1. Elkins , H. B. 1959. The Chemistry of Industrial Toxicology, 2nd ed., 29New York: John Wiley & Sons.
2. Browning , E. 1961. Toxicity of Industrial Metals, 125–129. London: Butterworth's.
3. Patty , F. A. , ed. 1963. Industrial Hygiene and Toxicology, 2nd ed., Vol. II, 1037New York: Interscience Publishers.
4. 1967. American Conference of Governmental Industrial Hygienists, Threshold Limit Values for 1967. 7Cincinnati I., Ohio