K. Sommer, M. Sperling, U. Karst

University of Münster, Institute for Inorganic and Analytical Chemistry, Corrensstr. 28/30, 48149 Münster

Gd-based contrast agents (GBCAs) are the most frequently used class of contrast agents for magnetic resonance imaging. Due to the toxicity of free Gd³⁺, it is administered in the form of stable complexes to prevent its toxic reactions in the body. Depending on the complexing agent, they are classified as either linear or macrocyclic GBCAs, where the macrocyclic contrast agents are the more stable complexes. Since only a small portion of the administered and excreted GBCAs is eliminated by sewage treatment plants, large amounts of contrast agents are released into the environment. Consequently, GBCAs can be detected in surface and drinking waters, especially in densely populated areas, with their ultimate fate being yet unclear. A class of potential environmental binding partners for GBCAs are humic substances, a mixture of high molecular weight organic compounds formed during the decay of plants.

By using a combined approach of ultracentrifugation and size exclusion chromatography – inductively coupled plasma – mass spectrometry (SEC-ICP-MS), the adduct formation of different GBCAs with humic substances was studied to gain further insight into possible distribution pathways of the contrast agents in the environment.

Ultracentrifugation of GBCA and humic substance mixtures results in the fractionation of compounds of high and low molecular weight and therefore offers the possibility to discriminate between intact GBCAs and Gd-humic substance adducts. The total Gd content in each fraction was determined via flow injection-ICP-MS, while SEC-ICP-MS provided information on the Gd-species, present.

This way, the binding behaviour of one macrocyclic and one linear contrast agent was compared in order to assess if humic substances are a feasible environmental binding partner for these compounds and to evaluate the influence of the complexing agent on their adduct formation.