About 5-20% of absorbed toluene is excreted by the lungs unchanged (Cohr and Stokholm, 1979; Carlsson, 1982; IPCS, 1985). The concentration of toluene in expired alveolar air correlates with the concentration in inspired air (Cohr and Stokholm, 1979; Apostoli et al., 1982) and blood (Brugnone et al., 1976; Carlsson,
1982; Brugnone et al., 1986). After cessation of exposure, the toluene concentration in expired air decreases rapidly and is highly correlated with blood concentrations (Veulemans and Masschelein, 1978a,b). Elimination of toluene from blood is rapid (Veulemans and Masschelein, 1978b; Carlsson, 1982; Nise et al., 1989; Löf et al., 1993) and is influenced by the respiratory and heart rates.
The breath of volunteers exposed to 75 and 150 ppm of toluene contained on average 7.65 ppm and 16.06 ppm of toluene respectively. The concentrations had dropped to 2.2 ppm and 4.05 ppm 20 minutes after exposure ceased. The expired air concentrations were 10.5% of the exposure dose at 75 ppm and 11.2% at 150 ppm, measured using a mixed air, not an alveolar air, sample (Echeverria et al., 1989).
Studies in workers have shown that the rate of elimination of toluene from blood is complex with at least three exponential components. The first two had median estimated half-lives of nine minutes and two hours. The third component had a median half-life of 90 hours. This reflected the decline of toluene in adipose tissue, where it had a median half-life of 79 hours (Nise et al., 1989). In another study of exposed workers the mean elimination half-life of toluene in alveolar air was 3.8 hours and in blood 4.5 hours (Brugnone et al., 1986). In chronic abusers the blood elimination half-life for toluene was 35-54 minutes in the first hour after cessation of exposure and 79-111 minutes in the second hour (Garriott et al., 1981). Elimination studies in two men found unconscious after acute exposure, found toluene in the blood and alveolar air 5 days later. This was due to the slow release of toluene from fat tissue. The elimination half-life from alveolar air and blood was 18.7 and 21.2 hours respectively (Brugnone et al., 1983).
About 80% of benzoic acid is excreted as hippuric acid and about 20% as benzoyl glucuronic acid (Cohr and Stokholm, 1979). In a volunteer study, 65% of the total toluene absorbed by inhalation was excreted as hippuric acid 4 hours after cessation of exposure; this rose to 78% by 20 hours post exposure (Löf et al., 1993).
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