmental Health Criteria Document (WHO, 1988) and National Toxicology
Program (NTP) status report (NTP, 2006) were also searched for relevant information.
REVIEW OF PERTINENT LITERATURE
Human Studies
Oral. No studies investigating the effects of acute, subchronic or chronic oral exposure to
vanadium pentoxide in humans were identified.
Inhalation. Health effects of inhalation exposure to vanadium pentoxide and other vanadium
compounds have been investigated since the early 1900s (Woodin et al., 1999; Lees, 1980).
Numerous occupational and case studies report respiratory tract irritation, bronchitis (often called
boilermakers' bronchitis), airway obstruction, chest pain, rhinitis, pharyngitis, laryngitis and
conjunctivitis in workers exposed to fuel-oil ash containing vanadium during cleaning of
oil-burning boilers (Woodin et al., 2000; Woodin et al., 1999; Hauser et al., 1995; Levy et al.,
1984; Lees, 1980; Sjoberg, 1955; Williams, 1952) or to vanadium-containing dust during
vanadium processing (Irsigler et al., 1999; Kiviluoto, 1980; Kiviluoto et al., 1979; Musk and
Tees, 1982; Zenz et al., 1962; Vintinner et al., 1955). With the exception of the studies reviewed
below, the chemical composition of fuel-oil ash particulate or vanadium dust (including
identification of specific vanadium compounds), or exposure measurements for vanadium
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pentoxide, were not reported; thus, limited information is available to define the
exposure-response relationship between inhaled vanadium pentoxide and adverse respiratory
effects in humans.
Sjoberg (1955) published seven case reports of respiratory symptoms, diagnosed as
"vanadium bronchitis," in workers following acute exposure to ash particles containing
vanadium pentoxide during cleaning of oil-burning boilers. Vanadium pentoxide concentrations
measured in two boilers on a single day during the cleaning process ranged from 2 to 85 mg/m3.
Although specific exposure durations were not reported, in general, cleaning time for each boiler
was 1-2 work days. Workers reported that respiratory symptoms, including cough, rhinitis,
wheeze, sore throat and conjunctivitis, developed "after" exposure from boiler cleaning.
Symptoms resolved within 2 weeks of exposure and re-developed in workers exposed during
subsequent boiler cleanings. No additional information regarding the chemical composition of
the fuel-oil ash was reported.
Severe respiratory tract irritation was reported in 74 of 100 workers exposed to vanadium
pentoxide in fuel-oil ash during an oil-to-coal conversion of a power plant (Levy et al., 1984).
Exposure occurred over a period of approximately 4 weeks, with typical exposure durations of
10 hours/day, 6 days/week. Eight air samples obtained from various parts of the boiler on a
single day near the end of the 4-week exposure period revealed vanadium pentoxide
concentrations ranging from 0.05 to 5.3 mg/m3; no additional air samples were obtained during
the exposure period. Although a complete assessment of the ash composition was not conducted,
levels of chromium, nickel and fumes of copper and iron oxide were reported as "within
acceptable limits" (no measured levels were reported). Data on workers' symptoms were
collected by questionnaires distributed approximately 1 month after exposure had ceased. The
most frequently reported symptoms were productive cough, sore throat, dyspnea on exertion and
chest pain or discomfort. The onset of symptoms occurred within the first 2 weeks of exposure.
Information regarding resolution of symptoms following cessation of exposure was not reported.
Zenz and Berg (1967) exposed nine volunteers to vanadium pentoxide dust for 8 hours to
evaluate respiratory effects. Volunteers (gender not reported) were exposed to 0.1 mg/m3 (n=2),
0.5 mg/m3 (n=5) or 1 mg/m3 (n=2) vanadium pentoxide in an environmental chamber; no control
group or control exposures were included in this study. Particle size analysis revealed that 98%
of particles had a diameter <0.5 |im. Post-exposure assessments of chest x-ray, blood, urine,
nasal smear samples and pulmonary function were compared with baseline values determined for
each subject prior to exposure. All subjects were observed for clinical symptoms for 11-19
months after exposure. Subjects exposed to 1 mg/m3 vanadium pentoxide developed sporadic
cough after 5 hours of exposure, which progressed to persistent cough during the last 3 hours of
exposure and continued for 8 days. No other signs of respiratory irritation were observed. Results
of pulmonary function tests and chest x-ray 1, 2 and 3 weeks after exposure were similar to
baseline (data not reported). Hematology and urinalysis parameters were not affected by
exposure (data not reported). Nasal smears obtained 24 hours, 72 hours and 1 week after
exposure were negative for eosinophilia. Three weeks after the initial exposure, these subjects
were accidentally exposed to a "heavy cloud" of vanadium pentoxide dust (concentration not
reported) for 5 minutes. Within 16 hours of exposure, both subjects developed a "marked"
productive cough with rales and expiratory wheeze, which continued for 1 week, although
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pulmonary function test results were comparable to baseline (data not reported). Blood and nasal
smear samples were negative for eosinophilia. Subjects in the 0.5 mg/m3 exposure group
developed a "loose" productive cough on the day after exposure, which lasted for 7-10 days. No
additional symptoms were observed and post-exposure pulmonary function and laboratory tests
were comparable to baseline results (data not reported). Subjects exposed to 0.1 mg/m3
developed "considerable" mucus formation, which was easily cleared by coughing, within 24
hours after exposure, lasting for 4 days. No other symptoms or positive findings for pulmonary
function or laboratory tests were observed. No treatment-related symptoms or clinical findings
were reported for any subject during the 11-19 months post-treatment period.
Animal Studies
Oral Subchronic Toxicity
No animal studies that have comprehensively examined histopathological, biochemical
and clinical endpoints of subchronic oral exposure were identified from the available literature.
Mountain et al. (1953) evaluated the effects of subchronic exposure of rats to dietary vanadium
pentoxide on body weight gain, erythrocyte count, hemoglobin and cystine content of hair.
Groups of five male Wistar rats were fed diets containing 0, 25, 50, 500 or 1000 ppm of
vanadium as vanadium pentoxide for 103 days (25 and 50 ppm groups; "low exposure" groups)
or 75 days (500 and 1000 ppm groups; "high exposure" groups). After 35 days of treatment,
dietary vanadium levels of the 25 and 50 ppm groups were increased to 100 and 150 ppm,
respectively. At the end of treatment, body weight gain and cystine content of hair were
measured in all groups, erythrocyte count and hemoglobin were measured in control and "low
exposure" groups, and relative liver weight was measured in control and 500 ppm groups.
Compared to control, body weight gain was increased in the 50 (54% increase) and 100 (45%
increase) ppm groups and decreased in the 500 ppm group (66% decrease) and 1000 ppm group
(details not reported); The increase in body weight gain at the low exposure levels was not
explained and statistical significance was not reported.for any result Relative liver weight in the
500 ppm group was significantly increased by 10% compared to control (data only reported for
control and 500 ppm groups). Erythrocyte count and hemoglobin level were significantly
decreased by 18 and 5%, respectively, in rats exposed to 100 ppm compared to control; no
changes in hematological parameters were observed in the 50 ppm group (data not reported for
500 and 1000 ppm groups). Cystine content of hair was significantly decreased compared to
control in all vanadium pentoxide treatment groups. Although the toxicological significance of
decreased hair cystine content has not been established, the researchers speculate that vanadium
may have inhibited enzymes, such as sulfur transferases, that decreased the availability of cystine
for hair growth. On the basis of decreased hair cystine, potentially a result of enzyme inhibition,
the lowest exposure of 50 ppm (5 mg/kg-day) is a LOAEL, although equivocal. Based on the low
number of animals and the varied dose regimen, this study is judged to be inadequate for
deriving a subchronic provisional RfD.
Oral Chronic Toxicity and Carcinogenicity
Studies investigating the effects of chronic oral exposure of animals to vanadium
pentoxide, including carcinogenicity studies, were not identified. According to the information
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provided by IRIS (U.S. EPA, 2007), the unpublished 2.5-year dietary study on vanadium
pentoxide in rats used as the basis of the chronic RfD (Stokinger et al., 1953) did not assess
comprehensive toxicity endpoints. IRIS states that "the criteria used to evaluate vanadium
toxicity were growth rate, survival, and hair cystine content." According to IRIS, "the only
significant change reported was a decrease in the amount of cystine in the hair of animals
ingesting vanadium." IRIS (U.S. EPA, 2007) did not report any additional information on the
results of this unpublished study; thus, it does not appear that the carcinogenic potential of oral
vanadium was evaluated. No additional oral chronic exposure studies in animals were identified
in the literature search updates for this document.
Oral Reproductive and Developmental Toxicity
Studies investigating the reproductive and developmental toxicity of subchronic or
chronic oral exposure to vanadium pentoxide were not identified. There are several studies,
however, addressing these endpoints following intraperitoneal administration of vanadium
pentoxide in mice and rats.
Intraperitoneal Reproductive and Developmental Toxicity
Male and female reproductive endpoints were evaluated in rats following prepubertal
intraperitoneal administration of vanadium pentoxide (Altamirano et al., 1991). Newborn male
and female rats were injected with 0 or 12.5 mg/kg vanadium pentoxide in saline on every
second day from birth to age 21 days; groups sizes were 5 (treated males) or 9 (male and female
controls and treated females). The males were sacrificed at 55 days of age and the females were
sacrificed on the day of first vaginal estrus. Other groups of females were injected with 0 or 12.5
mg/kg-day vanadium pentoxide (n = 10 and 6, respectively) from age 21 days to the day of first
vaginal estrus, at which time they were sacrificed. Reported endpoints in the males consisted of
absolute weights of testis, prostate, seminal vesicles, adrenals, pituitary, thymus, liver, kidneys
and submandibular glands. The only effects in treated males were statistically significant
increases in seminal vesicle, thymus and submandibular gland weights (20.1, 29.5 and 19.2%
higher than controls, respectively). Endpoints in the females included body weight, absolute
organ weights (ovaries, uterus, adrenals, pituitary, thymus, liver, kidneys and submandibular
glands), age at vaginal opening, number of ova in oviducts and ovulation rate. The only effects in
treated females occurred in the group treated from 21 days of age; these consisted of statistically
significant increases in body weight (12.5% higher than controls) and weights of thymus,
submandibular gland and liver (31.1, 15.8 and 28.4%, respectively).
Developmental toxicity was evaluated in groups of 13 or 15 female CD-I mice that were
administered 0 or 8.5 mg/kg vanadium pentoxide in distilled water, respectively, by
intraperitoneal injection on days 6-15 of gestation (Altamirano-Lozano et al., 1993). No maternal
toxicity was reported (endpoints not specified). Developmental endpoints were assessed on
gestation day 18 and included numbers of implants, resorptions and live fetuses, fetal weight and
sex, and external malformations (all fetuses) and skeletal abnormalities (two-thirds of fetuses);
fetal internal soft-tissue examinations do not appear to have been conducted. The treated group
had statistically significant increases in the number of litters with abnormal fetuses (9/15
compared to 3/13 in controls), number of abnormal fetuses (15/149 compared to 3/124), and
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number of fetuses with short limbs (8/149 compared to 0/124 in controls). Additionally, the
numbers of ossification centers in forelimbs and hindlimbs were significantly reduced in the
treated fetuses.
Fertility and sperm assessments were performed in male CD-I mice following
intraperitoneal administration of vanadium pentoxide (Altamirano-Lozano et al., 1996). In the
fertility assessment, groups of 20 and 15 male mice were injected with 0 and 8.5 mg/kg
vanadium pentoxide in saline, respectively, every 3 days for 60 days and mated 24 hours after
the last injection. Statistically significant effects in the treated group included reduced fertility
rate in the males (33% compared to 85% in controls), and reduced numbers of implantations sites
and live fetuses and increased number of resorptions in the mated females. In the sperm
assessment, 30 males were injected with 8.5 mg/kg vanadium pentoxide every 3 days for up to
60 days with groups of 5 evaluated after 10, 20, 30, 40, 50 or 60 days of treatment. Statistically
significant effects included reduced sperm motility after >10 days, reduced sperm count and
increased percentage of abnormal sperm after >20 days, decreased absolute testicular weight
after >50 days (relative weight not reported), and decreased body weight after 60 days.
The results of three developmental studies published in the Chinese language are
available only as English abstracts. Zhang et al. (1991) evaluated the developmental toxicity in
NIH mice following intraperitoneal injection of 5 mg/kg-day vanadium pentoxide on days 1-5, 6-
15, 7, 8, 9, 10, 11 or 14-17 of gestation. There were no adverse effects on preimplantation or
implantation, teratogenicity, or premature births. Increased frequencies of resorption or fetal
death were observed for gestation days 6-15, 7 and 14-17. Delayed ossification (sites not
specified) was observed for gestation days 6-15, 8, 10 and 14-17. In a second study, Zhang et al.
(1993a) evaluated developmental toxicity in Wistar rats following intraperitoneal injection of
0.33, 1.0 or 3.0 mg/kg-day on days 6-15 of gestation. Decreased placental weight and increases
in embryo-fetus mortality and external or skeletal malformations (unspecified) occurred at 1.0
and 3.0 mg/kg-day. Maternal toxic symptoms (unspecified), decreased maternal weight gain
during treatment and fetal growth retardation were observed at 3.0 mg/kg-day. In the third study,
Zhang et al. (1993b) evaluated developmental toxicity in Wistar rats following intraperitoneal
injection of vanadium pentoxide in doses of 3 mg/kg-day on days 6-15 of gestation or 5 mg/kg-
day on days 9, 10, 11 or 9-12 of gestation. Effects in rats exposed on gestation days 6-15 and 9-
12 included decreased maternal weight gain, increased fetal mortality, decreased fetal weight and
crown-rump length, delayed ossification of unspecified bones, and increased incidences of
subcutaneous hemorrhage, wavy ribs, and dilation of lateral ventricles and renal pelvis. Effects in
rats exposed on a single day of gestation included subcutaneous hemorrhage and unspecified
visceral anomalies following exposure on days 9, 10 and 11, and increased fetal mortality and
delayed ossification of unspecified bones following exposure on day 10. Additional study details
were not reported in the abstracts. Altogether, the three studies identified an intraperitoneal
developmental-toxicity LOAEL for vanadium pentoxide of 1 mg/kg-day (Zhang et al., 1993a).
Although the IP studies show the potential of vanadium pentoxide to induce reproductive
and developmental effects in rodents, the studies are of little use in the quantitation of vanadium
pentoxide toxicity, as equivalent oral or inhalation exposures cannot be established.
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Inhalation Subchronic Toxicity
Subchronic toxicity of inhalation exposure to particulate aerosols of vanadium pentoxide
was assessed in male and female rats (F344/N) and mice (B6C3Fi) in a series of studies
conducted as part of the NTP (2002) chronic exposure cancer bioassay. Standard toxicological
assessments were conducted after exposure durations of 16 days and 3 months. In addition,
16-day exposure studies included immunotoxicity studies, cell proliferation studies and detailed
histopathological evaluations to determine the time-to-onset and extent of early lung injury. The
3-month exposure studies also included evaluations of cardiovascular function, pulmonary
function, sperm motility and vaginal cytology and analysis of pulmonary lavage fluid.
NTP (2002) 16-Day Exposure Studies in Rats. Groups of five male and five female rats were
exposed (whole-body exposure) to particulate aerosols of vanadium pentoxide at concentrations
of 0, 2, 4, 8, 16 or 32 mg/m3 by inhalation, 6 hours per day, 5 days/week for 16 days (NTP,
2002). Particle size mean mass aerodynamic diameter and geometric standard deviation
(MMAD±GSD) for each dose groups was as follows: 2 mg/m3=1.0±2.7; 4 mg/m3=1.2±2.8; 8
mg/m3=1.3±2.4; 16 mg/m3=1.2±2.8; 32 mg/m3=1.2±2.8. Three male rats in the 32 mg/m3 group
died on day 6 of exposure; researchers considered mortalities to be treatment-related. Although
the cause of death was not explicitly stated, rats became emaciated, exhibited shallow, labored
breathing, and had diarrhea. No deaths occurred in other treatment groups for male rats or in any
group for female rats. During the first week of exposure, shallow, rapid respiration was observed
in all rats in the 16 and 32 mg/m3 exposure groups and red nasal discharge was observed in all
rats in the 32 mg/m3 exposure group. From exposure days 8 to 16, ocular and nasal discharge
was observed in rats in the 16 mg/m3 exposure group and rats in the 32 mg/m3 groups became
emaciated and had hunched or abnormal posture. Dose-related decreases in body weight gain and
increases in lung weights (absolute and relative) were observed, as summarized in Table 1.
Significant dose-related decreases in body weight gain were observed in males and females at
concentrations of 8 mg/m3 and greater. Absolute lung weight was significantly increased in male
rats in the 16 mg/m3 group and in female rats in the 2, 16 and 32 mg/m3 groups. Relative lung
weights were significantly increased in female rats in all vanadium pentoxide groups and in male
rats exposed to concentrations of 4 mg/m3 and above. No consistent changes were observed for
absolute or relative weights of other organs. Other endpoints assessing general toxicity were not
monitored in the 16-day study. No data on food or water consumption throughout the treatment
period were reported.
