United States
Environmental Protection
1=1 m m Agency
EPA/690/R-11/024F
Final
3-30-2011
Provisional Peer-Reviewed Toxicity Values for
2,4-Dimethylaniline
(CASRN 95-68-1)
Superfund Health Risk Technical Support Center
National Center for Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
-------
AUTHORS, CONTRIBUTORS, AND REVIEWERS
CHEMICAL MANAGER
J. Phillip Kaiser, PhD
National Center for Environmental Assessment, Cincinnati, OH
DRAFT DOCUMENT PREPARED BY
ICF International
9300 Lee Highway
Fairfax, VA 22031
PRIMARY INTERNAL REVIEWERS
Audrey Galizia, Dr PH
National Center for Environmental Assessment, Washington, DC
Geniece M. Lehmann, PhD
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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2,4-Dimethylaniline
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TABLE OF CONTENTS
COMMONLY USED ABBREVIATIONS iii
BACKGROUND 4
HISTORY 4
DISCLAIMERS 4
QUESTIONS REGARDING PPRTVS 5
INTRODUCTION 5
REVIEW OF POTENTIALLY RELEVANT DATA (CANCER AND NONCANCER) 7
HUMAN STUDIES 11
ANIMAL STUDIES 11
Oral Exposure 11
Inhalation Exposure 13
OTHER STUDIES 15
Short-term Oral Studies 15
Acute Oral Studies 17
Acute Inhalation Studies 17
Other Exposure Routes 18
Metabolism Studies 18
Genotoxicity 19
DERIVATION 01 PROVISIONAL VALUES 23
DERIVATION OF ORAL REFERENCE DOSE 23
Derivation of Chronic and Subchronic Provisional RfD 23
DERIVATION OF INHALATION REFERENCE CONCENTRATIONS 23
Derivation of Chronic and Subchronic Provisional RfC 23
CANCER WEIGHT-OF-EVIDENCE DESCRIPTOR 24
DERIVATION OF PROVISIONAL CANCER POTENCY VALUE 27
Derivation of Provisional Oral Slope Factor (p-OSF) 27
Derivation of Provisional Inhalation Unit Risk (p-IUR) 28
APPENDIX A. PROVISIONAL NONCANCER SCREENING VALUES 29
APPENDIX B. DATA TABLES 35
APPENDIX C. BENCHMARK DOSE CALCULATIONS FOR THE RfD 36
APPENDIX D. BENCHMARK DOSE CALCULATIONS FOR THE ORAL SLOPE
FACTOR 50
APPENDIX E. REFERENCES 54
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COMMONLY USED ABBREVIATIONS
BMC
benchmark concentration
BMCL
benchmark concentration lower bound 95% confidence interval
BMD
benchmark dose
BMDL
benchmark dose lower bound 95% confidence interval
HEC
human equivalent concentration
HED
human equivalent dose
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
NOAELhec
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
POD
point of departure
p-OSF
provisional oral slope factor
p-RfC
provisional reference concentration (inhalation)
p-RfD
provisional reference dose (oral)
RfC
reference concentration (inhalation)
RfD
reference dose (oral)
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-DIMETHYLANILINE (CASRN 95-68-1)
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
in question. PPRTVs are periodically updated; therefore, users should ensure that the values
contained in the PPRTV are current at the time of use.
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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.
Dimethylaniline, 2,4- (also called 2,4-xylidine) is a colorless to yellow or dark brown
liquid used as an intermediate for pesticides, pharmaceuticals, dyes, wood preservatives, wetting
agents for textiles, frothing agents for ore dressing, metal complexes, special lacquers, and
photographic chemicals (HSDB, 2009; OSHA, 2009b). The empirical formula for
2,4-dimethylaniline is CgHnN, and its structure are shown in Figure 1, and Table 1 provides
several physicochemical properties for this compound. In this document, "statistically
significant" denotes a/rvalue of <0.05.
INTRODUCTION
NH,
CH.
3
Figure 1. Structure of 2,4-Dimethylaniline
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Table 1. Physicochemical Properties Table (2,4-Dimethylaniline)
Property (unit)
Value
Boiling point (°C)
214a
Melting point (°C)
14.3b
"3
Density (g/cm )
0.9723b
Vapor pressure (mm Hg at 25°C)
0.133 mm Hgb
pH (unitless)
Data not available
Solubility in water (g/L at 20°C)
5 (slightly soluble)0
Relative vapor density (air =1)
Data not available
Molecular weight (g/mol)
121.18a
Flash point (°C)
90a
Octanol/water partition coefficient (unitless) at pH of 7.5
47.86 (log Kow = 1.68)°
aColumbia Analytical Services (2010).
Values from NTP (2009).
°ChemBlink (2010).
No reference dose (RfD), reference concentration (RfC), or cancer assessment for
2,4-dimethylaniline (or 2,4-xylidine) is included in the EPA IRIS database (U.S. EPA, 2010a) or
on the Drinking Water Standards and Health Advisories List (U.S. EPA, 2009a). No acute
exposure guideline levels (AEGLs) for 2,4-dimethylaniline have been derived by the EPA's
Office of Pollution Prevention and Toxics (U.S. EPA, 2009b). No assessments were reported on
the Chemical Assessments and Related Activities (CARA) list (U.S. EPA, 1994a).
The EPA has published a Health and Environmental Effects Profile (HEEP) for
2,4-dimethylaniline and 2,4-dimethylaniline hydrochloride. The human carcinogen potency
factor (ql*) for 2,4-dimethylaniline is 0.75 (mg/kg-day)"1 for oral exposure, and the Reportable
Quantity (RQ) value is 1000 pounds under CERCLA (Comprehensive Environmental Response,
Compensation, and Liability Act) (U.S. EPA, 1987). The HEAST lists an oral unit risk for
2,4-dimethylaniline of 2.1 x 10 5 (|ig/L) 1 based on mouse lung tumors (Weisburger et al.,
1978). HEAST classifies 2,4-dimethylaniline as a Group C carcinogen ("possibly carcinogenic
to humans: agents with limited animal evidence and little or no human data") (U.S. EPA, 2010b).
The International Agency for Research on Cancer (IARC) reviewed the carcinogenic
potential of 2,4-dimethylaniline and concluded that no adequate human data existed and
inadequacies of animal studies did not allow for an evaluation of carcinogenicity (IARC, 1978).
An IARC update subsequently classified the chemical in Group 3 ("not classifiable as to
carcinogenicity to humans") (IARC, 1987). In addition, the Health Council of the Netherlands
(2002) has concluded that there is insufficient information to classify 2,4-dimethylaniline for
carcinogenicity.
CalEPA has not derived toxicity values for exposure to 2,4-dimethylaniline nor have they
derived quantitative estimates of the carcinogenic potential of 2,4-dimethylaniline (CalEPA,
2008, 2009a,b,c). 2,4-Dimethylaniline is not included in the 11th Report on Carcinogens (NTP,
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2005). The toxicity of 2,4-dimethylaniline has not been reviewed by ATSDR or the World
Health Organization (WHO) (ATSDR, 2009; WHO, 1986).
No occupational exposure limits or guidelines have been derived by the Occupational
Safety and Health Administration (OSHA), National Institute of Occupational Safety and Health
(NIOSH), or the American Conference of Governmental Industrial Hygienists (ACGIH) for
2,4-dimethylaniline (ACGIH, 2001; NIOSH, 2009; OSHA, 2009a). However, exposure limits
have been derived for mixed xylidine isomers (CASRN 1300-73-8). For mixed xylidine isomers
(including 2,4-dimethylaniline), the OSHA permissible exposure limit (PEL) time-weighted
"3
average (TWA) is 2 ppm (10 mg/m ) [skin], the NIOSH recommended exposure limit (REL)
TWA is also 2 ppm (10 mg/m3) [skin], and the ACGIH threshold limit value (TLV) is 0.5 ppm
(2.5 mg/m3) as a TWA (inhalable vapor; skin) (NIOSH, 1994; OSHA, 2009b; ACGIH, 2001;
RTECS, 2009). The NIOSH Immediately Dangerous to Life or Health (IDLH) concentration is
50 ppm for mixed xylidine isomers, but this is stated to be possibly conservative due to the lack
of relevant acute toxicity data for human workers (NIOSH, 1996). The ACGIH (ACGIH, 2008)
has classified mixed xylidine isomers in Group A3 ("confirmed animal carcinogen with
unknown relevance to humans") (HSDB, 2009).
Literature searches were conducted on sources published from 1900 through
October 2010 for studies relevant to the derivation of provisional toxicity values for
2,4-dimethylaniline (CAS No. 95-68-1). Searches were conducted using EPA's Health and
Environmental Research Online (HERO) evergreen database of scientific literature. HERO
searches the following databases: GRICOLA; American Chemical Society; BioOne; Cochrane
Library; DOE: Energy Information Administration, Information Bridge, and Energy Citations
Database; EBSCO: Academic Search Complete; GeoRef Preview; GPO: Government Printing
Office; Informaworld; IngentaConnect; J-STAGE: Japan Science & Technology; JSTOR:
Mathematics & Statistics and Life Sciences; NSCEP/NEPIS (EPA publications available through
the National Service Center for Environmental Publications [NSCEP] and National
Environmental Publications Internet Site [NEPIS] database); PubMed: MEDLINE and
CANCERLIT databases; SAGE; Science Direct; Scirus; Scitopia; SpringerLink; TOXNET
(Toxicology Data Network): ANEUPL, CCRIS, ChemlDplus, CIS, CRISP, DART, EMIC,
EPIDEM, ETICBACK, FEDRIP, GENE-TOX, HAPAB, HEEP, HMTC, HSDB, IRIS, ITER,
LactMed, Multi-Database Search, NIOSH, NTIS, PESTAB, PPBIB, RISKLINE, TRI; and
TSCATS; Virtual Health Library; Web of Science (searches Current Content database among
others); World Health Organization; and Worldwide Science. The following databases outside
of HERO were searched for risk assessment values: CGIH, ATSDR, CalEPA, EPA IRIS, EPA
HEAST, EPA HEEP, EPA OW, EPA TSCATS/TSCATS2, NIOSH, NTP, OSHA, and RTECS.
REVIEW OF POTENTIALLY RELEVANT DATA
(CANCER AND NONCANCER)
Table 2 contains information on all the potentially relevant studies, and the principal
study (PS) has been bolded.
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Table 2. Summary of Potentially Relevant Data for 2,4-Dimethylaniline (CASRN 95-68-1)
Notes3
Category
Number of
Male/Female
Species, Study Type,
and Duration
Dosimetry6
Critical Effects
NOAELbc
BMDL/
BMCL"
LOAELbc
Reference
Comments
Human
1. Oral
None
2. Inhalation
None
Animal
1. Oral
PS
Chronic
10 M/10 F Osborne-
Mendel rats per
group, oral 2,4-
dimethylaniline,
6 months
Male ADJ: 18,
36,148, 329, or
1137 mg/kg-
day
Female ADJ:
26, 55, 209,
511, or 1304
mg/kg-day
Increased relative liver and
kidney weights observed at all
doses in a dose-related manner;
cholangiofibrosis, bile duct
proliferation, occasional necrosis
and foci of hyperplastic cells in
liver; in the kidney, tubuli,
edema, papillary necroses and
casts; relative kidney and liver
weights increased at all doses
None
18.87
mg/kg-day
(increased
relative
kidney wt.,
females)
18 mg/kg-
day (males),
26 mg/kg-
day
(females)
Lindstrom et
al. (1963)
Short-term
5/5 Sprague-Dawley
rats, gavage, 4 wks
Male/F emale
ADJ: 475
mg/kg-day
Hepatomegaly and enlargement of
hepatocytes; decreased liver
glycogen and glucose-6-
phosphatase activity with
occasional necrotic cells; increased
absolute and relative liver weights,
decreased body weight in male
rats; elevated glucuronyl
transferase concentration
N/A
Not run
475 mg/kg-
day
Magnusson et
al. (1979)
Dose of 400 mg/kg-day
adjusted by authors after
1 week to
500 mg/kg-day; LOAEL
identified by causing
10% increase in absolute
and relative liver weight
considered to be
biologically significant
5/5 Sprague-Dawley
rats per group,
gavage, 4 wks
Male/F emale
ADJ: 20, 100,
or 600 mg/kg-
day
Increased liver and kidney weights
at all doses; at highest dose, bile
duct proliferation and liver cell
necrosis, with decreased
hematocrit and hemoglobin levels
100
mg/kg-day
Not run
600 mg/kg-
day
Magnusson et
al. (1971)
High dose of 500 mg/kg-
day adjusted by authors
after 2 weeks to 700
mg/kg-day; LOAEL
identified by causing
10% increase in liver and
kidney weight considered
to be biologically
significant
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Table 2. Summary of Potentially Relevant Data for 2,4-Dimethylaniline (CASRN 95-68-1)
Notes3
Category
Number of
Male/Female
Species, Study Type,
and Duration
Dosimetry6
Critical Effects
NOAELbc
BMDL/
BMCL"
LOAELbc
Reference
Comments
1/1 Beagles per
group, gavage, 4 wks
Male/F emale
ADJ: 2, 10, 50
mg/kg-day
Highest dose resulted in increased
liver weight, and fatty
degeneration; two highest doses
induced emesis, body wt. reduction
and increased liver to body wt.
ratio
N/A
Not run
N/A
Magnusson et
al. (1971)
No statistical significance
tests performed in study
10 F344 rats per
duration of 5,10, or
20 d
Male ADJ: 117
mg/kg-day
Liver lesions in rats: extensive
cloudy swelling and necrosis, early
periacinar necrosis with connective
tissue proliferation, biliary
hyperplasia for the shortest
duration; at the longest duration,
periacinar vacuolar degeneration
with occasional discrete foci;
liver and kidney weights elevated
in all duration groups
N/A
Not run
117 mg/kg-
day
Short et al.
