Chlorine is a poisonous, greenish-yellow gas described as having a choking odor.
It is a very corrosive, hazardous chemical. Usually combined with other chemicals, it is used to disinfect water, purify metals, bleach wood pulp and make other chemicals. Dangerous levels of a very harmful gas can be released. Most of the chlorine that enters lakes, streams, or soil evaporates into the air or combines with other chemicals into more stable compounds. Chlorine-containing chemicals that seep through soil down into groundwater can remain unchanged for many years.