Reductive dehalogenation of iopromide by zero-valent iron

Iodinated X-ray contrast media (ICM), as derivatives of 2, 4, 6-triiodo benzoic acid, are applied in high doses to humans and are excreted unchanged via urine within 24 h. Common as well as advanced wastewater treatment is not able to remove the iodinated compounds leading to an environmental pollution. A specific treatment of contaminated urine or hospital wastewater could minimise the emission. For that reason the deiodination of iopromide, the most commonly used ICM, was investigated using zero-valent iron. Initial experiments carried out in stirred batch reactors with an initial pH of 2 using iron powder and iopromide dissolved in ultra pure water showed that iopromide can be deiodinated by zero-valent iron. Even in contaminated urine collected in a hospital a deiodination of ICM was possible. Further experiments at different constant pH values, temperatures and stirring speeds were performed. The kinetic studies at constant pH showed that the deiodination can be described by pseudo-first order for equal iopromide and iron concentrations. In general, the reaction depends strongly on the pH, the temperature and the stirring speed. The observed rate constant K(obs) has an optimum at pH 3 and rises with increasing temperature and stirring speed.