Environmental study on the river sediments using chemical speciation of iron by Mossbauer spectroscopy.

城市河口沉积物富含有机物，提供厌氧环境，通过微生物和/或海水中的硫酸盐离子的化学还原，大量产生硫化氢，硫化氢是造成恶臭的物质之一，最终以硫化铁的形式从水中转移到沉积物中。本文采用^<57>Fe穆斯堡尔谱法研究了城市河流沉积物中铁的化学状态及其垂直分布。河口沉积物穆斯堡尔谱由3个双峰和1个六峰组成，分别属于顺磁性高自旋Fe^<2+>、顺磁性高自旋Fe^<3+>、黄铁矿（FeS_2）和磁性高自旋Fe^<3+>。黄铁矿的相对含量在距地表20 ~ 40 cm处达到最大值，顺磁体Fe^<2+>的相对含量与黄铁矿相辅相成。这表明该成分在河口沉积物中在还原条件下转化为黄铁矿。这一趋势没有明显的季节变化。在东京的运河河流北竹根河和泰特河的沉积物中也发现了黄铁矿的分层分布。另一方面，在相龟河沉积物中并不总是发现黄铁矿，但在污水处理厂附近收集的沉积物中发现了相同的黄铁矿分布趋势。为了明确硫酸盐还原菌对沉积物中黄铁矿形成的贡献，我们用电镀法测定了沉积物中硫酸盐还原菌活菌数的垂直分布。这种分布与黄铁矿的分布一致。

Urban estuarine sediments are rich in organic materials and provide an anaerobic environment where hydrogen sulfide, one of the substances responsible for malodor, is intensively produced through microbial and/or chemical reduction of sulfate ions from seawater and finally removed from water to the sediment in the form of iron sulfides. In this study, the chemical states of iron, and its vertical distribution, have been investigated by ^<57>Fe Mossbauer spectroscopy for the sediments collected from several urban rivers. Mossbauer spectra of the estuarine sediments consist of three doublets and one sextet, which are ascribable to paramagnetic high-spin Fe^<2+>, paramagnetic high-spin Fe^<3+>, pyrite (FeS_2) and magnetic high-spin Fe^<3+>, respectively. The relative amount of pyrite shows a maximum at the depth of 20-40 cm from the surface, whereas that of paramagnetmc Fe^<2+> changes complementarily to pyrite. This suggests that this component in the estuarine sediments converted to pyrite under reducing conditions. No significant seasonal variation was found in this trend. The stratified distribution of pyrite was also found in the sediment collected from Kitajukken-river and Tate-river, which are canal-rivers in Tokyo. On the other hand, pyrite was not always found in the Sagami-river sediments, but the same trend of pyrite distribution was found in the sediment collected near a sewage treatment plant. In order to clarify the contribution of sulfate-reducing bacteria to pyrite formation in the sediments, we determined the vertical distribution for number of living sulfate-reducing bacteria in the sediments by plating method. This distribution was found to be consistent with that of pyrite.