柳树对叔丁醇的降解试验

Degradation tests of tert-butyl alcohol by willow trees

甲基叔丁基醚(MTBE)是目前北美燃料市场最常用的汽油添加剂.由于其化学稳定性强且难于转化,MTBE已成为一种蔓延性的地下水污染物.有氧微生物降解技术被认为是目前对MTBE污染治理最为有效的方法之一,其作用机理是:MTBE在细胞色素酶(CYP-450s)的作用下首先分解成为叔丁醇(TBA),进而完全转化为CO2和H2O.细胞色素酶(CYP-450s)是维管束植物中最为常见的一种酶,我们有理由相信维管束植物细胞能降解MTBE,但试验研究表明超过25种以上的常见植物细胞并不能降解MTBE.TBA是MTBE降解过程中最为稳定的中间产物,植物对其降解的研究目前尚未见报道.本实验用一自行设计的植物反应器来研究柳树(Salixalba)对TBA降解的可能性.长出新根须和嫩叶的柳树枝条在一容积500ml的植物反应器中生长12 d(其中TBA溶液450ml)来观察TBA对柳树生长的影响,同时测定柳树对TBA的吸收和降解.TBA及其它可能的降解产物用气相色谱来检测.本实验结果表明在为期12 d的时间内,水溶液中15.26%的TBA可以通过柳树的蒸腾作用去除,但是没有检测到任何可能的降解产物,在植物体内也只发现了少量的TBA残留(＜1%).同时柳树的根细胞和叶细胞也用来研究对TBA的降解可能性,在为期3d的试验中,柳树的根细胞和叶细胞对TBA的吸收是非常有限的(＜10%),也没有检测到任何可能的降解产物.本研究结果表明柳树同样也不能降解TBA,也许TBA难被降解就是富含CYP-450s酶的维管束植物不能降解MTBE的原因所在.

Methyl tert-butyl ether (MTBE) is the most commonly used gasoline oxygenate in the North American's fuel industry. Its persistence in groundwater is of significant concern, which provides a major stimulus for the investigation and research on the environmental sites contaminated with MTBE. There is evidence that MTBE has become one of the most common contaminants in urban groundwater. Aerobic biodegradation has been viewed as one of the most effective methods for treating MTBE contamination, in which MTBE is broken down to the intermediate tert-butyl alcohol (TBA) through the activities of the enzymes cytochrome P-450 monooxygenase (CYP 450s), and TBA is further metabolized to the final products CO2 and H2O. Enzymes of the CYP 450s are the typical enzyme of vascular paints to play a critical role in the plant metabolism and we therefore have good reasons to believe that paints would be able to metabolize MTBE. Initial studies indicated that more than 24 plants from 15 families were found to be unable to degrade MTBE. Currently there is no data available in the research of phytoremediation of TBA. This paper examined the degradation potential of rert-butyl alcohol (TBA) by willow trees (Salix alba) within a carefully designed bioreactor. Pre-rooted willow trees were kept in an Erlenmeyer flask of 500 mL with 450 mL spiked aqueous solution for 12 days. TBA and other possible intermediates of TBA were measured by GC/FID. Willow tree uptake tests indicated that 15.26% TBA mass in aqueous solution was removed through willow tree activities at 15癈 over a 12-day period of exposure. No any other possible metabolite of TBA was tracked and trace amounts of TBA mass (< 1%) were found within the willow tree biomass as insoluble residue during the entire period of tests. Excised willow roots and leaves were also used to investigate the potential of willow trees to degrade TBA within glass vessels with 25 mL spiked solution for 3 days. Results of metabolism tests with excised roots and leaves indicated that significant TBA reduction (>10%) was not observed in any of the tests and any other known metabolite of TBA was not detected. It is to conclude that TBA is also persistent to the attack of plant enzymes of willow trees. The persistency of TBA may be the key to inhibit and /or disrupt the CYP-450s enzymes of willow trees in the processes of the MTBE metabolism.