Chlorine in Nature
Chlorine is a highly reactive element which
practically does not exist by itself in nature, but only in
combination with other elements. In some rare situations, such as
in human tears, free chlorine as such can be
It is one of the most common elements in nature,
where it is even more plentiful than carbon. Among the
inorganic chlorinated substances, common salt is of course
the best example. Key natural sources of organic
chlorinated substances - organochlorines - are the oceans, forest
fires and fungal activity.
Natural organochlorines are
produced as a result of natural chlorinated substances reacting
with organic material in the environment.
They have some surprising sources and
- a Chinese folk medicine plant contains five natural
- an Ecuadorian tree frog produces a chlorinated
alkaloid, with pain-killing properties several hundred times more
powerful than morphine
- a natural organochlorine antibiotic, vancomycin, is
a key defence against hospital Staphylococcus
- and some natural organochlorinated products exhibit
potent antibacterial and anticancer properties
A large family
Organohalogens - organic compounds containing
chlorine, bromine, iodine or fluorine - have been made by
nature throughout the earth's history.
Deposits have been found in lignite samples (woody
textured rock) of 15 million years old and bituminous coal of
300 million years old.
More than 4,000 organohalogen substances are known
today, of which many occur in living organisms and of which more
than half contain chlorine. Chlorine-based compounds are made by
marine organisms (sponges, corals, sea slugs, jellyfish and
seaweeds), plants, seeds, fungi, lichens, bacteria, freshwater
algae and insects.
Seaweeds produce at least 400 organohalogens, and
certain phytoplankton and seaweeds produce chlorinated metabolites
tentatively identified as trichloroethylene and perchloroethylene,
compounds well known as chlorinated
organohalogens play an essential role in the survival of these
Wherever you go...
The oceans release some three million tonnes of
methyl chloride into the atmosphere every year. In addition, some
5,000 - 15,000 million tonnes of inorganic chlorine go into the
marine atmosphere each year as a fine mist of sea salt. Most of
this inorganic chlorine is returned to the ocean surface, but 3-35%
remains as "inorganic chlorine vapour", including hydrogen chloride
and probably other inorganic compounds including molecular
chlorine, hypochlorous acid and nitryl chloride.
Part of this vapour is ultimately converted into
chlorine atoms which may react with natural organic compounds to
On land, some 300 natural chlorine-based compounds are known to
be produced by terrestrial fungi and plants. These range from the
chloromethane released by wood-rotting fungi to complex chlorinated
polyacetylenes made by plants of the Aster family. In terrestrial
plants, organochlorines often act as anti-feedants to protect the
plant from attack by insects or other herbivores.
Last update : 09/2011