United States
Environmental Protection
1=1 m m Agency
Provisional Peer-Reviewed Toxicity Values for
2,4,6-Trichloroaniline
(CASRN 634-93-5)
and
2,4,6-Trichloroaniline Hydrochloride
(CASRN 33663-50-2)
Superfund Health Risk Technical Support Center
National Center for Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
EPA/690/R-10/026F
Final
9-29-2010
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AUTHORS, CONTRIBUTORS, AND REVIEWERS
CHEMICAL MANAGER
Harlal Choudhury, DVM, Ph.D., DABT
National Center for Environmental Assessment, Cincinnati, OH
DRAFT DOCUMENT PREPARED BY
SRC, Inc.
7502 Round Pond Road
North Syracuse, NY 13212
PRIMARY INTERNAL REVIEWERS
Geniece M. Lehmann, Ph.D.
National Center for Environmental Assessment, Research Triangle Park, NC
Paul G. Reinhart, Ph.D., DABT
National Center for Environmental Assessment, Research Triangle Park, NC
This document was externally peer reviewed under contract to
Eastern Research Group, Inc.
110 Hartwell Avenue
Lexington, MA 02421-3136
Questions regarding the contents of this document may be directed to the U.S. EPA Office of
Research and Development's National Center for Environmental Assessment, Superfund Health
Risk Technical Support Center (513-569-7300)
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TABLE OF CONTENTS
BACKGROUND 1
HISTORY 1
DISCLAIMERS 1
QUESTIONS REGARDING PPRTVS 2
INTRODUCTION 2
REVIEW 01 PERTINENT DATA 4
HUMAN STUDIES 4
ANIMAL STUDIES 4
Oral Exposure 4
Subchronic Studies 4
Chronic Studies 5
Reproductive Studies 8
Inhalation Exposure 8
OTHER STUDIES 9
Acute or Short-term Studies 9
Genotoxicity 9
Acid-Base Interactions 9
DERIVATION OF PROVISIONAL SUBCHRONIC AND CHRONIC ORAL RfD
VALUES I OR 2.4.6-TRICI II.OROAMI.INi: 10
FEASIBILITY OF DERIVING PROVISIONAL SUBCHRONIC AND CHRONIC
INHALATION RfC VALUES FOR 2.4.6-TRICI II.OROAMI.INi: 10
PROVISIONAL CARCINOGENICITY ASSESSMENT FOR
2.4.6-TRICI II.OROAMI.INi: 11
WEIGHT-OF -E VIDEN CE DESCRIPTOR 11
QUANTITATIVE ESTIMATES OF CARCINOGENIC RISK 11
REFERENCES 12
APPENDIX A. PROVISIONAL SCREENING VALUES 15
DERIVATION OF SCREENING PROVISIONAL ORAL REFERENCE DOSES 15
Derivation of Screening Chronic Provisional RfD (Chronic p-RfD) 15
DERIVATION OF SCREENING PROVISIONA1 CANCER POTENCY VALUES 15
Derivation of Screening Provisional Oral Slope Factor (p-OSF) 15
APPENDIX B. DETAILS OF BENCHMARK DOSE MODELING FOR ORAL SLOPE
FACTOR (OSF) 18
MODEL-FITTING PROCEDURE FOR CANCER INCIDENCE DATA 18
MODEL-FITTING RESULTS FOR THE INCIDENCE OF VASCULAR TUMORS
IN MALE CD-I MICE (WEISBURGER ET AI... 1978) 18
l
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COMMONLY USED ABBREVIATIONS
BMC
Benchmark Concentration
BMD
Benchmark Dose
BMCL
Benchmark Concentration Lower bound 95% confidence interval
BMDL
Benchmark Dose Lower bound 95% confidence interval
HEC
Human Equivalent Concentration
HED
Human Equivalent Dose
IRIS
Integrated Risk Information System
IUR
inhalation unit risk
LOAEL
lowest-observed-adverse-effect level
LOAELadj
LOAEL adjusted to continuous exposure duration
LOAELhec
LOAEL adjusted for dosimetric differences across species to a human
NOAEL
no-ob served-adverse-effect level
NOAELadj
NOAEL adjusted to continuous exposure duration
NOAELrec
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 reference concentration (inhalation)
p-RfD
provisional reference dose (oral)
POD
point of departure (oral)
RfC
reference concentration (inhalation)
RfD
reference dose
UF
uncertainty factor
UFa
animal-to-human uncertainty factor
UFC
composite uncertainty factor
UFd
incomplete-to-complete database uncertainty factor
UFh
interhuman uncertainty factor
UFl
LOAEL-to-NOAEL uncertainty factor
UFS
subchronic-to-chronic uncertainty factor
WOE
weight of evidence
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PROVISIONAL PEER-REVIEWED TOXICITY VALUES FOR
2,4,6-TRICHLOROANILINE (CASRN 634-93-5) AND
2,4,6-TRICHLOROANILINE HYDROCHLORIDE (CASRN 33663-50-2)
BACKGROUND
HISTORY
On December 5, 2003, the U.S. Environmental Protection Agency's (EPA) 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 (PPRTVs) 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 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 a
panel of six EPA scientists and external peer review by three independently selected scientific
experts. PPRTVs differ from IRIS values in that PPRTVs do not receive the multiprogram
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 5-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 documents 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 Resource Conservation and Recovery Act (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 circumstances at the Superfund site or RCRA facility
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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 document 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.
INTRODUCTION
No RfDs, RfCs, or cancer assessments for 2,4,6-trichloroaniline or 2,4,6-trichloroaniline
hydrochloride (see Figure 1 for chemical structures) are included on the IRIS database (U.S.
EPA, 2009) or the Drinking Water Standards and Health Advisories List (U.S. EPA, 2006). No
RfD or RfC values were reported in the HEAST (U.S. EPA, 1997). The Chemical Assessments
and Related Activities (CARA) list (U.S. EPA, 1994, 1991) included a Health and
Environmental Effects Document (HEED) for trichloroanilines (U.S. EPA, 1987) that did not
derive noncancer toxicity values for 2,4,6-trichloroaniline or 2,4,6-trichloroaniline hydrochloride
due to inadequate noncancer data and potential carcinogenicity of the chemicals (see below).
