Chemical forms of arsenic in the modern sediments under microbiologically controlled condition concerned with arsenic polluted groundwater

高砷污染的地下水，在世界范围内造成严重的健康危害，大量存在于现代沉积物中。本文通过对大阪盆地地下水、河口水和现代沉积物的分析，探讨了大阪盆地砷的释放机制，冲绳伊里莫特岛潮间带沉积物记录了一个自然平衡的固砷系统，积累的砷化合物主要固定在氢氧化铁/氧化物转化的硫化物矿物(S)中。这一转变似乎是由成岩作用初期停滞含水层中的微生物反应所介导的。如果砷固相化合物之间的转化速率稳定，则不太可能向地下水中大量释放砷，因为浮游植物及其身体在河口沉积物中积累了砷，这表明大阪群沉积物中海相粘土层中的高浓度砷(7-20ppm)也是这种微生物积累的结果。沉淀后，大部分砷最终固定在黄铁矿中。在大阪盆地南部的仙州地区，春季至秋季地下水中硫酸盐-硫的重硫同位素比值(20-27CDT)表明，硫的来源是沉积物中的黄铁矿。硫铁矿分解后将砷提供给地下水，砷浓度的变化与细菌活动产生的还原条件下氢氧化铁的溶解相协调。该井水的观察表明，黄铁矿是大阪盆地砷的主要来源，但砷的释放取决于氢氧化铁的溶解度，主要受井中细菌活动产生的氧化还原条件控制。

The highly arsenic-contaminated groundwaters, causing serious health hazards in the world, monstly present in the modern sediments. In this study, arsenic releasing mechanism is discussed based on the analyses of groundwaters, estuarine waters, and modern sediments of the Osaka basin, and the intertidal sediments from the iriomote island, OkinawaSediments of the intertidal zone of lriomote island record a naturally balanced arsenic-fixation system, where accumulated arsenic compounds are largely fixed into sulfide mineral(s) transformed by iron hydroxide/oxide. This transformation appears to be mediated by microbial reactions in the stagnant aquitard during the initial stage of diagenesis. Significant release of arsenic to groundwater would be unlikely to occur if the transformation rates among arsenic solid phase compounds are stablePhytoplankton and its body accumulates arsenic in the estuarine sediments, suggesting that high concentration of arsenic in the marine clay layers of Osaka Group sediments, from 7 to 20 ppm, is also the results of such a microbial accumulation. After the deposition, most of the arsenic is finally fixed in pyite. In the southem part of Osaka Basin, Senshu area, The heavy suifur isotope ratios (20-27 CDT) of sulfate-sulfur in the groudwater from the spring to fall indicate that the source of the sulfur is the pyite in the sediments. Afterpyrite decomposition supplies the arsenic into the groundwater, arsenic concentrations changes in harmony with dissolution of iron oxyhydroxide in reduced condition produced by bacterial activity. The observation in this well water suggests that the pyrite was he primary source of arsenic in the Osaka Basin, however, arsenic release is dependent on the solubility of iron oxyhydroxide, mainly controlled by the redox condition produced by the bacterial activity in the well