1. E. J. UNDERWOOD, Trace Elements in Human and Animal Nutrition, 3rd ed., Academic Press, New York, 1971.
2. H. J. M. BOWEN, Environmental Chemistry of the Elements, Academic Press, New York, 1979.
3. Trace Elements in Human Nutrition, World Health Organization, Geneva, Technical Report Series No. 532, 1973.
4. Report of a Working Party of the Panel on Child Nutrition, Committee on Medical Aspects of Food Policy, Department of Health and Social Security, Report on Health and Social Subjects No. 20, 1980.
5. N. W. SOLOMONS, R. A. JACOB, Am. J. Clin. Nutr., 34 (1981) 475.