Tracing the Environmental Fate and Bioavailability of Anthropogenic Gadolinium

The distribution of rare earth elements (REE) in the environment is governed by their input, removal, transport, and biogeochemical cycling. Untangling these processes to understand REE cycles is now a major focus in marine geochemistry. Such knowledge is essential for predicting future changes along the land-ocean continuum driven by natural and anthropogenic factors, such as pollution and climate change. Some REE, particularly gadolinium (Gd), are also contaminants of emerging concern. Over the past 25 years, Gd concentrations have increased significantly in both freshwater and seawater systems due to the extensive use of Gd-based contrast agents in magnetic resonance imaging (MRI). While Gd³⁺ is highly toxic, it is administered in the form of non-toxic stable, soluble complexes that are rapidly excreted from the human body. However, these complexes mostly pass through wastewater treatment plants without removal, resulting in environmental contamination. This leads to substantial anomalies in normalized REE patterns and anthropogenic Gd may accumulate into biota, indicating that at least some fraction of Gd complexes is bioavailable. Their bioavailability may depend on the specific type of contrast agent (e.g., linear vs macrocyclic) and its environmental half-life, among other factors yet to be determined. Gd complexes are also bioaccessible to humans if ingested orally. This bioaccessibility raises concerns about the long-term health effects of gadolinium exposure. By combining REE measurements across multiple environmental matrices and using them as tracers of natural and anthropogenic processes, we examine the distribution and speciation of anthropogenic Gd in the environment, along with its potential implications for ecosystems and human health.