United States
Environmental Protection
1=1 m m Agency
EPA/690/R-10/016F
Final
9-30-2010
Provisional Peer-Reviewed Toxicity Values for
Hexachlorobenzene
(CASRN 118-74-1)
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
Harlal Choudhury, DVM, Ph.D., DABT
National Center for Environmental Assessment, Cincinnati, OH
DRAFT DOCUMENT PREPARED BY
SRC, Inc.
7502 Round Pond Road
North Syracuse, NY 13212
PRIMARY INTERNAL REVIEWERS
Anuradha Mudipalli, M.Sc., Ph.D.
National Center for Environmental Assessment, Research Triangle Park, NC
Audrey Galizia, Dr. PH.
National Center for Environmental Assessment, Washington, DC
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)
-------
TABLE OF CONTENTS
COMMONLY USED ABBREVIATIONS ii
BACKGROUND 1
HISTORY 1
DISCLAIMERS 1
QUESTIONS REGARDING PPRTVS 2
INTRODUCTION 2
REVIEW 01 PERTINENT DATA 4
HUMAN STUDIES 4
ANIMAL STUDIES 5
Oral Exposure 5
Principal Study for Chronic RfD (U.S. EPA, 2009) and Chronic Oral MRL
(ATSDR, 2002) 5
Critical Studies for ATSDR Intermediate-Duration Oral MRL 6
Subchronic, Developmental, or Reproductive Toxicity Studies Published Since
ATSDR (2002) 10
Short-term Studies Published Since ATSDR (2002) 14
Inhalation Exposure 17
DERIVATION OF PROVISIONAL SUBCHRONIC AND CHRONIC ORAL RfD
VALUES I OR HEXACHLOROBENZENE 17
SUBCHRONIC p-RlD 17
CHRONIC p-RfD 22
FEASIBILITY OF DERIVING PROVISIONAL SUBCHRONIC AND CHRONIC
INHALATION RfC VALUES FOR HEXACHLOROBENZENE 22
PROVISIONAL CARCINOGENICITY ASSESSMENT FOR
HEXACHLOROBENZENE 22
REFERENCES 22
l
Hexachlorobenzene
-------
COMMONLY USED ABBREVIATIONS
BMC
benchmark concentration
BMD
benchmark dose
BMCL
benchmark concentration lower bound 95% confidence interval
BMDL
benchmark dose lower bound 95% confidence interval
HEC
human equivalent concentration
HED
human equivalent dose
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
p-OSF
provisional oral slope factor
p-RfC
provisional reference concentration (inhalation)
p-RfD
provisional reference dose (oral)
POD
point of departure
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
11
Hexachlorobenzene
-------
FINAL
9-30-2010
PROVISIONAL PEER-REVIEWED TOXICITY VALUES FOR
HEXACHLOROBENZENE (CASRN 118-74-1)
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.
1
Hexachlorobenzene
-------
FINAL
9-30-2010
It is important to remember that a provisional value alone tells very little about the
adverse effects of a chemical or the quality of evidence on which the value is based. Therefore,
users are strongly encouraged to read the entire PPRTV document and understand the strengths
and limitations of the derived provisional values. PPRTVs are developed by the EPA Office of
Research and Development's National Center for Environmental Assessment, Superfund Health
Risk Technical Support Center for OSRTI. Other EPA programs or external parties who may
choose of their own initiative to use these PPRTVs are advised that Superfund resources will not
generally be used to respond to challenges of PPRTVs used in a context outside of the Superfund
Program.
QUESTIONS REGARDING PPRTVS
Questions regarding the contents of the PPRTVs and their appropriate use (e.g., on
chemicals not covered, or whether chemicals have pending IRIS toxicity values) may be directed
to the EPA Office of Research and Development's National Center for Environmental
Assessment, Superfund Health Risk Technical Support Center (513-569-7300), or OSRTI.
INTRODUCTION
IRIS (U.S. EPA, 2009) contains an RfD for hexachlorobenzene (see Figure 1 for structure
of hexachlorobenzene) of 8 x 10"4 mg/kg-day, based on a NOAEL of 0.08 mg/kg-day (estimated
from a dietary concentration of 1.6 ppm) for liver effects in rats from a study by Arnold et al.
(1985) and an uncertainty factor (UF) of 100. The study by Arnold et al. (1985) identifies a
LOAEL of 0.29 mg/kg-day (estimated from a dietary concentration of 8 ppm). IRIS cited the
Health Assessment Document (HAD) for Chlorinated Benzenes (U.S. EPA 1985) and the
Drinking Water Criteria Document (DWCD) for Hexachlorobenzene (U.S. EPA, 1988a) as
source documents for the existing assessment. The IRIS RfD of 8 x 10"4 mg/kg-day is also
included on the Drinking Water Standards and Health Advisories list (U.S. EPA, 2006) and the
HEAST (U.S. EPA, 1997). The Chemical Assessments and Related Activities (CARA) lists
(U.S. EPA, 1994, 1991) included the previously mentioned HAD and DWCD documents as well
as a 1984 Health Effects Assessment (HEA) for hexachlorobenzene (U.S. EPA, 1984) that did
not derive toxicity values.
CI
Figure 1. Chemical Structure of Hexachlorobenzene
2
Hexachlorobenzene
-------
FINAL
9-30-2010
ATSDR published a toxicological profile for hexachlorobenzene (ATSDR, 2002) that
includes
• an acute-duration oral minimal risk level (MRL) of 0.008 mg/kg-day based on a
developmental LOAEL of 2.5 mg/kg-day for hyperactivity in offspring of rats treated
prior to mating (Goldey and Taylor, 1992) and a UF of 300;
• an intermediate-duration oral MRL of 1 x 10"4 mg/kg-day based on a LOAEL of
0.01 mg/kg-day for minimal ovarian effects in monkeys (Bourque et al., 1995;
Jarrell et al., 1993) and a UF of 90; and
• a chronic-duration oral MRL of 5 x 10"5 mg/kg-day based on a LOAEL of
0.016 mg/kg-day for hepatic effects in male F1 rats in a multigeneration study
(Arnold etal., 1985) and aUF of 300.
The World Health Organization (WHO, 1997) published a criteria document for
hexachlorobenzene in which a tolerable daily intake (TDI) of 1.7 x 10"4 mg/kg-day was derived
on the basis of the lowest reported NOEL of 0.05 mg/kg-day (with hepatic effects at higher doses
in pigs and rats) and a UF of 300. The National Toxicology Program (NTP) has assessed the
oral toxicity of hexachlorobenzene in a 13-week gavage study with female Sprague-Dawley rats
(NTP, 2001) and a 6-month oral continuous breeding study with male and female
Sprague-Dawley rats (Wolfe and Pepperl, 2005).
No RfC for hexachlorobenzene is available on the IRIS database (U.S. EPA, 2009); lack
of data precluded derivation of an RfC. Likewise, ATSDR (2002) did not derive inhalation
MRLs due to the lack of human or animal studies. The American Conference of Governmental
Industrial Hygienists (ACGIH, 2008) lists a threshold limit value (TLV) for hexachlorobenzene
of 0.002 mg/m3 as an 8-hour time-weighted average (TWA) to protect against porphyria, skin
damage, and central nervous system impairment. This assessment was based on oral exposure
data because of the lack of human or animal inhalation data. The National Institute of
Occupational Safety and Health (NIOSH, 2009) and the Occupational Safety and Health
Administration (OSHA, 2009) do not report permissible exposure limits for hexachlorobenzene.
A cancer assessment for hexachlorobenzene is available on IRIS (U.S. EPA, 2009). A
weight-of-evidence (WOE) of classification of B2 (Probable Human Carcinogen) was assigned
on the basis of sufficient animal evidence (i.e., increased incidence of liver, thyroid, and kidney
tumors in mice, rats, and hamsters) and inadequate human evidence. The existing cancer
assessment was conducted under the EPA (1986) Guidelines for Carcinogen Assessment, and
was subsequently revised in 1998. Hexachlorobenzene has not been evaluated under the EPA
(2005) Guidelines for Carcinogen Risk Assessment. An oral slope factor (OSF) of 1.6 per
(mg/kg-day) was derived using a data set for hepatocellular carcinomas in female
Sprague-Dawley rats. In deriving the final OSF, EPA (2009) considered 14 different data sets
from three species, four studies, and various tumor endpoints. The OSFs derived from these data
sets all fell within a range of approximately one order of magnitude (0.083-1.7). An inhalation
unit risk (IUR) of 4.6 x 10"4 per (|ig/m3) was derived by route-to-route extrapolation from the
oral data set. IRIS cited the EPA (1985) HAD for chlorinated benzenes and the EPA (1988a)
DWCD for hexachlorobenzene as source documents for the cancer assessment.
The International Agency for Research on Cancer (IARC) has evaluated the
carcinogenicity of hexachlorobenzene (IARC, 2001, 1987, 1979) and assigned a WOE
3
Hexachlorobenzene
-------
FINAL
9-30-2010
classification of 2B (Possibly Carcinogenic to Humans). This classification is based on
inadequate evidence in humans and sufficient evidence in animals. Hexachlorobenzene is
included in the 11th Report on Carcinogens (NTP, 2005) and is classified as Reasonably
Anticipated to be a Human Carcinogen. ACGIH (2008) gives a cancer designation of A3
{ConfirmedAnimal Carcinogen with Unknown Relevance to Humans). WHO (1997) estimated a
tumorigenic dose associated with a 5% excess incidence of tumors (TD5) of 0.81 mg/kg-day
based on the incidence of neoplastic nodules of the liver in female F1 rats in the study reported
by Arnold et al. (1985). Citing insufficient mechanistic data, WHO (1997) applied a UF of 5,000
to the TD5 to derive a guidance value of 1.6 x 10"4 mg/kg-day.
