Formation of chloroacetic acids from soil, humic acid and phenolic moieties

Abstract

The mechanism of formation of chloroacetates, which are important toxic environmental substances, has been controversial. Whereas the anthropogenic production has been well established, a natural formation has also been suggested. In this study the natural formation of chloroacetic acids from soil, as well as from humic material which is present in soil and from phenolic model substances has been investigated. It is shown that chloroacetates are formed from humic material with a linear relationship between the amount of humic acid used and chloroacetates found. More dichloroacetate (DCA) than trichloroacetate (TCA) is produced. The addition of Fe 2þ , Fe 3þ and H 2 O 2 leads to an increased yield. NaCl was added as a source of chloride. We further examined the relationship between the structure and reactivity of phenolic substances, which can be considered as monomeric units of humic acids. Ethoxyphenol with built-in ethyl groups forms large amounts of DCA and TCA. The experiments with phenoxyacetic acid yielded large amounts of monochloroacetate (MCA). With other phenolic substances a ring cleavage was observed. Our investigations indicate that chloroacetates are formed abiotically from humic material and soils in addition to their known biotic mode of formation.

Biogeochemical cycles of chlorine in the coniferous forest ecosystem: practical implications

“…Keppler et al (2000) reported abiotic chlorination of SOM mediated by iron(III) leading to aliphatic haloderivatives; Fahimi et al (2003) demonstrated another kind of abiotic formation of chloroacetates (this process was successfully explained by the Fenton reaction); and Biester et al (2004) found halogen retention in peat bogs. It seems that formation of hydroxyl radicals is the basis of either microbial or abiotic chlorination of organic matter by hypochlorous acid (HOCl) formed from chloride present in the soil (Laturnus et al 2005, Matucha et al 2007a).…”

X-ray spectromicroscopic investigation of natural organochlorine distribution in weathering plant material

“…Metals such as Fe are often the key cofactors in the reaction centers of haloperoxidative enzymes (Sundaramoorthy et al, 1995). In addition, abiotic (non-enzymatic) metal-catalyzed chlorination of aliphatic and aromatic substrates has been documented in natural systems (Keppler et al, 2000;Schoeler and Keppler, 2002;Fahimi et al, 2003;Holmstrand et al, 2006) and as part of biomimetic synthetic schemes in the laboratory (Delaude and Laszlo, 1990;Walker et al, 1997).…”

“…In addition to these non-specific natural chlorination products, individual chlorinated metabolites have been isolated from soil fungi and lichen for decades (Yosioka et al, 1968;Turner and Aldridge, 1983;Wijnberg, 1998;Gribble, 2003). Abiotic (nonenzymatic) chlorination has also been shown to occur naturally and is thought to be catalyzed by metal ions in the low-pH soil environment (Keppler et al, 2000;Schoeler and Keppler, 2002;Fahimi et al, 2003;Holmstrand et al, 2006). This evidence collectively indicates that terrestrial Cl undergoes complex biogeochemical transformations.…”

Iron-catalysed oxidation and halogenation of organic matter in nature

“…Based on studies with several phenolic derivatives (catechol, hydroquinone, and recorcinol), [166,167] [159] (2) chloroethene and chloroalkanes, [160] (3) chlorinated acetic acid, [118,161] (4) muconic, formic, acetic, oxalic, malonic, fumaric and maleic acids, [162][163][164] (5) chloroethyne, [165] (6) carbon suboxide, [166] (7) trihalomethanes, [167] (8) furan. [168,169] In the corresponding enzymes and model systems, the iron species are transformed to the resting state, top left.…”

“…13). [172] This mechanism can explain the formation of haloacetic acid [161] but, in contrast to the experimental conditions, it assumes basic conditions for the release of trihalomethanes. [167] A review of the literature on natural trichloromethane formulation in peatlands, tundra and forest soils found strong evidence that also in acidic environments the liberation of trichloromethane is conclusive.…”