Pattern and sources of naturally produced organohalogens in the marine environment: biogenic formation of organohalogens

The pattern of organohalogens found in the marine environment is complex and includes compounds, only assignable to natural (chloromethane) or anthropogenic (hexachlorobenzene, PCBs) sources as well as compounds of a mixed origin (trichloromethane, halogenated methyl phenyl ether).The chemistry of the formation of natural organohalogens is summarized. The focus is put on volatile compounds carrying the halogens Cl, Br, and I, respectively. Though marine natural organohalogens are quite numerous as defined components, they are mostly not produced as major compounds. The most relevant in terms of global annual production is chloromethane (methyl chloride). The global atmospheric mixing ratio requires an annual production of 3.5-5 million tons per year. The chemistry of the group of haloperoxidases is discussed. Incubation experiments reveal that a wide spectrum of unknown compounds is formed in side reactions by haloperoxidases in pathways not yet understood.