CalEPA (2003) has established a Public Health Goal (PHG) for hexachlorobenzene of
0.03 ppb (0.03 |ig/L) in drinking water. The PHG is based on carcinogenic effects in animals
and is estimated from the observed incidence of adrenal pheochromocytomas and
hepatocarcinomas in female rats exposed to dietary hexachlorobenzene (Arnold and Krewski,
1988, Lambrecht et al., 1983a,b). CalEPA (2009) lists an IUR value of 5.1 x 10"4 (iig/m3)"1 and
an OSF of 1.8 per (mg/kg-day) for hexachlorobenzene on the Air Toxics Hot Spot Program Risk
Assessment Guidelines.
Because IRIS contains both a chronic oral RfD and cancer assessment for
hexachlorobenzene (U.S. EPA, 2009), this PPRTV document aims only to provide subchronic
p-RfD derivation and subchronic and chronic p-RfC development. Given the size of the
toxicological database for hexachlorobenzene, earlier assessments for hexachlorobenzene,
including the IRIS assessment (last revised in 1991) and the ATSDR (2002) toxicological profile
were consulted to identify information relevant to this PPRTV. Literature searches were
conducted from January, 2002 through September 3, 2010 for studies published since the
ATSDR (2002) toxicological profile that might be relevant to the derivation of provisional
toxicity values for hexachlorobenzene. Databases searched included MEDLINE, TOXLINE
(with the National Technical Information Service [NTIS]), BIOSIS, TSCATS/TSCATS2,
CCRIS, DART, GENETOX, HSDB, RTECS, Chemical Abstracts, and Current Contents (last
6 months).
REVIEW OF PERTINENT DATA
HUMAN STUDIES
A number of recent studies have examined associations between hexachlorobenzene in
human biological fluids and various health outcomes. For example, recent studies have
correlated the concentration of hexachlorobenzene in umbilical cord serum at birth with
decreased gestational length (Fenster et al., 2006), poor social competence (Ribas-Fito et al.,
2007), increased body mass index and weight during childhood (Smink et al., 2008), and
increased urinary coproporphyrins in childhood (Sunyer et al., 2008). There are also numerous
studies that investigate correlations between serum or tissue concentrations of
hexachlorobenzene and various disease states in adult humans. However, none of the available
studies can be used for quantitative risk assessment due to the confounding effects of exposure to
other organochlorines and due to the lack of exposure information.
4
Hexachlorobenzene
-------
FINAL
9-30-2010
Dietary exposure to hexachlorobenzene by ingestion of bread made from contaminated
grain resulted in an outbreak of porphyria cutanea tarda and mixed porphyria in Turkey during
1955-1959 (Peters et al., 1987; Gocman et al., 1986). Exposed adults and older children
experienced effects that included muscle weakness, loss of appetite, photosensitivity with
formation of bullae (blisters) and milia (whiteheads) on sun-exposed areas, hyperpigmentation,
hypertrichosis (excessive hair growth), orthopedic abnormalities including osteoporosis and
arthritis, fragile skin, goiter, hepatomegaly, and porphyrinuria. Thirty years after exposure,
many of these effects were still prevalent in the exposed population. Almost all children born to
mothers who consumed hexachlorobenzene-contaminated bread during pregnancy died within
1 year, after exhibiting weakness, convulsions, and characteristic skin lesions. In addition to in
utero exposure, some of these children were presumed to have been exposed postnatally by
lactational transfer. Of 188 pregnancies that occurred during 1977-1981 in 42 women who were
exposed as children or young adults, there were 15 fetal deaths (13 miscarriages and 2 stillbirths)
and 173 live births (Peters et al., 1987). The human data are not suitable for use in quantitative
risk assessment because actual exposure doses and durations are not known. However, the
original investigators of the epidemic estimated that the amount of hexachlorobenzene ingested
by the victims was approximately 0.05-0.2 g/day (0.7-2.9 mg/kg-day for a 70-kg person) "for a
relatively long period before the skin manifestations of the disease became apparent" (Cam and
Nigogosyan, 1963).
ANIMAL STUDIES
Oral Exposure
The database for oral toxicity of hexachlorobenzene (HCB) is extensive (see ATSDR,
2002). Because this review is limited to an assessment of oral data pertinent to the derivation of
a subchronic p-RfD, and given the size of the toxicological database, the text that follows
summarizes only studies that might be useful in deriving a subchronic p-RfD. The studies
considered potentially relevant to subchronic p-RfD derivation included (1) the principal study
(Arnold et al., 1985) used to derive the chronic RfD on IRIS (U.S. EPA, 2009) and the chronic-
duration oral MRL (ATSDR, 2002) because this study included a subchronic-duration exposure
component (F0 generation); (2) the key studies used by ATSDR (2002) to derive the
intermediate-duration oral MRL; and (3) any short-term, subchronic, developmental, and
reproductive toxicity studies published since the ATSDR (2002) toxicological profile.
Principal Study for Chronic RfD (U.S. EPA, 2009) and Chronic Oral MRL
(ATSDR, 2002)
Arnold et al. (1985)—In a single-generation reproductive toxicity study that included
chronic-duration exposure of offspring, Sprague-Dawley rats (64-66/sex/group) were fed diets
containing 0, 0.32, 1.6, 8.0, or 40.0 ppm of hexachlorobenzene (purity not specified) dissolved in
corn oil for 90 days (Arnold et al., 1985). Doses are estimated to be 0, 0.03, 0.14, 0.69, and
3.4 mg/kg-day for males and 0, 0.03, 0.16, 0.78, and 3.9 mg/kg-day for females, based on EPA
(1988b) reference values for body weight (male = 0.267 kg, female = 0.204 kg) and food intake
(male = 0.023 kg/day, female = 0.020 kg/day) for subchronic-duration exposure in
Sprague-Dawley rats. Individual rat body weight and cage-group feed consumption were
measured weekly. Animals were mated after 90 days of treatment; it is unclear whether animals
were also exposed to hexachlorobenzene during gestation and lactation. The F0 parental animals
were sacrificed after the lactation period. Hematological variables (not specified), gross
pathology, organ weights (i.e., liver, kidneys, heart, spleen, testes or ovaries, adrenals, and
brain), and histopathological examination of liver, kidneys, and grossly abnormal areas of
5
Hexachlorobenzene
-------
FINAL
9-30-2010
dermal, supportive,1 or skeletal tissues were used to assess F0 parental toxicity. Fertility,
gestation, viability, and lactation from the F0 mating were assessed as measures of reproductive
toxicity.
In the F0 parental animals, body weight and feed consumption were not affected by
treatment (data not shown). Although sporadic statistical differences in hematological
parameters were seen among the F0 males (hematocrit values in the 0.32-ppm group, monocyte
number in the 40-ppm group, and bone-marrow myeloid and erythroid series results for the
1.6-and 8.0-ppm groups [no further information provided]), the study authors indicated that their
occurrence was not dose-related and probably not due to hexachlorobenzene exposure. Also in
F0 males, significant (p < 0.05) organ-weight increases were reported in the 8-ppm (i.e., absolute
and relative heart and brain weights and relative liver weights) and 40-ppm (i.e., absolute heart
and relative liver weights) exposure groups (data not shown). In the F0 females, no treatment
effects on organ weights or hematology were observed. No differences in gross or microscopic
pathology were noted between control and hexachlorobenzene-treated F0 animals. Treatment
did not alter the fertility, gestation, or lactation indices, but the viability index was significantly
reduced at 40 ppm (data not shown), indicating increased mortality of pups between birth and
Postnatal Day (PND) 4 at this dose. The NOAEL for parental toxicity in the F0 generation
(exposed subchronically) is 1.6 ppm (0.14 mg/kg-day); the LOAEL is 8 ppm (0.69 mg/kg-day)
based on increased organ weights. The NOAEL for reproductive toxicity is 8 ppm
(0.69 mg/kg-day); the LOAEL based on decreased viability between birth and PND 4 is 40 ppm
(3.4 mg/kg-day).
In the chronic-duration exposure portion of the study, the F1 animals were reduced to
50/sex/dose group at weaning and were fed their parents' diets for the remainder of their lifetime
(130 weeks). However, F1 animals were not bred; thus, there are no reproductive data for this
generation. The chronic-duration study was used to derive the RfD on the IRIS database; EPA
determined that 1.6 ppm (0.08 mg/kg-day) was a NOAEL and 8 ppm (0.3 mg/kg-day) was a
LOAEL for increased hepatic centrilobular basophilic chromogenesis (U.S. EPA, 2009).
Critical Studies for ATSDR Intermediate-Duration Oral MRL
Jarrell et al. (1993); Foster et al. (1992); Babineau et al. (1991); Sims et al. (1991)—
Ovarian function and histopathology were studied in female Cynomolgus monkeys (captive bred,
approximately 5 years of age, four/dose group) that were given hexachlorobenzene (purity not
stated) mixed with sucrose in gelatin capsules at doses of 0, 0.1, 1, or 10 mg/kg-day for 90 days
(Jarrell et al., 1993; Foster et al., 1992; Babineau et al., 1991; Sims et al., 1991). During the first
menstrual period following the end of dosing, the monkeys were treated with hormones to induce
superovulation. The hormone treatments consisted of six daily injections of human menopausal
gonadotropin (a mixture containing follicle stimulating [FSH] and luteinizing hormones [LHs])
beginning on Menstrual Day 2 or 3, followed by an injection of human chorionic gonadotropin
(HCG) on Day 9 or 10 of the cycle. Laparotomy for follicle aspiration and recovery of oocytes
and granulosa cells was performed 35 hours after the HCG treatment (i.e., within 2 hours of the
estimated time of ovulation). The animals were then sacrificed, and both ovaries were removed
from each monkey for examination by thin-section histological techniques on one ovary and
transmission electron microscopy (TEM) on the other ovary. Recovered oocytes were used for
in vitro fertilization, and granulosa cells were incubated with HCG to measure progesterone (by
'This is the term used by the study authors; the tissues included in this category are not specified.
