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Description of key information

The oral LD50 values in male and female rats were 2200 and 2400 mg/kg (Gaines 1969) and 2600 in a study that did not differentiate by sex. LD50 values in male and female mice were 533 and 710 mg/kg, respectively (Shopp et al. 1984).  Exposure to 77 ppm naphthalene for 4 hours by the inhalation route did not cause any deaths in rats. The LC50 for naphthalene vapour in Wistar albino rats is greater than 77.7 ppm, (0.4 mg/L) naphthalene (Fait 1985). No treatment-related deaths occurred within the 14-day observation period when naphthalene was applied at 2500 mg/kg to the skin of male and female rats (Gaines 1969) or when doses of up to 16,000 mg/kg were applied to the skin of male and female Sprague-Dawley rats for 24 hours (Korte 1980).

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records
Reference
Endpoint:
acute toxicity: oral
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1984
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well documented study performed equivalent to OECD guideline.
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 401 (Acute Oral Toxicity)
Deviations:
yes
Remarks:
Acclimatisation period of test animals only 4 days instead of at least 5 days.
GLP compliance:
not specified
Test type:
standard acute method
Limit test:
no
Species:
mouse
Strain:
other: CD-1 ICR
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories, Wilmington, Mass.
- Age at study initiation: 6 weeks
- Housing: in plastic cages with hardwood bedding (PWI Hardwood Sawdust, Lowville, N.Y.)
- Diet (e.g. ad libitum): Purina Rodent Chow No. 5001 (Ralston Purina Co., St. Louis, MO.) ad libitum
- Water (e.g. ad libitum): deionised water ad libitum
- Acclimation period: 4 days
- Fasting period: Mice were fasted for 18 hr prior to oral dosing, with food being returned 1 hr after dosing.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21-24°C
- Humidity (%): 40-60%.
- Photoperiod (hrs dark / hrs light): light-dark cycle was maintained on 12-hr intervals
Route of administration:
oral: gavage
Vehicle:
corn oil
Details on oral exposure:
PREPARATION OF DOSING SOLUTIONS:
A corn oil (Mazola Pure Corn Oil, Best Food, Englewood Cliffs, N.J., Lot No. 6-0729) suspension of naphthalene was prepared daily and stirred continuously during dosing

VEHICLE
- Concentration in vehicle: Concentrations of the corn oil-naphthalene suspension were prepared such that all doses could be delivered in a volume of I0 ml/kg body wt.
- Vehicle: Mazola Pure Corn Oil, Best Food, Englewood Cliffs, N.J.
- Lot/batch no. (if required): Lot No. 6-0729
- Purity: pure
Doses:
Five dose levels (200, 400, 600, 800, 1000 mgjkg) were employed to determine the acute oral LD50.
No. of animals per sex per dose:
8
Control animals:
yes
Details on study design:
- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: The mice were continuously observed for 1 hr after dosing, hourly for the next 4 hr, and then twice each day for the next 14 days.
- Necropsy of survivors performed: yes All mice that died during the observation period and those that survived the 14-day period were necropsied.
Statistics:
All mice that died during the observation period and those that survived the 14-day period were necropsied. The LDIO, LDSO, and LD90 were computed for each sex by the Log Probit Analysis as described by Finney (1971).
Sex:
female
Dose descriptor:
LD50
Effect level:
710 mg/kg bw
Based on:
test mat.
95% CL:
> 584 - < 827
Sex:
male
Dose descriptor:
LD50
Effect level:
533 mg/kg bw
Based on:
test mat.
95% CL:
> 397 - < 659
Mortality:
The majority of the naphthalene-associated deaths occurred within the first 5 hr after dosing, and all deaths occurred within the first 5 days.
Clinical signs:
With the exception of the low dose mice (200 mg/kg in males and 400 mg/kg in females) all mice developed ptosis with clear red secretions around the eye within 1 hr after dosing. Death followed depressed breathing and ataxia.
Interpretation of results:
Toxicity Category IV
Remarks:
Migrated information Criteria used for interpretation of results: EU
Conclusions:
Naphthalene did not induce haemolytic anaemia or cataract formation in CD 1 mice at the dosage levels employed. Male CD-1 mice (LD50 533 mg/kg body weight) are more susceptible to naphthalene than females (710 mg/kg body weight).
Executive summary:

An interesting finding in these studies was the lack of either naphthalene induced haemolytic anaemia or cataract formation in CD 1 mice at the dosage levels employed. Both these pathological lesions have been associated with human exposure to naphthalene.The acute toxicity data reported indicate that male CD-1 mice are more susceptible to naphthalene than females. Since little is known about the mechanisms associated with the acute toxicity of this compound, including whether the toxicity is associated with the parent compound or a metabolite, an understanding of the mechanisms responsible for the sex differences must await further investigation.

