Influence of solvents and adsorbents on dermal and intestinal absorption of TCDD

Abstract

The liver concentration of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) was measured as a means of following the uptake of this chemical by the intestinal and dermal routes. Accumulation of the (radiolabelled) compound in the liver was found to provide a good and reproducible method of comparing TCDD uptake from different formulations. After oral administration of 14·7 ng TCDD using 50% ethanol as vehicle, 36·7% of the total dose was found in the liver after 24 hr. When the compound was administered in a mixture with soil particles, adsorption occurred and only about half of this amount was found in the liver. The liver level also decreased with increasing duration of contact between the soil and the dioxin. Adsorption onto activated carbon almost completely prevented uptake of the compound. Similar effects were observed after dermal application of TCDD in the various formulations. The highest liver content, 14·8% of the dose, was found after contact of the pure compound with the skin surface. The inhibiting effects of soil and activated carbon were even more pronounced. After incorporation of the dioxin into vaseline (a lipophilic ointment), 1·4% of the dose was found in the liver, whereas, after incorporation into polyethylene glycol 1500 (a hydrophilic ointment) containing 15% water, 14·1% was found in the liver. The potency of TCDD (applied in similar formations) to produce chloracne in the rabbit ear was tested. Threshold levels for the induction of lesions were between 1 μg for the pure compound and 160 μg when the compound was adsorbed onto charcoal.