EPA/600/8-87/055F
November 1987
Summary Review of Health Effects
Associated with Naphthalene
Health Issue Assessment
ENVIRONMENTAL CRITERIA AND ASSESSMENT
OFFICE
OFFICE OF HEALTH AND ENVIRONMENTAL
ASSESSMENT
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NC 27711
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Disclaimer
This document has been reviewed in accordance with U.S. Environmental
Protection Agency policy and approved for publication. Mention of trade
names or commercial products does not constitute endorsement or
recommendation for use.
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Preface
The Office of Health and Environmental Assessment has prepared this
summary health assessment to serve as a source document for EPA use The
summary health assessment was developed for use by the Office of Air
Quality Planning and Standards to support decision making regarding
possible regulation of naphthalene as a hazardous air pollutant
In the development of the summary health assessment document the
scientific literature has been inventoried through October, 1987 key studies
have been evaluated, and summary/conclusions have been prepared so that
the chemicals' toxicity and related characteristics are qualitatively identified
Observed effect levels and other measures of dose-response relationships
are discussed, where appropriate, so that the nature of the adverse health
responses is placed in perspective with observed environmental levels
Any information regarding sources, emissions, ambient air
concentrations, and public exposure has been included only to give the
reader a preliminary indication of the potential presence of this substance in
the ambient air. While the available information is presented as accurately as
possible, it is acknowledged to be limited and dependent in many instances
on assumption rather than specific data. This information is not intended nor
should it be used, to support any conclusions regarding risk to public health
it a review of the health information indicates that the Agency should
consider regulatory action for this substance, a considerable effort will be
undertaken to obtain appropriate information regarding sources, emissions
and ambient air concentrations. Such data will provide additional information
for drawing regulatory conclusions regarding the extent and significance of
public exposure to this substance.
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Abstract
Naphthalene, a white crystalline solid that is nearly insoluble in water, is
released into ambient air via industrial gaseous and paniculate emissions
tobacco use, and through consumer use. Naphthalene is the principal
inqredient of mothballs. . ,
The data base concerning exposure of humans via inhalation and
associated health effects is virtually nonexistent. Human data consist
principally of accidental overexposure and occupational case reports.
Overexposure often results in acute hemolytic anemia and has been
associated with cataract formation. There are no available dose-response
'ln laboratory animals, two principal target tissues have been identified:
nonciliated bronchiolar epithelial (Clara) cells and eye tissue. Effects on Clara
cells appear to correlate with the degree of covalent binding of reactive
metabolites. The absence of such effects in some studies suggest that strain
and/or exposure variables may play a role. The metabol.te(s) that is
responsible for Clara cell damage is unknown. There are no published studies
involving inhalation exposure. .
Administration of naphthalene by routes other than inhalation has been
shown to produce cataracts in rats, rabbits, and one mouse strain. Animal
strains with pigmented eyes develop cataracts faster and more severely than
albino strains. The likely causative agent is polyphenol oxidase, found only in
pigmented eyes, that catalyzes the formation of 1 ,2-naphthoqumone which
binds to lens tissue. .
Only a limited number of mutagenicity studies have been conducted.
Negative results have been reported for gene mutations (Salmonella),
unscheduled DNA synthesis in rat hepatocytes and micronuclei in mouse
bone marrow. Limited teratology studies in rats and rabbits reported no gross
abnormalities. In a single dose (300 mg/kg) study in mice, both maternal and
fetal toxicity were reported.
The effects of chronic inhalation exposure of mice to 10 and 30 ppm have
been examined in a lifetime study by the National Toxicology Program.
Results are not expected to be published until the latter part of 1988. This
study should provide for a more definitive judgment of the toxicologic and
carcinogenic potential of naphthalene..
IV
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Table of Contents
Preface ,-jj
Abstract '.'.'.'.'. jv
List of Tables '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'." vii
List of Figures '.'.'.'.'.'.'.'.'.'" viii
Authors, Contributors, and Reviewers jx
1. Summary 1
2. Background Information 5
2.1 Chemical Characterization '.'.'.'.'.'.'.'.'.'. 5
2.2 Environmental Release and Exposure '.'.'.'.'.'"' 5
2.3 Environmental Fate and Effects 7
3. Metabolism 11
3.1 Pharmacokinetics and Metabolism 11
3.1.1 Absorption 11
3.1.2 In Vivo Metabolism ' 11
3.1.2.1 Oral Administration 11
3.1.2.2 Intraperitoneal Administration 15
3.1.3 In Vitro Metabolism 16
3.2 Mechanisms of Metabolite-Induced Toxicities 21
3.2.1 Ocular Toxicity '. 21
3.2.2 Pulmonary Toxicity 22
4. Health Effects 25
4.1 Acute Toxicity 25
4.1.1 Oral '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 25
4.1.2 Dermal '.'.'.'.'.'.'.'. 26
4.1.3 Inhalation '.'.'.'.'.'.'. 26
4.1.4 Intraperitoneal ' 26
4.1.5 Subcutaneous '//_ 27
4.1.6 Eye Irritation 27
4.1.7 Dermal Irritation and Sensitization 27
4.2 Subchronic Toxicity 27
4,2.1 Oral '.'.'.'.'.'.'.'.','.'.'.'.'. 27
4,3 Chronic Toxicity '.'.'.'.'.'. 30
4.4 Carcinogenicity '.'.'.'.'.'. 30
4.5 Mutagenicity 32
4.6 Teratogenicity and Reproductive Effects 32
4.7 Neurotoxicity 33
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4.8 Effects on Humans 33
4.8.1 Hemotoxicity 33
4.8.2 Skin Sensitization 36
4.8.3 Ocular Toxicity 36
4.8.4 Carcinogenicity 37
5. References
39
VI
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No.
2-1
3-1
3-2
4-1
4-2
List of Tables
Current domestic manufacturers of naphthalene and their
production capacities
Metabolism of p4C]Naphthalene in control'and bile-duct-'
cahnulated rates
Naphthalene metabolites in urine
Acute toxicity values of naphthalene in laboratory animals
Tumor incidence in female A/J strain mice exposed to
naphthalene via inhalation for 6 months 31
6
13
17
25
VII
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List of Figures
No.
Page
3-1 Proposed in vitro and in vivo pathways for the metabolism of
naphthalene by rats 14
3-2 In vitro metabolism of naphthalene 18
VIII
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Authors, Contributors, and Reviewers
The following personnel of Dynamac Corporation were involved in the
preparation of earlier drafts of this document: Nicolas P. Hajjar Ph D
(Department Manager); Finis Cavender, Ph.D. (Department Director/Principal
Author); Louis Borghi, Dana Cazzulino, Guillermo Millicovsky, Ph D William
Richards, Ph.D., and Patricia Turck (Authors); William McLellan Ph D
(Reviewer); Anne Gardner (Technical Editor); and Gloria Fine (Information
Specialist).
The final report was prepared by Mark Greenberg, Environmental Criteria
and Assessment Office, U.S. Environmental Protection Agency.
Drafts of this document have been reviewed for scientific and technical
merit by the following scientists: Professor Alan Buckpitt, School of Veterinary
Medicine, Department of Veterinary Pharmacology and Toxicology University
of California, Davis, California; Professor Marjorie G. Horning Institute for
Lipid Research, Baylor College of Medicine, Houston, Texas; and Dr. George
M. Shopp, Jr., Inhalation Toxicology Research Institute, Albuquerque, New
Mexico. This document has also been reviewed by scientists in the
Carcinogen Assessment Group (CAG), Reproductive Effects Assessment
Group (REAG), and the Exposure Assessment Group (EAG) of the Office of
Health and Environmental Assessment (OHEA), U.S. EPA, Washington DC as
well as scientists from the Environmental Criteria and Assessment Office
Cincinnati, OH. Special acknowledgement is made to Fred Hauchman the
Office of Air Quality Planning and Standards, for his many helpful scientific
and editorial suggestions throughout the preparation of this document.
IX
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1. Summary
in wran h/ ±te> TV*0 £rystalline solid tha* * nearly insoluble
£J£ i i released to ambient air via industrial gaseous and
part.culate emissions, aqueous wastestreams, tobacco use and throuah
consumer use into indoor environments mrougn
EPA^nn^T"4;5,?! 'tis tconMati™ ^ ambient air are limited. One U.S
EPA report indicated levels are in the range of 0.03 to 0.10 ng/rr.3 Levels are
known to be considerably higher (in the low ppb range) in The vfcS* of
industrial sources of naphthalene. In air, naphthalene is subfeSSd to
photochemical degradation. During sunlight hours, naphthalene reacts wih
SnhSfV raKICa'S and has a half-|ife of 8 nours During darkness
SL raS'T^nf r^H ^IHife °f 15 h°urs as a result °f reacSS
nitrate radicals. Thus, naphthalene is not expected to be persistent in the
ftTsTubiect TSr ' "fPhtha'ene levels are generally no hig'he? San 2%/L
n^vf^J de9radatlon by microorganisms and is known to sorb to
particulates in aqueous environments.
«ir Jneadata btasf co^n'nQ naphthalene exposure of humans via ambient
D ncioaNv 0fCS ? * ^^ * Virtua"y nonexistent. Human data conS
ina2nSly nf h £ overexposure and occupational case reports. In these
instances of human overexposure, acute hemolytic anemia has been a
frequen finding and there is suggestive evidence that Overexposure is
af ocjated with cataract formation. One factor identified as increasing risk for
SSve d^Ztr 'S ,9|ucose-6-Pnosphate dehydrogenase deficiency
n^rLlr derrnatt'salso can result upon direct contact with naphthalene
There are no available dose-response data
effeSsShaSeShPPneHinf°rr!lati0n -ela,?n9 naPnthalene to adverse health
effects has been derived principally from limited laboratory animal
experimentation. Data available from inhalation exposures are minimal
eDithenalS^fr.^9^ !jsfuesHhave been identified: nonciliated bronchiolar
epithelial cells (Clara cells) and eye tissue. In mice, single intraperitoneal
£2 TVf^' '" a dose-dePendent necrosis of Clara cells. The eS and
severity of this les.on appears to correlate with the degree of covalent bindinq
6 metab°"tes of naphthalene in the lung. The nature of the react ve
h-and 'ts,?ource (whether the Clara cell or liver) have not been
. While naphthols have been identified as being partially responsible
to hP a ,T I0?'"? °bServed in Clara cells' they have n°l been demonstrated
Sine fh t0r '" Producm9 Pulmonary necrosis. The absence of such
lesions ,n other mouse studies, including subchronic studies, suggests strain
™t Si""6 !fKable! may P'ay a role- The data base for o^er species (eg
rat, rabbt, and hamster) is limited but there are indications that the mouse is
' neCr°SiS haS not been
jre an extensive number of metabolites (>30) that have been
in the rat and mouse. The metabolic profile differs between these
species. In hmitedI studies with humans, only 1- and 2-naphthol have beln
conclus,vely ,dent,fied. Most metabolites excreted in the urine are conjugates
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of qlucuronides or mercapturic acids. The metabolic profile between rodents
•wd Sates' suggests interspecies differences. In rodents .conjugation of
naphSne with glutathione (GSH) appears.to be the principal mechanism o
exCretion. In primates, conjugation with GSH may ^ <**"£**"**
metabolic pathway. It is not known whether this metabolic d«erenf®. 1S
Sgniticant in eliciting differences in adverse responses between the species.
The metabolism of naphthalene in primates has been studied only with acute
oral exposure. Information from oral studies suggests that reactive
mf abolites are produced in a stereoselective manner ,n the liver and have a
sufficiently long half-life that enables them to reach the lung and eye,
eacuo50 values for mice and rats indicate that naphthalene is
not particularly toxic. For mice, LD50 values are in the range of 500 to 700
mg/kg while for rats, the range is 2,009 to 3,310 mg/kg. It is not known what
the comparable inhalation LC5o values are. . u . t- K h^^n
Administration of naphthalene by routes other than inhalation has been
shown to produce cataracts in rats, rabbits, and one mouse strain. IT irate. jaye
pigmentation is an important factor in cataract formation. P'gmentec Is ams
develop cataracts faster and more severely than albino strains. A I ke y
causative factor is the occurrence of polyphenol oxidase, found only in
pigmented tissue, that catalyzes formation of 1 -2-naP/lth^TtonfJr°^q1l'J"
dihydroxynaphthalene. 1 ,2-naphthoquinone is known to bind to tens tissue.
