This study investigates the impact of different types of carbon nanomaterials (CNMs) namely C60, multi-walled carbon nanotubes (MWCNTs) and fullerene soot on the catabolism of (14)C-phenanthrene in soil by indigenous microorganisms. Different concentrations (0%, 0.01%, 0.1% and 1%) of the different CNMs were blended with soil spiked with 50 mg kg(-1) of (12)C-phenanthrene, and aged for 1, 25, 50 and 100 days. An increase in the concentration of MWCNT- and FS-amended soils showed a significant difference (P = 0.014) in the lag phase, maximum rates and overall extent of (14)C-phenanthrene mineralisation. Microbial cell numbers did not show an obvious trend, but it was observed that control soils had the highest population of heterotrophic and phenanthrene degrading bacteria at all time points.