United States
Environmental Protection
1=1 m m Agency
EPA/690/R-07/021F
Final
4-05-2007
Provisional Peer Reviewed Toxicity Values for
Malononitrile
(CASRN 109-77-3)
Superfund Health Risk Technical Support Center
National Center for Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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Acronyms and Abbreviations
bw body weight
cc cubic centimeters
CD Caesarean Delivered
CERCLA Comprehensive Environmental Response, Compensation and Liability Act
of 1980
CNS central nervous system
cu.m cubic meter
DWEL Drinking Water Equivalent Level
FEL frank-effect level
FIFRA Federal Insecticide, Fungicide, and Rodenticide Act
g grams
GI gastrointestinal
HEC human equivalent concentration
Hgb hemoglobin
i.m. intramuscular
i.p. intraperitoneal
i.v. intravenous
IRIS Integrated Risk Information System
IUR inhalation unit risk
kg kilogram
L liter
LEL lowest-effect level
LOAEL lowest-observed-adverse-effect level
LOAEL(ADJ) LOAEL adjusted to continuous exposure duration
LOAEL(HEC) LOAEL adjusted for dosimetric differences across species to a human
m meter
MCL maximum contaminant level
MCLG maximum contaminant level goal
MF modifying factor
mg milligram
mg/kg milligrams per kilogram
mg/L milligrams per liter
MRL minimal risk level
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MTD
maximum tolerated dose
MTL
median threshold limit
NAAQS
National Ambient Air Quality Standards
NOAEL
no-observed-adverse-effect level
NOAEL(ADJ)
NOAEL adjusted to continuous exposure duration
NOAEL(HEC)
NOAEL adjusted for dosimetric differences across species to a human
NOEL
no-observed-effect level
OSF
oral slope factor
p-IUR
provisional inhalation unit risk
p-OSF
provisional oral slope factor
p-RfC
provisional inhalation reference concentration
p-RfD
provisional oral reference dose
PBPK
physiologically based pharmacokinetic
PPb
parts per billion
ppm
parts per million
PPRTV
Provisional Peer Reviewed Toxicity Value
RBC
red blood cell(s)
RCRA
Resource Conservation and Recovery Act
RDDR
Regional deposited dose ratio (for the indicated lung region)
REL
relative exposure level
RfC
inhalation reference concentration
RfD
oral reference dose
RGDR
Regional gas dose ratio (for the indicated lung region)
s.c.
subcutaneous
SCE
sister chromatid exchange
SDWA
Safe Drinking Water Act
sq.cm.
square centimeters
TSCA
Toxic Substances Control Act
UF
uncertainty factor
Hg
microgram
(.imol
micromoles
voc
volatile organic compound
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PROVISIONAL PEER REVIEWED TOXICITY VALUES FOR
MALONONITRILE (CASRN 109-77-3)
Background
On December 5, 2003, the U.S. Environmental Protection Agency's (EPA's) Office of
Superfund Remediation and Technology Innovation (OSRTI) revised its hierarchy of human
health toxicity values for Superfund risk assessments, establishing the following three tiers as the
new hierarchy:
1. EPA's Integrated Risk Information System (IRIS).
2. Provisional Peer-Reviewed Toxicity Values (PPRTV) used in EPA's Superfund
Program.
3. Other (peer-reviewed) toxicity values, including:
~ Minimal Risk Levels produced by the Agency for Toxic Substances and Disease
Registry (ATSDR),
~ California Environmental Protection Agency (CalEPA) values, and
~ EPA Health Effects Assessment Summary Table (HEAST) values.
A PPRTV is defined as a toxicity value derived for use in the Superfund Program when
such a value is not available in EPA's Integrated Risk Information System (IRIS). PPRTVs are
developed according to a Standard Operating Procedure (SOP) and are derived after a review of
the relevant scientific literature using the same methods, sources of data, and Agency guidance
for value derivation generally used by the EPA IRIS Program. All provisional toxicity values
receive internal review by two EPA scientists and external peer review by three independently
selected scientific experts. PPRTVs differ from IRIS values in that PPRTVs do not receive the
multi-program consensus review provided for IRIS values. This is because IRIS values are
generally intended to be used in all EPA programs, while PPRTVs are developed specifically for
the Superfund Program.
Because new information becomes available and scientific methods improve over time,
PPRTVs are reviewed on a five-year basis and updated into the active database. Once an IRIS
value for a specific chemical becomes available for Agency review, the analogous PPRTV for
that same chemical is retired. It should also be noted that some PPRTV manuscripts conclude
that a PPRTV cannot be derived based on inadequate data.