To assess the onset and extent of early lung tissue changes from inhalation exposure to
vanadium pentoxide, lung tissue was evaluated in additional groups of 40-60 female rats exposed
to vanadium pentoxide (NTP, 2002). Rats were exposed to 0, 1, 2 or 4 mg/m3 by inhalation for
6hours/day, 5 days/week for 16 days. On days 6 and 13, the lungs of 10 rats per group were
evaluated for histopathological changes and cell proliferation was measured by incorporation of
BrdU (Bromodeoxyuridine) implanted 140±3 hours earlier. Histopathology was also performed
on lung tissue from four animals in each exposure group on days 1, 2, 5, 10 and 16 (data not
presented in study report). Incidences of nonneoplastic lesion of the lung of female rats on days 6
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Table 1. Body Weight Gain and Lung Weight in Rats (F344/N) Exposed to Vanadium
Pentoxide by Inhalation for 16 Days (Values are Means±Standard Error) (NTP, 2002)
Parameter
Exposure
Control
2 mg/m3
4 mg/m3
8 mg/m3
16 mg/m3
32 mg/m3
Male Rats
Body weight gain
during 16-day
exposure period (g)
89±5
87±3
84±4
73±3a
59±5b
4±9b
Absolute lung
weight (g)
1.6±0.2
1.7±0.1
1.9±0.1
1.9±0.1
2.1±0.2a
1.5±0.1
Relative lung
weight
7.3±0.9
8.1±0.4
9.9±0.4a
9.7±0.3b
11.3±0.6b
7.1±0.8b
Female Rats
Body weight gain
during 16-day
exposure period (g)
38±2
38±2
35±2
30±la
23±2b
4±4b
Absolute lung
weight (g)
1.1±0.1
1.5±0.1b
1.3±0.1
1.3±0.05
1.4±0.1a
1.4±0.1a
Relative lung
weight
7.7±0.6
10.7±0.6b
9.8±0.7b
10.2±0.4b
11.5±0.5b
13.2±0.2b
aSignificantly different from control by William's test (p< 0.05)
bSignificantly different from control by William's test (p< 0.01)
and 13 are summarized in Table 2. Hyperplasia of the alveolar and bronchiolar epithelium was
observed in almost every rat exposed to 2 or 4 mg/m3 for 6 or 13 days, and alveolar epithelial
hyperplasia was observed in 3 of 10 animals exposed to 1 mg/m3 for 13 days. Increased numbers
of alveolar macrophages (histiocytic infiltrate) were observed in rats treated with 2 or 4 mg/m3
for 6 days and in all vanadium pentoxide-exposed rats after 13 days of treatment. Minimal to
mild interstitial inflammation was observed in all rats exposed to 2 or 4 mg/m3 for 6 or 13 days,
and in 3 of 10 and 8 of 10 rats exposed to 1 mg/m3 for 6 or 13 days, respectively. On day 6,
inflammation was characterized by small numbers of mononuclear cells localized primarily
around blood vessels. On day 13, mononuclear cells were also observed in the septae of alveolar
ducts. Minimal to mild interstitial fibrosis was observed in 6 of 10 animals exposed to 4 mg/m3
for 13 days. A lowest-observed-adverse-effect level (LOAEL) of 1 mg/m3 was identified for
nonneoplastic lung lesions in female rats exposed to vanadium pentoxide by inhalation for
13 days; a 13-day NOAEL was not established. Since the severity of interstitial fibrosis was
rated as minimal to mild, the LOAEL of 1 mg/m3 is considered a minimal LOAEL.
Results of cell proliferation studies (measured by incorporation of BrdU) in rats exposed
to 0, 1, 2 or 4 mg/m3 vanadium pentoxide for days 6 and 13 are summarized in Table 3 (NTP,
2002). Cell turnover rates in the terminal bronchioles increased with increasing exposure
concentration on days 6 and 13 (statistical significance not reported). Rates on day 13 were
similar to those observed on day 6. In contrast, the incidence of alveolar cell proliferation in only
the 4 mg/m3 group was greater than that in the control group on day 6. By day 13, rates were
increased in all groups of exposed rats, but not in a concentration-related manner.
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Table 2. Incidences of Nonneoplastic Lesions of the Lung in Female Rats (F344/N)
Exposed to Vanadium Pentoxide by Inhalation for 6 or 13 Days (NTP, 2002)
Endpoint
Number of Animals with Lesion"
Control
1 mg/m3
2 mg/m3
4 mg/m3
Day 6
Alveolar epithelium, hyperplasia
0
0
10b (1.1)
8b (1.4)
Bronchiole epithelium, hyperplasia
1 (1.0)
0
10b (1.7)
10b (1.8)
Histiocytic infiltrate
2(1.0)
6(1.3)
10b (1.4)
10b (1.8)
Inflammation
0
3 (1.0)
10b (1.5)
10b (2.5)
Day 13
Alveolar epithelium, hyperplasia
0
3 (1.0)
10b(1.0)
10b (2.0)
Bronchiole epithelium, hyperplasia
0
0
10b(1.0)
10b (1.8)
Histiocytic infiltrate
0
10b (1.3)
10b (1.9)
10b (2.2)
Inflammation
0
8b (1.3)
10b (1.7)
10b (2.0)
Fibrosis
0
0
0
6b (1.5)
a10 rats/treatment group; numbers in parentheses indicate average severity grade in affected animals: l=minimal,
2=mild, 3=moderate, 4=marked
bSignificantly different from control group by the Fisher exact test (p< 0.05)
Table 3. Bromodeoxyuridine-Labeled Lung Nuclei in Female Rats (F344/N) Exposed to
Vanadium Pentoxide by Inhalation for 6 or 13 days (NTP, 2002)
Lung Location
Exposure Groupa'b
Control
1 mg/m3
2 mg/m3
4 mg/m3
Terminal Bronchiole
Day 6
21.88±1.43
33.58±1.77
56.08±3.36
83.08±5.56
Day 13
24.24±1.12
45.91±2.04
62.72±2.04
91.96±4.65
Alveoli/Alveolar Duct Area
Day 6
0.75±0.03
0.54±0.03
0.76±0.05
1.68±0.12
Day 13
0.83±0.03
1.82±0.07
1.72±0.10
1.56±0.07
aData are given as the number of bromodeoxyuridine-labeled nuclei/mm basement membrane (mean±standard error)
b10 animals per exposure group
Additional groups of 22 male rats were exposed to 0, 4, 8 or 16 mg/m3 for 16 days to
assess the effects of treatment on pulmonary inflammation by analysis of pulmonary lavage fluid
and systemic immunity as measured by pulmonary bactericidal activity (NTP, 2002). Analysis of
bronchoalveolar lavage (BAL) fluid showed a localized inflammatory response in the lung of
male rats (9-10 per exposure group) based on increases in cell number, protein, neutrophils and
lysozymes. There was also a significant decrease in macrophages in lavage fluids of male rats
exposed to 8 or 16 mg/m3. Data are summarized in Table 4. To assess pulmonary bactericidal
activity, lungs from 12 male rats per dose group were exposed to viable radiolabeled
10
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Table 4. Pulmonary Lavage Parameters for Male Rats (F344/N) Exposed to Vanadium
Pentoxide by Inhalation for 6 Hours/Day, 5 Days/Week for 16 Days (NTP, 2002)a
Parameter and Species
Exposure Level
Control
4 mg/m3
8 mg/m3
16 mg/m3
Total cells (10s)
11.07±1.9 (10)
18.61±6.6b (10)
18.94±8.3b (9)
21.70±7.7b (10)
Macrophages (%)
98±2 (10)
91±8 (10)
78±14b (10)
69±10b (10)
Lymphocytes (%)
2±2 (10)
3±4 (10)
7±4 (10)
7±5 (10)
Neutrophils (%)
0±0 (10)
6±6 (10)
16±16b (10)
25±12b (10)
Lavage fluid protein (ng/mL)
117±32 (10)
221±23b (10)
268±38b (10)
253±38b (10)
Lysozyme (ng/mL)
60±2 (10)
65±3b (10)
65±5b (10)
71±4b (10)
Lysozyme (|ig/|ig protein)
0.54±0.14 (10)
0.30±0.03b (10)
0.24±0.03b (10)
0.28±0.04b (10)
aData are presented as means±standard deviations; numbers in parentheses are the number of animals per group
bSignificantly different from control group (p< 0.05) by Dunnett's test
[35S\-Klebsiellapneumoniae and evaluated for pulmonary bactericidal activity 3 hours after
inoculation. No treatment-related effects were observed in male rats for any vanadium pentoxide
group.
NTP (2002) 16-Day Exposure Studies in Mice. Groups of five male and five female mice were
exposed (whole-body exposure) to vanadium pentoxide aerosol at concentrations of 0, 2, 4, 8, 16
or 32 mg/m3 by inhalation, 6 hours per day, 5 days/week for 16 days (NTP, 2002). All male mice
exposed to 32 mg/m3 died or were sacrificed due to severe toxicity and one male exposed to
8 mg/m3 died before completion of the study; researchers did not indicate if the death in the
8 mg/m3 was considered related to treatment. Hypoactivity was observed in male and females in
the 32 mg/m3 group, with labored breathing observed in one female. Males in the 32 mg/m3
group had hunched posture, and one was emaciated. Body weight gain and absolute and relative
lung and liver weights of male and female mice are summarized in Table 5. Body weight gain
over the 16-day treatment period was significantly reduced by 7% in male mice in the 16 mg/m3
group and 28% in female mice in the 32 mg/m3 compared to control. Absolute lung weights were
significantly increased in a dose-dependent fashion in males exposed to 4 mg/m3 or greater and
relative lung weights were increased in males exposed to 2 mg/m3 or greater. Absolute and
relative lung weights were significantly increased in females in all exposure groups. Maximum
increases in relative lung weights were 74% above control in males exposed to 16 mg/m3 and
88%) above control in females exposed to 16 mg/m3. Relative liver weights were increased in
males and females exposed to 4 mg/m3 and greater compared to control, with the maximum
increase of 18%> for males observed in the 16 mg/m3 group and of 20% for females in the
32 mg/m3 group. Absolute liver weights were increased in males in the 16 mg/m3 group but
decreased in females in the 32 mg/m3 group. Mediastinal lymph nodes of several males and
females exposed to 2 (females only), 4, 8 or 16 mg/m3 were enlarged. While complete
histopathology was not done, grossly enlarged nodes were confirmed histologically as lymphoid
hyperplasia (data not presented in study report).
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Table 5. Body Weight Gain, Lung and Liver Weights in Mice (B6C3Fi) Exposed to
Vanadium Pentoxide by Inhalation for 16 Days (Values are Means±Standard Error)
(NTP, 2002)
Parameter
Exposure
Control
2 mg/m3
4 mg/m3
8 mg/m3
16 mg/m3
32 mg/m3
Male Mice
Body weight gain
during 16-day
exposure period (g)
4.5±0.4
4.1±0.5
3.6±0.3
3.3±0.5
2.5±0.5b
c
Absolute lung
weight (g)
0.2±0.01
0.2±0.01
0.3±0.01b
0.3±0.01b
0.3±0.01b
c
Relative lung
weight
7.1±0.4
8.1±0.4a
10.1±0.2b
ll.l±0.5b
12.4±0.5a
c
Absolute liver
weight (g)
1.56±0.05
1.54±0.03
1.69±0.06
1.66±0.02
1.70±0.05a
c
Relative liver
weight
55.6±1.0
55.5±0.7
62.0±1.9b
62.3±1.4b
65.3±l.lb
c
Female Mice
Body weight gain
during 16-day
exposure period (g)
3.5±0.3
4.1±0.4
2.4±0.4
1.5±0.4
2.4±0.3
-2.4±1.0b
Absolute lung
weight (g)
0.2±0.02
0.3±0.01b
0.2±0.01a
0.3±0.01b
0.3±0.01b
0.3±0.01b
Relative lung
weight
8.6±0.7
11.4±0.5a
11.0±0.5a
13.1±0.7b
16.1±0.8b
16.1±0.7b
Absolute liver
weight (g)
1.24±0.02
1.25±0.01
1.30±0.03
1.24±0.04
1.29±0.04
1.08±0.1a
Relative liver
weight
54.1±1.2
56.0±0.5
59.3±1.2b
59.8±1.3b
61.9±1.3b
64.8±0.3b
aSignificantly different from control by William's test (p< 0.05)
bSignificantly different from control by William's test (p< 0.01)
°Not measured; animals died prior to completion of treatment period
To assess the onset and extent of early lung tissue changes from inhalation exposure to
vanadium pentoxide, lung tissue was evaluated in additional groups of 40-60 female mice that
were exposed to vanadium pentoxide as part of the NTP (2002) 16-day study. Mice were
exposed to 0, 2, 4 or 8 mg/m3 by inhalation for 6 hours per day, 5 days/week for 16 days. On
days 6 and 13, the lungs of 10 mice per group were evaluated for histopathological changes and
cell proliferation measured by the incorporation of BrdU implanted 140±3 hours earlier.
Histopathology was also performed on lung tissue from four animals in each exposure
group on days 1, 2, 5, 10 and 16 (data not presented in report). Incidences of nonneoplastic lung
lesions in female mice on days 6 and 13 are summarized in Table 6. Hyperplasia of the alveolar
and bronchiolar epithelium was observed in almost every exposed mouse, with severity generally
increased with increasing exposure concentration and time. Hyperplasia was graded as minimal
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Table 6. Incidences of Nonneoplastic Lesions of the Lung in Female Mice (B6C3Fi)
Exposed to Vanadium Pentoxide by Inhalation for 6 or 13 Days (NTP, 2002)
Parameter/Species
Number of Animals with Lesion"
Control
2 mg/m3
4 mg/m3
8 mg/m3
Day 6
Alveolar epithelium, hyperplasia
0
9b (1.0)
10b (1.1)
9b (1.3)
Bronchiole epithelium, hyperplasia
0
10b(1.0)
10b(1.0)
9b (1.3)
Histiocytic infiltrate
0
0
0
4b (1.0)
Day 13
Alveolar epithelium, hyperplasia
0
10b (1.3)
10b (2.0)
10b (2.0)
Bronchiole epithelium, hyperplasia
0
10b (1.3)
10b (1.9)
10b (1.6)
Histiocytic infiltrate
0
1 (1.0)
10b(1.0)
10b (1.1)
Inflammation
0
8b (1.0)
10b (2.0)
10b (2.1)
a10 rats/treatment group; numbers in parentheses indicate average severity grade in affected animals: l=minimal,
2=mild, 3=moderate, 4=marked
bSignificantly different from control group by the Fisher exact test (p< 0.05)
to mild in all cases and involved the distal airways and alveolar ducts and alveoli. Alveolar
macrophages (histiocytic infiltrate) were also observed in the alveoli of mice exposed to 8 mg/m3
on days 6 and 13 and in mice exposed to 4 or 8 mg/m3 on day 13. Minimal to mild interstitial
inflammation, characterized by small numbers of mononuclear cells around vessels, small
airways and into septae of alveolar ducts, was observed in most exposed mice after 13 days. The
LOAEL for nonneoplastic lung lesion in female mice was 2 mg/m3; a NOAEL was not
established. Since lesion severity was classified as minimal to mild, the LOAEL of 2 mg/m3 is
considered as minimal.
Results of cell proliferation studies (as measured by incorporation of BrdU) in mice
exposed to 0, 2, 4 or 8 mg/m3 vanadium pentoxide for days 6 and 13 are summarized in Table 7
(NTP, 2002). Cell turnover rates in the terminal bronchioles were increased for all treatment
groups on day 6 and day 13.
Additional groups of 50 female mice were exposed to 0, 4, 8 or 16 mg/m3 for 16 days to
assess inflammatory and immune responses (NTP, 2002). Effects of treatment on pulmonary
inflammation were evaluated by analysis of pulmonary lavage fluid and systemic immunity by
pulmonary bactericidal activity analysis, influenza virus challenge, mixed lymphocyte culture
response and cytotoxic T cell response after 16 days of exposure. Analysis of bronchoalveolar
lavage (BAL) fluid showed a localized inflammatory response in the lung of female mice (9-10
per exposure group) based on increases in cell number, protein, neutrophils and lysozymes
(Table 8). There was also a significant decrease in macrophages in lavage fluids of mice exposed
to 8 or 16 mg/m3.
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Table 7. Bromodeoxyuridine-Labeled Lung Nuclei in Female Mice (B6C3Fi) Exposed to
Vanadium Pentoxide by Inhalation for 6 or 13 Days (NTP, 2002)
Lung Location
Exposure Group3'b
Control
2 mg/m3
4 mg/m3
8 mg/m3
Terminal Bronchiole
Day 6
46.63±3.18
80.66±4.02
109.84±3.34
125.28±7.41
Day 13
44.37±2.42
75.45±3.67
92.59±4.38
63.02±3.22
Alveoli/Alveolar Duct Area
Day 6
0.63±-0.05
0.46±0.02
0.43±0.02
0.87±0.06
Day 13
0.49±0.03
1.15±0.05
2.01±0.10
2.32±0.08
"Data are given as the number of bromodeoxyuridine-labeled nuclei/mm basement membrane (mean±standard error)
b10 animals per exposure group
Table 8. Pulmonary Lavage Parameters for Female Mice Exposed to Vanadium Pentoxide
by Inhalation for 16 Days (NTP, 2002)a
Parameter
Exposure Level
Control
4 mg/m3
8 mg/m3
16 mg/m3
Total cells (106)
3.42±3.15 (9)
9.03±4.98 (10)
12.38±7.20b (10)
15.27±12.02b (10)
Macrophages (%)
99±1 (10)
95±4 (10)
88±10b (10)
80±10b (10)
Lymphocytes (%)
1±1 (10)
5±4b (10)
5±4b (10)
5±3b (10)
Neutrophils (%)
0±0 (10)
0±0 (10)
7±8 (10)
15±10b (10)
Lavage fluid protein (|ig/mL)
124±87 (10)
187±37b (10)
207±41b (10)
262±47b (10)
Lysozyme (|ig/mL)
20±3 (10)
29±5b (10)
31±3b (10)
29±4b (10)
Lysozyme (|ig/|ig protein)
0.21±0.09 (10)
0.16±0.03 (10)
0.15±0.04 (10)
0.11±0.02b (10)
aData are presented as means±standard deviations; numbers in parentheses indicate the number of animals per group
bSignificantly different from control group (p< 0.05) by Dunnett's test
To assess pulmonary bactericidal activity, lungs from 12 female mice per group were
exposed to viable radiolabeled [35S]-K pneumoniae and evaluated for pulmonary bactericidal
activity 3 hours after inoculation. No treatment-related effects were observed for any vanadium
pentoxide group. No treatment-related affects were observed in groups of 20 female mice per
dose instilled intranasally with influenza virus and evaluated for moribundity for 14 days.
Groups of eight female mice per dose were evaluated for mixed lymphocyte response to
allogenic splenocytes and induction of cytotoxic T lymphocytes; no treatment-related effects
were observed. Thus, results of immunotoxicity studies indicate that inhalation exposure of
female mice to vanadium pentoxide at concentration up to 16 mg/m3 for 16 days was not
immunotoxic.
NTP (2002) 3-Month Exposure Studies in Rats. The 3-month exposure studies in F344/N rats
were conducted to evaluate the cumulative toxic effects of subchronic inhalation exposure to
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vanadium pentoxide (NTP, 2002). Groups of 10 male and 10 female rats were exposed (whole-
body exposure) to aerosols of vanadium pentoxide at concentrations of 0, 1, 2, 4, 8 or 16 mg/m3,
6 hours per day, 5 days/week for 3 months. Particle size MMAD±GSD for each dose groups was
as follows: 1 mg/m3=1.2±2.8; 2 mg/m3=l.l±2.8; 4 mg/m3=1.2±2.8; 8 mg/m3=1.0±2.8;
16 mg/m3=1.2±2.8. Additional groups of 10 male and 10 female rats were exposed to 4, 8 or
16 mg/m3 for 12 (females) or 13 (males) weeks to investigate effects of exposure on
cardiovascular function, pulmonary function and pulmonary inflammation. Clinical findings
were recorded weekly and animals were weighed weekly and at the end of the study. Blood and
urine were collected from core study rats at study termination and blood was collected for
hematology and clinical chemistry determinations from cardiopulmonary physiology study rats
on days 4 and 23. Necropsy and histopathological evaluations (light microscopy of
comprehensive tissues) were performed on all core study animals and samples for sperm motility
and vaginal cytology evaluations were collected from core study rats exposed to 0, 2 (male rats
only), 4, 8 or 16 (female rats only) mg/m3 at the completion of the study.
