1,4-Dichlorobenzene

Overview
1,4-Dichlorobenzene (para-dichlorobenzene or p-DCB) is a white solid with a strong, pungent odor, the characteristic smell of urinal cake. It is an aromatic chemical compound having the chemical formula C6H4Cl2. It consists of two chlorine atoms substituted onto a benzene ring. It is used to control moths, molds, and mildew, and to deodorize restrooms and waste containers. Its primary use is in most modern mothballs in which it is a replacement for the more traditional naphthalene. Trade names for p-DCB include Paramoth, Para crystals, and Paracide reflecting its widespread use as a pesticide to kill moths. p-DCB is also used as a precursor in the production of the polymer poly(p-phenylene sulfide), and is used in urinal deodorant blocks because of its volatility.

When exposed to air, p-DCB slowly sublimates from a solid to a vapour. It is the vapour that acts as a deodorizer or insect killer. Most people recognize the odor as the smell of mothballs or urinal deodorant, and can smell p-DCB in the air at very low levels. Most p-DCB in the environment comes from its use in moth repellent products and in toilet deodorizer blocks.

Environmental effects
In air, 1,4-Dichlorobenzene breaks down to harmless products in about one month. 1,4-Dichlorobenzene does not dissolve easily in water, and is not easily broken down by soil organisms. Like many hydrocarbons p-DCB is lipophilic and accumulates in the fatty tissue of plants, marine life, and animals.

Health effects
There is no evidence that moderate use of common household products that contain p-DCB will result in harmful effects to human health. Harmful effects, however, may occur from high exposures. Very high usage of p-DCB 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 before they first began to feel ill.

Workers breathing high levels of p-DCB (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 p-DCB products regularly for months to years because of its sweet taste. These people had skin blotches and lower numbers of red blood cells.

The US Department of Health and Human Services (DHHS) has determined that p-DCB 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 United States Environmental Protection Agency (EPA) has set a maximum contaminant level of 75 micrograms of p-DCB per liter of drinking water (75 μg/L).

p-DCB is also an EPA-registered pesticide. Manufacturers must provide certain information to EPA for it to be used as a pesticide.

The US Occupational Safety and Health Administration (OSHA) has set a maximum level of 75 parts of p-DCB per million parts air in the workplace (75 ppm) for an 8-hour day, 40-hour workweek.

Toxicity to humans
Children are exposed to p-DCB in many of the same ways that adults are. Children may be at higher risk, due to accidental exposures such as swallowing p-DCB used in the home in mothballs or toilet bowl deodorant blocks. There is very little information on how children react to p-DCB exposure, but children would probably show the same effects as adults. There have also been reported cases of dichlorobenzene in mothballs being used recreationally.

No studies in people or animals show that p-DCB crosses the placenta or can be found in fetal tissues. Based on other similar chemicals, it is possible that this could occur. There is no credible evidence that p-DCB causes birth defects. One study found dichlorobenzenes in breast milk, but p-DCB has not been specifically measured.

Children should not be allowed to play with or drink toilet bowl water because it may contain p-DCB. Do not let children rub mothballs or cleaners containing p-DCB on their skin. Pesticides, bathroom deodorizers, and mothballs containing p-DCB should be stored out of reach of young children. Always store household chemicals in their original containers. Never store them in containers children would find attractive to eat or drink from, such as old soda bottles.

Tests are available to measure exposure to p-DCB. The most common test measures a breakdown product of p-DCB called 2,5-dichlorophenol in urine and blood. If there is 2,5-dichlorophenol in the urine, it indicates that the person was exposed to p-DCB within the previous day or two. The test that measures p-DCB in your blood is less common.