The metabolism and toxicity of lead, cadmium, mercury, and manganese in the postnatal period was studied in rats. Absorption, whole body retention, and organ distribution of 203Pb, "1115Cd, 203Hg, and 54Mn were determined after oral and parenteral administration of these radioisotopes. The acute oral toxicity (LD50) was determined after a single application of metal chlorides. The results obtained in sucklings show a very high intestinal absorption of all metals which is partly attributed to milk diet; a higher whole body retention, higher blood levels and a much higher accumulation in the brain; and a higher oral toxicity. These results indicate age specific differences in the pharmacokinetics of metals in sucklings. It seems reasonable to consider the early neonatal age as a critical period for metal accumulation and therefore for metal toxicity. The results are interpreted on the basis of current concepts of developmental physiology and pharmacology and suggestions for future research trends are made.

Cadmium metabolism in the young and in conditions of dietary contamination with ash from coal gasification were investigated. The experiments were performed in adult rats which received ash in the diet (5%) and/or cadmium in drinking water (100 ppm) over a period of five weeks and in sucklings whose mothers were given the same treatment throughout pregnancy and lactation. In pharmacokinetic studies, 115mCd was administered orally or intraperitoneally to determine the intestinal absorption, retention, and distribution. Cadmium toxicity (LD,O) was determined in different age groups of animals treated with ash for five weeks before a single oral or intraperitoneal administration of cadmium chloride. After intraperitoneal administration, "15"'Cd body retention decreased with age and was independent of the dietary treatment. Sucklings had a higher retention in the blood, carcass, and gut than adults. After oral administration, sucklings had a much higher body retention than adults regardless of the dietary treatment of their mothers. Cadmium toxicity was also independent of the dietary treatment. Most striking was a very high oral toxicity of cadmium in sucklings. It is concluded that the young might be at a special risk at the same level of environmental cadmium exposure because of the high oral cadmium toxicity at this age which is most probably due to a high cadmium retention in the gut. It is also concluded that the mixture of elements contained in ash is not likely to influence cadmium metabolism and toxicity in conditions of dietary exposure.