Seven male rats and three female rats exposed to 16 mg/m3 vanadium pentoxide died
during the study (NTP, 2002). Abnormal breathing, thinness, lethargy, abnormal posture and
ruffled fur were observed in male and female rats exposed to concentrations of 8 mg/m3 and
above. Diarrhea and nasal/eye discharge were also observed in some rats exposed to 16 mg/m3.
Weight gain and absolute and relative lung weights are summarized in Table 9. Weight gain over
the 3-month treatment period was significantly decreased compared to control in males exposed
to 4 (6% decrease), 8 (10% decrease) and 16 (60% decrease) mg/m3 and in females exposed to
16 mg/m3 (30%) decrease). Absolute lung weights were significantly increased in males exposed
to concentrations of 2 mg/m3 and greater and in females exposed to 4 mg/m3 and greater.
Relative lung weights were significantly greater than control in males exposed to 2 (16%>
increase), 4 (30%> increase), 8 (51%> increase) or 16 (145% increase) mg/m3 and in females
exposed to 4 (19%> increase), 8 (76%> increase) or 16 (117% increase) mg/m3. Other organ weight
differences were considered by the researchers to be related to body weight decreases.
Results of hematology assessments are presented in Table 10. Erythrocyte count was
significantly increased in the 8 and 16 mg/m3 groups and hematocrit was significantly increased
in the 16 mg/m3 group in male and female rats. Hemoglobin was significantly increased in
females exposed to 16 mg/m3 and somewhat elevated in males exposed to 16 mg/m3.
Microscopic evaluation of the red blood cell morphology detected increased polychromasia and
hypochromia in rats in the 16 mg/m3 groups (data not presented). Significantly decreased mean
cell hemoglobin concentrations were observed in males exposed to 8 and 16 mg/m3 and in
females exposed to 4, 8, and 16 mg/m3. Reticulocyte count was significantly increased in males
and females exposed tol6 mg/m3. Mean cell volume was significantly decreased, indicative of
microcytosis, in male rats at concentrations of 2 mg/m3 and above and in female rats at
concentrations of 4 mg/m3 and above. The researchers state that the observed hematological
changes, including erythrocytosis, are consistent with pulmonary lesions that reduce pulmonary
oxygen transfer, resulting in tissue hypoxia and stimulation of erythropoiesis by increased renal
production of erythropoietin. Erythrocyte microcytosis is consistent with ineffective
erythropoiesis, suggestive of altered iron metabolism and heme/hemoglobin production.
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Table 9. Body Weight Gain, Lung and Liver Weights in Rats (F344/N) Exposed to
Vanadium Pentoxide by Inhalation for 3 Months (Values are Means± Standard Error)
(NTP, 2002)
Parameter
Exposure
Control
1 mg/m3
2 mg/m3
4 mg/m3
8 mg/m3
16 mg/m3
Male Rats
Weight gain during
3-month exposure
period (g)
8.4±0.9
7.4±0.8
8.2±0.6
7.7±0.5
6.2±0.2a
5.6±0.7b
Absolute lung
weight (g)
0.2±0.01
0.2±0.01
0.3±0.01b
0.3±0.01b
0.3±0.01b
0.4±0.01b
Relative lung
weight
7.0±0.2
6.9±0.2
7.8±0.3
9.3±0.2b
10.0±0.3b
12.7±0.5a
Female Rats
Weight gain during
3-month exposure
period (g)
9.7±1.0
10.0±1.0
8.1±0.4
5.8±0.5b
6.1±0.4b
5.4±0.3b
Absolute lung
weight (g)
0.2±0.01
0.3±0.01
0.3±0.01
0.3±0.02b
0.4±0.02b
0.4±0.02b
Relative lung
weight
8.1±059
8.8±0.3
9.7±0.5
13.2±0.9b
13.2±0.6b
16.3±0.5b
aSignificantly different from control by William's test (p< 0.05)
bSignificantly different from control by William's test (p< 0.01)
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Table 10. Selected Hematology Parameters in Rats (F344/N) Exposed to Vanadium
Pentoxide by Inhalation for 3 Months (NTP, 2002)a
Parameter
Exposure
Control
1 mg/m3
2 mg/m3
4 mg/m3
8 mg/m3
16 mg/m3
Male Rats
Number
9
9
10
9
10
3
Erythrocytes (10'/|iL)
9.2±0.1
9.0±0.1
9.1±0.1
9.3±0.2
9.7±0.2b
15.1±0.3C
Reticulocytes (10'/|iL)
0.2 ±0.02
0.22±0.03
0.19±0.02
0.23±0.03
0.25±0.02
0.8 ±0.08 b
Hematocrit (%)
48.5±0.6
47.7±0.5
47.6±0.6
48.7±0.9
49.9±0.7
71.2±2.8b
Hemoglobin (g/dL)
15.8±0.1
15.5±0.1
15.5±0.2
15.9±0.2
16.1±0.2
20.4±0.8
Mean cell volume (fL)
52.9±0.2
52.9±0.1
52.3±0.1b
52.2±0.2b
51.3±0.2°
46.8±1.0°
Mean cell hemoglobin
(Pg)
17.3±0.2
17.2±0.1
17.1±0.1
17.1±0.02
16.5±0.2°
13.4±0.4°
Female Rats
Number
10
10
9
10
10
6
Erythrocytes (10'/|iL)
8.0±0.1
7.8±0.1
8.1±0.2
8.3±0.1
8.6±0.1b
12.5±0.34°
Reticulocytes (10'/|iL)
0.15 ±0.02
0.17 ±0.01
0.17 ±0.01
0.16 ±0.02
0.17 ±0.02
0.45 ± 0.08°
Hematocrit (%)
45.8±0.5
44.3±0.4
46.1±1.2
46.4±0.4
47.2±0.6
60.8±1.4°
Hemoglobin (g/dL)
15.5±0.2
15.0±0.1
15.5±0.2
15.6±0.1
15.8±0.1
18.2±0.3°
Mean cell volume (fL)
56.9±0.1
56.9±0.1
56.6±0.1
55.8±0.1°
55.0±0.2°
48.7±0.6°
Mean cell hemoglobin
(Pg)
19.3±0.2
19.3±0.2
19.0±0.2
18.7±0.2°
18.5±0.2°
14.6±0.3°
aValues are means±standard error
bSignificantly different from control (p< 0.05)
cSignificantly different from control (p< 0.01)
Sporadic alterations in clinical chemistry and urinalysis variables were observed at
various time-points in exposed males and females; however, no dose- or duration-related pattern
of effect was observed. Sporadic changes in serum liver enzyme activities were not consistent
with hepatocellular injury. Vanadium pentoxide exposure did not affect reproductive endpoints
in males (sperm count, spermatid heads, sperm motility), but it did increase estrous cycle length
by 10% in females exposed to 8 mg/m3, but not 16 mg/m3, and reduced the number of cycling
females in surviving rats in the 16 mg/m3 group (percent reduction not reported).
Complete histopathological assessments were performed on rats exposed to 0, 8 and
16 mg/m3 for 3 months; except for nonneoplastic lesions of the lung and nose, findings were not
considered related to treatment (NTP, 2002). Results of histopathological evaluations of lung and
nasal tissue from male and female rats exposed to 1, 2, 4, 8 and 16 mg/m3 for 3 months are
summarized in Table 11. Significant increases in the incidences of epithelial hyperplasia of the
lung were observed in male and female rats exposed to concentrations of 2 mg/m3 or greater.
Epithelial hyperplasia occurred in the distal airways and associated alveolar ducts and alveoli.
The incidences of inflammation or fibrosis were significantly increased in males exposed to
2 mg/m3 or greater and females exposed to 4 mg/m3 or greater. The incidences of hyperplasia
17
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Table 11. Incidences of Selected Nonneoplastic Lesions of the Lung and Nose in Rats
(F344/N) Exposed to Vanadium Pentoxide by Inhalation for 3 Months (NTP, 2002)
Lesion Location and
Numbers of Animals with Lesions
Type
Control
1 mg/m3
2 mg/m3
4 mg/m3
8 mg/m3
16 mg/m3
Male Rats"
Lung
Epithelium,
hyperplasia
0
0
10b (2.0)
10b (3.0)
10b (3.6)
10b (3.3)
Inflammation
0
0
9b (1.0)
10b(1.0)
10b (1.6)
10b (2.1)
Fibrosis
0
0
2 (1.0)
10b (1.9)
10b (3.2)
10b (3.1)
Bronchiole, exudates
0
0
0
0
7b (1.0)
8b (1.4)
Nose
Epithelium,
hyperplasia
0
0
0
1 (1.0)
10b (1.2)
10b (2.0)
Epithelium, squamous
metaplasia
0
0
0
1 (1.0)
10b (1.2)
10b (1.8)
Inflammation
0
0
0
0
0
7b (1.6)
Female Rats"
Lung
Epithelium,
hyperplasia
0
0
10b (1.3)
10b (2.9)
10b (3.5)
10b (3.2)
Inflammation
0
0
0
10b(1.0)
10b (1.9)
10b (1.2)
Fibrosis
0
0
0
10b(1.0)
10b (2.9)
10b (3.2)
Bronchiole, exudates
0
0
0
0
10b(1.0)
8b(1.1)
Nose
Epithelium,
hyperplasia
0
0
0
10b(1.0)
10b (1.8)
10b (2.7)
Epithelium, squamous
metaplasia
0
0
0
8b (1.0)
10b (1.8)
10b (2.8)
Inflammation
0
0
0
0
1 (1.0)
9b (1.6)
a10 animals per treatment group; numbers in parentheses indicate average severity grade of lesions in affected
animals: l=minimal, 2=mild, 3=moderate, 4=marked
bSignificantly different from control by Fisher exact test (p< 0.01)
and metaplasia of the nasal respiratory epithelium were significantly increased in males exposed
to 8 or 16 mg/m3 and in females exposed to 4 mg/m3 or greater. Nasal hyperplasia and
metaplasia involved the respiratory epithelium covering the ventral portion of the nasal septum,
the vomeronasal organ, and, to a lesser extent, the ventral lateral walls of the anterior portion of
the nasal cavity. Inflammation of the nose was significantly increased in males and females
exposed to 16 mg/m3.
Cardiopulmonary assessments were conducted in groups of 4-10 male and female rats
exposed to 0, 4, 8 and 16 mg/m3 for 3 months (NTP, 2002). No treatment-related changes in
18
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cardiovascular function, as assessed by blood pressure (systolic, diastolic and mean), heart rate
and electrocardiogram, were observed in rats exposed to 4 or 8 mg/m3. Decreased heart rate and
diastolic, systolic and mean blood pressure observed in male and female rats exposed to
16 mg/m3 were considered to be a reflection of the poor condition of the animals, coupled with
an effect from anesthesia. Significant exposure-related decreases in pulmonary function (as
assessed by respiratory rate, tidal and minute volume, expiratory resistance, vital and total
capacity, diffusing capacity, and dynamic and peak compliance) were observed in male and
female rats in all vanadium pentoxide groups tested. Observed changes in impaired capacity to
diffuse carbon monoxide and reduced static and dynamic lung volumes at exposure
concentrations of 4 mg/m3 and greater are suggestive of a restrictive lesion. Changes in forced
expiratory maneuvers in rats exposed to 16 mg/m3 suggest the presence of an obstructive disease.
It is not clear whether pulmonary function results are indicative of obstructive disease or merely
reflect the deteriorating condition of the 16 mg/m3 rats, since histopathological finding in lungs
of rats exposed to 8 and 16 mg/m3 were similar. Taken together, results of pulmonary function
tests indicate that a restrictive injury was present in male and female rats exposed to 4 mg/m3 or
greater, while an obstructive lung injury may have been present in rats exposed to 16 mg/m3.
Pulmonary inflammation as assessed by analysis of pulmonary lavage fluid was
evaluated in rats exposed to 0, 4, 8 and 16 mg/m3 for 3 months (NTP, 2002).
Concentration-related increases were observed in the total numbers of cells, lymphocytes,
neutrophils and protein recovered in pulmonary lavage fluid from rats exposed to vanadium
pentoxide at concentrations of 4 and 8 mg/m3, demonstrating a pulmonary inflammatory
response in male and female rats. These endpoints also were increased in the 16 mg/m3 group,
but to a lesser extent, most likely due to the overt toxicity of vanadium pentoxide at this dose.
Results of this study show that inhalation exposure of male and female rats to vanadium
pentoxide aerosol for 3 months produced adverse effects on the hematological system and the
lung (NTP, 2002). Microcytic erythrocytosis, which was possibly secondary to impaired
pulmonary function, was observed at concentrations of 2 mg/m3 and greater in males and
4 mg/m3 and greater in females. Absolute and relative lung weights were significantly increased
compared to controls at concentrations of 4 mg/m3 and greater in females and 2 mg/m3 and
greater and 4 mg/m3 and greater, respectively, in males. The incidence of nonneoplastic lesions
of the nose was increased in male and female rats at concentrations of 8 mg/m3 and greater and
4 mg/m3 and greater, respectively, and the incidence of nonneoplastic lesions of the lung was
increased in male and female rats 2 mg/m3 and greater. Results of pulmonary function tests
consistent with restrictive lung disease were observed at concentrations of 4 mg/m3 and greater.
Based on decreased erythrocyte size in male rats and nonneoplastic lung lesions in male and
female rats, the NOAEL and LOAEL values identified for 3-month inhalation exposure to
vanadium pentoxide aerosols were 1 and 2 mg/m3, respectively.
NTP (2002) 3-Month Exposure Studies in Mice. Three-month exposure studies in B6C3Fi mice
were conducted to evaluate the toxicity of subchronic inhalation exposure to vanadium pentoxide
(NTP, 2002). Groups of 10 male and 10 female mice were exposed (whole-body exposure) to
aerosols of vanadium pentoxide at concentrations of 0, 1, 2, 4, 8 or 16 mg/m3, 6 hours per day, 5
days/week for 3 months. Particle size MMAD±GSD for each dose groups was as follows:
1 mg/m3=1.2±2.8; 2 mg/m3=l.l±2.8; 4 mg/m3=1.2±2.8; 8 mg/m3=1.0±2.9; 16 mg/m3=1.2±2.8.
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Clinical findings were recorded weekly and animals were weighed weekly and at the end of the
study. Necropsies were performed in all study animals. Histopathological examinations of lungs
were performed in all mice in the 0, 1, 2, 4, 8 or 16 mg/m3 groups and of thymus in all mice in
the 0, 8 or 16 mg/m3 groups. At the end of the 3-month exposure period, samples for sperm
motility and vaginal cytology evaluations were collected from mice exposed to 0, 4, 8 or
16 mg/m3. Complete histopathological examination was performed in mice in the control and
16 mg/m3 groups, although results were not reported. Assessments of cardiopulmonary function,
pulmonary inflammation (analysis of pulmonary lavage), and hematological parameters were not
conducted in mice.
One male mouse in the 16 mg/m3 group died before the end of the study. The animal that
died early appeared thin, but no other signs of toxicity were reported (NTP, 2002). No other
treatment-related clinical findings were observed in any other mice in any treatment group.
Weight gain and absolute and relative lung weights are summarized in Table 12. Weight gain
over the 3-month treatment period was significantly decreased compared to control in males
exposed to 8 (6% decrease) and 16 (10% decrease) mg/m3 and in females exposed to 4 (11%
decrease), 8 (10% decrease) and 16 (12% decrease) mg/m3. Absolute lung weights were
significantly increased compared to control at concentrations of 2 mg/m3 and higher in males and
4 mg/m3 and higher in females. Relative lung weights were significantly greater than control in
males exposed to 4 (33% increase), 8 (43% increase) or 16 (82% increase) mg/m3 and in females
exposed to 4 (62% increase), 8 (63% increase) or 16 (101% increase) mg/m3. Other organ weight
differences were considered to be related to decreases in body weight by the researchers. The
epididymal spermatozoal motility of males exposed to 8 or 16 mg/m3 was significantly decreased
by 13 and 5%, respectively. No treatment-related effects were observed for assessments of
estrous cycle (estrous cycle length and number of cycling females).
Results of histopathogical evaluations of lung tissue from male and female mice exposed
to 0, 1, 2, 4, 8 and 16 mg/m3 for 3 months are summarized in Table 13 (NTP, 2002). Epithelial
hyperplasia was observed in male and female mice exposed to concentrations of 2 mg/m3 and
above, with lesion severity increasing with exposure concentration. Hyperplasia involved
alveolar and, to a lesser extent, bronchiolar epithelium. Inflammation, which was characterized
by multiple foci of a mixed cellular infiltrate oriented around blood vessels and bronchioles, was
observed in male mice exposed to 4 mg/m3 and above and in female mice exposed to 2 mg/m3
and above. Infiltrate was composed primarily of macrophages with abundant cytoplasm and
fewer lymphocytes and neutrophils. Histopathological evaluations of the thymus of male and
female mice exposed to 0, 8 and 16 mg/m3 for 3 months showed lymphoid depletion in mice
exposed to 16 mg/m3 (males: control, 0/9; 8 mg/m3, 0/8; 16 mg/m3, 2/7; females: 0/9, 0/9, 1/10).
Results of the 3-month inhalation study in mice indicate that the lung is the primary
target organ for vanadium pentoxide toxicity (NTP, 2002). Based on increases in absolute lung
weights at concentrations of 2 mg/m3 and greater (males) and inflammation of the respiratory
epithelium at concentrations of 2 mg/m3 and greater (males and females), NOAEL and LOAEL
values were identified as 1 and 2 mg/m3, respectively.