In rabbits, depletion of antioxidants is believed to be the critical step because
the reserve of antioxidants is considerably less than ,n rate. Cataract forma ,on
and other damage to the eye have been reported in C57BL/6J mice in
s, some naphthalene is likely to enter the systemic
circulation. In this event, metabolism by the liver may result in the formation
of reactive metabolites similar to those identified in non-inhalation studies
and associated with pulmonary cell damage and cataract formation. However
there are insufficient dose-response and pharmacokinetic data to estimate
likely effect levels via the inhalation route. ..-•»• ^ /o
Naphthalene was found to cause a statistically significant increase (p
<005) in the number of adenomas per tumor-bearing mouse lung but not in
the number of adenomas per mouse in female A/J strain mice after • € i months
of inhalation exposure. These results are inconclusive with regard to the
carcinogenic potential of naphthalene. Effects of chronic exposure of mice (to
10 and 30 ppm naphthalene) have been examined in a 2-year inhalation
study by the National Toxicology Program. Results have not yet been
published. This study should provide information with which one can evaluate
ihe carcinogenic potential of naphthalene. According to U.S. Environmental
Protection Agency Guidelines for Carcinogen Risk Assessment naphthalene
is classified as a Group D carcinogen. The evidence is inadequate to evaluate
the carcinogenic potential of naphthalene for man. ,,,,<•«,
Only a limited number of mutagenicity studies have been conducted with
naphthalene. Negative results have been reported for gene mutations in
Salmonella, unscheduled DNA synthesis in rat hepatocytes, and micronuclei
10 TnTsingle dose (300 mg/kg) teratology study in mice, both maternal and
fetal toxicity were reported. Limited teratology studies in rats and rabbits
reported no gross abnormalities from naphthalene exposure.
A more definitive judgment of the impact of naphthalene exposure via
ambient air on human health can only be made after completion of the
National Toxicology Program (NTP) chronic bioassay and additional studies
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on selected biological endpoints. A reassessment of naphthalene effects
associated with inhalation exposure should be carried out once the NTP
results become available.
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2. Background Information
2.1 Chemical Characterization
Naphthalene (CAS No. 91-20-3) has the empirical formula C10H8. It is
a white crystaline sohd with a molecular weight of 128.16. Naphthatene is
Ha T^r?/rle'" ,Watern(3° mg/L) and has a low vaP°r Pressure <1 mm
mg/m3 (Toxicology Data Bank). At 25°C, 1 part per million = 5.2
Domestic production capacity of naphthalene was estimated to be 660
million pounds annually as of January 1, 1984. Six manufacturers produce the
3°UN ^h"',06 Plant Sites as shown in Table 2'1 ' and use as a moth repellant
(2 percent) (Chemical Economics Handbook, 1981).
2.2 Environmental Release and Exposure
Naphthalene is released into the environment via industrial gaseous and
particulate emissions aqueous waste streams, and through consumer uses
MNIiamT^, To«lfn deteCted in aerosols from a coal gasification plani
Williams et al 1982), gaseous emissions from aluminum manufacturing
Hung and Bermer 1983), rendering plant emissions (Van Langenhove et al
1982), spent pulp bleaching liquor (Kringstad et al., 1984), and wastewater
from oil and gas fields (Middleditch, 1982). Oil spills are another important
source of naphthalene release into the aquatic environment (U.S EPA 1980)
The compound is also released into the atmosphere via the combustion gases
of coal-fired boHers (Warman, 1983), residential wood stoves (Jaasma and
mt™ 't ^' ,Chfnotaw e"9'nes
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Table 2-1 Current Domestic Manufacturers of Naphthalene and Their
Production Capacities (million pounds) •;
Manufacturer
Annual Capacity
Allied Corporation, Allied Chemical, Ironton, OH
Ashland Oil, Inc., Ashland Chemical Company Division,
Petrochemicals Division,
Catlettsburg, KY
El. du Pont de Nemours & Company, Inc., Conoco Inc.,
subsidiary, Conoco Chemicals Company Division,
Chocolate Bayou, TX
Getty Oil Company, Getty Refining and Marketing
Company, subsidiary, Delaware City, DE
Koppers Company, Inc., Organic Materials Group,
Cicero, IL
Follansbee, WV
Fontana, CA
United States Steel Corporation, USS Chemicals Division,
Clairton, PA
Gary, IN
Total
75"
660
aFrom petroleum; naphthalene is sold on the merchant market.
t>From petroleum (ethylene coproduct); naphthalene is used used captively.
cFrom coal tar; naphthalene is used captively and sold on the merchant market.
dFrom coal tar; naphthalene is used captively.
Source: SRI International (1984)
coal gasification sites at concentrations of 380 to 1,800 ppb 15 months after
gasification activity had ended. Pankow et al. (1984) reported mean dissolved
naphthalene concentrations of 11 and 72 ng/L in rainwater samples collected
in semirural and residential locations, respectively, in Oregon.
Naphthalene was detected in ambient air samples collected in Denver,
CO (Hutte et al 1984), and near abandoned chemical waste dumps (Durchm
and Pendleton, 1983). In 1977, ambient air concentrations were reported to
range from 0.03 to 0.10 ng/m3 (for vapor) and 0.003 to 0.25 ng/rr.3 (for
particulates) (U.S. EPA, 1980). In a field study of mobile homes, Connor et al.
(1985) reported naphthalene levels have been 0.3 and 11.8 ppb. Naphthalene
has also been detected in fly-ash samples from municipal waste incinerators
in Canada and Norway at concentrations of 130 to 760 ng/g (Viau et al.,
1984) The compound has been found to be adsorbed to the particulate
matter emitted in diesel engine exhaust; Yergey et al. (1982) determined an
average emission rate of 329 iig/g of particle.
Estimates of occupational exposures to naphthalene have been reported
in industrial hygiene surveys performed by the National Institute for
Occupational Safety and Health (NIOSH). According to the National
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Occupational Hazard Survey (NOHS), 121,977 workers were potentially
exposed to naphthalene in domestic workplace environments in 1970
SS'Sffi- f th°* in9r^in the Nati°nal Optional Exposure Survey
to the com ouffd * rS' includin9 1'535 women, were exposed
„ J,h6K Occupational Safety and Health Administration (OSHA 1983)
nS^f fn nan 8£nUr time-wei9nted ^erage (TWA) permissible exposure
limit of 10 ppm (50 mg/m3) for naphthalene; the American Conference of
Governmenta Industnal Hygienists (ACGIH, 1984) recommended an 8-hour
TWA threshold Hm* value (TLV) of 10 ppm and a 15-minute short-term
exposure limit-TLV of 15 ppm (75 mg/m3)
Van Langenhove et al. (1982) detected naphthalene in the workplace
atmosphere of a rendering plant. Bjorseth et al. (1978a) reported naphthalene
vapor concentrations of 0.7 to 60 ppb (4 to 311 ug/m3) in atmospheric
samples and 0.01 to 0.7 ppb (0.09 to 4 .g/mS) (as SSJuSsff^SSS
samples taken at an aluminum reduction plant. Atmospheric samples at a
coke plant showed mean naphthalene concentrations of 0.2 ppb (12 uq/m3)
1 } 1^1 1f/Pb (646 t0 653 *9/m3> <9aseous> (Bjorseth et al.
'" y> naPhtna|ene vapor concentrations up to 230 ppm
^EpX, x>place atmospheres where m™en
A 1977 report (U.S. EPA, 1980) listed groups of workers that were among
those having potential exposure to naphthalene. These workers were involved
in the use or manufacture of beta naphthol, celluloid, coal tar, dye chemicals
fungicides, hydronaphthalene, lampblack, moth repellants, phthalic anhydride'
reduction3 ^^ ta"nery products' textile chemicals, and aluminum
Gas chromatography (GC) coupled with mass spectrometry (MS) is the
method most commonly used to characterize naphthalene in environmental
media and workplace atmospheres; flame ionization detection has been used
"1 TS10? With GC/MS to obtain quantitative concentration data (Pankow
P * " IOAO: I0"9 ^la'" 1984: Viau et al" 1984: Dernier et al., 1982 Yergey
et al., 1982; Bjorseth et al., 1978a).
2.3 Environmental Fate and Effects
Naphthalene is expected to be released into the atmosphere from
sources that include petroleum fuel combustion (Biermann et al., 1985) and
mothball subl.mation. In the atmosphere, the compound exists predominantly
"] ioa3?0,! P u: as ^Pared to being bound to particulates (Biermann et
al., 1985). It is subject to various photo-oxidative or oxidative reactions
beveral recent articles suggest that naphthalene may be subject to
hydroxy (OH) radical attack during the daytime and to nitrate (N03) radical
f^fnCH tt I"9 iJT3"" et al" 1985: Atkinson et al- 1984>- Biermann et al.
found that naphthalene reacts rapidly with OH radicals at room temperature-
they determined a rate constant of 2.35 x 10-" cm3/mo|-sec, which gives a
ftmnTrfh a ot°f approximately 8 hours (lifetime of 12 hours), assuming an
atmosphenc OH radical concentration of 1 x 106 mol/crr.3. Atkinson et al
presumably provided the first direct evidence for the gas phase reaction of .
NOs radicals with naphthalene and determined a rate constant of 64 x 10-15
cmJ/mol-sec. Recent evidence suggests that N03 radicals may be a
common constituent of nighttime air over many U.S. continental areas with
maximum concentrations in excess of 10 pot and probably close to 100 ppt in
populated areas (Platt et al., 1984). Assuming an atmospheric N03 radical
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concentration of 80 ppt, the nighttime half-life for naphthalene is
approximately 15 hours. .
Atkinson et al. (1987) observed that gas-phase reactions of naphthalene
with OH radicals in the presence of nitrogen oxides resulted in the production
of 1- and 2-nitronaphthalenes and 1- and 2-naphthols. Nitronaphthalenes
have been detected in ambient air (Arey et al., 1987).
The mechanisms and products of these reactions have not been fully
elucidated. These reactions are likely to proceed via initial radical addition to
the aromatic ring, but subsequent reaction mechanisms and products under
atmospheric conditions are not known (Biermann et al., 1985; Atkinson et al.,
1984) For the OH radical, analogies can be made with monocyclic
hydrocarbons. Initially, the aromatic ring would stay intact, with products such
as hydroxynaphthalene and nitronaphthalene expected to form. However it is
possible that the aromatic ring could cleave, leading to products such as
dibenzaldehyde (Biermann et al., 1985).
Naphthalene is expected to enter the aqueous environment from botn
natural and anthropogenic sources (U.S. EPA, 1979). The initial fate of the
compound is determined by three competing physical processes: sorption to
particulates, evaporation, and water solubility. Sorption to organic matter is
linearly related to the log octanol/water partition coefficient for naphthalene
concentrations up to 60 to 70 percent of its water solubility (30 mg/L),
whereas increased sorption occurs at higher concentrations (Kanckhoff et aL,
1979) Given naphthalene's log octanol/water partition coefficient of 3.37
adsorption to particulates would seem to be moderately strong; however at
low naphthalene concentrations, this may not be true. At a concentration of 25
up/L Lee et al. (1978) found that only 2 percent of naphthalene bound to
suspended particulates in seawater following a 3-hour incubation period. No
data on the organic content or the concentrations of the particulates in the
seawater were reported.
Southworth (1979) calculated volatilization rates of naphthalene from a
model stream with a depth of 1.0 m. The half-life for volatilization varied
from about 80 hours for a stream with a velocity of 0.1 m/sec and a wind
velocity of 0.25 m/sec, to about 3 hours for a stream with a velocity of 1.0
m/sec and a wind velocity of 4 m/sec. He concluded that the rate of
volatilization would be low in relatively deep, slow-moving rivers but that it
may be competitive with other removal processes such as adsorption in clear,
rapidly flowing shallow streams. .
Lee and Anderson (1977) studied the fate of naphthalene in a model
ecosystem. When 2 g of naphthalene were added to the ecosystem to make
a concentration of 34 ng/L, 220 mg were detected in the sediment after 4
days Thus about 11 percent of the naphthalene settled to the sediment,
approximately 44 percent remained in the water column, and the remaining
45 percent was unaccounted for. The naphthalene may have evaporated,
photo-oxidized, or adsorbed to the sides of the container, but the authors
suggested that biodegradation played the major role.
A laboratory method for measuring the volatilization rate of naphthalene
and other low volatility chemicals from water has been described by Smith et
al. (1981). The use of XAD-2 resin as an adsorbent for trace quantities of
naphthalene in water was described by Wigilius et al. (1987).
Many microorganisms found in the environment are capable of degrading
naphthalene. These include algae (Cerniglia et al., 1979), fungi (Cerniglia et
al 1978) and bacteria (Gibson, 1972; Davies and Evans, 1964). In addition,
treatment of wastewater effluents has been shown to effectively degrade
naphthalene (Tabak et al., 1981; Malaney et al., 1967). At concentrations of 5
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and 10 mg/L, complete primary degradation of naphthalene was observed in a
Sabak ^ ai°U Qft^*^ Hith d,°meStiC wastewater "sed *> an inoculum
(Tabak et al., 981). Biodegradation of naphthalene to CO2 has been
3CtiVated Slud9e system where'2,500 mg/L
hem'ICa* °xygen demand ran9ing from 32.8
/(l oxygen demand (Malaney et al. 1967) Lee
(197?) dettermined the biodegradation ratesof naphthalene by
present in marine water at depths of 5 to 10 m These
andhH^^ 14C-"aPntha'ene at a concentration oTso^/L
and incubated for 3 days. Rapid adaptation to naphthalene as a carbon
^/^ the ^adation rates Banged from 0.1 yg/L/day on
l-9/L/day on day 3. Under anaerobic conditions however,
dation pf naphthalene is not likely. Delaune et al. (1980) found tha
f H °fhS hi bi°de9rade under a"aerobic conditions that are
prevalent at depths below 2 cm in sediments
bePnS£iMriHiHhepmiCr°bial biode9radative pathways of naphthalene have
been eluadated. For pseudomonads and most other bacteria, naphthalene is
broken down to catechol as shown below. "wiene is>
OH
HO
COOH
: o
OH
COOH
CHO
Catechol is further degraded by these microorganisms to CO2 and HoO
Chough the metabolic pathways vary among differing species (Barnslev'
H^h I i°o Jr?81 bacteria- the initl'a' metabolite of naphthalene is c/s-1 2-
dihydro-1,2-dihydroxynaphthalene, in contrast to naphthalene-1 2-oxide
wh.ch is thought to be the initial metabolite for fungi, eukaryotes, and other
bacteria (Cern.glia et al., 1984). This arene oxide is very unstable and can
undergo other reactions, predominantly to 1-naphthol. It rearranges
probably nonenzymatically, to 1-naphthol; some 2-naphthol is also formed'
I he oxide also will react nonenzymatically or enzymatically with water to form
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1,2-dihydroxy-1,2-dihydronaphthalene with glutathione to form the
glutathione analog of the dihydrodiol.
