Despite the long association of organohalogen compounds with human
activities, nature is the producer of nearly 5,000 halogen-containing
chemicals. Once dismissed as accidents of nature or isolation artifacts,
organohalogen compounds represent an important and ever growing class of
natural products, in many cases exhibiting exceptional biological
activity. Since the last comprehensive review in 1996 (Vol. 68, this
series), there have been discovered an additional 2,500 organochlorine,
organobromine, and other organohalogen compounds. These natural
organohalogens are biosynthesized by bacteria, fungi, lichen, plants,
marine organisms of all types, insects, and higher animals including
humans. These compounds are also formed abiogenically, as in volcanoes,
forest fires, and other geothermal events.In some instances, natural
organohalogens are precisely the same chemicals that man synthesizes for
industrial use, and some of the quantities of these natural chemicals
far exceed the quantities emitted by man.