ANTHROPOGENIC ORIGIN OF POSITIVE GADOLINIUM ANOMALIES IN RIVER WATERS

Positive Gd anomalies in shale-normalised rare earth element (REE(SN)) patterns of natural waters may provide information on the types of li gands which control surface complexation of REE on particle surfaces. However, REE(SN) patterns of rivers which drain densely populated and industrialised areas in Central Europe and North America are character ised by pronounced positive Gd-SN anomalies, whereas rivers in thinly populated, non-industrialised areas in Varmland and Dalama, central Sw eden, and Hokkaido, Japan, do not show such anomalies. Acidification e xperiments suggest that, unlike the other REE, the excess Gd found in German rivers is almost completely related to the 'dissolved' REE frac tion (< 0.2 mu m) in a water sample and not to the acid-soluble partic ulate fraction, suggesting a negligible particle reactivity of the exc ess Gd, The positive Gd-SN anomalies are of anthropogenic origin and a re most likely to result from the application of gadopentetic acid, Gd (DTPA)2-, in magnetic resonance imaging (MRI), In MRI, gadopentetic ac id, which is an organic aqueous Gd(lII) complex with very high stabili ty constant, is used as a paramagnetic contrast agent. Since positive Gd-SN anomalies in rivers, lakes, semi-closed sea basins, and coastal seas, which receive riverine REE input from industrialised, densely po pulated areas may (partly) be of anthropogenic origin, the positive Gd -SN anomaly can no longer be used as a natural geochemical indicator.