The toxicity of 2,4,6-trichloroaniline and 2,4,6-trichloroaniline hydrochloride has not been
reviewed by ATSDR (2009) or the World Health Organization (WHO, 2009). CalEPA
(2009a,b) has not derived toxicity values for exposure to 2,4,6-trichloroaniline or
2,4,6-trichloroaniline hydrochloride. No occupational exposure limits for 2,4,6-trichloroaniline
or 2,4,6-trichloroaniline hydrochloride have been derived by the American Conference of
Governmental Industrial Hygienists (ACGIH, 2009), the National Institute of Occupational
Safety and Health (NIOSH, 2009), or the Occupational Safety and Health Administration
(OSHA, 2009).
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HCI
2,4,6-Trichloroaniline
2,4,6-Trichloroaniline Hydrochloride
Figure 1. Chemical Structures of 2,4,6-Trichloroaniline and
2,4,6-Trichloroaniline Hydrochloride
The HE AST reported an EPA (1986) cancer weight-of-evidence classification of
Group C (.Possible Human Carcinogen) and an oral slope factor (OSF) of
2.9 x 10"2 (mg/kg/day)"1 for 2,4,6-trichloroaniline hydrochloride based on an increased incidence
of vascular tumors in male mice in an 18-month study (Weisburger et al., 1978). The HEAST
cited the HEED (U.S. EPA, 1987) as the source of the OSF. The HEAST and HEED also
reported a Group C classification {Possible Human Carcinogen) and an OSF of
3.4 x 10"2 (mg/kg/day)"1 for 2,4,6-trichloroaniline based on the same study and calculated by
multiplying the OSF for 2,4,6-trichloroaniline hydrochloride by the ratio of molecular weights
(232.92 for 2,4,6-trichloroaniline hydrochloride and 196.46 for 2,4,6-trichloroaniline). Neither
compound has been evaluated under the 2005 Guidelines for Carcinogen Risk Assessment
(U.S. EPA, 2005). The International Agency for Research on Cancer (IARC, 2009) has not
reviewed the carcinogenic potential for 2,4,6-trichloroaniline or 2,4,6-trichloroaniline
hydrochloride. 2,4,6-Trichloroaniline and 2,4,6-trichloroaniline hydrochloride have not been
evaluated for potential carcinogenicity by the National Toxicology Program (NTP, 2009)
subsequent to the study by Weisburger et al. (1978), and neither compound is included in the
11th Report on Carcinogens (NTP, 2005). CalEPA (2009b) has not prepared a cancer assessment
for 2,4,6-trichloroaniline or 2,4,6-trichloroaniline hydrochloride.
Literature searches were conducted from the 1960s through March 2010 for studies
relevant to the derivation of provisional toxicity values for 2,4,6-trichloroaniline and
2,4,6-trichloroaniline hydrochloride. Databases searched included MEDLINE, TOXLINE (with
NTIS), BIOSIS, TSCATS/TSCATS2, CCRIS, DART, GENETOX, HSDB, RTECS, Chemical
Abstracts, and Current Contents (last 6 months). The HEED (U.S. EPA, 1987) was also
reviewed for pertinent studies.
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REVIEW OF PERTINENT DATA
Literature searches for toxicological data on 2,4,6-trichloroaniline hydrochloride did not
identify any information (although the chemical tested by Weisburger et al. [1978] was reported
as 2,4,6-trichloroaniline hydrochloride in the HEED, it is likely that the test material was actually
the free base). In fact, there are data suggesting that 2,4,6-trichloroaniline hydrochloride is not
likely to be stable in the environment, with rapid conversion to the free base under most
conditions (see discussion of Acid-Base Interactions under Other Studies, below). Due to the
lack of data on the toxicity of 2,4,6-trichloroaniline hydrochloride and the high likelihood that
any exposure to this chemical in the environment will be to the free base variant, the following
review is limited to information on 2,4,6-trichloroaniline (with the exceptions noted above), and
toxicity values are derived only for this form of the chemical.
HUMAN STUDIES
No data on the effects of 2,4,6-trichloroaniline in humans following inhalation or oral
exposure were located in the literature searches.
ANIMAL STUDIES
Oral Exposure
Subchronic Studies—Groups of white rats (128 rats of both sexes; strain and number of
rats per group not specified) were administered 2,4,6-trichloroaniline (purity not specified) via
gavage in an 8% oil solution (type not specified) at 0, 80, 160, or 800 mg/kg-day for 45 days
(Sapegin et al., 1985). Animals were monitored for mortality and clinical signs. Changes in
body weight, hematology (including the concentration of formed elements and serum
hemoglobin), clinical chemistry (residual nitrogen, pyruvic acid, catalase, alanine
aminotransferase [ALT], and aspartate aminotransferase [AST] levels in serum), and other
parameters (EKG at lead II and oxygen consumption) were recorded before the start of the
experiment and on Treatment Days 10, 20, 30, and 45. Absolute and relative organ weights (not
specified) were measured at study termination; lactate dehydrogenase (LDH) and succinic
dehydrogenase (SDH) activities in the liver and kidney were determined. Histological analyses
were performed, but the organs examined were not specified.
No mortality was reported (Sapegin et al., 1985). Rats administered the high dose
exhibited clinical signs of toxicity including depression, cyanosis, hair loss, and hematuria; a lag
in body-weight gain compared to controls was also noted (data not shown). The concentration of
hemoglobin in the blood (Day 45) and the total number of red blood cells (RBCs) were
statistically significantly (p < 0.05) reduced in the high-dose group (approximately 25 and
27% less than controls, respectively; see Table 1). Data were presented for the control and
high-dose groups at one time point only. Polychromaphilic and hypochromic RBCs, signs of
anisocytosis, poikilocytosis, and a tendency toward leucopenia were noted in the high-dose
group (data not shown). The activities of ALT and AST in the serum were increased
approximately by about 45% and 20%, respectively, and the ALT/AST ratio was decreased in
high-dose rats compared to controls. Levels of residual serum nitrogen and serum pyruvic acid
were statistically significantly (p < 0.05) increased, and rates of oxygen consumption and serum
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catalase activity were statistically significantly (p < 0.02) decreased in the high-dose group (see
Table 1). Inhibition of SDH and LDH activities in the liver and the kidneys of high-dose rats
was reported (data not shown).
