Chlorine is a common element on the Earth, but it is not found naturally in its pure state as it is very reactive and tends to form compounds with other elements. At room temperature and normal pressure, it is a yellow-green gas that is heavier than air. Although some of its compounds are essential to many life forms — including humans — in its elemental form, the gas is very toxic. Chlorine is used industrially to produce plastics, insecticides, and pharmaceuticals; to sanitize water for drinking and in swimming pools; and as a bleaching agent in the paper industry.
Many chlorine compounds have been implicated in damage to ecosystems, wildlife, and the environment. Chlorine and compounds derived from it can find their way into rivers and lakes though waste water from pulp mills and from homes with chlorinated water or where bleach has been used. If present in sufficient amounts, it may be harmful to aquatic life, either directly or through accumulation of its compounds in the food chain.
The health effects resulting from most chlorine exposures begin within seconds to minutes. The severity of the signs and symptoms caused by chlorine will vary according to amount, route and duration of exposure. It is corrosive and irritating to the eyes, skin, and respiratory tract.
Your body absorbs more chlorine, and more importantly disinfection byproducts (DBPs), by swimming in a chlorinated pool than you would by drinking tap water for one week.