The sonochemical degradation of 5 microg l(-1) triclosan, a priority micro-pollutant, in various environmental samples (seawater, urban runoff and influent domestic wastewater) as well as in model solutions (pure and saline water) was investigated. Experiments were conducted with a horn-type sonicator operating at 80 kHz frequency and a nominal applied power of 135 W, while solid-phase microextraction coupled with gas chromatography-electron capture detector (SPME/GC-ECD) was employed to monitor triclosan degradation. The latter followed pseudo-first order kinetics with the rate constant being (min(-1)): 0.2284 for seawater>0.1051 for 3.5% NaCl in deionised water>0.0597 for centrifuged urban runoff approximately 0.0523 for untreated urban runoff >0.0272 for deionised water >0.0063 for wastewater influent. SPME/GC-ECD and SPME coupled with gas chromatography-mass spectrometry (SPME/GC-MS) were also used to check for the formation of chlorinated and other toxic by-products; at the conditions in question, the presence of such compounds was not confirmed.