(1983)
LOAEL based on
significantly increased
liver and kidney weights
Carcinogenic
50 Sprague-Dawley
male rats, oral, 2 yrs
Not known
Excess subcutaneous fibromas or
fibrosarcomas in treated animals;
excess hepatomas also occurred
N/A
Not run
N/A
IARC (1978)
as cited in
HSDB (2009)
Statistical analyses not
available, data possibly
from an abstract
25 Sprague-Dawley
male rats, oral,
24 months
Male HED:
10.9 and 22.1
mg/kg-day;
duration
adjusted over
24 mos
None; no effects observed even at
highest dose
22.1
mg/kg-day
Not run
N/A
Weisburger
etal. (1978)
Feed concentrations
adjusted by authors
PS
Carcinogenic
25/25 CD-I
HaM/ICR mice,
oral, 21 months
Male HED: 2.8
and 5.6 mg/kg-
day
Female HED:
2.9 and
5.8 mg/kg-day;
adjusted for
21 mos
None in males; lung tumors
statistically significant at highest
dose in females
2.9 mg
mg/kg-day
Not run
5.8 mg/kg-
day
Weisburger
et al. (1978)
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Table 2. Summary of Potentially Relevant Data for 2,4-Dimethylaniline (CASRN 95-68-1)
Notes3
Category
Number of
Male/Female
Species, Study Type,
and Duration
Dosimetryb
Critical Effects
NOAELbc
BMDL/
BMCL"
LOAELbc
Reference
Comments
2. Inhalation
Subchronic
LAS and Swiss strain
mice, rats (unknown
strain), rabbits, cats,
dogs, monkeys, and
chicks; up to 40 wks
7 hrs/d, 5 d/wk,
223 mg/m3
vapor (isomeric
mixture)
Mortality (except monkeys and
chicks) and liver damage (except
chicks) in all species; cats, dogs,
mice had elevated methemoglobin
levels and increased numbers of
Heinz bodies
N/A
Not run
223 mg/m3
based on
isomeric
mixture
Von
Oettingen et
al. (1947)
Isomeric mixture used;
dose not converted to
HEC nor adjusted for
study duration
Unknown numbers of
rats (unknown strain),
guinea pigs, rabbits,
cats, monkeys,
unspecified duration
7 hrs/d, 5 d/wk,
doses ranging
from 36 mg/m3
to 703 mg/m3
Mortality, pneumonitis,
degeneration of cells in heart,
liver, kidneys
Not stated
Not run
Not stated
Treon et al.
(1950)
Isomeric mixture used;
dose not converted to
HEC nor adjusted for
study duration
aNotes: PS = Principal study.
^Dosimetry, NOAEL, BMDL/BMCL and LOAEL values are converted to Human Equivalent Dose (HED in mg/kg-day) or Human Equivalent Concentration (HEC in mg/m3)
units. Noncancer oral data are only adjusted for continuous exposure. Dose = Feed Concentration x Food Consumption per Day x (1 -r- Body Weight) x (Days Dosed Total
Days), where daily Food Consumption rates used were from EPA's (1988) default subchronic for Osborne Mendel rats [0.023 kg (males), 0.019 kg (females)]. Dose = Adjusted
Dose, since both Days Dosed and Total Days were 182.
cNot reported by the study author, but determined from data.
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HUMAN STUDIES
No data on the effects of 2,4-dimethylaniline in humans following inhalation or oral
exposure were located in the literature searches. It has been noted that occupational hazards
include burns to the skin and eyes, and that the chemical is toxic via inhalation, ingestion, and
dermal absorption (HSDB, 2009). In addition, it was stated that a 1-hour exposure to 400 ppm or
long-term exposure to 10 ppm of mixed methylaniline isomers would be lethal to humans,
although no epidemiological or occupational information exists (ACGIH, 1988, as cited in
OSHA, 2009b; ACGIH, 2001).
ANIMAL STUDIES
Oral Exposure
In a published peer-reviewed chronic-duration study, Lindstrom et al. (1963)
administered dietary doses of 0, 375, 750, 2500, 5000, and 10,000 ppm (0, 18, 36, 148, 329, and
1137 mg/kg-day in males, 0, 26, 55, 209, 511, and 1304 mg/kg-day in females [the calculations
for adjusted doses are shown in Table 2]) of 2,4-dimethylaniline (purity unknown) to groups of
10 Osborne-Mendel rats per sex, per group for 6 months (n = 120). This study was selected as
the principal study for derivation of the screening chronic and subchronic p-RfDs. In this
study, corn oil (3% in feed) was used as a vehicle even in control feed (Lindstrom et al., 1963).
Food and water were provided ad libitum, and rats were weighed weekly. At the end of 3
months, 4/20 rats from each dose level were chosen for sacrifice; only high-dose rats were
additionally given microscopic examinations of the liver, kidneys, and testes (males) or adrenals
and spleen (females). After 6 months, the remaining 96 rats were sacrificed, and 26 rats (4 from
each dose group, plus 6 controls) were chosen for sacrifice in an unbiased fashion (by order of
animal number) for microscopic examination of liver, kidneys, and spleen. Another 8/20 rats
were sacrificed from the high-dose group for examination of the pancreas, stomach, small
intestine, colon, and adrenals. Also at the termination of the study at 6 months, blood analyses
were collected from 10 animals per dose group, and organ-weight data were reported. In this
study, the authors were not consistent with time period reporting; results were reported at
12 weeks or 13 weeks or 3 months, as well as 6 months or 26 weeks. Explanations were not
given for the varying time periods reported.
A total of four rats (one from the control group and three from the 2,4-dimethylaniline
groups) died before the completion of the study. However, no differences in mortality rates were
observed, while statistically significant decreases in body-weight gain were observed at the three
highest dose levels, both at 12 weeks and at 6 months in male and female rats. Data on body
weight changes at 6 months are shown in Appendix C. At 6 months, target cell anemia was
observed in a dose-related fashion, but statistical analyses were not shown by the authors.
After 6 months, relative (liver-to-body-weight) liver weight was statistically significantly
increased in both males and females in a dose-related fashion (Lindstrom et al., 1963). Data on
relative liver weight changes at the end of 6 months are shown in Appendix C. There were
elevated relative liver weights observed even at the lowest dose, significant at thep < 0.05 level
in males and females. Livers at the two highest doses (5000 and 10000 ppm) demonstrated pale
foci ranging from 0.5 mm to >2 mm scattered throughout the parenchyma (presumed in both
sexes). At the 2500 ppm dose, a half-dozen pinpoint-sized foci were observed, but no foci were
observed below this dose. High-dose animals sacrificed at 3 months did not show the same gross
liver and kidney effects observed in high-dose animals at 6 months, although milder changes (not
described) were noted. On microscopic examination of animals sacrificed at 6 months, three of
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the four (2 males, 1 female) highest dose animals showed large foci of 0.5 to 3.0 mm diameter of
cholangiofibrosis (nonneoplastic bile duct proliferation) while one female rat had none. Ducts
were irregular, relatively large, and often filled with necrotic debris; surrounding the ducts was
considerable fibrosis. Of the four high-dose animals examined at 13 weeks, one (sex
unspecified) showed early stages of this process. Rats at lower doses of treatment were not
microscopically examined at 13 weeks.
In addition, in livers at the highest dose, there was a moderate amount of scattered new
small bile duct formation; at 13 weeks, there was limited evidence of this at the highest dose, but
it was less defined (Lindstrom et al., 1963). The authors also noted rounded foci of hepatic cell
hyperplasia ranging from 0.5 to 4 mm in diameter, with some irregularly shaped foci.
Occasional individual necrotic cells were seen at 6 months, but at 13 weeks, necrosis was more
pronounced. At the highest dose at Week 13, liver damage was graded as slight (2/4) and
moderate (2/4), while at 6 months, livers were graded as slight to moderate (1/4), moderate (1/4),
or moderate to marked (2/4); there were no sex differences observed at either period. At the
second highest dose of 5000 ppm, there was less liver damage than in the high dose—including
an absence of cholangiofibrotic foci and reduction of new small bile duct formation.
Hyperplastic foci were present but less well defined. Overall liver damage in this group was
slight in the two males and slight-to-moderate in the two females. In the third dose group of
2500 ppm, livers appeared relatively normal, but slight formation of new bile ducts and a few
poorly-defined hyperplastic hepatic cell foci were still evident in females. Overall liver damage
was graded as minimal but definite in the two females, intermediate in one male rat, and almost
normal in the other male rat. No liver abnormalities attributable to treatment could be
determined in the two lower dose groups of 375 and 750 ppm.
Relative kidney weight (kidney-to-body weight) was statistically significantly increased
in both males and females in a dose-related fashion (Lindstrom et al., 1963). Data on
kidney-weight changes at the end of 6 months are shown in Appendix C. At the lowest dose,
relative kidney weights were significantly increased at thep < 0.05 level in males and females.
Gross pathology revealed slight or moderate irregular pitting or depressed scarring at the highest
dose (presumed in both sexes), and microscopic examination revealed similar effects as observed
in the livers. The effects included cortical foci of tubular atrophy and interstitial fibrosis with
chronic inflammation progressing to depressed scar formation, as well as papillary changes
(edema, cast formation in small looped tubules, progression to necrosis in the lower end of the
papilla). In addition, there were less serious changes observed such as cystic dilation of tubular
segments around the corticomedullary junction. Across all doses, kidney damage varied from
little to moderate gradation among the animals and averaged at least slight. The same general
changes were seen at 13 weeks as those seen at 6 months, though in earlier stages and less
noticeable on gross examination. At the second highest dose, 5000 ppm, some kidney damage
was evident, but it was so slight that the authors could not say whether it was due to
treatment-related effects. Forestomachs of rats showed slight hyperkeratosis at the highest dose.
All other rat organs at the highest dose were normal at 6 months, and similarly, no abnormalities
were seen at the highest dose at 13 weeks. Rats at lower doses of treatment were not
microscopically examined at 13 weeks.
This study supports the development of a p-RfD because of the well documented and
scientifically acceptable nature of the publication. The LOAEL for Lindstrom et al. (1963) is
12
2,4-Dimethylaniline
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identified as 375 ppm (18 mg/kg-day [males]; 26 mg/kg-day [females]) for significantly
increased liver and kidney weights at the lowest dose; no NOAEL is identified.
Inhalation Exposure
In one inhalation study, mice (6-29 weeks), rats (28 weeks), rabbits (23 weeks), cats
(3 weeks), dogs (6.5 weeks), chicks (11 weeks), and monkeys (40 weeks) were exposed to
45 ppm (223 mg/m3) of an isomeric mixture of xylidine vapor (purity not known) for
7 hours/day, 5 times/week, respectively (Von Oettingen et al., 1947). Strain (Swiss and LAS)
was only mentioned for mouse. Mortality (except monkeys and chicks) and liver damage
(except chicks) were reported in all species. Cats, dogs, and mice (but not rats, rabbits, chicks,
or monkeys) had elevated methemoglobin levels and increased number of Heinz bodies. This
study does not provide adequate information regarding the toxicity of 2,4-dimethyaniline due to
the employment of an isomeric mixture of xylidines (Von Oettingen et al., 1947).
In a second study, monkeys, rats, guinea pigs, rabbits, and cats exposed to
2,4-dimethylaniline vapor at concentrations of 7.8 to 142 ppm (36 to 703 mg/m3) for
7 hours/day, 5 times/week, for an unspecified duration had mortality, pneumonitis and
degeneration of cells in the heart, liver, and kidneys (Treon et al., 1950). Strain was not
mentioned for any of the experimental animals and it appears that there was no control group.
All species except for the cat, which demonstrated liver toxicity, tolerated doses of 17.5 ppm
"3
(87 mg/m ). One monkey (not mentioned previously) and two cats tolerated 92 exposures at
7.8 ppm (36 mg/m3) without any effect. Animals were treated with an isomeric mixture of
xylidines and the amount of 2,4-dimethyaniline in this mixture is unknown.
