Distribution and elimination of chlorinated phenoxyacetic acids in animals.

The distribution and elimination of two phenoxyacetic acids, 2,4-D and 2,4,5-T, were studied with a chemical method in rats, pigs, calves and chickens. When administered orally as amine or alkali salts, the compounds were readily absorbed and distributed over the organism in all species studied. The absorption of 2,4-D in the form of an ester was incomplete, however, the ensuing plasma and tissue levels of 2,4-D being only low. (Intact ester could not be detected in plasma). The highest tissue levels of 2,4-D and 2,4,5-T were found in liver, kidney, lung and spleen, the levels sometimes exceeding the plasma level. In blood cells 10–20 of the plasma level was found. Penetration of 2,4-D into adipose tissue and into the central nervous system was restricted, whereas a ready placental transfer was demonstrated in swine. The distribution pattern did not show any significant species or — in rats — sex differences. Elimination of the compounds was rapid, the plasma half-life being about 3 hours in rats, about 8 hours in calves and chickens and about 12 hours in pigs. The tissue half-life values ranged between 5 and 30 hours, the lower values being found in rats. No retention in tissues was noted, nor was accumulation seen on repeated administration. In pigs and chickens an increased elimination rate was observed after repeated administration. The major excretory route seemed to be via the kidneys in all species studied. Hens excreted small amounts of 2,4-D with the eggs.