Short communication: Biodegradation of 1-naphthol in the presence of humic acid

Biodegradation of 1-naphthol by a pure culture was measured in the presence (65 mg C L^-1) and absence of a forest soil humic acid (HA). Experiments were performed under nongrowth conditions and controlled ionic strength (I equivalent to 10 mM LiCl) at pH 8.0. 1-Naphthol was allowed to react with HA under aerobic conditions in the dark for 7 days to promote sorption prior to bacterial inoculation. During this abiotic sorption period, 3.7-12% of 1-naphthol was transformed into oxidative products (naphthoquinones). At low initial 1-naphthol concentrations (<2.7 mg L^-1), 1-naphthol mineralization (measured by ¹⁴CO₂ production) decreased from 25-35% to 9-16% with HA. 1-Naphthol was biodegraded to concentrations below HPLC-PDA detection limit (0.10 mg L^-1) except at the highest 1-naphthol concentrations tested (>9.0 mg L^-1) with or without HA. Both abiotic and biotic 1-naphthol transformation pathways accumulated similar products, and these products were more recalcitrant than 1-naphthol. The sorption of 1-naphthol abiotic transformation products and bacterial metabolites to HA (not 1-naphthol) reduced 1-naphthol mineralization.