Kengo Morimoto

Effect of humic substances on the enzymatic formation of OCDD from PCP

Abstract Enzymatic reaction of pentachlorophenol (PCP) catalyzed by horseradish peroxidase (HRP) was investigated under the influence of humic precursors. Six phenolic acids were used as the humic precursors. Three of them were substituted p -hydroxy cinnamic acids and others were substituted p -hydroxy benzoic acids. When PCP was incubated alone, about 40% of PCP was enzymatically transformed by HRP and 4% of that was converted to octachlorodibenzo- p -dioxin (OCDD). The presence of phenolic acids containing no methoxyl groups, i.e., p -coumaric acid and p -hydroxybenzoic acid, accelerated the PCP transformation significantly and lessened production of OCDD. In the presence of p -coumaric acid, more than 90% of PCP was removed in the first 15 min and no OCDD was detected in addition to almost no other products. The color of the solution mixture turned slightly yellow and no precipitates were observed. The solution with p -hydroxy benzoic acid showed similar results. Ferulic acid kept PCP decreasing more than 20 minutes that caused the final degradation rate to be larger and also lessened the amount of products. Vanillic acid however did not seem to affect the transformation of PCP to any great extent. Phenolic acids with two methoxyl groups interfered with PCP degradation for the first 15 min of incubation. Thus the number of methoxyl groups adjacent to the hydroxyl group is very important in evaluating the effects of phenolic acids to the enzymatic reaction of PCP.

Peroxidase catalyzed co-polymerization of pentachlorophenol and a potential humic precursor.

The transformation of xenobiotics in the soil was studied in a model experimental system using pentachlorophenol (PCP), an enzyme, and a potential humic precursor. It has been shown that potential humic precursors such as p-coumaric acid greatly accelerated the peroxidase-catalyzed reaction of PCP (Morimoto K. and Tatsumi K, 1997. EAect of humic substances on the enzymatic formation of OCDD from PCP. Chemosphere 34, 1277‐1283). About 90% of the PCP reacted but almost no transformation products were detected by GC/MS analysis. Most of the transformed PCP was detected in the polymeric products by the determination of the adsorbable organic halide (AOX) in gel permeation chromatography (GPC) fractions. Pyrolysis gas chromatography/mass spectrometry (py-GC/MS) of the polymers showed that tetrachlorophenol (TeCP) was the major pyrolysis product. This accords with the ion chromatography observation that about 20% of the PCP chlorine was released as chloride ion. However, nitrobenzene oxidation produced only a small amount of PCP and no TeCP. Based on the selectivity of the two degradation methods, it is concluded that TeCP is bound to the polymer by a diphenylether linkage, and PCP by an ether linkage to the aliphatic side chain. Thus, it was concluded that the major part of the PCP was incorporated into the polymer from p-coumaric acid by the release of a chlorine atom from the PCP molecule to form a diphenylether linkage with the p-hydroxyl group of the p-coumaric acid polymer. 7 2000 Elsevier Science Ltd. All rights reserved.

Enhancing the release and plant uptake of PAHs with a water-soluble purine alkaloid.

The effect of a common plant alkaloid, caffeine, on the release and plant uptake of some polycyclic aromatic hydrocarbons (PAHs) in soils was investigated. Cucurbita pepo (ssp. pepo cv. Gold Rush) was grown in PAH-spiked media in the presence and absence of caffeine. Solubility tests initially confirmed the ability of caffeine to dissolve PAHs mixtures of anthracene, phenanthrene, pyrene, benzo[a]pyrene and benzo[ghi]perylene. Extraction experiments also highlighted its potential as a PAH-releasing agent from an aged soil. Phytoextraction from a low organic sand medium (f(OC)=0.056+/-0.03%) indicated a significant enhancement of pyrene uptake with three weeks daily watering with 500mgL(-1) caffeine solution. The average pyrene content of roots was 35.3 and 16.0microgg(-1), in caffeine and non-caffeine set-ups, respectively. In the shoots, the corresponding values were 3.60 and 1.67microgg(-1). Both showed more than twofold increase with caffeine. Caffeine also accumulated mainly in the leaves of the treated samples at 2800mgkg(-1) dry weight. Further tests with a 1-year aged soil (f(OC)=5.2+/-1%) containing a mixture of phenanthrene and pyrene yielded parallel results. However, lower PAH content in these samples were observed due to the stronger PAHs partitioning in aged-soil matrix. After four weeks of caffeine, phenanthrene in shoots and roots increased by one and a half and four times, respectively. The corresponding enhancements for pyrene were two and a half and three and a half times.

Effect of phenolic acids in humic acid on the degradation of pentachlorophenol by the photo‐Fenton reaction

Abstract At pH = 5.0, the degradation of pentachlorophenol (PCP) by the photo‐Fenton reaction was facilitated in the presence of humic acid (HA). To identify the functional groups in HA that contributed to this facilitation, the degradation kinetics of PCP were investigated for six types of phenolic acids. The pseudo‐first‐order rate constants of PCP degradation (K 3) increased with those for the photoreduction of Fe(III) (k 1 ).This indicates that the photoreduction of Fe(III) is an important step in the degradation of PCP by the photo‐Fenton reaction. Moreover, the K 3values for gallic, protocatechuic and caffeic acids were larger than those for syringic, vanillic and ferulic acids. This shows that the phenolic acids in HA, which contain neighboring hydroxyl groups, are major contributors to the facilitation of PCP degradation.

Aniline removal by Photocatalytic reaction of iron(iii) mediated with dissolved organic matter

When light (> 370 nm) was allowed to interact with an aqueous solution containing dissolved organic matter (DOM) and Fe(III), removal of aniline (AN) was observed. This was due to the photocatalytic reaction of Fe(III) mediated by DOM. Syringic acid (SYA) and humic acid (HA) were used as DOM in the present study. The 15N‐NMR spectrum of the product mixture from the light irradiation of the SYA/Fe(III) system demonstrated that AN was covalently bound to SYA. The kinetics of AN removal were, therefore, interpreted by assuming covalent binding between DOM and AN. The amounts of covalent binding sites and the apparent second‐order rate constants could be evaluated, and the amounts of covalent binding sites decreased with the increases of the concentration of DOM. This is attributed that the polymerization of DOM by the photo‐oxidation competed with the covalent binding between AN and DOM.