Synergetic effect of potassium persulfate on photodegradation of para-arsanilic acid in Fe(III) oxalate system

The p-arsanilic acid (p-ASA) is widely used in agriculture as a food additive to control parasites. It leaves the body almost unchanged and is subsequently destroyed by environmental factors with the formation of toxic forms of inorganic arsenic. UVA irradiation of p-ASA with the addition of the Fe(III) oxalate complex leads to an effective photodegradation of the target compound. However, this method needs high concentrations of reagents and the keeping high [oxalate]:[Fe(III)] ratio to maintain proper efficiency of Fe(III) oxalate system. In this work, to overcome these problems, potassium persulfate (PS) was used as an additional oxidizer to improve Fe(III) oxalate system. It was found that the sulfate radical produced upon PS activation reacts readily with both neutral and monoanionic forms of p-ASA yielding corresponding organic cation radical, bimolecular rate constants are (7.3 ± 0.6) × 10 9 and (2.4 ± 0.4) × 10 9  M −1 s −1 , accordingly. Addition of 1 mM of PS reduces to one order (from 1.6 to 0.12 mM) the working concentration of oxalate and allows to achieve the complete degradation of both p-ASA and organic byproducts to inorganic As(V). Also the proposed approach demonstrates high efficiency in a wide range (from <0.5 to 3 ppm) of p-ASA concentrations.