Removal of acetaminophen using enzyme-mediated oxidative coupling processes: II. Cross-coupling with natural organic matter.

The influence of natural organic matter (NOM) on the transformation of acetaminophen in laccase-mediated oxidative coupling systems was investigated in this study. It was found that the removal of acetaminophen was enhanced while the self-coupling of acetaminophen was suppressed in the presence of dissolved NOM, likely resulting from cross-coupling between dissolved NOM and acetaminophen. In additionto cross-coupling with acetaminophen, NOM moieties could couple to each other upon reaction with laccase. This was evidenced by the development of a characteristic absorbance band centered at 472 nm. According to the rate of the absorbance change at 472 nm, the NOM coupling reactions in four different NOM solutions were evaluated. Apparently, the tendency of NOM coupling reactions correlates with the tendency of acetaminophen cross coupling with NOM in these solutions. Possible reaction pathways of cross-coupling were explored using guaiacol as a model NOM proxy, and the products were extracted and analyzed with mass spectrometry (MS). The results suggested that acetaminophen and guaiacol molecules were cross-coupled via the formation of C-O-C bonds.