NP₁EC Degradation Pathways Under Oxic and Microxic Conditions

The degradation pathway of nonylphenol ethoxyacetic acid (NP1EC) and the conditions favoring dicarboxylated alklyphenol ethoxyacetic acid (CA(0)P(1)EC; where n = the number of aliphatic carbon atoms) formation were studied in oxic microcosms constructed with organic carbon-poor soil from the Mesa soil aquifer treatment (SAT) facility (Arizona) and pristine organic carbon-rich sediments from Coyote Creek (California). Results suggest that the availability of dissolved oxygen determines the dominant biodegradation pathway; ether cleavage and the formation of NP is favored by oxic conditions, while alkyl chain oxidation and the formation of CAP(1)ECs is favored under microxic conditions. In the Mesa microcosms, para-NP1EC was transformed to para-nonyl phenol (NP) before being rapidly transformed to nonyl alcohols via ipso-hydroxylation. In the Coyote Creek microcosms, large quantities of CAP(1)ECs were observed. Initially, CA(8)P(1)ECs were the dominant metabolites, but as biodegradation continued, CA(6)P(1)ECs became the dominant metabolites. Compared to the CA(8)P(1)ECs, the number of CA(6)P(1)ECs peaks observed was small (< 6) even though their concentrations were high. Several novel metabolites, tentatively identified as 3-alkylchroman-4-carboxylic acids (with alkyl groups ranging from C-2 to C-5), were formed in the Coyote Creek microcosms. These metabolites are presumably formed from ortho-CAPIECs by intramolecular ring closure.