Satapanajaru T, Comfort S D, Shea P J
Department of Environmental Science, Kasetsart University, Bangkok, Thailand 10900.
J Environ Qual. 2003 Sep-Oct;32(5):1726-34. doi: 10.2134/jeq2003.1726.
Pesticide-contaminated soil may require remediation to mitigate ground and surface water contamination. We determined the effectiveness of zerovalent iron (Fe(0)) to dechlorinate metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methyl ethyl) acetamide] in the presence of aluminum and iron salts. By treating aqueous solutions of metolachlor with Fe(0), we found destruction kinetics were greatly enhanced when Al, Fe(II), or Fe(II) salts were added, with the following order of destruction kinetics observed: Al2(SO4)3 > AlCl3 > Fe2(SO4)3 > FeCl3. A common observation was the formation of green rusts, mixed Fe(II)-Fe(III) hydroxides with interlayer anions that impart a greenish-blue color. Central to the mechanism responsible for enhanced metolachlor loss may be the role these salts play in facilitating Fe(II) release. By tracking Al and Fe(II) in a Fe(0) + Al2(SO4)3 treatment of metolachlor, we observed that Al was readily sorbed by the corroding iron with a corresponding release of Fe(II). The manufacturing process used to produce the Fe(0) also profoundly affected destruction rates. Metolachlor destruction rates with salt-amended Fe(0) were greater with annealed iron (indirectly heated under a reducing atmosphere) than unannealed iron. Moreover, the optimum pH for metolachlor dechlorination in water and soil differed between iron sources (pH 3 for unannealed, pH 5 for annealed). Our results indicate that metolachlor destruction by Fe(0) treatment may be enhanced by adding Fe or Al salts and creating pH and redox conditions favoring the formation of green rusts.
受农药污染的土壤可能需要进行修复，以减轻对地下水和地表水的污染。我们测定了零价铁（Fe(0)）在铝盐和铁盐存在下对甲草胺[2-氯-N-(2-乙基-6-甲基苯基)-N-(2-甲氧基-1-甲基乙基)乙酰胺]的脱氯效果。通过用Fe(0)处理甲草胺水溶液，我们发现添加Al、Fe(II)或铁盐时，降解动力学大大增强，观察到的降解动力学顺序如下：Al2(SO4)3 > AlCl3 > Fe2(SO4)3 > FeCl3。一个常见的现象是形成了绿锈，即具有层间阴离子的混合Fe(II)-Fe(III)氢氧化物，呈现出蓝绿色。导致甲草胺损失增加的机制的核心可能是这些盐在促进Fe(II)释放中所起的作用。通过在Fe(0) + Al2(SO4)3处理甲草胺的过程中追踪Al和Fe(II)，我们观察到Al很容易被腐蚀的铁吸附，同时相应地释放出Fe(II)。用于生产Fe(0)的制造工艺也对降解速率有深远影响。用盐改性的Fe(0)处理甲草胺时，退火铁（在还原气氛下间接加热）的降解速率比未退火铁的大。此外，不同铁源在水和土壤中甲草胺脱氯的最佳pH值不同（未退火的为pH 3, 退火的为pH 5）。我们的结果表明，添加Fe或Al盐并创造有利于形成绿锈的pH值和氧化还原条件，可能会增强Fe(0)处理对甲草胺的降解效果。
