Saturday, March 14, 2009

MIBK by inhalation - Easy Come, Easy Go

Simulation of repeated dose kinetics of methyl isobutyl ketone in humans from experimental single-dose inhalation exposure
Regulatory Toxicology and Pharmacology, Volume 52, Issue 2, November 2008, Pages 180-188

Shakil A. Saghir, David L. Rick

Methyl isobutyl ketone (MIBK) is a solvent used in numerous products and processes and may be present in the air of the workplace as a vapor. The American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value-time-weighted average (TLV-TWA) and TLV-short term exposure limit (TLV-STEL) for MIBK are 50 and 75 ppm, respectively. These workplace air concentration limits were set to protect workers from irritation, neurasthenic symptoms and possible adverse effects to their livers and kidneys. A recent revision of the ACGIH limit value has been proposed, to reduce the current TLV-TWA to 30 ppm. This article predicts the kinetics and accumulation of MIBK in humans exposed repeatedly in various exposure scenarios (8, 12, and 24 h/day for 7 days) to the current ACGIH TLV-TWA of 50 ppm. The kinetic parameters of the model were derived from published human time-course blood MIBK data from a single 2 h inhalation exposure to 48.9 ppm MIBK. The model correctly simulated single exposure experimental data with a rapid rise in blood concentration to 1.06 μg/ml within 1 h and approached 99% steady-state blood level in 4 h of exposure. MIBK was predicted to be rapidly eliminated from blood after terminating the exposure, reaching 0.53 μg/ml and 0.13 μg/ml within 0.5 and 2 h post-exposure, respectively. Within 4 h after the termination of exposure, blood concentration would be expected to

Brooklyn Dodger(s) comments: This is the last of the MIBK trilogy. For this chemical, the TLV and PEL are now the same, a sign of no new data or no material change in perception of toxic potential or potency since 1968. The important finding is that this solvent reaches equilibrium in blood level after 4 hours at 50 ppm.

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