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Table 12. Body Weight Gain, Lung and Liver Weights in Mice (B6C3Fi) Exposed to
Vanadium Pentoxide by Inhalation for 3 Months (Values are Means±Standard Error)
(NTP, 2002)
Parameter
Exposure
Control
1 mg/m3
2 mg/m3
4 mg/m3
8 mg/m3
16 mg/m3
Male Mice
Weight gain during
3-month exposure
period (g)
8.4±0.9
7.4±0.8
8.2±0.6
7.7±0.5
6.2±0.2a
5.6±0.7b
Absolute lung
weight (g)
0.2±0.01
0.2±0.01
0.3±0.01b
0.3±0.01b
0.3±0.01b
0.4±0.01b
Relative lung
weight
7.0±0.2
6.9±0.2
7.8±0.3
9.3±0.2b
10.0±0.3b
12.7±0.4b
Female Mice
Weight gain during
3-month exposure
period (g)
9.7±1.0
10.0±1.0
8.1±0.4
5.8±0.5b
6.1±0.4b
5.4±0.3b
Absolute lung
weight (g)
0.2±0.01
0.3±0.01
0.3±0.01
0.3±0.02b
0.4±0.02b
0.4±0.02b
Relative lung
weight
8.1±0.5
8.8±0.3
9.7±0.5
13.2±0.9b
13.2±0.6b
16.3±0.52b
aSignificantly different from control by William's test (p< 0.05)
bSignificantly different from control by William's test (p< 0.01)
Table 13. Incidences of Selected Nonneoplastic Lesions of the Lung in Mice (B6C3Fi)
Exposed to Vanadium Pentoxide by Inhalation for 3 Months (NTP, 2002)
Lesion Type
Numbers of Animals with Lesions"
Control
1 mg/m3
2 mg/m3
4 mg/m3
8 mg/m3
16 mg/m3
Male
Number
10
10
10
10
10
10
Inflammation
0
1 (1.0)
3 (1.0)
4b (1.0)
10c (2.0)
10c (2.0)
Epithelium, hyperplasia
0
1 (1.0)
4b (1.0)
5b (1.0)
10° (1.3)
10c (3.0)
Female
Number
10
9
10
9
10
10
Inflammation
0
1 (1.0)
7°(1.0)
9°(1.9)
10c (1.9)
10c (2.5)
Epithelium, hyperplasia
0
0
6°(1.0)
9°(1.5)
10° (1.5)
10c (2.5)
aNumbers in parentheses indicate average severity grade of lesions in affected animals: l=minimal, 2=mild,
3=moderate, 4=marked
bSignificantly different from control by Fisher exact test, p< 0.05
Significantly different from control by Fisher exact test, p< 0.01
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Knecht et al. (1985). The lung was also identified as a target organ for acute inhalation exposure
to vanadium pentoxide. Sixteen male cynomologus monkeys were exposed to aerosols of 0.5 or
5 mg/m3 vanadium pentoxide by whole-body inhalation for 6 hours (Knecht et al., 1985), with
exposures conducted at one-week intervals. Effects on airway function were evaluated by
comprehensive pulmonary function tests (PFTs) in monkeys performed after exposure to 0.5 and
5 mg/m3 and on pulmonary inflammation by analysis of bronchoalveolar lavage (BAL) fluid in
monkeys performed after exposure to 5 mg/m3. Post-exposure values for PFTs and BAL were
compared with baseline values determined for each animal prior to each exposure. Pulmonary
function tests were not affected by acute exposure to 0.5 mg/m3. Significant changes in
pulmonary function parameters compared to baseline values were observed following exposure
to 5 mg/m3 as follows: 16% increase in pulmonary resistance; 11% decrease in peak expiratory
flow rate; 5-22% decreases in forced expiratory flow maneuvers; 33% increase in residual
volume; and 24% increase in forced residual capacity. Results are consistent with air-flow
limitation in both small peripheral and large central airways. A significant increase
(approximately 87%; data presented graphically) in the total number of cells recovered in BAL
fluid was observed 1 day after exposure to 5 mg/m3 vanadium pentoxide. The increase in BAL
fluid total cell number was primarily due to a marked increase (approximately 425%; data
presented graphically) in the number of polymorphonuclear leukocytes. Results suggest that
pulmonary inflammation and release of bronchoconstrictive mediators from inflammatory cells
may play a role in vanadium pentoxide-induced air-flow restriction. An acute (single 6-hour
exposure) LOAEL for vanadium pentoxide of 5 mg/m3 for pulmonary function in monkeys was
established in this study, with aNOAEL of 0.5 mg/m3 evident.
Knecht et al. (1992). Pulmonary reactivity was evaluated in adult male cynomolgus monkeys
that were exposed to vanadium pentoxide dust aerosol by inhalation for 6 hours/day, 5
days/week for 26 weeks (Knecht et al., 1992). One control group exposed to filtered, conditioned
air (n=8) and two exposed groups (n=8 each) receiving nominally equal weekly vanadium
pentoxide exposures (concentration x time) with different exposure profiles were used. One
exposed group (peak exposure group) received an actual concentration of 0.16 (+0.01) mg/m3
(0.1 mg/m3 nominal) vanadium pentoxide on Mondays, Wednesdays and Fridays and 1.38
(+0.07) mg/m3 (1.1 mg/m3 nominal) vanadium pentoxide on Tuesdays and Thursdays, and the
other exposed group (constant exposure group) received a constant daily actual concentration of
0.57 (+0.03) mg/m3 (0.5 mg/m3 nominal). The constant exposure regimen corresponded to a
continuous exposure of 0.10 mg/m3 after adjusting for exposure protocol (0.57 mg/m3 x 6/24 x
5/7). The peak exposure regimen averaged to a slightly higher continuous exposure of 0.12
mg/m3 after adjusting for exposure protocol. Provocation challenges consisting of single 6-hour
exposures to 0.5 or 3.0 mg/m3 vanadium pentoxide were used to compare pulmonary reactivity
before and after the 26-week subchronic exposures. Vanadium pentoxide particle size was
determined weekly during challenges and biweekly during exposures. Average particle size for
the subchronic constant exposure group was 3.15 |im (MMAD), with a GSD of 3.25 jam. Particle
sizes (MMAD+GSD) for the peak exposure group were 3.17+2.48 and 3.10+2.45 for the 0.1
mg/m3 and 1.1 mg/m3 exposures, respectively. Pulmonary function tests, cytological and
immunological analyses of blood and bronchoalveolar lavage fluid, and skin sensitivity tests
were conducted before the pre- and post-exposure provocation challenges. Pulmonary function
tests and bronchoalveolar lavage fluid analyses were also performed one day after the
provocation challenges. Cytological endpoints included complete and differential blood cell
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counts and leukotriene C4 levels. Pulmonary function endpoints included total pulmonary
resistance (RL), forced expiratory flow (FEF), forced vital capacity (FVC), residual volume
(RV) and dynamic lung compliance (CLdyn). Immunological endpoints included total IgE, total
IgG, albumin and total protein. The skin sensitivity tests assessed immediate and delayed
responses to intradermal injections of vanadium pentoxide-monkey serum albumin conjugate.
Respiratory distress, characterized by audible wheezing and coughing, occurred in 3/8 monkeys
from the peak exposure group on peak exposure days during the first few weeks of the 26-week
exposure; the responses developed within 3-4 hours of exposure and occasionally required early
removal of the affected monkeys from the exposure chamber. The pre-exposure challenges
produced an impairment in pulmonary function at 3.0 mg/m3 characterized by airway obstructive
changes (a 14% increase in RL and 13% decrease in FEV50/FVC accompanied by a 14%
increase in RV and 3% decrease in FVC). Analysis of bronchoalveolar lavage fluid showed that
the airway obstruction was accompanied by a significant influx of inflammatory cells
(polymorphonuclear leukocytes) into the lung. Pulmonary function and other study endpoints
were not significantly different between the three exposure groups (control, peak and constant) at
either challenge concentration when the monkeys were rechallenged following subchronic
exposure. The authors suggested that the absence of increased pulmonary reactivity to vanadium
pentoxide following subchronic inhalation may be related to the development of tolerance. The
study establishes a subchronic NOAEL[Adj] of 0.10 mg/m3 (continuous exposure) for pulmonary
function. No subchronic LOAEL was indicated. However, an apparent acute, but reversible,
LOAEL of 1.38 mg/m3 is evidenced by the respiratory distress observed at that exposure level
early in the study.
Avila-Costa etal. (2004, 2005, 2006). Results of three recent studies by Avila-Costa et al. (2004,
2005) suggest that inhalation exposure to vanadium pentoxide produces morphological changes
to the central nervous system. Male CD-I mice (n=48) were exposed to vanadium pentoxide by
whole-body inhalation for 1 hour/day, 2 days/week for up to 8 weeks (Avila-Costa et al., 2004,
2005). Particle size was not reported in either study. The exposure concentration was reported as
0.02 M (Avila-Costa et al., 2004, 2005, 2006) or "1.4 mg/m3" (Avila-Costa et al., 2005). The
same group of investigators (Gonzalez-Villalva et al., 2006; Mussali-Galante et al., 2005) using
the same exposure protocol reported that the 0.02 M solution generated an average chamber
concentration of 1.44 mg/m3, as vanadium metal (MW = 50.94). This exposure level corresponds
to 5.13 mg/m3 as vanadium pentoxide (MW = 181.9). The number of immunoreactive-TH+
neurons in the substantia nigra region of the basal ganglia in the mesencephalon was measured at
the end of each week of exposure and morphology of the blood-brain barrier was assessed after 8
weeks of exposure. No clinical signs of toxicity or other toxicological endpoints were reported in
either study. A duration-dependent decrease in the number of immunoreactive-TH+ neurons was
observed from week 3 (decrease of approximately 30%; data presented graphically) through
week 8 (decreased by approximately 63%; data presented graphically) of exposure (Avila-Costa
et al., 2004). Morphological changes to the blood-brain barrier (cilia loss, cell sloughing and
ependymal cell layer detachment) were observed after 8 weeks of exposure (Avila-Costa et al.,
2005). Using a similar protocol, Avila-Costa et al. (2006) assessed the effects of vanadium
pentoxide on memory and morphology of brain hippocampal neurons in male CD-I mice that
were exposed by whole-body inhalation for 1 hour/day, 2 days/week for up to 4 weeks. Groups
of 6 exposed mice and 6 vehicle control mice (inhaling deionized water droplets) were evaluated
after 24 hours and weekly for 4 weeks. No clinical signs or body weight changes were observed.
23
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Spatial memory was tested using a modified Morris water maze task that was learned pre-
exposure. Performance on this test, as assessed by latency (swimming time) to locate a hidden
platform, was significantly impaired in the exposed mice at all time points in an increasing, time-
related manner. Pyramidal neurons from the hippocampus CA1 region were evaluated for
cytological and ultrastructural changes, because spatial memory mainly depends on this region of
the brain. The cytological analysis assessed numbers of dendritic spines in the hippocampal cells;
results showed a significant loss of dendritic spines in the exposed mice at all time points in an
increasing time-related manner that correlated with the memory impairments. The ultrastructural
analysis showed a significantly increased percentage of necrotic hippocampal cells at all time
points that increased to a maximum of 33% after 4 weeks; other findings included hyperdense
postsynaptic terminals and edema in mitochrondria, dendrites, dendritic spines and presynaptic
terminals. These three studies establish a LOAEL for morphological changes to the central
nervous system accompanied by behavioural effects from short-term intermittent exposure to
vanadium pentoxide at 5.13 mg/m3.
Gonzalez-Villalva et al. (2006). In another study by the same group as for the previously
described studies (i.e., Avila-Costa et al., 2004, 2005, 2006), hematological effects of vanadium
pentoxide were assessed in male CD-I mice that were exposed by whole-body inhalation for 1
hour/day, 2 days/week for up to 12 weeks (Gonzalez-Villalva et al., 2006). A 0.02 M aqueous
solution of vanadium pentoxide was aerosolized generating a reported average vanadium
chamber concentration of 1436 |ig/m3 (1.44 mg/m3), corresponding to 5.13 mg/m3 as vanadium
pentoxide. Groups of 8 exposed mice and 8 vehicle control mice (inhaling deionized water
droplets) were evaluated after 24 hours and weekly for 12 weeks. Evaluations consisted of a
complete blood count and morphological examination of platelets. Platelet count was
significantly increased in the exposed mice on weeks 3-12; counts increased from week 3 to a
maximum at week 9 and subsequently declined, but still remained above controls (quantitative
data inadequately reported). The morphology examinations showed the presence of giant
platelets at unspecified longer exposure times. The study establishes an apparent LOAEL for
increased platelet count and altered platelet morphology from short-term intermittent exposure to
vanadium pentoxide at 5.13 mg/m3. A continuous exposure equivalent concentration cannot be
estimated with any confidence, as the intermittency of the exposure protocol is extreme.
Inhalation Chronic Toxicity and Carcinogenicity
NTP (2002) 2-Year Exposure Studies in Rats. The toxicity of chronic exposure to vanadium
pentoxide was assessed in groups of 50 male and 50 female F344/N rats exposed (whole-body
exposure) to particulate aerosols of vanadium pentoxide concentrations of 0, 0.5, 1 or 2 mg/m3 6
hours/day, 5 days/week for 104 weeks (Ress et al., 2003; NTP, 2002). Particle
MM AD±geometric standard deviation for each dose group was as follows: 0.5 mg/m3=1.2±2.9;
1 mg/m3=1.2±2.9; 2 mg/m3=1.3±2.9. Body weights and clinical findings were recorded
throughout the exposure period. Necropsy and complete histopathological evaluation were
performed on all animals. No clinical findings related to vanadium pentoxide exposure were
observed. Mean body weights of females exposed to 2 mg/m3 were marginally less (3-6%;
statistical significance not reported) than that of controls throughout the 2-year study; mean body
weights of exposed male rats were similar to controls throughout the study. The number of male
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and female rats surviving for the entire 104-week exposure period was low, but greater than that
for control animals for all vanadium pentoxide groups (Table 14).
The incidences of nonneoplastic lesions of the respiratory tract in male and female rats
are summarized in Table 14 (Ress et al., 2003; NTP, 2002). In male rats, the incidences of
nonneoplastic lesions of the lungs (alveolar and bronchiole epithelium hyperplasia and alveolar
histiocyte infiltration), larynx (inflammation and epiglottis degeneration, hyperplasia and
squamous metaplasia) and nose (goblet cell hyperplasia) were significantly increased compared
to control in all vanadium pentoxide exposure groups. In female rats, the incidences of
nonneoplastic lesions of the lungs (interstitial fibrosis and alveolar histiocyte infiltration) and
larynx (inflammation and epiglottis degeneration and hyperplasia) were significantly increased
compared to control in all vanadium pentoxide exposure groups. In general, the incidences and
severity ratings of respiratory lesions increased with exposure level. No treatment-related
histopathological findings were observed in other tissues. The LOAEL of 0.5 mg/m3 was
established for nonneoplastic lesions of the respiratory tract in male and female rats; a NOAEL
was not identified.
The incidences of respiratory tumors in male and female rats exposed to vanadium
pentoxide for 2 years are summarized in Table 15 (Ress et al., 2003; NTP, 2002). Compared to
control, the incidences of alveolar/bronchiolar adenoma, alveolar/bronchiolar carcinoma or
combined alveolar/bronchiolar adenoma or carcinoma were not significantly different compared
to control (Poly-3 test) for male or female rats. NTP (2002) reports that the incidences of
alveolar/bronchiolar adenoma in 0.5 and 2 mg/m3 males and 0.5 mg/m3 females,
alveolar/bronchiolar carcinoma in 0.5 and 2 mg/m3 males, and combined alveolar/bronchiolar
carcinoma in 0.5, 1 and 2 mg/m3 males and in 0.5 mg/m3 females exceed historical ranges for
F344/N rats in inhalation chamber controls given NIH-07 diet, the same diet used in the NTP
(2002) study (see Table 15 footnotes). Statistical comparisons of NTP (2002) tumor incidence
data in rats and historical incidence data were not conducted. The researchers conclude that
results of the NTP (2002) study were equivocal since the incidence of lung tumors in male and
female rats could not be conclusively attributed to exposure to vanadium pentoxide. However,
NTP (2002; Ress et al., 2003) also concluded that lung neoplasms were most likely related to
vanadium pentoxide exposure, since tumor incidence in the NTP (2002) study exceeded that for
historical controls.
