| The contamination of soils by polycyclic aromatic hydrocarbons (PAHs) has posed a serious threat to public health and ecosystems. Bioremediation of PAH-contaminated soils is a low-cost and relatively clean strategy. However, the bioremediation is not always successful, and one of the major causes is the limited PAH bioavailability to microorganisms in the soil system. Surfactant addition is a common strategy to increase the bioavailability of PAHs in the soil. We evaluated two nonionic surfactants, one hydrophobic (Brij 30) and one hydrophilic (C12E8), for their ability to enhance the biodegradation of PAHs and their influence on groups of PAH-degrading bacteria in the bioreactor community that had previously been identified by DNA-based stable-isotope probing. The effects of each surfactant were evaluated at doses corresponding to equilibrium aqueous-phase concentrations well above the surfactant's critical micelle concentration (CMC), slightly above the CMC, and below the CMC. The concentrations of all 3- and 4-ring PAHs were significantly reduced in the soil amended with Brij 30 at the two lower doses compared to controls, whereas removal of only the 3-ring PAHs was significantly enhanced at the highest Brij 30 dose. In contrast, C12E8 did not enhance PAH removal at any dose. Brij 30 addition at the lowest dose significantly increased the desorption of most PAHs, whereas the addition of C12E8 at the lowest dose actually decreased the desorption of all PAHs. Two groups of organisms containing naphthalene- or salicylate-degrading bacteria increased in abundance substantially after incubation with both surfactants. In contrast, Brij 30 inhibited a third group of naphthalene/salicylate degraders and two groups of pyrene-degrading bacteria, and it modestly inhibited the predominant phenanthrene degrader at the highest dose. Overall, this study demonstrates that the effects of the surfactants on PAH biodegradation could be explained by their effects on PAH bioavailability, and that surfactant addition can have differential effects on populations of organisms known to be responsible for contaminant degradation within a microbial community. |
