Biodegradability of iopromide products after UV/H₂O₂ advanced oxidation

Iopromide is an X-ray and MRI contrast agent that is virtually non-biodegradable and persistent through typical wastewater treatment processes. This study determined whether molecular transformation of iopromide in a UV/H₂O₂ advanced oxidation process (AOP) can result in biodegradable products. The experiments used iopromide labeled with carbon-14 on the aromatic ring to trace degradation of iopromide through UV/H₂O₂ advanced oxidation and subsequent biodegradation. The biotransformation assay tracked the formation of radiolabeled ¹⁴CO₂ which indicated full mineralization of the molecule. The results indicated that AOP formed biodegradable iopromide products. There was no ¹⁴C released from the pre-AOP samples, but up to 20% of all radiolabeled carbon transformed into ¹⁴CO₂ over the course of 42 days of biodegradation after iopromide was exposed to advanced oxidation (compared to 10% transformation in inactivated post-AOP controls). In addition, the quantum yield of photolysis of iopromide was determined using low pressure (LP) and medium pressure (MP) mercury lamps as 0.069 ± 0.005 and 0.080 ± 0.007 respectively. The difference in the quantum yields for the two UV sources was not statistically significant at the 95% confidence interval (p = 0.08), which indicates the equivalency of using LP or MP UV sources for iopromide treatment. The reaction rate between iopromide and hydroxyl radicals was measured to be (2.5 ± 0.2) × 10⁹ M^-1 s^-1. These results indicate that direct photolysis is a dominant degradation pathway in UV/H₂O₂ AOP treatment of iopromide. Other iodinated contrast media may also become biodegradable after exposure to UV or UV/H₂O₂.