Is Naphthalene safe in indoor air?

Naphthalene is classified as a possible human carcinogen (IARC Group 2B) and by the U.S. EPA as a Group C, possible human carcinogen, with chronic exposure associated with respiratory tract lesions and tumors in animal studies.

Why here

Naphthalene is a common indoor air pollutant emitted from sources such as mothballs, cigarette smoke, combustion byproducts, and various consumer products, making inhalation a primary exposure route.

What would have to be true

Indoor air concentrations are typically below 10 μg/m³, but can reach up to 300 μg/m³ in environments with new construction, furnishing materials, or certain disinfectants, and over 100 μg/m³ in homes using mothballs. The U.S. EPA's draft inhalation cancer unit risk estimate of 1 × 10⁻⁴ per µg m⁻³ suggests a chronic inhalation concentration of 0.01 μg m⁻³ corresponds to a 10⁻⁶ cancer risk.

Inhalation exposure to naphthalene in indoor air can cause respiratory irritation, headache, and nausea.

Why here

Naphthalene is a volatile organic compound (VOC) commonly found in indoor air, with a distinct 'mothball-like' odor that can be detected at low concentrations.

What would have to be true

Indoor exposures are often noted by odor, which can be detected at levels as low as 1 μg/m³. Irritation of the eyes, nose, or throat may occur at levels of 15,000 ppbv (approximately 79,000 µg/m³). The U.S. EPA has set a chronic reference concentration (RfC) of 3 µg/m³ for non-cancer effects, based on nasal effects observed in animal studies.

Inhalation exposure to high levels of naphthalene can damage or destroy red blood cells, leading to hemolytic anemia, particularly in infants and individuals with glucose-6-phosphate dehydrogenase (G-6-PD) deficiency.

Why here

Naphthalene can be released into indoor air from sources like mothballs, and infants have developed hemolytic anemia following inhalation exposure to items stored with naphthalene.

What would have to be true

Hemolytic anemia has been reported in infants following inhalation exposure to clothing, blankets, linens, or diapers stored in or around naphthalene. People with G-6-PD deficiency are at greater risk.

Children exposed to high levels of naphthalene in indoor air are at increased risk for chromosomal aberrations (CAs), including translocations, which have been previously associated with cancer.

Why here

Naphthalene is a common indoor air pollutant, with mothballs being a significant source, and some families use them as air fresheners, leading to potential exposure in children.

What would have to be true

This risk is associated with high levels of naphthalene exposure in children, indicated by elevated levels of its metabolites (1- and 2-naphthol) in urine samples. A doubling of these metabolite levels was linked to a 1.55 to 1.92 times higher frequency of translocations.

Inhalation of naphthalene is classified as possibly carcinogenic to humans (IARC Group 2B) and reasonably anticipated to be a human carcinogen (NTP), based on sufficient evidence from animal studies showing increased incidence of nasal and lung tumors.

Why here

Naphthalene is a volatile organic compound that can be inhaled from various indoor and outdoor sources, including mothballs, tobacco smoke, and combustion byproducts.

What would have to be true

Chronic inhalation exposure, with animal studies showing effects at concentrations as low as 10 ppm. The EPA has a reference concentration (RfC) of 3 μg/m3 for non-cancer effects on nervous and respiratory systems.

The other side

The International Agency for Research on Cancer (IARC) notes inadequate evidence for carcinogenicity in humans.

Inhalation of naphthalene can cause acute intravascular hemolysis, particularly in individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency, leading to hemolytic anemia, jaundice, and potential renal and hepatic dysfunction. Infants are more susceptible to these effects.

Why here

Naphthalene is readily absorbed into the systemic circulation following inhalation. Its metabolites produce oxidative stress, leading to hemoglobin oxidation and red blood cell hemolysis.

What would have to be true

Acute or chronic inhalation of naphthalene vapors. Case reports indicate illness from extensive use of mothballs in indoor environments.

Inhalation of naphthalene vapors can cause irritation to the eyes, nose, and throat, as well as neurological symptoms such as headache, confusion, nausea, vomiting, dizziness, and malaise.

Why here

Naphthalene is a volatile compound with a low odor threshold, and its vapors directly contact the respiratory tract and eyes upon inhalation.

What would have to be true

Acute or sub-chronic inhalation exposure. Symptoms can occur at levels above the odor threshold (e.g., 40 ppbv for smell, 15,000 ppbv for irritation).