Occupational hygiene conditions in scrap-tire shredding facilities were assessed to identify potential health risk factors for workers and provide a basis for developing future control measures. Specifically, noise, volatile organics and particulate levels were measured at two plants. Particulate/dust levels were measured via filter collection, and were analyzed gravimetrically. Sound pressure levels were measured and their spectral properties analyzed. Moreover, the major chemical species in the samples were identified using GC/MS. Finally, the mutagenic activity associated with the airborne particulates was assessed using a typical Ames test applied to Salmonella strains TA98 and TA100, with or without bio-activation. The noise levels were steady and high throughout the facilities, ranging from 85 to approximately 100 dBA. The octave band spectrum analysis reveals pattern similarity among the different areas. Levels of volatile organics were not significant, but a few mutagens/carcinogens, such as styrene, benzothiazole, phthalate ester and naphthalene were identified. Total particulate levels ranged from 0.43 to 6.54 mg/m(3), while respirable particulates were in the range 0.23-1.25 mg/m(3). Ames testing revealed indirect mutagenicity on strain TA98, indicating possible effects of frame-shift type mutagens. Chemical analysis of airborne particulates confirmed the presence of amines, aniline, quinoline, amides and benzothiazole, which are potentially convertible to frame-shift type mutagenic nitrosoamines. Noise appears to be an occupational hazard for workers at scrap-tire shredding facilities, but the risk associated with the mutagenic/carcinogenic property of particulates requires further confirmation.