A partition coefficient determination method for nonvolatile chemicals in biological tissues.

Partition or distribution coefficients are critical elements in efforts designed to describe the uptake, distribution, biotransformation, and excretion of organic chemicals in biological systems. In order to estimate the partition coefficients needed to describe the biological distribution of low-volatility compounds, an experimental method was developed to measure partitioning of nonvolatile compounds into biological tissues. Blood, fat, muscle, liver, and skin were individually incubated in a saline solution containing the chemical of interest. Each sample was centrifuged and 2.0 ml of the supernatant was removed and placed into a prewashed, low binding 10,000 MW cutoff Millipore filter cell. Each cell was fitted with a magnetic stirrer and 32 psi nitrogen was applied to the closed cell. The filtrate was collected, extracted, and analyzed for the chemical of interest. The chemicals evaluated were parathion, lindane (hexachlorocyclohexane), paraoxon, perchloroethylene, trichloroacetic acid, and dichloroacetic acid. These chemicals were chosen to develop this method because their vapor pressures range from 9 x 10(6) to 14.2 mm Hg at 20 degrees C. For the one volatile chemical evaluated, perchloroethylene, the method provided partition coefficient results that were in good agreement with values obtained using the vial equilibration method. The nonvolatile partition coefficient method described in this paper demonstrates an approach for evaluation of chemicals with diverse chemical structure and solubility properties.