10
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3. Metabolism
3.1 Pharmacokinetics and Metabolism
With the exception of one study (Mackell et al., 1951), there is no
information concerning the metabolism of naphthalene in man There are
however, a number of studies that have investigated the in vitro and in vivo
metabolism of naphthalene pertinent to laboratory animals, particularly the
rabbit and rat. These data, coupled with limited information from subhuman
primates, appear sufficient to enable one to draw relevant conclusions for
msn.
3.1.1 Absorption
The few case reports available in the literature suggest that ingestion of
naphthalene results in absorption and subsequent acute toxicity (Gidron and
^f' 1956: Chusid and Fried- 1955= Macke" et al- 1951; Zuelzer and Apt
1949) A recent case report identified naphthalene ingestion as the cause of
death (Ijiri et al., 1987). Dermal absorption also is likely based on the reports
by Dawson et al. (1958), Cock (1957), and Schafer (1951). Only one inhalation
case report associated with toxicity has been identified (Valaes et al., 1963)
Bock et al. (1979) studied the absorption and metabolism of naphthalene
in the rat jejunum in situ. i^C-naphthalene was injected into the isolated
intestinal loop, and the concentrations of naphthalene and its metabolites in
M IT?" and portal blood were determined after a 30-minute incubation
Naphthalene was rapidly absorbed and found mostly unchanged (about 84
percent of the dose) in portal blood. The major ether-soluble metabolites
were identified as naphthalene-1,2-dihydrodiol and 1-naphthol
Conjugates comprised about 40 percent of the metabolites and were mostly
glucuronides of the dihydrodiol and 1-naphthol. This study indicates that
metabolism can occur prior to first-pass through the liver.
3.1.2 In Vivo Metabolism
3.1.2.1 Oral Administration
Recently, Bakke et al. (1985) studied the metabolism of 14<>
naphthalene in male Sprague-Dawley rats in an effort to determine the
catabohsm of premercapturic acid pathway metabolites of naphthalene to
napnthols and methylthio-containing metabolites. Mercapturic acids are n-
acetyl cysteinyl thioethers of the form:
R-S-CH2-CH-COOH
I
CH3-CO-NH
R represents an aryl radical.
14C-naphthalene (2 mg/0.5 nCi in 0.5 ml ethanol) was administered
orally to two groups of control rats, 4 groups of bile duct-cannulated rats and
11
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to 4 germ-free rats (2 mg/1.0 nCi). Bile, urine, and feces from control and
cannulated rats were collected for 72 hr (urine and bile samples from each
group were separately pooled for metabolite identification). In control rats, the
recovered dose in urine was 77 to 93 percent and 6 to 7 percent in feces; in
cannulated rats, urine represented 25 to 43 percent while bile represented 49
to 76 percent (feces contained < 1 percent).
Urinary naphthols and naphthol glucuronides represented 4.6 percent of
the dose administered (methylthioglucuronide also represented 4.6 percent)
in control rats. In contrast, bile and urine from cannulated rats and urine from
germ-free rats contained no labeled methylthio derivative and only trace
amounts of labeled naphthols or conjugates. The principal metabolites in
control urine were identified as 1,2-dihydro-1-hydroxy-2-S-(N-acetyl)
cysteinyl naphthalene (38 percent) and 1,2-dihydro-1,2-
dihydroxynaphthalene glucuronide (24 percent). In germ-free rats, the major
urinary metabolite was 1,2-dihydro-1-hydroxyl-2-S(N-acetyl)-
cysteinyl 14C-naphthalene (89 percent). Identified metabolites are shown in
Table 3-1.
Figure 3-1 highlights the proposed in vitro and in vivo pathways, with a
focus on the pre-mercapturic acid pathway. As shown in Figure 3-1, it is
likely that naphthol formation in rats is derived from pre-mercapturic acid
metabolites, possibly from the action of intestinal microflora. Oral
administrations of compounds I or II to control rats resulted in the formation of
both naphthols and the methylthio derivatives; elimination of acid hydrolysis in
the stomach as a mechanism was confirmed when compounds I and II were
injected intracecally. Both naphthol and methylthio derivative increased
significantly above oral values.
Rozman et al. (1982) determined the urinary, fecal, and biliary excretion
of thioethers and hepatic GSH content (by liver biopsy) in rhesus monkeys
following administration of a single oral dose of naphthalene (in sesame oil) at
0, 30, 75, or 200 mg/kg. Naphthalene had no significant effect on the urinary
and fecal excretion of thioethers or the hepatic GSH content. Bile excretion of
thioethers increased from 6.4 to 14.6 iimol/kg/24 hours, but the amount
corresponded to only 0.5 percent of the administered dose. Bakke et al.
(1985) found that methylthio derivatives were about 5 percent of administered
dose to rats. The data of Rozman et al. (1982) suggest that naphthalene
conjugation with GSH is apparently not a major metabolic pathway in rhesus
monkeys. Similarly, a single dose of naphthalene in sesame or corn oil at 200
mg/kg did not increase the urinary excretion of mercapturic acids in four
chimpanzees (Summer et al., 1979). However when SPF Wister rats were
administered naphthalene (0, 30, 75 or 200 mg/kg), up to 39 percent of the
dose (30 mg/kg) was excreted in the urine as mercapturic acids (Summer et
al., 1979).
There were no GSH conjugates of naphthalene in the bile and only trace
amounts were found in the urine of humans receiving a single oral dose of 0.5
g naphthalene (Boyland and Sims, 1958). These data are consistent with the
hypothesis that primates do not conjugate naphthalene with GSH to the extent
that rodents do (Rozman et al., 1982; Summer et al., 1979), possibly because
of a slow rate of naphthalene-epoxide formation or a higher epoxide
hydrolase activity in primates (Rozman et al., 1982). Increased epoxide
hydrolase activity would result in increased formation of naphthols at the
expense of mercapturic acids. Lower activities of GSH transferases in
primates, as suggested by the studies of Chasseaud (1973), also may be an
additional factor. It also is known that a variety of isozymes of GSH
transferases exist and which may differ among species (Ketterer, 1986).
12
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Table 3-1. Metabolism of [14C]Naphthalene in Control and Bile-Duct-
Cannulated Rates
% of 14C dose
Metabolite(s)
Bile duct
Control cannulated
Urine
Urine
Bile
1,2-Dihydro-1 -hydroxy-2-S-cysteinyl-
naphthalene (1)'
1,2-Dihydro-l-hydroxy-2-S-(N-acetyl)
cysteinylnaphthalene (II)'
1,2-Dihydro-1-hydroxy-2-S-
cysteinylglycine-
naphthalene'
Dihydroxynaphthalene
Dihydrodihydroxylnaphthalene
l,2-Dihydro-1,2-dihydroxynaphthalene
glucuronide(lll)
1,2-Dihydro-1-hydroxy-2-
methylthionaphthalene
glucuronide*
Naphthols
Naphthol glucuronides
Uncharacterized""
38.1
4.9
23.9
4.6
1.6
3.0
2.4
14.1
1.5
14.5
16.9
0.7
9.6
6.4
26.8
3.0(4) 6.0(5)
Urine from control rats and urine and bile from bile-duct-cannulated rats were
collected for 24 hr after dosing; these contained 75.6, 29.9, and 66.8% of the 14C
dose, respectively, —not detected (limit of detection was <0.5% of the 14C
dose).
"Assumed to have the 1,2-dihydro-l-hydroxy structure as deducted by Jefferv
and Jerina (1975).
"Numbers in parentheses indicate the number of chromatographic fractions.
Source: Bakke (1985).
In a study by Corner and Young (1954) the comparative metabolism of
naphthalene in male rabbits, male guinea pigs, hooded male rats, and male
white mice was assessed by paper chromatographic identification of urinary
metabolites. All animals were given a single dose of naphthalene in arachis oil
at 500 mg/kg. Rabbits were dosed by stomach tube; guinea pigs and mice
were dosed by intraperitoneal injection; and rats were dosed by both
intraperitoneal injection and stomach tube. The same metabolites were found
in the urine of rats dosed with naphthalene intraperitoneally or orally. All four
species converted naphthalene to 1- and 2-naphthol, 1 2-
dihydronaphthalene-1,2-diol, 1-naphthyl-sulfuric acid, and '1-
naphthylmercapturic acid. In addition, rabbits and rats excreted 1-
naphthylglucuronic acid and 1,2-dihydronapthalene-1,2-diol glucuronic
acid; mice excreted 1-naphthylglucuronic acid; and guinea pigs excreted
1,2-dihydroxynaphthalene. Chromatographic analyses suggested
13
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-glutathione
-cysteinylglycine
-cysteine (I)
-(h-acetyl)cysteine (II)
preMAP-metabolites
SCH3
Figure 3-1 Proposed in vitro (••••
metabolism of naphthalene by rats.
Source: Bakke et al. (1985).
•) and in vivo (•
••) pathways for the
interspecies difference in the amounts of 1- and 2-naphthol produced.
Hooded rats were found to secrete glucuronic acid conjugates of both levo-
and dextro-rotary forms of 1,2-dihydronaphthalene-1,2-diol. In rabbits,
the glucuronic acid conjugate (Corner et al., 1954) was found. No evidence
was found for the occurrence of the glucuronic acid conjugates in either
guinea pigs or mice (Corner and Young, 1954).
Boy land and Sims (1958) detected 1-naphthyl-mercapturic acid in the
acidified urine of rabbits dosed with naphthalene in arachis oil (5 ml of 20%,
w/v). Acidification of urine also resulted in the concomitant production of
naphthols and indications that N-acetylcysteine may have been formed. The
precursor of 1-naphthylmercapturic acid was suggested to be N-acetyl-
S-(1,2-dihydro-2-hydroxynaphthyl)-L-cysteine. Other species shown
to form this precursor included both male and female rats, mouse, hamster,
guinea pig, and man. Bourne and Young (1934) detected a-
naphthylmercapturic acid in urine of rabbits administered naphthalene in
warm paraffin.
In a study designed to elucidate the impaired metabolic step in an
inherited disorder, Kodama et al. (1974) found high concentrations of cystine,
N-monoacetylcystine, and S-(2-hydroxy-2-carboxyethylthio)cysteine in
the urine of rabbits dosed orally with 3 g of naphthalene (approximately 1.2
g/kg) daily for 3 weeks.
14
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3.1.2.2 Intraperitoneal Administration
In a study with female Sprague-Dawley rats, 24 and 60 percent of the
l-T*C-napnthalene dose (100 mg/kg) administered intraperitoneally, was
found in the urine 24 and 72 hours after dosing, respectively (Chen and
Dorough, 1979). In addition, about 14 percent of the dose was found in the
feces 72 hours after dosing. 1,2-Dihydro-1,2-dihydroxynaphthalene
(naphthalene-1,2-dihydrodiol) and 1-naphthol were the major ether-
extractable metabolites in the urine, accounting for about 6 percent of the
administered dose. This is similar to the amount formed by control rats in the
oral dosing study by Bakke et al. (1985). Four water-soluble radiolabeled
metabolites were found in the urine of rats after 72 hours. These metabolites
were tentatively identified as 1-naphthol, 1,2-dihydro-1,2-dihydroxy-1-
naphthyl sulfate (most probably the 1,2-dihydro-2-hydroxy-1-naphthyl
sulfate), N-acetyl-S-(1,2-dihydro-2-hydroxy-1-naphthyl)cysteine
(most probably N-acetyl-S-(1,2-dihydro-1 -hydroxyl-2-
naphthyl)cysteine or possibly N-acetyl-S-(2-naphthyl)cysteine), and
1,2-dihydro-2-hydroxy-1-naphthyl glucuronide, and accounted for 5.0
8.0, 65.0, and 16.8 percent, respectively, of the total radiolabel found in the
water-soluble fraction. It was concluded that in rats, glutathione (QSH) and
mercapturic acid derivatives were the major conjugates in the metabolism of
naphthalene.
