Natural production of organohalide compounds in the environment

More than 5000 natural organohalogen compounds have been identified. In terrestrial environments, the bulk of the organochlorine is locked up in humic polymers, collectively accounting for a global organochlorine storage of several million Gg. Natural sources are primarily responsible for the global budget of chloromethane and chloroform. Basidiomycete fungi involved in the decomposition of forest litter produce large quantities of chlorinated phenolic methyl ethers. In marine environments naturally occurring chlorinated and brominated bipyrroles as well as methoxypolybrominated phenyl ethers biomagnify in sea mammals. There are at least five distinct halogenating enzyme systems: (1) methyl transferases; (2) heme haloperoxidases; (3) vandadium haloperoxidases; (4) flavin-dependent halogenases and (5) α-ketoglutarate/Fe(II) dependent halogenases. Natural halogenated phenolic metabolites are subject to biotransformation including O-demethylation and organohalide respiration. Naturally occurring phenolics are also polymerized by oxidative enzymes to dioxins and chlorohumus.