U.S. Environmental Protection Agency
Hazard Characterization Document
September, 2014
SCREENING-LEVEL HAZARD CHARACTERIZATION
Benzenemethanethiol
(CASRN 100-53-8)
The High Production Volume (HPV) Challenge Program1 was conceived as a voluntary initiative
aimed at developing and making publicly available screening-level health and environmental
effects information on chemicals manufactured in or imported into the United States in quantities
greater than one million pounds per year. In the Challenge Program, producers and importers of
HPV chemicals voluntarily sponsored chemicals; sponsorship entailed the identification and
initial assessment of the adequacy of existing toxicity data/information, conducting new testing if
adequate data did not exist, and making both new and existing data and information available to
the public. Each complete data submission contains data on 18 internationally agreed to "SIDS"
(Screening Information Data Setl1'2) endpoints that are screening-level indicators of potential
hazards (toxicity) for humans or the environment.
The Environmental Protection Agency's Office of Pollution Prevention and Toxics (OPPT) is
evaluating the data submitted in the HPV Challenge Program on approximately 1400 sponsored
chemicals by developing hazard characterizations (HCs). These HCs consist of an evaluation of
the quality and completeness of the data set provided in the Challenge Program submissions.
They are not intended to be definitive statements regarding the possibility of unreasonable risk of
injury to health or the environment.
The evaluation is performed according to established EPA guidance2'3 and is based primarily on
hazard data provided by sponsors; however, in preparing the hazard characterization, EPA
considered its own comments and public comments on the original submission as well as the
sponsor's responses to comments and revisions made to the submission. In order to determine
whether any new hazard information was developed since the time of the HPV submission, a
search of the following databases was made from one year prior to the date of the HPV
Challenge submission to the present: (ChemID to locate available data sources including
Medline/PubMed, Toxline, HSDB, IRIS, NTP, AT SDR, IARC, EXTOXNET, EPA SRS, etc.),
STN/CAS online databases (Registry file for locators, ChemAbs for toxicology data, RTECS,
Merck, etc.), Science Direct and ECHA4. OPPT's focus on these specific sources is based on
their being of high quality, highly relevant to hazard characterization, and publicly available.
OPPT does not develop HCs for those HPV chemicals which have already been assessed
internationally through the HPV program of the Organization for Economic Cooperation and
Development (OECD) and for which Screening Initial Data Set (SIDS) Initial Assessment
Reports (SIAR) and SIDS Initial Assessment Profiles (SIAP) are available. These documents are
presented in an international forum that involves review and endorsement by governmental
1	U.S. EPA. High Production Volume (HPV) Challenge Program; http://www.epa.gov/chemrtk/index.htm.
2	U.S. EPA. HPV Challenge Program - Information Sources; http://www.epa.gov/chemrtk/pubs/general/guidocs.htm.
3	U.S. EPA. Risk Assessment Guidelines; http://cfpub.epa.gov/ncea/raf/rafguid.cfm.
4	European Chemicals Agency, http://echa.europa.eu.

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U.S. Environmental Protection Agency
Hazard Characterization Document
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authorities around the world. OPPT is an active participant in these meetings and accepts these
documents as reliable screening-level hazard assessments.
These hazard characterizations are technical documents intended to inform subsequent decisions
and actions by OPPT. Accordingly, the documents are not written with the goal of informing the
general public. However, they do provide a vehicle for public access to a concise assessment
ofthe raw technical data on HPV chemicals and provide information previously not readily
available to the public.
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Hazard Characterization Document
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Chemical Abstract
Service Registry Number
	(CASRN)	
100-53-8
Chemical Abstract Index
Name
Benzenemethanethiol
SH
Structural Formula
SMILES: SCc(ccccl)cl
Summary
Benzenemethanethiol is a liquid with moderate vapor pressure and high water solubility. It is
expected to have moderate mobility in soil. Volatilization is considered moderate based on the
Henry's Law constant, but may be attenuated because it will exist partially in anionic form
under alkaline conditions. The rate of hydrolysis is considered negligible. The rate of
atmospheric photooxidation is considered moderate. Benzenemethanethiol is not readily
biodegradable. Benzenemethanethiol is expected to have low persistence (PI) and low
bioaccumulation potential (Bl).
Acute oral and dermal toxicity of benzenemethanethiol to rats is moderate and low,
respectively. The acute inhalation toxicity of benzenemethanethiol to rats and mice is high.
No data are available for the repeated-dose/reproductive/developmental toxicity endpoints.
Benzenemethanethiol did not induce gene mutations in bacterial cells in vitro. No data are
available for the chromosomal aberrations endpoint. Benzenemethanethiol is not irritating to
rabbit and guinea pig skin, nor is it a dermal sensitizer to guinea pigs. Benzenemethanethiol
did not induce gene mutations in bacterial cells in vitro.