It was briefly reported in a third study that the NOEL, after repeated inhalation of
"3
2,4-dimethylaniline as an aerosol-vapor mixture, was 6 ppm (30 mg/m ), and that effects
included chronic inflammation of the airways; methemoglobinemia; and damage to the liver,
kidneys, and heart, which was detected by histopathological exams (Anonymous-German, 1993,
as cited in HSDB, 2009). Study duration or species tested was unknown, and no other study
details were reported; the original study was not available for review at this time and, therefore,
it was not possible to determine whether this study referred to the previous study by Treon et al.
(1950).
Chronic or Cancer Studies
Two carcinogenicity studies have been identified in the literature for 2,4-dimethylaniline.
In the first, 50 male Charles River (Sprague-Dawley) rats were given 2,4-dimethylaniline (purity
not known) in feed for 2 years. Thirty-nine percent (39%) of treated rats had subcutaneous
fibromas or fibrosarcomas compared to only 16% of controls. The study also noted excess
hepatomas in treated rats, but the original source (an abstract, according to the Health Council of
the Netherlands, 2002) was not available for review at this time (IARC, 1978, as cited in HSDB,
2009).
In a published peer-reviewed carcinogenicity study, Weisburger et al. (1978)
administered 2,4-dimethylaniline hydrochloride (97-99% purity) in the diet to male Charles
River rats and male and female albino CD-I HaM/ICR mice. The chemical was one of
21 aromatic amines or derivatives tested for carcinogenicity in rats and mice. The doses were
administered in the diet at the maximum tolerated dose (MTD) and half of the known MTD;
however, weight gain was monitored carefully such that if gains were equal or greater than
13
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10% lower than in corresponding controls, or death occurred, doses were lowered. Control
animals were observed simultaneously and received only laboratory chow. Complete
histological examination was done for all grossly abnormal organs, and statistical analysis of
tumors was performed using Fisher's exact test. Nonneoplastic degenerative or inflammatory
lesions were recorded but were discussed only if they were considered to be compound related.
Twenty-five male rats per group were treated for 18 months, followed by 6 months of
observation. Feed concentration correction was needed in rats during the study
(Weisburger et al., 1978). The low concentration (administered in feed) was 2000 mg/kg for
3 months, 250 mg/kg for 2 months, and then 500 mg/kg for 13 months. High-dose rats received
4000 mg/kg for 3 months, 500 mg/kg for 2 months, and then 1000 mg/kg for 13 months in feed.
Duration-adjusted for the 24-month study, controls received 0 mg/kg-day, low-dose rats received
542 mg/kg 2,4-dimethylaniline in feed per day, while high-dose rats received 1083 mg/kg
1 2
2,4-dimethylaniline in feed per day (0, 37, and 75 mg/kg-day, respectively ). The
corresponding Human Equivalent Doses (HEDs) were 0, 10.9, and 22.1 mg/kg-day3,
respectively. These HEDs are shown in Table 2 and have been calculated based on
duration-adjusted doses during the 24 months of the study, using EPA (1988) default factors for
Sprague-Dawley rats. A NOAELhed of 22.1 mg/kg-day is identified based on no effects being
observed at any dose in male Sprague-Dawley rats.
In the same carcinogenicity study, albino CD-I HaM/ICR mice were administered
2,4-dimethylaniline hydrochloride in the diet according to a similar study protocol investigating
21 aromatic amines (Weisburger et al., 1978). Twenty-five mice per sex per dose group were
treated for 18 months followed by 3 months of observation. This mouse study by
Weisburger et al., 1978 is selected as the principal study for deriving the provisional oral
slope factor (p-OSF). Concentrations administered were equivalent to 125 and 250 mg/kg in
feed followed by 3 months of observation and were duration-adjusted for the 21 months of the
study to 107 and 214 mg/kg in feed per day4 (0, 19, and 39 mg/kg-day in males, 20 and
40 mg/kg-day in females5). The corresponding HEDs were 0, 2.8, and 5.6 mg/kg-day and 0, 2.9,
and 5.8 mg/kg-day for males and females, respectively3. Male mice did not have tumor
incidences in excess of controls. In females, however, lung tumors occurred in 28% of animals
(5/18) at the low dose, and in 58% (11/19) at the high dose, compared to 23% in concurrent
controls. Lung tumors in female mice occurred with a statistically significant positive trend
(Cochran-Armitage trend test performed for this analysis,/* = 0.01), and the tumor incidence was
significant at the high dose compared to concurrent controls by Fisher's exact test (p < 0.05).
'Calculated by averaging feed concentrations for the 24 months of study duration (3 months at the initial concentration, then
2 months at the next concentration, then 13 months at the last concentration, followed by 6 months of recovery).
2Adjusted dose = Average Feed Concentration during treatment x Food Consumption per Day x (1 Body Weight) x (Months
Dosed -s- Total Months), where body weights used were from EPA's (1994b) default chronic values for male Sprague-Dawley
Rats (0.523 kg) and where feed intakes used were from EPA's (1988) default chronic values for male Sprague-Dawley Rats
(0.036 kg); Months Dosed was 18, and Total Months was 24.
3Eluman Equivalent Dose = Adjusted dose x [BW^a! BWhuman]°25 where BWamml was obtained from EPA's (1994b) default
chronic values for male Sprague-Dawley Rats (0.523 kg) and 'Other' mouse strains (0.0317 kg males, 0.02875 kg, females) and
where BWhuman(70 kg) was obtained fromEPA's Exposure Bactors Elandbook (1997).
Calculated by averaging feed concentrations for the 21 months of study duration (18 months of treatment followed by 3 months
of recovery).
'Adjusted dose = Beed Concentration x Bood Consumption per Day x (1 Body Weight) x (Months Dosed Total Months),
where body weights used were from EPA's (1994) default chronic values for 'Other' mouse strains (0.0317 kg males,
0.02875 kg, females) and where feed intakes used were from EPA's (1988) default chronic values for 'Other' mouse strains
(0.0057 kg males, and 0.0053 kg females); Months Dosed was 18, and Total Months was 21.
14
2,4-Dimethylaniline
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Based on increased lung tumor incidence, a LOAELhed of 5.8 mg/kg-day is identified. A
NOAELhed is identified as 2.9 mg/kg-day. The study supports the development of a p-OSF
because of the well documented and scientifically acceptable nature of the publication.
OTHER STUDIES
Short-term Oral Studies
In a 4-week study, five Sprague-Dawley derived CFY rats per sex (n= 10) were gavaged
once daily with 0 or 400 mg/kg of 2,4-dimethylaniline during the first week and then 500 mg/kg
for the following 3 weeks (thus having a duration-adjusted dose of 475 mg/kg-day for treated
animals) (Magnusson et al., 1979). Control rats were given saline at the same dosage volumes as
the treated group. Rats were observed daily and weighed once per week. Autopsies were
performed on all rats regardless of when they died. Biochemical parameters were measured,
including cytochrome P450, aniline hydroxylase, and glucuronyl transferase. Statistical analyses
were performed using Bartlett's /-test to compare treated rats to controls.
No deaths were attributed to treatment, but there was a statistically significant decrease in
male body weights (Magnusson et al., 1979). Both sexes had increased liver and liver-to-body
weight ratios (p < 0.05). Enlargement of hepatocytes was observed, and this effect was
statistically significant in females, primarily in the centrilobular regions. Occasional isolated
necrotic cells were found, along with a centrilobular decrease in liver glycogen that was most
pronounced in males. Glucose-6-phosphatase enzyme activity was statistically significantly
decreased (p < 0.05) in the centrilobular region in male rats. In addition, proliferation of smooth
endoplasmic reticulum was observed along with isolated degenerative hepatocytes containing
vacuoles and inclusion bodies. There were also dilated bile canaliculi associated with loss or
atrophy of microvilli and occasional pigmented Kupffer cells. Biochemical results demonstrated
that the concentration of glucuronyl transferase was statistically significantly elevated in both
male and female rats (p < 0.05). Hepatic microsomal protein content was statistically
significantly increased in male rats but not significantly elevated in female rats. Other enzyme
elevations were observed but were not statistically significant. The authors postulated that
hypertrophy and hyperplasia may have occurred in the liver of treated rats, based on hepatocyte
size and increased liver weights (Magnusson et al., 1979). LOAEL of 475 mg/kg-day is
identified by causing 10% increase in absolute and relative liver weight considered to be
biologically significant.
In a 4-week study, 10 young Sprague-Dawley rats, 5 of each sex per dose, were treated
by gavage once per day (no dose adjustment needed) with 0, 20, 100, or 500 mg/kg
2,4-dimethylaniline (Magnusson et al., 1971). After 2 weeks of treatment, the dose in the highest
dose group was increased to 700 mg/kg-day resulting in an adjusted dose of 600 mg/kg-day.
Food and water were given ad libitum, and rats were observed daily for clinical effects.
Hematology and blood chemistry were examined upon termination of the study. Liver and
kidneys were examined microscopically. Tests of statistical significance were not shown or
discussed by the authors in this study.
There were six mortalities that occurred during the study at the highest dose, from Days 6
to 25 (Magnusson et al., 1971). In females and in males at the highest dose, decreased weight
gain (qualitative statement given) was observed. Clinical examination found decreased
hemoglobin concentrations and hematocrit concentrations at the highest dose, particularly in
females. Serum urea-nitrogen levels were normal, but increased values for ornithine
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2,4-Dimethylaniline
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carbamyltransferase (OCT) were observed in 2/10, 1/10, and 4/4 rats at the low, mid-, and high
dose, respectively. Hyperkeratosis of the forestomachs was observed at the highest dose, which
likely represented irritation of the stomach. Gross pathology revealed liver enlargement and
increased liver weights in treated rats at all doses; high-dose livers contained occasional reddish
and greyish foci in sizes of 0.5-2 mm. These foci were most evident in rats that died, but
otherwise, livers did not show any other biologically significant change.
Microscopic examination revealed necrosis and vacuolization of hepatocytes in all rat
livers at the highest dose, with necrosis appearing as scattered foci in primarily the midzone of
hepatic lobules (Magnusson et al., 1971). Necrotic foci were small and well defined, while large
foci were more irregular in shape. Some necrotic areas had hemorrhage and cellular infiltration
of histiocytes with some neutrophilic granulocytes. In the centrilobular areas, various sized
vacuoles, either empty or with filamentous content, were observed in hepatic cells. Proliferation
of bile ducts was observed at the highest dose as well. No fatty change in liver was evident, and
the kidneys had a normal appearance. The authors postulated that focal hepatic necrosis likely
resulted from insufficient nutrition of liver cells due to low blood pressure and reduced
circulation, supported by the fact that the necrosis was most common in rats that died, and, thus,
focal hepatic necrosis was not a toxic effect of the chemical itself. Although statistical
significance was not discussed by authors, the identified NOAEL is 100 mg/kg-day, and the
LOAEL is 600 mg/kg-day based on the biological significance of a 10% increase in relative liver
and kidney weight in Sprague-Dawley rats.
The same authors conducted the same study in dogs; one male and one female beagle
were administered 0, 2, 10, or 50 mg/kg-day of 2,4-dimethylaniline (purity not known) orally in
capsules daily for 4 weeks (Magnusson et al., 1971). Tests of statistical significance were not
possible given the small sample size used in this study. Dogs at the two highest doses vomited
within the first 4 hours after treatment, with more vomiting seen at the highest dose. At the two
highest doses, body weights were reduced, and liver-to-body-weights were increased. Values for
clinical chemistry were within normal ranges. The highest dose showed enlarged, pale liver;
microscopic pathology showed fatty degeneration at the highest dose level. The kidneys were
not markedly affected by treatment.
In another study, male F344 rats were administered 2,4-dimethylaniline (98.7% purity)
by gavage at doses of 117 mg/kg-day (25% of the LD50 determined by study authors) for either 0,
5, 10, or 20 days (Short et al., 1983). Ten animals in each dose group plus 30 controls were
sacrificed at the appointed time (n = 60). Daily observations of body weight and food and water
consumption were obtained. Histopathology of liver, spleen, thyroid, bladder, and kidneys was
conducted. Analysis of body and organ weight was done using ANOVA and Dunnett's test,
while scoring for lesions and mortality were analyzed using Fisher's exact test.
Two rats died in the mid-duration group, and one died from the longest-duration group;
however, mortality was stated as not significant (Short et al., 1983). Clinical observation
revealed thinness and rough hair coat. In addition, body weight was depressed at all durations of
treatment. Liver weights and liver-to-body-weight ratios, as well as kidney weights (and
kidney-to-body weight ratios) were statistically significantly increased (p < 0.05) in all duration
groups. Histopathology revealed no significant treatment-related effects on spleen or bone
marrow. In the liver, statistically significant toxicity was noted at the shortest duration (5 days)
with extensive cloudy swelling and necrosis, early periacinar necrosis with connective tissue
16
2,4-Dimethylaniline
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proliferation, and biliary hyperplasia. At the longest duration (20 days), periacinar vacuolar
degeneration with occasional discrete foci was observed. According to the researchers, the study
demonstrated toxic hepatopathy as characterized by liver lesions in rats (Short et al., 1983). The
LOAEL is identified to be 117 mg/kg-day based on significantly increased absolute kidney and
liver weight in male Fischer 344 rats.