Table 1. Significant Changes in White Rats Treated with 2,4,6-Trichloroaniline
via Gavage for 45 Days
Dose in mg/kg-day
Parameter
Control
800a
Hematology
Concentration of hemoglobin on Day 45
(g%)
15.88 ±0.82b
12.02 ±2.08c
Number of RBCs (millions)
6.38 ±0.25
4.63 ± 0.79d
Clinical chemistry
ALT (mmole)
2.57 ±0.37
4.69 ± 0.5d
AST (mmole)
2.95 ±0.27
3.74 ± 0.45°
Residual serum nitrogen (mg%)
34 ±2.4
45.5 ±6d
Serum pyruvic acid (mg%)
1.67 ±0.1
2.36 ± 0.32d
Catalase activity (index)
1.04 ±0.11
0.18 ± 0.13d
Oxygen consumption at 15 minutes (mL/100 g)
56.4 ±7.2
42.2 ± 6.3e
"Data for other dose groups were not reported
bValues are presented as means ± standard deviation (SD)
Significantly different from control atp< 0.02
dSignificantly different from control atp< 0.001
"Significantly different from control atp< 0.01
Source: Sapegin et al. (1985)
Relative weights of the heart, liver, kidneys, and spleen were increased in high-dose rats
compared to controls (data not shown) (Sapegin et al., 1985). Degenerative changes, including
evidence of hemorrhage in the myocardium, kidneys, liver, spleen, and brain were observed in
rats administered the high dose (incidence data not shown). Decreased weight and volume of the
testicles were noted in high-dose animals. Histological alterations were noted in the testicles
(increased incidence of tubules with desquamated spermatogenic epithelium), but not the
ovaries, of high-dose rats (data not shown). The researchers reported that similar, but less
pronounced, evidence of toxicity was apparent in mid-dose rats, and that insignificant changes in
some of the parameters occurred at the low dose (data not shown). This study is limited by
inadequate data reporting. Strain, size, and sex distribution of the control and treatment groups
and the statistical methods utilized are not given. In addition, the data presented by the authors
are limited to only a few endpoints for the control and high-dose groups at a single time point.
Complete histopathology examinations were not performed. Though with severe uncertainties in
reporting, the available data provide limited evidence for a NOAEL and a LOAEL of
80 mg/kg-day and 160 mg/kg-day, respectively.
Chronic Studies—In a chronic study conducted by the same researchers, 180 white rats
(120 females and 60 males; strain, size, and sex distribution/group not specified) were
administered 2,4,6-trichloroaniline (purity not specified) via gavage as 0.04, 0.4, or 4% oil
solutions (type not specified) at doses of 0.4, 4, or 40 mg/kg-day (0.3, 3.0, and 29 mg/kg-day,
adjusted by multiplying 5/7), respectively, 5 days/week, for 6 months (Sapegin et al., 1985).
Although a control group was reportedly used, neither the size nor sex distribution of this group
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was reported. The condition of the animals was monitored every 30 days throughout the
treatment period. In addition to the toxicological parameters assessed in the subchronic study,
conditioned reflexes and methemoglobin concentration in the blood were evaluated in the
chronic study (time points not specified). Relative organ weights and LDH and SDH activities in
the liver and kidneys were measured at terminal sacrifice. Organs (not specified) were examined
for gross pathology; histology was apparently limited to the reproductive organs.
Mortality was not reported by the researchers (Sapegin et al., 1985). As with the
subchronic study, data were presented for the control and high-dose groups at a single time point
only. Decreased weight gain was noted in high-dose rats when compared with controls (data not
shown). Rats administered the high dose had increased numbers of hypochromic RBCs (data not
shown) and doubled levels of methemoglobin in the blood in the 6th month of treatment (p < 0.02
when compared to controls). Other hematological alterations, including anisocytosis,
poikilocytosis, reticulocytosis, hypochromia, and the presence of Heinz bodies in the RBCs were
noted at the high dose (incidence data not shown). Oxygen consumption at 15 minutes was
statistically significantly (p < 0.05) decreased in high-dose rats with respect to controls (see
Table 2). High-dose rats required statistically significantly (p < 0.001) higher numbers of
associations for conditioned reflexes compared to controls (see Table 2). Changes in the relative
weights of the brain (increased) and liver (decreased) were reported at the high dose (data not
shown). Levels of SDH activity in the liver and LDH activity in the liver and kidneys were
reportedly reduced in high-dose rats compared to controls (data not shown). Degenerative
changes (not specified) were noted in the blood vessels of the brain, liver, and kidneys of
high-dose rats (data not shown). The researchers reported that similar—but less
pronounced—evidence of toxicity was apparent in mid-dose rats; only insignificant changes in
some of the parameters occurred at the low dose (data not shown). This study is limited by
inadequate data reporting including the strain, size, and sex distribution of the control and
treatment groups, and the statistical methods utilized. In addition, the data presented by the
authors were limited to only a few endpoints for the control and high-dose groups at one
(unspecified) time point. Complete histopathology examinations were not performed. These
limitations preclude the identification of NOAEL and LOAEL values for this study. From
information available qualitatively, a NOAEL at 0.3 mg/kg-day and a LOAEL at 3 mg/kg-day
can be identified for hematologic and degenerative changes in brain, liver, and kidneys.
