Why the chemical is of concern:
Naphthalene is an organic compound found in coal, petroleum and related products such as creosote and asphalt. Naphthalene exposure has been shown to lead to hemolytic anemia in humans, a condition in which red blood cells break down and die prematurely (see here, here and here). High levels of exposure can also cause nausea, vomiting, headaches, dizziness, diarrhea, blood in the urine and yellowing of the skin (jaundice). Ingestion of naphthalene likely causes liver and kidney damage. Other hazards include eye irritation and cataracts.
Animal studies have shown an increased incidence of lung and nasal tumors, as well as eye injuries resulting in cataracts. A few case studies suggest that the latter effect may also occur in humans, but this has not been substantiated in formal epidemiological studies. Naphthalene is carcinogenic in animal studies, and has been classified as possibly carcinogenic to humans by the International Agency for Research on Cancer (IARC) and as reasonably anticipated to be a human carcinogen by the Environmental Protection Agency (EPA).
Workers employed in the coal-tar, wood preservation, tanning, ink and fabric dying industries may be exposed to high levels of naphthalene in the workplace.
In the human body, naphthalene is metabolized to form several compounds, including 1- and 2- naphthol and naphthoquinones which are themselves toxic. These metabolites can cause methemoglobinemia (an abnormal build-up of hemoglobin). Reaction of naphthalene metabolites with sulfate or glucuronic acid – termed conjugation – aids in their excretion. Newborns are unable to conjugate naphthalene, however, and are thus more susceptible to napthalene toxicity.
Children have exhibited hemolytic anemia after ingesting mothballs or using fabrics treated with naphthalene insecticides. Pregnant women, through their own exposure, may also pass naphthalene to their unborn children. Naphthalene can move from the mother’s blood into the unborn baby’s, and can also be transferred through breastfeeding. In one case study, a woman inhaled fumes from mothballs while pregnant. She and her newborn child exhibited symptoms of hemolytic anemia and methemoglobinemia, and in treating the infant a double-volume blood transfusion was required.
In a case study of 21 newborns in Greece, naphthalene exposure was linked to hemolytic anemia, jaundice and kernicterus, a severe, potentially fatal jaundice-related syndrome producing neurological effects (also see here). Twelve of the newborns in the study were deficient for the enzyme glucose-6-phosphate dehydrogenase (G-6-PD), while the remaining nine infants had normal enzyme levels. This enzyme deficiency is genetically inherited and affects the body’s ability to break down and excrete naphthalene and its metabolites.
Individuals with the G-6-PD deficiency are at a greater risk of developing hemolytic anemia. The frequency of the G-6-PD deficiency varies across different populations, placing some at higher risk for naphthalene-induced illness. This enzyme deficiency is more common in African-Americans and people of Middle Eastern or Mediterranean descent. In a cohort study of 500 African American newborns, G-6-PD deficiency was found in 12.8% of the infants. The G-6-PD deficient infants in this study had a higher occurrence of hemolysis and jaundice, and required higher levels of treatment, than infants without the enzyme deficiency.
Naphthalene is released into the environment from industrial and domestic sources. The chemical partially dissolves in water, and binds weakly to soil. It may evaporate from the surface of bodies of water, or be broken down by aquatic bacteria. In the atmosphere, naphthalene breaks down from moisture and sunlight, usually within one day.
Where the chemical is found:
As noted earlier, naphthalene is found naturally in fossil fuels like coal and petroleum (crude oil). The burning of fossil fuels and wood releases naphthalene into the air, and as a result, naphthalene is a common pollutant found in urban air. It is also the single most abundant compound found in coal tar.
Naphthalene is used in the synthesis of several chemicals, including phthalate plasticizers, dyes, resins, and synthetic leather tanning agents. It is commonly used in industry as a starting material in the manufacture of synthetic plastics, including polyvinyl chloride (PVC) plastics. Naphthalene is used in toilet deodorant blocks, household and automobile products, and as a repellant in moth balls and moth flakes. Naphthalene is present in cigarette smoke and motor vehicle exhaust.
Occupational exposure to naphthalene is regulated by the Occupational Safety and Health Administration (OSHA). In the workplace, naphthalene levels may not exceed 10 parts per million (ppm) over an 8 hour work day, during a 40 hour work week. The National Institute for Occupational Safety and Health (NIOSH) has stated that naphthalene exposure exceeding 500 ppm is immediately dangerous to life and health.
The Environmental Protection Agency (EPA) considers naphthalene to be reasonably anticipated to be a human carcinogen and has recommended safe levels of naphthalene in drinking water. EPA has determined that it is unsafe for children to drink water containing greater than 0.5 ppm of naphthalene for more than 10 days, or greater than 0.4 ppm of naphthalene for longer than seven years. For adults, EPA advises not drinking water contaminated with greater than 1 ppm naphthalene for more than 7 years or drinking water with more than 0.1 ppm naphthalene over a lifetime.
What should be done:
To limit your exposure to naphthalene, avoid generating and inhaling smoke from fireplaces, heating, and cooking appliances that use petroleum-based fuels or wood. Avoid tobacco smoke, and check toilet deodorizers to see if they use naphthalene before bringing them into your home. Extreme precaution should be taken when handling naphthalene-containing moth repellants as well as blankets and clothing stored with them. Some moth-repellant alternatives are suggested here.
Individuals with G-6-PD deficiency should be especially wary of products containing naphthalene and avoid exposure entirely. Workers in naphthalene-related industries should wear appropriate personal protective equipment and work in well ventilated areas.
The hazards presented by consumer products containing naphthalene raise a much bigger issue: the inadequate regulation of toxic chemicals in the U.S. Consumers are often not appropriately informed of the presence of toxic chemicals in the products they use or are otherwise exposed to, and the possible harms such chemicals pose to their health. Current legislation, most notably the Toxic Substances Control Act (TSCA), fails to adequately regulate substances like naphthalene. Some 60,000 existing chemicals, including naphthalene, were grandfathered into TSCA at the time of its enactment in 1976 without requiring any health or safety data or assessment. Unfortunately, this lack of data and safety assessment hasn’t improved much in the past 35 years. This outdated legislation is in need of serious reform to give EPA the authority is needs to require basic information on chemicals from the chemical industry. Effective reform, like that presented by Senator Lautenberg in the Safe Chemicals Act of 2011, would help ensure the safety of chemicals before they reach or as a condition for staying on the market, offering better protection for consumers. Help make this possible by showing your support here.