In an oral exposure study, 10 male and 10 female Charles River CD (Manston) rats were
given 0 or 400 mg/kg-day 2,4-dimethylaniline (purity unknown) for 7 days in an oral saline
solution (Gopinath et al., 1980). A control group was given an equal volume of saline; both
groups were given feed and water ad libitum. Blood samples were then collected, and serum bile
acid and enzyme concentrations were measured as an indicator of liver cell injury. Clinical
biochemistry measures included alkaline phosphatase (AP), glutamate pyruvic transaminase
(GPT), glutamic dehydrogenase (GDH), and total and conjugated bilirubin. Liver histopathology
was examined as well. Statistical significance was not given, but rather results were shown by
histograms, which demonstrated elevated GPT, GDH, and bile acids (but not AP) in treated
animals. Treated male rats showed higher elevations than females. Examination of the liver
revealed cell enlargement, occasional cell necrosis, and/or minimal bile duct hyperplasia and
degeneration. Electron microscopy revealed dilated bile canaliculi with loss of microvilli and
proliferation of smooth endoplasmic reticulum. There appeared to be an overall reduction in the
canalicular ATPase in the treated rats. The authors concluded that treatment with
2,4-dimethylaniline induced hepatotoxicity and altered liver function (Gopinath et al., 1980).
Acute Oral Studies
An acute lethality study determined an LD50 of 470 mg/kg (ranging from
320-690 mg/kg) in rats and an LD50 of 250 mg/kg (ranging from 150-420 mg/kg) in mice
(Vernot et al., 1977). Another acute study in rats determined the oral LD50 to be 1259 mg/kg
(Lindstrom et al., 1969).
In a brief abstract, it was reported that Takahashi et al. (1974) administered a single oral
dose of 157.6 mg/kg of 2,4-dimethylaniline HC1 (purity not known) to mice (strain and number
unspecified). Biochemical and morphological changes were observed, with acidophilic granules
and bodies appearing 24 hours after dosing and increasing markedly by 48 hours after dosing.
Microscopic examination revealed increased lysosomes, dilatation of endoplasmic reticulum, and
autolysome and focal degeneration of hepatocytes at 24 hours. Glucose-6-phosphate
dehydrogenase and lysosomal enzymes in liver soluble fractions were increased at 12 and
48 hours after dosing and did not recover by 72 hours after dosing. In addition, radioactive
2,4-dimethylaniline- H demonstrated highest radioactivity levels during a 72-hour period.
In rabbits (strain and number unspecified), it was stated that an isomeric mixture of an
unknown impure composition consisting of 2,4-dimethylaniline dissolved in isooctane was fatal
even at doses of 0.5 g/animal while 0.1 g/animal was tolerated (Anonymous-German, 1993, as
cited in HSDB, 2009).
Acute Inhalation Studies
An acute inhalation lethality study determined an LC50 (4-hour) of 1.53 mg/L for the rat
(strain and number unspecified); irritation of the eyes and snout were seen in addition to labored
breathing. Furthermore, exhaustion, dyspnea, and terminal convulsions were evident
(Anonymous-German, 1993, as cited in HSDB, 2009). The LC50 (7-hour) in mice (strain not
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2,4-Dimethylaniline
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"3
known) is reported to be 149 ppm or 738 mg/m (von Oettingen et al., 1947, as cited in NIOSH,
1996).
Other Exposure Routes
Following a single intravenous injection of 20 mg, the blood methemoglobin content of
rats (number or strain not discussed) increased from 1.5% to 3.5% after 1 hour (IARC, 1978 in
HSDB, 2009). In another intravenous injection study in cats, 0.25 mmol/kg of mixed
methylaniline isomers caused a 6.3%-38.3% increase in methemoglobin (McLean et al., 1969).
The compound is considered irritating to the skin and eyes of rabbits
(Anonymous-German, 1993, as cited in HSDB, 2009). Mixed methylaniline isomers can be
absorbed through the skin in rabbits to cause cyanosis and death (Proctor et al., 1988, as cited in
OSHA, 2009b). Exposure to mixed methylaniline isomers caused injury to the rabbit cornea on
a scale of 5/10, where 10/10 was the most severe (Grant, 1986, as cited in OSHA, 2009b).
Liver damage and effects on the blood were observed after repeated dermal application of
an isomeric methylaniline mixture to dogs and cats (Anonymous-German, 1993, as cited in
HSDB, 2009). No additional details were available.
In cats, dermal administration of 2000 mg/kg for 24 hours resulted in methemoglobin
formation and increases in Heinz bodies in the blood. It was noted that the compound tested in
these studies was an isomeric mixture of unknown composition rather than pure
2,4-dimethylaniline (Anonymous-German, 1993, as cited in HSDB, 2009).
In a study of unknown route, cats exposed to a mixed methylaniline isomer concentration
of 138 ppm became uncoordinated, prostrate, and cyanotic before death. Duration of exposure
was unknown, and study details were not available for review at this time. Autopsy revealed
edema of the lungs, pneumonia, and damage to the liver and kidneys (Proctor et al., 1988, as
cited in OSHA, 2009b).
Metabolism Studies
In a urine metabolite study, 117 mg/kg-day (25% of the LD50 determined by the study
authors) of 2,4-dimethylaniline (>99% purity) was administered in a corn oil gavage for 10 days
to 16 young male F344 rats (Short et al., 1989). Pooled 24-hour urine samples were collected on
Days 1 and 10 and analyzed for the parent compounds and metabolites. Animals were weighed
on Day 5, and doses were adjusted accordingly to maintain a constant mg/kg dose. A paired
Mest was used to compare effect of length of treatment (Day 1 vs. 10) on urine excretion
products within each dosing group. The study authors found that the chemical was excreted as
A'-acetyl-4-amino-3-methylbenzoic acid (AAMBA), the parent compound, and the sulfate or
glucuronide conjugates of these compounds. There was no significant difference in the total
excretion of either the parent compound or AAMBA between Days 1 and 10, thus demonstrating
that the chemical did not induce its own metabolism. The authors hypothesized that the
metabolite AAMBA and its conversion to A'-hydroxy-2,4-di methyl aniline could be responsible
for the liver toxicity observed in rats.
In the same study, five purebred beagle dogs received 25 mg/kg-day of
2,4-dimethylaniline (98.7% purity) for 10 days, administered orally in gelatin capsules with no
vehicle (Short et al., 1989). Dogs were weighed every 5 days and doses adjusted. Twenty-four-
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hour urine samples were collected on Days 1 and 10 and analyzed. The chemical was excreted
as 6-hydroxy-2,4-dimethylaniline (6-HDMA), the parent compound, and 4-amino-3-
methylbenzoic acid (4-AMBA). In both rats and dogs, A',2,4-tri methyl amine was detected at low
concentrations inadequate for quantitation. There were no marked differences in urine content of
A',2,4-tri methyl amine at either Day 1 or 10. The authors noted that 2,4-dimethylaniline was
markedly less toxic in the dog than the rat, possibly due to rapid 6-hydroxylation of the parent
compound or the diminished amount of 4-AMBA produced.
Genotoxicity
Results from genotoxicity tests are mixed but generally positive; results are shown in
Tables 3 (in vitro) and 4 (in vivo). In the Ames mutagenicity assay, Zeiger et al. (1988) tested
mutagenicity of 2,4-dimethylaniline with Salmonella typhimurium strains TA 97, TA 98,
TA 100, TA 1535, and TA 1537. Strains TA 98 and TA 100 with both hamster and rat liver
S9 metabolic activation resulted in positive tests for mutagenicity at concentrations of
10-1000 [j,g/plate, while only the hamster S9 mix tested positive in strain TA 97 at the same
concentrations. Strains TA 97, TA 98, TA 100, and TA 1535 were tested with no metabolic
activation and found to be negative at concentrations of 33-1666 [j,g/plate, and even with
metabolic activation using hamster and rat liver S9 mix, strains TA 1535 and TA 1537 tested
negative. Shimizu and Takemura (1983, as cited in CCRIS, 2005) also tested strains TA 98 and
TA 100 in the Ames assay; TA 98 tested negative both with and without activation at
0-5000 |ig/plate, while TA 100 was negative without activation but positive with S9 activation
at 0-5000 [j,g/plate.
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Table 3. Genotoxicity Studies of 2,4-Dimethylaniline In Vitro
Test System
Endpoint
Test
Conditions
Results"
Dosec
Reference
Without
Activation
With
Activationb
Salmonella
typhimurium
TA 97, 98, TA
100
Reverse
mutation
Plate
incorporation
assay
+
1666 ng/plate (non
activation),
10-1000 ng/plate
(activation)
Zeigeretal. (1988)
Salmonella
typhimurium
TA 1535
Reverse
mutation
Plate
incorporation
assay
1666 ng/plate
Zeigeretal. (1988)
Salmonella
typhimurium
TA 1537
Reverse
mutation
Plate
incorporation
assay
ND
1666 ng/plate
Zeigeretal. (1988)
Salmonella
typhimurium
TA 98
Reverse
mutation
Plate
incorporation
assay
5000 ng/plate
Shimizu and
Takemura (1983,)
as cited in CCRIS
(2005)
Salmonella
typhimurium
TA 100
Reverse
mutation
Plate
incorporation
assay
+
0-5000 ng/plate
Shimizu and
Takemura (1983),
as cited in CCRIS
(2005)
Salmonella
typhimurium
TA 98, 100
Reverse
mutation
Plate
incorporation
assay
+
100 |iL/platc
Nohmi et al. (1983)
Salmonella
typhimurium
TA 98, 100
Reverse
mutation
Plate
incorporation
assay
+
5-50 nmol/plate
Nohmi et al. (1984)
Salmonella
typhimurium
TA 100
Reverse
mutation
Plate
incorporation
assay
ND
+
5-1000 ng/plate
Chung et al.
(1981), as cited in
CCRIS (2005)
Salmonella
typhimurium
TA 100
Reverse
mutation
Plate
incorporation
assay
ND
+
0-15 nmol/plate
Zimmer et al.
(1980)
Salmonella
typhimurium
TA 98, 1537
Reverse
mutation
Plate
incorporation
assay
-?d
-?
0-15 nmol/plate
Zimmer et al.
(1980)
Salmonella
typhimurium
TA 100
Reverse
mutation
Plate
incorporation
assay
ND
+
25 (ig/plate
Anonymous-
German (1993) as
cited in HSDB
(2009)
Salmonella
typhimurium
TA 100
Reverse
mutation
(presumed)
Plate
incorporation
assay
+
1 (imol/plate
Kimmel et al.
(1986), as cited in
RTECS (2009).
Chinese Hamster
V79 fibroblasts
Alkaline
elution
DNA
breakage test
ND
—
1.0, 3.0 mM
(2 hr and 4 hr)
Zimmer et al.
(1980)
Bacillus subtilis
Transforming
DNA activity
Loss of DNA
transforming
activity
ND
10 mM
Nohmi et al. (1984)
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Table 3. Genotoxicity Studies of 2,4-Dimethylaniline In Vitro
Test System
Endpoint
Test
Conditions
Results"
Dosec
Reference
Without
Activation
With
Activationb
Rat hepatocytes
Unscheduled
DNA
Synthesis
DNA Repair
test
+
ND
1-1000 (imol
Yoshimi et al.
(1988), as cited in
CCRIS (2005)
Chinese Hamster
Lung (CHL) cells
Chromosomal
aberrations
DNA Repair
test
+
0.013-0.2 mg/mL
(6-hr exposure, 18-hr
recovery)
Japan Chemical
Industry Ecology
(1996), as cited in
CCRIS (2005)
Chinese Hamster
Lung (CHL) cells
Chromosomal
aberrations
DNA Repair
test
+
ND
0.13-0.5 mg/mL
(24-hr and 48-hr
treatment)
Japan Chemical
Industry Ecology
(1996), as cited in
CCRIS (2005)
a+ = positive, - = negative, ± = equivocal, ND = no data.
bExogenous metabolic activation used.
°Lowest effective dose for positive results, highest dose tested for negative or equivocal results.
d? = Positive or negative results identified, but activation status unknown.
Table 4. Genotoxicity Studies of 2,4-Dimethylaniline In Vivo
Test System
Endpoint
Test Conditions
Results"
Doseb
Reference
B6C3F1 mouse
bone marrow
DNA damage
Alkaline single cell gel
electrophoresis ("comet") assay
+
200 mg/kg
Przybojewska
(1997)
B6C3F1 mouse
liver cells
DNA damage
Alkaline single cell gel
electrophoresis ("comet") assay
+
100, 200 mg/kg
Przybojewska
(1999)
Female Wistar
rat liver
DNA adducts
Single oral gavage dose
0.5 M solution
(0.1 mL/lOOg
body weight)
Jones and
Sabbioni (2003)
Female Wistar
rat hemoglobin
DNA adducts
Single oral gavage dose
+
0.5 M solution
(0.1 mL/lOOg
body weight)
Jones and
Sabbioni (2003)
Male mouse
testicle
DNA synthesis
Oral application or
intraperitoneal injection
+
200 mg/kg
(p.o.) or
100 mg/kg (i.p.)