The 48-h EC50 for aquatic invertebrates exposed to benzenemethanethiol is 0.15 mg/L. No
data were provided to evaluate acute toxicity to fish or toxicity to aquatic plants.
Data gaps for repeated-dose/reproductive/developmental, genetic (chromosomal aberrations)
toxicity, acute toxicity to fish and toxicity to aquatic plants toxicity endpoints were identified
as data gaps under the HPV Challenge Program.
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The sponsor, Chevron Phillips Chemical Company LP, submitted a Test Plan and Robust
Summaries to EPA for benzenemethanethiol (CASRN 100-53-8; 9th CI name:
benzenemethanethiol) on April 6, 2004. EPA posted the submission on the ChemRTK HPV
Challenge website on April 19, 2004
(http://www.epa.gov/chemrtk/pubs/summaries/benzmeth/cl5166tc.htm). EPA comments on the
original submission were posted to the website on March 3, 2005. Public comments were also
received and posted to the website.
The sponsor proposed the use of phenyl mercaptan (CASRN 108-98-5) as a supporting chemical
to address human health and ecotoxicity endpoints for the sponsored chemical,
benzenemethanethiol (benzyl mercaptan, CASRN 100-53-8). For human health, EPA does not
consider phenyl mercaptan (thiophenol) an appropriate supporting chemical for benzyl
mercaptan because significant differences in the metabolic profiles of the two substances are
expected. Phenyl mercaptan is also not used as a supporting chemical for assessing the
physical-chemical properties, environmental fate or aquatic toxicity of benzenemethanethiol.
1. Chemical Identity
1.1	Identification and Purity
In the robust summaries, the purity of benzenemethanethiol (CASRN 100-53-8) ranges from 97
to 99.3%, where indicated.
1.2	Physical-Chemical Properties
Benzenemethanethiol is a liquid with moderate vapor pressure and high water solubility.
The physical-chemical properties of benzenemethanethiol are summarized in Table 1.
Table 1. Physical-Chemical Properties of Benzenemethanethiol1
Property
Value
CASRN
100-53-8
Molecular Weight
124.21
Physical State
Liquid
Melting Point
-30°C (measured)
Boiling Point
194-195°C (measured)
Vapor Pressure
71.883 - 289.171 mm Hg at 120.766 -162.852°C
(measured)2;
0.66 mm Hg at 25°C (estimated)3
Dissociation Constant (pKa)
9.39 (estimated)4
Henry's Law Constant
2.1 x 10"4 atm-m3/mole (estimated)5
Water Solubility
1,029 mg/L at 25°C (estimated)5
Log Kow
2.48 (estimated)5
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Chevron Phillips Chemical Company LLP. 2004. Revised Test Plan and Robust Summary for
Benzenemethanethiol. Available online at
http://www.epa.gov/chemrtk/pubs/summaries/benzmeth/cl5166tc.htm as of March 8, 2012.
2Osborn AG; Scott DW. 1980. Vapor pressure of 17 miscellaneous organic compounds. J Chem
Thermodynamic 12(5): 429-38 (1980).
3N0M05. 1987. Programs to Enhance PC-Gems Estimates of Physical Properties for Organic Compounds. The
Mitre Corp.
4SPARC. October 2011. Online pKa/Property Calculator, w4.2.1405-s4.2.1408. University of Georgia, Athens,
GA, USA. Available online at http://ibmlc2.chem.uga.edu/sparc/ as of March 16, 2012.
5U.S. EPA. 2012. Estimation Programs Interface Suite™ for Microsoft® Windows, v4.10. U.S. Environmental
Protection Agency, Washington, DC, USA. Available online at
http://www.epa.gov/opptintr/exposure/pubs/episuitedl.htm as of March 8, 2012.
2. General Information on Exposure
2.1	Production Volume and Use Pattern
Benzenemethanethiol had an aggregated production and/or import volume in the United States
between 1 to 10 million pounds during calendar year 2005. Industrial processing and uses for the
chemical were claimed confidential. No commercial and consumer uses were reported for the
chemical.
2.2	Environmental Exposure and Fate
Benzenemethanethiol is expected to have moderate mobility in soil. Volatilization is considered
moderate based on the Henry's Law constant, but may be attenuated because it will exist partially
in anionic form under alkaline conditions. The rate of hydrolysis is considered negligible. The
rate of atmospheric photooxidation is considered moderate. Benzenemethanethiol is not readily
biodegradable. Benzenemethanethiol is expected to have low persistence (PI) and low
bioaccumulation potential (Bl).
The environmental fate properties for benzenemethanethiol are provided in Table 2.
