Mothballs are small balls of chemical pesticide and deodorant sometimes used when storing clothing and other articles susceptible to damage from mold or moth larvae (especially clothes moths like Tineola bisselliella).
Use of mothballs when clothing is stored out-of-season has given rise to the colloquial usage of the terms "mothballed" and "put into mothballs" to refer to anything which is put into storage or whose operation is suspended.
Older mothballs consisted primarily of naphthalene, but due to naphthalene's flammability, many modern mothball formulations instead use 1,4-dichlorobenzene. The latter formulation may be somewhat less flammable, although both chemicals have the same NFPA 704 rating for flammability. The latter chemical is also variously labeled as para-dichlorobenzene, p-dichlorobenzene, pDCB, or PDB, making it harder to identify unless all these synonyms are known to a potential purchaser. Both of these formulations have the strong, pungent, sickly-sweet odor often associated with mothballs. Both naphthalene and 1,4-dichlorobenzene undergo sublimation, meaning that they evaporate from a solid state directly into a gas; this gas is toxic to moths and moth larvae.
Naphthalene and 1,4-dichlorobenzene should not be mixed, as they react chemically to produce a liquid which may cause damage to items being preserved.
Due to the health risks of 1,4-dichlorobenzene, and flammability of naphthalene, other substances like camphor are sometimes used (though camphor has its own toxicity issues).
In addition to repelling or killing insects such as moths and silverfish, mothballs have been suggested for use as a stovepipe cleaner, a snake repellent, and to keep away mice or other pests. However, a major concern about the use of mothballs as a snake, mouse, or animal repellent or poison is their easy access to children, pets, and beneficial animals. Leaving them in a garden or in a living space unprotected makes it very easy for unintended victims such as children and pets to gain access to them. Mothballs are highly toxic when ingested (they have a sweet odor and taste, making this more likely), and will cause serious illness or death. In addition to this, using a large quantity of mothballs in a basement or a living space may cause serious respiratory problems in people living in the space.
Mothballs have been promoted as a squirrel repellent, and are an ingredient in some commercial repellent products. They are generally ineffective, and are not a substitute for physical measures to exclude squirrels from building interiors.
Older-formula mothballs have also been used by drag racers to enhance the octane rating of fuel by dissolving the mothballs in some of the fuel and filtering out the remains with a filter paper. In the MythBusters episode "Scuba Diver, Car Capers", it was shown to be "plausible" that adding mothballs to a car's fuel tank would increase its horsepower.
The US Department of Health and Human Services (DHHS) has determined that 1,4-dichlorobenzene "may reasonably be anticipated to be a carcinogen". This has been indicated by animal studies, although a full-scale human study has not been done. The National Toxicology Program (NTP), the International Agency for Research on Cancer (IARC), and the state of California consider 1,4-dichlorobenzene to be a carcinogen.
Exposure to naphthalene mothballs can cause acute haemolysis (anemia) in people with glucose-6-phosphate dehydrogenase deficiency. IARC classifies naphthalene as possibly carcinogenic to humans and animals (see also Group 2B). IARC points out that acute exposure causes cataracts in humans, rats, rabbits, and mice. Chronic exposure to naphthalene vapors is reported to also cause cataracts and retinal hemorrhage. Under California's Proposition 65, naphthalene is listed as "known to the State to cause cancer".
Alternatives to mothballs to control clothes moths include freezing, dry cleaning, washing in hot water, or thorough vacuum cleaning. Camphor is also used as a moth repellent, and unlike naphthalene and dichlorobenzene, it has medicinal applications and is not regarded as a carcinogen, though it is toxic in large doses.
- Clothing moth — for alternative treatments for clothes moths
- Urinal deodorizer block — some types contain similar chemicals to mothballs
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