Naphthenic acids (NAs) are naturally occurring, linear and cyclic carb- oxylic surfactants associated with the acidic fraction of petroleum. NAs account for most of the acute aquatic toxicity of oil sands process-affected water (OSPW). The toxicity of OSPW can be reduced by microbial degradation. The aim of this research was to determine the extent of NA degradation by sedi- ment microbial communities exposed to varying amounts of OSPW.
Methods and Results: Eleven wetlands, both natural and process-affected, and one tailings settling pond in Northern Alberta were studied. The natural wet- lands and process-affected sites fell into two distinct groups based on their water chemistry. The extent of degradation of a 14C-labelled monocyclic NA surrogate [14C-cyclohexane carboxylic acid (CCA)] was relatively uniform in all sediments (approximately 30%) after 14 days. In contrast, degradation of a bicyclic NA surrogate [14C-decahydronaphthoic acid (DHNA)]was significantly lower in non process-affected sediments. Enrichment cultures, obtained from an active tailings settling pond, using commercially available NAs as the sole carbon source, resulted in the isolation of a co-culture containing Pseudomonas putida and Pseudomonas fluorescens. Quantitative GC–MS analysis showed that the co-culture removed >95% of the commercial NAs, and partially degraded the process NAs from OSPW with a resulting NA profile similar to that from ‘aged wetlands’.