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After breathing rate and extrahepatic metabolism had been set to conservative (protective) values (the 97.5th and 2.5th percentiles, respectively) the model predicted that pre-final-shift breath levels of < or =10 micromol/m3 and post-final-shift levels of < or =150 micromol/m3 corresponded to average workplace exposure levels of < or =50 ppm toluene. Alternately, we used the distributions and covariances of the measured and fit model parameters to yield conservative pre-final-shift levels of < or =7.3 micromol/m3 and post-final-shift breath levels of < or =120 micromol/m3 that were reflective of workplace exposure levels of < or =50 ppm toluene.

Health risks from ostensible occupational and environmental toxicant exposure are difficult to quantify. Maximal use of limited biological measurements of xenobiotic or metabolite concentration in the body is therefore essential. Elimination rates of exhaled [2H8]toluene and urinary metabolites were analyzed from 33 exposures of males to 50 ppm [2H8]toluene for 2 h at rest. It was hypothesized that the shapes from our decay curves would be applicable to any occupational or environmental toluene exposure. Except for a rapid decline in toluene blood and breath levels in the 0-0.1 h period, this "curve reconstruction" method successfully fit data from published studies. Urinary hippuric acid concentrations were not well fit due to substantial background levels, whereas o-cresol levels were accurately described. Our approach was able to reconstruct data from studies where exposure duration ranged from 10 min to 7 h, and where activity level ranged from rest to 150 W (strenuous exercise). Using this approach, limited biological data following toluene exposure could be back-extrapolated to immediate postexposure concentrations, which in turn could be compared to biological indicators of exposure to determine risk.