Official URL: http://www.springerlink.com/content/tkmcvlwvwxbw0v...

When deriving health based exposure limits in recent years, attention has been drawn to susceptible subpopulations, in particular to children. We investigate the differences in kinetics between children and adults during inhalation of styrene as a typical category 3 volatile organic compound (VOC), i.e. a gas with a high rate of alveolar absorption (due to low reactivity and low water solubility). Internal exposure was simulated using a physiologically based kinetic model over a broad range of airborne concentrations (1 to 1000 ppm) and for an exposure time of up to eight hours according to the scenario in the acute exposure guideline level (AEGL) program. Age-specific anatomical and physiological parameters and compound-specific data were derived from the literature. The calculated concentrations in arterial blood are higher in children than in adults, and are highest in the newborn. For an 8-hour exposure to low concentrations, the calculated arterial concentration in the newborn is higher by a factor of 2.3 than in the adult. This is mainly due to the relatively high ventilation rate and the immature metabolism. With increasing airborne concentration, the ratio of arterial concentrations (newborn/adult) increases to a maximum of 3.8 at 130 ppm in ambient air, and declines with further increments of concentration to a value of 1.7. This is because the metabolism of the newborn becomes non-linear at lower concentrations than in adults. At high concentrations, metabolism is saturated in both age groups. For shorter exposures, the dose-dependency of the concentration ratios (newborn/adult) is less pronounced. This is the first article to show that the intraspecies uncertainty factor may vary with concentration and duration of exposure.