A study of dechlorination of organic matter in forest soil using 36Cl as a tracer

Abstract: During the Fukushima Daiichi power plant incident sea water was used in an attempt to cool reactor Unit 3. Since sea water contains an excessive amount of chloride, 36Cl has likely been formed and spread in the environment. Because of the long residence time and the presumed high mobility in water there is an increased interest to learn more about the biogeochemical cycle of chlorine from a radiation risk assessment perspective. Chlorine occurs in inorganic form as chloride (Clin) or bound to organic matter as organic chlorine (Clorg) and is commonly found in the environment due to both anthropogenic and natural processes. Though there are still uncertainties regarding all of the components of the chlorine cycle in soil, the chlorination of organic matter has been exemplified by research. The reverse process, Clorg mineralizing into Clin, has however not been thoroughly investigated. For this study the objective was to observe at what rate Clorg mineralizes into Clin, this by using 36Cl as a tracer in forest soil. 36Cl was added to the soil and 36Clorg was formed over a period of approximately 100 days. After chlorination the samples were incubated in different conditions and the amount of 36Clorg was observed over a period of time (180 days). The result showed no evident dechlorination during the experiment period which indicates that Clorg can be stable in the organic horizon in forest soil.