Hospital effluents as a source of gadolinium in the aquatic environment

Total annual Gd emission of a hospital offering a maximum spectrum medical services using Gd complexes in magnetic resonance imaging was computed and independently measured by ICP/MS. The Gd emission was between 2.1 and 4.2 kg per year, yielding a theoretical concentration of 8.5-30.1 mu g per L in the hospital's effluent. Gd concentrations measured on different days were below detection limit (1 mu g per L) and 55 mu g per L, and annual average concentrations were between 10.5 and 20.5 pg per L as calculated from analytical results, water flow, and total water consumption. The concentrations in the influent of the municipal sewage treatment plant (STP) receiving the effluent were always below detection limit indicating that there was no other major discharge of Gd. Based on consumption data, total Gd input by German hospitals is estimated to be roughly 132 kg per year. An elevation of the natural concentration of Gd in German surface waters by 0.003-0.004 mu g per L will result from this amount, if there is no elimination in sewage treatment plants. Using the number of MRI apparatus used in Germany the annual emission by hospitals is 484 and 1160 kg by hospitals and practices, resulting in an additional Gd concentration in German surface water of 0.011 and 0.026 mu g per L, respectively. Therefore, the emission of Gd compounds used in magnetic resonance imaging have to be considered as one source among others of anthropogenic Gd anomaly in surface waters.