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Table 2. Significant Changes in White Rats Treated with 2,4,6-Trichloroaniline
via Gavage for 6 Months
Parameter
Dose in mg/kg-day
Control
29a
Number of associations required for conditioned
reflexes
8.3 ±1.6b
23.2 ± 2.2°
Concentration of methemoglobin: Month 6 (%)
4.04 ± 1.2
8.07 ± 0.89d
Oxygen consumption at 15 minutes (mL/100 g)
57.0 ±3.8
46.4 ± 2.8e
Chromosomal aberrations: bone marrow cells (%)
0.4
1.6e
aData for other dose groups were not reported
bValues are presented as means ± SD
Significantly different from control atp< 0.001
dSignificantly different from control atp< 0.02
eSignificantly different from control atp< 0.05
Source: Sapegin et al. (1985)
In a chronic carcinogenicity study of 21 aromatic amines, Charles River CD rats
(25 males/group) were administered 2,4,6-trichloroaniline (97-99% pure; purity of individual
test compounds not specified) at concentrations of 0, 3,000, or 6,000 ppm in the diet for
5 months, followed by 0, 1,500 or 3,000 ppm, respectively, in the diet for 13 months
(Weisburger et al., 1978). Doses of 0, 79, or 303 mg/kg-day (based on time-weighted average
concentrations of 0, 1,917, or 3,833 ppm) were calculated for this review.1 Rats were observed
for up to 6 months after the end of the treatment period. Animals were monitored daily for
mortality and clinical signs of toxicity. Body weights were recorded periodically. Complete
necropsies were conducted on all animals that died after >6 months of treatment or at study
termination. Histological examinations of grossly abnormal organs, tumor masses, the lung,
liver, kidneys, spleen, adrenal, heart, bladder, stomach, intestines, reproductive organs, and
pituitaries were performed.
Doses were lowered after 5 months of treatment; according to the study protocol, this
action was taken either when there were treatment-related deaths or when body-weight gains in
exposed animals were lower than corresponding controls by at least 10% (Weisburger et al.,
1978). The study authors did not specify which effect led to the decrease in doses of
2,4,6-trichloroaniline. The results reported in the study were limited to neoplastic changes; no
data on mortality, clinical signs of toxicity, body weights, or nonneoplastic findings were given.
No significant increase in tumor incidence was observed in any group of rats (data not shown).
In a companion mouse study, albino CD-I mice (25/sex/group) were treated with
concentrations of 0, 6,000, or 12,000 ppm in the diet for 18 months and observed for an
additional 3 months following treatment (Weisburger et al., 1978). Doses of 0, 1,040, or
2,070 mg/kg-day for female mice and 0, 1,030, or 2,060 mg/kg-day for male mice were
estimated for this review.2 The same toxicological parameters that were evaluated in rats were
1 Based on chronic reference values for food consumption and body weight in rats (U.S. EPA, 1988).
2Based on chronic reference values for food consumption and body weight in mice (U.S. EPA, 1988).
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also evaluated in mice, and the same tissues were subjected to histological examination—except
that pituitaries were not examined. No data regarding mortality, clinical signs of toxicity, or
body weights were reported; however, there was no dose modification during the study,
suggesting that body-weight gains remained within 10% of corresponding controls
(Weisburger et al., 1978).
No significant increase in tumor incidence was observed in either exposed group of
female mice (data not shown; Weisburger et al., 1978). However, a dose-related, statistically
significant (p < 0.025 ) increase in the incidence of vascular tumors (not further characterized)
was observed in dosed male mice (56 and 75% for the low- and high-dose groups, respectively)
compared to concurrent controls (13%) and compared to pooled controls from similarly designed
experiments (5%; see Table A-l). The incidence of hepatocellular carcinomas in male mice was
statistically significantly (p < 0.025 ) increased in the low-dose group—but not the high-dose
group—compared to the incidence in pooled, but not concurrent, controls (incidences in the
pooled control, concurrent control, low-dose, and high-dose groups were 7/99, 1/16, 5/18, and
1/16, respectively). The lack of a dose-response relationship suggests that the effect was not
treatment related. This carcinogenicity study is limited in that small sample sizes were used,
only two positive doses were tested, and data reporting was incomplete (growth and survival data
were not reported).
Reproductive Studies—The chronic toxicity study conducted by Sapegin et al. (1985)
included a reproductive toxicity component. White rats (120 males and 60 females; strain, size,
and sex distribution/group not specified) were administered 2,4,6-trichloroaniline via gavage as
oil solutions (type not specified) at doses of 0.4, 4, or 40 mg/kg-day, 5 days/week, for 6 months
(adjusted to 0.3, 3, or 29 mg/kg-day). Although a control group was reportedly used, neither the
size nor sex distribution of this group was reported. The animals were mated at the end of the
6-month treatment period. At study termination, microscopic examination of the reproductive
organs was performed. Effects on spermatogenesis and ovogenesis, embryotoxicity, and
teratogenicity were assessed (specific endpoints evaluated and methods utilized were not further
specified). The authors indicated that there were no significant variations in the
"morphofunctional" indices (endpoints not specified) for the male and female reproductive
organs (data not shown). Increased incidences of pre- and postimplantation fetal mortality and
decreased numbers of fetuses/dam were reported at the mid-dose (data not shown; statistical
analyses not reported). Massive hematomas were observed in the abdominal cavities of
mid-dose adult rats. The researchers did not indicate whether the effects reported for mid-dose
rats also occurred in high-dose rats. This study is limited by inadequate data reporting, including
the strain, size, and sex distribution of the control and treatment groups, the methods utilized,
and the endpoints evaluated. Based on available information, although limited, a reproductive
NOAEL at 0.3 mg/kg-day and a LOAEL at 3 mg/kg-day can be identified for critical endpoints,
such as implantation losses and decreased number of fetuses per dams.
Inhalation Exposure
No data on the effects of 2,4,6-trichloroaniline in animals following subchronic or
chronic inhalation exposure to 2,4,6-trichloroaniline were located in the literature searches.
