In this study, effects of an increase in concentration of ftillerene-C-60, single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) or fullerene soot (FS) on overall microbial activity was investigated over a 21 d incubation period. Microbial utilisation of C-14-glucose and uptake of C-14-glucose into the microbial biomass was investigated. For CNM-amended soils, greater extents of C-14-glucose mineralisation were found in the C-60-amended soils compared to MWCNT-, SWCNT- or FS-amended soils. In addition, the 100 and 1000 mg kg(-1) were consistently found to have higher extents of mineralisation in C-60, MWCNT, SWCNT or FS-amended soils, respectively. Further, the incorporation of C-14-glucose into the microbial biomass declined slightly with an increase in concentration in the amended soils, but no consistent pattern was observed. As a result, the biophysical quotient (BQ) increased significantly (P