Anthropogenic gadolinium in tap water and in tap water-based beverages from fast-food franchises in six major cities in Germany

Abstract

Gadolinium-based contrast agents used in magnetic resonance imaging are difficult to impossible to remove in wastewater treatment plants, and may enter groundwater production wells and hence municipal tap water via bank filtration. As anthropogenic gadolinium (Gd) may be accompanied by other, more harmful waste water-derived (micro)pollutants such as endocrine disruptors, we investigated the potential pathway of anthropogenic Gd into popular tap water-based beverages sold in highly frequented fast food restaurants. We, therefore, determined the concentration and distribution of geogenic and anthropogenic rare earth elements (REE) in tap water and in a related tap water-based popular soft drink (Coca Cola) from two fast food franchises (McDonalds and Burger King) in six major German cities. We observed anthropogenic Gd in both tap water and corresponding soft drinks in all investigated cities, extending the database for anthropogenic Gd in tap waters and highlighting its widespread distribution. In Berlin and Düsseldorf, where tap water is (mainly) produced by river bank filtration, 85 to 99% of the total Gd is of anthropogenic origin. The surprisingly high anthropogenic fraction (91%) in tap water from Munich reveals that even the shallow groundwater tapped in two Alpine valleys is eventually exposed to anthropogenic pollution. The REE distribution in post-mix soft drinks generally follows that of the corresponding tap water, except for enrichments of ytterbium (Yb), lutetium (Lu) and cerium (Ce), which are derived from the syrup. The concentration of anthropogenic Gd is similar in the soft drinks and in the corresponding tap water, demonstrating that the highly stable Gd-based contrast agents are not removed in soda fountains but are directly transferred to the beverages. This study highlights a pathway for anthropogenic waste water-derived xenobiotics such as pharmaceuticals and endocrine disruptors into the food chain, and hence, reveals the potential for human exposure to potentially harmful anthropogenic compounds.

Keywords: Anthropogenic gadolinium; Cola; Micropollutant; Soft drinks; Tap water.