White spirit appears to undergo biphasic elimination. It has an initial, short distribution phase with rapid elimination from the blood, followed by a longer distribution phase with a slower elimination rate (half-life of approximately 46 hours) (IPCS, 1996). White spirit has been detected in blood 66 hours after a single inhalation exposure (IPCS, 1996).

Urinary excretion of metabolites and expiration of parent compounds are thought to be the major routes of elimination. In a human volunteer study, seven subjects were exposed to 100 ppm white spirit (99% paraffins C8-C12) 6 hours daily for 5 days. The mean concentration in fat was 41.1 mg/kg after 5 days and this fell to 31.7 mg/kg after two exposure free days. The estimated mean and median half-life in fat was 7 and 8 days respectively, and the time to reach steady state was 5-8 weeks. The concentration of white spirit in the brain at steady state was estimated to be 11 mg/kg maximum, while the half-life in the brain was estimated to be 18-19 hours maximum. It was concluded that, during exposure at the threshold limit value (100 ppm), white spirit accumulates in depot fat over weekends and in brain over working days. However, it is almost eliminated from the brain during weekends (Pedersen et al., 1984). In a subsequent study the same authors revised these values and calculated the half-life for white spirit in adipose tissue as 46-48 hours. This second value was considered more accurate as it took into account a redistribution phase (Pedersen et al., 1987). In rats elimination of white spirit in blood and brain was biphasic, and monophasic in fat tissue. The half-lives were: blood 1 and 8 hours; brain 2 and 15 hours; fat tissue 30 hours (Löf et al., 1999).

Löf et al. (1999) investigated the disposition of de-aromatised white spirit in male rats exposed to concentrations of 0, 400 ppm and 800 ppm, for 6 hours/day, 5 days/week for up to three weeks. Five rats from each group were sacrificed immediately after exposure and additionally at periods of one, two, or three weeks post exposure. After three weeks of exposure to 400 ppm or 800 ppm the concentration of total white spirit in blood was 1.5 mg/kg and 5.6 mg/kg, in brain 7.1 mg/kg and 17.1 mg/kg and in fat tissue 432 mg/kg and

1,452 mg/kg, respectively. The total white spirit concentrations in blood and brain were not affected by the duration of exposure. The fat concentration of white spirit decreased very slowly compared with the rate of decrease in blood and brain, suggesting that long lasting redistribution from fat to brain may occur. The blood and brain concentrations of individual components of white spirit (n-nonane, n-decane, and n-undecane) also decreased rapidly compared with the decrease in fat tissue. It was concluded that total white spirit behaved similarly to the n-alkanes in blood, brain and fat tissue, indicating that the non-n-alkane components of white spirit possess toxicokinetic properties similar to the n-alkanes.

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