Hashimoto Shunji, Watanabe Kiyohiko, Nose Kazutoshi, Morita Masatoshi
National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 305-8506, Japan.
Chemosphere. 2004 Jan;54(1):89-96. doi: 10.1016/S0045-6535(03)00673-8.
The effectiveness of subcritical water extraction (SCWE) was examined for removing dioxins from contaminated soil. Most dioxins in the soil sample were reduced at 300 degrees C or more, but decreased dioxin concentrations were also observed at 150 degrees C. After 4 h of extraction, 99.4%, 94.5% and 60% of PCDDs were removed from samples at 350, 300 and 150 degrees C, respectively. It was also determined that degradation of dioxins had occurred, since the sum of dioxins in the soil plus water extracts after the experiments had considerably decreased. This study revealed that pressurizing is not essential for the removal of dioxins. Reduction was complete within 30 min at 350 degrees C; however, it took a much longer time at lower temperatures. The results of addition experiments in which OCDDs were added to different types of soil samples have shown that dechlorination is one of the major reaction pathways. After addition of OCDD to soil samples, experiments were carried out to examine in detail the degradation pathways of PCDDs. The removal rates and congener profiles varied among soil types. Although it was previously assumed that removal rates and congener profiles depended on the chemical components in soil, nonparametric statistical analysis revealed no significant relationship between the rate of reduction and elements present in the soil. It was confirmed from isomer patterns that dechlorination of the 2,3,7,8-positions in PCDDs takes place somewhat faster than for the 1,4,6,9-positions.
研究了亚临界水萃取（SCWE）从污染土壤中去除二噁英的效果。土壤样品中的大多数二噁英在300摄氏度及以上时减少，但在150摄氏度时也观察到二噁英浓度降低。萃取4小时后，在350、300和150摄氏度下，分别从样品中去除了99.4%、94.5%和60%的多氯二苯并对二噁英（PCDDs）。还确定二噁英发生了降解，因为实验后土壤和水提取物中二噁英的总量大幅下降。这项研究表明，加压对于去除二噁英并非必不可少。在350摄氏度下30分钟内降解完成；然而，在较低温度下需要更长时间。将八氯二苯并对二噁英（OCDDs）添加到不同类型土壤样品的添加实验结果表明，脱氯是主要反应途径之一。向土壤样品中添加OCDD后，进行了实验以详细研究PCDDs的降解途径。去除率和同系物分布因土壤类型而异。尽管之前认为去除率和同系物分布取决于土壤中的化学成分，但非参数统计分析表明，还原速率与土壤中存在的元素之间没有显著关系。从异构体模式证实，PCDDs中2,3,7,8位的脱氯比1,4,6,9位稍快。
