Degradation pathways of low-ethoxylated nonylphenols by isolated bacteria using an improved method

Abstract

Nonylphenol ethoxylates (NPEOs) with low ethoxylation degree (NP av2 EO; containing two ethoxy units on average) and estrogenic properties are the intermediate products of nonionic surfactant NPEOs. To better understand the environmental fate of low-ethoxylated NPEOs, phylogenetically diverse low-ethoxylated NPEO-degrading bacteria were isolated from activated sludge using gellan gum as the gelling reagent. Four isolates belonging to four genera, i.e., Pseudomonas sp. NP522b in γ-Proteobacteria, Variovorax sp. NP427b and Ralstonia sp. NP47a in β-Proteobacteria, and Sphingomonas sp. NP42a in α-Proteobacteria were acquired. Ralstonia sp. NP47a or Sphingomonas sp. NP42a, have not been reported for the degradation of low-ethoxylated NPEOs previously. The biotransformation pathways of these isolates were investigated. The first three strains (NP522b, NP427b, and NP47a) exhibited high NP av2 EO oxidation ability by oxidizing the polyethoxy (EO) chain to form low-ethoxylated nonylphenoxy carboxylates, and then further oxidizing the alkyl chain to form carboxyalkylphenol polyethoxycarboxylates. Furthermore, Sphingomonas sp. NP42a degraded NP av2 EO through a nonoxidative pathway with nonylphenol monoethoxylate as the dominant product.