Inhalation toxicology of sodium sulfite aerosols in rats

Rats were exposed to well-characterized aerosols of sodium sulfite, at levels ranging from 0.1 to about 15 mg/m³ and particle sizes of about 1 μm (mass median aerodynamic diameter). The responses of rats to breathing these aerosols for 3 days were evaluated by measurements of glycoprotein secretion rates by cultured tracheal explants from these rats, by measurement of protein, DNA, and RNA levels of lung homogenates prepared from these rats, and by quantitation of wet to dry weight ratios of right apical lung lobes from these rats. Increased rates of glycoprotein secretion were observed for tracheae from rats exposed to 5 or to 15 mg/m³ of Na₂SO₃ aerosol, and increased wet to dry weight ratios of right apical lobes were also observed after exposure to these levels, as well as after exposure to 1 mg/m³ of Na₂SO₃ aerosol. Control experiments involving exposure to a sulfate (Na₂SO₄) aerosol at 15 mg/m³ indicated that the observed effects were indeed due to exposure to the sulfite moiety. Exposure to aerosols of sodium hydroxymethane sulfonate (the product of addition of formaldehyde to sodium sulfite) aerosols (5 mg/m³) elicited less response in these assays than did exposure to sodium sulfite aerosol at the same concentration. We conclude that exposure of rats to well-characterized 1-μm aerosols of sodium sulfite at concentrations equivalent to amounts of SO₂ of about 0.2 – 2.7 ppm results in responses of the rats that may be conveniently evaluated when sensitive enough toxicological indexes are quantitated.