Quantitative sampling of iodinated X-ray contrast media in water by diffusive gradients in the thin-films technique

Iodinated X-ray contrast media (ICM) have emerged as persistent contaminants due to their high polarity, persistence and biological inertness. In this work, a sampling method for monitoring the time-integrated concentrations of six ICMs, iohexol, iopamidol, iomeprol, iopromide, iodixanol and ioversol, in sewage effluents has been developed, using diffusive gradients in the thin-films (DGT) technique based on a graphene nanosheet gel as the binding layer and commercial polyethersulfone membrane as the diffusion layer (G-DGT). The uptakes of the G-DGT for the six ICMs were evaluated in synthetic solutions and found to be independent of pH in the range of 4-9, ionic strength ranging from 1 × 10^-4 to 0.1 mol L^-1, and dissolved fulvic acid and tannic acid ranging from 0 to 20 mg L^-1. Three spiked freshwater samples showed good precision and good agreement between C_DGT and C_SOLN, confirming that G-DGT is capable of accurately determining the six ICMs in freshwater samples. The time-integrated concentrations of ioversol and iopamidol can be determined with better reproducibility with respective to the grab sampling technique, enabling accurate monitoring of outflows from a clinical practice. These results illustrate that G-DGT is an effective sampling tool for obtaining time-integrated concentrations of ICMs in complex sewage effluent.