Abiotic transformations of Fe and PO43− in humic water from Finnish forest lakes were studied by Sephadex G‐100 gel filtration following incubation of filtered (0.2 µm) epilimnetic water samples to which both 55FeCl3·6H2O and 32PO43− had been added. The simultaneous movement of 55Fe and 32P to higher molecular‐weight fractions (10,000–20,000 MW) depended on the presence of dissolved humic substances (DHS). In the absence of DHS almost all 55Fe, probably as inorganic hydrolyzed iron particles, sorbed to the Sephadex. The binding of 55Fe by DHS was not affected by increasing the natural ionic strength (I = ∼3 × 10−4 M) by a factor of 102. In the absence of quasi‐equilibrium between free and DHS‐bound 32PO43−, the DHS‐Fe‐PO43− complex readily released 32PO43−‐P. Compared to the 32P binding, 55Fe binding was rapid. More than 20% of the Fe had been bound after only 1 min, whereas for labeled PO43− this percentage was reached only after 24 h.
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Haan et al. (1990) studied this question.