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OTHER STUDIES
Acute or Short-term Studies
2,4,6-Trichloroaniline (purity not specified) was administered to 80 white rats and
95 white mice (size and sex not specified) via gavage as an oil solution (type not specified) at
unspecified doses in an acute lethality study (Sapegin et al., 1985). LD50 values were calculated
as 3850-4228 mg/kg in rats and 5681-5800 mg/kg in mice. Clinical signs of toxicity (including
signs of CNS depression, hypoxia, dyspnea, cyanosis, and weak reactions to external stimuli)
were noted in treated animals. Focal hemorrhages, vascular thrombosis, and unspecified
degenerative changes to the myocardium, brain, liver, and kidneys were reported (data not
shown).
Genotoxicity
Limited information is available regarding the potential genotoxicity of
2,4,6-trichloroaniline. 2,4,6-Trichloroaniline did not induce mutations in Salmonella
typhimurium strains TA98, TA100, or TA1537 in the presence or absence of metabolic
activation in plate-incorporation assays; microsomal-suspension assays using the same strains
and metabolic-activation preparations were also negative (Zimmer et al., 1980). However, using
the preincubation method, 2,4,6-trichloroaniline tested positive for mutagenicity in Salmonella
and Escherichia coli (strains not specified) (Shimuzu and Takemura, 1984).
2,4,6-Trichloroaniline tested negative in the Salmonella umu (SOS response) assay (Ono et al.,
1992) and failed to induce DNA repair in rat hepatocytes (Yoshimi et al., 1988). In vivo,
2,4,6-trichloroaniline was mutagenic in the wing spot test in Drosophila
(Kugler-Steigmeier et al., 1989). Rats treated orally with 2,4,6-trichloroaniline at 40 mg/kg-day
(but not 0.4 or 4 mg/kg-day) for 6 months showed a small but statistically significant increase
(p < 0.05) in the number of bone marrow cells containing chromosomal aberrations when
compared with controls (1.6% vs. 0.4%, respectively); however, this study did not provide any
study design details (Sapegin et al., 1985).
Acid-Base Interactions
2,4,6-Trichloroaniline is a weak base. Like other bases, 2,4,6-trichloroaniline may be
protonated under acidic conditions to form salts (e.g., 2,4,6-trichloroaniline hydrochloride). The
property that determines this behavior is the acid dissociation constant, or pKa
(Lyman et al., 1990). When the pH equals the pKa, the protonated and free-base forms of the
chemical are in equilibrium. The higher the pH relative to the pKa, the greater the proportion of
the chemical found as the free base (increase of an order of magnitude for each unit of pH above
pKa). The SPARC on-line calculator (SPARC, 2009) was used to estimate pKa for
2,4,6-trichloroaniline based on the chemical's structure. The pKafor 2,4,6-trichloroaniline was
estimated as -0.25, which is very low. The associated speciation plot indicated that there would
be essentially no protonated 2,4,6-trichloroaniline at pH >2. Therefore, any
2,4,6-trichloroaniline hydrochloride in the environment (pH 5-9) is expected to dissolve in
moisture and immediately convert to the free base, 2,4,6-trichloroaniline.
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DERIVATION OF PROVISIONAL SUBCHRONIC AND CHRONIC
ORAL RFD VALUES FOR 2,4,6-TRICHLOROANILINE
Oral data are limited to poorly reported subchronic and chronic toxicity studies (including
a reproductive toxicity component) in rats (Sapegin et al., 1985) and chronic cancer bioassays in
rats and mice (Weisburger et al., 1978). The cancer bioassays (Weisburger et al., 1978) were not
designed to assess noncancer endpoints and provided no information relevant to noncancer
toxicity assessment. Clinical signs of toxicity, decreased body-weight gain, serum chemistry
changes, hematological effects, organ weight changes, degenerative changes, and reproductive
effects (including increased pre- and postimplantation losses, decreased numbers of fetuses/dam,
and hematomas in the abdominal cavity) were reported in rats by Sapegin et al. (1985).
Although sufficient dose-response information for all exposed doses pertinent to critical effects
are unavailable, the chronic studies (Sapegin et al., 1985) clearly identified a point of departure
(POD) at 0.3 mg/kg-day. Lack of quantitative data precluded BMD analysis. Based on this
information, the NOAEL (0.3 mg/kg-day) can be used to derive p-RfD values by applying a
composite UF of 300 and 3000 for subchronic and chronic RfDs, respectively.
The subchronic p-RfD for 2,4,6-trichloroaniline based on the NOAEL of 0.4 (adjusted to
0.3 mg/kg-day in rats [Sapegin et al., 1985]) is derived as follows:
Subchronic p-RfD = NOAELadj ^ UF
= 0.3 mg/kg-day ^ 1000
= 0.0003 mg/kg-day or 3 x 10"4 mg/kg-day
The composite UF of 300 is composed of the following UFs:
UFh: A factor of 10 is applied for extrapolation to a potentially susceptible human
subpopulation in the absence of data on variability of response in humans.
UFa: A factor of 10 is applied for animal-to-human extrapolation.
UFd: A factor of 10 is applied due to lack of developmental and multigenerational
studies.
Derivation of the chronic p-RfD requires an additional uncertainty factor of 10 for
extrapolation to chronic values. Since the composite uncertainty factor is 10,000, a provisional
screening chronic p-RfD is presented in Appendix A of this document.
FEASIBILITY OF DERIVING PROVISIONAL SUBCHRONIC AND CHRONIC
INHALATION RFC VALUES FOR 2,4,6-TRICHLOROANILINE
No data on the effects of 2,4,6-trichloroaniline in humans or animals following inhalation
exposure were located in the literature searches. Derivation of p-RfC values for
2,4,6-trichloroaniline is precluded by the absence of data.
