Table III. Comparison of three models for ion toxicity.

For the FIAM, toxicity is expressed in terms of the activity in the bulk-phase rooting medium according to the equation RRE = 100/exp[(α{M}_b)^β]. For the SIAM, toxicity is expressed in terms of the activity at the PM exterior surface according to the equation RRE = 100/exp[(α{M}₀^o)^β]. For the ETM, toxicity is expressed in terms of the PM surface activity and electrical potentials (ψ₀^o) according to the equation RRE = 100/exp{[α(1 + bψ₀^o){M}₀^o]^β}. {M} refers to one of the ions below; α, β, and b are coefficients: α is a strength coefficient and β is a shape coefficient. All of the presented values for coefficients are statistically significant (95% confidence intervals do not encompass 0). All activities are expressed in μm.

Ion	Experiment No.	α	β	b	n	r2
FIAM
Cu2+	11	0.933	1.29		45	0.843
Cu2+	12	1.69	0.901		51	0.745
Cu2+	13	1.72	2.32		36	0.654
Al3+	14	0.227	1.21		50	0.660
H2AsO4−	15	0.456	1.95		100	0.903
SIAM
Cu2+	11	0.040	0.781		45	0.749
Cu2+	12	0.122	0.639		51	0.878
Cu2+	13	0.312	1.88		36	0.835
Al3+	14	0.143	3.26		50	0.919
H2AsO4−	15	1.82	1.57		100	0.919
ETM
Cu2+	11	0.210	1.43	0.0187	45	0.956
Cu2+	12	0.281	0.908	0.0143	51	0.921
Cu2+	13	0.552	2.36	0.0186	36	0.889
Al3+	14	0.155	3.63	0.0164	50	0.949
H2AsO4−	15	0.628	1.94	−0.0607	100	0.937