A laboratory study was conducted to determine whether commercial surfactants enhance the bioremediation of PAH‐contaminated sediments. Phenanthrene was chosen as a representative PAH; an inoculum of PAH‐degrading microorganisms, enriched from an aquatic sediment, was used in sediment‐water slurry microcosm biodegradation experiments. Of seven nonionic surfactants tested, only one (Triton X‐100) did not inhibit phenanthrene mineralization at concentrations above the critical micelle concentration (CMC). Temporal studies on Triton X‐100 revealed that while it initially inhibited mineralization in sediment‐free microcosms, after 1 week Triton X‐100 slightly improved phenanthrene biotransformation and mineralization in microcosms with and without sediment. For all treatments, phenanthrene disappearance was complete after 9 d, and mineralization reached 50 to 65% after 12 d. Sorption to the sediment appears to have reduced the free aqueous surfactant concentration, thereby reducing surfactant toxicity to the microorganisms. These results suggest that many surfactants are toxic to PAH‐degrading microorganisms, and while surfactant addition may not always have adverse effects on biodegradation, the use of surfactants might not be desirable to achieve complete contaminant removal.

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