Conclusion: Benzenemethanethiol is a liquid with moderate vapor pressure and high water
solubility. It is expected to have moderate mobility in soil. Volatilization is considered
moderate based on the Henry's Law constant, but may be attenuated because it will exist partially
in anionic form under alkaline conditions. The rate of hydrolysis is considered negligible. The
rate of atmospheric photooxidation is considered moderate. Benzenemethanethiol is not readily
biodegradable. Benzenemethanethiol is expected to have low persistence (PI) and low
bioaccumulation potential (Bl).
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Hazard Characterization Document
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Table 2. Environmental Fate Properties of Benzenemethanethiol1
Property
Value
CASRN
100-53-8
Photodegradation Half-life
2.9 hours (estimated)2
Hydrolysis Half-life
Stable
Biodegradation
40.7%) after 28 days (not readily biodegradable)
Bioaccumulation Factor
BAF = 15 (estimated)2
Log Koc
2.6 (estimated)2
Fugacity

(Level III Model)2

Air (%)
0.9
Water (%)
20.8
Soil (%)
77.9
Sediment (%)
0.4
Persistence3
PI (low)
Bioaccumulation3
B1 (low)
Chevron Phillips Chemical Company LLP. 2004. Revised Test Plan and Robust Summary for
Benzenemethanethiol. Available online at http://www.epa.gov/chemrtk/pubs/summaries/benzmeth/cl5166tc.htm
as of March 8, 2012.
2U.S. EPA. 2012. Estimation Programs Interface Suite™ for Microsoft® Windows, v4.10. U.S. Environmental
Protection Agency, Washington, DC, USA. Available online at
http://www.epa.gov/opptintr/exposure/pubs/episuitedl.htm as of March 8, 2012.
3Federal Register. 1999. Category for Persistent, Bioaccumulative, and Toxic New Chemical Substances. Federal
Register 64, Number 213 (November 4, 1999) pp. 60194-60204.
3. Human Health Hazard
A summary of the health effects data submitted for SIDS endpoints is provided in Table 3.
Acute Oral Toxicity
Wistar rats (5 males/dose) were administered benzenemethanethiol (97% purity) via oral gavage
at 132, 264, 528 or 1056 mg/kg and observed for a minimum of 2 weeks after dosing. Mortality
occurred at doses > 528 mg/kg within 5 days of dose administration.
(15-Day) LDso = 493 mg/kg
Acute Dermal Toxicity
Sprague-Dawley rats (5/sex) were administered benzenemethanethiol via the dermal route at
2000 mg/kg (99.3% purity) under semi-occlusive conditions for 24 hours and observed for 14
days. No mortalities were observed.
LDso > 2000 mg/kg
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Acute Inhalation Toxicity
(1)	Wistar rats (6 males/dose) were exposed to benzenemethanethiol vapor (97% purity) via
whole-body inhalation at measured concentrations of 58, 98, 130, 145, 185 or 235 ppm (~ 0.29,
0.50, 0.66, 0.74, 0.94 or 1.19 mg/L, respectively) for 4 hours and observed for a minimum of 2
weeks after dosing for clinical signs and mortality. Mortalities occurred at 0.94 (1/6) and 1.19
(1/6) mg/L groups.
LCso > 1.19 mg/L
(2)	Swiss mice (10 males/dose) were exposed to benzenemethanethiol vapor (97% purity) via
whole-body inhalation at measured concentrations of 58, 98, 130, 145, 185 or 235 ppm (~ 0.29,
0.50, 0.66, 0.74, 0.94 or 1.19 mg/L, respectively) for 4 hours and observed for a minimum of 2
weeks after dosing for clinical signs and mortality. Three deaths occurred by day 4; and six
deaths occurred by day 15 in the 0.94 mg/L group. All animals from the highest dose group
(1.19 mg/L) died within 24 hrs of exposure.
(15-Day) LC50(estimated) = 0.90 mg/L
Repeated-Dose Toxicity
No Data.
Reproductive Toxicity
No Data.
Developmental Toxicity
No Data.
Genetic Toxicity - Gene Mutations
In vitro
In a bacterial mutation assay, Salmonella typhimurium strains TA98, TA100, TA1535, TA1537,
and TA1538 were exposed to benzenemethanethiol (purity not reported) in DMSO at five
concentrations (not specified) in the presence and absence of metabolic activation. The cytotoxic
concentration was not provided. Positive controls were run concurrently and responded
appropriately.
Benzenemethanethiol did not induce gene mutations in this assay.
Genetic Toxicity - Chromosomal Aberrations
In vitro
No Data.
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Additional Information
Skin Irritation
(1)	New Zealand White rabbits (three males) were exposed dermally exposed to undiluted
benzenemethanethiol (0.5 mL, 99.3% purity) on clipped, intact skin under semi-occlusive
conditions for 4 hours and skin was examined for 15 days. Very slight to slight erythema was
observed in all rabbits and slight edema was observed in one rabbit.
