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

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.