Penetration of rat skin by N-nitrosodiethanolamine and N-nitrosomorpholine.

N-Nitrosomorpholine (NMOR) and N-nitrosodiethanolamine (NDELA) were painted on the clipped upper dorsal skin of male F344 rats. NDELA was applied undiluted, dissolved in water, and dissolved in cutting oil; NMOR was applied dissolved in water and in ethyl acetate. Aqueous solutions of the nitrosamines were used for gavage. Rats were housed individually. Blood and urine samples were analyzed for nitrosamines by chromatography combined with a Thermal Energy Analyzer. Maximum penetration of NMOR was approximately equal to 34% 2 hours after application of 5 mg to the skin or by gavage; less than 1% appeared in the urine in 24 hours. Skin painting with NDELA in water (20 mg/100 microliters) and in cutting oil (25 mg/25 microliters) yielded small concentrations of NDELA (always < 25 micrograms/ml blood). When 50 mg of undiluted NDELA was painted on the skin, 130 to 220 micrograms/ml of blood was recovered after 1 hour. Administering 50 mg NDELA in water by gavage yielded similar blood concentrations. Maximum skin penetration observed with NDELA was 78% 1 hour after application of 50 mg. From 20 to 30% of the NDELA applied undiluted and by gavage appeared in the urine in 24 hours. Although animals and humans differ, skin exposure to NMOR or NDELA represents a risk due to absorption.