In contact with aerated natural waters, iron salts convert to the ferric form. Near neutral pH, ferric ions form insoluble solids and are thus not bioavailable. EDTA (and other chelating agents) address this problem, by forming soluble complexes that resist formation of hydroxides.
Together with pentetic acid (DTPA), EDTA is widely used for sequestering metal ions. Otherwise these metal ions catalyze the decomposition of hydrogen peroxide, which is used to bleach pulp in papermaking. Several million kilograms EDTA are produced for this purpose annually.
Iron chelate is commonly used for agricultural purposes to treat chlorosis, a condition in which leaves produce insufficient chlorophyll. Iron and ligand are absorbed separately by the plant roots whereby the highly stable ferric chelate is first reduced to the less stable ferrous chelate. In horticulture, iron chelate is often referred to as 'sequestered iron' and is used as a plant tonic, often mixed with other nutrients and plant foods (e.g. seaweed). It is recommended in ornamental horticulture for feeding ericaceous plants like Rhododendrons if they are growing in calcareous soils. The sequestered iron is available to the ericaceous plants, without adjusting the soil's pH, and thus, lime-induced chlorosis is prevented.
Ferric EDTA can be used as a component for the Hoagland solution or the Long Ashton Nutrient Solution.According to Jacobson (1951), the stability of ferric EDTA was tested by adding 5 ppm iron, as the complex, to Hoagland's solution at various pH values. No loss of iron occurred below pH 6. In addition to Jacobson's original recipe and a modified protocol by Steiner and van Winden (1970), an updated version for producing the ferric EDTA complex is presented in Table (1).
