1. APHA, AWWA, & WPCF (Eds.). (1985). Standard methods for examination of water and wastewater. Washington, D.C.: APHA.
2. Bollard, E. G. (1983). Involvement of unusual elements in plant growth and nutrition. In A. I. Lauchli & R. L. Bieleski (Eds.), Inorganic plant nutrition (pp. 695–730). Berlin: Springer.
3. Brown, P. H. (2007). Nickel. In A. V. Barker & D. J. Pilbeam (Eds.), Handbook of plant nutrition (pp. 395–410). Boca Raton: CRC, Taylor and Francis Group.
4. Cabrera, F., Clemente, L., Diaz Barrientos, E., Lopez, R., & Murillo, J. M. (1999). Heavy metal pollution of soils affected by Guadiamar toxic flood. Science of the Total Environment, 242, 117–129.
5. Cooper, E. M., Sims, S. D., Cunningham, J. W., Huang, J. W., & Berti, W. R. (1999). Chelate assisted phytoextraction of lead from contaminated soils. Journal of Environmental Quality, 28, 1709–1719.