6
Hexachlorobenzene
-------
FINAL
9-30-2010
radioimmunoassay) in the supernatant. Menstrual cycle length and duration, and circulating
levels of estradiol (E2) and progesterone (P4) during the cycle were assessed based on daily
vaginal swabs and serum analyses. Concentrations of hexachlorobenzene were measured in
serum (weekly) and postmortem tissues (e.g., liver, kidney, brain, fat). Other study endpoints
included weekly measurements of body weight, biweekly collection of urine and blood samples
for serum gamma glutamyl transferase (GGT), aspartate aminotransferase (AST, or serum
glutamic-oxaloacetic transaminase [SGOT]), sorbital dehydrogenase (SDH), urinary d-glucaric
acid and porphyrins, and serum HCB levels, and terminal measurements of organ weights
(unspecified except for ovary) and liver histology.
Specific endpoints were reported in different publications as follows: systemic toxicity,
hexachlorobenzene tissue concentrations, primordial follicle histology, and oocyte function
(Jarrell et al., 1993); serum oestradiol and progesterone concentrations and menstrual cycling
(Foster et al., 1992); morphological effects on the ovarian surface epithelium as assessed by thin
section light microscopy (Sims et al., 1991); and ultrastructural changes in the ovarian surface
epithelium as assessed by TEM (Babineau et al., 1991). Effects reported in these studies are
discussed below.
Serum and tissue concentrations of hexachlorobenzene increased in a dose- and
time-dependent manner, with the highest levels occurring in the tissues with the highest lipid
content (Jarrell et al., 1993). No clinical signs of systemic toxicity, effects on weight gain, or
changes in liver enzyme or urinary porphyrin levels were found in any of the monkeys, and
response to in vitro fertilization was effective in all animals. Dose-related histopathological
effects occurred in the liver at >1 mg/kg-day, including accentuated zonation, increased portal
density, mid-zonal vacuolation, and intrahepatic cholestasis. Liver and adrenal weights (data not
reported) were significantly increased at 10 mg/kg-day (Jarrell et al., 1993).
Hexachlorobenzene caused a statistically significant (p < 0.05) decrease in serum
progesterone concentrations during the luteal phase of the menstrual cycle at >1 mg/kg-day
(Foster et al., 1992). There were no exposure-related changes in serum progesterone during the
follicular and periovulatory phases, serum estradiol levels, menstrual cycle length, or duration of
menses. Although no statistical differences were found in mean cycle length, Foster et al. (1992)
reported increased variability in cycle length at 10 mg/kg-day (ranged from 29-58 days
compared with 28-36 days in controls).
A statistically significant (p < 0.05; see Table 1) decline in the total number of primordial
follicles was observed at 10 mg/kg-day (Jarrell et al., 1993). Histological changes in the ovarian
follicles occurred at all dose levels and increased in severity with increasing dose; changes
included decreased distinctiveness of follicular nuclear and nucleolar membranes; increased
granularity, density, and irregular shape of oocyte nuclei; increased vacuoles and aggregated
lysosomes in oocyte cytoplasm; and pyknotic granulosa cells in antral and preantral follicles.
7
Hexachlorobenzene
-------
FINAL
9-30-2010
Table 1. Significant Effects of 90-Day Oral Exposure to Hexachlorobenzene on Serum
Hexachlorobenzene Concentration and Ovarian Histology in Monkeys
Endpoint
Dose (mg/kg-day)
0
0.1
1.0
10.0
Number examined unless noted
otherwise
4
4
4
4
Serum hexachlorobenzene (ppm)
O.OliO.Ol3-15
0.16± 0.10
0.37 ±0.06
1.31 ± 1.00
Number of primordial ovarian
follicles
26,348 ± 9,860
19,473 ± 4,504
24,027 ±3,717
8,737± 3,047°
Mean proportion of normally shaped
(cuboidal) cells in surface epithelium
(number of animals)
77.6 ± 5.2%
(503 cells from
four animals)
23.0 ± 7.2%d
(375 cells from
two animals)
11.8 ± 4.6%d
(381 cells from
three animals)
30.2 ± 5.7%d
(454 cells from
four animals)
"Mean ± SEM.
bSerum concentrations increased significantly in a dose-dependent manner, p = 0.0005.
cp < 0.05, significantly different from controls per analysis of variance and Duncan's multiple range test.
Significantly different from controls per study authors, but />-value and test were not specified.
Sources: Jarrell et al. (1993); Sims et al. (1991).
TEM examination of the ovarian follicles confirmed the dose-related histological
changes. Jarrell et al. (1993) reported the following changes: increased numbers of lysosomal
elements in the ooplasm of the developing ova and irregularly arranged cells in the thecal layer at
0.1 mg/kg-day; loss of chromatin and pyknosis in the nucleus of the developing ovum,
occasional necrosis in the ooplasm, and mild-to-moderate degenerative changes in follicular cells
at 1 mg/kg-day; and vacuolated and necrotic ooplasm and loss of typical stratified arrangement
of follicular cells at 10 mg/kg-day.
Light and TEM microscopy of the surface epithelium (SE) of the ovary also showed
dose-related effects (Babineau et al., 1991; Sims et al., 1991). Dose-dependent proliferative and
degenerative changes of increasing severity were noted at all dose levels, including increasingly
severe and frequent changes in cell shape, from squamous and cuboidal to tall columnar. At
0.1 mg/kg-day, the SE lengthened from normally flat, cuboidal-shaped cells into narrow
columnar cells, and some stratification (proliferation) and areas of degeneration were noted.
Intracellular alterations occurred mainly in the columnar cells; nuclei were elongated and had
migrated toward the apical surface, and cytoplasmic degradation was apparent as indicated by
reduced number of organelles (except lysosomes). At 1 mg/kg-day, lipid accumulations
concentrated within clusters of cells, cytoplasmic degeneration was observed in some affected
cells including vacuolation and flattening of cells, and cellular necrosis and denuding were
observed, although most of the SE remained intact. At 10 mg/kg-day, mixed cell morphology
(normal, columnar, cuboidal, and squamous shapes) was observed interspersed with regions of
cell death. In the cytoplasm, lipid inclusions were present, and frequent myelin-like bodies and
irregular and swollen microvilli were observed. Separation of SE from the connective tissues
was also apparent at this dose. Stratification of the SE occurred, and surface indentations
accentuated by edema were observed. A quantitative analysis of the observed morphological
changes as assessed by light microscopy indicated that the proportion of normal cells in the
exposed groups was significantly (p < 0.05) lower than in the controls when cell shape was
8
Hexachlorobenzene
-------
FINAL
9-30-2010
measured (see Table 1) but not when lipid accumulation was used as a criterion (Sims et al.,
1991).
Based on the multiple histological findings in the ovarian follicles and surface
epithelium, 0.1 mg/kg-day (the lowest dose tested) is a LOAEL for these studies.
Bourque et al. (1995)—As a follow-up to the previous studies, a detailed ultrastructural
study of ovarian follicles in hexachlorobenzene-exposed monkeys was conducted with the
addition of a lower dose (Bourque et al., 1995). Female Cynomolgus monkeys (4/dose,
6-13 years of age) were administered hexachlorobenzene (purity not stated) mixed with glucose
in gelatin capsules, daily, at doses of 0, 0.01, 0.1, 1.0, or 10 mg/kg-day for 13 weeks. Controls
received only glucose. After the period of treatment, monkeys were given FSH and LH during
Days 2 through 7 of the following menstrual period. On the eighth day of the cycle, HCG was
given; an ovary from each monkey was subsequently removed 35-38 hours later. Ovaries were
sectioned, and primordial, primary, and growing follicles from controls and each
hexachlorobenzene treatment group were examined by TEM.
Ultrastructural changes were noted in the ovarian follicles of all
hexachlorobenzene-exposed monkeys (Bourque et al., 1995). Incidences of the observed effects
were not given; a narrative description of the increasing severity of effects follows. In control
monkeys, the developing ova had normal mitochondria that were typically distributed, and
follicular cells surrounding the ova were also described as normal in shape and content of their
nuclei. In ova of monkeys treated with hexachlorobenzene at a dose of 0.01 mg/kg-day, the
majority of mitochondria were condensed with swollen cristae; follicular cells were generally
unaffected, but "a few cells" contained abnormal nuclei. In ova of monkeys treated with
hexachlorobenzene at a dose of 0.1 mg/kg-day, the mitochondria contained coarsely granular
matrices and/or exhibited irregular shapes; many of the follicular cells contained abnormal nuclei
(infolding of the nuclear membrane). In ova of monkeys treated with hexachlorobenzene at a
dose of 1 mg/kg-day, mitochondria were condensed and swollen; in addition, herniation of the
ooplasm (suggesting rupture of the zona pellucida) was noted, along with abnormal nuclei in
follicular cells and abnormal spaces between follicular cells. In ova of monkeys treated with
hexachlorobenzene at a dose of 10 mg/kg-day, the mitochondrial changes were more severe
(many had electron-lucent matrices); in follicular cells, the nuclear membrane was highly folded
with deep indentations, and there was an abnormal amount of lipid in the cells. Further, the cells
of the theca folliculi of the stroma were affected (deformed nuclei) only in monkeys treated with
10 mg/kg-day. The study authors concluded that a NOAEL was not defined (Bourque et al.,
1995). The LOAEL for this study is 0.01 mg/kg-day based on degenerative changes in primary
and growing ovarian follicles.
