Cumulative toxicity potential of methomyl aerosol by repeated inhalation.

There are few investigations concerning the cumulative toxicity of agricultural chemicals by repeated inhalation. In this study, Wistar male rats were exposed to methomyl powder (mass median aerodynamic diameter, 4.4 microns) for a single 4-hr exposure, or for 4 hr/day, 5 days/week for 3 months. The average exposure concentrations were controlled at 9.9 mg/m3 for the single exposure and at 14.8 mg/m3 for repeated exposures by a dust generator consisting of a continuous fluidized bed with an overflow pipe and a screw feeder. After the repeated exposures, plasma and red cell cholinesterase activities, and lipid concentrations of the rat lungs were measured and histopathological examinations were performed. There was no evidence of cumulative effects on the red cell cholinesterase activity, histopathological changes and lipid concentration in 3-month repeated inhalation.