Benzenemethanethiol was not irritating to rabbit skin in this study.
(2)	In the dermal sensitization study described below, guinea pigs that were applied undiluted
benzenemethanethiol (99.3% purity) topically under occlusive conditions for 24 hours, showed a
similar level of severity in the skin reactions than the control groups. The microscopic
examination of the skin samples indicated that the skin reactions consisted of skin irritation.
Benzenemethanethiol was not irritating to guinea pig skin in this study.
Dermal Sensitization
In a maximization test, Dunkin-Hartley Guinea pigs (10/sex) were administered an intradermal
injection of benzenemethanethiol (10% of active substance in paraffin oil; volume injected not
provided) in Freund's adjuvant, followed 8 days later by dermal application of
benzenemethanethiol (volume applied was not provided) under occlusive conditions for 48
hours. Five guinea pigs per sex were allocated as a control group. Twenty days after the initial
treatment, animals were challenged with a dermal application of undiluted benzenemethanethiol
(99.3%) purity) under occlusive conditions for 24 hours. Skin reactions were evaluated up to 72
hours following completion of the challenge exposure. No cutaneous sensitization was observed
Benzenemethanethiol did not produce dermal sensitization in this study.
Conclusion: Acute oral and dermal toxicity of benzenemethanethiol to rats is moderate and low,
respectively. The acute inhalation toxicity of benzenemethanethiol to rats and mice is high. No
data are available for the repeated-dose/reproductive/developmental toxicity endpoints.
Benzenemethanethiol did not induce gene mutations in bacterial cells in vitro. No data are
available for the chromosomal aberrations endpoint. Benzenemethanethiol is not irritating to
rabbit and guinea pig skin, nor is it a dermal sensitizer to guinea pigs. Benzenemethanethiol did
not induce gene mutations in bacterial cells in vitro.
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Table 3. Summary Table of the Scr
under the U.S. HPV Cha
Human Healt
eening Information Data Set
llenge Program -
1 Data
Endpoint
Benzenemethanethiol
(100-53-8)
Acute Oral Toxicity
LD5o (mg/kg)
493
Acute Dermal Toxicity
LD5o (mg/kg)
>2000
Acute Inhalation Toxicity
LCso (mg/L)
> 1.19
(rat)
0.90
(mouse)
Repeated-Dose Toxicity
NOAEL/LOAEL (mg/kg/day)
No Data
Reproductive Toxicity
NOAEL/LOAEL (mg/kg-day)
No Data
Developmental Toxicity
NOAEL/LOAEL (mg/kg/day)
No Data
Genetic Toxicity - Gene Mutation
In vitro
Negative
Genetic Toxicity - Chromosomal Aberrations
In vitro
No Data
Additional Information
Skin Irritation
Skin Sensitization
Not Irritating
Not Sensitizing
Measured data in bold
4. Hazard to the Environment
A summary of aquatic toxicity data submitted for SIDs endpoints is provided in Table 4.
Acute Toxicity to Fish
No data were provided.
Acute Toxicity to Aquatic Invertebrates
Water fleas (Daphnia magna; 4 replicates per test concentration, 5 per replicate) were exposed to
benzenemethanethiol at nominal concentrations of 0, 0.09, 0.16, 0.29, 0.53, 0.95, 1.71, 3.09, 5.56
or 10 mg/L under static conditions for 48 hours. The corresponding mean measured
concentrations were 0, 0.08, 0.14, 0.25, 0.44, 0.79, 1.42, 2.56, 4.59 and 8.27 mg/L. Temp. =
19.5-20.5 °C and pH ranged from: 7.97-8.17. At 48 hours, immobility rates of 20, 15 and 85%
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were observed at concentrations of 0.08, 0.14 and 0.25 mg/L, respectively, and 100% immobility
was observed at concentrations > 0.44 mg/L.
48-h ECso = 0.15 mg/L
Toxicity to Aquatic Plants
No data were provided.
Conclusion: The 48-h EC50 for aquatic invertebrates exposed to benzenemethanethiol is 0.15
mg/L. No data were provided to evaluate acute toxicity to fish or toxicity to aquatic plants.
Table 4. Summary of the Screening Information Data Set
as Submitted under the U.S. HPV Challenge Program - Aquatic Toxicity Data
Endpoint
Benzenemethanethiol
(100-53-8)
Fish
96-h LCso (mg/L)
No Data
Aquatic
Invertebrates
48-h ECso (mg/L)
0.15
Aquatic Plants
72-h ECso (mg/L)
No Data
Bold = experimental data (i.e., derived from testing)
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