Foster et al. (1995)—Effects of hexachlorobenzene on ovarian steroidogenesis and
menstrual cycle characteristics were investigated in groups of four feral female Cynomolgus
monkeys (estimated 6-18 years of age) treated daily with capsules containing 0-, 0.1-, 1.0-, or
10-mg hexachlorobenzene/kg-day in glucose for 90 days (Foster et al., 1995). The 0.1- and
1.0-mg/kg-day dose levels were selected to provide circulating levels in the monkey equivalent
to levels found in the general population and in people with occupational exposure to
hexachlorobenzene. The dosing period was preceded by a 10-week acclimation phase, included
three menstrual cycles, and was followed by ovulation induction with FSH and LH on Cycle
9
Hexachlorobenzene
-------
FINAL
9-30-2010
Days 2-7, ovulation stimulation with HCG on Cycle Day 8, and oophorectomy on Cycle Day 10
via laparotomy. Study endpoints included tissue levels of hexachlorobenzene (serum, fat, and
follicular fluid), clinical signs, body weight, routine clinical chemistry and hematology indices,
serum indicators of ovarian function (E2, P4, and inhibin [INH]), and menstrual cycle length and
duration of menses. The menstrual cycle evaluations included both exposed-control group
comparisons and comparisons in which the monkeys served as their own controls (i.e., third
cycle during treatment compared with cycle preceding treatment).
Dose-related increases in concentrations of hexachlorobenzene in fat, serum, and
follicular fluid were detected. No effects on clinical signs, hematologic parameters, body
weight, or food and water consumption were observed. The level of hexachlorobenzene in the
follicular fluid was increased at >1 mg/kg-day (not detected at 0 and 0.1 mg/kg-day) and
statistically significantly (p < 0.05) correlated with follicle volume. Other exposure-related
effects included alterations in menstrual cycle duration and ovarian function. Comparison of
mean menstrual cycle lengths showed no significant differences in the treated and control groups
during the pretreatment or treatment periods. Comparison of pretreatment and treatment values
for each group, however, showed that cycle length was statistically significantly (p < 0.05)
longer during the treatment period at 10 mg/kg-day compared with controls; the mean menstrual
cycle lengths during treatment were 1.5, 2.5, 9.1, and 12.4 days longer than pretreatment values
at 0, 0.1, 1, and 10 mg/kg-day, respectively. No treatment-related changes in mean length of the
follicular and luteal phases were found using either method of comparison. An effect on ovarian
function was indicated by statistically significantly (p < 0.05) reduced serum levels of estradiol
during ovulation at 10 mg/kg-day, as determined by analysis of areas under time-concentration
curves (AUCs) or exposed-control group comparisons of peak estradiol levels (p = 0.03,
Dunnett's test). There was no difference in the number of oocytes recovered, volume of antral
follicles, or number of corpora lutea (data not reported). The NOAEL for this study is
1 mg/kg-day. The LOAEL is 10 mg/kg-day for increased mean menstrual cycle length
accompanied by reduced serum estradiol during ovulation.
Subchronic, Developmental, or Reproductive Toxicity Studies Published Since
ATSDR (2002)
Long et al. (2004), Johnson etal. (2005)—Long et al. (2004) and Johnson et al. (2005,
abstract only) reported selected findings from a sub chronic-duration study of hexachlorobenzene
conducted by the NTP. Draft body weight, survival, clinical observations, and neoplastic and
nonneoplastic effect incidence data are available online,2 but it is uncertain as to when the final
data and/or full report may be posted. According to the available information, female
Sprague-Dawley rats (10/dose) were administered hexachlorobenzene (purity >99%) in corn oil
by gavage at doses of 0, 0.03, 0.1, 0.3, 1.0, 3.0, 10.0, or 25 mg/kg-day, 5 days/week, for
13 weeks. Few details are available on toxicological evaluations. Long et al. (2004) reported
that animals were observed twice daily for morbidity and mortality, and that, at terminal
sacrifice, three transverse sections through the nose were excised at specific landmarks to
facilitate examination of the right and left maxillary incisors and the right and left second molars.
Sections were stained with hematoxylin and eosin and were evaluated by an NTP Pathology
Working Group. In an abstract, Johnson et al. (2005) reported the following findings: increased
mean body weight at 25 mg/kg-day but no treatment-related effect on survival; decreased total
2http://ntp-apps.niehs.nih.gov/ntp_tox/index.cfm?fuseaction=shorttermbioassaydata.datasearch&chemical
name=Hexachlorobenzene&cas_no= 118-74- l&study_no=C98004&study_length= 13%20 Weeks.
10
Hexachlorobenzene
-------
FINAL
9-30-2010
thyroxine (T4) (>10 mg/kg-day); decreased free T4 (>1 mg/kg-day); decreased triiodothyronine
(T3) (25 mg/kg-day); no effects on thyroid-stimulating hormone (TSH); dose-related increase in
hepatic CYP1A1 (>1 mg/kg-day), CYP2B (>0.03 mg/kg-day), and CYP1A2 (>0.3 mg/kg-day)
and pulmonary CYP1A1 (25 mg/kg-day) activities; increased liver cell proliferation
(>10 mg/kg-day); increased absolute and relative organ weights (spleen, liver, and lung at doses
>3, >10, and 25 mg/kg-day, respectively); hepatocellular hypertrophy (>3 mg/kg-day);
pulmonary focal interstitial fibrosis and histolytic infiltration (>1 mg/kg-day); mammary gland
hyperplasia (>10 mg/kg-day); thymic atrophy (>10 mg/kg-day); dermal suppurative
inflammation and ulceration (25 mg/kg-day); splenic hematopoietic cell proliferation
(>3 mg/kg-day); and lymphoid hyperplasia (>10 mg/kg-day). The focus of the report by
Long et al. (2004) was dental effects. Long et al. (2004) reported that maxillary incisor
degeneration was observed at doses of >1 mg/kg-day. No evidence of thrombosis, hemorrhage,
or vasculitis was noted by the study authors. Table 2 shows incidence and severity of incisor
degeneration. Based on the available information, these studies appear to support a NOAEL of
0.3 mg/kg-day and a LOAEL of 1 mg/kg-day for pulmonary focal interstitial fibrosis and
histolytic infiltration, maxillary incisor degeneration, and effects on thyroid hormones (decreased
free T4). These effect levels are considered tentative until the full NTP report or a publication
providing the remaining data becomes available.
Table 2. Incidence and Severity of Incisor Degeneration in Female SD Rats
Exposed Orally to Hexachlorobenzene for 13 Weeks
Severity
Dose (mg/kg-day)
0
0.03
0.1
0.3
1
3
10
25
Minimal
0
0
0
0
5
5
1
0
Mild
0
0
0
0
0
5
7
1
Moderate
0
0
0
0
0
0
2
9
Marked
0
0
0
0
0
0
0
0
Number examined
10
10
10
10
10
10
10
10
Source: Long et al. (2004).
Wolfe andPepperl (2005)—Wolfe and Pepperl (2005) evaluated the reproductive toxicity
of hexachlorobenzene in a continuous breeding study conducted for the NTP. The study report
was not published and is not available on the NTP Web site, but is available through NTIS. The
initial task of the study consisted of a dose-range finding experiment; eight/sex/group
Sprague-Dawley rats were exposed to 1, 10, 100, or 1,000 |ig/kg-day hexachlorobenzene
(99% purity) by daily gavage for 1 week prior to mating and during mating, gestation, and
through parturition to PND 1. Parental observations were limited to clinical signs of toxicity,
body weight, and food and water consumption. Litter sizes were recorded, and pups were
weighed and sexed. In addition, anogenital distance (AGD) of male and female pups was
measured, and gross examination of the reproductive system and kidneys was performed.
As no systemic or reproductive effects were observed in the dose-range finding study, the
doses were increased in the main study, in which groups of 20 male and 20 female
Sprague-Dawley rats were administered doses of 0, 0.5, 2.5, or 12.5 mg/kg-day for
two generations (Wolfe and Pepperl, 2005). The F0 adults were bred continuously to produce
11
Hexachlorobenzene
-------
FINAL
9-30-2010
Fla, Fib, and Flc pups; Flc pups were raised and bred continuously to produce F2a, F2b, and
F2c pups. Males in the F0 generation were dosed from the initiation of the study, and females in
the F0 generation were dosed from Study Day 15 until the day before necropsy (Study Days 161,
162, or 163). Parental body weights were measured regularly. A comprehensive assessment of
reproductive and teratogenic endpoints was conducted on Fla and Fib litters, while reproductive
system development and neurotoxicity endpoints were evaluated in Flc litters. In addition,
one male and five females from the control and low-dose groups were sacrificed and necropsied
at weaning; blood samples were also collected at this time for analysis of thyroid hormones.
F2 litters were evaluated for litter size, numbers of live and dead pups, sex ratio, and AGD, but
no other parameters. Major organs and those of the reproductive system were weighed and
examined microscopically in F0 and F1 parents. Table 3 provides an outline of the tasks and
evaluations performed in this study.
Table 3. Summary of Tasks and Evaluations in Reproductive Assessment by
Continuous Breeding Protocol for Hexachlorobenzene
Task 1: Dose range-finding study
Parental systemic
Parental reproductive
Pups
Mortality
Pregnancy index
Litter observations3
Body weight, food consumption,
water consumption
Anogenital distance
Task 2: Main study
F0 systemic
F0 reproductive
Fla and Fib pups
Flc pups
Mortality
Sperm analysis
Litter observations3
Litter observations3
Body weight, food consumption
Vaginal cytology
Thyroid hormone levels'5
Anogenital distance
Thyroid hormone levels'5
Pregnancy index
Anogenital distance
Viability to weaning
Necropsy
Gestation
Visceral evaluation
Body weight to weaning
Organ weights0
Lactation
Skeletal evaluation
Surface righting
Histopathologyd
Functional observational
battery, startle response
Task 3: Crossover mating
NA
Task 4: F1 offspring mating and assessment
Flc weanling
Flc adult systemic
Flc adult reproductive
F2a, b, c pups
Testicular descent
Mortality
Sperm analysis
Litter observations3
Hypospadias
Body weight, food consumption
Vaginal cytology
Anogenital distance
Nipple retention
Thyroid hormone levels'3
Pregnancy index
Cleft clitoris
Necropsy
Gestation
Vaginal thread
Organ weights0
Lactation
Preputial separation
Histopathologyd
Vaginal opening
Vaginal cytology
Organ weights0
Necropsy
aLitter observations include live and dead pups, sex ratio, and litter and individual body weights,
included T3, T4, and TSH. Results not provided in study.
