Isotope Chemistry for the Studies on COS・DMS Generating Mechanism and Their Behavior in Environment

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Carbonyl sulfide(COS) is produced by microbes such as Thiobacilius thioparus under the presence of thiocyanates in soil. On the other hand dimethly sulfide(DMS) is produced in the sea by algae and the sulfur in the compound comes from the sea water sulfate. In both cases microbes use inorganic sulfur to generate COS and DMS. Why they don't use organic sulfur? To elucidate this problem the experimental generation of COS and DMS were examined by adding organic sulfur compounds in the medium. In the case of cultivating Thiobacillus thioparus by adding aryl isothianate as organic sulfur, microbes did not breed. For DMS it took long times to find algae which breed effectively in the laboratory. Cricosphaera roscoffensis NIES 8 and Alexandrium catenella NIES 677 were recognized to generate DMS in the sea water medium experimentally.The predominant means to identify the origin of sulfur in the compounds is isotopic (^<32>S/^<34>S) measurement. For the isotopic measurement the collection method of COS and DMS were investigated. COS was introduced in ethane, added by Zn(CH_3COO)_2 to form ZnS which is converted to Ag_2S. DMS was adsorbed on silica gel with titanium oxide photo catalyst which is then irradiated by ultraviolet ray(350〜380nm). The formed SO_2 is introduced to hydrogen peroxide solution to be oxidized to SO_4^<-2> which is finally converted to Ag_2S. The sulfur isotopic measurement is carried out for SO_2 formed from Ag_2S described above. For COS isotopic fractionation by microbe metabolism was observed. δ^<34>S value (6.1‰) of thiocyanate sulfur as a standing material went to be lower as 3.8‰. This result is expected to be useful for the discussion of behavior of environmental sulfur.