Naphthalene appears to be more toxic in mice when administered orally than parenterally.

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
LD50
Value:
533 mg/kg bw
Quality of whole database:
acceptable for assessment

Acute toxicity: via inhalation route

Link to relevant study records
Reference
Endpoint:
acute toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1985
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP study according to OECD guideline.
Qualifier:
according to
Guideline:
other: EPA TSCA
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 403 (Acute Inhalation Toxicity)
Deviations:
yes
Remarks:
: A limit test was performed but the highest achievable concentration was approximately 0.4 mg/L rather than 2 mg/L.
Qualifier:
equivalent or similar to
Guideline:
EPA OPPTS 870.1300 (Acute inhalation toxicity)
GLP compliance:
yes
Test type:
standard acute method
Limit test:
yes
Species:
rat
Strain:
Wistar
Sex:
male/female
Details on test animals and environmental conditions:
NAME:
- Name: Hilltop-Wistar Albino rats, (HLA(WI)BR

SOURCE:
- Age at study initiation: Male 48 days, female 62 days
- Weight at study initiation: Males 269 – 290, Females 240 - 265
- Fasting period before study: None
- Housing: 2 to 3 per sex
- Diet (e.g. ad libitum): ad libitum, except during exposure
- Water (e.g. ad libitum): ad libitum, except during exposure
- Acclimation period: 8 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 – 22°C
- Humidity (%): 30 – 44%
- Air changes (per hr):
- Photoperiod (hrs dark / hrs light): 12/ dark/12light

IN-LIFE DATES:
- From: To: 2/13/1985 to 2/27/1985 (day of exposure to death)
Route of administration:
inhalation: vapour
Type of inhalation exposure:
whole body
Vehicle:
other: Air, filtered compressed
Details on inhalation exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION:
- Exposure apparatus: Naphthalene was generated using a Compact Tube Furnace. Seven ampoules containing a known amount of naphthalene were placed in the furnace tube at overlapping times and heated at a mean temperature of 101±4°C. Filtered compressed air was passed through a desiccant prior to entering the furnace tube. This air then entered the chamber holding the animals. The resulting chamber airflow rate was 25 litres per minute
- Exposure chamber volume: 120 L
- Method of holding animals in test chamber: Individually housed in 21 x 12.5x 18 cm stainless steel wire-mesh cages held in a cuboidal Plexiglas chamber
- Source and rate of air: 25 L/minute
- Method of conditioning air: Filtered compressed air passed through a desiccant prior to entering furnace tube.
- Treatment of exhaust air: None
- Temperature, humidity, pressure in air chamber: Temperature 24°C, Humidity 49%

TEST ATMOSPHERE:
- Brief description of analytical method used: Perkin-ElmerSigma 2000 gas chromatograph (GC) with flame ionization detector. Column 10% SP 2100 on 80/100 Suplecoport. Column temperature 180°C. Carrier nitrogen with hydrogen and air.
- Samples taken from breathing zone: yes

VEHICLE (if applicable):
- Composition of vehicle (if applicable): Not applicable
- Concentration of test material in vehicle (if applicable): Not applicable
- Justification of choice of vehicle: Not applicable
- Lot/batch no. (if required): Not applicable
- Purity: Not applicable