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PROVISIONAL CARCINOGENICITY ASSESSMENT
FOR 2,4,6-TRICHLOROANILINE
WEIGHT-OF-EVIDENCE DESCRIPTOR
Under the 2005 Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005), there is
"Suggestive Evidence of [the] Carcinogenic Potential" of 2,4,6-trichloroaniline. No information
on the carcinogenicity of 2,4,6-trichloroaniline in humans was located. Weisburger et al. (1978)
observed an increased incidence of tumors in male CD-I mice administered
2,4,6-trichloroaniline in the diet for 18 months. Although the Weisburger et al. (1978) report
was ambiguous about the exact identity of the test material, and a previous EPA assessment
(U.S. EPA, 1987) considered it to be 2,4,6-trichloroaniline hydrochloride, it is concluded here
that the test material was the free base, 2,4,6-trichloroaniline. This study reported a statistically
significant (p < 0.025), dose-related increase in the incidence of vascular tumors in treated male
mice (see Table A-l). A statistically significant (p < 0.025) increase in the incidence of
hepatocellular carcinomas was observed in low-dose, but not high-dose, male mice. This study
was limited by incomplete data reporting, small numbers of animals/group, and lack of details
regarding the nature and sites of the observed vascular tumors. Although growth and survival
data were not presented, the authors reported using doses intended to correspond to the
maximum tolerated dose (MTD) and V2 the MTD (Weisburger et al., 1978).
Although in vitro studies suggest that 2,4,6-trichloroaniline is predominantly
nonmutagenic, 2,4,6-trichloroaniline has given positive results in vivo. 2,4,6-Trichloroaniline
tested positive for mutation in one study in bacteria (Shimuzu and Takemura, 1984) but did not
induce mutations in other bacterial assays (Zimmer et al., 1980); this compound also tested
negative in the Salmonella umu (SOS response) assay (Ono et al., 1992) and failed to induce
DNA repair in rat hepatocytes (Yoshimi et al., 1988). However, 2,4,6-trichloroaniline was
mutagenic in the wing spot test in Drosophila in vivo (Kugler-Steigmeier et al., 1989). Rats
treated orally with 2,4,6-trichloroaniline at 40 mg/kg-day (but not 0.4 or 4 mg/kg-day) for
6 months showed a statistically significant increase in the number of bone marrow cells
containing chromosomal aberrations; however, few study details were presented (Sapegin et al.,
1985).
No other information is available on the mode of action by which 2,4,6-trichloroaniline
acts in the development of tumors. In summary, the data are insufficient to postulate a mode of
action for 2,4,6-trichloroaniline-induced vascular tumors in mice.
QUANTITATIVE ESTIMATES OF CARCINOGENIC RISK
Since the cancer descriptor is "Suggestive Evidence of [the] Carcinogenic Potential, "
quantitative treatment is provided in Appendix A as a screening p-OSF.
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REFERENCES
ACGIH (American Conference of Governmental Industrial Hygienists). (2009) Threshold limit
values for chemical substances and physical agents and biological exposure indices. Cincinnati,
OH.
ATSDR (Agency for Toxic Substances and Disease Registry). (2009) Toxicological profile
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Available online at http://www.atsdr.cdc.gov/toxpro2.html (accessed September 15, 2009).
CalEPA (California Environmental Protection Agency). (2009a) Search chronic RELs. Office of
Environmental Health Hazard Assessment. Available online at http://www.arb.ca.gov/toxics/
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September 15, 2009).
CalEPA (California Environmental Protection Agency). (2009b) Search toxicity criteria
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air/hot_spots/pdf/Appendix%20I2002.pdf (accessed September 15, 2009).
IARC (International Agency for Research on Cancer). (2009) IARC monographs on the
evaluation of carcinogenic risks to humans. Available online at http://www.monographs.iarc.fr/
ENGMonographs/allmonos90.php (accessed September 15, 2009).
Kugler-Steigmeier, ME; Friederich, U; Graf, U; et al. (1989) Genotoxicity of aniline derivatives
in various short-term tests. Mutat Res 21:279-289.
Lyman, WJ; Reehl, WF; Rosenblatt, DDH. (1990) Handbook of chemical property estimation
methods: environmental behavior of organic compounds. American Chemical Society,
Washington, DC.
NIOSH (National Institute for Occupational Safety and Health). (2009) NIOSH pocket guide to
chemical hazards. Index by CASRN. Available online at http://www.cdc.gov/niosh/npg/
npgdcas.html (accessed September 15, 2009)
NTP (National Toxicology Program). (2005) 11th report on carcinogens. U.S. Department of
Health and Human Services, Public Health Service, National Institutes of Health, Research
Triangle Park, NC. Available online at http://ntp-server.mehs.nih.gov/index.cfm?objectid=
32BA9724-F1F6-975E-7FCE50709CB4C932 (accessed September 15, 2009.
NTP (National Toxicology Program). (2009) Management status report. Available online at
http://ntp.niehs.nih.gov/index.cfm?objectid=78CC7E4C-FlF6-975E-72940974DE301C3F
(accessed September 15, 2009).
Ono, Y; Somiya, I; Kawaguchi, T. (1992) Genotoxic evaluation on aromatic organochlorine
compounds by using the umu test. Water Sci Technol 26:61-69.
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2,4,6-Trichloroaniline Hydrochloride
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OSHA (Occupational Safety and Health Administration). (2009) OSHA standard 1915.1000 for
air contaminants. Part Z, toxic and hazardous substances. Available online at
http://www.osha.gov/pls/oshaweb/owadisp. show_document?p_table=STANDARDS&p_id=102
86 (accessed September 15, 2009).
Sapegin, DI; Fomochkin, IP; Pis'ko, GT; et al. (1985) Hygienic standardization of
2,4,6-trichloroaniline in water. Gig Sanit 3:83-84.
Shimuzu, H; Takemura, N. (1984) Mutagenicity of some aniline derivatives. In: Proc 11th Int
Congr Occup Health Chem Ind pp. 497-506.
SPARC (2009) SPARC on-line calculator, September 2009 release v4.5. Available online at
http://sparc.chem.uga.edu/sparc/ (accessed December 8, 2009).
U.S. EPA (Environmental Protection Agency). (1986) Guidelines for carcinogen risk assessment.
Prepared by the Risk Assessment Forum, U.S. Environmental Protection Agency. Washington,
DC.
U.S. EPA (Environmental Protection Agency). (1987) Health and Environmental Effects
Document (HEED) for trichloroanilines. Environmental Criteria and Assessment Office, Office
of Health and Environmental Effects, Cincinnati, OH. ECAO-CIN-G006. March.
