Acute inhalation toxicity of eugenol in rats

Abstract

The acute toxicity of inhaled eugenol was assessed by exposure of three groups of five male and five female rats to a submicron aerosol of eugenol for 4 h followed by a 14-day observation period. A fourth group, also of five male and five female rats and exposed to air only under similar conditions, served as a control group for comparison. The three concentrations of eugenol to which the different groups were exposed were 2.58, 1.37 and 0.77 mg/l. The mass median aerodynamic diameters and geometric standard deviations of the aerosols were, respectively, 0.82 μm (σg 2.26), 0.88 μm (σg 2.05) and 0.9 μm (σg 1.87). Clinical signs observed during exposure consisted principally of moderately increased salivation and restlessness (indicative of irritation) and abnormal breathing patterns. The signs were graded, being less marked in animals exposed to the lower concentrations of eugenol. All three groups, exposed to high, medium and low levels of eugenol, lost weight overnight following exposure. Associated with the weight loss were marked reductions in food and water intake. The responses appeared to be largely independent of the concentration of eugenol inhaled, although there was some evidence of a graded effect on water intake. There was rapid recovery, with food and water consumption data comparable with control values throughout most of the remainder of the 14-day observation period. Also, by the end of the observation period, group mean body weights were comparable. Upon sacrifice and macroscopic examination of the animals, abnormalities were detected in the lungs only of a few animals: 3/10 control, 2/10 eugenol 2.58 mg/l, and 2/10 eugenol 0.77 mg/l. These consisted of dark red/red (raised) areas up to 4×4 mm. Such abnormalities are not uncommon in the lungs of laboratory maintained rats and their presence with equal incidence in control animals suggests that they are unlikely to be related to inhalation of eugenol. Lung weight to body weight ratio values for all groups were similar, providing no evidence of any persistent effect of eugenol on the lungs of the rats. Similarly, histopathological examination of the lung failed to reveal any treatment-related changes. A few incidental lesions present were considered spontaneous in origin and therefore of no toxicological importance.