The following organs were weighed: liver, kidneys, spleen, thyroid/parathyroid, thymus, testes, epididymis, ventral and
dorsolateral prostate, seminal vesicles with coagulating glands, ovaries, and uterus/cervix/vagina.
dThe following organs were examined microscopically in control and high-dose animals: liver, kidneys, pituitary,
spleen, thyroid/parathyroid, thymus, forestomach, testes, epididymis, and uterus/cervix/vagina.
Source: Wolfe and Pepperl (2005).
12
Hexachlorobenzene
-------
FINAL
9-30-2010
Wolfe and Pepperl (2005) did not report the results of thyroid hormone analyses or an
immunological assay mentioned briefly in the methods section, noting that these results would be
published separately. In F0 parental animals, there were no treatment-related effects on
mortality and the incidence of clinical signs. Food consumption was slightly increased in the
exposed groups during Weeks 6 and 16. F0 males exposed to 12.5 mg/kg-day had statistically
significantly (p < 0.05) decreased total sperm per cauda (25% less than controls), statistically
significantly (p < 0.05) decreased body weight, and a large increase in abnormal sperm (80-fold
higher than controls) (see Table 4). Among F0 females, no differences were found in estrus
cycle length, number of cycles, or in number of cycling females; however, the number of females
with regular cycles was significantly reduced in the 2.5- and 12.5-mg/kg-day groups (see
Table 4). At termination, a number of statistically significant (p < 0.05) organ weight changes
were observed (increased liver, kidney, thyroid, and spleen weights, as well as decreased thymus,
epididymis, and prostate weights); however, the study authors concluded that only the
liver-weight changes were related to treatment, as histopathology findings were limited to the
liver (increased incidences of hepatocellular degeneration and fatty degeneration in the high-dose
group; data not shown). Absolute and relative liver weights were increased by 25-39% in
F0 males and females exposed to 12.5 mg/kg-day, and absolute liver weight was increased by
9% in F0 females exposed to 2.5 mg/kg-day, as shown in Table 4.
Table 4. Selected Findings in Rats Treated with Hexachlorobenzene
in a Continuous Breeding Protocol
Dose in mg/kg-day
Endpoint
Control
0.5
2.5
12.5
F0
Absolute liver weight, male (g)
25.72 ± 0.702a
25.58 ±0.74
25.61 ±0.70
32.59 ± 1.02b
Relative liver weight, male (mg/g bw)
33.84 ±0.61
34.05 ±0.59
34.60 ±0.58
46.98 ± 1.0b
Absolute liver weight, female (g)
13.01 ±0.30
12.87 ±0.25
14.24 ±0.40b
17.13 ±0.55b
Relative liver weight, female (mg/g bw)
35.32 ±0.61
36.01 ±0.60
36.80 ±0.74
44.06 ± 1.29b
Total sperm per cauda
26.84 ± 1.09
27.72 ±0.883
24.13 ±0.989
20.02 ± 1.577b
Percent abnormal sperm (%)
0.1 ±0.07
NA
NA
8.1 ± 3.61b
Number females with normal cycle length
16/18°
16/20
1 l/20b
8/19b
Fla and Fib Litters
Incidence of litters with skeletal variations,
Fla
6/19
8/20
7/20
17/20d
Incidence of litters with skeletal variations,
Fib
6/18
3/18
5/19
14/20d
Flc Litters
Pup survival to PND 4
0.96 ± 0.026
0.99 ±0.008
1.00 ±0.004
0.77 ± 0.068b
Average pup weight PND 4, male (g)
9.71 ±0.476
10.86 ±0.494
10.47 ±0.396
7.72 ± 0.252b
Average pup weight PND 4, female (g)
9.34 ±0.441
10.42 ±0.383
9.98 ±0.461
7.49 ± 0.294b
Live pups per litter, PND 4-21
8.0 ±0.00
7.8 ±0.17
7.0 ± 0.49b
6.8 ± 0.48b
Day of preputial separation
42.9 ±0.41
43.2 ±0.38
44.8 ± 0.49b
NA
aMean ± standard error
bSignificantly different from control atp< 0.05
°Number affected/number examined
Significantly different from control atp< 0.05 by Fisher's exact test performed for this review.
Source: Wolfe and Pepperl (2005).
13
Hexachlorobenzene
-------
FINAL
9-30-2010
In the Fla and Fib litters, there were no effects on litter parameters, thyroid hormone
levels, or the incidences of malformations (Wolfe and Pepperl, 2005). The incidence of litters
with skeletal variations was statistically significantly (p < 0.05) increased at the high dose of
12.5 mg/kg-day; the types of variations were not reported. The only other statistically significant
(p < 0.05) finding was increased AGD in Fla males (8% greater than controls) and Fib females
(4% greater than controls) exposed to 12.5 mg/kg-day.
All of the Flc pups exposed to 12.5 mg/kg-day died by PND 9; the cause of death was
not reported. Body weight was decreased significantly (p < 0.05) in these pups by 20-25%
compared with control values. Among surviving Flc pups, a delay in preputial separation was
noted in males exposed to 2.5 mg/kg-day (see Table 4). The only statistically significant
(p < 0.5) findings in the neurotoxicity tests of surviving Flc male pups were not biologically
significant: surface-righting reflex was accelerated by 1.2 days, and hindlimb grip strength was
increased by 38% in males exposed to 2.5 mg/kg-day. Analysis of sperm in Flc parents did not
reveal any statistically significant differences among the groups. In addition, there were no
effects on vaginal cytology, pregnancy, gestation, or lactation indices. No effects on litter
observations or AGD were noted in F2a, b, or c litters; as noted earlier, F2 pups were not
examined for teratogenic effects or thyroid hormone levels.
The study authors concluded that hexachlorobenzene produced general toxicity (e.g.,
increased liver weights and increased incidences of hepatocellular degeneration and fatty
changes) and developmental toxicity (e.g., pup mortality and decreased pup weights) at
12.5 mg/kg/day, and that there was no evidence of reproductive toxicity at any dose (Wolfe and
Pepperl, 2005). EPA (2009) considers the 2.5-mg/kg-day dose to be a systemic and
developmental LOAEL based on increased absolute liver weight in F0 females, decreased
number of F0 females with normal cycle length, decreased number of live Flc pups per litter
between PNDs 4 and 21, and delayed preputial separation in Flc offspring. The low dose,
0.5 mg/kg-day, is a NOAEL.
Short-term Studies Published Since ATSDR (2002)
Hadjab etal. (2004)—Hexachlorobenzene (purity not stated) in olive oil was
administered by daily gavage to male Sprague-Dawley rats (12/dose) at doses of 0, 0.16, 4, or
16 mg/kg-day for 28 days to study auditory function and thyroid hormone status (Hadjab et al.,
2004). Each rat had an electrode implanted in the vicinity of the left auditory nerve prior to
hexachlorobenzene treatment. Cochlear sensitivity was assessed by measuring the threshold of
auditory nerve compound action potential (CAPs). CAP and thyroid hormone levels (blood and
to total plasma concentrations of tri-iodothyronine [T3] and thyroxine [T4]) were measured prior
to initiation of the study and after 1, 2, 3, and 4 weeks of exposure. Cochleae were removed,
dissected, and examined by light and scanning electron microscopy after the final CAP
measurements and blood sample collection.
No loss of acoustic sensitivity or histological changes was noted in rats that received
0.16 mg/kg-day (Hadjab et al., 2004). Deficits in cochlear sensitivity as determined by CAP
were noted at doses >4 mg/kg-day. At 4 mg/kg-day, the deficits were in the mid-frequency
range (2-16 kHz), and there was recovery following cessation of treatment. However, at a dose
of 16 mg/kg-day, deficits were observed over a broader range of frequencies (1-32 kHz), and the
change was irreversible. Morphological analyses revealed no loss of cochlear hair cells (<1% of
14
Hexachlorobenzene
-------
FINAL
9-30-2010
inner hair cells affected in the highest-dose group) or changes in stereocilia at any dose. The
effect of hexachlorobenzene on thyroid hormone levels is less clear. Statistically significant
(p < 0.05) decreases in T4 were noted after 1 week of exposure at 4 mg/kg-day (about half the
control value) and after 4 weeks of exposure at the 4- and 16-mg/kg-day doses (approximately
half of the control value). There was little change in T3 levels compared with control values,
with the exception of a significant increase (less than double) in the low-dose group after 1 week
of exposure. The NOAEL for this study is 0.16 mg/kg-day. The LOAEL is 4 mg/kg-day for
deficits in cochlear sensitivity.
Bitri et al. (2007)—Note: This study is in French with an abridged English version and
an English abstract. Hexachlorobenzene (purity not stated) in olive oil was administered to male
and female Mongolian gerbils (groups of 15-18/sex/dose) via gavage at doses of 0, 1.6, 4, or
16 mg/kg-day for 30 days (Bitri et al., 2007). The purpose of the study was to investigate the
effects of hexachlorobenzene on the liver and thyroid. Body weight, organ weights, plasma liver
enzyme concentrations (AST and ALT), and plasma thyroid hormone concentrations (T3 and T4)
were evaluated upon terminal sacrifice after 30 days of exposure. Relative liver weights
increased statistically significantly (p < 0.01) in the 4- and 16-mg/kg-day groups. In the
highest-dose group, T4 levels decreased statistically significantly (p < 0.01) in males, and T3
levels decreased statistically significantly (p < 0.01) in females (see Table 5); no other
statistically significant effects on thyroid hormones were noted. Plasma ALT activity was 2- to
3-fold higher than controls in high-dose males and females (see Table 5) but was not affected at
lower doses. There were no significant differences in AST activity between treated and control
animals. Histological changes in the liver were dose related and consisted of centrilobular
congestion and cellular necrosis (>1.6 mg/kg-day), centrilobular and periportal vein congestion,
cellular necrosis, and cytoplasmic vacuolization (>4 mg/kg-day). The aforementioned effects
were more severe, with more pronounced vacuolization and the disappearance of cellular
junction, at the highest-dose level (16 mg/kg-day). No quantification of incidence or severity of
these effects was presented. The LOAEL for this study is 1.6 mg/kg-day (the lowest dose tested)
based on hepatocellular necrosis and centrilobular congestion at this dose.