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Disclaimers
Users of this document should first check to see if any IRIS values exist for the chemical
of concern before proceeding to use a PPRTV. If no IRIS value is available, staff in the regional
Superfund and RCRA program offices are advised to carefully review the information provided
in this document to ensure that the PPRTVs used are appropriate for the types of exposures and
circumstances at the Superfund site or RCRA facility in question. PPRTVs are periodically
updated; therefore, users should ensure that the values contained in the PPRTV are current at the
time of use.
It is important to remember that a provisional value alone tells very little about the
adverse effects of a chemical or the quality of evidence on which the value is based. Therefore,
users are strongly encouraged to read the entire PPRTV manuscript and understand the strengths
and limitations of the derived provisional values. PPRTVs are developed by the EPA Office of
Research and Development's National Center for Environmental Assessment, Superfund Health
Risk Technical Support Center for OSRTI. Other EPA programs or external parties who may
choose of their own initiative to use these PPRTVs are advised that Superfund resources will not
generally be used to respond to challenges of PPRTVs used in a context outside of the Superfund
Program.
Questions Regarding PPRTVs
Questions regarding the contents of the PPRTVs and their appropriate use (e.g., on
chemicals not covered, or whether chemicals have pending IRIS toxicity values) may be directed
to the EPA Office of Research and Development's National Center for Environmental
Assessment, Superfund Health Risk Technical Support Center (513-569-7300), or OSRTI.
INTRODUCTION
The HE AST (U.S. EPA, 1997) lists both subchronic and chronic RfD values for
malononitrile: 2E-4 and 2E-5 mg/kg-day, respectively. The source document for this assessment
was a Health and Environmental Effects Profile (HEEP) for Malononitrile (U.S. EPA, 1986a)
wherein a LOAEL of 0.21 mg/kg-day was established for adverse effects in the liver and spleen
of rats receiving malononitrile by gavage for 120 days (Panov et al., 1972). The RfD was
reviewed by the RfD/RfC Work Group, but was not verified due to deficiencies in the critical
study (Panov et al., 1972) and inadequate documentation (U.S. EPA, 1986b). A toxicity
assessment for malononitrile is not available on IRIS (U.S. EPA, 2007) or in the Drinking Water
Standards and Health Advisories list (U.S. EPA, 2000). The CARA list (U.S. EPA, 1991, 1994)
includes no documents for malononitrile other than the aforementioned HEEP (U.S. EPA,
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1986a). Although it is not listed in the HEAST, the HEEP also contains a carcinogenicity
assessment that placed malononitrile in cancer weight-of-evidence group D, not classifiable as to
human carcinogenicity, due to lack of relevant data. NTP (2002a,b) has not conducted a cancer
bioassay for malononitrile, but has tested malononitrile for genotoxicity. A toxicological review
of malononitrile is not available from ATSDR (2002), IARC (2002) or WHO (2002).
Malononitrile has not been evaluated by ACGIH (2001) or OSHA (2002), but NIOSH (2002)
lists a REL of 8 mg/m3 (3 ppm) for this chemical. This exposure limit is based on analogy to
acetonitrile and isobutyronitrile, due to lack of adequate toxicity data for malononitrile. A recent
toxicity review paper of cyanides and nitriles by Cohrssen (2001) was consulted for relevant
information. Literature searches were conducted from 1985 through November 2001 for studies
relevant to the derivation of provisional toxicity values for malononitrile. Databases searched
included: TOXLINE, MEDLINE, CANCERLIT, TSCATS, RTECS, CCRIS, DART, EMIC/
EMICBACK, HSDB and GENETOX. Using the same databases, additional literature searches
were conducted for the period for 2002 through January 2007. This document has passed the
STSC quality review and peer review evaluation indicating that the quality is consistent with the
SOPs and standards of the STSC and is suitable for use by registered users of the PPRTY system.
REVIEW OF PERTINENT DATA
Human Studies
Limited data are available regarding the toxicity of malononitrile to humans. In the late
1940s, malononitrile was used experimentally by Hyden and Hartelius in the treatment of
schizophrenia and depression (Cohrssen, 2001). Patients were given an intravenous infusion of
5% malononitrile for 10-69 minutes. The total dose during each treatment ranged from 1 to 6
mg/kg. Treatments were given 2-3 times/week, with intervals of at least 1 day between doses.