Several studies were conducted on the metabolism of 1-14C-
naphthalene in male Sprague-Dawley rats following intraperitoneal injection
at a dosage of 100 mg/kg in 0.5 ml corn oil (Horning et al., 1980a; Horning et
al., 1980b; Stillwell et al., 1978). Of the administered radiolabeled dose, 20 to
30 and 3 to 11 percent was excreted in the urine in 0 to 24 and 24 to 48
hours, respectively. Unconjugated (neutral) and conjugated (acidic)
metabolites accounted for 5 to 20 and 80 to 95 percent, respectively, of the
total metabolites excreted in urine. Of the radioactivity excreted as
conjugates, 20 to 40 percent was liberated after glucuronide and sulfate
hydrolysis; the remainder was accounted for as mercapturic and
premercapturic acids (Horning et al., 1980b). Twenty-one suggested
metabolites were isolated and characterized by GC and GC/MS. The major
metabolites were 1-naphthol, 2-naphthol, frans-1,2-dihydrodiol (1f32a-
dihydroxy-1,2-dihydronaphthalene), ?rans-1,4-dihydrodiol (rac-trans-
1,4-dihydroxy-1,4-dihydronaphthalene), and 1,2-, 1,7-, and 26-
dihydroxynaphthalene. Other metabolites included O-methylcatech'ol
trihydroxy naphthalenes, trihydroxydihydronaphthalenes'
tetrahydroxynaphthalenes, and tetrahydroxy-tetrahydronaphthalenes. The
authors also suggested that in addition to naphthalene-1,2-oxide, several
other epoxides, including two naphthalene dihydrodiol epoxides one
diepoxide, and a cyclic peroxide, were intermediates in the in vivo metabolism
of naphthalene. These epoxides and the cyclic peroxide, in turn, lead to the
formation of the di, tri-, and tetrahydroxynaphthalenes, dihydronaphthalenes
and tetrahydronaphthalenes as urinary excretion products (Horning et al.,
1980a; Horning et al., 1980b). In addition, 10 methylthio metabolites were
isolated (Horning et al., 1980a; Stillwell et al., 1978). These metabolites were
identified as 1-methyl-thionaphthalene, methylthiohydroxynaphthalene and
methylthio derivatives with a dihydronaphthalene or a tetrahydronaphthalene
structure. The methylthio derivatives accounted for only a minor part of the
metabolites excreted. The two major methylthio metabolites
(methylthiodihydrodiol and dimethylthiotetrahydrodiol) accounted for 02 to
15
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1.0 percent of the administered dose (Stillwell et al., 1978). This finding is in
contrast to that of Summer et al. (1979) in which Wistar rats converted about
39 percent of the dose to thioethers.
Stillwell et al. (1982) conducted a similar study with male Swiss mice
dosed intraperitoneally with naphthalene dissolved in corn oil at 100 or 150
mg/kg. Approximately 65 percent of the administered dose was excreted in
the urine after 24 hours and 3 percent between 24 and 48 hours. Neutral
metabolites accounted for only 4 percent of the metabolites excreted in the
urine, whereas 96 percent were excreted as conjugates with approximately 20
percent of these as glucuronides or sulfates. Three major neutral metabolites
were identified in the urine after enzyme hydrolysis; these were 1-naphthol
(I), frans-1-hydroxy-2-methylthio-1,2-dihydronaphthalene (II), and
1fj,2a-dihydroxy-1,2-dihydro-naphthalene (III). In addition, eight minor
sulfur-containing metabolites were isolated.
Most of the neutral metabolites isolated from mouse urine also were
present in rat urine, but the profiles of the urinary metabolites were quite
different for the two species. 1-Naphthol was the major neutral metabolite in
hydrolyzed urine from mice (8 to 10 percent of the dose), whereas the trans-
1,2-dihydrodiol was the major metabolite in hydrolyzed urine from rats (18 to
24 percent of the dose). In mice, the order of excretion of the five major
metabolites was l>ll>lll>1-methylthionaphthalene>2-naphthol. In rats,
the order of excretion of the four major metabolites was ll>l>2-
naphthol > 1,7-dihydroxynaphthalene (III is a minor metabolite). It was
suggested that these differences between mice and rats were associated with
differences in mono-oxygenase and epoxide hydrolase activities for each
species.
Seven acidic sulfur-containing metabolites were also identified. A
product identified as N-acetyl-S-(l-hydroxy-1,2-dihydro-2-
naphthalenyl)-cysteine was the major metabolite and accounted for 38
percent of the administered dose of naphthalene. A number of other sulfur-
containing metabolites, accounting for approximately 1 percent of the dose,
were isolated.
A variety of naphthalene metabolites also has been identified in the bile
of cannulated rats dosed i.p. (until rats became ill) with solutions of
naphthalene (75 mg), 1,2-dihydro-naphthalene (50 mg), or 1,2-epoxy-
1:2:3:4 tetrahydronaphthalene (25 mg) in 0.5 ml arachis oil (Boyland et al.,
1961). The bile of rats treated with naphthalene contained 1- and 2-
naphthol, 1-naphthylglucuronic acid, 1,2-dihydroxynaphthalene and 1-
and 2-glucuronic acid conjugates of trans naphthalene. Sulfuric esters 1,2-
dihydrodiol were not detected. In rats treated with 1,2-dihydronapthalene,
bile contained all metabolites seen upon naphthalene administration as well
as S-(1:2:3:4-tetrahydro-2-hydroxy-1-naphthyl) glutathione. Large
amounts of 2-naphthol were produced. Detection was made by paper
chromatography.
The metabolites identified in the in vivo studies are presented in Table
3-2.
3.1.3 In Vitro Metabolism
The in vitro metabolism of naphthalene has been studied by several
investigators (Booth et al., 1960; Jerina et al., 1968, 1970; Chen and Dorough,
1979; Holtzman et al., 1967a,b; Oesch and Daly, 1972; Bock et al., 1976; van
Bladeren et al., 1984, 1985; Hesse and Mezger, 1979; Hesse et al., 1982).
Jerina et al. (1970, 1968) demonstrated, in radioisotope trapping experiments
16
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Table 3-2. Naphthalene Metabolites in Urine
Metabolite Rab-
bit
1-naphthol 1>7
2-naphthot 7,7
1-naphthyl sulfate ij
1-naphthyl glucuronic acid 1,7
S-(1 -naphthyl)-L-cysteine
1-naphthyl mercapturic acid 1,7
l,2-dihydro-1,2-dihydroxy 1,7
naphthalene
l,2-dihydro-2-hydroxy- 1,7
1-naphthyl -
glucuronic acid
1,2-dihydro- 1 -hydroxy-
2-naphthyl-
glucuronic acid
N-acetyl-S-(l,2-dihydro- 1
2-hydroxy-l -naphthyl)-
L-cysteine
2-hydroxy-l-naphthyl t
sulfate
l-hydroxy-2-naphthyl z
sulfate
1 ,2-dihydroxynaphthalene
l,2-dihydro-1-hydroxy-
2-methylthiono-
naphthalene
glucuronide
1 ,2-dihydro-2-hydmxy-
1-naphthyl sulfate
1 ,4-dihydrodiol, naphthalene
1 ,7-dihydrodiol, naphthalene
2,6-dihydrodiol, naphthalene
0-methy catechol
trihydroxynaphthalene
trihydroxydihydro-
naphthalene
tetrahydroxynaphthalene
tetrahydroxytetrahydro-
naphthalene
1,2-dihydro-1-hydroxy-
2-methylthio-
naphthalene
1 -methylthiononaphthalene
S-(2-hydroxy-2- g
carboxvethylthio)cysteine
Found in:
pin Mouse Rat "af" Man
7 5,7 2,3,7 8
7 727 8
777
7 7
1,7 1,7 1.7 1
7 5,7 3,4,7
2,3,7
2
1 1,5 1,2,3
7 2
2
3
4
4
4
4
4
4
4
5
5
References: 1. Boyland and Sims (1958); 2. Bakke et a/. C7985,); 3. Chen and
Sf« (197^); 4' H°r?'"9 et al' <1980a'b): still»e" ^ al.(1978); 5. Stillwell et al.
>!of?, Kodama et al (1974>: 7- c°™er and Young (1954); and 8. Mackell et al.
(1951).
17
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and by direct isolation, the formation of 1,2-naphthalene oxide from
naphthalene following incubation with rat liver microsomes. Incubations of
rabbit liver microsomes with the oxide resulted in the formation of the trans-
dihydrodiol with a 35 to 40 percent yield (see Figure 3-2). The formation of
RS H
Glutathione conjugate
OH
Naphthalene
1,2-Dihdro-1,2-
dihydroxynaphthalene
Figure 3-2 In vitro metabolism of naphthalene. Source: Jerina et al. (1968).
small amounts of naphthol is apparently a result of a nonenzymatic
isomerization of the oxide during incubation. When the GSH-conjugating
system and GSH were added to the microsomal preparations, the GSH
conjugate increased at the expense of the other two metabolites. Thus, 1,2-
naphthalene oxide appears to be obligatory in the formation of all three
metabolites. When racemic 1,2-naphthalene oxide was incubated with
microsomes, an optically active diol identical with the diol from naphthalene
with respect to stereochemistry and source of the oxygen atom in the 2
position, was produced (Jerina et al., 1970). Inhibition of epoxide hydrase
increased the yield of naphthol at the expense of the diol. Small amounts of
2-naphthol were shown to be formed during non-enzymatic isomerization
of 1,2-naphthalene oxide. .
Similar results were reported by Chen and Dorough (1979). Formation ot
water-soluble products from the metabolism of 1-14C-naphthalene in vitro
was increased from 34 to 61 and 74 percent upon addition of 300 and 600 yg
of GSH, respectively. Buckpitt (1985) has suggested that 2-glutathione
18
-------
conjugates formed in vitro upon incubation of naphthalene with lung and liver
microsomes from mice were stereoisomers of 1-hydroxy-1 2-dihydro-
2-s-glutathionyl-naphthalene.
Holtzman et al. (1967a; 1967b) utilized i8Q-enriched air and
demonstrated that the enzymatic conversion of naphthalene to naphthalene
dihydrodiol proceeds with the incorporation of one oxygen atom from
molecular oxygen; the second oxygen atom is derived from water. The initial
attack on naphthalene occurs at the 1-position, and the product formed is
the frans-diequatorial diol as shown by nuclear magnetic resonance (NMR)
spectroscopy.
Oesch and Daly (1972) studied the in vitro metabolism of naphthalene
with liver preparations from male guinea pigs, utilizing naphthalene and 1,2-
naphthalene oxide as substrates and a variety of biochemical (metabolic
inhibitors and inducers) and radiolabel tracing techniques. They reported the
presence of a coupled monooxygenase-hydrase system in liver microsomal
preparations that catalyzes the overall conversions of naphthalene to the
dihydrodiol. Bock et al. (1976) studied the glucuronidation of naphthalene
1,2-dihydrodiol in isolated hepatocytes and liver microsomal fraction from
male Sprague-Dawley rats. Naphthalene 1,2-dihydrodiol glucuronide was a
major metabolite in hepatocytes incubated with naphthalene, NADPH
regenerating system, and UDP-glucuronic acid. In microsomes, the
glucuronide conjugate was formed only when UDP-N-acetylglucosamine,
the positive allosteric effector of UDP-glucuronyltransferase was added. The
authors suggested that the activation of UDP-glucuronyltransferase by
UDP-N-acetylglucosamine may be an important factor in the coupling of
glucuronidation to functionally linked microsomal enzyme reaction.
Strong evidence against such a coupled mechanism has recently been
presented by Jerina and colleagues (van Bladeren et al., 1984, 1985), who
showed that a more likely alternative is an enantioselectivity by epoxide
hydrolase toward the enantiomers of naphthalene-1,2-oxide formed in
different ratios by specific isozymes of cytochrome P-450. Through the
application of trapping techniques for establishing the enantiomer ratios of
metabolically formed arene oxides, it was found that cytochrome P-450b
(the major isozyme induced in rats by phenobarbital) metabolized
naphthalene predominantly to the (-)-(1S,2R) epoxide isomer (74 percent of
total), while cytochrome P-450c (the isozyme induced in rats treated with
3-methylcholanthrene) metabolized naphthalene primarily to the ( + )-
(1R.2S) epoxide isomer (73->95 percent). Epoxide hydrolase preferentially
metabolized the (+ )-naphthalene oxide to the (-)-1 R,2R-dihydrodiol. In
comparison, the (-)-(1S,2R)-naphthalene oxide was metabolized by
epoxide hydrolase to both the (-)-(1R,2R) and the ( + )-(1S,2S)-
dihydrodiols. The apparent Km for the epoxide hydrolase-mediated hydration
of ( + )-(1R,2S)-naphthalene oxide was 1 nM, while for (-)-(1S,2R)-
naphthalene oxide the apparent Km was 12 pM.
The identification of 1-napthol as an intermediate in the metabolism has
led several groups of investigations to explore further the conversion of 1-
naphthol to additional metabolites.
Hesse and Mezger (1979), using [1-i4C]-1-naphthol in a rat liver
microsomal preparation, identified covalently bound products which they
suggested might be naphthoquinones and/or naphthosemiquinones. Because
binding was not decreased by SKF-525A or 7,8-benzoflavone, they
concluded 1-naphthol metabolism was not mediated by cytochrome P450.