NTP (2002) 2-Year Exposure Studies in Mice. The toxicity of chronic exposure to vanadium
pentoxide was assessed in groups of 50 male and 50 female B6C3Fi mice that were exposed
(whole-body exposure) to particulate aerosols of vanadium pentoxide concentrations of 0, 1, 2 or
4 mg/m3, 6 hours per day, 5 days/week, for 104 weeks (Ress et al., 2003; NTP, 2002). Particle
MMAD±GSD for each dose group was reported as follows: 1 mg/m3=1.3±2.9;
2 mg/m3=1.2±2.9; 4 mg/m3=1.2±2.9. Body weights and clinical findings were recorded
throughout the exposure period. Necropsy and complete histopathological evaluation were
performed on all animals. Many animals exposed to vanadium pentoxide were thin and exhibited
abnormal breathing, particularly those exposed to 2 or 4 mg/m3 vanadium pentoxide (specific
incidence data not reported). Mean body weights were generally less than control in males
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Table 14. Selected Nonneoplastic Lesions of the Respiratory System in Rats Exposed to
Vanadium Pentoxide for 2 Years (NTP, 2002)
Lesion Type and Location"
Exposure Group
Control 0.5 mg/m3 1 mg/m3 2 mg/m3
Male Rats
Percent survival
40
58
52
54
Lung
(Number of animals examined)
50
49
48
50
Alveolar epithelium, hyperplasia
7 (2.3)
24b (2.0)
34b (2.0)
49b (3.3)
Bronchiole epithelium, hyperplasia
3 (2.3)
17b (2.2)
31b (1.8)
48b (3.3)
Alveolar epithelium, squamous metaplasia
1 (1.0)
0
0
21b (3.6)
Bronchiole epithelium, squamous
metaplasia
0
0
0
7b (3/7)
Inflammation, chronic active
5 (1.6)
8(1.8)
24b (1.3)
42b (2.4)
Interstitial, fibrosis
7(1.4)
7 (2.0)
16° (1.6)
38b (2.1)
Alveolus, histiocyte infiltration
22(1.3)
40b (2.0)
45b (2.3)
50b (2.1)
Larynx
(Number of animals examined)
49
50
50
50
Inflammation, chronic
3 (1.0)
20b (1.1)
17b (1.5)
28b (1.6)
Epiglottis epithelium, degeneration
0
22b (1.1)
23b (1.1)
33b (1.5)
Epiglottis epithelium, hyperplasia
0
18b (1.5)
34b (1.5)
32b (1.9)
Epiglottis epithelium, squamous
metaplasia
0
9b (1.7)
16b (1.8)
19b (1.9)
Nose
(Number of animals examined)
49
50
49
48
Goblet cell, hyperplasia
4(1.8)
15b (1.8)
12° (2.0)
17b (2.1)
Female Rats
Percent survival
28
40
34
30
Lung
(Number of animals examined)
49
49
50
50
Alveolar epithelium, hyperplasia
4(1.0)
8(1.5)
21b (1.2)
50b (3.1)
Bronchiole epithelium, hyperplasia
6(1.5)
5 (1.6)
14° (1.3)
48b (3.0)
Alveolar epithelium, squamous metaplasia
0
0
0
6°(3.0)
Bronchiole epithelium, squamous
metaplasia
0
0
0
1 (2.0)
Inflammation,chronic active
10(1.5)
10(1.1)
14(1.2)
40b (1.7)
Interstitial, fibrosis
19 (1.4)
7b (1.3)
12 (1.6)
32b (1.4)
Alveolus, histiocyte infiltration
26(1.4)
35° (1.3)
44b (2.0)
50b (1.9)
Larynx
(Number of animals examined)
50
49
49
50
Inflammation, chronic
8(1.8)
26b (1.5)
27b (1.3)
38b (1.4)
Epiglottis epithelium, degeneration
2(1.0)
33b (1.2)
26b (1.3)
33b (1.5)
Epiglottis epithelium, hyperplasia
0
25b (1.4)
26b (1.3)
33b (1.5)
Epiglottis epithelium, squamous
metaplasia
2 (2.0)
7(1.9)
9(1.7)
16b (1.4)
Nose
(Number of animals examined)
50
50
50
50
Goblet cell, hyperplasia
12 (2.0)
19 (2.0)
16(1.9)
30b (2.0)
aNumber of animals with lesion; numbers in parentheses indicate average severity grade of lesions in affected animals:
l=minimal, 2=mild, 3=moderate, 4=marked
bSignificantly different from control by the Poly-3 test (p< 0.01)
cSignificantly different from control by the Poly-3 test (p< 0.05)
26
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Table 15. Incidences of Respiratory Tumors in Rats Exposed to Vanadium Pentoxide for
2 Years (NTP, 2002)a
Tumor Type
Exposure Group
Control
0.5 mg/m3
1 mg/m3
2 mg/m3
Male Rats
Number of animals examined
50
49
48
50
Alveolar/bronchoalveolar adenomab
4 (8%)
8 (16%)°
5 (10%)
6 (12%)°
Alveolar/bronchoalveolar
carcinomad
0 (0%)
3 (6%)°
1 (2%)
3 (6%)°
Alveolar/bronchoalveolar adenoma
or carcinoma"
4 (8%)
10 (20%)°
6 (12%)°
9 (18%)°
Female Rats
Number of animals examined
49
49
50
50
Alveolar/bronchoalveolar adenomaf
0 (0%)
3 (6%)°
1 (2%)
0 (0%)
Alveolar/bronchoalveolar carcinoma
0 (0%)
0 (0%)
0 (0%)
1 (2%)
Alveolar/bronchoalveolar adenoma
or carcinoma8
0 (0%)
3 (6%)°
1 (2%)
1 (2%)
aNumbers in parentheses indicate percent incidence; particle size mass mean aerodynamic diameter (MMAD±GSD):
0.5 mg/m3=1.2±2.9; 1 mg/m3=1.2±2.9; 2 mg/m3=1.3±2.9
bHistorical incidence of alveolar/bronchoalveolar adenoma male F344/N rats fed in inhalation chamber controls
given NIH-07 diet: range 0-10%
Incidence exceeds historical control (statistical comparison between NTP (2002) data and historical data not
conducted)
historical incidence of alveolar/bronchoalveolar carcinoma maleF344/N rats fed in inhalation chamber controls
given NIH-07 diet: range 0-4%
"Historical incidence of combined alveolar/bronchoalveolar adenoma or carcinoma male F344/N rats fed in
inhalation chamber controls given NIH-07 diet: range 0-10%
historical incidence of alveolar/bronchoalveolar adenoma female F344/N rats fed in inhalation chamber controls
given NIH-07 diet: range 0-4%
historical incidence of combined alveolar/bronchoalveolar adenoma or carcinoma female F344/N rats fed in
inhalation chamber controls given NIH-07 diet: range 0-4%
exposed to 4 mg/m3 (decreases of 5-15%) and in females for all exposure groups (1 mg/m3,
decreases of 4-10%; 2 mg/m3, decreases of 14-20%; and 4 mg/m3, decreases of 4-19%)
(statistical significance not reported). The number of mice surviving for the entire 104-week
exposure period was similar to control for all exposure groups for female mice and for males in
the 1 and 2 mg/m3 groups, but survival was significantly decreased in males exposed to 4 mg/m3
(Table 16).
The incidences of nonneoplastic lesions of the respiratory tract in male and female mice
are summarized in Table 16 (Ress et al., 2003; NTP, 2002). In male mice, the incidences of
nonneoplastic lesions of the lungs (hyperplasia of the alveolar and bronchiole epithelium,
inflammation, alveolus histiocyte infiltration), larynx (squamous metaplasia of the epiglottis) and
nose (olfactory and respiratory epithelium degeneration in males and olfactory epithelial
degeneration and atrophy in females) were significantly increased compared to control in all
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Table 16. Selected Nonneoplastic Lesions of the Respiratory System in Mice Exposed to
Vanadium Pentoxide for 2 Years (NTP, 2002)
Lesion Type and Location"
Exposure Group
Control
1 mg/m3
2 mg/m3
4 mg/m3
Male Mice
Percent survival
78
66
72
50b
Lung
(Number of animals examined)
50
50
50
50
Alveolar epithelium, hyperplasia
3 (3.0)
41° (2.2)
49° (3.3)
50° (3.9)
Bronchiole epithelium, hyperplasia
0
15° (1.0)
37° (1.1)
46° (1.7)
Inflammation, chronic
6(1.5)
42° (2.4)
45° (1.6)
47° (2.0)
Alveolus, histiocyte infiltration
10 (2.4)
36° (2.4)
45° (2.6)
49° (3.0)
Interstitial, fibrosis
1 (1.0)
6(1.7)
9°(1.2)
12° (1.7)
Larynx
(Number of animals examined)
49
50
48
50
Epiglottis epithelium, squamous
metaplasia
2(1.0)
45° (1.0)
41° (1.0)
41° (1.0)
Nose
(Number of animals examined)
50
50
50
50
Inflammation, suppurative
16(1.3)
11(1.4)
32° (1.2)
23b (1.3)
Olfactory epithelium, atrophy
6 (1.0)
7 (1.6)
9(1.3)
12 (1.2)
Olfactory epithelium, degeneration
1 (1.0)
7b (1.0)
23b (1.1)
30° (1.2)
Respiratory epithelium, degeneration
8(1.1)
22° (1.0)
38° (1.2)
41° (1.4)
Bronchial Lymph Node
(Number of animals examined)
40
38
36
40
Hyperplasia
7(2.1)
7 (2.4)
12(2.1)
13 (2.2)
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Table 16. Selected Nonneoplastic Lesions of the Respiratory System in Mice Exposed to
Vanadium Pentoxide for 2 Years (NTP, 2002)
Lesion Type and Location"
Exposure Group
Control
1 mg/m3
2 mg/m3
4 mg/m3
Female Mice
Percent survival
76
64
60
64
Lung
(Number of animals examined)
50
50
50
50
Alveolar epithelium, hyperplasia
31° (1.6)
38° (2.0)
50° (3.3)
Bronchiole epithelium, hyperplasia
0
12° (1.0)
34° (1.0)
48° (1.5)
Inflammation, chronic
0
37° (1.3)
39° (1.8)
49° (2.0)
Alveolus, histiocyte infiltration
4(1.0)
34° (2.4)
35° (2.4)
45° (2.7)
Interstitial, fibrosis
0
1 (2.0)
4b (2.5)
8°(1.5)
Larynx
(Number of animals examined)
50
50
49
50
Epiglottis epithelium, squamous
metaplasia
0
39° (1.0)
45° (1.0)
44° (1.1)
Nose
(Number of animals examined)
50
50
50
50
Inflammation, suppurative
19(1.1)
14(1.2)
32° (1.2)
30° (1.3)
Olfactory epithelium, atrophy
2(1.5)
8b (1.3)
5 (1.0)
14° (1.3)
Olfactory epithelium, degeneration
11(1.2)
23° (1.0)
34° (1.2)
48° (1.3)
Respiratory epithelium, degeneration
35 (1.3)
39(1.5)
46° (1.7)
50° (1.8)
Bronchial Lymph Node
(Number of animals examined)
39
40
45
41
Hyperplasia
3 (2.0)
13°(1.8)
14° (2.3)
20° (2.3)
aNumber of animals with lesion; numbers in parentheses indicate average severity grade of lesions in affected
animals: l=minimal, 2=mild, 3=moderate, 4=marked
bSignificantly different from control by the Poly-3 test (p< 0.05)
Significantly different from control by the Poly-3 test (p< 0.01)
vanadium pentoxide exposure groups. In general, the incidences and severity ratings of lesions
increased with exposure level. No treatment-related histopathological findings were observed in
other tissues. The LOAEL of 1 mg/m3 was established for nonneoplastic lesions of the
respiratory tract in male and female mice; a NOAEL was not identified.
The incidences of tumors of the respiratory tract in male and female mice exposed to
vanadium pentoxide for 2 years are summarized in Table 17 (Ress et al., 2003; NTP, 2002). The
incidences of alveolar/bronchiolar adenoma, alveolar/bronchiolar carcinoma and combined
alveolar/bronchiolar adenoma or carcinoma were significantly increased in all groups of exposed
female mice. In male mice, the incidences of alveolar/bronchiolar carcinoma and combined
alveolar/bronchiolar adenoma or carcinoma were significantly increased compared to control in
all vanadium pentoxide groups and alveolar/bronchiolar adenoma was significantly increased in
the 2 mg/m3 group.
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Table 17. Incidences of Respiratory Tumors in Mice Exposed to Vanadium Pentoxide for
2 Years (NTP, 2002)
Exposure Group
Tumor Type"
Control
1 mg/m3
2 mg/m3
4 mg/m3
Male Mice
Number of animals examined
50
50
50
50
Alveolar/bronchoalveolar adenomab
13 (26%)
16 (32%)
26° (53%)d
15 (30%)
Alveolar/bronchoalveolar carcinoma6
12 (24%)
29° (58%)d
30° (60%)d
35° (70%)d
Alveolar/bronchoalveolar adenoma or
carcinomaf
22 (28%)
42° (84%)d
43° (86%)d
43° (86)d
Female Mice
Number of animals examined
50
50
50
50
Alveolar/bronchoalveolar adenoma8
1 (2%)
17° (34%)d
23° (46%)d
19° (38%)d
Alveolar/bronchoalveolar carcinoma11
0 (0%)
23c (46%)d
18° (36%)d
22° (44%)d
Alveolar/bronchoalveolar adenoma or
carcinoma1
1 (2%)
32° (64%)d
35° (70%)d
32° (64%)d
aNumber of animals with tumor; numbers in parentheses indicate percent incidence; particle size mass mean aerodynamic
diameter (MMAD±GSD): 1 mg/m3= 1.3±2.9; 2 mg/m3= 1.2±2.9; 4 mg/m3=1.2±2.9
bHistorical incidence of alveolar/bronchoalveolar adenoma male B6C3Ft mice fed in inhalation chamber controls given NIH-07
diet: range 8-36%
cSignificantly different from control by the Poly-3 test (p<0.01)
incidence exceeds historical control (statistical comparison with NTP (2002) tumor incidence not conducted)
historical incidence of alveolar/bronchoalveolar carcinoma male B6C3F! mice fed in inhalation chamber controls given NIH-07
diet: range 0-21%
historical incidence of combined alveolar/bronchoalveolar adenoma or carcinoma male B6C3F! mice fed in inhalation chamber
controls given NIH-07 diet: range 14-42%)
BHistorical incidence of alveolar/bronchoalveolar adenoma female B6C3F! mice fed in inhalation chamber controls given NIH-07
diet: range 0-14%
hHistorical incidence of alveolar/bronchoalveolar carcinoma female B6C3F] mice fed in inhalation chamber controls given
NIH-07 diet: range 0-12%
'Historical incidence of combined alveolar/bronchoalveolar adenoma or carcinoma female B6C3F! mice fed in inhalation
chamber controls given NIH-07 diet: range 4-16%
Inhalation Reproductive and Developmental Toxicity
Mussali-Galante etal. (2005). Effects of vanadium pentoxide on gamma-tubulin in testicular
cells were assessed in male CD-I mice that were exposed by whole-body inhalation for 1
hour/day, 2 days/week for up to 12 weeks (Mussali-Galante et al., 2005). A 0.02 M aqueous
solution of vanadium pentoxide was aerosolized, generating a reported average vanadium
chamber concentration of 1.44 mg/m3, as vanadium metal (MW = 50.94). This exposure level
corresponds to 5.13 mg/m3 as vanadium pentoxide (MW = 181.9). Groups of 3 exposed mice
and 3 vehicle control mice (inhaling deionized water droplets) were evaluated weekly for 12
weeks. Gamma-tubulin is a key cellular protein involved in centrosome function and necessary
for cell division. Immunohistochemistry was used to determine percentages of gamma-tubulin-
immunopositive Sertoli, Leydig and germ cells. Vanadium exposure significantly decreased the
percentage of immunopositive cells for all three testicular cell types beginning at week 2 or 3.
The responses were duration-dependent with the lowest percentages of immunoreactive cells
occurring at the end of exposure period; values at week 12 ranged from 1.2% for germ cells and
1.5% for Sertoli cells to 10.1% for Leydig cells (compared to 87-88% in controls).
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Fortoul et al. (2007). Ultrastructure of the seminiferous tubules was evaluated in the testes of
male CD-I mice that were exposed to vanadium pentoxide by whole-body inhalation for 1
hour/day, 2 days/week for up to 12 weeks (Fortoul et al., 2007). The exposure concentration was
reported as 0.02 M, which apparently refers to the concentration of an aqueous solution of
vanadium pentoxide that was aerosolized. Reports of other studies by the same group of
investigators using the same exposure protocol indicate that the 0.02 M solution generated an
average vanadium chamber concentration of 1.44 mg/m3 (5.13 mg/m3 as vanadium pentoxide)
with 0.5-5 |im aerosol droplets (Avila-Costa et al., 2006; Gonzalez-Villalva et al., 2006;
Mussali-Galante et al., 2005). Five exposed mice and three vehicle control mice (inhaling
deionized water droplets) were sacrificed per week from the first to the 12th week of exposure.
No overt toxicosis or changes in body or testicular weight were observed. Necrosis of the
spermatogonium, spermatocytes and Sertoli cells occurred throughout most of the study. The
most susceptible cells to necrosis appeared to the spermatogonia. Spermatogonial mortality was
increased during weeks 2-12 with a maximum at weeks 6-7 (40% necrotic cells). Spermatocyte
and Sertoli cell mortality were increased during weeks 3-12 with maximums at weeks 5-6 (25%
and 15%) necrotic cells, respectively). Vacuolation occurred simultaneously with necrosis in the
Sertoli cells. Testicular vanadium concentration was increased after the first week of exposure
and remained stable throughout the exposure period; the average level was 33 times higher than
controls.
Together the two studies (Mussali-Galante et al., 2005; Fortoul et al., 2007) establish a
LOAEL for vanadium pentoxide for testicular effects from short-term intermittent expousre to
5.13 mg/m3. A continuous exposure equivalent concentration cannot be estimated with any
confidence, as the intermittency of the exposure protocol is extreme.
SUPPORTING STUDIES
Oral Toxicokinetic — Studies investigating the toxicokinetics of orally administered
vanadium pentoxide in humans or animals were not identified.
Inhalation Toxicokinetic — The toxicokinetics of inhaled vanadium has been studied
for several vanadium compounds; however, few studies have evaluated the toxicokinetics of
inhaled vanadium pentoxide. Studies investigating the toxicokinetics of inhaled vanadium
pentoxide in humans were not identified. Although occupational studies indicate that inhaled
vanadium is absorbed, as indicated by an increase in blood and urine vanadium, studies do not
identify the vanadium compounds that workers were exposed to or adequately quantify exposure
(Barth et al., 2002; Kiviluoto et al., 1981).
Results of toxicokinetics studies of inhaled or intratracheally administered vanadium
pentoxide in rats indicate that vanadium pentoxide is absorbed from the lung, undergoes a wide
distribution and is eliminated primarily into the urine (Dill et al., 2004; NTP, 2002; Rhoads and
Sanders, 1985). As part of the NTP (2002) cancer bioassay, lung and blood vanadium
concentrations and lung clearance half-times of vanadium were determined in groups of five
female F344/N rats and B6C3F1 mice exposed to 0, 1 (rats only), 2 or 4 (mice only) mg/m3 for 6
hours/day, 5 days/week for 16 days. Tissue burden analyses and lung and blood vanadium
31
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concentration analyses were performed immediately following exposure on day 16, and
elimination of vanadium from blood and lung was determined up to 8 days after exposure. Blood
vanadium concentrations in exposed and chamber control rats were highly variable. The small
increases in blood vanadium concentrations in exposed rats indicate that either very little
vanadium was absorbed or that vanadium was eliminated rapidly from the blood. No significant
differences were observed in blood vanadium concentrations between exposed groups. In mice,
blood vanadium concentrations in chamber control and exposed mice were below the limit of
detection (value not reported) in 37 of 45 samples tested. In both species, lung burdens were
proportional to exposure concentration, and lung vanadium concentrations were consistent with
linear kinetics over the exposure range studied. Lung clearance half-times ranged from 4.42 to
4.96 days in rats and from 2.40 to 2.55 days in mice, and were not significantly different between
exposure groups.
Dill et al. (2004) examined the lung deposition and clearance of inhaled vanadium
pentoxide in rats and mice following chronic inhalation exposure. Groups of 3-5 female
F344/N rats and B6C3F1 mice were exposed to vanadium pentoxide concentrations of 0, 0.5,
1 or 2 mg/m3 and 0, 1, 2 or 4 mg/m3, respectively, by whole-body inhalation, 6 hours/day,
5 days/week for 1, 5 and 12 days and 1, 2, 6, 12 and 18 months. The same data were also
reported by NTP (2002) as part of the cancer bioassay. Lung weights and lung vanadium burdens
were determined in all animals at all time points, and blood vanadium concentrations were
determined in up to five animals per group after 1, 2, 6, 12 and 18 months of exposure. Blood
vanadium concentrations in exposed groups were significantly higher than in controls in both
rats and mice, although it was not possible to determine if blood vanadium concentrations were
proportional to exposure concentration due to the small sample size and small differences in
blood concentrations between groups. Vanadium lung burden tended to be proportional to
exposure concentration and reached steady-state levels within 1-2 months in mice and 6 months
in rats in the lowest exposure group, but lung burden declined after 12 and 18 months in the mid-
and high-dose group for both species. Declines in vanadium lung burden at higher doses were
attributed to vanadium-induced pathological changes to the lung. Clearance of vanadium from
the lung was faster for mice compared to rats, with modeled estimates for lung elimination
half-life ranging from 6.26 to 13.9 days in mice and from 37.3 to 61.4 days in rats. Due to slower
lung clearance in rats, lung retention after 18 months of exposure was higher for rats than mice.
Rhoads and Sanders (1985) investigated the absorption, distribution and excretion of a
single dose of radiolabeled vanadium pentoxide (40 |ig) administered by intratracheal instillation
to young adult female rats of either the Wistar or Fischer strains. Vanadium in tissues was
determined at several time-points during the first 24 hours and at 3, 5, 7 and 14 days after dosing.
