Fitting results of simple linear model using eqn (1). (a) R1 versus [Mn] when only CN and MnT groups are considered. (b) R2 versus [Mn] when only CN and MnT groups are considered. (c) R1 versus [Mn] when all four groups (CN, MnT, FeDMnT, FeSMnT) are considered. (d) R2 versus [Mn] when all four groups (CN, MnT, FeDMnT, FeSMnT) are considered. (e) R1 versus [Fe] when all four groups (CN, MnT, FeDMnT, FeSMnT) are considered. (f) R2 versus [Fe] when all four groups (CN, MnT, FeDMnT, FeSMnT) are considered.