Table 5. Significant Effects on the Liver and Thyroid of Mongolian Gerbils Exposed
to Hexachlorobenzene by Gavage for 30 Days
Dose (mg/kg-day)
Endpoint
0
1.6
4
16
Males
ALT (U/L)
52.66 ± 8.29a
not reported13
not reported
170 ± 24.7°
T4 (nmol/1)
40.59 ± 1.08
not reported
not reported
21.95 ±7.46c
Females
ALT (U/L)
56 ±5
not reported
not reported
120 ± 12.47°
T3 (nmol/L)
3.96 ±0.48
not reported
not reported
1.42 ± 0.11°
aMean ± SEM, n = 15-18/dose but precise values were not specified for each endpoint.
bOnly control and significant values were reported in the text.
><0.01.
Source: Bitri et al. (2007).
15
Hexachlorobenzene
-------
FINAL
9-30-2010
Bitri et al. (2008)—Note: This study is in French with an abridged English version and
an English abstract. Hexachlorobenzene (purity not stated) mixed with olive oil was
administered daily by gavage to male Mongolian gerbils (15-18 per dose group) at doses of 0,
1.6, 4, or 16 mg/kg-day for 30 days (Bitri et al., 2008). Plasma testosterone concentrations were
measured (details of timing were not provided in the abridged English version), and testes and
seminal vesicles were evaluated histologically. Significant results are shown in Table 6. Plasma
testosterone concentrations were statistically significantly decreased (p < 0.01) at doses of
4 mg/kg-day (0.48 ± 0.08 ng/ml) and 16 mg/kg-day (0.54 ± 0.07 ng/ml) compared to controls
(1.08 ± 0.1 ng/ml). Hexachlorobenzene exposure had no effect on the diameter of the
seminiferous tubules, but a decrease in spermatozoid content was observed in parallel with
decreased testicular "spermatic activity" in the testes (this measure was not defined) at all doses;
relative seminal vesicle weight was unaffected by treatment. Relative testes weight (relative to
body weight) was significantly decreased at all doses (see Table 6). The LOAEL for this study is
1.6 mg/kg-day (lowest dose tested) for decreased testicular spermatozoid content and relative
testes weight.
Table 6. Significant Effects on the Testes of Mongolian Gerbils Exposed
to Hexachlorobenzene by Gavage for 30 Days
Endpoint
Dose (mg/kg-day)
0
1.6
4
16
Relative testes weight (% body weight)
1.6 ± 0.03a
1.25 ± 0.07b
1.38 ± 0.09°
1.41 ± 0.07°
"Spermatic activity" in testes
(%, not further defined)
88 ±4.89
82 ± 5.83b
80 ± 5.77b
60 ± 3.16b
Plasma testosterone (ng/mL)
1.08 ±0.01
not reported
0.48 ± 0.08b
0.54± 0.07b
aMean ± SEM, n = 15-18/dose but precise values were not specified for each endpoint.
V<0.01
cp < 0.05
Source: Bitri et al. (2008).
Chiappini et al. (2009)—Hexachlorobenzene (>99% purity) was administered as a
suspension in water containing Tween 20 (0.5/100 ml) by gavage to Wistar rats (3 females/dose)
at doses of 0, 0.1, 1, 10, 100, or 500 mg/kg-day, 5 days/week, for 30 days (Chiappini et al.,
2009). The objective of the study was to assess the possible disruptive effects of
hexachlorobenzene on thyroid growth regulation, apoptosis, and cell proliferation in thyroid
tissue. On the day following the final dose, thyroid hormones in the plasma were measured by a
commercial chemoluminescence kit. Histomorphology was assessed in thyroid glands; a subset
of 200 follicles taken from the glands of three rats per dose was selected for parametric
measurement of follicle morphology. Follicular cell proliferation was measured in animals given
an intraperitoneal injection of bromodeoxyuridine (BrdU) 30 minutes prior to terminal sacrifice;
thyroid sections were incubated with mouse antiBrdU, and then stained. The number of labeled
cells with BrdU compared to the total number of cells in the selected area was used as the
measure of proliferation. Apoptotic nuclei were identified in thyroid sections by the detection of
DNA breaks with the Terminal Transferase dUTP Nick End Labeling (TUNEL) technique.
Thyroid growth factor P-l (TGF-P-1) mRNA expression was assessed by reverse
transcriptase-polymerase-chain-reaction analysis. Protein fractions, including cytochrome C,
active caspase 8 (results of procaspase-8 cleavage), and active caspase 9 (result of procaspase-9
16
Hexachlorobenzene
-------
FINAL
9-30-2010
cleavage), in thyroid follicular cells were assessed by Western blotting with appropriate
antibodies.
No effects were observed in rats exposed to 0.1 mg/kg-day (Chiappini et al., 2009). At
doses >1 mg/kg-day, dose-related increases in cytochrome C, active caspase-9, increases in
expression of TGF-P-1, and significant (p < 0.01) increases in apoptosis were observed. No
changes in active caspase-8 were observed at any dose. However, there was no significant effect
on thyroid-follicular cell proliferation, as evaluated by BrdU incorporation into DNA, and no
effects on T3 or TSH levels. At 500 mg/kg-day, T4 was significantly decreased relative to
controls (see Table 7), and significant morphological changes (increase in the colloid area with a
decrease in epithelial height) occurred. Thyroid weight relative to body weight was not affected
at any dose including the highest dose. In addition, no other effects were seen at any of the
lower doses. The study authors concluded that hexachlorobenzene does not disrupt thyroid
hormone economy, cell proliferation, or cell morphology at doses <500 mg/kg-day but is capable
of initiating induction of TGF-P-1 expression and the cascade of effects on cytochrome C and
procaspase-9 that result in the observed apoptotic response3 at doses of >1 mg/kg-day. The
NOAEL for this study is 100 mg/kg-day, and the LOAEL is 500 mg/kg-day on the basis of
significant decreased circulating T4 and morphological changes in the thyroid.
Table 7. Significant Effects on the Thyroid of Female Wistar Rats Exposed to
Hexachlorobenzene by Gavage for 30 Days
Dose (mg/kg-bw)
Endpoint
0
0.1
1
10
100
500
T4 (ng/dL)
3.67 ± 0.52a
NA
3.55 ±0.43
3.88 ±0.36
3.32 ±0.29
2.21± 0.19b
aMean± SEM.
bSignificantly different from control rats (p < 0.05).
Source: Chiappini et al. (2009).
Inhalation Exposure
Studies relevant to the derivation of provisional chronic or subchronic inhalation RfC
values were not located.
DERIVATION OF PROVISIONAL SUBCHRONIC AND CHRONIC ORAL RfD
VALUES FOR HEXACHLOROBENZENE
SUBCHRONIC p-RfD
There are a large number of short-term and subchronic oral studies of
hexachlorobenzene. Given the size of the toxicological database, this review focused on those
studies most relevant to derivation of a subchronic p-RfD. The studies considered pertinent to
subchronic p-RfD derivation included (1) the principal study (Arnold et al., 1985) used to derive
the chronic RfD on IRIS (U.S. EPA, 2009) and the chronic-duration oral MRL (ATSDR, 2002),
as this study included a subchronic-duration exposure component (F0 generation); (2) the key
Cytochrome C and capsase-9 are mitochondrial upstream regulatory elements in proposed apoptotic pathways.
17
Hexachlorobenzene
-------
FINAL
9-30-2010
studies used by ATSDR (2002) to derive the intermediate-duration oral MRL; and (3) any
short-term, subchronic, developmental, and reproductive toxicity studies published since the
ATSDR (2002) toxicological profile. These studies are summarized in Table 8. The principal
study that has been chosen for the determination of the subchronic RfD is Bourque et al. (1995),
which provided the lowest LOAEL (0.01 mg/kg-day) representing the most sensitive effect in the
subchronic database (see Table 8). The critical effect is degenerative changes in primary ovarian
follicles of monkeys; the selection of the POD is supported by other studies that reported
degenerative changes in ovarian follicles and surface epithelium in monkeys given
hexachlorobenzene for 90 days with an overall LOAEL of 0.1 mg/kg-day (Jarrell et al., 1993;
Foster et al., 1992, 1995; Babineau et al., 1991; Sims et al., 1991). Furthermore, these studies
provide evidence that hexachlorobenzene is toxic to the mammalian ovary and may interfere
with mechanisms regulating ovarian steroidogenesis (ATSDR, 2002; Foster et al., 1992). The
LOAEL for the database is 0.01 mg/kg-day for degenerative changes in primary ovarian follicles
of female Cynomolgus monkeys exposed to hexachlorobenzene for 13 weeks (Bourque et al.,
1995). Bourque et al. (1995) did not provide quantitative data that could be used in benchmark
dose (BMDL) modeling to identify a point of departure (POD). Therefore, the POD selected for
the derivation of a subchronic p-RfD is the LOAEL of 0.01 mg/kg-day from Bourque et al.
(1995).
