In Situ Study on Biodegradation Differences Between Dissolved Phenanthrene and Methylphenanthrene Using First Derivative Synchronous Fluorescence Spectrometry With Double Scans

A rapid and highly sensitive first derivative synchronous fluorescence spectrometry with double scans was successfully optimized for the simultaneous determination of dissolved phenanthrene (Phe), 1-methylphenanthrene (1-MP), and 3-methylphenanthrene (3-MP) and their metabolites such as 1-hydroxy-2-naphthoic acid (1H2NA) and salicylic acid (SA) in the biodegradation processes of Phe, 1-MP, and 3-MP by Novosphingobium pentaromativorans US6-1. Δλ of 55 and 109 nm were selected for Phe, 1-MP, 3-MP, 1H2NA, and SA, respectively. The intensities of the first derivative synchronous fluorescence detected at λex of 289, 292, 291, 354, and 312 nm for Phe, 1-MP, 3-MP, 1H2NA, and SA varied linearly with the concentrations of them in the ranges of 0.20 × 10⁻⁷–44.89 × 10⁻⁷, 0.20 × 10⁻⁷–13.04 × 10⁻⁷, 0.20 × 10⁻⁷–13.04 × 10⁻⁷, 0.22 × 10⁻⁷–76.30 × 10⁻⁷, and 0.11 × 10⁻⁷–52.00 × 10⁻⁷ mol/L. The limits of detection were 0.11 × 10⁻⁹, 0.30 × 10⁻⁹, 0.27 × 10⁻⁹, 0.33 × 10⁻⁹, and 2.90 × 10⁻⁹ mol/L for Phe, 1-MP, 3-MP, 1H2NA, and SA, respectively, with RSD less than 2%. The method was successfully applied in situ to detect the instantaneous concentrations of the PAHs and their metabolites, especially SA, during their biodegradation processes under simulated conditions in the lab. The results demonstrated that the upper metabolic pathways of 1-MP and 3-MP by US6-1 were distinctly different from that of Phe owing to steric hindrance of the methyl group.