Plant seed germination and root elongation, the first phase of plant development, are sensitive to adverse environmental stress. The objectives of this study were (1) to use a millet root elongation method for measuring phytotoxicity of heavy metals and (2) to develop a mathematical model to relate the phytotoxicity of the metals to the root elongation effect and also to provide a basis for linear transformation of the data. The results show that the order of decreasing phytotoxicity of the metals is Cu, Ni, Cd, Cr(VI), Zn, Mn, and Ba. The metal toxicity is on the same order of magnitude in the millet, fish, and duckweed tests.

A mathematical model was developed: P−PMPM =A[M] BK⁢+ [M]K⁢+ [M] where A, B, and K are constants under conditions where metal concentration M is the only experimental variable. P_M is the root elongation in the presence of added metal ions and P is that in the control group.

A computer program has been developed to calculate the theoretical values of these metals. These values are in good agreement with experimental values. This model is likely to be applicable to other toxicity tests as well.