OBJECTIVES: Animal studies demonstrate that the formation of the neurotoxic metabolite, 2,5-hexanedione (HD) decreases during co-exposure to methyl ethyl ketone (MEK). The aim of the present study was to describe the influence of co-exposure to MEK on n-hexane toxicokinetics in humans. METHODS: Four healthy male volunteers were exposed, on different occasions, to three different combinations of vapor of these solvents, namely: 50 ppm n-hexane alone, and in combination with 100 and 200 ppm MEK, for 2 h during light physical exercise (50 W). Arterialized capillary blood, venous blood, and urine were sampled at scheduled intervals before, during, and up to 24 h after the onset of the exposure. HD in venous blood and urine was analyzed by gas chromatography with electron capture detector after derivatization with O-(pentafluorobenzyl) hydroxylamine. RESULTS: Serum HD decreased with increasing exposure to MEK at 2 h after the onset of the exposure, from an average concentration of 2.2 micromol/l in the n-hexane-alone condition to 1.2 and 0.44 micromol/l in the 100 and 200-ppm MEK conditions, respectively. The area under the concentration-time curve of HD in venous blood and the concentration of HD at 2 and 4 h after the end of exposure decreased with increasing MEK. These results suggest that combined exposure to MEK and n-hexane at occupationally realistic levels depresses the metabolism of n-hexane in a dose-dependent fashion. CONCLUSION: The internal exposure to the toxic metabolite of n-hexane decreased with co-exposure to MEK in a dose-dependent fashion. Estimation of external exposure by HD in serum or urine could be confounded by the co-exposure to MEK.
OBJECTIVES: Animal studies demonstrate that the formation of the neurotoxic metabolite, 2,5-hexanedione (HD) decreases during co-exposure to methyl ethyl ketone (MEK). The aim of the present study was to describe the influence of co-exposure to MEK on n-hexane toxicokinetics in humans. METHODS: Four healthy male volunteers were exposed, on different occasions, to three different combinations of vapor of these solvents, namely: 50 ppm n-hexane alone, and in combination with 100 and 200 ppm MEK, for 2 h during light physical exercise (50 W). Arterialized capillary blood, venous blood, and urine were sampled at scheduled intervals before, during, and up to 24 h after the onset of the exposure. HD in venous blood and urine was analyzed by gas chromatography with electron capture detector after derivatization with O-(pentafluorobenzyl) hydroxylamine. RESULTS: Serum HD decreased with increasing exposure to MEK at 2 h after the onset of the exposure, from an average concentration of 2.2 micromol/l in the n-hexane-alone condition to 1.2 and 0.44 micromol/l in the 100 and 200-ppm MEK conditions, respectively. The area under the concentration-time curve of HD in venous blood and the concentration of HD at 2 and 4 h after the end of exposure decreased with increasing MEK. These results suggest that combined exposure to MEK and n-hexane at occupationally realistic levels depresses the metabolism of n-hexane in a dose-dependent fashion. CONCLUSION: The internal exposure to the toxic metabolite of n-hexane decreased with co-exposure to MEK in a dose-dependent fashion. Estimation of external exposure by HD in serum or urine could be confounded by the co-exposure to MEK.