U.S. EPA (U.S. Environmental Protection Agency). (1988) Recommendations for and
documentation of biological values for use in risk assessment. Cincinnati, OH.
U.S. EPA (Environmental Protection Agency). (1991) Chemical Assessments and Related
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U.S. EPA (Environmental Protection Agency). (1997) Health Effects Assessment Summary
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National Center for Environmental Assessment, Cincinnati, OH for the Office of Emergency and
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U.S. EPA (U.S. Environmental Protection Agency). (2000) Benchmark dose technical guidance
document [external review draft], EPA/630/R-00/001. Available online at http://www.epa.gov/
iris/backgr-d.htm.
U.S. EPA (U.S. Environmental Protection Agency). (2005) Guidelines for carcinogen risk
assessment. Risk Assessment Forum, Washington, DC; EPA/630/P-03/001F. Federal Register
70(66): 17765-17817.
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U.S. EPA (U.S. Environmental Protection Agency). (2006) 2006 Edition of the drinking water
standards and health advisories. Office of Water, Washington, DC. EPA 822-R-06-013.
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dwstandards.pdf (accessed September 15, 2009).
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(IRIS). Office of Research and Development, National Center for Environmental Assessment,
Washington, DC. Available online at http://www.epa.gov/iris/ (accessed September 15, 2009).
Weisburger, EK; Russfield, AB; Humbuger, F; et al. (1978) Testing of twenty-one
environmental aromatic amines or derivatives for long-term toxicity or carcinogenicity.
J Environ Pathol Toxicol 2(2):325-356.
WHO (World Health Organization). (2009) Online catalogs for the Environmental Health
Criteria series. Available online at http://www.who.int/ipcs/publications/ehc/ehc_alphabetical/
en/index.html (accessed September 15, 2009).
Yoshimi, N; Sugie, S; Iwata, H; et al. (1988) The genotoxicity of a variety of aniline derivatives
in a DNA repair test with primary cultured rat hepatocytes. Mutat Res 206:183-191.
Zimmer, D; Mazurek, J; Petzold, G; et al. (1980) Bacterial mutagenicity and mammalian cell
damage by several substituted anilines. Mutat Res 77:317-326.
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APPENDIX A. PROVISIONAL SCREENING VALUES
For reasons noted in the main PPRTV document, it is inappropriate to derive provisional
toxicity values for 2,4,6-trichloroaniline. However, information is available for this chemical
which, although insufficient to support derivation of a provisional toxicity value, under current
guidelines, may be of limited use to risk assessors. In such cases, the Superfund Health Risk
Technical Support Center summarizes available information in an Appendix and develops a
"screening value." Appendices receive the same level of internal and external scientific peer
review as the PPRTV documents to ensure their appropriateness within the limitations detailed in
the document. Users of screening toxicity values in an appendix to a PPRTV assessment should
understand that there is considerably more uncertainty associated with the derivation of an
appendix screening toxicity value than for a value presented in the body of the assessment.
Questions or concerns about the appropriate use of screening values should be directed to the
Superfund Health Risk Technical Support Center.
DERIVATION OF SCREENING PROVISIONAL ORAL REFERENCE DOSES
Derivation of Screening Chronic Provisional RfD (Chronic p-RfD)
A screening chronic p-RfD based on hematological and reproductive effects reported
above (Sapegin et al., 1985) can be derived by dividing the NOAELadj of 0.3 mg/kg-day by a
composite UF of 3000, as shown below:
Screening Chronic p-RfD = NOAELadj UF
= 0.3 mg/kg-day ^ 10,000
= 0.00003 mg/kg-day or 3 x 10"5 mg/kg-day
The composite UFs for the screening chronic p-RfD are similar to the subchronic p-RfD.
A UFs of 10, however, is applied for duration of exposure (6 months).
Confidence in the principal study is low. The subchronic and reproductive study
evaluated multiple dose levels administered by gavage using adequate endpoints. However,
results were poorly reported, making evaluation difficult. There are no developmental and
multigenerational studies available. Overall confidence in the data and subchronic and screening
chronic p-RfD values is low.
DERIVATION OF SCREENING PROVISIONAL CANCER POTENCY VALUES
Derivation of Screening Provisional Oral Slope Factor (p-OSF)
Weisburger et al. (1978) reported an increased incidence of vascular tumors in male
CD-I mice administered 2,4,6-trichloroanline in the diet for 18 months and observed for
3 additional months. As shown in Table A-l, a statistically significant (p < 0.025) increase in
tumor incidence was observed in both low-dose and high-dose male mice. The dose-response
data for vascular tumors shown in Table A-l can be used to derive an OSF for
2,4,6-trichloroaniline. In order to determine a POD for OSF derivation, animal doses in the
Weisburger et al. (1978) study were first adjusted for lifetime exposure as follows:
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Doscadj = dose (mg/kg-day) x (months of treatment [months of treatment
+ months of observation period])
= dose (mg/kg-day) x (18 21)
Table A-l. Incidences of Tumors in Male CD-I Mice Treated with 2,4,6-Trichloroaniline
for 18 Months
Dose
(mg/kg-day)
Incidence of
Vascular Tumors
Incidence of
Hepatocellular Carcinomas
0 (concurrent)
2/16
1/16
0 (pooled)
5/99
7/99
1030
10/183
5/18b
2060
12/16a
1/16
"Significantly different from incidence in concurrent and pooled controls atp< 0.025
bSignificantly different from incidence in pooled controls atp< 0.025
Source: Weisburger et al. (1978)
The dose-adjusted values, shown in Table A-2, were then converted to human equivalent
doses (HEDs) by adjusting for differences in body weight between humans and mice. In
accordance with EPA (2005) Guidelines for Carcinogen Risk Assessment, a factor of BW3/4 was
used for cross-species scaling. Using this scaling factor, the dose in humans (mg) is obtained by
multiplying the animal dose (mg) by the ratio of human:animal body weight raised to the
3/4 power. For doses expressed per unit of body weight (mg/kg or mg/kg-day), the relationship is
reciprocal, and the human dose is obtained by multiplying the animal dose (mg/kg) by the ratio
of animal :human body weight raised to the ]A power. Since Weisburger et al. (1978) did not
report body weights of mice used in the principal study, a default body-weight value for chronic
exposure of 0.0373 kg for male B6C3Fi mice (U.S. EPA, 1988) was used to calculate the
animal:human body-weight ratios. The equation used to calculate the HED values is shown
below; the HED values are presented in Table A-2.
