1. Papp, J.F., in US Bureau of Mines Minerals Yearbook 1986, Volume 1: Metals and Minerals. US Dept of Interior, Washington, DC (1988), 225–244.
2. Stern, R.M., in Biological and Environmental Aspects of Chromium, ed. Langård, S. Elsevier, Amsterdam (1982), Chapter 2.
3. Adriano, D.C., Trace Elements in the Terrestrial Environment. Springer-Verlag, New York (1986).
4. Mertz, W. and Schwarz, K., Arch Biochem. Biophys. 58 (1955), 504–508.
5. Anderson, R.A., Sci. Total Environ. 17 (1981), 13–29.