Toxicity Profiles

RAGs A Format for 1,4-Dichlorobenzene - CAS Number 106467

1,4-Dichlorobenzene is a chemical used to control moths, molds, and mildew and to deodorize restrooms and waste containers. Other names include Paramoth, Para crystals, and Paracide, reflecting its widespread use to kill moths. At room temperature, 1,4-dichlorobenzene is a white solid with a strong, pungent odor. When exposed to air, it slowly changes from a solid to a vapor. The vapor acts as a deodorizer or insect killer. The odor, which is present at even low levels, is the smell of mothballs. Most 1,4-dichlorobenzene in the environment comes from its use in moth repellent products and in toilet deodorizer blocks.

There is no evidence that moderate use of common household products that contain 1,4-dichlorobenzene will result in harmful effects to humanr health. Harmful effects, however, may occur from high exposures. Very high usage of 1,4-dichlorobenzene products in the home can result in dizziness, headaches, and liver problems. Some of the patients who developed these symptoms had been using the products for months or even years after they first began to feel ill. Workers breathing high levels of 1,4-dichlorobenzene (1,000 times more than levels in deodorized rooms) have reported painful irritation of the nose and eyes. There are cases of people who have eaten 1,4-dichlorobenzene products regularly for months to years because of its sweet taste; these people had skin blotches and lower numbers of red blood cells. 1,4-Dichlorobenzene is primarily absorbed via inhalation and ingestion.

No epidemiologic studies or case reports addressing the carcinogenicity of 1,4-dichlorobenzene in humans were available. In a 2-year study, female rats and male and female mice were gavaged with 1,4-dichlorobenzene. The following tumors were described as being present in the animals: renal tubular adenocarcinomas, mononuclear cell leukemia, hepatocellular carcinomas, and hepatocellular adenomas. These findings resulted in a speculation that 1,4-dichlorobenzene was acting as a tumor promotor for liver tumors in male and female mice. This substance has not undergone a complete evaluation and determination under US EPA's IRIS program for evidence of human carcinogenic potential. However, The Department of Health and Human Services (DHHS) has determined that 1,4-dichlorobenzene may reasonably be anticipated to be a carcinogen. There is no direct evidence that p-DCB can cause cancer in humans; however, animals given very high levels in water developed liver and kidney tumors.

The following is a presentation of the toxicity information associated with 1,4-Dichlorobenzene.

Noncarcinogenic Health Effects

• The Inhalation Chronic Reference Concentration is 8.00E-01 (mg/m³).
• The Inhalation Chronic Reference Concentration has a modifying factor of 1.
• The Inhalation Chronic Reference Concentration has an uncertainty factor of 100.
• The Inhalation Chronic Reference Concentration is based on the Chlorobenzene Producers Assn. study from 1986.
• The Inhalation Chronic Reference Concentration study target organ is liver.
• The Inhalation Chronic Reference Concentration study critical effect is increased weight in females.
• The overall confidence in the Inhalation Chronic Reference Concentration is medium.

Carcinogenic Health Effects

• The Oral Slope Factor is 2.40E-02 (mg/kg-day)^-1.
• The Oral Slope Factor study target organ is liver.
• The Oral Slope Factor study cancer type is tumors.
• The Oral Slope Factor is based on the U.S. EPA study from 1987.
• The Dermal Slope Factor is 2.67E-02 (mg/kg-day)^-1.
• The Dermal Slope Factor is based on a gastrointestinal absorption factor of 0.9000.