Seiler et al.
(1977) as cited
in ACGIH
(2001) and
RTECS (2009)
a+ = positive, - = negative
bLowest effective dose for positive results, highest dose tested for negative or equivocal results.
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In other microsome tests, Salmonella typhimurium strain TA 100 with S9 activation
tested positive with concentrations of 25 [j,g/plate or higher (Anonymous-German, 1993, as cited
in HSDB, 2009) and 5-1000 [j,g/plate (Chung et al., 1981 as cited in CCRIS, 2005), and was
weakly mutagenic at 0-15 [j,mol/plate (Zimmer et al., 1980). The study authors noted that the
chemical was not mutagenic in TA 98 and TA 1537 strains. In another study, mutations in
Salmonella typhimurium TA 100 were observed with metabolic activation at concentrations of
1 [j,mol/plate (Kimmel et al., 1986, as cited in RTECS, 2009).
In the alkaline elution/DNA breakage test, 2,4-dimethylaniline did not induce DNA
damage in Chinese hamster V79 lung fibroblasts with activation at 1.0 and 3.0 mM for 2-hour
and 4-hour exposure periods, respectively (Zimmer et al., 1980). In three additional in vitro tests
using Chinese hamster lung (CHL) cells, one test was found to be negative for chromosomal
aberrations without activation at concentrations of 0.013-0.2 mg/mL (6-hour treatment, 18-hour
recovery) while two tests were positive, either with no metabolic activation at concentrations of
0.13-0.5 mg/mL (24 and 48 hour continuous treatment) or with rat liver S9 activation at
concentrations of 0.013-0.2 mg/mL (6-hour treatment, 18-hour recovery) (Japan Chemical
Industry Ecology, 1996, as cited in CCRIS, 2005). Also, Yoshimi et al. (1988) examined
unscheduled DNA synthesis (UDS) in rodent hepatocytes and found that 2,4-dimethylaniline
elicited positive repair responses in the DNA repair test.
Nohmi et al. (1983) tested the mutagenicity of 2,4-dimethylaniline metabolites in the
plate incorporation assay using Salmonella typhimurium strains TA 98 and 100. Out of several
metabolites, 2,4-dimethylphenylhydroxylamine was identified as being directly mutagenic to
TA 100 cells, whereas 2,4-dimethylaniline was only mutagenic in the presence of S9 mixture,
with the TA 100 strain more sensitive than the TA 98 strain. In a second study, the authors again
tested the mutagenicity of both 2,4-dimethylaniline as well as the A-hydroxy derivative of
2,4-dimethylaniline, 2,4-dimethylphenylhydroxylamine, in S. typhimurium strains TA 98 and
100 for the plate incorporation assay (Nohmi et al., 1984). The authors observed that
2,4-dimethylaniline was negative without metabolic activation at concentrations of
5-50 nmoles/plate but showed positive results with liver S9 mix, inducing less than 10 (to the
power of 3) revertants per |imol; the A-hydroxy compound was mutagenic even in the absence of
activation and induced more than 10 (to the power of 4) revertants per |imol.
In the Rec-assay using Bacillus subtilis, a metabolite of 2,4-dimethylaniline tested
positive. Nohmi et al. (1984) tested the chemical and its A'-hydroxy metabolite in the Bacillus
subtilis-transforming DNA assay (thus giving an assessment of the reactivity of the chemical
with DNA). The chemical 2,4-dimethylaniline exerted no marked effect on the transforming
activity of the DNA, and remaining activity of transforming DNA was 98%; however, its
phenylhydroxyl amine derivative caused a decrease in the activity of transforming DNA by more
than 50% during an incubation time of 30 minutes.
Several in vivo genotoxicity tests have also been conducted. Przybojewska (1997) tested
the genotoxicity of 2,4-dimethylaniline using the alkaline single cell gel electrophoresis (or
"comet") assay. A single intraperitoneal injection at the oral LD50 concentration (200 mg/kg), as
determined by study authors, was given to six male B6C3F1 mice 16 hours prior to sacrifice.
Bone marrow suspensions were then analyzed to detect the presence of DNA damage in
individual cells (e.g., single-strand breaks). The single dose of 2,4-dimethylaniline resulted in an
increased number of bone marrow cells with DNA damage as evidenced by an increased extent
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of DNA migration in bone marrow cells of treated mice compared to controls. Przybojewska
(1999, as cited in RTECS, 2009) also conducted another comet assay under alkaline conditions
to measure the DNA damage in the liver cells of B6C3F1 mice following a single intraperitoneal
injection of 2,4-dimethylaniline at doses of 100 or 200 mg/kg body weight, respectively. The
chemical damaged DNA in the liver cells of the mice, but no further details could be obtained as
the original study was not available for review at this time.
Jones and Sabbioni (2003) examined the formation of DNA adducts in two female Wistar
rats, who were given a single oral gavage dose of 2-methylaniline in calf thymus DNA. DNA
adducts were not detected in the liver but were detected in hemoglobin. Additionally, a
presumed single oral application of 200 mg/kg or intraperitoneal injection of 100 mg/kg to male
mice inhibited testicular DNA synthesis (Seiler et al., 1977, as cited in ACGIH, 2001 and
RTECS, 2009). The original source was unavailable for review at this time.
DERIVATION OF PROVISIONAL VALUES
DERIVATION OF ORAL REFERENCE DOSE
Derivation of Chronic and Subchronic Provisional RfD
An evaluation of the available oral studies indicated that the 6-month chronic-duration
toxicity study by Lindstrom et al. (1963) was identified as the principal study and deemed
adequate for the derivation of a chronic and subchronic p-RfD. However, it was determined that
the UFc would be >3000. A screening subchronic and a chronic p-RfD is provided in
Appendix A. The benchmark dose calculations for the screening subchronic and chronic p-RfD
can be found in Appendix D.
DERIVATION OF INHALATION REFERENCE CONCENTRATIONS
Derivation of Chronic and Subchronic Provisional RfC
There are two main inhalation studies identified in the database. The first study exposed
"3
mice, rats, rabbits, cats, dogs, chicks, and monkeys to a single dose of 45 ppm (223 mg/m ) of an
isomeric xylidine vapor mixture for 7 hours/day, 5 times/week, for up to 40 weeks (Von
Oettingen et al., 1947). Some effects noted included mortality in all species (except monkeys
and chicks), liver damage in all species except chicks and elevated methemoglobin levels and
increased number of Heinz bodies in cats, dogs, and mice. Due to the use of a single dose,
known data gaps in the study, and the use of an impure xylidine vapor mixture, it is not possible
to derive a chronic or subchronic p-RfC from this study.
Similarly, in a second study, multiple species of animals (i.e., rats, guinea pigs, rabbits,
cats, and monkeys) exposed to 2,4-dimethylaniline vapor at concentrations of 50 to 142 ppm
(36 to 703 mg/m3) for 7 hours/day, 5 days/week, for an unspecified duration (Treon et al., 1950)
experienced increased mortality, pneumonitis, and degeneration of cells in the heart, liver, and
kidneys. All species except for the cat, which demonstrated liver toxicity, tolerated doses of
3 3
17.5 ppm (86 mg/m ). One monkey and two cats tolerated 92 exposures at 7.8 ppm (36 mg/m )
without any effect. Due to the use of an impure xylidine vapor mixture, it is not possible to
derive a chronic or subchronic p-RfC from this study.
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CANCER WEIGHT-OF-EVIDENCE DESCRIPTOR
Table 5 identifies the cancer weight-of-evidence descriptor for 2,4-dimethylaniline.
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Table 5. Cancer WOE Descriptor for 2,4-Dimethylaniline
Possible WOE
Descriptor
Designation
Route of Entry (Oral,
Inhalation, or Both)
Comments
"Carcinogenic to
Humans"
N/A
N/A
No human cancer studies are available.
"Likely to Be
Carcinogenic to
Humans"
N/A
N/A
No strong animal cancer data are available.
"Suggestive
Evidence of
Carcinogenic
Potential"
X
Oral
dietary
administration
Under the 2005 Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005), 2,4-dimethylaniline is
considered to have "Suggestive Evidence of Carcinogenic PotentiaF'' for humans by the oral route of exposure.
Previously, EPA classified 2,4-dimethylaniline as a Group C carcinogen ("possibly carcinogenic to humans:
agents with limited animal evidence and little or no human data") (U.S. EPA, 2010b), according to the 1986
guidelines for Carcinogenic Risk Assessment (U.S. EPA, 1986).
Although Weisburger et al. (1978) did not find excess incidence of tumors in male rats nor in male mice, there
was a statistically significantly increased incidence of lung tumors in female mice (p < 0.05). Lung tumors in
female mice also occurred with a statistically significant positive trend (Cochran-Armitage trend test, p = 0.01).
Furthermore, an additional 2-year dietary study suggests neoplastic effects from exposure to
2,4-dimethylaniline. It was reported that a 23% excess incidence of subcutaneous fibromas or fibrosarcomas
and hepatomas was observed in male Sprague-Dawley rats, but no other details could be obtained from the
source, which was possibly from an abstract (Health Council of the Netherlands, 2002; IARC, 1978, in HSDB,
2009). EPA has previously published a HEEP for 2,4-dimethylaniline and 2,4-dimethylaniline hydrochloride.
The human carcinogen potency factor (ql*) for 2,4-dimethylaniline is 0.75 (mg/kg-day) 1 for oral exposure, and
the EPA's HEAST lists an oral unit risk for 2,4-dimethylaniline of 2.1 x 10 " (|ig/L) 1 based on mouse lung
tumors as observed in Weisburger et al. (1978).
Genotoxicity studies for 2,4-dimethylaniline have demonstrated mixed but generally positive results. Results
from plate incorporation mutagenicity assays show positive results in S. typhimurium especially in the presence
of metabolic activation (Zeiger et al., 1988; Shimizu and Takemura, 1983; Chung et al., 1981; Zimmer et al.,
1980; Nohmi et al., 1983; Nohmi et al., 1984). Yoshimi et al. (1988) found positive results for unscheduled
DNA synthesis in rodent hepatocytes at concentrations of 1-1000 (imols, and Przybojewska (1997, 1999 as
cited in RTECS, 2009) found increased DNA damage in bone marrow cells and liver cells of B6C3F1 using the
comet assay. Inhibition of testicular DNA synthesis was observed in an oral mouse study (Seiler et al., 1977, as
cited in ACGIH, 2001 and HSDB, 2009). Some negative tests found that 2,4-dimethylaniline did not induce
DNA damage in Chinese hamster V79 lung fibroblasts with activation (Zimmer et al., 1980), while Jones and
Sabbioni (2003) did not find DNA adducts in liver, but did find adducts in hemoglobin. Nohmi et al. (1984)
found that 2,4-dimethylaniline itself did not decrease Bacillus subtilus DNA-transforming activity but attributed
mutagenic activity of 2,4-dimethylaniline to its Y-hvdroxy derivative.
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Table 5. Cancer WOE Descriptor for 2,4-Dimethylaniline
Possible WOE
Descriptor
Designation
Route of Entry (Oral,
Inhalation, or Both)
Comments
"Inadequate
Information to
Assess
Carcinogenic
Potential"
N/A
N/A
Available data are judged inadequate to assess carcinogenic potential.
"Not Likely to Be
Carcinogenic to
Humans"
N/A
N/A
No strong evidence of noncarcinogenicity in humans is available.
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DERIVATION OF PROVISIONAL CANCER POTENCY VALUE
Derivation of Provisional Oral Slope Factor (p-OSF)
The mouse study by Weisburger et al. (1978) is selected as the principal study. The
critical endpoint is the incidence of lung tumors in CD-I HaM/ICR female mice. This study is
generally well conducted, and the data from this study are able to support a quantitative cancer
dose-response assessment. This study is a peer-reviewed technical report from the National
Cancer Institute, has been performed according to GLP standards, and has an acceptable study
design and performance with numbers of animals, examination of potential toxicity endpoints,
and presentation of information. This study is the only available, acceptable study with a
positive tumor response following 2,4-dimethylaniline oral exposure. A mode of action for this
chemical to induce lung tumors cannot be clearly identified from the available studies (see
Tables 3-5); therefore, a linear approach is appropriate to model these data.
The oral data are sufficient to derive a quantitative estimate of cancer risk using
benchmark dose (BMD) modeling. The dose-response data for lung tumors in female mice (see
Table 6) can be used to derive a p-OSF for 2,4-dimethylaniline. Statistical significance tests
were conducted and the results indicate that lung tumors in female mice occurred with a
statistically significant positive trend (Cochran-Armitage trend test, p = 0.01), and a statistically
significant increase in tumor incidence was observed at the highest dose (Fisher's exact test,
p < 0.05).
