Figure 5
(a) Fraction of complexed zinc in a system with [Zn] = 10–6 mol dm−3 and [citrate] = 10–5 mol dm−3 modelled at infinite dilution using intrinsic stability constants determined (i) by fitting the parameterised version of the Extended Debye-Hückel equation to the full set of conditional stability constant data (ii–vi) by using the Davies equation to calculate activity coefficients and adjusting the citrate stability constants separately at 0.05, 0.15, 0.30, 0.50, and 1.00 mol dm−3. The dashed lines show the error on the respective curves. The error was calculated by re-running the analysis, starting with high and low estimates for the experimental stability constants. For the EDH and 0.05 mol dm−3 Davies corrected models, the error is too small to display. (b) Formation of Zn-DMA complexes in the pH range 2 and 8 calculated using logβ values from Weiss and co-workers30 with no corrections made for ionic strength dependent changes in formation constants. Note the similar range where Zn is complexed and the sigmoidal curve shape. (c) pH profiles between root wall and bulk solution measured in flooded rice fields40,42. pH at the root/soil interface can be acidic (pH 4), leading to the release of Zn from the complex.
