On the origin of organohalogens found in the environment

Sammanfattning: The natural production of halogenated organic compounds in the environment is often assumed to be negligible compared to the anthropogenic production of such compounds. A change in this general view is advocated in the present thesis.Amounts of halogenated organic compounds were measured by detennination of AOX (adsorbable organic halogen) or TOX (total organic halogen), and it was found that these compounds are more widespread than previously assumed. A national organohalogen budget was established by calculating chlorine-to-carbon ratios for different types of samples and then combining these values with studies of organic carbon pools in Sweden. The obtained budget showed that the major fraction of organohalogens is stored in soil and freshwater sediments (approx. 5000 x J03 and 2000 x J03 tonnes, respectively).It was also found that soil extracts obtained by using an enzyme extraction procedure were able to catalyze chlorination of organic compounds. The reaction did not proceed in the absence of hydrogen peroxide or after the soil extract had been heated; furthermore the catalyst had a molecular weight that was greater than 10,000, exhibited decreasing activity with time and rising temperature, and was inhibited by phloroglucinol, resorcinol, orcinol and ethanol. In all these respects the soil derived catalyst resembled a commercial chlorperoxidase. Based on these findings, it was concluded that a chloroperoxidase-like catalyst is present in soil. In this context it is also noteworthy that a net production of organohalogens ~as found in soil stored under controlled conditions.The soil-extract-catalyzed chlorination, the detected net production in soil, and the background concentration of organohalogens in surface water were all found to increase with decreasing pH. This implies that the natural production of halogenated organic compounds may increase with acidification of soil and surface water.