TOXICOLOGY AND APPLIED PHARMACOLOGY 55, 229-234 (1980) Inhalation Toxicology of Sodium Sulfite Aerosols in Rats JEROLD A. LAST, PURNENDU K. DASGUPTA, AND JAMES R. ETCHISON CaliJornia Primate Research Center, University of California, Davis, California 95616 Received March 20. 1980; accepted May 6, 1980 Inhalation Toxicology of Sodium Sulfite Aerosols in Rats. LAST, J. A., DASGUPTA, P. K., AND ETCHISON, J. R. (1980). Toxicol. Appl. Pharmacol. 55,229-234. Rats were ex- posed to well-characterized aerosols of sodium sulfite, at levels ranging from 0.1 to about 15 mgim” and particle sizes of about 1 wrn (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 1.5 mg/m3 of Na,S03 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 mgim” of Na2S0, aerosol. Control experiments involving exposure to a sulfate (Na,SO,) aerosol at 15 mg/m” indicated that the observed effects were indeed due to exposure to the sulfite moiety. Ex- posure to aerosols of sodium hydroxymethane sulfonate (the product of addition of formal- dehyde to sodium sulfite) aerosols (5 mpim3) 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 l-pm aerosols of sodium sulfite at concentrations equivalent to amounts of SO, of about 0.2-2.7 ppm results in responses of the rats that may be con- veniently evaluated when sensitive enough toxicological indexes are quantitated. Relatively little is known about the inhala- the respiratory rate of mice during 1- 10 min tion toxicology of metal sulfites (SO:-), bi- exposures. Sodium sulfite (200 ppm, 10 min) sulfites (HSO;), and pyrosulfites (meta- immediately preceding SO, (238 ppm, 10 bisulfites, S,O:-), especially as compared min) or in conjunction with SO, (200 + 238 with the more extensive literature on the ppm, 10 min) was reported in this study to toxicity of sulfur dioxide and of aerosols of elicit responses that were attributable to the sulfuric acid and various metallic sulfates SO, alone. In contrast, bisulfites of sodium (SO:-). Alarie et al. (1973) have suggested and potassium (300-400 ppm, l-10 min) that, at low concentrations, pyrosulfites may and SO, (250 ppm, l- 10 min) depressed be more irritating to the respiratory tract respiratory frequency about 40-50% in (as evaluated by their effect on respiratory parallel assays. (All of the above concen- rate in mice) than is SO,. Sodium sulfite trations are expressed in terms of SO,.) at high concentrations for short times (306 Gunnison and his colleagues have studied ppm, 10 min) had no effect in this study on extensively the reaction of sulfites with the respiratory rate observed for mice. In protein-bound SH groups to give rise to addition, Wakisaka (1976) has reported that S-sulfonates, a potential mechanism whereby neither sodium sulfite (47-350 ppm) nor sulfites may be metabolized in the lung potassium sulfite (53-423 ppm) affected (Gunnison and Palmes, 1973, 1978; Gunni- 229 004 1-008X/80/ 110229-06$02.00/O Copyright 0 1980 by Academic Press, Inc. All rights of reproduction in any form reserved.