The studies of Doherty and Cohen (1984), using a similar protocol, found that
[1-i4C]-l-naphthol was metabolized to methanol-soluble products
19
-------
including 1,4-naphthoquinone and covalently bound species. It was
suggested that 1,4-naphthoquinone most probably was formed via
autooxidation of 1,4-dihydroxy naphthalene. Hesse et al. (1982) reported that
inhibition of glucuronidation and sulfation in isolated rat hepatocytes led to
several fold increase in covalent binding of i4C-naphthalene-derived
metabolites. Results suggested saturation of detoxification pathways may play
an important role at high levels of naphthalene.
To more fully evaluate the role of cytochrome P450, Doherty et al. (1985)
conducted additional experiments with purified P450 from hepatic
microsomes of male Wistar albino rats, that had been pretreated with sodium
phenobarbitone in drinking water for 6 days.
Incubation of [1-14C]-1-napthol in the fully reconstituted P450 system
and NADPH led to the formation of methanol-soluble products. The
predominant metabolite, identified by HPLC, was 1,4-naphthoquinone. 1,2-
naphthoquinone was not found in any significant amount. Production of 1,4-
naphthoquinone was rapid and dependent on the P450 concentration. The
apparent Km for 1-naphthol was 17 urn and in agreement with the value
previously obtained (Doherty and Cohen, 1984; Hesse and Mezger, 1979).
The metabolism was inhibited by classic P450 inhibitors: metyrapone, SKF-
525A and CO:C>2 (9:1). The apparent discrepancy with the results of Hesse
and Mezger (1979) may have been due to the higher concentration of 1-
naphthol used in the Hesse and Mezger study. When GSH, which reacts with
both 1,2- and 1,4-naphthoquinone was added, the radioactivity associated
with the HPLC peak for 1,4-naphthoquinone disappeared and new
metabolites formed. When ethylenediamine, which reacts specifically with
1,2-naphthoquinone was added, the metabolite profile was not altered.
Addition of ethylenediamine to the reaction mixture was found to signifi-
cantly inhibit covalent binding indicating that 1,2-naphthoquinone may have
been involved. Inhibition of binding was greater when GSH was used. The
authors suggested that 1,2-naphthoquinone per se may not be involved but
rather another metabolic product possessing quinone groups. Such a product
could arise from further metabolism of 1,4-naphthoquinone or 1,4-
dihydroxynaphthalene.
The in vitro metabolism of naphthalene by human lung microsomes was
investigated by Buckpitt and Bahnson (1986). Fresh lung tissue was obtained
from two elderly individuals, one of which was identified as a smoker. The
preparation from patient 1 catalyzed the metabolism of naphthalene to the
dihydrodiol and three GSH conjugates. The rate of dihydrodiol formation
nearly equalled the total rate of formation of the GSH conjugates. This
observation is consistent with that of Oesch et al. (1980) who demonstrated
high activities of epoxide hydrolase in lung microsomes. Cyclohexene oxide,
an inhibitor of dihydrodiol formation, was added to the preparation from
patient 2 and was found to shunt metabolism, as expected, to formation of the
three GSH conjugates. Addition of lung microsomes (patient 1) to a mouse
liver microsomal preparation resulted in a marked inhibition of naphthalene
metabolism. This was not seen when microsomes from patient 2 were
substituted. The existence of an inhibitor, possibly released during tissue
homogenization was hypothesized as an explanation for the inhibition
observed.
Because studies (Cohen et al.. 1983; Wilson et al., 1985) had shown that
1-naphthol has potential selective toxicity to human colonic tumor tissue,
Doherty et al. (1986) examined the peroxidase activation of 1-naphthol.
Horseradish peroxidase was incubated with [1-14C]-1-naphthol and HaOg
in the presence and absence of bovine serum albumin (BSA). The amount of
20
-------
radiolabelled material covalently bound to BSA also was assessed The
mechanism of action was evaluated by spectrophotometry and electron spin
resonance (ESR). Results indicated that 62 percent of the radiolabel was
covalently bound to protein following a 60 min incubation. GSH inhibited
binding in a dose-dependent manner. Evidence indicated that GSH acts as a
radical scavenger (napthoxy or naphthoxy-derived). In the absence of GSH
ESR studies showed that napththoxy radicals decayed extremely readily and
resulted in polymeric products and covalently bound species. At high GSH
levels, naphthoxy radicals are repaired with concomitant formation of GS
radicals. GS radicals react to form GSSG, resulting in depletion of GSH with
very little loss of 1-naphthol.
In an in-vitro system with a human colonic adenocarcinoma cell line the
MA^r,uCtlon of 1-naPntho1 was potentiated by dicoumarol, an inhibitor of
NADPH qumone reductase (Cohen et al., 1983). Wilson et al. (1985) found
that normal colon, in vitro formed significantly more 1-naphthyl sulfate than
1-naphthyl-B-D-glucuronide.
3.2 Mechanisms of Metabolite-Induced Toxicities
3.2.7 Ocular Toxicity
Ocular toxicity, particularly cataract formation, has long been associated
with naphthalene administration in rodents and other laboratory animals
lovlmS> 1930; van Heyninaen and Pirie, 1966; Lindberg, 1922; Koch et al.,
19/6}.
Oral administration of naphthalene is believed to result in its metabolism
in the liver and metabolites then travel through the bloodstream to the eye
where further metabolism takes place (van Heyningen, 1979). Evidence in rats
and rabbits suggest that 1,2-dihydroxy naphthalene is enzymatically
converted to 1,2-napthoquinone which then reacts with eye proteins
resulting in damage (Pirie and van Heyningen, 1966; Rees and Pirie, 1967;
t in©, 1968).
Van Heyningen (1979), in her review of the literature, hypothesized that
susceptibility to naphthalene-induced cataracts is more pronounced in rat
and rabbit strains with lightly pigmented or dark eyes, due to the presence of
polypnenol oxidase. This nonspecific enzyme, found only in pigmented
tissues, catalyzes the formation of melanin from tyrosine. Nagata (1984)
detected o-diphenol oxidase activity in strain ACI rats, which have
pigmented eyes but not in albino Wistar rats.
A significant increase in o-diphenol oxidase activity in the lens tissue of
naphthalene-fed rabbits also was reported by Srivastava and Nath (1969)
-, o Van Heynin9en and Pirie (1967) suggested that the toxic metabolite is
1,2-dihydroxy naphthalene. In gavage studies in which naphthalene was
administered daily to 39 rabbits at 1 gm/kg, they detected 1,2-dihydroxy
naphthalene and 1,2-naphthoquinone in the eyes and three metabolites in
blood: (1) naphthalene 1,2-dihydrodiol, (2) 1,2-dihydro-1,2-dihydroxy-
1-naphthyl glucuronic acid and (3) 2-hydroxy-1-naphthyl sulfate It was
shown that each blood-borne metabolite could be converted by a different
enzyme in the eye to 1,2-dihydroxynaphthalene. In more than half the
rabbits, lens opacities and degeneration of the retina were observed
Occasional hemorrhages of the ear and intestine were also observed In
addition, 1,2-naphthoquinone can oxidize ascorbic acid present in the
aqueous and vitreous humors, resulting in oxalic acid formation as the
ascorbic acid concentration decreases (van Heyningen, 1970a,b) Although
ascorbic acid decreases in aqueous and vitreous humors, the level is
21
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maintained or increases in the eye lens itself (van Heynigen, 1970b).
Presumably dehydroascorbic acid, formed by oxidation by naphthoquinones,
penetrates the lens and is reduced to ascorbic acid. Ascorbic acid diffuses
only slowly from the lens (Wachtl and Kinsey, 1958). Excessive depletion of
ascorbic acid may account for the appearance of calcium oxalate crysta s
(Pirie and van Heyningen, 1966). GSH appears to be maintained at high levels
in the eye lens in spite of extensive oxidative reactions (van Heyningen,
Although ocular toxicity of naphthalene is similar in both rat and rabbit,
the severity of effect may differ to some extent because of mterspecies
' evan Heyningen (1970a) found that the albino Wistar rat has only about 3
percent of the concentration of catechol reductase (an enzyme which
catalyzes the interconversion of quinones and diols) found in the rabbit lens.
The rat also has less ascorbic acid in aqueous humor than the rabbit (van
Heyningen 1979). This would result in a higher level of 1,2-naphthoqumone.
Thus polyphenol oxidase may be the most important factor in the rat eye
while catechol reductase may play a crucial role in ocular toxicity in the
Rao and Pandya (1981) reported increased lipid peroxidation in the eyes
of male albino rats administered 1 gm naphthalene daily for 10 days. Alkaline
phosphatase showed a slight increase and aniline hydroxylase activity was
not detected. Liver peroxide levels were elevated but serum lipid peroxides
were not measured. .
Lipid peroxides have been suggested as a causal factor in cataract
formation. Yamauchi et al. (1986) investigated this aspect in relation to
naphthalene. Naphthalene (1 gm/kg) in acacia oil was administered to male
Wistar rats daily for up to 18 days. GSH content in lens and serum and liver
lipid peroxide levels were measured during interim sacrifice. Serum peroxide
levels increased significantly on the 4th day and reached a maximum on the
7th day Liver peroxide levels had a similar pattern. GSH content in lenses
decreased to about 64 percent on the fourth day and remained depressed.
The authors suggested that lipid peroxides are stable enough to reach the
lens and cause ocular damage. Microscopic observation indicated slight
cataractous changes in some rats on the 14th day when serum lipid peroxide
levels were elevated (Yamauchi et al.. 1986). It was suggested that peroxides
may play a role in cataract formation, in addition to role played by 1,2-
naphthaquinone. A decrease in nonprotein sulfhydryl content in lens has
previously been associated with naphthalene-induced cataracts in rabbits
(Ikemoto and Iwata, 1978).
3.2.2 Pulmonary Tox/cfty
Various investigators have observed that i.p. administration of
naphthalene to rodents results in selective pulmonary bronchiolar epithelial
cell (Clara) necrosis, but not hepatic or renal necrosis (Tong et al., 1982;
Warren et al., 1982; Tong et al., 1981; Mahvi et al., 1977; Reid et al., 1973).
Rats and hamsters were reported to be much less sensitive than mice
(Buckpitt et al., 1984).
In an effort to determine the mechanism of action, numerous studies have
focused on the biochemistry of naphthalene and the covalent binding
characteristics of its metabolites.
Shank et al. (1980) found that mice pretreated with diethyl maleate prior
to i.p. injection of naphthalene had three times the level of covalently-bound
22
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naphthalene metabolites in lung, liver, kidney, and spleen. Studies with 14C-
naphthalene injected into mice revealed a similar binding pattern: binding was
highest in the lung but low in spleen. Increased binding corresponded to rapid
and significant depletion of GSH in lung and liver, and to a lesser extent in
kidney. Covalent binding was dose-dependent and exhibited a threshold at
dosages between 200 and 400 mg/kg. Warren et al. (1982) suggested that
lung damage may be mediated by P450 dependent metabolism and GSH
depletion.
Buckpitt and Warren (1983) extended these studies, utilizing a variety of
metabolic inhibitors. The results suggested that some of the metabolites
involved in GSH depletion and covalent binding in extrahepatic tissues
originated in the liver. In vitro studies (Buckpitt et al., 1984) with mouse liver
and lung microsomes indicated the formation of three GSH conjugates.
Evidence indicated that two conjugates are stereoisomers of 1-hydroxy-
1,2-dihydro-2-S-glutathionyl naphthalene (Buckpitt, 1985). The rates of
formation differed; conjugate 2 was predominant in lung but not liver
preparations and was considered due to P450 selectivity or epoxide
hydrolases. Buckpitt (1985) suggested that the differences in the rates of
formation between target and nontarget tissues may reflect the
stereochemistry of epoxidation by the tissue-specific P450 isozymes. This
may, in turn, relate to the selective pulmonary necrosis observed in mice.
Van Bladeren et al. (1984) found that P450 catalyses the formation of
naphthalene 1,2-oxide in a stereoselective manner (see Section 3.1.1) and
that epoxide hydrolase determines the enantiomeric composition of the 1,2-
dihydrodiols formed.
Confirmation that P450 was involved in pulmonary necrosis was obtained
in the studies of Buckpitt et al. (1986). Liver microsomes from phenobarbitol-
induced mice administered 300 mg naphthalene/kg i.p. exhibited 73 percent
less covalent binding in the presence of piperonyl butoxide, a P450 inhibitor,
than controls. A similar degree of inhibition also was observed with SKF 525A.
It was reported that piperonyl butoxide also blocked the pulmonary injury
exhibited by naphthalene in controls. Covalent binding was higher in
nontarget tissues. Differences in covalent binding between tissues were
attributed to the possibility that only some metabolites are toxicologically
active and that reactive metabolites are stable enough to circulate in the blood
(Buckpitt and Warren, 1983; Richieri and Buckpitt, 1985).
Buckpitt et al. (1985) provided evidence that 1-naphthol is not an
obligate intermediate in the covalent binding or pulmonary necrosis caused
by naphthalene. While 1-naphthol is formed at a higher rate by mouse lung
rather than liver microsomes, the rate of covalent binding after 1*C-1-
naphthol administration was not higher than that after 14C-naphthalene
administration. In addition, pulmonary necrosis was not observed after either
intraperitoneal or intravenous administration of 1-naphthol.