Clearance of vanadium from the lung exhibited a biphasic pattern, with a rapid initial phase
(half-life =11 minutes), followed by a slower phase (half-life =1.9 days). Vanadium was
distributed to liver, kidney, bone, blood, gastrointestinal tract and ovary, with peak levels
reached in all tissues within 3 days. The highest peak was observed in bone (17.2% of
administered dose), followed by blood (15.7% of administered dose). After 14 days, bone
retained 12.1% and the "carcass" retained 40% of the administered dose. Less than 2% of the
administered dose remained in each of the other tissues. Over the 14-day observation period,
approximately 28% of the administered dose was eliminated in urine and 14% in the feces.
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Whole body clearance exhibited biphasic kinetics, with a rapid initial phase (half-life =11
hours), following by a slower phase (51 days).
Genotoxicity
Results of in vitro assays of mutagenicity of vanadium pentoxide are summarized in
Table 18. Vanadium pentoxide produced gene mutations in most bacterial test systems, although
negative results were reported by NTP (2002) in a reverse mutation assay in Salmonella
typhimurium. Negative results were also reported in a gene mutation assay in Chinese hamster
V79 fibroblast cells (Zhong et al., 1994). Positive results were observed in cultured mammalian
cells for DNA strand breaks, micronuclei formation, aneuploidy, altered mitosis, cell
transformation and altered mitosis at concentrations that were not cytotoxic; negative results
were reported for sister chromatid exchange and chromosomal aberrations.
Experimental data in animals provide conflicting evidence of genotoxicity following in
vivo exposure to vanadium pentoxide. Vanadium pentoxide administered for 3 months by
inhalation to male and female mice (1, 2, 4, 8 or 16 mg/m3) did not increase the frequency of
micronucleated normochromatic erythrocytes in peripheral blood (NTP, 2002). Additional
details of exposure are provided in the NTP (2002) study summary (see Animal Inhalation
Subchronic Toxicity section).
Altamirano-Lozano et al. (1993, 1996, 1999). Genotoxicity was evaluated in male CD-I mice
following single intraperitoneal injections of 5.75, 11.5 or 23 mg/kg vanadium pentoxide
(Altamirano-Lozano et al., 1993, 1996). Exposure caused no treatment-related effects on mitotic
index, average generational time or sister chromatid exchanges in bone marrow cells
(Altamirano-Lozano et al., 1993), although all doses induced DNA damage in testicular germ
cells (Altamirano-Lozano et al., 1996). Altamirano-Lozano et al. (1999) assessed DNA damage
in male CD-I mice 24 hours following single intraperitoneal injections of 0, 23.0, 11.5 or
5.75 mg/kg vanadium pentoxide (corresponding approximately to the LD50, V2 LD50 and V4
LD50, respectively). Comet test results show the number of cells with DNA damage (primarily
single strand breaks and alkali labile damage) was increased in liver, kidney, lung, spleen and
heart, although increases did not exhibit dose-dependence. No evidence of DNA damage was
observed in bone marrow.
Evidence demonstrating mutagenic activity of vanadium pentoxide in vivo in humans is
lacking. The in vivo genotoxicity of vanadium pentoxide in lymphocytes and whole blood
leukocytes obtained from 49 male workers exposed to vanadium pentoxide at a processing plant
was compared to 12 non-exposed controls (Ivanscits et al., 2002). The average exposure duration
for workers was 12.4 years. Measurements or estimates of worker exposure to vanadium
pentoxide were not reported, although exposure to vanadium was confirmed through
measurement of serum and urine vanadium. No significant differences between vanadium-
exposed and control workers were observed for DNA stand breaks (as assessed by alkaline
comet assay), 8-hydroxy-2'deoxyguanosine (an oxidized DNA base common indicative of
oxidative stress) or the frequency of sister chromatid exchange.
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Table 18. Genotoxicity of Vanadium Pentoxideiw Vitro
Test System
Endpoint
Results"
Reference
With
Activation
Without
Activation
Bacillus subtilis (recombinant
repair phenotype -assay)
Recombination repair
+
+
Kadaetal., 1980
Escherichia coli (reverse
mutation)
Gene mutation
No data
+
Kanematsu et al.,
1980
Salmonella typhimurium (reverse
mutation)
Gene mutation
No data
+
Kanematsu et al.,
1980
S. typhimurium (reverse
mutation)
Gene mutation
-
-
NTP, 2002
Chinese hamster V79 fibroblast
cell line
Gene mutation
No data
-
Zhongetal., 1994
Chinese hamster V79 fibroblast
cell line
Mitosis
No data
+
Zhongetal., 1994
Chinese hamster V79 fibroblast
cell line
Sister chromatid exchange
No data
-
Zhongetal., 1994
Chinese hamster V79 fibroblast
cell line
Micronucleus formation
No data
+
Zhongetal., 1994
Human lymphocytes
Chromosomal aberrations
Not applicable
-
Roldan and
Altamirano, 1990
Human lymphocytes
Sister chromatid exchange
Not applicable
-
Roldan and
Altamirano, 1990
Human lymphocytes
Aneuploidy
Not applicable
+
Ramirez et al., 1997
Human lymphocytes
Polyploidy
Not applicable
+
Roldan and
Altamirano, 1990
Human lymphocytes
DNA strand breaks
Not applicable
+
Rojas et al., 1996
Human lymphocytes
DNA strand breaks
Not applicable
+
Ivancsits et al., 2002
Human fibroblasts
DNA strand breaks
Not applicable
+
Ivancsits et al., 2002
Syrian hamster embryo cell
Cell transformation
Not applicable
+
Kerckaert et al., 1996
a - = negative; + = positive
Other Potential Effects
Vanadium salts have emerged as potential agents in the treatment of diabetes due to their
ability to lower blood glucose and mimic insulin activity. Several recent publications have
reviewed the anti-diabetic action of numerous vanadium compounds, including inorganic
vanadium salts, peroxovanadium complexes and organic vanadium compounds (Mukjerjee et al.,
2004; Marzban and McNeill, 2003; Domingo, 2002; Cam et al., 2000; Srivasta, 2000). The
glucose-lowering activity of vanadium compounds is attributed to vanadyl (the cationic form of
vanadium), which is the predominant intracellular form of vanadium, rather than to specific
vanadium compounds or complexes (Marzban and McNeill, 2003). Studies assessing the
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anti-diabetic action of vanadium pentoxide were not located; therefore, the potential for
vanadium pentoxide to lower blood glucose is unknown.
FEASIBILITY FOR DERIVING A PROVISIONAL SUBCHRONIC RfD
FOR VANADIUM PENTOXIDE
No studies investigating the effects of acute, subchronic or chronic oral exposure to
vanadium pentoxide in humans were identified. No animal studies that have comprehensively
examined histopathological, biochemical and clinical endpoints of subchronic oral exposure
were identified. Mountain et al. (1953) evaluated the effects of exposure of rats to dietary
vanadium pentoxide for 103 days on body weight gain, erythrocyte count, hemoglobin and
cystine content of hair, but did not report any information on other endpoints. A chronic RfD of
9E-03 mg/kg-day for vanadium pentoxide is available on IRIS based on a 2.5-year dietary
NOAEL of 17.85 ppm (equivalent to 0.89 mg/kg/day) for decreased hair cystine content in an
unpublished study in rats by Stokinger et al. (1953); no effects on growth or survival were seen
in this study. The lack of adequate subchronic oral data for humans or animals precludes
derivation of a subchronic p-RfD for vanadium pentoxide. In the absence of a subchronic p-RfD,
the chronic RfD of 9E-03 mg/kg-day can be applied to subchronic exposures, as is the standard
practice.
DERIVATION OF PROVISIONAL SUBCHRONIC AND CHRONIC RfCs
FOR VANADIUM PENTOXIDE
Provisional Subchronic RfC
The available human and animal data identify the respiratory tract as the primary target
for subchronic exposure to vanadium pentoxide. Irritation of the upper and lower respiratory
tract has been reported in several acute and subchronic occupational and case studies of workers
exposed to vanadium pentoxide in fuel-oil ash and vanadium dust (Woodin et al., 2000; Irsigler
et al., 1999; Woodin et al., 1999; Hauser et al., 1995; Levy et al., 1984; Musk and Tees, 1982;
Kiviluoto, 1980; Lees, 1980; Kiviluoto et al., 1979; Zenz et al., 1962; Sjoberg, 1955; Vintinner et
al., 1955; Williams, 1952). Symptoms of irritation include bronchitis, airway obstruction, chest
pain, rhinitis, pharyngitis, laryngitis and conjunctivitis. Although subchronic occupational
exposure studies provide supportive evidence for the respiratory tract as a target for inhaled
vanadium pentoxide, studies failed to adequately quantify vanadium pentoxide exposure.
Furthermore, occupational exposures were most likely to a complex mix of chemicals, rather
than to vanadium pentoxide only. Thus, the available occupational exposure studies are not
suitable as the basis for the subchronic p-RfC. Results of an uncontrolled acute inhalation study
in volunteers provide supportive evidence for the respiratory irritant effects of vanadium
pentoxide, with symptoms of respiratory irritation (cough and increased mucous production)
observed at a concentration of 0.1 mg/m3 (Zenz and Berg, 1967). However, due to the lack of
control exposure, short exposure duration (8 hours) and low number of subjects (n=2) studied,
these data are not suitable for deriving the subchronic p-RfC.
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Results of the NTP (2002) study in rats and mice provide evidence of toxicity to the
upper and lower respiratory tract, including increased lung weight, inflammation, nonneoplastic
lesions, and decreased pulmonary function following 13-day, 16-day or 3-month inhalation
exposure to vanadium pentoxide. A significant increase in pulmonary inflammation and
histiocytic infiltrate of minimal to mild severity was observed in female rats (assessments not
made in male rats) exposed to vanadium pentoxide for 13 days, with a LOAEL of 1 mg/m3; a
NOAEL was not established (Table 2). Similar results were observed for female mice
(assessments not made in male mice) exposed for 13 days, with a LOAEL of 2 mg/m3 for
minimal to mild epithelial hyperplasia and inflammation; a NOAEL was not established (Table
6). Nonneoplastic lung lesions were observed in male and female rats and mice exposed for 3
months, with NOAEL and LOAEL values of 1 and 2 mg/m3, respectively, for minimal to mild
epithelial hyperplasia (Tables 11 and 13). Significant exposure-related decreases in pulmonary
function were observed in male and female rats, with a LOAEL of 4 mg/m3 (pulmonary function
not assessed in mice) (NTP, 2002). An acute exposure study in cynomologus monkeys
established NOAEL and LOAEL values of 0.5 and 5 mg/m3, respectively, for decreased
pulmonary function (Knecht et al., 1985). Knecht et al. (1985) did not assess histopathological
changes to the respiratory tract. Other targets identified from subchronic inhalation studies are
the hematopoietic system and the central nervous system. Mild microcytosis was observed in
male and female rats exposed to inhaled vanadium pentoxide for 3 months (Table 10);
hematological endpoints were not examined in mice (NTP, 2002). The NOAELs for mild
microcytosis were 1 mg/m3 in male rats and 4 mg/m3 in female rats. NTP (2002) stated that the
observed erythrocytosis was consistent with tissue hypoxia resulting from reduced oxygenation
caused by the pulmonary lesions. Consequently, the erythrocytosis is considered to be a
secondary effect arising from the primary lung lesions. Avila-Costa et al. (2004, 2005, 2006)
reported morphological changes in the substantia nigra region of the basal ganglia and the
blood-brain barrier in male mice exposed to 1.4 mg/m3 for up to 8 weeks; effects on central
nervous system function or other comprehensive endpoints were not reported. This study did not
provide any information on the exposure-response relationship for morphological changes to the
central nervous system since only one exposure level was tested.
The most sensitive endpoints by species, gender and duration identified by acute and
subchronic inhalation studies with vanadium pentoxide are summarized in Table 19. Adverse
effects to the respiratory system were reported in rats and mice following exposure for 13 days,
16 days and 3 months (NTP, 2002) and in monkeys (Knecht et al., 1985), and humans (Zenz and
Berg, 1967) following acute exposure. Adverse systemic effects identified were microcytic
erythrocytosis in male rats exposed for 3 months (NTP, 2002) and morphological changes to the
central nervous system (CNS) in male mice exposed for up to 8 weeks (Avila-Costa et al., 2004,
2005). Knecht et al. (1985) reported NOAEL and LOAEL values of 0.5 and 5 mg/m3,
respectively, for respiratory effects; however, due to the short exposure duration (a single 6-hour
inhalation exposure) and small number of animals studied, these data were not used for
derivation of the subchronic p-RfC. The study in humans (Zenz and Berg, 1967) was not useful
for derivation of the subchronic p-RfC due to the absence of control exposure; furthermore,
subjective symptoms limit utility of the data. Morphological changes in the CNS reported by
Alvila-Costa et al. (2004, 2005) were not considered as the critical effect due to inconsistencies
in reporting of the exposure concentration.
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Table 19. Most Sensitive Endpoints by Species, Gender and Duration Identified in Acute
and Subchronic Inhalation Studies with Vanadium Pentoxide
Species
(sex)
Exposure
Duration
Effect
NOAELadj
(mg/m3)
LOAELadj
(mg/m3)
Reference
Monkey
(male)
6 hours
Air-flow restriction (measured
by pulmonary function tests)
0.5a
5.0
Knechtetal., 1985
Human
(not reported)
8 hours
Respiratory irritation, cough,
mucus formation
—
0.1a
Zenz and Berg, 1967
Rat
(females)
13 days
Nonneoplastic lung lesions
(histiocytic infiltrate,
inflammation)
0.18
NTP, 2002
Mouse
(females)
13 days
Lung inflammation
—
0.36
NTP, 2002
Mouse
(both)
16 days
Relative lung weight
—
0.36
NTP, 2002
Mouse
(males)
8 weeks
Morphological changes to CNS
—
5.6b
Avila-Costa et al.,
2004, 2005
Mouse
(males)
12 weeks
Testicular effects
5.6b
Mussali-Galante
2005; Fortoul et al.,
2007
Rat
(both)
3 months
Microcytic erythrocytosis, lung
epithelial hyperplasia and
inflammation
0.18
0.36
NTP, 2002
Mouse
(both)
3 months
Inflammation of respiratory
epithelium; increased absolute
lung weights
0.18
0.36
NTP, 2002
Monkey
(male)
6 months
No adverse effects
0.1
—
Knechtetal., 1992
Single exposures not adjusted for continuous expsoure
b Not adjusted for continuous exposure because of the highly intermittent exposure protocol (1 hr/day, 2 days/wk)
To determine the most sensitive endpoint for derivation of the subchronic p-RfC, human
equivalent concentration (HEC) conversions were calculated for systemic effects (microcytic
erythrocytosis) and respiratory tract effects in rats and mice reported in the 2-week and 3-month
studies conducted by NTP (2002). Duration adjusted-concentrations (NOAEL[Adj] and
LOAEL[adj]) used to calculate HEC values are summarized in Table 20. Using the RDDR
computer program, as specified in the RfC guidelines (U.S. EPA, 1994b), NOAEL[Hec]S and
LOAEL[hec]S (in mg vanadium pentoxide/m3) were calculated using mean body weights for
males and females reported by NTP (2002) and the average particle size MMAD±GSD of
1.2±2.8 for rats and mice as reported by NTP (2002) for effects occurring in the lung or
systemically. Based on results of the HEC conversions, the respiratory system was identified as
the primary target for vanadium pentoxide toxicity. The most sensitive endpoint for respiratory
effects within the subchronic exposure period is inflammation of the broncho-alveolar region of
the lung in female rats exposed to vanadium pentoxide for 13 days, with a LOAEL[Hec] of
0.11 mg/m3 (NTP, 2002). As discussed previously, based on the classification of lesion severity
of minimal to mild, the LOAEL was considered minimal. As shown in Table 21, the incidence of
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Table 20. Human Equivalent Concentrations Corresponding to Short-term and
Subchronic NOAEL and LOAEL Values for Lung Effects3 in Rats and Mice Exposed to
Inhaled Vanadium Pentoxide (NTP, 2002)
Species
(sex)
Exposure
Duration
(days)
NOAEL (mg/m3)
LOAEL(mg/m3)
RDDRC
NOAEL[hec]
(mg/m )d
LOAEL[hec]
(mg/m)11
Actual
Adjustedb
Actual
Adjustedb
Rat
(females)
13
—
—
1
0.18
0.616
—
0.11
Mouse
(males)
13
—
—
2
0.36
1.340
—
0.48
Mouse
(females)
13
—
—
2
0.36
1.145
—
0.41
Rat
(males)
90
1
0.18
2
0.36
0.692
0.12
0.25
Rat
(females)
90
1
0.18
2
0.36
0.616
0.11
0.22
Mouse
(males)
90
1
0.18
2
0.36
1.340
0.24
0.48
Mouse
(females)
90
1
0.18
2
0.36
1.145
0.21
0.41
a Generally bronchiolar or alveolar epithelial hyperplasia and inflammation
b Adjusted to continuous 24-hr/7-day exposures from 6-hr/5-day exposure protocol
0Regionally Deposited Dose Ratio per RfC methodology (U.S. EPA, 1994b)
dN(L)OAEL(ADj) x RDDR
Table 21. Incidences of Nonneoplastic Lesions of the Lung in Female Rats (F344/N)
Exposed to Vanadium Pentoxide by Inhalation for 13 Days (NTP, 2002)
Parameter/Species
Number of Animals with Lesion"
Control
1 mg/m3
2 mg/m3
4 mg/m3
Histiocytic infiltrate
0
10b (1.3)
10b (1.9)
10b (2.2)
Inflammation
0
8b (1.3)
10b (1.7)
10b (2.0)
a10 rats/treatment group; numbers in parentheses indicate average severity grade in affected animals: l=minimal,
2=mild, 3=moderate, 4=marked
bSignificantly different from control group by the Fisher exact test (p< 0.05)
inflammation was 100% or nearly 100% in all vanadium pentoxide groups; therefore, data were
not suitable for benchmark dose (BMD) analysis. Thus, the NOAEL/LOAEL approach was used
to identify the POD for derivation of the subchronic p-RfC. A subchronic p-RfC based on the
most sensitive respiratory effect would be protective for microcytosis, which occurred at higher
exposure levels than respiratory effects. The slightly longer-term 6-month NOAEL[Adj] of 0.1
mg/m3 in monkeys (Knect et al., 1992) also supports the choice of the POD.
