1. R. Iffland , in Handbook on Toxicity of Inorganic Compounds, ed. H. G. Seiler and H. Sigel, Marcel Dekker, New York, 1988.
2. R. R. Lawreys and P.Hoet, Industrial Chemical Exposure, Guidelines for Biological Monitoring, Lewis Publishers, Boca Raton, FL, 1993, 2nd edn., p. 19.
3. D. G. Elinder and L.Friberg, in Handbook on the Toxicology of Metals, ed. L. Friberg, G. F. Nordberg and V. B. Vouk, Elsevier, Amsterdam, 1979, p. 283.
4. B. Venugopal and T. D.Luckey, Metal Toxicity in Mammals, Vol. 2, Chemical Toxicity of Metals and Metalloids, Plenum Press, New York, 1978.