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Natural organic chlorine compounds
Chlorine and its compounds are natural components of the Earth - as every element has its place in biosynthesis, so it is with chlorine too. Therefore, it is little wonder that almost 2% of chlorine contained in the oceans as well as bromine and iodine, is utilised by numerous sea organisms (algae, shelp, microbes and molluscs). Almost 5 million tonnes of methyl chloride, 0.3 million tonnes of methyl bromide and 1.3 million tonnes of methyl iodide which occur naturally in the sea each year, as well as large tonnages of various other poly-halogenated methane derivatives, including chloroform and carbon tetrachloride, far exceed the industrially manufactured amounts of these chemicals. In addition, chlorine is brought in by oceanic aerosols, volcanoes and weathering. It is also produced and utilised on the land, both by numerous soil microbes and worms, and by higher plants to synthesise organic chlorine compounds. So far some 4,000 naturally-produced organohalogen1 chemicals have been identified and there are currently hundreds of new organohalogen compounds pending identification. Besides simple structures like methylchloride, nature generates complex chlorinated molecules which can contain very high amounts of chlorine. Even "typical industrial" organic chlorine compounds such as pentachlorophenol, Polychloropyrols, polychlorinated biphenyls (PCB) and even tetrachlorodibenzodioxins (TCDD) have been identified as naturally-formed substances which have also been detected in 8,000 year old sediments. Industry learned from nature to utilise chlorine compounds in health protection, for example as antibiotics. Global emission of organic chlorine compounds from natural sources is highLarge amounts of naturally-occurring chlorine-containing humus elements are components of marshy wetland and rivers left in their natural state. Data evolution shows a reduction in the anthropogenic discharge of organochlorines into the Rhine river of 80 to 90% over the period from 1986 until the present. The present levels in the Rhine are, therefore, close to natural background levels. The emissions of organochlorines from nature are evenly spread, which implies low local concentration. In global terms, the annual natural production of organic chlorine compounds is much greater than that of industry. In nature, various mechanisms to control and degrade chlorine compounds exist. For example dehalogenation, hydrolysis, photolysis and biodegradation. The end result of these processes are mostly chlorides such as hydrogen chloride and common salt. Modern environmental research is intensely concerned with gathering information on the process and intermediate products resulting from breakdown of organic chlorine compounds, whether they are of natural or industrial origin. Euro Chlor positionEuro Chlor encourages further research in this area in order to learn from nature how chlorinated compounds are formed and metabolised. Research can also help identify new chemical compounds which have and will continue to play a key role in the progress of health care. Useful ReferencesAsplund G, Grimvall A., Organohalogens in Nature, Env. Sci. Technol., 25, 8, 1347-1350, 1991 Grimvall A., TAPPI Journal, May 1991, 197-203 Harper PB (1985) Halomethane from halidion, Nature Vol 315 Hashimoto S, Chemosphere, 21, 825, 1991 Hoekstra EJ, E.W.B. de Leer, AOX levels in the river Rhine, Water Sc. Technol., 29, No.3, 1994, 133-136 Holland HD (1978) The Chemistry of the Atmosphere and Oceans - Wiley, Interscience - New York Naumann K, Chemie in unserer Zeit 27 (1993) 33. Paasvirta J., Chemosphere, 17, 137, 1988
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