Naphthalene (i.p., 225/kg) was shown to reduce the activity of a number
of rat lung, but not liver, microsomal enzymes (Tong et al., 1981, 1982).
Enzymes studied included benzphetamine N-demethylase, arylhydrocarbon
hydrolyase, NADPH cytochrome c reductase, 17-ethoxyresorufin o-
deethylase, and styrene epoxide hydrolase. Inhibition ranged from 30 to 70
percent and lasted from 8 to 15 days. Changes in enzyme activity were
reported to correlate with morphologic changes in the bronchiolar epithelium.
There were no morphologic changes noted in liver tissue.
Buckpitt et al., (1986) also investigated the role of prostaglandin
synthetases in mediating the pulmonary toxicity of naphthalene. Prostaglandin
synthetases have been shown to catalyze the metabolism of aromatic
23
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hydrocarbons and dihydrodiols and detectable activities have been measured
in Clara cells, a site of naphthalene-induced toxicity. Naphthalene was
administered to phenobarbitol-induced mice at a dose of 300 mg/kg.
Indomethacin, an inhibitor of prostaglandin synthetases but not P450, was
administered both 1 hr before and 6 hr after naphthalene. In an in vitro
microsomal system containing either an NADPH-generating system or
arachidonic acid (the precursor to prostaglandin production), it was observed
that arachidonic acid failed to catalyze the formation of covalently bound
metabolites in any of the tissues studied. Indomethacin treatment of the mice
failed to protect against bronchiolar necrosis.
24
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4. Health Effects
4.1. Acute Toxicity
The acute effects of naphthalene have been studied in rats, mice, rabbits,
cats, and dogs following administration of the compound by various routes
The acute toxicity values of naphthalene for these laboratory animals are
summarized in Table 4-1. Additional information is presented in Section 3.2.
Table 4-1. Acute Toxicity Values of Naphthalene in Laboratory Animals
Lethal Concentration
Route of
Administration
Oral
Species/Sex
Rat/M
Rat/F
Rat/M
Rat/F
Ratl-b
Ratl-
MouselM
Mouse/F
Mouse/F
Catl-
Dogl-
Rabbitl-
inyi
u>50
2,009
3,310
2,200
2,400
1,780
9,430
533
710
353
1,000
400
3
ny-
LCso Reference
Mallory et al. (1985a)
Mallory et al. (1985a)
Gaines (1969)
Gaines (1969)
TDB
U.S. EPA (1980)
Shopp et al. (1984)
Shopp et al. (1984)
Plasterer et al. (1985)
TDB
TDB
TDB
Dermal Rat/M >2,500
Rat/F > 2,500
Rabbit/M > 2,000
Rabbit/F > 2,000
Gaines (1969)
Gaines (1969)
Mallory et al. (1985b)
Mallory et al. (1985b)
Inhalation
Intraperitoneal Mouse/M 380
Subcutaneous Mouse/- 969
Warren et at. (1982)
Irie et al. (1973)
aUnless otherwise noted.
bData not available.
4.1.1. Oral
The acute LD50 values of naphthalene dissolved in peanut oil for male and
female Sherman rats were 2,200 and 2,400 mg/kg, respectively (Gaines,
1969). In two other studies, the LD50 values for rats were 1,780 (Toxicology
25
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Data Bank) and 9,430 mg/kg (U.S. EPA, 1980), but the strain and sex of the
animals were not specified. For male and female CD-I m.ce, the acute oral
Rvalues of naphthalene in corn oil were 533 and 710 rng/kg respect.vely
(Shopp et al., 1984). In a recent study (unpublished) conducted by Mai ory et
al. (1985a). the acute LD50 values of naphthalene in corn oil for mate and
female Sprague-Dawley rats were reported, to be 2,009 and 3310 mg/kg
respectively. In a sub-acute study, at doses ranging from 125 to 2,000
mg/kg given daily for 8 days, an LD50 of 353 mg/kg was determined for CD-
1 mice (Plasterer et al., 1985).
Althouah cataract formation following oral administration of naphthalene
has been known for many years (Fitzhugh and Buschke, 1949), recent studies
have shown that ocular changes can result from a single dose of naphthalene^
Van Heyningen and Pirie (1967) found that lens changes developed in the
eyes of rabbits after a single dose of naphthalene (1 000 mg/kg) was
administered by gavage. In CD-1 mice, oral doses of >400 mg/kg for males
and a 600 mg/kg for females resulted in ptosis with clear, red secretions
around the eyes within 1 hr of dosing (Shopp et al., 1984).
Ikemoto and Iwata (1978) reported that oral administration of naphthalene
(1 qm/kg) to male and female albino rabbits for 2 consecutive days resulted in
cataract formation. Occurrence of cataracts was accompanied by a decrease
in sulfhydryl content in both soluble and insoluble lens protein.
4.1.2. Dermal
No deaths occurred when 2,500 mg/kg of naphthalene was applied to the
skin of male and female Sherman rats (Gaines, 1969) Theappl.cat.on of
2,000 mg naphthalene/kg (dissolved in acetone to the skin of New Zealand
white rabbits) did not cause mortality; the LD50 was > 2,000 mg/kg (Mallory et
al 1985b) This study suggests that naphthalene may not be as readily
absorbed through the skin as it is through the intestinal mucosa.
4.1.3. Inhalation
It previously had been reported that the 8-hour LC5o value for
naphthalene was 100 ppm (Union Carbide, 1968). However, Buckpitt (1985)
suggested that this value may be too low. He estimated that m 8 hours the
bod? burden would be less than 30 mg/rat, or about 150 to 200 mg/kg. This
concentration is far less than the oral or intraperitoneal LD50 values for rats
Fait and Nachreiner (1985) reported that exposure of male and female Wistar
rats to 78 ppm for 4 hr resulted in no mortalities, nor any lung, liver, kidney,
or nasal passage abnormalities. In an unpublished inhalation study with male
Swiss-Webster mice, no deaths were noted following nose-only exposures
to 90 ppm for 4 hours. However, lung lesions were reported to be prominent
(Buckpitt, 1985).
4.1.4. Intraperitoneal
The 24-hour LD50 value of naphthalene in Swiss-Webster mice was 380
(350 to 413) mg/kg following intraperitoneal injection (Warren et al., 198^;
Shank et al., 1980). All deaths occurred within 24 hours, with survivors being
observed for an additional 6 days. The target organ was identified as the
lungs (see Section 4.1.6 below). .
Tona et al (1982) found remarkable histological changes in the lungs of
C57BL/6J mice dosed intraperitoneally with naphthalene at 225 mg/kg. One
day after dosing, the Clara cells in the terminal bronchioles were pyknotic,
26
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and hypereosinophilic nuclei were apparently detaching from the bronchiolar
wall. Three days after dosing, some surfaces appeared to be completely
denuded of Clara cells, whereas other surfaces appeared to have immature
Clara cells scattered circumferentially. Five days after treatment, there was
still evidence of incomplete recovery; by 8 days, most of the terminal
bronchioles were reepithelialized; and by 15 days, mature Clara cells were
common, but recovery was evidently not complete. Similar findings had
previously been reported by Reid et al. (1973) in C57BL/6J mice dosed i D
with approximately 350 mg naphthalene/kg.
Shank et al. (1980) found that GSH plays an important role in naphthalene
toxicity. When male Swiss-Webster mice were pretreated with diethyl
maleate prior to i.p. injection of naphthalene doses ranging from 0 to 500
mg/kg, severely damaged lungs were seen in mice given 40 mg/kg. None of
the animals given 300 mg/kg survived 24 hr. In contrast, piperonyl butoxide
decreased toxicity.
See Section 3.2.2 for additional information related to pulmonary toxicitv
and metabolite formation.
4.1.5. Subcutaneous
Irie et al. (1973) studied the effects of naphthalene in mice (strain not
specified) following single subcutaneous injections at doses of 650 to 1 348
mg/kg. Vigorous tremors were noted in the mice for 3 to 4 days following
dosing. The LD50 value was calculated to be 969 (891 to 1053) mg/kg.
4.1.6. Eye Irritation
Acute ocular irritation was noted in two of six New Zealand white rabbits
receiving no postdose rinse after 24 and 48 hours of exposure to 0 1 mq
naphthalene (Mallory et al., 1985c). This response included slight iritis
moderate redness and slight swelling and discharge. All animals were normal
by 72 hours postdosing. No positive response was noted in rabbits (three)
receiving a postdose rinse.
4.1.7. Dermal Irritation and Sensitization
Naphthalene (moistened with 2 mL of acetone) was found to be slightly to
moderately irritating to the skin of male and female New Zealand white rabbits
30 to 60 minutes postdosing (Mallory et al., 1985d). Dermal irritation was still
evident up to 5 days after test material application. Fissuring of the skin was
also noted.
Naphthalene (100 percent) did not cause delayed hypersensitivity in
Hartley guinea pigs (Mallory et al., 1985e).
4.2. Subchronic Toxicity
Naphthalene toxicity has been investigated in repeated dose studies
following oral administration. Additional studies have been conducted to
determine the ocular effects of naphthalene following administration bv
various routes.
4.2.1. Oral
Shopp et al. (1984) conducted a 14-day and a 90-day study on groups
of male and female CD-1 mice administered naphthalene in corn oil by oral
27
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gavage. In the 14-day study, six groups of male and female mice (40 to
112/group) were given doses of 0 (naive), 0 (vehicle), 27, 53, or 267
mg/kg/day; the highest dose was one-half the LD50 for male mice. Male
mice demonstrated lower survival rates than females, apparently due to the
aggressive behavior of group-housed male mice; however, the mortality in
the high-dose groups of male and female mice was 5 to 10 percent higher
than the control groups. There was a significant decrease (7 to 13 percent) in
body weight in male and female mice receiving the high dose. The high-
dose males exhibited a 30 percent decrease in thymus weight, while females
exhibited a decrease in spleen weight and an increase in lung weight. Gross
pathology but not histopathology was performed. No biologically relevant
changes were noted in treated animals for hematology, clinical chemistry,
hexabarbital sleeping time, or immunotoxicity (humoral immune response,
lymphocyte responsiveness, popliteal lymph node response, and bone
marrow function).
For the 90-day study, five groups of 112 male and 112 female mice
were given doses of 0 (naive), 0 (vehicle), 5.3, 53, or 133 mg/kg/day. A
positive control for immunotoxicity received 50 mg/kg cyclophosphamide
intraperitoneally on days 87, 88, 89, and 90. The mortality seen among all
groups of male mice appeared to be due to the aggressive behavior of
group-housed male mice.
No significant effects on body weight were noted for males or females. A
significant decrease in the absolute weight of the brain, spleen, and liver was
noted for females receiving 133 mg/kg; however, organ-to-body weight
ratios were significantly different only for the spleen. Of the changes noted in
the clinical chemistry data, the increase in blood protein content in males and
females receiving 53 or 133 mg/kg, the decrease in blood urea nitrogen in all
treated female groups, and the decrease in calcium ion concentrations in
males receiving 53 or 133 mg/kg were considered to be treatment related. No
significant changes were noted in hematology, the mixed-function oxidase
activity, or immunotoxicity assays for either sex. Histopathology data were not
presented and it is not known if naphthalene caused bronchiolar lesions.
No evidence of cataract formation or hemolytic anemia was observed in
CD-1 mice. Since the CD mouse is an albino strain, cataract formation was
In a subchronic oral toxicity study performed for the NTP (1980a),
naphthalene in corn oil was administered by gavage to male and female F344
rats (10/sex/dose) at dose levels of 0, 25, 50, 100, 200 or 400 mg/kg/day, 5
day/week for 13 weeks. At 400 mg/kg, two males died during the first week
and the treatment caused diarrhea, lethargy, hunched posture and roughened
haircoats in rats of both sexes. A significant (i.e., >10%) decrease in body
weight gain was observed among males and females at 200 and 400 mg/kg
and in females at 100 mg/kg. Food consumption was not affected.
