Acute and repeated vapor exposure toxicity of 3-(methylthio)propionaldehyde

Because of its vapor pressure (0.6 torr at 20 C) there is a potential For v apor exposure to 3-(methylthio)propionaldehyde (3-MTP) vapor. Liquid 3-MTP may contain trace amounts of acrolein (up to 0.1%), and therefore acrolein vapor may also be present, Acute exposure (24 min to 4 h) of rats to substa ntially saturated atmospheres of 3-MTP generated statically (measured conce ntrations of 261-951 ppm) resulted in marked ocular and respiratory irritan cy followed by death. Deaths occurred either during exposure or a few days postexposure, depending on exposure time. Measured acrolein vapor concentra tions in these static studies were 16.7-216 ppm. In contrast, when substant ially saturated vapor atmospheres were generated dynamically (277-320 ppm 3 -MTP) only minor transient signs of irritancy were present, and only 1/40 e xposed animals died, Acrolein vapor concentrations ranged 0-6.8 ppm. These findings indicate that the toxicity associated with acute static exposures to 3-MTP vapor was due to accumulated acrolein vapor, and that 3-MTP per se has a low order of acute vapor inhalation toxicity. In a first 9-d repeate d vapor exposure study (6 h/d) rats were exposed to 0, 23.6, 96.8 or 246.2 ppm 3-MTP vapor; the mean acroiein concentration was 1.34 ppm (range 1.08-1 .72 ppm). There were no mortalities, but exposure concentration-related ind ications of toxicity were present. These included reduced body weights, hem atology (increased lymphocytes), serum chemistry (reduced total protein and globulin), and respiratory tract histopathology. The latter consisted main ly of squamous metaplasia in the anterior nasal passages at all concentrati ons, being minimal at 23.6 ppm. At the high concentration there was also ol factory atrophy and squamous metaplasia in the larynx, trachea, and larger bronchi; 23.6 ppm was a threshold effect level. The respiratory tract histo pathology was compatible with exposure to acrolein vapor. In a second 9-d s tudy, rats were exposed to 0, 0.47, 4.99 or 50.5 ppm (6 h/d): no acrolein c ould be detected in the chamber air samples. There were no differences betw een the controls (air alone) and 3-MTP exposed animals with respect to sign s, body weights, food consumption, hematology, serum chemistry, urinalysis, and gross and microscopic pathology. Without detectable acrolein vapor, 50 .5 ppm 3-MTP was a no observable effects level.