CLASS METHOD (if applicable)
- Rationale for the selection of the starting concentration: Highest achievable vapour concentration
Analytical verification of test atmosphere concentrations:
yes
Remarks:
every 30 minutes. Perkin-ElmerSigma 2000 gas chromatograph (GC) with flame ionization detector. Column 10% SP 2100 on 80/100 Suplecoport. Column temperature 180°C. Carrier nitrogen with hydrogen and air.
Duration of exposure:
4 h
Concentrations:
77.7 ppm, ~ 0.4 mg/L (highest concentration technically achievable)
No. of animals per sex per dose:
5
Control animals:
no
Details on study design:
- Duration of observation period following administration: 14 days (or other?) 14 days
- Frequency of observations and weighing: Clinical prior to exposure, during exposure and daily for 14 days: Weekly weights
- Necropsy of survivors performed: yes
- Other examinations performed: clinical signs, body weight, organ weights, histopathology, other: Clinical signs, body weights, gross pathology.
Statistics:
Mean and standard deviations for body weights, body weight changes, exposure concentrations, temperature and humidity.
Sex:
male/female
Dose descriptor:
LC50
Effect level:
> 77.7 ppm
Based on:
other: 100% naphthalene
Exp. duration:
4 h
Remarks on result:
other: Clinical signs observed on the day of exposure included closed eyes, lacrimation and mouth breathing.
Sex:
male/female
Dose descriptor:
LC50
Effect level:
> 0.4 mg/L air (analytical)
Based on:
other: 100% naphthalene
Exp. duration:
4 h
Remarks on result:
other: Clinical signs observed on the day of exposure included closed eyes, lacrimation and mouth breathing.
Sex:
male/female
Dose descriptor:
LC0
Effect level:
77.7 ppm
Based on:
test mat.
Exp. duration:
4 h
Mortality:
No effect
Clinical signs:
other: Clinical signs observed on the day of exposure included closed eyes, lacrimation and mouth breathing. No effects on post-treatment day 7 or 14.
Body weight:
No effect
Gross pathology:
No effect
Interpretation of results:
other: The toxicity category cannot be determined because the highest achievable dose was 0.4 mg/L.
Remarks:
Criteria used for interpretation of results: expert judgment
Conclusions:
Not toxic at highest attainable concentration of 0.4 mg/L.
Executive summary:

A single four-hour exposure of 77.7 ppm of naphthalene produced no mortality. Clinical signs observed for both sexes during the exposure period included signs of ocular and respiratory irritation. There were no clinical signs observed following the exposure or during the 14-day post-exposure period. Body weight gains were observed for all animals except for one female on post-exposure day seven considered to be non-treatment related. No exposure-related gross pathologic lesions were observed at necropsy. The results of this study indicate that the LC50 for naphthalene vapour in Wistar albino rats is greater than 77.7 ppm, (0.4 mg/L) naphthalene. The 77.7 ppm concentration was the highest naphthalene vapour concentration obtainable under the conditions of the study.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Quality of whole database:
acceptable for assessment / note: LC50 > 400 mg/m3 = maximum concentration technically achievable.

Acute toxicity: via dermal route

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
discriminating dose
Value:
2 000 mg/kg bw
Quality of whole database:
acceptable for assessment, performed under more stringent conditions than required (no removal of excess test substance after 24h exposure).

Additional information

The following discussion is partly quoted from the "Toxicological Profile for Naphthalene, 1 -Methylnaphthalene and 2 -Methylnaphthalene" published by U.S. Department of Health and Human Services (Public Health Service), Agency for Toxic Substances and Disease Registry (ASTR) in 2005 [ATSDR 2005] and the EU Risk Assessment Report on naphthalene [ECB 2003]

Acute oral exposure to naphthalene causes haemolytic anaemia, which may be fatal. Individuals deficient in G-6-PD are more susceptible to the effects of naphthalene. There is little quantitative information available, although severe haemolytic anaemia, which may have proved lethal in the absence of clinical intervention, was reported in a female who had ingested naphthalene. Death has been documented in humans who intentionally ingested naphthalene. A 17-year-old male died 5 days after the ingestion of an unknown quantity of naphthalene mothballs. Death was preceded by vomiting, evidence of gastrointestinal bleeding, blood-tinged urine, and coma. A 30-year-old female died following similar sequelae 5 days after reportedly swallowing 40 mothballs (25 were recovered intact from the stomach upon autopsy). Several animal studies have been conducted to estimate lethal doses of naphthalene. A series of well-conducted, unpublished acute toxicity limit tests were available in which groups of 5 male and 5 female Sprague-Dawley rats were treated with 2000 mg/kg naphthalene (Hazleton 1990a,b,c: c not shown). Over a 14-day period of observation 2 deaths occurred in a total of 30 animals. Diarrhoea was reported in 17 of the 30 animals on days two to nine. No macroscopic changes were observed. An oral LD50 of greater than 2000 mg/kg for rats is therefore indicated. The oral LD50values in male and female rats were 2200 and 2400 mg/kg, respectively, in another study (Gaines 1969), and 2600 in a third study that did not differentiate by sex. LD50values in male and female mice were 533 and 710 mg/kg, respectively. It can be concluded, that naphthalene is of low toxicity in rats, with mice being more sensitive. However, studies in animal models (mainly rats, mice and rabbits) have indicated that the toxic effects of naphthalene seen in these species are different from those in humans. Of the species studied, only dogs (in a poorly conducted study) demonstrated naphthalene-induced haemolytic anaemia. It appears that rodents are not suitable animal models for the acutely toxic human health effects of naphthalene in relation to haemolytic anaemia. Thus, while the LD50results from the rat suggest relatively low acute toxicity in this species, the available information in humans indicates significant toxicity (for human toxicity: see 7.10.3).