All the rats in the study were necropsied and comprehensive
histopathological examinations were performed on rats from the 0 and 400
mg/kg groups. Histopathological examinations of the kidneys and thymus
were performed on rats from the 200 mg/kg group (according to the
histopathology tables; the 100 mg/kg group according to the text). The
authors stated that lesions of the kidney in males and thymus in females of
the 400 mg/kg group may have been compound-induced, and that no eye
lesions were found. The incidences of lesions of kidney and thymus were,
however, very low. The renal lesions, which did not occur in females, were
observed at incidences of 0/10 in controls, 2/10 in the 200 mg/kg group and
1/10 in the 400 mg/kg group. These renal lesions consisted of focal cortical
28
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Hiff f H", °r,fOCal tubular generation in the two 200 mg/kg
tinn n? h tt 'ar de9eneration in »e one 400 mg/kg male. Lymphoid
deplet.on of the thymus occurred in 2/10 females of the 400 mg/kg group and
'" "6 M *he tTtr°' ?r 2°° mg/k9 females and in none <* *e male! of These
fnd hi" Hfmat°lo9'ca' analvses revealed marginal decreases in hemoglobin
and hematocrit in males and females of the 400 mg/kg group and a moderate
of^mnh1" *?e nUmb^ °f mature neutrophils andaL9creaPse ?n the ±£
of lymphocytes m males of the 400 mg/kg group, relative to controls No
hematological changes were observed at the lower dosages
In a similar ^study naphthalene was administered in corn oil by gavage at
?itJ M \?" o°° °r 20° m9'kg/day, 5 day/week, to B6C3F1 mice
fem£ nf'S pnn3 "%** (NTP' 198°b)' Seven mice one female of the 25 ma/ka group and one
control male) died durmg the 2nd, 3rd and 4th weeks of the study from
gavage trauma or accident. Transient signs of toxicity (lethargy, rough
haircoats and decreased food consumption) occurred at weeks 3 to 5 in the
w^Kh9 9H°HPS- ?''trea*ed 9rouPs °f <"a'e mice gained somewhat more
weight than did control males. Dose-related decreases in body weight oain
were seen in females but were not significant. All the mice were necropiied
and comprehensive fustopathological examinations were performed on the
mice from the 0 and 200 mg/kg groups. No compound-related lesio^werl
0rganS' includinQ kidneys- thvmus- ey^ and lungs
'
Fitzhugh and Buschke (1949) noted the formation of cataracts within 3
n^tT*! '" ^ fed dietS C°ntainin9 2 percent naphthalene or one
naphthalene derivatives. The effects of pigmentation on cataract
n- GrouPs of 15 mice were fed
ad libitum laboratory chow which had been soaked for at least 24 hr in corn
«n <:?ritaini;j9.15 or 10 mg/ml naphthalene. Feeding regimen was continued for
do^f nf •?£ !h9ff0,n I3S "Ot calculated by the authors. Concomitant
doses of 3-methylcholanthrene or p-naphthoflavone were given twice
weekly. A 6.7% incidence in cataract formation was observed in C57BL/6J
29
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mice at each dose. No cataracts were observed in DBA/2N mice All mice
treated with 3-methylcholanthrene died within 6 weeks. In addition to
cataract formation, tissue degeneration in the choroid, ciliary body, and iris
occurred.
4.3. Chronic Toxicity
A chronic inhalation study of naphthalene in mice has recently been
conducted by the National Toxicology Program (NTP, 1985). The exposure
phase of the 2-year inhalation study has been completed, but the
histopathology data and the final report are not yet available. No other chronic
toxicity data were found.
4.4. Carcinogenicity
There is only limited information available on the carcinogenic potential of
naphthalene following oral, dermal or subcutaneous administration to
laboratory animals. The results of an inhalation study in mice conducted by
the National Toxicology Program (NTP) have not yet been Published.
Histopathology is currently being evaluated. Exposure levels in this study
were 10 and 30 ppm (NTP, 1985).
Recently, Adkins et al. (1986) exposed groups of 30 female A/J strain
mice via inhalation to naphthalene at concentrations of 0, 10 or 30 ppm fa
hours a day, 5 days a week for 6 months. At the beginning of the study, the
mice were 6 to 8 weeks of age and weighed 15 to 25 g each. After the 6-
month exposure period, a pulmonary tumor bioassay was performed on
excised lungs. Naphthalene did not result in changes in tumors per mouse
but did cause a statistically significant increase (p <0.05) in the number of
adenomas per tumor-bearing mouse lung (Table 4-2). The tumors were
described as alveolar adenomas consisting of large cuboidal or columnar
epithelial cells supported by a sparse fibroblastic stroma and arranged in
poorly defined acinar structures with papillary formations. No apparent dose-
response was observed. Alveolar epithelial hyperplasia was present in lungs
of most treated mice with adenomas. This lesion was considered as a
possible precursor to adenomas. Bronchiolar epithelial hyperplasia was not
° Sescnmahl (1955) reported that naphthalene, administered in food or by i.p.
injection was not carcinogenic in rats (in-house strains BDI and BDIM).
Naphthalene was dissolved in oil and given six times weekly in food. The
daily dose was between 10 and 20 mg. After reaching a total dose of 10
am/rat (food intake was not reported), treatment was stopped and animals
observed until spontaneous death, between 700 and 800 days of age In the
i p experiments, 10 control rats were used and 10 were injected i.p. The daily
dose was 20 mg/rat. Injections were given weekly for 40 weeks. Animals were
observed until spontaneous death. Tissues were examined historically in
each experiment. It was reported that naphthalene caused no carcinogenic
effeCBoyland et al. (1964) implanted naphthalene into the bladder of stock
Chester Beatty mice (23) and followed the mice for 30 weeks. Tumor
incidence was as low as when paraffin wax was used and lower than with
cholesterol. Naphthalene was judged to be inert and to have no advantage
over cholesterol as a base for implantation pellets.
A study was conducted on carcinogenicity testing of coal tar derived
naphthalene that contained about 10 percent unidentified impurities (Knake,
1956) White rats (40, sex unspecified) were given 7 subcutaneous injections
30
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Table 4-2. rumor Incidence in Female A/J strain Mice Exposed to
Naphthalene via Inhalation for 6 Months *M>
Surviving Animals
Exposure
Level
(ppm)
0
10
30
Survivors0
29/30
27130
29/30
Total No.
of Tumors
6
10
11
Animals
with
Tumors
(%)
21
29
30
Tumors/
Moused
0.21 ±0.39
0.35 ±0.55
0.37+0.55
Tumor/
Tumor-
Bearing
Mouse
Lungd
1.00 ±0.00
1.25 ±0.07'
1.25+0.07'
aTaken from Adkins et al. (1986).
bBased on animals that survived to study termination.
^Number of survivors at end of study/number of animals at start of studv
"Mean ± SO.
'Significantly different from control (p<0.05).
of 500 mg/kg naphthalene in sesame oil at 2-week intervals
Lymphosarcomas were found in 5 of 34 surviving rats at 18 months (147
percent), whereas vehicle controls had a 2 percent incidence of these tumors
Mice (25, inbred black mice) were painted with 0.5 percent naphthalene in
benzene 5 days a week for life. Four treated mice developed leukemias in
contrast to 0 of 21 vehicle controls; the negative control incidence was 04
percent. The value of these studies for assessing carcinogenicity is very
limited because the impurities may very well be carcinogenic. The vehicle in
the mouse study has been shown to cause leukemias and the site of injection
in the rat study was painted, prior to injection, with carbofuchsin, a known
carcinogen.
Kennaway (1930) reported that naphthalene was not carcinogenic in skin
painting studies in mice. The concentration, purity, dosing regimen, and other
details were not provided. The reaction product of naphthalene and aluminum
trichloride was carcinogenic but the product was not identified.
/D Schmeltz et al- <1978) tested the carcinogenic activity of benzo(a)pyrene
(BaP) and naphthalene in female ICR/HA (Sprague-Dawley) mice. A 100-ul
test solution containing 0.25 percent naphthalene and 0.003 percent BaP was
painted on the shaved backs of 30 mice 3 times a week for 78 weeks
Naphthalene inhibited BaP-induced tumors; approximately 42 percent of the
mice had skin tumors with BaP alone, and about 20 percent had skin tumors
when naphthalene and BaP were administered together.
Naphthalene was not active in causing cellular transformation in a Fischer
rat embryo cell line at a level of 100 ng/mL (Freeman et al., 1973) or in an
AKR leukemia, virus-infected Swiss mouse embryo cell line at 5 ua/mL
(Rhim et al., 1974). a
Tsuda et al. (1980) administered a single gavage dose of 100 mg/kq
naphthalene in corn oil to a group of 10 young adult F344 rats (sex not
specified) at 12 hours after partial hepatectomy. A vehicle control group of 10
rats was included. At 2 weeks after surgery, 2-acetylaminofluorene was
added to the diet at 200 ppm to inhibit proliferation of "nonresistant"
hepatocytes. After 1 week of dietary 2-acetylaminofluorene, a single 20
ml/kg dose of carbon tetrachloride was given to necrotize "nonresistant"
31
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hepatocytes and permit proliferation of "resistant" hepatocytes. Feeding of
2-acetylaminofluorene continued for 1 week, followed by a basal diet for 1
week The rats were then sacrificed and livers were sectioned and
histochemically examined for the number and size of gamma-glutamyl
transpeptidase (QGT) positive foci. These foci contain cells that are
"resistant" to the necrotizing effects of carbon tetrachlonde and to the
proliferation-inhibiting effects of 2-acetylaminofluorene and are considered
to represent preneoplastic transformations. Neither the number nor the size of
GGT foci appeared to be increased in naphthalene-treated rats compared
with vehicle controls. The role of GGT as a biochemical market_ Of
preneoplastic foci has recently been assessed by Hendnch and Pitot (1987).
4.5. Mutagenicity
Naphthalene was reported to be nonmutagenic in Salmonella strains
TA98 A100, TA1535, and TA1537 when tested with or without S9 activation at
levels of up to 1,000 ug/plate (McCann et al., 1975). Similarly, Godek et al.
(1985) reported that naphthalene at concentrations up to 300 ng/plate was
negative in S. typhimurium strains TA1535, TA1537, TA1538 TA98, and
TA100 with or without metabolic activation. Connor et al. (1985) reported
naphthalene was not mutagenic in two DNA-repair deficient strains of^S_
typhimurium, TA100 and TA98 and two other strains UTH8414 and UTH8413
which have full DNA repair capacity, both with and without S9 activation.
Naphthalene at 250 mg/kg in corn oil did not induce micronuclei in bone
marrow of CD-1 mice (Sorg et al., 1985). This dose level was determined to
be the maximum tolerated dose in a range-finding study and is
approximately 50 percent of the oral LD50 for CD-1 mice (Shopp et al.,
1984) Barfknecht et al. (1985) reported that naphthalene at concentrations up
to 16 ug/mL (0.32 ng) did not induce unscheduled DNA synthesis in rat
hepatocytes. Concentrations greater than 16 yg/mL were found to be
extremely cytotoxic.
4.6. Teratogenicity and Reproductive Effects
In what appears to be the results of the same study (Plasterer et al.,
1985- Booth et al., 1983), single oral doses (300 mg/kg) of naphthalene were
administered daily for 8 consecutive days to 50 pregnant mice beginning on
day 7 of gestation. This dose was estimated to be at or just below the
maximum tolerated dose for acute lethality. A significant increase in maternal
lethality (p <0 05) and a decrease in mean maternal body weights as well as
the number of live pups per litter (p <0.05) on postpartum day 1 were noted
when compared to the controls. There was not a concomitant increase in
dead pups There were no effects on pup survival and mean body weights.
No gross congenital abnormalities were detected in the pups, although the
method used to examine the pups was not reported.
Hardin et al. (1981) administered naphthalene i.p. (395 mg/kg) in corn oil
to pregnant Sprague-Dawley rats on day 1 of gestation. Daily injections
continued through day 15. Treatment-related effects were reported to be
limited to evidence of maternal or fetal toxicity.
In a pilot range-finding study, 20 artificially inseminated New Zealand
white rabbits (at least 24 weeks of age and weighing 4 to 5 kg) were orally
dosed with naphthalene (in 1% methylcellulose vehicle) at 50 to 1,000 mg/kg
from gestational days (GD) 6 to 18. Maternal lethality and/or abortion were
increased at doses of 630 mg/kg or greater, but no data were collected. No
32
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differences in reproductive parameters were noted, and no malformations or
fetal death occurred at the lower dose levels (Naismith and Matthews 1985)
In the mam study by Naismith and Matthews (1986), 18 a'rtificiallv
n"fnehTfed %? Ze£la1nd11white rabbits per 9rouP were oral|y dosed with
naphthalene (1% methylcellulose vehicle) at 0, 40, 200, or 400 mg/kg from
QD 6 to 18 (age was not specified; body weights were reported but data were
incomplete). Maternal body weights and body weight gains were comparable
among all test groups and controls. Food consumption of high-dose (400
mg/kg) animals was significantly greater (p <0.05) than controls during GD 7
to 15 and significantly greater (p <0.05) than controls during GD 23 to 25 and
*'}° 29-\ Pnarmacotoxic signs observed during the study included decreased
activity, dyspnea, weight loss, cyanosis, salivation, and loose stools or
diarrhea, and occurred in an apparent dosb-related manner Gross
examination of dams and controls indicated no differences in reproductive
parameters: number of corpora lutea, total number of implantations, viable or
nonviable fetuses, pre- or postimplantation loss, fetal body weights, and fetal
sex distribution. Several malformations and variations were observed
However, they were equally distributed among groups; no dose-related
trends were apparent. The study authors concluded that oral administration of
naphthalene to pregnant rabbits did not evoke a teratogenic effect However
the teratogenic potential could not be adequately assessed because of lack of
information on the methods of fetal sacrifice and of visceral and skeletal
/nn (1982) rePorted that naphthalene administered by oral gavage
(0.015, 0.15, and 1.5 mg/kg) on a chronic basis to pregnant female albino rats
was associated with adverse effects on reproductive function and
development of progeny (English translation of complete study). The reported
threshold for effects was 0.075 mg/kg. Because of a lack of information on
££ u h SP!?' l?sts jor significance, experimental data, these reported
results should be viewed with caution until substantiated.
4.7. Neurotoxicity
No reports were found in the available literature that described any
neurotoxic effects due to naphthalene exposure except for retinal effects in
rats and rabbits, which are discussed in Section 4.4.2.
