^Pierzynski, Gary M., and J. T. Sims. Soils and Environmental Quality. Boca Raton: Lewis, 1994. 72. Print.
^Nathanail, Judith, and Paul Bardos. Contaminated Land Management: Ready Reference. Nottingham: Land Quality :, 2002. 44. Print.
^Russell, E. J.; Appleyard, A. . The Atmosphere of the Soil: Its Composition and the Causes of Variation. The Journal of Agricultural Science. 1915, 7: 1. doi:10.1017/S0021859600002410.