Influence of irradiation time and solution concentration on the photochemical degradation of EDDHA/Fe3+: effect of its photodecomposition products on soybean growth

BACKGROUND: Ethylenediamine-N,N'-bis(2-hydroxyphenylacetic acid (EDDHA) is one of the most efficient iron-chelating agents employed to relieve iron chlorosis in plants. It has been well known for decades that this compound is photosensitive, but in spite of this fact its degradation pathways are virtually unknown. The aim of this work was to evaluate how the length of sunlight exposure and the concentration of irradiated EDDHA/Fe3+ solutions influence the photostability of the chelate at constant pH. Moreover, the possible toxic effect of the chelate photodegradation products, elsewhere proposed, on soybean growth has been tested. RESULTS: The photodecomposition of the chelate increased as the time of sunlight exposure increased, and resulted in a partial decomposition of the organic ligand. Moreover, EDDHA/Fe3+ photodecomposition was highly correlated with the concentration of solution exposed. Plants did not present differences in recovery from chlorosis among treatments with and without decomposition products. CONCLUSIONS: EDDHA/Fe3+ undergoes photodegradation, like other aminopolycarboxylic acids, being more degraded as solution concentration decreases and exposure time increases. The photodecomposition products salicylic acid, salicylaldehide and Salicylaldehyde ethylenediamine diimine tested did not have negative effects on soybean growth, at least in the short-term hydroponic experimental design tested. (C) 2011 Society of Chemical Industry