WERNER G. JAFFÉ
Lack of selenium in feeds is an economic problem in several countries because of the occurrence of white musc1e disease in calfs and lambs and exudative diathesis in chicks. A relation between kwashiorkor in human infants and low selenium intake has been suggested recently.
The toxicity of high selenium intake for cattle and horses is well known; a teratogenic action has been described for various animal species and cancerogenic and anti-cancerogenic effects have been c1aimed. The effect of chronic selenium intake in humans has been little studied.
A survey in a high selenium area of Venezuela among III school children revealed high selenium blood and urine levels (0.81 mcg/ml and 0.64 mcg/ml respectively) and slight1y low values for hemoglobin and hematocrit. No correlation between high selenium blood values and low hemoglobin and hematocrit values was detectable. Protrombine activity is low and transaminases and alkaline phosphatase values are high in rats kept on a high selenium diet for 6 weeks. These parameters were normal in the children studied. Dermatitis, pathological nails, and loose hair were observed more often in children from the seleniferous than from the control area. The incidence of congenital malformations in humans was not higher in the seleniferous region than in the whole country. It is conc1uded that under the specific conditions of the survey no serious toxic effects of selenium were apparent.
Most essential elements may exhibit some toxic effects when ingested in excessive amounts. In the case of selenium, the doses required to prevent deficiency symptoms and those which might produce toxicity signs are very close. Exact levels are not easy to define because they depend on many factors, namely animal species, age, sex, nutritional and other physiological conditions, and the selenium compound used. A level of 0.1 ppm in the diet is considered satisfactory under most conditions to prevent deficiency symptoms for the chick (Thompson & Scott, 1969). Toxic effects may be observed at levels of 3 ppm, so that the safety range would be 1 ; 30 or less.