Anthropogenic origin of positive gadolinium anomalies in river waters

Recent studies show that high-technology rare earth elements (REEs) of anthropogenic origin occur in the environment including in aquatic systems, suggesting REEs are contaminants of emerging concern. However, compared to organic contaminants, there is a lack of comprehensive reviews on the anthropogenic sources, environmental behaviour, and public and ecological health risks of REEs. The current review aims to: (1) identify anthropogenic sources, transfer mechanisms, and environmental behaviour of REEs; (2) highlight the human and ecological health risks of REEs and propose mitigation measures; and (3) identify knowledge gaps and future research directions. Out of the 17 REEs, La, Gd, Ce and Eu are the most studied. The main sources of anthropogenic REE include; medical facilities, petroleum refining, mining and technology industries, fertilizers, livestock feeds, and electronic wastes and recycling plants. REEs are mobilized and transported in the environment by hydrological and wind-driven processes. Ecotoxicological effects include reduced plant growth, function and nutritional quality, genotoxicity and neurotoxicity in animals, trophic bioaccumulation, chronic and acute toxicities in soil organisms. Human exposure to REEs occurs via ingestion of contaminated water and food, inhalation, and direct intake during medical administration. REEs have been detected in human hair, nails, and biofluids. In humans, REEs cause nephrogenic systemic fibrosis and severe damage to nephrological systems associated with Gd-based contrast agents, dysfunctional neurological disorder, fibrotic tissue injury, oxidative stress, pneumoconiosis, cytotoxicity, anti-testicular effects, and male sterility. Barring REEs in medical devices, epidemiological evidence directly linking REEs in the environment to human health conditions remains weak. To minimize health risks, a conceptual framework and possible mitigation measures are highlighted. Future research is needed to better understand sources, environmental behaviour, ecotoxicology, and human epidemiology. Moreover, research on REEs in developing regions, including Africa, is needed given prevailing conditions predisposing humans to health risks (e.g., untreated drinking water).

The rare-earth elements (REEs) are becoming increasingly important in the transition to a green economy, due to their essential role in permanent magnets, lamp phosphors, catalysts, rechargeable batteries etc. With China presently producing more than 90% of the global REE output and its increasingly tight export quota, the rest of the world is confronted with a REE supply risk. Mining companies are now actively seeking new exploitable REE deposits while some old mines are being reopened. Because of the absence of economical and/or operational primary deposits on their territory, many countries will have to rely on recycling of REEs from pre-consumer scrap, industrial residues and REE-containing End-of-Life products. REE recycling is also recommended in view of the so-called “balance problem”. For instance, primary mining of REE ores for neodymium generates an excess of the more abundant elements, lanthanum and cerium. Therefore, recycling of neodymium can reduce the total amount of REE ores that need to be extracted. Despite a vast, mostly lab-scale research effort on REE recycling, up to 2011 less than 1% of the REEs were actually recycled. This is mainly due to inefficient collection, technological problems and, especially, a lack of incentives. A drastic improvement in the recycling of REEs is, therefore, an absolute necessity. This can only be realized by developing efficient, fully integrated recycling routes, which can take advantage of the rich REE recycling literature. This paper provides an overview of this literature, with emphasis on three main applications: permanent magnets, nickel metal hydride batteries and lamp phosphors. The state of the art in preprocessing of End-of-Life materials containing REEs and the final REE recovery is discussed in detail. Both pyrometallurgical and hydrometallurgical routes for REE separation from non-REE elements in the recycled fractions are reviewed. The relevance of Life Cycle Assessment (LCA) for REE recycling is emphasized. The review corroborates that, in addition to mitigating the supply risk, REE recycling can reduce the environmental challenges associated with REE mining and processing.

The occurrence and fate of pharmaceutically active compounds (PhACs) in the aquatic environment has been recognized as one of the emerging issues in environmental chemistry. In some investigations carried out in Austria, Brazil, Canada, Croatia, England, Germany, Greece, Italy, Spain, Switzerland, The Netherlands, and the U.S., more than 80 compounds, pharmaceuticals and several drug metabolites, have been detected in the aquatic environment. Several PhACs from various prescription classes have been found at concentrations up to the μg/l-level in sewage influent and effluent samples and also in several surface waters located downstream from municipal sewage treatment plants (STPs). The studies show that some PhACs originating from human therapy are not eliminated completely in the municipal STPs and are, thus, discharged as contaminants into the receiving waters. Under recharge conditions, polar PhACs such as clofibric acid, carbamazepine, primidone or iodinated contrast agents can leach through the subsoil and have also been detected in several groundwater samples in Germany. Positive findings of PhACs have, however, also been reported in groundwater contaminated by landfill leachates or manufacturing residues. To date, only in a few cases PhACs have also been detected at trace-levels in drinking water samples.

After administration, pharmaceuticals are excreted by the patients into wastewater. Unused medications are sometimes disposed of in drains. The drugs enter the aquatic environment and eventually reach drinking water if they are not biodegraded or eliminated during sewage treatment. Additionally, antibiotics and disinfectants are supposed to disturb the wastewater treatment process and the microbial ecology in surface waters. Furthermore, resistant bacteria may be selected in the aeration tanks of STPs by the antibiotic substances present. Recently, pharmaceuticals have been detected in surface water, ground water and drinking water. However, only little is known about the significance of emissions from households and hospitals. A brief summary of input by different sources, occurrence, and elimination of different pharmaceutical groups such as antibiotics, anti-tumour drugs, anaesthetics and contrast media as well as AOX resulting from hospital effluent input into sewage water and surface water will be presented.

Mg-poor hydrothermal fluids from the high-temperature discrete flow at the Broken Spur site at the Mid-Atlantic Ridge show high Y concentrations between 1880 and 2639 pmol/kg, and almost chondritic Y/Ho molar ratios between 52 and 55. A sample contaminated with ambient seawater is lower in Y (661 pmol/kg), and yields an elevated Y/Ho ratio of 84. The diffuse flow at the TAG hydrothermal mound shows between 628 and 1785 pmol/kg of Y, and Y/Ho molar ratios between 57 and 65. Similar Y/Ho ratios in black-smoker fluids and MORBasalts argue against an important role of Rare Earths and Yttrium (REY) fluoride complexes in the solutions, but are compatible with a REY speciation dominated by chloride complexes and `free' REY³⁺ ions. Close to the vent orifice, Y behaves conservatively during mixing of high-temperature hydrothermal fluid with entrained seawater. This is in marked contrast to the behaviour of the rare earth elements (REE) which are partly scavenged by Fe oxyhydroxides within less than 1 m distance from the vent orifice, resulting in a strong increase of the Y/Ho ratio. Non-conservative mixing behaviour of the REE may result in underestimation of REE concentrations in the hydrothermal end-member when calculations are based on conservative elements, such as Mg. An approach combining Mg concentration and Y/Ho ratio may reduce this problem. Despite the lower particle-reactivity of Y compared to the REE, there is no hydrothermal Y input into present-day oxic seawater, and marine hydrothermal vent sites are sinks for dissolved Y rather than sources. However, REE elemental and Nd isotopic systematics of Precambrian banded iron-formations reveal the existence of a high-temperature hydrothermal REY flux into Early Precambrian an- or suboxic seawater. The results of our study indicate a chondritic Y/Ho ratio of this black-smoker-type hydrothermal REY input, and suggest that Paleoproterozoic surface seawater showed super-chondritic Y/Ho ratios similar to those of present-day seawater.