A subchronic p-RfD was derived as follows:
Subchronic p-RfD = LOAEL UF
= 0.01 mg/kg-day 1000
= 0.00001 or 1 x 10"5 mg/kg-day
The composite UF of 300 is composed of the following:
• UFa: A factor of 10 is applied for animal-to-human extrapolation to account for
toxicokinetic and dynamic differences between monkey and humans. There are no
data to determine whether humans are more sensitive than monkeys to ovarian
degeneration.
• UFh: A factor of 10 is applied for extrapolation to a potentially susceptible human
subpopulation because data for evaluating a susceptible human response are
insufficient.
• UFd: The database for oral exposure to hexachlorobenzene is extensive and includes
both developmental and multigeneration reproductive toxicity studies, as reviewed by
ATSDR (2002). A factor of 1 is applied for database inadequacies because all
requirements for database completeness are satisfied and additional sources of data
seem unlikely to result in a lower POD.
• UFl: A factor of 10 is applied for extrapolation from a LOAEL to a NOAEL.
18
Hexachlorobenzene
-------
FINAL
9-30-2010
Table 8. Summary of Oral Noncancer Dose-response Information Pertinent to Derivation of Subchronic p-RfD
Species
(«/sex/group)
Exposure
NOAEL
(mg/kg-d)
LOAEL
(mg/kg-d)
Duration-
adjusted"
NOAEL
(mg/kg-d)
Duration-
adjusted"
LOAEL
(mg/kg-d)
Responses at the
LOAEL
Comments
Reference
Principal Study for Chronic RfD (U.S. EPA, 2009) and Chronic-Duration OralMRL (ATSDR, 2002)
Rat, Sprague-
Dawley (64-
66/sex/group)
0, 0.32, 1.6, 8.0, or
40.0 ppm in the diet (0,
0.03,0.14, 0.69, and
3.4 mg/kg-d for males
and 0,0.03,0.16,0.78,
and 3.9 mg/kg-d for
females) for 90 d
premating, and possibly
during gestation and
lactation for one
generation
0.69
0.14
3.4
0.69
0.69
0.14
3.4
0.69
Reproductive toxicity:
Decreased viability of
offspring between birth
and PND 4
Parental toxicity:
increased organ weights
(liver, heart, and brain
weight and livenbody-
weight ratio in males)
Data for organ weights
were not shown. F1
generation was
exposed chronically;
F1 results were not
considered for
subchronic p-RfD
derivation
Arnold et al. (1985)
Critical Studies for ATSDR Intermediate-Duration OralMRL (ATSDR, 2002)
Monkey,
Cynomolgus
(4 F/group)
0, 0.1, 1, or 10 mg/kg-d in
gelatin capsules for 90 d
ND
0.1
ND
0.1
Degenerative changes in
ovarian follicles and
surface epithelium
Jarrell et al. (1993);
Foster etal. (1992);
Babineau et al.
(1991); Sims et al.
(1991)
Monkey,
Cynomolgus
(4 F/group)
0,0.01,0.1, 1.0, or
10 mg/kg-d in gelatin
capsules for 13 wks
ND
0.01
ND
0.01
Degenerative changes in
primary ovarian
follicles
Bourque et al.
(1995)
Monkey,
Cynomolgus
(4 F/group)
0, 0.1, 1.0, or 10 mg/kg-d
in capsules for 90 d
1
10
1
10
Increased mean
menstrual cycle length
was accompanied by
reduced serum estradiol
during ovulation
Foster etal. (1995)
19
Hexachlorobenzene
-------
FINAL
9-30-2010
Table 8. Summary of Oral Noncancer Dose-response Information Pertinent to Derivation of Subchronic p-RfD
Species
(«/sex/group)
Exposure
NOAEL
(mg/kg-d)
LOAEL
(mg/kg-d)
Duration-
adjusted"
NOAEL
(mg/kg-d)
Duration-
adjusted"
LOAEL
(mg/kg-d)
Responses at the
LOAEL
Comments
Reference
Subchronic and Short-Term Developmental, or Reproductive Toxicity Studies Published since A TSDR (2002)
Rat, Sprague-
Dawley
(9-10 F/group)
0,0.03,0.1,0.3, 1.0,3.0,
10, or 25 mg/kg-d by
gavage, 5 d/wk, for
13 wks
0.3
1.0
0.2
0.71
Pulmonary interstitial
fibrosis and histolytic
infiltration; maxillary
incisor degeneration;
decreased free T4
The NTP has not yet
published a full report
of this study
Long et al. (2004),
Johnson et al.
(2005, abstract
only)
Rat, Sprague-
Dawley
(20/group)
0, 0.5, 2.5, or 12.5 mg/kg-
d by daily gavage for two
generations in a
continuous breeding
protocol
0.5
2.5
(systemic
and
develop-
mental)
0.5
2.5
(systemic
and
develop-
mental)
Increased absolute liver
weight in F0 females;
decreased number of F0
females with normal
cycle length; decreased
number of live Flc pups
per litter (PND 4-21),
and delayed preputial
separation in Flc litters.
Wolfe and Pepperl
(2005)
Rat, Sprague-
Dawley
(12 M/group)
0, 0.16, 4 or 16 mg/kg-d
by gavage daily for 28 d
0.16
4
0.16
4
Deficits in cochlear
sensitivity without
cochlear hair cell loss or
ciliary changes
Study of auditory
function
Hadjab et al. (2004)
Gerbil,
Mongolian
(15-18/sex/dose)
0, 1.6, 4, or 16 mg/kg-d
by gavage for 30 d
ND
1.6
ND
1.6
Hepatocellular necrosis
and centrilobular
congestion
Study published in
French with abridged
English version and
not translated for this
review
Bitri et al. (2007)
Gerbil,
Mongolian
(15-18 M/dose)
gavage
0, 1.6, 4, or 16 mg/kg-d,
by gavage for 30 d
ND
1.6
ND
1.6
Decreased spermatozoid
content and relative
weight of testes; also
sperm activity (not
further described)
Study published in
French with abridged
English version and
not translated for this
review
Bitri et al. (2008)
20
Hexachlorobenzene
-------
FINAL
9-30-2010
Table 8. Summary of Oral Noncancer Dose-response Information Pertinent to Derivation of Subchronic p-RfD
Species
(«/sex/group)
Exposure
NOAEL
(mg/kg-d)
LOAEL
(mg/kg-d)
Duration-
adjusted"
NOAEL
(mg/kg-d)
Duration-
adjusted"
LOAEL
(mg/kg-d)
Responses at the
LOAEL
Comments
Reference
Rat, Wistar
(3 F/dose)
0,0.1, 1, 10, 100, or
500 mg/kg-d by gavage, 5
d/wk, for 30 d
100
500
71
357
Changes in thyroid cell
morphology and thyroid
hormone levels.
Investigation limited to
thyroid effects
Chiappini et al.
(2009)
aAdjusted for continuous exposure as follows: NOAELadj = NOAEL x Exposure Days/7 days.
21
Hexachlorobenzene
-------
FINAL
9-30-2010
Confidence in the principal study is medium. The study was conducted for a 90-day time
period and conducted a thorough evaluation of the target organ; in addition, the critical effect is
supported by other monkey studies: Jarrell et al. (1993), Foster et al. (1992, 1995),
Babineau et al. (1991), and Sims et al. (1991). However, the number of monkeys per group
(n = 4) tested by Bourque et al. (1995) was small, and a NOAEL for the critical effect was not
defined. Confidence in the database is high. There are numerous subchronic toxicity studies in
multiple species, reproductive, and developmental toxicity studies in multiple species, and
short-term, repeated-dose toxicity studies (see ATSDR, 2002). Medium confidence in the p-RfD
follows.
CHRONIC p-RfD
IRIS (U.S. EPA, 2009) contains a chronic p-RfD for hexachlorobenzene of
8 x 10"4 mg/kg-day, based on a NOAEL of 0.08 mg/kg-day (estimated from a dietary
concentration of 1.6 ppm and a food factor of 5%) for liver effects in F1 rats exposed chronically
in the study by Arnold et al. (1985) and a UF of 100. The subchronic p-RfD is lower than the
chronic IRIS RfD due to the availability of newer data.
FEASIBILITY OF DERIVING PROVISIONAL SUBCHRONIC AND CHRONIC
INHALATION RfC VALUES FOR HEXACHLOROBENZENE
The existing database for hexachlorobenzene does not include studies that can be used to
derive inhalation p-RfC values for hexachlorobenzene.
PROVISIONAL CARCINOGENICITY ASSESSMENT
FOR HEXACHLOROBENZENE
A provisional carcinogenicity assessment was not prepared for hexachlorobenzene
because IRIS (U.S. EPA, 2009) includes a cancer assessment for this compound.
REFERENCES
ACGIH (American Conference of Governmental Industrial Hygienists). (2008) Threshold limit
values for chemical substances and physical agents and biological exposure indices. Cincinnati,
OH.
Arnold, DL; Krewski, D. (1988). Long-term toxicity of hexachlorobenzene [letter]. Food Chem
Toxicol 26:169-174. (as cited in CalEPA, 2003)
Arnold, DL; Moodie, CA; Charbonneau, SM; et al. (1985) Long-term toxicity of
hexachlorobenzene in the rat and the effect of dietary vitamin A. Food Chem Toxicol
23 (9): 779-793.
22
Hexachlorobenzene
-------
FINAL
9-30-2010
ATSDR (Agency for Toxic Substances and Disease Registry). (2002) Toxicological profile for
hexachlorobenzene. Online, http://www.atsdr.cdc.gov/toxpro2.html (accessed September 4,
2009)
Babineau, K; Singh, A; Jarrell, J; et al. (1991) Surface epithelium of the ovary following oral
administration of hexachlorobenzene to the monkey. J Submicrosc Cytol Pathol 23:457-464.
Bitri, L; Dhaouadi, N; Ouertani, L; et al. (2007) [Toxicity of hexachlorobenzene in Meriones
unguiculatus: effects on thyroid and liver], Comptes Rendus Biologies 330(5):410-418.
