Characterization of presystemic elimination of trichloroethylene and its nonlinear kinetics in rats.

1,1,2-Trichloroethylene (TCE) is a volatile organic chemical which contaminates drinking water and food supplies and is primarily of concern because of the risk of cancer it may pose. The objectives of the present study were to evaluate the efficiency and dose dependency of presystemic elimination of TCE in rats. Cannulas were surgically implanted into male Sprague-Dawley rats (330-380 g) 24 hr before TCE dosing. TCE (0.17, 0.33, 0.71, 2, 8, 16, and 64 mg/kg) in a 5% aqueous Alkamuls emulsion was administered over 30 sec into the carotid artery, jugular vein (JV), hepatic portal vein, or the stomach. Serial arterial blood samples of 1-500 microliters were collected for up to 12 hr from the unanesthetized animals and analyzed for TCE content by headspace gas chromatography. Pharmacokinetic analyses indicated that TCE was eliminated through dose-dependent nonlinear processes. A three-compartment model with Michaelis-Menten and first-order elimination was derived to fit simultaneously the TCE blood data following JV administration. Total presystemic elimination of TCE was inversely related to dose, ranging from approximately 60 to < 1%. A dose-dependent decrease in hepatic extraction was primarily responsible for the reduction in total first-pass elimination at high doses, whereas pulmonary extraction (i.e., 5-8%) was relatively constant over the dosage range. When metabolic saturation was minimal or absent, hepatic presystemic elimination of TCE accounted for approximately 45-55% of the administered dose. These findings indicate that a substantial proportion of trace amounts of VOCs ingested in environmental media may not enter the systemic circulation nor reach extrahepatic target organs.