The following dosimetric adjustments were made for diet treatment in adjusting doses for
derivation of a p-OSF:
DOSEadj, hed
Body-weight adjustment
BWn
BWa
Body-weight adjustment
(DOSEadj, hed)
(DOSEadj, hed)
Dose x Food Consumption per Day x (1 Body
Weight) x (Days Dosed Total Days) x
body-weight adjustment
-.1/4
= (BWa - BWh)
= 70 kg (human reference body (U.S. EPA , 2010b)
= 0.02875 kg (average body weight for female mice
(U.S. EPA, 1994)
= (0.02875 -70)1/4 = 0.142
= (Dose)„ x (0.0053 kg/day) x (1 - 0.02875 kg) x
(18 months 21 months) x 0.142
= 125 mg/kg x (0.0053 kg/day) x (34.78 kg"1) x 0.857
x 0.142
= 0.663 mg/day x 34.78 kg"1 x 0.857 x 0.142
= 23.04 mg/kg-day x 0.122
= 2.9 mg/kg-day
Table 6 presents BMD input data for incidence of lung tumors in female mice
exposed to 2,4-dimethylaniline by diet for 21 months.
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Table 6. BMD Input for Incidence of Lung Tumors in
the Female CD-I HaM/ICR Mouse Exposed to 2,4-Dimethylaniline by Diet for 21 Months"
(Dose)„ (mg/kg-day)
(DOSEA|).|,|||.;|))„
(mg/kg-day)
Number of Subjects
Response
Lung Tumorsb'c
0
0
22
5(23)
20
2.9
18
5(28)
40
5.8
19
ll(58)d
aWeisburger et al. (1978).
bNumber of mice with tumors, () = percentage of mice with lung tumors.
Statistically significant trend using Cochrane-Armitage test for dose-response relationship.
Statistically significant in pairwise test versus control.
Table 7 shows the modeling results. Adequate model fit is obtained for the lung tumor
incidence data using the 1-degree multistage-cancer model. The BMD modeling results for lung
tumors yield a BMDiohed of 1.241 mg/kg-day and a BMDLiohed of 0.674 mg/kg-day (see
Table 7). The BMD output for increased incidence of lung tumors in female mice can be seen in
Figure D-l.
Table 7. Goodness-of-Fit Statistics, BMDiohed, and BMDLiohed Values for
Dichotomous Models for Lung Tumors in the Female Mouse Exposed to
2,4-Dimethylaniline in Diet for 21 Months"
Goodness-of-Fit
BMD10hed
BMDL10hed
Multistage Cancer Model
p-V alueb
AIC
(mg/kg-day)
(mg/kg-day)
Multistage Cancer
0.28
75.914
1.241
0.674
aWeisburger et al. (1978).
bValues >0.1 meet conventional goodness-of-fit criteria.
p-OSF — BMR ¦+- BMDLiohed
= 0.1 0.674 mg/kg-day
= 0.148 or 2 x 10"1 (mg/kg-day)"1
Derivation of Provisional Inhalation Unit Risk (p-IUR)
The available data are inadequate for the derivation of a quantitative cancer risk estimate
from inhalation exposure to 2,4-dimethylaniline (i.e., all data are from exposure conditions
employing isomeric mixtures of chemicals).
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APPENDIX A. PROVISIONAL NONCANCER SCREENING VALUES
Considering the uncertainties in the 2,4-dimethylaniline database described below (see
Table A-2), the total composite UF for the derivation of a provisional chronic p-RfD is 10,000,
consisting of four areas of maximum uncertainty. In the report, A Review of the Reference Dose
and Reference Concentration Processes (U.S. EPA, 2002) the RfD/RfC technical panel
concluded that, in cases where maximum uncertainty exists in four or more areas of uncertainty,
or when the total UF is 10,000 or more, it is unlikely that the database is sufficient to derive a
reference value. Because of this uncertainty, a provisional chronic p-RfD for
2,4-dimethylaniline is not derived. However, information is available which, although
insufficient to support derivation of provisional RfD values, 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 a supplemental appendix and develops a screening value.
Appendices receive the same level of internal and external scientific peer review as the main
document to ensure their appropriateness within the limitations detailed in the document. Users
of screening toxicity values in a supplement to a PPRTV assessment should understand that there
is considerably more uncertainty associated with the derivation of a supplement 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 Heath Risk
Technical Support Center.
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Table A-l. Benchmark Dose Modeling Results for Decreased Body-Weight Gain and
Increased Relative Kidney Weights in Osborne-Mendel Rats (Lindstrom et al., 1963)
Endpoint
Species
Sex
Model
Homogeneity
Variance
p-Value
Goodness-of-Fit
p-Value
AIC for
Fitted
Model
BMDio
(mg/kg-day)
BMDL10
(mg/kg-day)
Conclusions
Decreased
Body-
Weight
Gain3
Rat
F
Continuous-
Linear
0.0001383
0.1888
668.072
297.65
237.21
Lowest AIC
Lowest BMDL
Continuous-
Polynomial
0.0001383
0.1888
668.072
297.65
237.21
Lowest AIC
Lowest BMDL
Maximum order beta = 0
(32 = 0, (33 = 0, (34 = 0
Continuous-
Power
0.0001383
0.1888
668.072
297.65
237.21
Lowest AIC
Lowest BMDL
Increased
Relative
Kidney
Weight
Rat
M
Continuous-
Hill
0.0001248
0.3735
65.6072
44.81
19.55
Lowest AIC
Lowest BMDL
Rat
F
Continuous-
Hill
0.002347
0.7339
60.3687
31.33
18.87
Lowest AIC
Lowest BMDL
aModeling for decreased body-weight gain was done using 1SD.
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DERIVATION OF SCREENING ORAL REFERENCE DOSE
Derivation of Screening Chronic and Subchronic p-RfD
The 6-month chronic-duration toxicity study by Lindstrom et al. (1963) was
identified as the principal study and deemed adequate for the derivation of a screening
chronic and subchronic p-RfD. This study had five dose groups in addition to controls and
tested 10 rats per sex per dose group (n = 120). Although this study reported some limited
toxicological data for rats at 13 weeks, the study was primarily designed with the duration of 6
months in mind. Microscopic examination was performed in every dose group at 6 months and
only in the highest dose group at 13 weeks as an indication of the types of effects that would be
seen at 6 months (e.g., only four rats at the highest dose at 13 weeks, compared to four rats at
each dose at 6 months). In addition, organ-weight data for kidneys, livers, and spleen were not
provided at 13 weeks nor was hematological analysis performed. Therefore, the results obtained
at 6 months were used to identify a point of departure (POD).
Decreases in body-weight gain were statistically significant in males and females at the
three highest dose levels (Lindstrom et al., 1963). In addition, relative liver weight was
statistically significantly increased at all dose levels in males and females. Relative kidney
weight was also statistically significantly increased at all dose levels in males and females.
Because these three endpoints were the most sensitive effects reported in this study, all of the
common continuous models (i.e., Linear, Polynomial, Power, and Hill models) available in the
EPA's Benchmark Dose Software (BMDS, version 2.1) were fit to the data. In general, model fit
was assessed by a x goodness-of-fit test (i.e., models withp < 0.1 failed to meet the goodness-
of-fit criterion) and the Akaike Information Criterion (AIC) value (i.e., a measure of the deviance
of the model fit that allows for comparison across models for a particular endpoint).
The initial modeling of all the data including all dose groups failed to provide an
adequate fit to the data, as assessed by the x goodness-of-fit test. After excluding the highest
dose group, the Linear, Polynomial, and Power models adequately fit the body-weight gain data
for female rats, and the Hill model adequately fit the male and female relative kidney weight
data. No adequate model fits were achieved with the relative liver-weight data even when the
three highest dose groups were excluded.
For the increase in relative kidney weight, the Hill model in female rats was considered
most appropriate because it produced a slightly lower BMDio and BMDLio of 31.33 and
18.87 mg/kg-day, respectively, compared to those from male rats. BMD outputs for increased
relative kidney weights in male and female rats using the Hill model, can be seen in Figures C-l
and C-2. Because both male and female relative liver weights did not provide adequate model
fits, the LOAEL of 18 mg/kg-day (male rats) was considered as an alternative POD. It is
important to note that increased relative liver weight was quantitatively the more sensitive
response compared to increased relative kidney weight based on the magnitude of change from
control (see Figure A-l). Specifically, at the LOAEL of 18 mg/kg-day in male rats, a -10%
increase in relative kidney weight was observed whereas a -40% increase in relative liver weight
was observed (compared to the respective control values [see Figure A-l]). A similar trend was
observed for relative liver weight in female rats. The general dose-response trend based on a
10%) change modeled for both relative kidney and liver weight in male rats as assessed by the
BMD (i.e., the maximum likelihood estimate not influenced by sample size) indicates that the
relative liver-weight response is more sensitive (BMDio = 6.56) than the relative kidney-weight
response (BMDio = 37.54). While the selection of the BMDLio from the relative kidney-weight
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dataset as the POD would protect against kidney toxicity, it may not confer protection against the
more sensitive endpoint of liver toxicity (i.e., increased relative liver weight). Therefore, the
LOAEL of 18 mg/kg-day based on increased relative liver weight in male rats
(Lindstrom et al., 1963) was chosen as the POD to derive both a screening chronic and
subchronic p-RfD.
The screening chronic p-RfD for 2,4-dimethylaniline was derived as follows:
Screening Chronic p-RfD = LOAEL UFc
= 18 mg/kg-day ^ 10,000
= 0.0018 or 2 x 10 3 mg/kg-day
The composite UF of 10,000 is estimated, as presented in Table A-2.
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Male Rats
Dose (mg/kg-day)
Figure A-l. Percent Increase Over Control for Relative Kidney Weight and Relative Liver
Weight in Male Osborne-Mendel Rats Exposed to 2,4-Dimethyaniline in Diet for 6 Months3
aLindstrom (1963).
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Table A-2. Uncertainty Factors for Screening Chronic p-RfD for 2,4-Dimethylaniline
UF
Value
Justification
UFh
10
A UFh of 10 is applied for intraspecies differences to account for potentially
susceptible individuals in the absence of information on the variability of
response to humans.
ufa
10
A UFa of 10 is applied for animal-to-human extrapolation to account for
potential toxicokinetic and toxicodynamic differences between rats and humans.
There are no data to determine whether humans are more or less sensitive than
rats to the kidney effects of 2,4-dimethylaniline.
ufd
10
A UFd of 10 is applied for database inadequacies because there are no
acceptable two-generation reproductive studies or developmental studies, and
there are no indications of any other studies that may be relevant for the
database uncertainty factor.
ufl
10
A UFl of 10 is applied because the POD was developed using a LOAEL.
UFS
1
A UFS of 1 is applied because further adjustments for duration of exposure are
not warranted when chronic toxicity data are used to develop a POD.
UFC>3000
10,000
A screening subchronic p-RfD of 0.002 mg/kg-day was derived by adopting the
screening chronic p-RfD as the screening subchronic p-RfD, in the absence of relevant chronic
data. There is low confidence in both the screening subchronic and screening chronic p-RfDs.
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APPENDIX B. DATA TABLES
Table B-l. Mean Body-Weight Gains, Relative Liver Weights, and Relative
Kidney Weights in Osborne-Mendel Rats Exposed to Oral 2,4-Dimethylaniline for
6 Months"
Adjusted
Dose
Group
(mg/kg-day)
Number
of Rats
Body-Weight
Gains (assumed
g) ± Std. Errorb
Relative Liver
Weights (g/kg body
weight) ± Std. Errorb
Relative Kidney
Weights (g/kg body
weight) ± Std. Error
Males
0
16
425.6 ±9.20
26.29 ±0.46
6.68 ±0.16
18
16
441.9 ±23.89
35.98 ± 1.56*
7.3 ±0.18*
36
16
437.6 ± 16.64
41.14 ± 1.51*
7.33 ±0.17*
148
16
343.3 ± 19.15*
47.55 ±0.97*
8.16 ±0.22*
329
16
304.5 ± 13.83*
61.72 ± 1.29*
8.31 ±0.41*
1137
16
157.3 ± 12.28*
94.79 ±3.05*
10.33 ±0.58*
Females
0
16
235.9 ± 15.75
28.88 ±0.76
7.47 ±0.15
26
16
224.4 ± 12.61
38.12 ±2.36*
8.21 ±0.18*
55
16
211.9 ± 7.58
43.4 ± 1.36*
8.57 ±0.16*
209
16
182.6 ±8.45*
56.4 ±2.52*
9.55 ±0.32*
511
16
141 ±5.18*
71.52 ±2.26*
9.99 ±0.30*
1304
16
100.7 ±4.37*
115.66 ±6.71*
12.55 ±0.82*
aValues obtained from Lindstrom et al. (1963), measured at study termination (6 months).
bStd. error (S.E.) converted to std. Deviation (S.D.) using S.D = SE x Vn.
*p < 0.05.