DoseHED = DoseADj x (animal BW ^ human BW)1 4
where
DoseADj = average daily dose adjusted for lifetime exposure (mg/kg-day)
animal BW = average male mouse body weight (0.0373 kg; default value from
U.S. EPA, 1988)
human BW = reference human body weight (70 kg; U.S. EPA, 1988)
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Table A-2. Dose-response Data for Incidence of Vascular Tumors in Male CD-I Mice
Treated with 2,4,6-Trichloroaniline for 18 Months
Animal Dose
DosCad.i"
HEDb
Incidence of
(mg/kg-day)
(mg/kg-day)
(mg/kg-day)
Vascular Tumors
0
0
0
2/16
1030
883
134
10/18
2060
1766
268
12/16
aDosc AI )J = Dose (mg/kg-day) x (months of treatment ^ [months of treatment + months of observation period]),
where (months of treatment ^ [months of treatment + months of observation period]) = (18 -^21)
bHED = DoseADi x (animal BW ^ human BW)1/4, where animal body weight = 0.0373 kg (default value from
U.S. EPA, 1988 for male mice) and human body weight = 70 kg
Source: Weisburger et al. (1978)
The tumor data shown in Table A-2 were modeled as described in Appendix A using a
benchmark response (BMR) of 10% extra risk (U.S. EPA, 2000). The BMDiohedand
BMDLiohed values predicted by the multistage cancer model for the data on vascular tumors in
male mice were 22 and 14 mg/kg-day, respectively. The BMDLiohed of 14 mg/kg-day was
selected as the POD for the screening p-OSF derivation. In the absence of information on the
cancer mode of action of 2,4,6-trichloroaniline, a linear extrapolation to the origin was
conducted. A screening p-OSF 2,4,6-trichloroanline was calculated as follows:
Screening p-OSF = BMR ^ BMDLiohed
= 0.1 ^ 14 mg/kg-day
= 0.007 or 7 x 10 3 (mg/kg-day)"1
The screening p-OSF for 2,4,6-trichloroaniline should not be used with exposures
exceeding the POD (BMDLiohed = 14 mg/kg-day) because, at exposures above these levels, the
fitted dose-response model better characterizes what is known about the carcinogenicity of
2,4,6-trichloroaniline. Table A-3 shows the doses associated with specific levels of cancer risk
based on the p-OSF for 2,4,6-trichloroaniline.
Table A-3. Doses of 2,4,6-Trichloroaniline Associated with
Specific Levels of Cancer Risk
Risk Level
Dose (mg/kg-day)
10"4
0.014
10"5
0.0014
10"6
0.00014
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APPENDIX B. DETAILS OF BENCHMARK DOSE MODELING
FOR ORAL SLOPE FACTOR (OSF)
MODEL-FITTING PROCEDURE FOR CANCER INCIDENCE DATA
The multistage-cancer model in the EPA benchmark dose software (BMDS) is fit to the
incidence data using the extra risk option and is run for all polynomial degrees up to n-1 (where
n is the number of dose groups including control). Adequate model fit is judged by three criteria:
goodness-of-fit/>-value (p > 0.1), visual inspection of the dose-response curve, and scaled
residual at the data point (except the control) closest to the predefined benchmark response
(BMR). Among all of the models providing adequate fit to the data, the lowest BMDL is
selected as the point of departure when the difference between the Benchmark Dose Lower
bound 95% confidence intervals (BMDLs) estimated from these models is more than 3-fold
(unless it is an outlier); otherwise, the BMDL from the model with the lowest Akaike
Information Criterion (AIC) is chosen. In accordance with EPA (2000) guidance, benchmark
doses (BMDs) and BMDLs associated with a BMR of 10% extra risk are calculated.
MODEL-FITTING RESULTS FOR THE INCIDENCE OF VASCULAR TUMORS IN
MALE CD-I MICE (WEISBURGER ET AL., 1978)
Applying the procedure outlined above to the human equivalent doses (HEDs) and
incidences of vascular tumors in male CD-I mice (see Table A-2), both the 1- and 2-degree
multistage-cancer models provided adequate fit to the data and gave the same results (see
Table B-l). The benchmark dose (BMDiohed) and associated 95% lower confidence limit
(BMDLiohed) were 21.84 and 14.44 mg/kg-day, respectively (see Table B-l).
Table B-l. Model Predictions for Vascular Tumors in Male CD-I Mice Treated
with 2,4,6-Trichloroaniline for 18 Months
Model
Degrees of
Freedom
x2
X2
Goodness-of-Fit
/7-Valuea
AIC
BMD10hed
(mg/kg-day)
BMDL10hed
(mg/kg-day)
Multistage-cancer
(degree = l)b
1
0.02
0.8817
58.80
21.84
14.44
Multistage-cancer
(degree = 2)b
1
0.02
0.8817
58.80
21.84
14.44
"Values <0.10 fail to meet conventional goodness-of-fit criteria.
''Betas restricted to >0.
AIC = Akaike Information Criterion
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Multistage Cancer Model with 0.95 Confidence Level
1
0.8
0.6
0.4
0.2
0
11:22 11/24 2009
BMD and BMDLs indicated are associated with an extra risk of 10% and are
human equivalent doses (HEDs) in units of mg/kg-day.
Source: Weisburger et al. (1978).
Figure B-l. Fit of Multistage-Cancer (1-Degree) Model to Incidence Data for
Vascular Tumors in Male CD-I Mice Administered 2,4,6-Trichloroaniline in
the Diet for 18 Months
Multistage Cancer
Linear extrapolation
BMDL
BMD
0 50 100 150 200 250
Dose
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