ISOTOPIC STUDIES ON COS AND DMS GENERATION AND THEIR BEHAVIOR IN THE ENVIRONMENTAL CYCLE OF SULFUR

本研究的目的是通过硫同位素测量来研究二甲基硫(DMS)和羰基硫(COS)在环境中的行为。研究人员已经测定了煤和石油的硫同位素组成，这些燃烧气体使环境酸化。DMS和COS具有天然来源，目前被认为是对环境的严重酸化。本文的研究成果总结由两部分组成：1)调查人员提出了赤潮使环境酸化的假说，根据一些报道，赤潮期间释放的DMS比平时增加了10^4倍。研制了用于赤潮预报的生物传感器。对赤潮期间产生DMS的藻类的培养进行了研究。为了确定海洋释放的DMS的硫同位素组成，对海洋表层空气中DMS的收集系统进行了研究。2)在实验室条件下采集硫化硫杆菌KSCN产生的COS，并测定其硫同位素组成。通过生物过程观察到了同位素分馏。下一步是收集土壤中释放的COS，并测定硫同位素组成。研究人员试图根据海水硫酸盐、火山气、二甲基硫、COS和化石燃料的硫同位素组成数据，区分空气、雨水、雪、河水、植物等环境样品中的硫源。

The purpose of this research is to investigate the behavior of dimethyl sulfide (DMS) and carbonyl sulfide (COS) in the environment by means of sulfur isotopic measurement. Investigaters have already determined sulfur isotopic compositions of coals and petroleum those combustion gas acidify the environment. Now DMS and COS which have a natural origin are considered seriously as acidifing the environment.Summary of this research results is composed of 2 parts : 1) Investigaters set forth a hypothesis that a red tide acidifies the environment, depending on some reports that 10^4 fold of DMS compared as usual is released at a period of red tide. The biosensor for forcasting a red tide was develored. Cultivation of algae which generate DMS at a period of red tide was examined. As a final goal is to determine the sulfur isotopic composition of DMS releasedfrom the sea, the collecting system of DMS from the surface air of the ocean was investigated. 2) COS generated from KSCN by Tiobacillus thioparus in the laboratory was collected and its sulfur isotopic composition was determined. An isotopic fractionation was observed by the biological process. The next step is to collect COS released from the soil and determine the sulfur isotopic composition. Investigaters are attempting to discriminate the sulfur source in the environmental samples such as air, rain water, snow, river water, plants based on the data of sulfur isotopic composition from the sea water sulfate, volcanic gas, DMS, COS and fossil fuels.