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APPENDIX C. BENCHMARK DOSE CALCULATIONS FOR THE RFD
Modeling Procedure For Continuous Data
The BMD modeling of continuous data was conducted with EPA's BMDS (version
2.1 beta). For these data (e.g., increased relative kidney weight), all continuous models available
within the software were fit using a default BMR of 10% extra risk. An adequate fit was judged
based on the % goodness-of-fit p-value (p> 0.1), magnitude of the scaled residuals in the
vicinity of the BMR, and visual inspection of the model fit. In addition to these three criteria for
judging adequacy of model fit, a determination was made as to whether the variance across dose
groups was homogeneous. If a homogeneous variance model was deemed appropriate based on
the statistical test provided in BMDS (i.e., Test 2), the final BMD results were estimated from a
homogeneous variance model. If the test for homogeneity of variance was rejected (p < 0.1), the
model was run again while modeling the variance as a power function of the mean to account for
this nonhomogeneous variance. If this nonhomogeneous variance model did not adequately fit
the data (i.e., Test 3; p-v alue < 0.1), the dataset was considered unsuitable for BMD modeling.
Among all models providing adequate fit, the lowest BMDL was selected if the BMDLs
estimated from different models varied greater than 3-fold; otherwise, the BMDL from the model
with the lowest AIC was selected as a potential POD from which to derive the RfD.
In addition, in the absence of a mechanistic understanding of the biological response to a
toxic agent, data from exposures much higher than the study LOAEL do not provide reliable
information regarding the shape of the response at low doses. Such exposures, however, can
have a strong effect on the shape of the fitted model in the low-dose region of the dose-response
curve. Thus, if lack of fit is due to characteristics of the dose-response data for high doses, then
the EPA Benchmark Dose Technical Guidance Document allows for data to be adjusted by
eliminating the high-dose group (U.S. EPA, 2000). Because the focus of BMD analysis is on the
low dose region of the response curve, eliminating high-dose groups is deemed reasonable.
Modeling was performed without constant variance because initial analyses with constant
variance models revealed poor model fit. Data outputs from the three modeled endpoints—after
dropping the highest dose from the dataset—were evaluated, and the outputs from decreased
body-weight gain and increased relative kidney weight (in female rats) were deemed valid and
are provided in Table A-l.
Relative Kidney Weight in Male and Female Rats Exposed to 2,4-Dimethylaniline for
6 Months (Lindstrom et al., 1963)
Relative liver and kidney weights were determined to be the most sensitive endpoints
and, therefore, all available continuous models in BMDS (version 2.1 beta) were fit to the
relative kidney- and liver-weight data (see Table A-2) from Osborne-Mendel rats exposed to
2,4-dimethylaniline for 6 months (Lindstrom et al., 1963). However, data from relative liver
weights failed to meet the modeling criteria. The initial modeling of the male and female rat
relative kidney weights including all dose groups failed to provide an adequate fit to the data, as
assessed by the % goodness-of-fit test. After excluding the highest dose (1304 mg/kg-day) group
to provide better model fit, as described in EPA (2000), only the Hill continuous model
adequately fit the data (see Tables C-la and C-lb). Therefore, only the BMD modeling results
based on the data without the highest dose group included are summarized in Tables C-2 and
C-3. Initial tests determined that constant variance was invalid for modeling these data. Thus,
all of the BMD modeling results shown in Tables C-2 and C-3 were obtained from nonconstant
36
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variance models. Estimated doses associated with 10% extra risk and the 95% lower confidence
limit on these doses (BMDio values and BMDLio values, respectively) were 44.81 and
19.55 mg/kg-day in male rats and 31.33 and 18.87 mg/kg-day in female rats, respectively.
Table C-la. Relative Kidney Weight in Male Osborne-Mendel Rats Exposed
to 2,4-Dimethylaniline for 6 Months"
Dose (mg/kg-day)
0
18
36
148
329
Number
16
16
16
16
16
Relative kidney weight
6.68 ±0.64
7.3 ± 0.72b
7.33 ± 0.68b
8.16 ± 0.88b
8.31 ± 1.23b
(g/kg body weight) ± SD
aLindstrom et al., (1963) Table 4.
bRelative kidney weight significantly increased compared to control (p < 0.05).
Table C-lb. Relative Kidney Weight in Female Osborne-Mendel Rats
Exposed to 2,4-Dimethylaniline for 6 Months"
Dose (mg/kg-day)
0
26
55
209
511
Number
16
16
16
16
16
Relative kidney weight
7.47 ±0.6
8.21 ± 0.72b
8.57 ± 0.64b
9.55 ± 1.28b
9.99 ± 1.20b
(g/kg body weight) ± SD
aLindstrom et al. (1963) Table 4.
bRelative kidney weight significantly increased compared to control (p < 0.05).
Table C-2. BMD Modeling Results on Increased Relative Kidney Weight in
Male and Female Rats Exposed to 2,4-Dimethylaniline for 6 Months
Model
Test 2
Test 3
X p-Value
AIC
BMDio
BMDL10
Males
Linear
0.0001
0.2411
0.1051
67.7751
128.39
91.95
Polynomial
0.0001
0.2411
0.1051
67.7751
128.39
91.95
Power
0.0001
0.2411
0.1051
67.7751
128.39
91.95
Hill
0.0001
0.2411
0.3735
65.6072
44.81
19.55
Females
Linear
0.0023
0.5089
<0.0001
79.1454
154.48
116.51
Polynomial
0.0023
0.5089
<0.0001
79.1454
154.48
116.51
Power
0.0023
0.5089
<0.0001
79.1454
154.48
116.51
Hill
0.0023
0.5089
0.7339
60.3687
31.33
18.87
37
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Table C-3. BMD Modeling Output Summary for 2,4-Dimethylaniline, Using Data from Lindstrom et al. (1963)
with Nonconstant Variance and Dropping the Highest Dose Data Point
Endpoint
Species
Sex
Model
Homogeneity
Variance
/7-Value
Goodness-of-Fit
/>-Valuca
AIC for
Fitted
Model
BMD10
(mg/kg-day)b
BMDL10
(mg/kg-day)
Conclusions
Decreased
body-weight
gain
Rat
M
Continuous-
Hill
0.00544
0.3269
764.4763
140.69
-999.00
Invalid BMDL
Poor variance model
Observed to modeled std.
dev. ratio >1.5
Continuous-
Linear
0.0054
0.1387
765.0135
172.13
128.98
Poor variance model
Observed to modeled std.
dev. ratio >1.5
Continuous-
Polynomial
0.0054
<.0001
1046.2256
-999.00
-999.00
Invalid BMD
Invalid BMDL
p-score 4 < 0.1
Poor variance model
Observed to modeled std.
dev. ratio >1.5
Continuous-
Power
0.0054
0.1387
765.0134
172.13
128.98
Poor variance model
Observed to modeled std.
dev. ratio >1.5
Decreased
body-weight
gain
Rat
F
Continuous-
Hill
0.0001
0.3884
667.186
191.35
-999.00
Invalid BMDL
Continuous-
Linear
0.0001
0.1888
668.072
297.65
237.21
Lowest AIC
Lowest BMDL
Continuous-
Polynomial
0.0001
0.1888
668.072
297.65
237.21
Lowest AIC
Lowest BMDL
Maximum order beta = 0
(32 = 0
(33 = 0
(34 = 0
Continuous-
Power
0.0001
0.1888
668.072
297.65
237.21
Lowest AIC
Lowest BMDL
38
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Table C-3. BMD Modeling Output Summary for 2,4-Dimethylaniline, Using Data from Lindstrom et al. (1963)
with Nonconstant Variance and Dropping the Highest Dose Data Point
Endpoint
Species
Sex
Model
Homogeneity
Variance
/7-Value
Goodness-of-Fit
/7-Valuea
AIC for
Fitted
Model
BMD10
(mg/kg-day)b
BMDL10
(mg/kg-day)
Conclusions
Increased
relative liver
weight
Rat
M
Continuous-
Hill
0.0001
<0001
355.4078
3.90
2.91
Lowest AIC
Lowest BMDL
p-score 4 < 0.1
Poor variance model
Observed to modeled std.
dev. ratio >1.5
Continuous-
Linear
0.0001
<.0001
6
35.72
N/D
p-score 4 < 0.1
Poor variance model
Observed to modeled std.
dev. ratio >1.5
Residual of interest >= 2
Continuous-
Polynomial
0.0001
<.0001
8
20.10
N/D
Invalid BMD
Invalid BMDL
p-score 4 < 0.1
Poor variance model
Observed to modeled std.
dev. ratio >1.5
Continuous-
Power
0.0001
<.0001
373.7113
37.48
32.88
p-score 4 < 0.1
Poor variance model
Observed to modeled std.
dev. ratio >1.5
Residual of interest >= 2
Increased
relative liver
weight
Rat
F
Continuous-
Hill
<.0001
0.1075
410.5187
8.36
5.60
Lowest AIC, lowest
BMDL, Poor variance
model, Observed to
modeled std. dev. ratio >
1.5
Continuous-
Linear
<0001
<.0001
536.7464
-999.00
79.42
p-score 4 < 0.1
Poor variance model
Observed to modeled std.
dev. ratio >1.5
39
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Table C-3. BMD Modeling Output Summary for 2,4-Dimethylaniline, Using Data from Lindstrom et al. (1963)
with Nonconstant Variance and Dropping the Highest Dose Data Point
Endpoint
Species
Sex
Model
Homogeneity
Variance
/7-Value
Goodness-of-Fit
/7-Valuea
AIC for
Fitted
Model
BMD10
(mg/kg-day)b
BMDL10
(mg/kg-day)
Conclusions
Continuous-
Polynomial
<0001
<.0001
8
20.84
N/D
Invalid BMD
Invalid BMDL
p-score 4 < 0.1
Poor variance model
Observed to modeled std.
dev. ratio >1.5
Maximum order beta = 0
(31 = 0
(32 = 0
(33 = 0
(34 = 0
Continuous-
Power
<0001
<.0001
433.6389
44.99
37.55
p-score 4 < 0.1
Poor variance model
Observed to modeled std.
dev. ratio >1.5
Increased
relative
kidney
weight
Rat
M
Continuous-
Hill
0.0001
0.3735
65.6072
44.81
19.55
Lowest AIC
Lowest BMDL
Continuous-
Linear
0.0001
0.1051
67.7751
128.39
91.95
Continuous-
Polynomial
0.0001
0.1051
67.7751
128.39
91.95
Maximum order beta = 0
(32 = 0
(33 = 0
(34 = 0
Continuous-
Power
0.0001
0.1051
67.7751
128.39
91.95
Increased
relative
kidney
weight
Rat
F
Continuous-
Hill
0.0023
0.7039
60.3687
31.33
18.87
Lowest AIC
Lowest BMDL
40
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Table C-3. BMD Modeling Output Summary for 2,4-Dimethylaniline, Using Data from Lindstrom et al. (1963)
with Nonconstant Variance and Dropping the Highest Dose Data Point
Endpoint
Species
Sex
Model
Homogeneity
Variance
/7-Value
Goodness-of-Fit
/7-Valuea
AIC for
Fitted
Model
BMD10
(mg/kg-day)b
BMDL10
(mg/kg-day)
Conclusions
Continuous-
Linear
0.0023
<.0001
79.1454
154.48
116.51
p-score 4 < 0.1
Continuous-
Polynomial
0.0023
<.0001
79.1454
154.48
116.51
p-score 4 < 0.1
Maximum order beta = 0
(32 = 0
(33 = 0
(34 = 0
Continuous-
Power
0.0023
<.0001
79.1454
154.48
116.51
p-score 4 < 0.1
aN/D = not determined.
'Body-weight gain was modeled using 1SD.
41
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Hill Model with 0.95 Confidence Level
9
8.5
a)
CO
c
o
Q.
CO
a)
Q1
c
ro
a)
7.5
7
6.5
0 50 100 150 200 250 300
dose
10:15 07/06 2010
Figure C-l. Nonconstant Variance Hill BMD Model-Increased Relative Kidney Weights in
Male Osborne-Mendel Rats after Dropping the Highest Dose (Lindstrom et al., 1963)
Hill Model. (Version: 2.14; Date: 06/26/2008)
Input Data File: C:\USEPA\BMDS21\Data\hil_RelKid_Methylaniline_mnohd_Hil-
ModelVariance-BMRlO-Restrict.(d)
Gnuplot Plotting File:
C:\USEPA\BMDS21\Data\hil_RelKid_Methyaniline_mnohd_Hil-ModelVariance-BMR10-
Restrict.pit
Tue Jul 06 10:15:35 2010
BMDS Model Run
The form of the response function is:
Y[dose] = intercept + v*dose^n/(k^n + dose^n)
Dependent variable = mean
Independent variable = dose
Power parameter restricted to be greater than 1
The variance is to be modeled as Var(i) = exp(lalpha + rho * ln(mean(i)))
42 2,4-Dimethylaniline
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Total number of dose groups = 5
Total number of records with missing values = 0
Maximum number of iterations = 250
Relative Function Convergence has been set to: le-008
Parameter Convergence has been set to: le-008
Default Initial Parameter Values
lalpha = -0.0295524
rho = 0
intercept = 6.68
v = 1.63
n = 0.135532
k = 237.735
Asymptotic Correlation Matrix of Parameter Estimates
( *** The model parameter(s) -n
have been estimated at a boundary point, or have been specified by
the user,
and do not appear in the correlation matrix )
lalpha rho intercept v k
lalpha 1 -1 -0.27 0.33 0.022
rho -1 1 0.27 -0.33 -0.025
intercept -0.27 0.27 1 0.2 0.64
v 0.33 -0.33 0.2 1 0.79
k 0.022 -0.025 0.64 0.79 1
Parameter Estimates
Interval
Variable
Limit
lalpha
7.48496
rho
11.6177
intercept
7.08006
v
3.4531
n
k
261.46
Estimate
-15.6119
7.57708
6.78014
2.22631
1
102.325
Std. Err.
