A subchronic inhalation study of a special test toner in rats.

A subchronic inhalation study, using SPF, F-344 rats, was conducted for 6 hr/da, 5 da/wk for 13 weeks. The special test toner was enriched about 10-fold, respirably (ACGIH), relative to product. Nominal exposure levels were 0, 1.0, 4.0, 16.0 and 64 mg/cubic meter (0, 0.35, 1.4, 5.6 and 22.4 mg/cubic meter, respirable). The exposures were well-tolerated, with no unscheduled deaths. Significant findings were restricted to the high exposure groups. The MTD (pulmonary) was determined relative to a defined Maximum Functionally Tolerated Dose (MFTD). At the lower exposures, clearance measurements of toner and a spike of iron oxide (Fe-59) were essentially unchanged from controls. At 16 mg/cubic meter, slight effects were observed. At 64 mg/cubic meter, no appreciable toner clearance occured after 60 da exposure. The MFTD was deemed to be exceeded at 64 mg/cubic meter and 16 mg/cubic meter was chosen for the chronic study high concentration. (ITA