Monitoring of iodine- and gadolinium-based contrast media in water treatment plants

Significance of the Topic

The extensive use of iodinated and gadolinium-based contrast media in medical diagnostics has resulted in their accumulation in wastewater and surface waters. Their resistance to conventional treatment, combined with the unknown long-term ecological and toxicological consequences, makes their monitoring and speciation essential for environmental safety and regulatory compliance.

Objectives and Study Overview

This investigation evaluates the behavior of representative contrast agents—Gadovist and Magnevist (gadolinium chelates) and Amidotrizoic acid and Iomeprol (iodinated media)—during flocculation with Fe3+ ions and ozonation. The study aims to elucidate metal displacement mechanisms, degradation kinetics, and the formation of inorganic by-products.

Methodology and Instrumentation

Analyses were performed by coupling ion chromatography (IC) with inductively coupled plasma mass spectrometry (ICP-MS), allowing simultaneous detection of Gd isotopes (156, 158, 160) and iodine (127) species without extensive sample preparation. Key analytical conditions included:

• Anion-exchange column (Metrosep A Supp 3) for separation of intact gadolinium chelates.
• Cation-exchange column (Nucleosil 5 SA) for quantifying free Gd3+ and added Fe3+.
• Bench-scale ozonation at 3 mg/L dissolved ozone, with sampling up to 120 minutes.

Key Findings and Discussion

Flocculation with Fe3+ showed pronounced gadolinium displacement from Magnevist (>80%) but minimal release from the macrocyclic Gadovist (<10%), reflecting differences in ligand architecture and complex stability. Ozonation experiments revealed:

• Amidotrizoic acid concentration dropped to 8% after 120 minutes, with 95% conversion to iodate and a total recovery of ~103%.
• Iomeprol exhibited 84% degradation under the same conditions, yet only 14% of iodate formed (recovery ~30%), suggesting the generation of unidentified iodine-containing by-products.

Benefits and Practical Applications

The IC-ICP-MS methodology provides rapid, sensitive speciation analysis of both intact contrast agents and their degradation products in water and biological matrices, supporting routine monitoring in treatment facilities and environmental assessments.

Future Trends and Applications

Future research should target the identification and toxicity assessment of unknown ozonation by-products, integration of high-resolution mass spectrometry for structural elucidation, and the development of real-time, online monitoring platforms to enhance water quality management.

Conclusion

IC-ICP-MS effectively characterizes the fate of contrast media during typical water treatment processes, highlighting environmental risks from released gadolinium ions and partially oxidized iodine species.

Used Instrumentation

• 850 Professional Ion Chromatograph (Metrohm).
• VG PQ ExCell Inductively Coupled Plasma Mass Spectrometer.
• Metrosep A Supp 3 and Nucleosil 5 SA ion-exchange columns.