Ten to 20 min after the beginning of the infusion, all patients experienced tachycardia. In
addition, patients experienced, with varying frequency, local redness, nausea, vomiting,
headaches, shivering, muscle spasms and numbness. Two patients experienced convulsions, and
one case of cardiac collapse was noted (Cohrssen, 2001). The treatments provided little or no
therapeutic benefit, and were discontinued (U.S. EPA, 1986a).
Chronic occupational exposure to other similar nitrile compounds (e.g., acetonitrile) has
resulted in interference of iodine uptake by the thyroid and some cases of goiter, presumably by
interference of thiocyanate produced during normal cyanide detoxification by the endogenous
rhodanese enzyme. Whether this occurs with malononitrile exposure is unknown (Cohrssen,
2001). No other toxicity studies involving human oral or inhalation exposure to malononitrile
were located.
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Animal Studies
Early studies reported that oral administration of malononitrile to mice at doses near the
LD50 (19 mg/kg in mice) caused gastric mucosal injury and a general hyperthermia of all organs
(Cohrssen, 2001). A study described by Cohrssen (2001) found pathologic changes in the spinal
ganglia in rats given a single dose (route unknown) of 6 to 8 mg/kg malononitrile (approximately
10% of rat LD50). Cohrssen (2001) also cites another study wherein lesions of the corpus
striatum were reported. No other details are available.
Panov et al. (1972, as cited by U.S. EPA, 1986a,b) administered 0, 0.25, or 0.5 mg/kg-day
of malononitrile in water by gastric intubation to male Wistar rats 6 days/week for 120 days. A
vehicle control group of 8 rats was used, whereas there were 7 rats in each of the malononitrile
dose groups. Rats were sacrificed for histopathological examination 2 months after the final
treatment. Administration of malononitrile did not result in mortality. Edema and inflammation
were noted in the gastrointestinal tracts of all treated rats, as well as alterations (generally
increasing, although fluctuating greatly) in histamine, histaminase, cholinesterase,
coproporphyrins and 5-hydroxyindoleacetic acid. Dose-related increases in the severity of
lesions in the liver and spleen were reported. In the liver, congestion was observed in both dose
groups (more marked at 0.5 mg/kg-day), and liver degeneration and necrosis were observed at
0.5 mg/kg-day. In the spleen, hemosiderosis and reticulocytosis were observed at 0.25 mg/kg-
day, with diminished hematopoiesis at 0.5 mg/kg-day. Control data were not reported. This
study identified a LOAEL of 0.25 mg/kg-day for histopathological changes in the liver and
spleen of rats exposed to malononitrile by gavage for 120 days, but was limited by small group
sizes, the two month gap between end of exposure and sacrifice for histopathology, and
inadequate reporting of control data.
Lonza (1989) evaluated the subchronic toxicity of malononitrile in Crl:CD(SD)BR rats
(10/sex/dose group) in a GLP study conducted for TSCA §4 compliance. Malononitrile (99.7%
pure) was administered by gavage in distilled water at 0, 0.4, 2 and 10 mg/kg-day for 90 days.
An additional group of rats (5/sex) was administered 0 or 10 mg/kg-day malononitrile for 90
days and retained without treatment for 28 days. The animals were examined weekly for clinical
signs, food consumption, and body weight. An ophthalmoscopic examination was conducted on
high-dose and control rats at study initiation and termination. Hematology (hemoglobin, cell
volume, total and differential white cell count, and platelet count), clinical chemistry (17
parameters), and urinalysis were examined at study termination. A complete necropsy with
organ weight (adrenals, brain, gonads, heart, kidneys, liver, lungs, and spleen) and
histopathologic examination of 40 tissues was conducted at study termination. Aside from
occasional salivation observed among several high-dose rats prior to dosing, no significant
clinical signs were reported during treatment, and there was no malononitrile-related mortality
(the death of one female control rat was attributed to intubation injury). Group mean body
weight of high-dose males was 6% lower than that of controls at 13 weeks. This difference
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began after 2 weeks of dosing, was fairly steady from week 7 to 13, and persisted throughout the
28-day recovery period. The authors reported that body weights were analyzed parametrically,
but there was no indication that the observed decrease in body weight was statistically
significant. Food consumption was not affected by treatment; food conversion efficiency was
lower in high-dose males compared to controls. Ophthalmology findings were unremarkable.
