Seasonal variations of rare earths and yttrium distribution in the lowland Havel River, Germany, by agricultural fertilization and effluents of sewage treatment plants

•Seasonal variations of REE abundance in surface waters depending on agricultural fertilisation and drainage flux.•Control of Eu in surface water by barite as a component of common NPK fertilisers.•Variation of anthropogenic Gd chelates in surface water due to sewage treatment management.

REE and Y (REY) distribution in the lowland Havel River passing the Federal State of Berlin, Germany, depends on contributions of point sources such pharmaceutical and high-tech industries, acid water from the open pit lignite mining, and medical application of very stable organic Gd chelates. Another omnipresent dispersed source of REY are water-soluble Ca-phosphates containing micro-amounts of Eu(II)-bearing barite as components of common agricultural fertilizers. After distribution in the field during the cold season (October through March) these Ca-phosphates dissolve and secondary phosphates and calcite precipitate both being enriched in light REE. Heavy REE are preferably exported by runoff together with part of the micro-contaminant barite leading to high Yb/Nd ratios in the Havel water and REY distribution patterns with only small Eu deficits. During the warm season (April through September) light REE together with phosphate are leached from secondary soil minerals by runoff. The micro-component barite is retained in vegetation-covered soil. Thus, REY patterns of Havel water show significant Eu deficits. The high Gd anomalies result from medical applications of Gd-chelates which after urination pass the sewage treatment plants. The seasonal variations of total Gd in the Havel River are artifacts based on seasonal locally varied discharge of effluents from sewage treatment plants. The natural Gd concentration of 8 pmol/l in the northern Havel is enhanced to 3300 pmol/l, when the Havel River leaves Berlin territory. The elimination of phosphate from Lake Tegel water affects the fractionation of REE but not the concentration of total Gd. Although enhanced in total phosphorus (TP), the REE concentrations in the water from the Spree River and the Teltow Canal are less than in the Havel water before their confluence. Only Yb and Lu do not decrease. The contributors of the Havel River are high in total organic carbon (TOC) and dissolved organic carbon (DOC) compared to the Havel water before their indicating that REY are preferentially sorbed by settling organic matter. Applying PHREEQC and assuming that only 10% of TP is present as ortho-phosphate yields that only carbonate complexes are essential.