Granato, T. C., Pietz, R. I., Knafl, G. J., CR, C., Tata, P., & Lue-Hing, C. (1969). Trace element concentrations in soil, corn leaves, and grain after cessation of biosolids applications. Journal Of Environmental Quality, 33(6), 2078-89. https://doi.org/10.2134/jeq2004.2078 (Original work published 1969)