Statistically significant changes in several hematology and clinical chemistry parameters
were noted at 2 and 10 mg/kg-day (Lonza, 1989). The mean alkaline phosphatase level of high-
dose females was greater than controls at week 13 (p<0.001). A decrease in mean total serum
cholesterol was reported for intermediate- and high-dose females (p<0.001 and p<0.01,
respectively). Increased mean plasma urea levels were noted at week 13 in high dose males and
intermediate and high dose females (p<0.01 as compared to controls for high dose males and
intermediate dose females). At week 13, a dose-dependent increase in platelet counts of the
intermediate- (trend) and high-dose (p<0.01 as compared to controls) males and high-dose
(trend) females was reported. These changes in hematology and clinical chemistry parameters
were not observed after the 28-day recovery period. Absolute and relative liver weights were
significantly increased in high-dose groups of both sexes (p<0.001 for both males and females),
and relative liver weight was increased in males at 2 mg/kg-day (p<0.05). This effect on liver
weight was partially reversed by the recovery period. There were no macroscopic findings that
suggested gross target organ toxicity related to malononitrile administration. Hepatocellular
hypertrophy (accompanied by vacuolization of the cytoplasm of the hepatocytes) was observed in
intermediate- and high-dose males and among high-dose females. This effect was not present
after the recovery period. Administration of malononitrile at 0.4 mg/kg-day for 90 days did not
result in any toxicologically significant adverse effects. This study established a NOAEL of 0.4
mg/kg-day and a LOAEL of 2 mg/kg-day for hepatic effects (increased relative liver weight and
hepatocellular hypertrophy and vacuolization) in male CD rats and changes in clinical pathology
profiles for both sexes.
Only one study of the inhalation toxicity of malononitrile is available. Panov (1970, as
cited by U.S. EPA, 1986a) exposed groups of 10 white rats (strain and sex were not reported) to
malononitrile vapors at concentrations of 0 or 36 mg/m3, 2 hours per day, for 35 days. The rats
exposed to malononitrile exhibited signs of irritation during exposure, a nonsignificant tendency
toward reticulocytosis, significantly decreased hemoglobin concentrations on days 22 and 35, and
significantly increased lung weight post mortem. No treatment-related increase in mortality was
reported. There were no effects on body weight, red or white blood cell counts, oxygen
consumption, or weights of brain, liver, or kidneys. The utility of this study for risk assessment
is limited by the brief (2 hours) daily exposures, the short (35-day) treatment period, use of only a
single exposure level, the limited number of endpoints studied, the marginal nature of the
findings, and incomplete reporting of methods and results.
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No studies of the possible reproductive or developmental hazards of malononitrile were
located, nor were any chronic toxicity studies of malononitrile available. The available data
show that malononitrile did not induce reverse mutations in Salmonella typhimurium (U.S. EPA,
1986a; NTP, 2002b).
DERIVATION OF PROVISIONAL SUBCHRONIC AND CHRONIC
ORAL RfD VALUES FOR MALONONITRILE
Limited information on the oral toxicity of malononitrile in humans and animals exists.
At the time of the 1986 HEEP (U.S. EPA, 1986a), information available for derivation of an oral
p-RfD was limited to the study by Panov et al. (1972), which identified a LOAEL of 0.21 mg/kg-
day for adverse effects in the liver and spleen of rats receiving malononitrile by gavage for 120
days. Subsequent to that assessment, Lonza (1989) published a high quality subchronic study
that identified a NOAEL of 0.4 mg/kg-day and a LOAEL of 2 mg/kg-day for hepatic effects
(increased relative liver weight and hepatocellular hypertrophy and vacuolization) in male CD
rats and changes in clinical pathology profiles for both sexes. The Panov et al. (1972) study was
limited by small group sizes, a two month gap between end of exposure and sacrifice for
histopathology, and inadequate reporting of control data. Therefore, the Lonza (1989) study is
more appropriate as the principal study for derivation of provisional subchronic and chronic oral
RfD values.
To the rat NOAEL of 0.4 mg/kg-day established by Lonza (1989), a combined uncertainty
factor of 300 (10 for interspecies extrapolation, 10 for human variability, and 3 for database
deficiencies, including lack of reproductive and developmental toxicity tests) was applied. No
modifying factor was used {i.e., the modifying factor = 1). A provisional subchronic oral RfD
of 1E-3 mg/kg-day was calculated as follows:
subchronic p-RfD = NOAEL / UF
= 0.4 mg/kg-day / 300
= 0.001 mg/kg-day or 1E-3 mg/kg-day
A provisional chronic oral RfD can also be derived by dividing the NOAEL of 0.4
mg/kg-day established by Lonza (1989) by a combined uncertainty factor of 3000 (10 to account
for extrapolation from a subchronic study, 10 for interspecies extrapolation, 10 for human
variability, and 3 for database deficiencies). No modifying factor was used (i.e., the modifying
factor = 1). A provisional chronic oral RfD of 1E-4 mg/kg-day was calculated as follows:
p-RfD = NOAEL / UF
= 0.4 mg/kg-day / 3000
= 0.0001 mg/kg-day or 1E-4 mg/kg-day
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These provisional subchronic and chronic RfD values are both five times higher than the
corresponding values derived in the HEEP (U.S. EPA, 1986a) and listed in the HEAST (U.S.
