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No direct studies are available concerning the mode of action of the substance. 1,3 -Diketones unfold metal chelating properties in vivo which may lead to inhibition of the activity of metal containing enzymes like peroxidases or cytochrome P450. In an inhalation study conducted in male Fischer 344 rats it could be shown that 14C-labeled-2,4- pentanedione was readily absorbed. Nose-only exposure to 400 ppm 14C labeled-2,4-pentanedione resulted in a rapid increase in plasma radioactivity during the first 3 hours of exposure. A plateau was formed at the end of the 6 hour exposure period. Unmetabolized 14C-labeled-2,4-pentanedione was present throughout the whole of the exposure phase. Immediately post exposure, radioacivity was present in all tissues examined, but on a concentration basis (μg equivalents/g) there was no preferential accumulation of 14C in any tissue or organ. On a total organ basis, highest contents were in liver and kidneys. Unmetabolized 14C-labeled-2,4-pentanedione declined rapidly to undetectable concentrations by 12 hours. Elimination of 14C from plasma followed a biphasic pattern with a terminal half-life of 30.72 hours. Excretion over 48 hours of 14C was approximately equivalent between urine (37.6 %, mainly not identified metabolites) and expired 14CO2 (36.3 %), which the most part of the radioactivity was eliminated in the first 12 hours. Expired volatiles, feces, tissues and carcass accounted for 2.29, 2.78, 1.66 and 17.15 % of the total administered radioactivity dose 48 hours postdosing, respectively [modified from OECD SIDS Dossier]