The toxicokinetics of d-limonene were studied in human volunteers exposed by inhalation (2 h, work load 50 W) in an exposure chamber on three different occasions. The exposure concentrations were approximately 10, 225, and 450 mg/m3 d-limonene. The relative pulmonary uptake was high, approximately 70% of the amount supplied. The blood clearance of d-limonene observed in this study, 1.1 l kg-1 h-1, indicates that d-limonene is metabolized readily. About 1% of the total uptake was eliminated unchanged in the expired air after the end of exposure, while approximately 0.003% was eliminated in the urine. A long half-time in blood was observed in the slow elimination phase, which indicates accumulation in adipose tissues. A decrease in vital capacity was observed after exposure to d-limonene at a high exposure level. The subjects did not experience any irritative symptoms or symptoms related to the central nervous system (CNS).

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Inhaled 3-carene at a concentration of 5,000 mg/m³ caused bronchoconstriction in isolated, ventilated and perfused guinea pig lungs. This effect was inhibited by the cyclooxygenase inhibitor diclofenac (100 µM) and the thromboxane/prostaglandin endoperoxide-receptor antagonist L-670,596 (1 µM). 3-Carene exposure also increased the amount of thromboxane in the perfusate from the lungs. In cultured calf pulmonary arterial endothelial cells 3-carene caused a dose-related release of arachidonic acid. Thus, the results obtained in this experimental model may have implications in the understanding of the pathophysiology of 3-carene-induced obstructive pulmonary disease in humans.

Exposure based waiving and triggering of tests within REACH