Fig. 4. Solid-state ¹⁵N nuclear magnetic resonance (NMR) spectra of hydrofluoric acid (HF)-treated [¹⁵N]- and [¹⁴C]-TNT spiked soils after 51 d of anaerobic incubation (P3) and after termination of the subsequent aerobic phase (total: 83 d of incubation) (P4)