Oxidative degradation of glyphosate and aminomethylphosphonate by manganese oxide
Oxidative degradation of glyphosate and aminomethylphosphonate by manganese oxide
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DOI：
10.1021/es051342d
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发表时间：
2005-12-01
影响因子：
11.4
通讯作者：
McBride, MB
中科院分区：
文献类型：
--
作者：
Barrett, KA;McBride, MB
甘氨酰（N-（膦酰基甲基）甘氨酸）是世界上最常用的除草剂，在大多数条件下在土壤中降解相对较快，可能是通过微生物过程。土壤和水中最常检测到的降解产物是AMPA（氨甲基膦酸）。我们报告的第一个证据的非生物途径的草甘膦和AMPA降解环境现实的条件下。草甘膦和AMPA在20摄氏度下在水钠锰矿（一种土壤中常见的氧化锰）的稀水悬浮液中降解，正磷酸盐在溶液中积累数天即可证明这一点。结果表明，草甘膦的非生物降解主要是由于锰氧化物表面的C-P键断裂引起的，而草甘膦的降解产物肌氨酸的C-N键断裂则主要是由于锰氧化物表面的C-P键断裂引起的，草甘膦的降解速度比AMPA快，温度越高（50 ℃），草甘膦和AMPA的降解速度越快。添加硫酸盐的溶液中没有显着的反应速率的影响，但Cu 2+添加抑制降解。由于该金属离子与草甘膦强烈络合，抑制作用可归因于Cu 2+将草甘膦配位限制在Mn氧化物表面的反应性氧化位点的能力。使用类似的实验设计，我们不能检测到草甘膦降解在MnCl 2（0.5 mM）的等摩尔溶液中。然而，我们证明了Mn 2+的氧化在溶液中和在惰性表面上都得到增强，在草甘膦（4：1 Mn-草甘膦摩尔比）的存在下。这一结果表明，在Mn 2+存在下草甘膦的氧化分解可能最终发生在锰的自发氧介导的氧化之后。
Glyphosate (N-(phosphonomethyl)glycine), the most commonly used herbicide worldwide, degrades relatively rapidly in soils under most conditions, presumably by microbial processes. The most frequently detected degradation product in soil and water is AMPA (aminomethylphosphonic acid). We report the first evidence for an abiotic pathway of glyphosate and AMPA degradation under environmentally realistic conditions. Both glyphosate and AMPA degraded at 20 degrees C in dilute aqueous suspensions of birnessite, a manganese oxide common in soils, as evidenced by the accumulation of orthophosphate in solution over a period of several days. It is concluded that the abiotic degradation involved C-P bond cleavage at the Mn oxide surface, although evidence for C-N bond cleavage in the case of glyphosate and sarcosine, a likely degradation product of glyphosate, was found. The degradation of glyphosate was faster than that of AMPA, and higher temperature (50 degrees C) resulted in faster degradation of both glyphosate and AMPA. The addition of sulfate to the solution had no marked effect on the reaction rate, although CU2+ addition inhibited degradation. As this metal ion complexes strongly with glyphosate, the inhibition can be attributed to the ability of Cu2+ to limit glyphosate coordination to reactive oxidation sites at the Mn oxide surface. Using a similar experimental design, we were unable to detect glyphosate degradation in an equimolar solution of MnCI2 (0.5 mM). However, we demonstrated that the oxidation of Mn2+ is enhanced both in solution and on an inert surface, in the presence of glyphosate (4:1 Mn-glyphosate molar ratio). This result suggests that the oxidative breakdown of glyphosate in the presence of Mn2+ may ultimately occur following the spontaneous oxygen-mediated oxidation of manganese.