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Naphthalene

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Introduction

Naphthalene is a white solid that evaporates easily. It is also called mothballs, moth flakes, white tar, and tar camphor. When mixed with air, naphthalene vapors easily burn. Fossil fuels, such as petroleum and coal, naturally contain naphthalene. Burning tobacco or wood produces naphthalene. The major products made from naphthalene are moth repellents, in the form of mothballs or crystals, and toilet deodorant blocks. It is also used for making dyes, resins, leather tanning agents, and the insecticide, carbaryl.

Naphthalene has a strong, but not unpleasant smell. Its taste is unknown, but must not be unpleasant since children have eaten mothballs and deodorant blocks. You can smell naphthalene in the air at a concentration of 84 parts naphthalene per one billion parts (ppb) of air. You can smell it in water when 21 ppb are present.

1-Methylnaphthalene is a naphthalene-related compound which is also called alpha methylnaphthalene. It is a clear liquid. Its taste and odor have not been described, but you can smell it in water when only 7.5 ppb are present. Another naphthalene-related compound, 2-methylnaphthalene, is also called beta methylnaphthalene. It is a solid like naphthalene. The taste and odor of 2-methylnaphthalene have not been described. Its presence can be detected at a concentration of 10 ppb in air and 10 ppb in water. 1-Methylnaphthalene and 2-methylnaphthalene are used to make other chemicals such as dyes, resins, and, for 2-methylnaphthalene, vitamin K. Along with naphthalene, they are present in cigarette smoke, wood smoke, tar, and asphalt, and at some hazardous waste sites.

Fate & Transport

Naphthalene enters the environment from industrial uses, from its use as a moth repellent, from the burning of wood or tobacco, and from accidental spills. Naphthalene at hazardous waste sites and landfills can dissolve in water. Naphthalene can become weakly attached to soil or pass through the soil into underground water.

Most of the naphthalene entering the environment is from the burning of woods and fossil fuels in the home. The second greatest release of naphthalene is through the use of moth repellents. Only about 10% of the naphthalene is from coal production and distillation, and less than 1% is attributable to naphthalene production losses. Cigarette smoking also releases small amounts of naphthalene.

Naphthalene evaporates easily. That is why you can smell mothballs. In the air, the moisture and sunlight make it break down, often within 1 day. The naphthalene can change to 1-naphthol or 2-naphthol. These chemicals have some of the toxic properties of naphthalene. Some naphthalene will dissolve in water in rivers, lakes, or wells. Naphthalene in water is destroyed by bacteria or evaporates into the air. Most of the naphthalene will be gone from rivers or lakes within 2 weeks. Naphthalene breaks down faster in water containing other pollutants, such as petroleum products.

Naphthalene binds weakly to soils and sediment. It easily passes through sandy soils to reach underground water. In soil, some microorganisms break down naphthalene. When near the surface of the soil, it will evaporate into air. Healthy soil will allow the growth of microorganisms which break down most of the naphthalene in 1 to 3 months. If the soil has few microorganisms, it will take about twice as long. Microorganisms may change the chemical structure of naphthalene. Some common bacteria grow on naphthalene, breaking it down to carbon monoxide.

Naphthalene does not accumulate in the flesh of animals and fish that you might eat. If dairy cows are exposed to naphthalene, some naphthalene will be in their milk; if laying hens are exposed, some naphthalene will be in their eggs. Naphthalene and the methylnaphthalenes have been found in very small amounts in some samples of fish and shellfish from polluted waters.

Scientists know very little about what happens to 1-methylnaphthalene and 2-methylnaphthalene in the environment. These compounds are similar to naphthalene and should act like it in air, water, and soil.

Exposure Pathways

You can be exposed to naphthalene if you live in a city that has polluted air. Typical air concentrations of naphthalene in cities are about 0.0000001 ppm (0.0000001 parts of naphthalene per million parts of air). Naphthalene is generally not found in water, but when it is present, the levels are usually lower than 0.01 ppm. The levels of naphthalene in typical urban, suburban or rural soils are not known. At hazardous waste sites, naphthalene and 2-methylnaphthalene are found more frequently in soils and sediments than in water.

You can be exposed to naphthalene in your home through the use of mothballs or by breathing air that contains tobacco smoke. Because it is unusual for naphthalene to be found in drinking water, you are not likely to be exposed by this route. The levels of naphthalene in foods are not known.

You can also be exposed to naphthalene if you work in an industry such as coal-tar production, wood preserving, tanning, or ink and dye production. The levels of naphthalene in the air at some workplaces might be over 1,000 times higher than the levels of naphthalene in the air of most cities.

Metabolism

Naphthalene and 2-methylnaphthalene can enter your body when you breathe air that contains these chemicals, when you eat or drink contaminated food or water, and through contact with your skin. Human exposure to naphthalene and 2-methylnaphthalene occurs mainly by breathing air that contains these compounds. The body changes naphthalene into other chemicals that leave your body in the urine over the course of several days. Little is known about how 2-methylnaphthalene leaves the body.

Health Effects

Hemolytic anemia (a condition involving the breakdown of red blood cells) is the primary health concern for humans exposed to naphthalene for either short or long periods of time. Other effects commonly found include nausea, vomiting, diarrhea, kidney damage, jaundice (yellowish skin or eyes) and liver damage. These effects can occur from either breathing or eating naphthalene. Cataracts (cloudy spots) might also occur in the eyes of persons who eat or breathe naphthalene.

Laboratory animals that breathed or ate naphthalene for several weeks showed effects on the blood, kidneys, and liver. Naphthalene can cause cataracts in the eyes of some animals.

Cancer has not been seen in humans or animals exposed to naphthalene. In pregnant women, naphthalene and its breakdown products in blood can reach the fetus. It is not known whether these substances can cause birth defects. Infants whose mothers were exposed to naphthalene during pregnancy developed blood problems (hemolytic anemia). In some animals injected with naphthalene, lung damage has developed.

Although there is some information about the effects that occur in humans from breathing or eating naphthalene, the levels of naphthalene at which these effects can occur are not known. Naphthalene can be smelled in air at a concentration of about 0.08 ppm and can be tasted in water at a concentration of about 0.02 ppm. 2-Methylnaphthalene can be tasted in water at levels of about 0.01 ppm; the concentration at which it can be smelled in air is not known.

The effects of skin contact with naphthalene or 2-methylnaphthalene have not been carefully studied. There have been several medical reports showing that babies dressed in clothing that had been stored in naphthalene mothballs developed liver problems and hemolytic anemia.

Information excerpted from:

Toxicological Profile for Naphthalene December 1990

Agency for Toxic Substances and Disease Registry
U.S. Dept. of Health and Human Services

Structural diagram:

National Institutes of Health