Uptake of 10 polar organic solvents during short-term respiration

Respiratory uptake was investigated for 10 polar organic solvents with high blood/air partition coefficients (lambda(blood/air)): ethyl acetate (lambd a(blood/air), 77), methyl iso-butyl ketone (90), methyl acetate (90), methy l propyl ketone (150), acetone (245), iso-pentyl alcohol (381), iso-propyl alcohol (848), methyl alcohol (2590), ethylene glycol monobutyl ether (EGBE , 7970), and propylene glycol monomethyl ether (PGME, 12380). Test-air conc entrations (C-inh) were 25 to 200 ppm. Four healthy male volunteers inhaled the test air for 10 min at rest and then room air for 5 min. The percentag e of solvent in the end-exhaled air and in the mixed-exhaled air increased after the start of the test-air respiration, and reached a quasi-steady-sta te level within a few min. The speeds of these increases at the start of th e test-air respiration became lower as lambda(blood/air) increased. The mea n uptakes ((U) over bar) for the last five min of the test air respiration were 67.3, 52.9, 60.4, 53.0, 52.6, 63.0, 60.3, 60.8, 79.7, and 81.3%, respe ctively, for ethyl acetate, methyl iso-butyl ketone, methyl acetate, methyl propyl ketone, acetone, iso-pentyl alcohol, iso-propyl alcohol, methyl alc ohol, EGBE and PGME. Thus, U values of the alcohols were higher than those of the ketones and lower than the glycol ethers. The overall view, except f or esters, showed that (U) over bar increased with lambda(water/air) increa ses. This tendency can be explained by a hypothesis that solvent absorbed i n the mucus layer of the respiratory tract is removed by the bronchial bloo d circulation. U values of ethyl acetate and methyl acetate were higher tha n those of methyl iso-butyl ketone and methyl propyl ketone, though the lam bda(blood/air) values of these esters were nearly equal to those of the ket ones. For the respiration of the esters, their metabolites, ethyl alcohol a nd methyl alcohol, were detected in the exhaled air. The exhalation percent age of the metabolites increased after the start of test-air respiration an d reached a quasi-steady-state level of 2 and 3%, respectively, by the 5th min. These data suggest that removal of the solvent via metabolism in the w all tissue of the respiratory tract plays an important role for the esters.