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

羰基硫化物（COS）是由土壤中硫氰酸盐存在下的硫代硫杆菌等微生物产生的。二甲基硫醚（DMS）是由藻类在海洋中产生的，化合物中的硫来自海水中的硫酸盐。在这两种情况下，微生物都利用无机硫生成COS和DMS。为什么不用有机硫呢？为了阐明这一问题，在培养基中加入有机硫化合物，考察了COS和DMS的实验生成。在添加异硫酸芳基作为有机硫培养硫代硫杆菌的情况下，微生物没有繁殖。DMS花了很长时间才在实验室里找到能有效繁殖的藻类。实验确认了在海水介质中产生DMS的是环蝇（Cricosphaera roscoffensis NIES 8）和亚历山大菌（Alexandrium catenella NIES 677）。确定化合物中硫来源的主要方法是同位素测量（^<32>S/^<34>S）。在同位素测量中，研究了COS和DMS的采集方法。在乙烷中引入COS，加入Zn(CH_3COO)_2生成ZnS， ZnS转化为Ag_2S。用氧化钛光催化剂将DMS吸附在硅胶上，然后用紫外线（350 ~ 380nm）照射。生成的SO_2被引入到双氧水中氧化为SO_4^<-2>, SO_4^<-2>最终转化为Ag_2S。对上述Ag_2S生成的SO_2进行了硫同位素测定。观察了微生物代谢对COS同位素的分离作用。硫氰酸硫的δ^<34>S值（6.1‰）降至3.8‰。这一结果有望为探讨环境硫的行为提供参考。

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.