EPA, 1997). The difference is due to the recent availability of higher quality data that better
define critical effect levels for this chemical.
Confidence in the principal study is high; it is a well-designed GLP study that examined a
number of relevant endpoints and identified both a LOAEL and a NOAEL. Confidence in the
database is low; supporting data for the critical study are available only from one other
subchronic study of uncertain reliability, no chronic study is available, and no information is
available on the potential of ingested malononitrile to induce developmental, reproductive, or
neurological effects (a potential target organ suggested by early acute studies). Confidence in the
provisional RfD is low.
DERIVATION OF PROVISIONAL SUBCHRONIC AND CHRONIC
INHALATION RfC VALUES FOR MALONONITRILE
No data regarding the inhalation toxicity of malononitrile in humans were found in the
available review documents (U.S. EPA, 1986a; Cohrssen, 2001) or the literature search. The
HEEP (U.S. EPA, 1986a) included one study involving repeated inhalation exposure of rats to
malononitrile; however, the study limitations preclude its use for quantitative risk assessment.
No other information was located regarding repeated inhalation exposure of animals to
malononitrile in the available review documents or the literature search. Derivation of a p-RfC
for malononitrile is precluded by the absence of relevant inhalation data.
DERIVATION OF A PROVISIONAL CARCINOGENICITY ASSESSMENT
FOR MALONONITRILE
The existing review documents (Cohrssen, 2001; U.S. EPA, 1986a) and update literature
search did not identify relevant studies regarding the carcinogenicity of malononitrile in humans
or animals following oral or inhalation exposure. Available genotoxicity data report that
malononitrile did not induce reverse mutations in Salmonella typhimurium (US. EPA, 1986a;
NTP, 2002b). In accordance with the cancer guidelines (U.S. EPA, 2005), the available data are
inadequate for an assessment of human carcinogenic potential.
Derivation of quantitative estimates (provisional oral slope factor or a provisional
inhalation unit risk) of cancer risk for malononitrile is precluded by the absence of
carcinogenicity data.
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REFERENCES
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Values for Chemical Substances and Physical Agents and Biological Exposure Indices. ACGIH,
Cincinnati, OH. p. 26.
ATSDR (Agency for Toxic Substances and Disease Registry). 2002. Internet HazDat-
Toxicolgical Profile Query. Examined March 8, 2002. Online.
http://www.atsdr.cdc.gov/toxpro2.html
Cohrssen, B. 2001. Cyanides and Nitriles. In: Patty's Toxicology. Volume 4, 5th ed. E.
Bingham, B. Cohrssen, and C.H. Powell, Ed. John Wiley and Sons, Inc., New York. p. 73-1456.
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Lonza (Lonza Incorporated). 1989. P0070: 90 Day Oral (Gavage) Subchronic Toxicity Study in
the Rat with a Four Week Treatment-Free Period. Hazleton Report No. 6055-733/277. TSCA
Section 4 Submission. EPA Document No. 40-8915337. FicheNo. OTS0526378.
NIOSH (National Institute for Occupational Safety and Health). 2002. Online NIOSH Pocket
Guide to Chemical Hazards. Index by CASRN. Examined January 2002. Online.
http://www.cdc.gov/niosh/npg/npgdcas.html
NTP (National Toxicology Program). 2002a. Health and Safety Information for Malononitrile
(CAS # 109-77-3). Examined March 8, 2002. Online, http://ntp-server.niehs.nih.gov
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Panov, I.K. 1970. [Toxicological study of dicyanomethane.] J. Eur. Toxicol. 3:58-63.
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Panov, I.K., M. Zlateva, and G. Antov. 1972. [Toxicological characteristics of dicyanomethane.
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Office of Health and Environmental Assessment, Environmental Criteria and Assessment Office,
Cincinnati, OH for the Office of Solid Waste and Emergency Response, Washington, DC.
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