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The LOAEL[hec] of 0.11 mg/m3 calculated for nonneoplastic lesions of the lung (alveolar
epithelial hyperplasia, histiocytic infiltrate and inflammation) in female rats (NTP, 2002) was
used to derive the subchronic p-RfC of 1E-04 mg/m3 as follows:
subchronic p-RfC = LOAEL[Hec] ^ UF
= 0.11 mg/m3 - 1000
= 0.0001 mg/m3 or 1E-04 mg/m3
The uncertainty factor (UF) of 1000 was composed of the following:
A partial UF of 3 (10°5) was applied for extrapolation from a minimal LOAEL to
a NOAEL. Although 80-100% of treated animals were affected, the effects at the
LOAEL were considered to be minimal biological effects based on the severity
classification of minimal to mild.
A default 10-fold UF for intraspecies differences was used to account for
potentially susceptible individuals in the absence of quantitative information or
information on the variability of response in humans. Individuals with
pre-existing respiratory disorders may be more susceptible to inhaled vanadium
pentoxide.
The default UF of 3 (10°5) when using the RfC dosimetry conversions (U.S. EPA,
1994b) was applied for interspecies extrapolation to account for potential
pharmacodynamic differences between rats and humans. .
The full default UF of 10 was used for database insufficiencies due to the lack of
adequate inhalation developmental toxicity studies and a multi-generation
reproduction study.
The exposure duration in the critical study was only 13 days, which is less than
subchronic. However, since the database included studies of subchronic duration,
an additional UF to account for exposure duration is not required.
Confidence in the LOAEL for respiratory effects is high. Respiratory tract toxicity has
been consistently reported in acute and subchronic exposure studies in mice, rats, monkeys and
humans, with LOAEL values ranging from 0.1 to 5 mg/m3. Chronic inflammation of the lung
was observed in rats at the same exposure level as the LOAEL (NTP, 2002). Confidence in the
key study is high. NTP (2002) assessed comprehensive endpoints in an appropriate number of
animals. Confidence in the experimental database is low. Although there is rigorous assessment
of subchronic toxicity in two species (NTP, 2002), data on the developmental or reproductive
toxicity of inhaled vanadium pentoxide are inadequate. There is evidence of testicular toxicity
following inhalation exposure (Mussali-Galante 2005; Fortoul et al., 2007), but a definite
LOAEL cannot be established given the intermittent exposure protocol. Reproductive and
developmental effects were reported in rats and mice injected subcutaneously with higher doses
(5 - 12.5 mg/kg), but an equivalent inhalation exposure cannot be determined from these studies
(Altamirano et al, 1991; Altamirano-Lozano et al, 1993, 1996; Zhang et al. 1991, 1993a, 1993b).
Overall confidence in the subchronic p-RfC is medium.
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Provisional Chronic RfC
The effects of chronic inhalation of vanadium pentoxide were assessed in a single 2-year
exposure study in rats and mice (NTP, 2002). The 26-month single-exposure cynomolgus
monkey study (Knecht et al., 1992) is the only other long-term study available. No additional
chronic exposure studies in animals were identified. Similar to subchronic exposure studies,
results of the NTP (2002) 2-year study identify the upper and lower respiratory tract as the target
for chronic inhalation exposure to vanadium pentoxide. Other target organs were not identified in
the chronic exposure studies conducted by NTP (2002). As discussed earlier, although irritation
of the upper and lower respiratory tract has been reported in several acute and subchronic
occupational and case studies of workers exposed to vanadium pentoxide in fuel-oil ash and
vanadium dust, exposure was not sufficiently quantified; therefore, data are not suitable for
deriving the p-RfC.
The NTP (2002) 2-year exposure study was chosen as the key study for the derivation of
the p-RfC based on nonneoplastic lesions of the respiratory tract in male and female rats and
mice. As summarized in Tables 14 and 16, numerous lesions of the upper and lower respiratory
tract were observed in male and female rats and mice at the lowest exposure concentrations
tested, yielding LOAELs of 0.5 mg/m3 in rats and 1 mg/m3 in mice; NOAELs were not
identified. In rats exposed to 0.5 mg/m3, lesions were observed in the nose, larynx, bronchioles
and lung of males and the nose and larynx of females. In mice exposed to 1 mg/mg3, lesions
were observed in the nose, bronchiole and lung of male mice and the nose, larynx, bronchioles
and lung of female mice. To identify the most sensitive endpoint for derivation of the p-RfC,
human equivalent concentration (HEC) conversions were calculated for each region of the
respiratory tract in which lesions were observed at the lowest concentration tested (e.g.,
LOAEL[hec])- Duration adjusted-concentrations (LOAEL[Adj]) used to calculate HEC values are
summarized in Table 22. Using the RDDR computer program, as specified in the RfC guidelines
(U.S. EPA, 1994b), LOAEL[Hec]S (in mg vanadium pentoxide/m3) were calculated for each
species and sex using mean body weights for males and females reported by NTP (2002) and the
average particle size MMAD±GSD of 1.2±2.9 for rats and mice as reported by NTP (2002)
study, with effects occurring in various regions of the respiratory tract (Table 22).
The Knecht et al. (1992) monkey study established aNOAEL[ADj] of 0.1 mg/m3. This
value is close to the LOAEL[Adj] of 0.09 mg/m3 for rats in the NTP (2002) study, bringing into
consdiration the relative HEC values. As there are no studies available to establish an RDDR for
monkeys, dosimetry modeling cannot be used to establish an HEC. Therefore, the full 10-fold
interspecies uncertainty factor would be applied to the NOAEL[Adj] if the monkey study was
used as the basis for the RfC. The resulting RfC would be twice the RfC based on the
LOAEL[hec] from the NTP (2002) study, so the monkey NOAEL[ADj] is not an appropriate
choice for the POD.
As shown in Table 22, the lowest LOAEL[Hec] of 0.016 mg/m3 was observed for
nonneoplastic lesions of the larynx of female rats, indicating that the larynx was the most
sensitive target for chronic inhalation exposure to vanadium pentoxide. Thus, nonneoplastic
lesions of the larynx in the female rat were chosen as the critical effect for the basis of the p-RfC.
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Table 22. LOAEL Values, Expressed in Terms of HEC, for Nonneoplastic Lesions of
Various Regions of the Respiratory Tract in Rats and Mice Exposed to Vanadium
Pentoxide by Inhalation for 2 Years (NTP, 2002)
Species
(Sex)
LOAEL
(mg/m3)
loael[ADJ] a
(mg/m3)
Lesion Location
RDDR
LOAEL[HEC]b
(mg/m3)
Rat
0.5
0.09
lung
0.398
0.036
(Male)
0.5
0.09
bronchiole
2.328
0.210
0.5
0.09
larynx and nose
0.340
0.031
Rat
0.5
0.09
lung
0.414
0.037
(Female)
0.5
0.09
larynx
0.182
0.016
Mouse
1
0.18
lung
0.975
0.176
(Male)
1
0.18
bronchiole
3.089
0.556
1
0.18
nose
0.338
0.061
Mouse (Female)
1
0.18
lung
0.942
0.170
1
0.18
bronchiole
2.993
0.539
1
0.18
lung and bronchiole
0.313
0.258
1
0.18
larynx and nose
1.433
0.056
aLOAEL[ADJ] = LOAEL x 6/24 x 5/7
bLOAEL[HEC] — I .OA HI. x RDDR
Incidence data for lesions of the larynx in female rats are summarized in Table 23. To
determine the point of departure for derivation of the p-RfC, benchmark dose modeling was
conducted for two lesions of the larynx, inflammation and epithelial hyperplasia, in the female
rat. Degeneration of the epiglottis epithelium was not selected for BMD modeling because the
incidence of this lesion did not exhibit dose-dependence, with the same incidence observed in the
low and high dose groups. Epithelial squamous metaplasia was not selected for BMD modeling
Table 23. Incidences of Nonneoplastic Lesions of the Larynx in Female Rats Exposed to
Vanadium Pentoxide by Inhalation for 2 Years (NTP, 2002)
Lesion Type"
HEC (mg/m3)
Control
0.016 mg/m3
0.033 mg/m3
0.067 mg/m3
Number of animals examined
50
49
49
50
Inflammation, chronic
8
26b
27b
38b
Epiglottis, epithelial hyperplasia
0
25b
26b
33b
Epiglottis, epithelial degeneration
2
33b
36b
33b
Epiglottis, epithelial squamous
metaplasia
2
7
9
16b
aNumber of animals with lesion
bSignificantly different from control by the Poly-3 test, p< 0.01
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because the incidence of this lesion was not significantly different from control at the low- and
mid-dose groups; thus, other lesions of the larynx were more sensitive endpoints. In all vanadium
pentoxide groups, lesion severity was classified as minimal to mild. Duration-adjusted exposure
concentrations (ConC[ADj]) of 0.09, 0.18 and 0.37 mg/m3, corresponding to nominal exposure
concentrations of 0.5, 1 and 2 mg/m3, were calculated as follows:
ConC[ADj] = Cone x 6/24 x 5/7
HECs were calculated by multiplying ConC[ADj] by the RDDR of 0.182 for lesions of the
larynx in female rats.
Modeling was performed using the Benchmark Dose Modeling Software (BMDS;
Version 1.3.1) developed by the National Center for Environmental Assessment (U. S. EPA,
2000). In accordance with the U.S. EPA (2000) BMD methodology, the default benchmark
response (BMR) of 10% increase in extra risk was used as the basis for the BMD (BMD10), with
the BMDL10 represented by the 95% lower confidence limit on the BMDi0. All available
dichotomous models were fit to the incidence data for chronic inflammation and epithelial
hyperplasia of the epiglottis (Table 23). Goodness-of-fit was evaluated using the Chi-square
statistic calculated by the BMDS program. Acceptable global goodness of fit was a p-value
greater than or equal to 0.1. Models that did not meet this criterion were eliminated from
consideration. Local fit was evaluated visually on the graphic output, by comparing the observed
and estimated results at each data point. The model with the lowest Akaike's information criteria
(AIC) value was considered to provide a superior fit.
Results of the BMDS modeling for chronic inflammation of the larynx are summarized in
Table 24. As assessed by the chi-square goodness-of-fit test, several models in the software
provided adequate fits to the data. The log-logistic model was determined to be the best-fitting
model, as indicated by the lowest AIC (Table 24 and Figure 2), with a BMDL10 of
0.0022 mg/m3.
Results of the BMDS modeling for epithelial hyperplasia of the epiglottis are summarized
in Table 25 and Figure 3. As assessed by the chi-square goodness-of-fit test, four of the models
provided adequate fits {%2 p-value >0.1). Three of the models (gamma, multi-stage and Weibull),
however, are mathematically equivalent (as an exponential distribution) as the power (or slope)
parameter was estimated at the constrained lower bound of 1. The BMDL10 of 0.0022 mg/m3
from the log-logistic model was selected based on the lowest AIC value (Table 24).
Benchmark dose modeling of incidence data for chronic inflammation of the larynx and
epithelial hyperplasia of the epiglottis yielded the same BMD10 of 0.003 mg/m3 and BMDL10 of
0.0022 mg/m3. The provisional RfC of 0.000007 mg/m3 or 7E-06 mg/m3 was derived as
follows:
p-RfC = BMDL10 - UF
= 0.0022 mg/m3 - 300
= 0.000007 mg/m3 or 7E-06 mg/m3
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Table 24. Goodness of Fit Statistics and BMDi0s and BMDLi0s From Models Fit to
Incidence Data for Chronic Inflammation of the Larynx of Female Rats Exposed to
Vanadium Pentoxide by Inhalation for 2 Years (NTP, 2002)
Model
Degrees of
Freedom
X2 Test
Statistic
X2 p-Valuea
AIC
BMD10
(mg/m3)
BMDL10
(mg/m3)
Gammab
2
3.54
0.1702
241.742
0.00526062
0.00404152
Logistic
2
7.36
0.0253
245.803
0.00978952
0.00806489
Log-Logistice'd
2
1.67
0.4348
239.886
0.00314813
0.00216334
Multistage
1-degree6
2
3.54
0.1702
241.742
0.00526063
0.00404152
Probit
2
7.36
0.0252
245.792
0.00971167
0.00811435
Log-probitd
2
5.95
0.0511
244.055
0.00919646
0.00699817
Weibullb
2
3.54
0.1702
241.742
0.00526061
0.00404152
aValues <0.1 fail to meet BMDS goodness-of-fit criteria
bPower restricted to > 1; lower bound on parameter estimate hit
°Best-fitting model as assessed by the lowest-AIC criterion
dSlope restricted to > 1; lower bound on parameter estimate hit
"Betas restricted to > 0; lowest degree polynomial model with an adequate fit is reported
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Log-Logistic Model with 0.95 Confidence Level
Log-Logistic
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
BMDL BMD
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
dose
14:20 05/04 2006
BMDs and BMDLs indicated are for a 10% extra risk and are in units of mg/m3
Figure 2. Observed and Predicted Incidences of Inflammation of the Larynx in Female
Rats Exposed to Vanadium Pentoxide by Inhalation for 2 Years by NTP (2002)
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Table 25. Goodness of Fit Statistics and BMDi0s and BMDLi0s From Models Fit to
Incidence Data for Epithelial Hyperplasia of the Epiglottis in Female Rats Exposed to
Vanadium Pentoxide by Inhalation for 2 Years (NTP, 2002)
Model
Degrees of
Freedom
X2 Test
Statistic
X2 p-Valuea
AIC
BMD10
(mg/m3)
BMDL10
(mg/m3)
Gammab
3
14.11
0.0028
214.607
0.00461527
0.00384345
Logistic
2
25.06
0.0000
237.359
0.012132
0.0101008
Log-Logistice'd
3
4.42
0.2191
206.048
0.00272969
0.00205055
Multistage
1-degree6
3
14.11
0.0028
214.607
0.00461527
0.00384345
Probit
2
24.99
0.0000
236.771
0.0117506
0.00992799
Log-probitd
3
19.14
0.0003
218.709
0.00757035
0.00635086
Quantal-linear
3
14.11
0.0028
214.607
0.00461528
0.00384345
Quantal-quadratic
2
33.14
0.0000
246.358
0.0205956
0.0172045
Weibullb
3
14.11
0.0028
214.607
0.00461528
0.00384345
aValues <0.1 fail to meet conventional goodness-of-fit criteria
bPower restricted to > 1
°Best-fitting model
dSlope restricted to > 1
eBetas restricted to > 0; degree polynomial model with the best fit is reported
45
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Log-Logistic Model with 0.95 Confidence Level
0.8
0.7
0.6
J °'5
O
0
11=
< 0.4
c
o
o
2 0.3
Ll_
0.2
0.1
0
Log-Logistic
BMDL ,BMD
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
dose
08:40 05/05 2006
BMD and BMDL indicated are for a 10% extra risk and are in units of mg/m3
Figure 3. Observed and Predicted Incidences of Epithelial Hyperplasia of the Epiglottis in
Female Rats Exposed to Vanadium Pentoxide by Inhalation for 2 Years by NTP (2002)
46
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The uncertainty factor of 300 was composed of the following:
A default 10-fold UF for intraspecies differences was used to account for
potentially susceptible individuals in the absence of quantitative information or
information on the variability of response in humans. Individuals with
pre-existing respiratory disorders may be more susceptible to inhaled vanadium
pentoxide.
A partial UF of 3 (10°5) was applied for interspecies extrapolation to account for
potential pharmacodynamic differences between rats and humans. Converting the
rat data to human equivalent concentrations by the dosimetric equations accounts
for pharmacokinetic differences between rats and humans; thus, it was not
necessary to use the default UF of 10 for interspecies extrapolation (U.S. EPA,
1994b).
The full default UF of 10 was used for database insufficiencies due to the lack of
adequate inhalation developmental toxicity studies and a multi-generation
reproduction study.
The POD was determined by benchmark dose analysis; therefore, a UF to
extrapolate from a minimal LOAEL to a NOAEL was not necessary.
Confidence in the key study is high. NTP (2002) assessed comprehensive endpoints in an
appropriate number of animals. Confidence in the experimental database is medium, since the
toxicity of chronic inhalation exposure to vanadium pentoxide was rigorously assessed in two
rodent species by NTP (2002). A long-term, although less than chronic, NOAEL was established
in monkeys, as well. Respiratory tract toxicity has been consistently reported in acute,
subchronic and chronic exposure studies in mice, rats, monkeys and humans, although little
quantitative data are available in humans. Data on the developmental or reproductive toxicity of
inhaled vanadium pentoxide are inadequate. There is evidence of testicular toxicity following
inhalation exposure (Mussali-Galante 2005; Fortoul et al., 2007), but a definite LOAEL cannot
be established given the intermittent exposure protocol. Reproductive and developmental effects
were reported in rats and mice injected subcutaneously with higher doses (5 - 12.5 mg/kg), but
an equivalent inhalation exposure cannot be determined from these studies (Altamirano et al,
1991; Altamirano-Lozano et al, 1993, 1996; Zhang et al. 1991, 1993a, 1993b). Overall
confidence in the p-RfC is medium.
PROVISIONAL CARCINOGENICITY ASSESSMENT
FOR VANADIUM PENTOXIDE
Weight of Evidence Descriptor
Under the 2005 Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005a), the
available evidence for inhalation exposure to vanadium pentoxide is suggestive of carcinogenic
potential. In the NTP (2002) study, there was some evidence of carcinogenic activity in male rats
but equivocal evidence in female rats. Although the incidence of bronchoalveolar tumors in
vanadium-pentoxide-treated rats was not significantly increased compared to control, tumor
incidence was elevated relative to historical control in most treatment groups in male rats and
47
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some treatment groups in female rats (Table 15). There was clear evidence of carcinogenesis in
both male and female mice based on the increased incidence of alveolar/bronchiolar tumors
(NTP, 2002; Ress et al., 2003). No studies evaluating the carcinogenic potential in humans
exposed to inhaled vanadium pentoxide were identified. No studies suitable for evaluation of the
oral carcinogenic potential for vanadium pentoxide were located. As a whole, the evidence is not
strong enough to support a classification of "likely to be carcinogenic to humans."
Mode of Action Discussion
The U.S. EPA (2005a) Guidelines for Carcinogen Risk Assessment defines mode of
action as a sequence of key events and processes, starting with the interaction of an agent with a
cell, proceeding through operational and anatomical changes, and resulting in cancer formation.
Examples of possible modes of carcinogenic action include mutagenic, mitogenic, anti-apoptotic
(inhibition of programmed cell death), cytotoxic with reparative cell proliferation and
immunologic suppression. Available evidence suggests that bronchoalveolar tumors observed in
animals following inhalation exposure to vanadium pentoxide may arise from genetic
mechanisms, although it is possible that tumors result from a proliferative response to injury in
the respiratory tract.
