Highlights ► Monolinuron is degraded by ultrasounds by OH or CO 3 - radicals. ► Ultrasound efficiency was improved in the presence of nanoparticles of TiO 2 and SiO 2 only at 20 kHz. ► Activated species may be formed at the TiO 2 surface that promote the formation of H 2O 2 and MLN decomposition.