Abstract
α-Pinene is a major compound contributing to indoor air pollution in Japanese residences together with many aliphatic or aromatic hydrocarbons. In the present study, the amounts of each enantiomer of α-pinene ((+)- and (−)-α-pinene) absorbed by a resident in a Japanese home were estimated by evaluating their inhalation toxicokinetics in rats. Measured amounts of the substances were injected into a closed chamber system in which a rat had been placed, and the concentration changes in the chamber were examined. The toxicokinetics of the substances were evaluated based on concentration-time courses using a nonlinear compartment model. The absorption amounts per unit time in rats exposed to the substances at constant concentration were simulated using the estimated values of the toxicokinetic parameters. The estimated amounts for the two enantiomers showed approximate agreement. When the values were compared with those for aliphatic or aromatic hydrocarbons examined in our previous studies, α-pinene was estimated to be absorbed more easily by inhalation than n-hexane, n-heptane, n-nonane, n-decane, toluene, xylenes, ethylbenzene and styrene, and to be absorbed about the same level as 1,2,4-trimethylbenzene. Their absorption amounts in human residents were extrapolated from the results for rats and the residential concentrations found in our previous study. The total amount of the two enantiomers absorbed was estimated to be 31 μg/60 kg of human body-weight while at home for 16 h (residential concentration: 4.4 μg/m3 as median value). The value was the highest after that for toluene. Similarly, in a residence where air pollution was marked, the absorption amount of α-pinene (13 mg for 16 h in a residence with an indoor maximum concentration of 1.8 mg/m3) was estimated to be much more than those of other substances. The value (13 mg) was the same level as the tolerable daily intake (TDI) calculated from the No Observed Adverse Effect Level (NOAEL) proposed by the Environmental Protection Agency (EPA).