Bitri, L; Darragi, W; Ouertani, L; et al. (2008) [Effect of hexachlorobenzene on some male
reproductive parameters in Meriones unguiculatus]. Comptes Rendus Biologies
331(5):380—388.
Bourque, AC; Singh, A; Lakhanpal, N; et al. (1995) Ultrastructural changes in ovarian follicles
of monkeys administered hexachlorobenzene. Am J Vet Res 56:1673-1677.
CalEPA (California Environmental Protection Agency). (2003) Public health goals for chemicals
in drinking water. Hexachlorobenzene. Online, http://www.oehha.ca.gov/water/phg/
pdf/Ph4HCB92603.pdf (accessed September 3, 2009).
CalEPA (California Environmental Protection Agency). (2009) Search toxicity criteria database.
Office of Environmental Health Hazard Assessment. Online.
http://www.oehha.ca.gov/risk/ChemicalDB/index.asp (accessed September 3, 2009).
Cam, C; Nigogosyan, G. (1963) Acquired toxic porphyria cutanea tarda due to
hexachlorobenzene. Report of 348 cases caused by this fungicide. J Am Med Assoc 183:88-91.
Chiappini, F; Alvarez, L; Lux-Lantos, V; et al. (2009) Hexachlorobenzene triggers apoptosis in
rat thyroid follicular cells. Toxicol Sci 108(2):301—310.
Fenster, L; Eskenazi, B; Anderson, M; et al. (2006) Association of in utero organochlorine
pesticide exposure and fetal growth and length of gestation in an agricultural population.
Environ Health Perspect 114(4): 597-602.
Foster, WG; McMahon, A; Villeneuve, DC; et al. (1992) Hexachlorobenzene (HCB) suppresses
circulating progesterone concentrations during the luteal phase in the Cynomolgus monkey. J
Appl Toxicol 12(1): 13-17.
Foster, WG; McMahon, A; Younglai, EV; et al. (1995) Alterations in circulating ovarian steroids
in hexachlorobenzene-exposed monkeys. Reprod Toxicol 9(6):541-548.
Gocman, A; Peters, HA; Cripps, DJ; et al. (1986) Porphyria turcica: hexachlorobenzene-induced
porphyria. IARC Sci Publ 77:567-573.
Goldey ES, Taylor DH. (1992) Developmental neurotoxicity following premating maternal
exposure to hexachlorobenzene in rats. Neurotoxicol Teratol 14:15-21.
23
Hexachlorobenzene
-------
FINAL
9-30-2010
Hadjab, S; Maurel, D; Cazals, Y; et al. (2004) Hexachlorobenzene, a dioxin-like compound,
disrupts auditory function in rat. Hearing Res 191(1-2): 125-134.
IARC (International Agency for Research on Cancer). (1979) Hexachlorobenzene. IARC
Summaries & Evaluations, 20:155. Online, http://www.inchem.org/documents/iarc/
vol20/hexachl orobenzene.html
IARC (International Agency for Research on Cancer). (1987) Hexachlorobenzene. IARC
Summaries & Evaluations, Supplement 7:219. Online, http://www.inchem.org/
documents/iarc/suppl7/hexachlorobenzene.html (accessed September 3, 2009).
IARC (International Agency for Research on Cancer). (2001) Hexachlorobenzene. IARC
Summaries & Evaluations, 79:493. Online, http://www.inchem.org/documents/iarc/vol79/79-
13.html (accessed September 3, 2009).
Jarrell, JF; McMahon, A; Villeneuve, D; et al. (1993) Hexachlorobenzene toxicity in the monkey
primordial germ cell without induced porphyria. Reprod Toxicol 7:41-47.
Johnson, JD; Vasconcelos, D; Ryan, M; et al. (2005) Subchronic toxicity study of
hexachlorobenzene (HCB) in female Harlan Sprague-Dawley rats. Toxicol Sci 84(1-S):242.
Lambrecht, R; Erturk, E; Gruden, E; et al. (1983a) Hepatocarcinogenicity of chronically
administered hexachlorobenzene in rats. Fed Proc 42. (as cited in CalEPA, 2003)
Lambrecht, R; Erturk, E; Gruden, E; et al. (1983b). Renal tumors in rats chronically exposed to
hexachlorobenzene. Fed Proc 24. (as cited in CalEPA, 2003)
Long, PH; Herbert, RA; Nyska, A. (2004) Hexachlorobenzene-induced incisor degeneration in
Sprague-Dawley rats. Toxicol Pathol 32(l):35-40.
NIOSH (National Institute for Occupational Safety and Health). (2009) NIOSH pocket guide to
chemical hazards. Index by CASRN. Available at http://www2.cdc.gov/nioshtic-2/
nioshtic2.htm (accessed September 3, 2009).
NTP (National Toxicology Program) (2001) TOX-77 Toxicity report tables and curves. Online.
http://ntp.niehs.nih.gov/index.cfm?objectid=CCC95C4F-FlF6-975E-710B4F5A57893B82
(accessed September 3, 2009).
NTP (National Toxicology Program). (2005) 11th report on carcinogens. U.S. Department of
Health and Human Services, Public Health Service, National Institutes of Health, Research
Triangle Park, NC. Online, http://ntp-server.niehs.nih.gov/ (accessed September 3, 2009).
OSHA (Occupational Safety and Health Administration). (2009) OSHA standard 1915.1000 for
air contaminants. Part Z, Toxic and Hazardous Substances. Online.
http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=999
2 (accessed September 3, 2009).
Peters, H; Cripps, D; Gocmen, A; et al. (1987) Turkish epidemic hexachlorobenzene porphyria a
30-year study. Annals N Y Acad Sci 514:183-190.
24
Hexachlorobenzene
-------
FINAL
9-30-2010
Ribas-Fito, N; Torrent, M; Carrizo, D; et al. (2007) Exposure to hexachlorobenzene during
pregnancy and children's social behavior at 4 years of age. Environ Health Perspect
115(3):447-450.
Sims, DE; Singh, A; Donald, A; et al. (1991) Alteration of primate ovary surface epithelium by
exposure to hexachlorobenzene: a quantitative study. Histol Histopathol 6:525-529.
Smink, A; Ribas-Fito, N; Garcia, R; et al. (2008) Exposure to hexachlorobenzene during
pregnancy increases the risk of overweight in children aged 6 years. Acta Paediatrica (Oslo)
97(10): 1465-1469.
Sunyer, J; Alvarez-Pedrerol, M; To-Figueras, J; et al. (2008) Urinary porphyrin excretion in
children is associated with exposure to organochlorine compounds. Environ Health Perspect
116(10): 1407—1410.
U.S. EPA (U.S. Environmental Protection Agency). (1984) Health effects assessment for
hexachlorobenzene. Environmental Criteria and Assessment Office Cincinnati OH.
ECAO-CIN-H017.
U.S. EPA (U.S. Environmental Protection Agency). (1985) Health assessment document for
chlorinated benzenes. Final report. EPA600884015F.
U.S. EPA (U.S. Environmental Protection Agency). (1986) Guidelines for carcinogen risk
assessment. Prepared by the Risk Assessment Forum, U.S. Environmental Protection Agency.
Washington, DC.
U.S. EPA (U.S. Environmental Protection Agency). (1988a) Drinking water criteria document
for hexachlorobenzene. Document No. ECAO-CIN-424.
U.S. EPA (U.S. Environmental Protection Agency). (1988b) Recommendations for and
documentation of biological values for use in risk assessment. Prepared by the Environmental
Criteria and Assessment Office, Office of Health and Environmental Assessment, Cincinnati,
OH. EPA/600/6-87-008. PB88-179874.
U.S. EPA (U.S. Environmental Protection Agency). (1991) Chemical Assessments and Related
Activities (CARA). Office of Health and Environmental Assessment, Washington, DC.
U.S. EPA (U.S. Environmental Protection Agency). (1994) Chemical Assessments and Related
Activities (CARA). Office of Health and Environmental Assessment, Washington, DC.
U.S. EPA (U.S. Environmental Protection Agency). (1997) Health effects assessment summary
tables. FY-1997 Update. Prepared by the Office of Research and Development, National Center
for Environmental Assessment, Cincinnati OH for the Office of Emergency and Remedial
Response, Washington, DC. EPA/540/R-97/036. NTIS PB97-921199.
U.S. EPA (U.S. Environmental Protection Agency). (2005) Guidelines for carcinogen risk
assessment. Risk Assessment Forum, Washington, DC; EPA/630/P-03/001F. Federal Register
70(66): 17765-17817.
25
Hexachlorobenzene
-------
FINAL
9-30-2010
U.S. EPA (U.S. Environmental Protection Agency). (2006) 2006 Edition of the drinking water
standards and health advisories. Office of Water, Washington, DC. EPA 822-R-06-013.
Washington, DC. Online, http://www.epa.gov/waterscience/drinking/standards/dwstandards.pdf
(accessed September 3, 2009).
U.S. EPA (U.S. Environmental Protection Agency). (2009) Integrated Risk Information System
(IRIS). Office of Research and Development, National Center for Environmental Assessment,
Washington, DC. Online, http://www.epa.gov/iris/.
WHO (World Health Organization). (1997) Hexachlorobenzene. Environmental Health Criteria,
No. 195. World Health Organization. Lyon, France. Online, http://www.who.int/pcs/
ehc/summaries/ehc_195.htm (accessed May 15, 2002).
Wolfe, GW; Pepperl, SG. (2005) Hexachlorobenzene: Reproductive assessment by continuous
breeding when administered to Sprague-Dawley rats by oral gavage, Volumes 1 and 2, GRA&I,
Issue 13:894. Sponsored by National Toxicology Program, Research Triangle Park, NC.
26
Hexachlorobenzene
------- |