There is no information on the effects of naphthalene following acute inhalation in humans. Exposure to 77 ppm naphthalene for 4 hours did not cause any deaths in rats. In addition, no definitive adverse clinical signs were observed during the 14 days after exposure, and no gross pathologic lesions were observed at necropsy.The results of this study indicate that the LC50 for naphthalene vapor in Wistar albino rats is greater than 77.7 ppm, (0.4 mg/L) naphthalene. The 77.7 ppm concentration was the highest naphthalene vapor concentration obtainable under the conditions of the study (Fait 1985). A high background mortality in the male control group precluded drawing conclusions regarding the effects of lifetime exposures to 10 and 30 ppm naphthalene (6 hours/day, 5 days/week) on lifetime mortality; no apparent effects on mortality occurred in the females (NTP 1992a). Similarly, exposure of male and female rats to 10, 30, or 60 ppm naphthalene (6 hours/day, 5 days/week) for 2 years did not affect survival, compared to controls (NTP 2000). It can be concluded that short-term inhalation of saturated naphthalene atmosphere (approximately 80 ppm) is not acutely toxic.

There is no information on the effects of naphthalene following acute dermal exposure in humans. Two cases of haemolytic anemia were observed in infants exposed to naphthalene-treated diapers. One case was fatal. Jaundice, methaemoglobinemia, haemolysis, and cyanosis were noted. In the fatal case the symptoms persisted, even after the naphthalene-containing diapers were no longer used. The author suggested that use of baby oil on the infant's skin might have facilitated the naphthalene absorption. No treatment-related deaths occurred within the 14-day observation period when naphthalene was applied at 2500 mg/kg to the skin of male and female rats (Gaines 1969) or when doses of up to 16,000 mg/kg were applied to the skin of male and female Sprague-Dawley rats for 24 hours (Korte 1980). There were also no deaths in New Zealand White rabbits after application of 2000 mg/kg naphthalene to intact and abraded shaved areas of skin in an LD50study.

[ECB 2003] European Union Risk Assessment Report NAPHTHALENE [CAS No: 91-20-3; EINECS No: 202-049-5] RISK ASSESSMENT European Communities, 2003

[http://ecb.jrc.ec.europa.eu/esis/]

[ATSDR 2005] Toxicological Profile for Naphthalene, 1-Methylnaphthalene, and 2-Methylnaphthalene No. 67, Agency for Toxic Substances and Disease Registry (ATSDR), Atlanta, Georgia 30333; U.S. Dep. Health & Human Services [http://www.atsdr.cdc.gov]


Justification for selection of acute toxicity – oral endpoint
Test performed with mice which proved to respond more sensitively to naphthalene than rats, moreover, endpoints, haemolytic anaemia and cataract, were included in pathologic examination.

Justification for selection of acute toxicity – inhalation endpoint
Only valid study available for this endpoint.

Justification for classification or non-classification

Naphthalene is classified as "harmful if swallowed", and there is no need for further classification regarding oral toxicity. The LC0 value for inhalation (0.4 mg/l) cannot be used for classification, as this value was the maximally achievable concentration in air, and the theoretical acute LC50 is considered to be much higher. Even a 2-years chronic exposure to a concentration of 60 ppm did not affect survival of rats compared to the control. Therefore, naphthalene is not classified as toxic regarding inhalation. All LD50values for dermal exposure with naphthalene exceed the threshold value of 2000 mg/kg body weight for classification.