4.14649
2.06157
0.153019
0.625923
NA
81.1928
95.0% Wald Confidence
Lower Conf. Limit Upper Conf.
-23.7389
3.53647
6.48023
0. 999528
-56.8103
NA - Indicates that this parameter has hit a bound
implied by some ineguality constraint and thus
has no standard error.
Table of Data and Estimated Values of Interest
43
2,4-Dimethylaniline
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Dose
Obs Mean
Est Mean
Obs Std. Dev Est Std. Dev
Scaled Res.
0
18
36
148
329
16
16
16
16
16
6. 68
7.3
7.33
8.16
8.31
6.78
7.11
7.36
8.1
8.48
0.64
0.72
0.68
0.88
1.64
0.574
0.689
0.783
1.12
1.34
-0.698
1.09
-0.151
0.226
-0.503
Model Descriptions for likelihoods calculated
Model A1: Yij = Mu(i) + e(ij)
Var{e(ij)} = SigmaA2
Model A2: Yij = Mu(i) + e(ij)
Var{e(ij)} = Sigma(i)^2
Model A3: Yij = Mu(i) + e(ij)
Var{e(ij)} = exp(lalpha + rho*ln(Mu(i)))
Model A3 uses any fixed variance parameters that
were specified by the user
Model R: Yi = Mu + e(i)
Var{e(i)} = Sigma^2
Likelihoods of Interest
Model
A1
A2
A3
fitted
R
Log(likelihood)
-36.236363
-24.721007
-26.818717
-27.803623
-49.675911
# Param's
6
10
7
5
2
AIC
84.472726
69.442013
67.637434
65.607247
103.351823
Test 1:
Test
Test
Test
Explanation of Tests
Do responses and/or variances differ among Dose levels?
(A2 vs. R)
Are Variances Homogeneous? (A1 vs A2)
Are variances adeguately modeled? (A2 vs. A3)
Does the Model for the Mean Fit? (A3 vs. fitted)
(Note: When rho=0 the results of Test 3 and Test 2 will be the same.)
Tests of Interest
Test
-2*log(Likelihood Ratio) Test df
p-value
Test
Test
Test
Test
49.9098
23.0307
4.19542
1.96981
<.0001
0.0001248
0.2411
0.3735
The p-value for Test 1 is less than .05. There appears to be a
difference between response and/or variances among the dose levels
It seems appropriate to model the data
The p-value for Test 2 is less than .1.
model appears to be appropriate
A non-homogeneous variance
44
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The modeled variance appears
The model chosen seems
to adequately describe the data
Benchmark Dose Computation
Specified effect = 0.1
Risk Type = Relative risk
Confidence level = 0.95
BMD = 4 4.8089
BMDL = 19.5498
The p-value for Test 3 is greater than .1.
to be appropriate here
The p-value for Test 4 is greater than .1.
45
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Hill Model with 0.95 Confidence Level
0 100 200 300 400 500
dose
10:18 07/06 2010
Figure C-2. Nonconstant Variance Hill BMD Model-Increased Relative Kidney Weights in
Female Osborne-Mendel Rats after Dropping the Highest Dose (Lindstrom et al., 1963)
Hill Model. (Version: 2.14; Date: 06/26/2008)
Input Data File: C:\USEPA\BMDS21\Data\hil_Rel_Kid_Methya_females_nhd_Hil-
ModelVariance-BMRlO-Restrict.(d)
Gnuplot Plotting File:
C:\USEPA\BMDS21\Data\hil_Rel_Kid_Methya_females_nhd_Hil-ModelVariance-BMR10-
Restrict.pit
Tue Jul 06 10:18:49 2010
BMDS Model Run
The form of the response function is:
Y[dose] = intercept + v*dose^n/(k^n + dose^n)
Dependent variable = mean
Independent variable = dose
Power parameter restricted to be greater than 1
The variance is to be modeled as Var(i) = exp(lalpha + rho * ln(mean(i)))
Total number of dose groups = 5
Total number of records with missing values = 0
Maximum number of iterations = 250
Relative Function Convergence has been set to: le-008
46
2,4-Dimethylaniline
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Parameter Convergence has been set to: le-008
Default Initial Parameter Values
lalpha = -0.135499
rho =
intercept =
v =
n =
k =
0
7.47
2.52
0.160973
337.857
Asymptotic Correlation Matrix of Parameter Estimates
( *** The model parameter(s) -n
have been estimated at a boundary point, or have been specified by
the user,
lalpha
rho
intercept
v
k
and do not appear in the correlation matrix )
lalpha
1
-1
-0.21
0.28
0.052
rho
-1
1
0.2
-0.29
-0.053
intercept
-0.21
0.2
1
-0.13
0.48
v
0.28
-0.29
-0.13
1
0.67
k
0.052
-0.053
0.48
0. 67
1
Interval
Variable
Limit
lalpha
5.86611
rho
8 . 6041
intercept
7.7559
v
3.79489
n
k
163.886
Parameter Estimates
Estimate Std. Err.
-12.4275 3.34769
5.56998 1.54805
7.49402 0.133614
2.97289 0.419397
1 NA
92.9577 36.1888
95.0% Wald Confidence
Lower Conf. Limit Upper Conf.
-18.9888
2 .53587
7.23215
2.15088
22.029
NA - Indicates that this parameter has hit a bound
implied by some inequality constraint and thus
has no standard error.
Table of Data and Estimated Values of Interest
Dose N Obs Mean Est Mean Obs Std. Dev Est Std. Dev Scaled Res.
0
16
7.47
7.49
0.6
0.546
-0.176
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26
16
8.21
55
16
8.57
209
16
9.55
511
16
9.99
8.14 0.72
8.6 0.64
9.55 1.28
10 1.2
0.689 0.385
0.801 -0.145
1.07 -0.00636
1.22 -0.0632
Model Descriptions for likelihoods calculated
Model A1: Yij = Mu(i) + e(ij)
Var{e(ij)} = SigmaA2
Model A2: Yij = Mu(i) + e(ij)
Var{e(ij)} = Sigma(i)^2
Model A3: Yij = Mu(i) + e(ij)
Var{e(ij)} = exp(lalpha + rho*ln(Mu(i)))
Model A3 uses any fixed variance parameters that
were specified by the user
Model R: Yi = Mu + e(i)
Var{e(i)} = Sigma^2
Likelihoods of Interest
Model Log(likelihood) # Param's AIC
A1 -31.998497 6 75.996995
A2 -23.715497 10 67.430993
A3 -24.875027 7 63.750054
fitted -25.184352 5 60.368704
R -59.949377 2 123.898754
Explanation of Tests
Test 1:
Test
Test
Test
Do responses and/or variances differ among Dose levels?
(A2 vs. R)
Are Variances Homogeneous? (A1 vs A2)
Are variances adeguately modeled? (A2 vs. A3)
Does the Model for the Mean Fit? (A3 vs. fitted)
(Note: When rho=0 the results of Test 3 and Test 2 will be the same.)
Tests of Interest
Test
-2*log(Likelihood Ratio) Test df
p-value
Test
Test
Test
Test
72.4678
16.566
2.31906
0.61865
<.0001
0. 002347
0.5089
0.7339
The p-value for Test 1 is less than .05. There appears to be a
difference between response and/or variances among the dose levels
It seems appropriate to model the data
The p-value for Test 2 is less than .1. A non-homogeneous variance
model appears to be appropriate
The p-value for Test 3 is greater than .1. The modeled variance appears
to be appropriate here
The p-value for Test 4 is greater than .1. The model chosen seems
48
2,4-Dimethylaniline
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to adequately describe the data
Benchmark Dose Computation
Specified effect
Risk Type
Confidence level
BMD
BMDL
0.1
Relative risk
0. 95
31.3304
18.8667
49
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APPENDIX D. BENCHMARK DOSE CALCULATIONS FOR
THE ORAL SLOPE FACTOR
Model-Fitting Procedure for Cancer Incidence Data
The model-fitting procedure for dichotomous cancer incidence data is as follows. The
multistage-cancer model in the EPA benchmark dose software (BMDS) is fit to the incidence
data using the extra risk option. The multistage-cancer model is run for all polynomial degrees
up to n-1 (where n is the number of dose groups including control). An adequate model fit is
judged by three criteria: goodness-of-fit p-walue (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 the models providing adequate fit to the data, the
lowest bound of the BMD (BMDL) is selected as the point of departure when the difference
between the BMDLs estimated from these models is more than 3-fold (unless it appears to be an
outlier); otherwise, the BMDL from the model with the lowest (Akaike Information Criterion)
AIC is chosen. In accordance with EPA (2000) guidance, BMDs and BMDLs associated with an
extra risk of 10% are calculated.
Model-Fitting Results for Lung Tumors in HaM/ICR Derived CD-I Female Mice
(Weisburger et al., 1978)
Table 6 shows the dose-response data on lung tumors in HaM/ICR derived CD-I female
mice administered 2,4-dimethylaniline via diet for 21 months (Weisburger et al., 1978).
Modeling was performed according to the procedure outlined above using BMDS version 2.1
with default parameter restrictions for females based on the duration- HEDs shown in Table 2.
Model predictions are shown in Table 7. For female mice, the multistage-cancer model provided
an adequate fit (goodness-of-fit p-w alue > 0.1). The 1-degree polynomial model yielded a
BMDiohed value of 1.241 mg/kg-day with an associated 95% lower confidence limit
(BMDLiohed) of 0.673 mg/kg-day. The fit of the 1-degree multistage-cancer model to the lung
tumor incidence data for female mice is shown in Table 7.
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BMDL
Multistage Cancer Model with 0.95 Confidence Level
0 12 3
dose
10:20 07/12 2010
Figure D-l. Multistage Cancer BMD Model for Female Lung Tumor Incidence
(Weisburger et al., 1978)
Multistage Cancer
Linear extrapolation
BMD Lower Bound
Multistage Cancer Model. (Version: 1.7; Date: 05/16/2008)
Input Data File: C:\USEPA\BMDS21\Data\msc_Weisburger_et_al_1978_Mscl-
BMR10.(d)
Gnuplot Plotting File: C:\USEPA\BMDS21\Data\msc_Weisburger_et_al_1978_Mscl-
BMR10.pit
Mon Jul 12 10:20:40 2010
BMDS Model Run
The form of the probability function is:
P[response] = background + (1-background)*[1-EXP(
-betal*doseAl) ]
The parameter betas are restricted to be positive
Dependent variable = Response
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Independent variable = Dose
Total number of observations = 3
Total number of records with missing values = 0
Total number of parameters in model = 2
Total number of specified parameters = 0
Degree of polynomial = 1
Maximum number of iterations = 250
Relative Function Convergence has been set to: le-008
Parameter Convergence has been set to: le-008
Default Initial Parameter Values
Background = 0.164 032
Beta(1) = 0.104684
Asymptotic Correlation Matrix of Parameter Estimates
Background Beta(l)
Background 1 -0.67
Beta (1) -0.67 1
Parameter Estimates
95.0% Wald Confidence
Interval
Variable Estimate Std. Err. Lower Conf. Limit Upper Conf.
Limit
Background 0.2 04 962 * * *
Beta(1) 0.0849098 * * *
* - Indicates that this value is not calculated.
Analysis of Deviance Table
Model
Full model
Fitted model
Reduced model
Log(likelihood)
-35.3582
-35.9571
-38.4115
# Param's
3
2
1
Deviance Test d.f.
1.19763
6.10645
P-value
0.2738
0.04721
AIC:
75.9141
Dose
Goodness of Fit
Est._Prob. Expected Observed Size
Scaled
Residual
0.0000
2.9000
5.8000
0.2050
0.3785
0.5141
4 .509
6.813
9.769
5.000
5.000
11.000
22
18
19
0.259
-0.881
0.565
Chi^2 = 1.16
d.f. = 1
P-value = 0.2809
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Benchmark Dose Computation
Specified effect = 0.1
Risk Type = Extra risk
Confidence level = 0.95
BMD = 1.24085
BMDL = 0.6738 65
BMDU = 4.84519
Taken together, (0.673865, 4.84519) is a 90 % two-sided confidence
interval for the BMD
Multistage Cancer Slope Factor = 0.148398
53 2,4-Dimethylaniline
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