It is very unstable and quickly reacts with many substances to form other chemicals.

Chlorine is an extremely important industrial chemical that is used in the production of thousands of products. It is also used for water disinfection, although the chlorine itself is quickly transformed into other chemicals at the beginning of the process.

A common misconception is that molecular chlorine (Cl2) is present in chlorinated water. During water chlorination, molecular chlorine gas may be added to the water at first; however, the chlorine is quickly transformed into other chemicals, which actually disinfect the water. Hypochlorous acid and hypochlorite anion are two of these chemicals that disinfect the water.

The terms �free chlorine� and �aqueous chlorine� in drinking water usually refers to the amount of hypochlorous acid and hypochlorite in the water. It is important to recognize that these compounds are different from molecular chlorine.

Chlorine is very unstable, and reacts with a variety of chemicals and water when it is released into the environment.

Air: Chlorine is broken down by sunlight within minutes.

Water: Chlorine dissolves in water and is converted into chloride and hypochlorous acid.

If chlorine is spilled into water or onto soil or if it is released from a tank into the air, the chlorine will evaporate very quickly forming a greenish-yellow cloud that can be carried away from the source by the wind.

Because chlorine is so reactive, it is not normally detected in the environment except for very low levels in the air above seawater.

If an accident involving chlorine takes place nearby, such as a liquid chlorine spill, a leak from a chlorine tank, or a leak from a facility that produces or uses chlorine, you may be exposed through breathing and skin and eye contact.

You may also be exposed to chlorine if you mix household chemicals such as toilet cleaner with bleach.

Hypochlorous acid is used to treat swimming pool water. You may be exposed to chlorine gas through the improper use of swimming pool chemicals.

People who work in places where chlorine is made or used may be exposed to low levels over a period of time.

People may be exposed to high levels if a large amount of chlorine is released during an accident.

Chlorine gas can enter your body through your nose or your mouth.

At low concentrations (less than 10 ppm), almost all of the chlorine is removed from the air in the upper part of the respiratory airways and only a very small amount may reach your lungs.

If you drink hypochlorite solution, it may react with the acids in your stomach and possibly form chlorine gas.

Chlorine gas reacts with the water in the cells located in the surface of the respiratory airways and forms other compounds that produce irritation of the airways.

Most of these compounds eventually are transformed into chloride ions, which are normal components of the body.

The following effects have been observed in humans briefly exposed to chlorine:

• mild nose irritation at 1�3 ppm
• eye irritation at 5 ppm
• throat irritation at 5�15 ppm
• immediate chest pain, vomiting, changes in breathing rate, and cough at 30 ppm
• lung injury (toxic pneumonitis) and pulmonary edema (fluid in the lungs) at 40�60 ppm
• death after 30 minute exposure to 430 ppm
• death after a few minutes exposure to 1,000 ppm

The concentrations listed above are approximate; the effects will depend also on exposure duration. In general, people who suffer from respiratory conditions such as allergies or hay fever, or who are heavy smokers, tend to experience more severe effects than healthy subjects or nonsmokers.

No significant harmful health effects were observed in workers exposed for years to relatively low concentrations of chlorine (around 1 ppm).

The tissues inside the nose were principally affected in animals exposed to chlorine for longer durations.

Drinking small amounts of hypochlorite solution (less than a cup) can produce irritation of the esophagus. Drinking concentrated hypochlorite solution can produce severe damage to the upper digestive tract and even death. These effects are most likely caused by the caustic nature of the hypochlorite solution and not from exposure to molecular chlorine.

There is no information on long-term ingestion of hypochlorite solution in humans. Animals that drank hypochlorite solution in water for up to 2 years did not show any significant health effects. The amount of hypochlorite solution in the water that the animals drank was much smaller than what is found in household bleach.

Spilling hypochlorite solution on the skin can produce irritation. The severity of the effects depends on the concentration of sodium hypochlorite in the bleach.

Short-term exposures (minutes) to high concentrations of chlorine affect children in the same manner they affect adults (i.e., mucous membrane and respiratory tract irritation). We do not know what the effects could be in children following longer-term (weeks or longer), low-level exposure to chlorine gas, but this type of exposure occurs only in workers and is not relevant to children. We also do not know what the effects could be in children following longer-term, low-level exposure to hypochlorite solution.

We do not know whether exposure to chlorine gas during pregnancy can result in damage to unborn babies because there are no studies of pregnant women or pregnant animals exposed to chlorine gas.

One study of rats exposed to hypochlorite solution during pregnancy found no evidence of birth defects or any other developmental alteration in the baby rats. The amount of chlorine that the rats consumed was many times higher than what people are normally exposed to through drinking water.

Chlorine gas can be released to the air when bleach is mixed with other cleaning solutions that contain an acid; for example, some toilet cleaners. Mixing bleach with ammonia also produces very hazardous gases, such as chloramines.

Always store household chemicals in their original labeled containers out of reach of young children to prevent accidental poisonings. Never store household chemicals in containers children would find attractive to eat or drink from, such as old soda bottles.

Chlorine gas can also be released to the air when chemicals used to chlorinate swimming pools are mishandled. If you have a swimming pool at home, read the labels of the chlorination products carefully and do not let children play with these products.

There are no medical tests to determine whether you have been exposed specifically to chlorine.

Chlorine is transformed in the body into chloride ions, which are normal components of the body. An enormous amount of chlorine has to be inhaled or ingested in order to detect a significant increase in chloride ions in the blood. This has occurred in a few cases of ingestion of large amounts of hypochlorite solution and one of them was a fatal case.

EPA established an environmental air limit of 0.5 ppm. Exposure to higher levels could result in discomfort and irritation. Dependent on the concentration,

OSHA set a legal limit of 1 ppm chlorine in air as a ceiling limit. At no time should a worker�s exposure exceed this limit.

EPA established a maximum contaminant level (MCL) and maximum residual disinfectant level (MRDL) of 4 mg/L for free chlorine in drinking water.