SCOEL/REC/179 trimethylamine : recommendation from the Scientific Committee on Occupational Exposure Limits.

Trimethylamine (TMA) occurs naturally in humans. It is produced endogenously by the gut bacteria and may also be ingested with food, especially fish. The critical effects of inhalation exposure to TMA are odour annoyance and irritative effects. Incompletely reported data have indicated moderate upper respiratory irritation during occupational exposure to TMA at 20 ppm (49 mg/m³). No effects were observed in unspecified routine medical surveillance in workers exposed to 0.1–8 ppm, most of the measurements being below 5 ppm as 8-hour TWAs (AIHA 2005). Van Thriel et al. (2006) reported an odour lateralisation threshold of TMA of 612 ppm (median) but stated that this might be higher than those observed in longer occupational exposure situations, and concluded that the assessment of a recommended OEL based on chemosensory thresholds is problematical. They stated that trigeminal nerve-mediated symptoms might increase with prolonged exposures duration, but did not examine this. Animal data with repeated inhalation exposure over 2 weeks revealed a LOAEC of 75 ppm based on slight respiratory irritation, hyperaemia, epithelial degeneration and squamous metaplasia of the respiratory epithelium in a rat study (Kinney et al 1990). After a recovery period of 2 weeks these effects had disappeared, but at 250 and 750 ppm were irreversible. Pathological studies in rats after inhalation exposure by Rotenberg and Mashbits (1967) demonstrated bronchopneumonia and haemorrhage in the lung tissues, with destruction of the alveolar septa, signs of passive hyperaemia, and isolated haemorrhages in the liver, kidneys, and spleen in the 75-mg/m3 (31 ppm) group. Analogous changes, though less marked, were also observed in the animals of the 25-mg/m³ (10 ppm) group. Owing to insufficient description of the study its outcome can only be used as supportive evidence for a marginal effect level for systemic effects at 10 ppm after long-term exposure in rats. It is also taken into account that the odour threshold is below 1 ppm and TMA has a strong, unpleasant odour.