4.8. Effects on Humans
4.8. 1 Hemotoxicity
Acute hemolytic anemia is the most frequent manifestation of
naphthalene poisoning in humans. Case reports have described the
.appearance of acute hemolytic anemia after: 1) naphthalene ingestion by
children (Jacobzmer and Raybin, 1964; Athreya et al., 1961; Gross et al
1958; Zinkham and Childs, 1958; Zinkham and Childs, 1957; Haggerty 1956:
SSnH,,r«andiQlif'J95l5:lIBre9man' 1954; MacGregor, 1954; Abelson and
Henderson, 1951; Mackell et al., 1951; Zuelzer and Apt, 1949;) and adults
^ul®wicz et al- 1959- Zinkham and Childs, 1958; Zinkham and Childs
1957; Gidron and Leurer, 1956); 2) combined dermal absorption and
inhalation of naphthalene vapor by neonates (Grigor et al., 1966; Naiman and
,ol?vy> ? : alaes et al" 1963: Dawsor> et al., 1958; Cock, 1957; Schafer
1951) and adults (Younis et al., 1957); 3) inhalation of naphthalene vap,.r by
neonates (Hanssler, 1964; Irle, 1964); 4) inhalation of naphthalene vapor by a
child and adults (Linick, 1983); and 5) transplacental exposure of the fetus to
33
-------
naphthalene that had been ingested by the mother (Anziulewicz et al, 1959;
Zinkham and Childs, 1958; Zinkham and Childs, 1957). - - •- • .
The reported mechanisms and range of exposure to na phthalene nn .these
case studies were: 1) chewing, sucking, or swal lowin g of mot hb Is (one to
numerous) as a single incident or for periods up to 3 months, 2) 'ngestion of
toilet bowl deodorant cakes (pure naphthalene) by a child overa penod I of a
year; 3) ingestion of naphthalene-containing deodorant in a diaper pail for an
unspecified period; 4) combined dermal absorption and 'nhalabon for a few
days of naphthalene vapor from apparel and bed clothing hat had been
stored in mothballs; 5) inhalation of vapor from a naohthalene-conta mng
medication; 6) inhalation of naphthalene vapor for several years from
excessive numbers of mothballs kept throughout the home, and I 7)
transplacental exposure, for about 3 months, of fetuses to naphthalene
ooap were not generally reported in these case studies
because of the poorly defined nature of the exposure. Tests to detect
naphthalene derivatives in the urine of the anemic individuals were negative in
some cases (Zinkham and Childs, 1958; Cock, 1957) and positive » in others
(Athreya et al., 1961; Mackell et al., 1951; Zuelzer and Apt, 1949 . Some
reports noted the odor of naphthalene in the urine at the time of
hospitalization (Cock, 1957; Mackell et al., 1951). HI*™™*
Symptoms of naphthalene toxicity that frequently precede he diagnosis
of acute hemolytic anemia in persons of all ages include mild I to severe
jaundice, dark urine (red, orange, or port wine colored), pallor, and lethargy
(Linick, 1983; Grigor et al., 1966; Irle, 1964; Jacobziner and Raybm, 1964
Naiman and Kosoy, 1964; Anziulewicz et al., 1959; Dawson et al., 1958
ZinSam and ChiWs, 1958; Cock, 1957; Younis et al. 1957; Zinkham and
Childs 1957; Gidron and Leurer, 1956; Haggerty, 1956; Chusid and Fned
i955; Bregman, 1954; MacGregor, 1954; Abelson and Henderson, 1951
Mackell et al- 1951; Schafer, 1951; Zuelzer and Apt, 1949; Nash, 1903).
Severe jaundice is often the reason for hospitalization since the jaundice
often develops before severe anemia becomes mamfest (Valaes et al 1963).
However, it is clear that anemia and jaundice can develop in Parallel as shown
by a time-course study of hematologic changes ma 16-year-old girt who
had ingested about 6 g of naphthalene in a suicide attempt (G.dron and
Leurer9 1956). Vomiting and tachycardia are occas lonally ^served as
preclinical signs of naphthalene poisoning in persons of all ages (Linick, 198,3,
Grigor et al., 1966; Athreya, 1961; Zinkham and Childs, 1958; Dawson et aL,
1958- Younis et al 1957; Zinkham and Childs, 1957; Haggerty, 1956,
Breqman 1954; MacGregor, 1954; Abelson and Henderson, 1951; Zuelzer
and Apt, 1949). Preclinical signs of naphthalene toxicity observed primarily •in
neonates or children include anorexia, cyanosis, shallow respiration or apnea
convu lions, and diarrhea (Grigor et al., 1966; Hanssler, 1964; Jacobzmer and
RaybUi 1964; Naiman and Kosoy, 1964; Athreya et al 1961; Anziulewicz et
al ,1959; Zinkham and Childs, 1958; Cock, 1957; Zmkham and Childs, 957,
Haaqerty 1956; Chusid and Fried, 1955; Abelson and Henderson, 951
MackeJ et al., 1951; Schafer, 1951; Zuelzer and Apt, 1949)^ P/eclimcal
symptoms of naphthalene poisoning reported by children or adults include
S, confusion, pain in abdominal or kidney region, pan at urination nausea^
headkche, fainting, and vertigo (Linick, 1983; Athreya et fl-, 1961, Zinkham
and Childs, 1958; Zinkham and Childs, 1957; Youn.s et al 1957; Haggerty
1956; Gidron and Leurer, 1956; Chusid and Fned 1955; MacGregor .954
Bregman, 1954; Mackell et al., 1951; Abelson and Henderson. 1951, Zuelzer
and Apt, 1949; Nash, 1903).
34
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Frequent laboratory findings indicative of severe :hemolytic anemia after
naphthalene poisoning in persons of all ages include depressed hemoglobin
hematocrit, and erythrocyte count; elevated leukocyte and reticuloeyte counts'
erythrocyte an.socytosis, polychromatophilia, fragmentation, spherocytosis'
and microspherocytosis; and occasional hemoglobinuria (Grigor et al 1966:
Hanssler 1964; Irle, 1964; Naiman. and Kosoy, 1964; Valais et alt S
Athreya et al., 1961; Anziulewicz et al., 1959; Zinkham and Childs 195*
Dawson et al., 1958; Younis et al., 1957; Cock, 1957; Haggerty 1956 Chusid
1954: Bre9man- 1954; '
Additional laboratory findings indicative of severe hemolytic anemia after
exposure of primarily neonates or children to naphthalene include erythrocyte
poikilocytosis and microcytosis; elevated serum bilirubin; occasional
£Sf£ H °f Hem2, b°dies. nucleated erythrocytes, and Howell-Jolly
bodies, and occasional observation of methemoglobinuria (Grigor et al 1966-
Hanssler, 1964; Irle 1964; Naiman and Kosoy, 1964; Valaes et al.',' 1963,:
Athreya et a., 1961; Anziulewicz et al., 1959; Zinkham and Childs 1958:
Dawson et a 1958; Cock, 1957; Haggerty, 1956; Chusid and Fried 1955!
1949^ Bregman, 1954; Mackell et al., 1951; Zuelzer and Apt,
Many of the studies of naphthalene toxicity in neonates included tests to
determine whether Rh sensitization was a complicating factor; these tests
Kosovn°ieqR?nve, °f blotod,9roup incompatibility (Hanssler, 1964; Naiman and
SV ' la,6S et al" 1963; Athreya et al- 1961; Anziulewicz et al
959; Dawson et al., 1958; Zinkham and Childs, 1958; Cock, 1957; Haggerty'
Si Bregman' , 954: Schafer- 1951>- When investigated in some of these
studies, sickle cell anemia also was not a complicating factor except in one of
the four subjects studied by Zuelzer and Apt (1949).
aft Jn most studies of Pfsons who have developed severe hemolytic anemia
± h,XP*Sr to naPnthalene- treatment with blood transfusions! treatment
with blood transfusions plus alkali therapy, or observation without either of
*™ r t3 ?XS-has led to comPlete P^ent recovery with no observed
SSSn Si (2r',90r ettalV 1?o«: HanSSler' 1964: lrle' 1964: Jacobinzer and
Raybm 1964, Valaes et al., 1963; Athreya et al., 1961; Anziulewicz et al
1959; Dawson et al 1958; Zinkham and Childs, 1958; Cock, 1957; Younis e
Rr^m/1 iQ^" M L^Urer' 1956= Ha99ertv- 1956: Chusid and Fried, 1955;
HPnS 1Qt;i M|cGre9°r- 1954; Mackell et al., 1951; Abelson and
Henderson, 1951; Zuelzer and Apt, 1949). However, deaths have been
observed after naphthalene-induced hemolytic anemia (Schafer, 1951;
Younis et al., 1 957; Valaes et al., 1 963; Naiman and Kosoy, 1 964)
tn n Wh^OUp^ °J '"^'duals have been shown to be especially susceptible
to naphthalene-induced hemolytic anemia: v,CHuuic
1. Persons whose erythrocytes are deficient in glucose 6-phosphate
dehydrogenase (G6PDH) or persons in whom erythrocyte GSH is rapidly
£ f iQRy/?/rtain °Xidant chemicals (Gri9°r et al., 1966; Naiman and
SVV 964; Valaes et al" 1963; AtnreVa et al- 1961; Dawson et al
1958; Gross et al.. 1958; Zinkham and Childs, 1958). The prec.se
mechanism by which GSH is depleted or a deficiency of G6PDH leads to
^f r£Dnune"'nd^Ced hemo|ysis in these cases is not clear. A deficiency
of G6PDH will decrease the rate of conversion of nicotinamide adenine
^TnDu oph°uSphate fr°m its oxidized
-------
will decrease the conversion of oxidized glutathione to GSH, reduce the
rate of conjugation and excretion of naphthalene metabolites and increase
the accumulation of naphthalene metabolites in the body A similar
hvDothesis may explain increased naphthalene sensitivity in individuals in
which erythrocyte GSH can be rapidly depleted by certain ox.dant
chemicals" (Naiman and Kosoy, 1964; Kellermeyeret a 1962; Dawson et
al 1958; Gross et al., 1958; Zinkham and Childs, 1958). Gross et aL
(1958) demonstrated a quantitative correlation between G6PDH
deficiency and diminished levels of GSH in infants beyond 55 hours of
age- however, diminished levels of erythrocyte GSH were observed in
infants of less than 55 hours of age despite high levels of G6PDH activity.
A second hypothesis for increased naphthalene sensitivity in G6PDH-
deficient individuals is that the decreased availability of NADPH will in
the presence of oxidant metabolites of naphthalene, allow the
accumulation of methemoglobin and products of its further irreversible
oxidation (Kellermeyer et al., 1962).
2. Neonates (Grigor et al., 1966; Naiman and Kosoy, 1964; Valaes et al
1963- Dawson et al.. 1958; Gross et al., 1958; Zinkham and Childs, 1958).
The sensitivity of neonates to naphthalene is explained in part by the
same factors that confer sensitivity to children and adults; namely,
G6PDH deficiency and/or diminished levels of GSH as described above.
Additional naphthalene sensitivity in newborns may be conferred by the
immaturity of pathways necessary for the conjugation and excretion of
naphthalene metabolites (Valaes et al., 1963). Evidence for the latter
hypothesis is suggested by the finding that glucuronide excretion by
human newborn infants increased gradually during the first week of hfe
and that the initial levels and the rate of increase were lower ini the
premature infant than in the full-term infant (Brown and Burnett 1957).
A single report described a case of aplastic anemia in a 68 year-old
woman who had been exposed to naphthalene in the workplace (Harden and
Baetjer, 1978). The interpretation of this finding is difficult, since the woman
had been simultaneously exposed to p-dichlorobenzene.
4.8.2. Skin Sensitization
Fanburg (1940) described the case of a man who had developed an
allergic reaction to naphthalene from clothing that had been stored in
mothballs The reaction was an exfoliative dermatitis resembling mycosis
funqoides The elimination of naphthalene from the patient's environment
resulted in prompt recovery, which lasted uninterruptedly for a 7-year period
of observation.
4.8.3. Ocular Toxicity
Case studies that describe the presence of cataracts in persons exposed
to naphthalene by the oral, dermal, or inhalation routes have been
summarized in an ambient water quality criteria document for naphthalene
(US EPA 1980) Ghetti and Mariani (1956) associated the occurrence of
cataracts in 8 of 21 workers with naphthalene exposure in a manufacturing
plant. Other cases of occupational instances of cataract formation have been
described by Hollwich et al. (1975).
36
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4.8.4. Carcinogenicity
Wolf (1976) reported 6 cases of carcinomas among 15 workers exposed
to vapors of naphthalene and coal tar for 7-32 years at a coal-tar
naphthalene production facility. Four of the workers developed carcinomas of
the larynx and all were smokers; the other two developed carcinomas of the
pylorus and cecum. There was no control group. Experiments in animals
however, suggest that coal tar fractions with boiling points higher than 270°C
contain most of the carcinogenic activity of the coal tar, and fractions with
lower boiling points, which include naphthalene, are generally not
carcinogenic (Kennaway, 1930).
37
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-------
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