Hypothesized Mutagenic Mode of Action
Key Events — The precise mechanism of vanadium pentoxide-induced carcinogenicity
has not been fully determined. There is evidence that vanadium pentoxide is capable of eliciting
genotoxic effects (Table 18). Although results of in vitro studies have yielded mixed results, in
general, genotoxic effects have been observed in bacterial and mammalian cell systems. In
cultured hamster fibroblasts, positive effects have been observed for mitosis and micronucleus
formation, although negative effects were reported for sister chromatid exchange and gene
mutation (Zhong et al., 1994). In cultured human fibroblasts, vanadium pentoxide induced DNA
strand breaks (Ivancsits et al., 2002). Thus, genotoxicity has been observed in in vitro test
systems of target organ cells. Experimental data in animals provide conflicting evidence of
genotoxicity following in vivo exposure to vanadium pentoxide. DNA damage (primarily single
strand breaks and alkali labile damage) was increased in liver, kidney, lung, spleen and heart 24
hours following single intraperitoneal injections of vanadium pentoxide to mice
(Altamirano-Lozano et al., 1999). Vanadium pentoxide administered for 3 months by inhalation
to male and female mice (1, 2, 4, 8 or 16 mg/m3) did not increase the frequency of
micronucleated normochromatic erythrocytes in peripheral blood (NTP, 2002), although
genotoxic effects on cells of the respiratory tract were not assessed. Evidence demonstrating
mutagenic activity of vanadium pentoxide in vivo in humans is lacking.
Strength, Consistency, Specificity of Association — Genotoxic activity has been
demonstrated in cultured hamster and human fibroblasts and in several tissues, including lung,
following single parenteral exposure of mice (Altamirano-Lozano et al., 1999), providing
evidence of genotoxicity in target organ cells. Although Altamirano-Lozano et al. (1999) show
evidence of genotoxicity in several tissue types, carcinogenicity following inhalational exposure
to vanadium pentoxide has only been observed in the respiratory tract. Data demonstrating
48
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genotoxicity following inhalation exposure to vanadium pentoxide in animals or humans are
lacking.
Dose-Response Concordance — A dose-response concordance has not been established
between the development of bronchoalveolar tumors and mutagenesis following inhalation
exposure to vanadium pentoxide. Although DNA damage was increased in liver, kidney, lung,
spleen and heart of mice exposed to single parenteral doses of vanadium pentoxide, effects did
not exhibit dose-dependence (Altamirano-Lozano et al., 1999).
Temporal Relationships — Genotoxicity was observed in liver, kidney, lung, spleen and
heart 24 hours after a single parenteral exposure (Altamirano-Lozano et al., 1999), indicating that
a mutagenic mechanism could be the initiating event in the development of respiratory tumors
following chronic inhalation exposure (Ress et al., 2003; NTP, 2002).
Biological Plausibility and Coherence — Based on DNA damage observed in the lung
of mice following single parenteral exposure to vanadium pentoxide (Altamirano-Lozano et al.,
1999) and results of in vitro studies in cultured hamster and human fibroblasts (Ivancsits et al.,
2002; Zhong et al., 1994), mutagenicity is plausible as the mode of action for bronchoalveolar
tumors. However, no direct evidence is available linking mutagenesis in respiratory cells to the
development of bronchoalveolar tumors following chronic inhalation exposure to vanadium
pentoxide.
Hypothesized Nonmutagenic Mode of Action
Key Events — It is generally accepted that sustained cell proliferation in response to cell
death from toxicity or other causes is a significant risk factor for cancer. One possible
nonmutagenenic mode of vanadium carcinogenic action is stimulation of cell proliferation
(mitogenic) and cytotoxicity with subsequent reparative cell proliferation (cytotoxic).
Regeneration of respiratory epithelial cells following injury from inhaled vanadium has the
potential to produce carcinogenesis as a result of replication errors becoming fixed mutations
before DNA repair can be completed.
Subchronic and chronic inhalation studies in rats and mice provide evidence that
vanadium causes cell injury with subsequent reparative cell proliferation, suggesting that
nonmutagenic actions may be involved in the development of bronchoalveolar tumors (NTP,
2002). Pulmonary inflammation and bronchoalveolar epithelial hyperplasia were observed
following exposure of mice to inhaled vanadium pentoxide for 6 and 13 days (Tables 6 and 8). In
addition, increases in cell proliferation, as measured by incorporation of BrdU, were observed in
mice exposed for 6 and 13 days (Tables 3 and 6). Nonneoplastic lesions indicative of cell
damage and proliferation, including chronic inflammation, hyperplasia and fibrosis, were
observed throughout the respiratory tract of mice exposed to inhaled vanadium pentoxide for 3
months or 2 years, demonstrating damage and repair in the region of tumor development (Tables
13,16 and 17). These observations demonstrate that cell injury in the respiratory tract may have
preceded the development of respiratory tumors in mice. Although results of the 2-year cancer
bioassay in rats were equivocal, bronchoalveolar cell damage and proliferation were also
observed in subchronic and chronic inhalations studies in rats (NTP, 2002). Vanadium pentoxide
49
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has been shown also to induce mediators of inflammatory responses and fibrogenesis (Pierce et
al., 1996; Bonner et al., 1998; Silbajoris et al., 2000) and to induce oxidative stress by generation
of reactive oxygen species (reviewed by Valko et al., 2006). All of these observations further
strengthen the evidence for a MOA for vanadium pentoxide based on stimulation of cell
proliferation.
Strength, Consistency, Specificity of Association — Inhaled vanadium pentoxide
produces cell damage with subsequent reparative cell proliferation in the respiratory tract of rats
and mice and bronchoalveolar carcinomas and adenomas in mice (NTP, 2002). Subchronic and
chronic studies identify the respiratory tract as the primary target organ for subchronic exposure
and the only target organ for chronic exposure to inhaled vanadium pentoxide (NTP, 2002). Data
demonstrating carcinogenesis of inhaled vanadium pentoxide in humans are lacking.
Dose-Response Concordance — Exposure of mice to inhaled vanadium pentoxide for
13 days or 3 months produced respiratory tract damage at the lowest concentrations tested,
yielding LOAELs of 2 and 1 mg/m3, respectively; NOAEL values were not established (NTP,
2002). A significant increase in the incidence of bronchoalveolar adenomas and carcinomas in
was observed at all exposure levels tested (1, 2 and 4 mg/m3). Thus, cell damage and
proliferation and tumors are observed at similar exposure levels. However, since NOAEL values
were not established in the subchronic and chronic exposure studies, it is not possible to
determine if cancer develops at doses below those producing cell damage. The 2-year cancer
bioassay in rats failed to clearly demonstrate tumorigenesis, although cell damage and
proliferation were observed in the 16-day, 3-month and 2-year studies at the lowest
concentrations tested (NTP, 2002).
Temporal Relationships — Histopathological findings of the 16-day, 3-month and
2-year inhalation studies in mice and rats show that inhaled vanadium pentoxide induces cell
damage and a reparative proliferative response throughout the entire respiratory tract (NTP,
2002). Lesions progress from inflammation and increased cell proliferation following 16-day
exposure, to hyperplasia following 3-month exposure and to fibrosis and tissue remodeling after
2-year exposure. The finding that bronchoalveolar tumors are found subsequent to tissue damage
and repair is consistent with the hypothesis that vanadium pentoxide acts through amode of
action dependent on cell toxicity (NTP, 2002).
Biological Plausibility and Coherence — It is generally accepted that sustained cell
proliferation in response to cytotoxicity can be a significant risk factor for cancer (Correa, 1996).
Sustained cytotoxicity and regenerative cell proliferation may result in the perpetuation of
mutations (spontaneous or directly or indirectly induced by the chemical), resulting in
uncontrolled growth. It is also possible that continuous proliferation may increase the probability
that damaged DNA will not be repaired. Reparative proliferation alone is not assumed to cause
cancer. Tissues with naturally high rates of turnover do not necessarily have high rates of cancer,
and tissue toxicity in animal studies does not invariably lead to cancer. Nevertheless,
regenerative proliferation associated with persistent cytotoxicity appears to be a risk factor of
consequence.
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Conclusions
The available evidence for the MOA for vanadium pentoxide tumorigenicity is
insufficient but there is some support for both a mutagenic MOA and a MOA dependent on
cellular cytotoxicity and reparative regeneration. In vitro and in vivo studies provide evidence
that vanadium pentoxide is capable of eliciting genotoxic and mutagenic effects in mammalian
respiratory cells; however, direct evidence linking mutagenicity to respiratory cells following
inhalation exposure is lacking. Results of the 16-day, 3-month and 2-year inhalation studies in
mice (NTP, 2002) are consistent with the hypothesis that vanadium pentoxide acts through a
mode of action dependent on cellular toxicity, based on the observations that cytotoxicity and
reparative proliferation occur following subchronic exposure and bronchoalveolar tumors are
produced at exposure levels that produce cytotoxicity and reparative proliferation. However,
dose-response data in mice for damage/repair and tumor development are limited since NOAEL
values were not established. Although evidence is generally supportive of mode of actions
involving mutagenicity or cellular toxicity and repair,, there is insufficient evidence to support
these hypotheses ; thus, a linear approach was taken to calculate the inhalation cancer unit risk in
accordance with the default recommendation of the 2005 Guidelines for Carcinogen Risk
Assessment (U.S. EPA, 2005a). It is possible that a mixed MOA, involving both MO As
discussed above, or an undetermined MOA, may be responsible for tumor induction. The use of
the default procedures for age-adjustment of unit risk for chemicals with a mutagenic MOA to
account for possible age-dependence of carcinogenic potency is not recommended (U.S. EPA,
2005b).
Quantitative Estimates of Carcinogenic Risk
According to the 2005 Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005a),
dose-response assessment estimates for potential risks to humans are recommended for agents
considered "Carcinogenic to Humans" and "Likely to Be Carcinogenic to Humans." However,
when the weight of evidence descriptor is "Suggestive Evidence of Carcinogenic Potential," a
dose-response assessment may be useful for some purposes "when the evidence includes a
well-conducted study." Thus, a quantitative analysis of cancer risk is justified for inhaled
vanadium pentoxide on the basis that the NTP (2002) cancer bioassay in mice was a
well-conducted study, assessing comprehensive toxicological endpoints for lifetime exposure in
an adequate number of animals. Risk assessors should be reminded that there is only suggestive
evidence of human carcinogenicity from vanadium pentoxide exposure so there is uncertainty
associated with quantitation of the database.
Oral Exposure. No human or animal studies examining the carcinogenicity of vanadium
pentoxide following oral exposure were located. Therefore, derivation of an oral slope factor is
precluded.
Inhalation Exposure. The NTP (2002) 2-year carcinogenicity study in mice was used for the
derivation of an inhalation unit risk, based on the dose-response relationship for
alveolar/bronchiolar (A/B) neoplasms (adenoma and carcinoma). Exposure concentrations in
these studies were adjusted to continuous exposure as follows:
51
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ConC[ADj] = Cone x 6/24 x 5/7
This adjustment resulted in duration-adjusted concentrations of 0, 0.18, 0.37 and
0.74 mg/m3 for the control, 1, 2 and 4 mg /m3 groups, respectively. Using the RDDR computer
program, as specified in the RfC guidelines (U.S. EPA, 1994b), HECs (in mg/m3) were
calculated at each exposure level for male and female mice using mean body weights for males
and females reported by NTP (2002) and the average particle size MMAD±GSD of 1.2±2.9 for
rats and mice as reported by NTP (2002) study for effects occurring in the thoracic region of the
respiratory tract. HECs were calculated by multiplying ConC[ADj] by the RDDR for male and
female mice (Table 26).
Table 26. Human Equivalent Concentrations (HEC) Corresponding to Adjusted Exposure
Concentrations for Thoracic Region of the Respiratory Tract in Mice
Species and Sexa
RDDR
Coiicjadj]
(mg/m3)
HEC
(mg/m3)
Male mice
1.481
0.18
0.267
0.37
0.548
0.74
1.096
Female mice
1.433
0.18
0.258
0.37
0.530
0.74
1.060
aDefault body weight values for chronic exposure for male and female Fisher rats and B3C6F1 mice listed in the
RfC guidelines (U.S EPA, 1994b): male mice = 37.3g; female mice = 35.3 g
Modeling was performed using the Benchmark Dose Modeling Software (BMDS;
Version 1.3.1) developed by the National Center for Environmental Assessment (U. S. EPA,
2000). Predicted concentrations associated with a 10% extra risk (BMD10) were calculated, with
the BMDL 10 represented by the 95% lower confidence limit on the BMD10. The multi-stage
cancer model was fit to the incidence data for tumors (combined alveolar/ bronchoalveolar
adenomas and carcinomas) in mice; males and females were modeled separately (Table 27). In
accordance with the U.S. EPA (2000) BMD methodology, the default benchmark response
(BMR) of 10%) increase in extra risk was used as the basis for the BMD, with the BMDL
represented by the 95% lower confidence limit on the BMD. Models were run using the default
restrictions on parameters built into the BMD software. Goodness-of-fit was evaluated using the
Chi-square statistic calculated by the BMDS program. Acceptable global goodness of fit was a
p-value greater than or equal to 0.1. The multi-stage model failed to fit adequately all but the
male mice data with the high dose dropped (Table 28). Therefore, all other BMDS dichotomous
models were fit to each of the data sets.
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Table 27. Incidences of Respiratory Tumors in Male and Female Mice Exposed to
Vanadium Pentoxide for 2 Years (NTP, 2002)
Male Micea
HEC
Control
0.267 mg/m3
0.548 mg/m3
1.096 mg/m3
Alveoloar/bronchoaleveolar
adenoma or carcinoma
22/50
42/50b
43/50b
43/50b
Female Mice a
HEC
Control
0.258 mg/m3
0.530 mg/m3
1.060 mg/m3
Alveoloar/bronchoaleveolar
adenoma or carcinoma
1/50
32/50b
35/50b
32/50b
"Number of animals with tumor
bSignificantly different from control by the Poly-3 test (p< 0.01)
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Table 28. Goodness of Fit Statistics and BMDi0s and BMDLi0s from Models Meeting
Goodness-of Fit Criteria for Incidence Data for Combined Bronchoalveolar Adenomas
and Carcinomas in Male and Female Mice Exposed to Vanadium Pentoxide by Inhalation
for 2 Years (NTP, 2002)
Model
Degrees of
Freedom
X2 Test
Statistic
X2 p-Valuea
AIC
BMD10
(mg/m3)
BMDL10
(mg/m3)
Male Mice - All Doses Included
Log-Logisticb
2
3.65
0.1610
200.956
0.0213865
0.0123449
Male Mice - High Dose Dropped
Gamma0
1
2.65
0.1033
159.738
0.0338493
0.0243233
Log-Logisticb
1
0.68
0.4093
157.726
0.015405
0.00836071
Multi-Stage
1-Degreed
1
2.65
0.1033
159.738
0.0338494
0.0243233
Multi-Stage
2-Degreed
1
2.65
0.1033
159.738
0.0338494
0.0243233
Probit
1
4.53
0.0333
161.775
0.0528617
0.0418641
Log-Probitb
1
2.48
0.1156
159.466
0.058643
0.0406918
Quantal-Linear
1
2.65
0.1033
159.738
0.0338494
0.0243233
Weibulf
1
2.65
0.1033
159.738
0.033849
0.0243233
Female Mice - High Dose Dropped
Gammab
1
4.44
0.0350
144.58
0.0373539
0.0301586
Logistic
1
17.95
0.0000
160.278
0.0991538
0.0801981
Log-Logisticbc
1
1.07
0.3004
141.289
0.0204481
0.0141445
Multi-Stage 1-
Degreed
1
4.44
0.0350
144.58
0.0373539
0.0301586
Multi-Stage 2-
Degree6
1
4.44
0.0350
144.58
0.0373539
0.0301586
Probit
1
17.62
0.0000
159.488
0.0962905
0.0792222
Log-Probitb
1
4.54
0.0332
144.589
0.0664798
0.053212
Quantal-Linear
NAe
NA
NA
NA
NA
NA
Quantal-Quadratic
1
23.11
0.0000
161.631
0.128423
0.11419
Weibullf
NA
NA
NA
NA
NA
NA
aValues >0.1 meet conventional goodness-of-fit criteria
bSlope restricted to > 1
°Power restricted to > 1
dBetas restricted to > 0
NA = Not applicable; model failed to converge
54
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The BMDS modeling results for models meeting goodness-of-fit criteria are summarized
in Table 28. For incidence data in male mice, the log-logistic model was the only model that met
goodness-of-fit criteria when all three vanadium pentoxide groups were included, predicting
BMDio and BMDLio values of 0.021 and 0.012 mg/m3, respectively (Figure 4). Since the
response did not increase monotonically with the high dose included, the impact of dropping the
high dose was explored. When the high dose was dropped, several models fit the incidence data
for male mice, with BMDio and BMDLio values ranging from 0.015 to 0.058 mg/m3 and from
0.008 to 0.042 mg/m3, respectively. The log-logistic model also yielded the best fit (i.e., lowest
AIC) to tumor incidence in males when the high dose was dropped (BMDLio of 0.008 mg/m3).
None of the dichotomous models fit tumor incidence data for female mice when all three
vanadium pentoxide groups were included. One model (log-logistic) fit the incidence data for
female mice when the high dose was dropped, predicting BMDio and BMDLio values of 0.020
and 0.014 mg/m3, respectively (Figure 5). The BMDLio of 0.012 derived for males including all
doses was similar to that of 0.014 for females with the high dose dropped. The lower BMDLio
of 0.012 for male mice was selected as the point of departure (POD) for derivation of the
inhalation unit risk.
The inhalation cancer unit risk of 8.3 (mg/m3)1 was calculated by dividing 0.1 by the
human equivalent BMDLi0[hec] of 0.012 mg/m3. Continuous lifetime exposure concentrations of
vanadium pentoxide that correspond with specified risk levels are shown in Table 29.
55
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Log-Logistic Model with 0.95 Confidence Level
Log-Logistic
0 0.2 0.4 0.6 0.8 1 1.2
dose
16:36 05/07 2006
BMD and BMDL indicated are for a 10% extra risk and are in units of mg/m3
Figure 4. Observed and Predicted Incidences of Combined Bronchoalveolar Adenenomas
and Carcinomas in Male Mice Exposed to Vanadium Pentoxide by Inhalation for 2 Years
by NTP (2002)
56
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Log-Logistic Model with 0.95 Confidence Level
Log-Logistic
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.1
0.2
0.3
0.4
0.5
dose
17:04 05/07 2006
Figure 5. Observed and Predicted Incidences of Combined Bronchoalveolar Adenenomas
and Carcinomas in Female Mice Exposed to Vanadium Pentoxide by Inhalation for 2
Years by NTP (2002) (High Dose Dropped)
57
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Table 29. Continuous Lifetime Exposure Concentrations Corresponding to Specified
Cancer Risk for Vanadium Pentoxide
Risk3
Exposure Concentration
lxlO"4 Risk
1.2xl0"5 mg/m3
lxlO"5 Risk
1.2xl0"6 mg/m3
lxlO"6 Risk
1.2xl0"7 mg/m3
aExtra risk due to vanadium pentoxide exposure
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