Toxicity Profiles

RAGs A Format for Naphthalene - CAS Number 91203

Naphthalene is a white solid that is found naturally in fossil fuels and that exhibits a typical mothball odor. Naphthalene is a polycyclic aromatic hydrocarbon composed of two fused benzene rings. Burning tobacco or wood produces naphthalene. It occurs in crude oil, from which it may be recovered directly as white flakes; it can also be isolated from cracked petroleum, coke-oven emissions, or from high-temperature carbonization of bituminous coal. The major products made from naphthalene are moth repellents. It is also used for making dyes, resins, leather, tanning agents, and the insecticide carbaryl.

Naphthalene can be absorbed by the oral, inhalation, and dermal routes of exposure and can cross the placenta in amounts sufficient to cause fetal toxicity. Exposure to large amounts of naphthalene may damage or destroy some red blood cells, causing a low level until the body replaces the destroyed cells. People, particularly children, have developed this problem after eating naphthalene-containing mothballs or deodorant blocks. Some of the symptoms of this problem are fatigue, lack of appetite, restlessness, and pale skin. Exposure to large amounts of naphthalene may also cause neurotoxic effects (confusion, lethargy, listlessness, vertigo), gastrointestinal distress, hepatic effects (jaundice, hepatomegaly, elevated serum enzyme levels), renal effects, and ocular effects (cataracts, optical atrophy). The estimated lethal dose of naphthalene is 5-15 g for adults and 2-3 g for children. Animals sometimes develop cloudiness in their eyes after swallowing naphthalene. It is not clear if this also develops in people. When mice were repeatedly exposed to naphthalene vapors for 2 years, their noses and lungs became inflamed and irritated.

Available cancer bioassays were insufficient to assess the carcinogenicity of naphthalene. Using the EPA's 1996 Proposed Guidelines for Carcinogen Risk Assessment, the human carcinogenic potential of naphthalene via the oral or inhalation routes "cannot be determined" at this time based on human and animal data. However, there is suggestive evidence (observations of benign respiratory tumors and one carcinoma in female mice only exposed to naphthalene by inhalation) that naphthalene may cause cancer. Additional support includes increase in respiratory tumors associated with exposure to 1-methylnaphthalene.

The following is a presentation of the toxicity information associated with Naphthalene.

Noncarcinogenic Health Effects
  • The Oral Chronic Reference Dose is 2.00E-02 (mg/kg-day).
  • The Oral Chronic Reference Dose has a modifying factor of 1.
  • The Oral Chronic Reference Dose has an uncertainty factor of 3000.
  • The Oral Chronic Reference Dose is based on the BCL study from 1980.
  • The Oral Chronic Reference Dose study critical effect is decreased mean terminal body weights in males.
  • The overall confidence in the Oral Chronic Reference Dose is low.

  • The Inhalation Chronic Reference Concentration is 3.00E-03 (mg/m3).
  • The Inhalation Chronic Reference Concentration has a modifying factor of 1.
  • The Inhalation Chronic Reference Concentration has an uncertainty factor of 3000.
  • The Inhalation Chronic Reference Concentration is based on the NTP study from 1992.
  • The Inhalation Chronic Reference Concentration study target organ is nasal.
  • The Inhalation Chronic Reference Concentration study critical effect is hyperplasia and metaplasia in respiratory & olfactory epithelium.
  • The overall confidence in the Inhalation Chronic Reference Concentration is medium.

  • The Dermal Chronic Reference Dose is 1.60E-02 (mg/kg-day).
  • The Dermal Chronic Reference Dose is based on a gastrointestinal absorption factor of 0.8000.