Highlights

• Croatian researchers found gadolinium concentrations 4-14x higher near hospitals and rare earth element (REE) nanoparticles throughout Zagreb's urban streams.
• The findings reveal how medical imaging, agriculture, and consumer technology contaminate waterways, even without mining activity.
• Agricultural runoff from phosphate fertilizers showed lanthanum and cerium levels up to 10x higher than reference sites.
• Rare earth nanoparticles detected near sewer outflows suggest unknown ecological risks from metal transformation.
• As Western nations diversify away from China's 85-90% rare earth processing monopoly, this study warns that expanded production without environmental safeguards could amplify contamination from essential services like healthcare and farming.

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A multinational Croatian research team led by Dr. Zoran Kiralj (opens in a new tab) of the Ruđer Bošković Institute (opens in a new tab), working with colleagues from academic and environmental chemistry institutions across Croatia, has presented a revealing study at the 25th European Meeting on Environmental Chemistry (EMEC 2025) in Chania, Greece.

Their work, “Dissolved Rare Earth Elements in Water of Zagreb Urban Streams: EUS-Normalization, Gd-anomaly and Selected Nanoparticles,” examines how rare earth elements (REEs)—critical to modern technology—are accumulating in urban waterways due to human activity. While the study is localized to Zagreb, Croatia, its findings carry potential global implications, especially when viewed against the backdrop of China’s near-monopoly over rare earth processing and refining.

What the Study Set Out to Do

Rare earth elements such as lanthanum, cerium, neodymium, and yttrium are essential inputs for smartphones, electric vehicles, wind turbines, advanced electronics, and medical imaging technologies. As global demand accelerates, so does environmental exposure—often quietly and outside the spotlight of mining operations themselves. As Rare Earth Exchanges™ reports, the Zagreb study set out to measure both dissolved rare earth elements and rare-earth-based nanoparticles in five urban streams, comparing relatively pristine reference sites with streams influenced by agriculture, hospitals, and dense urban infrastructure.

Study Methods—Explained Simply

Researchers collected water samples during dry, low-flow conditions, when pollutants are least diluted and most detectable. Samples were filtered and analyzed using inductively coupled plasma mass spectrometry (ICP-MS), a widely accepted method for detecting trace metals. To distinguish natural geological background from human-driven contamination, the team applied European Shale (EUS) normalization, a standard geochemical reference technique. In addition, single-particle ICP-MS was used to detect and size rare earth nanoparticles—an emerging but still poorly understood form of environmental contamination.

Key Findings

The results revealed clear and measurable human fingerprints on rare earth distributions:

Agricultural Influence: One stream (Čret, CRT), located downstream from vineyards and an experimental agricultural station, showed the highest concentrations of several rare earth elements, including lanthanum and cerium—up to ten times higher than reference streams. The likely source is phosphate fertilizers, which are naturally enriched with rare earth elements and can be mobilized through soil erosion and runoff.

Medical Gadolinium (Gd) Pollution: Streams near hospitals and dense sewer networks exhibited strong positive gadolinium anomalies, with concentrations four to fourteen times higher than background levels. Gadolinium is widely used as a contrast agent in MRI scans and is excreted unmetabolized, entering wastewater systems and ultimately surface waters.

Nanoparticles on the Rise: Rare earth nanoparticles (lanthanum, cerium, and yttrium) were detected in all streams. The highest concentrations appeared near sewer outflows. Notably, some streams showed low dissolved rare earth concentrations but elevated nanoparticle levels, suggesting that local environmental conditions may promote the transformation of dissolved metals into nano-forms with unknown ecological consequences.

Why This Matters Beyond Zagreb

At first glance, this may appear to be a narrowly focused environmental chemistry study. However, it intersects with a much broader strategic reality: China currently controls roughly 85–90% of global rare earth processing and refining capacity. As Western economies pursue supply-chain diversification—through new mining projects, recycling initiatives, and domestic processing facilities—the environmental footprint of rare earth use is likely to expand geographically.

This study highlights an uncomfortable truth: even without active mining, rare earth elements are already dispersing through ecosystems via agriculture, medicine, and consumer technologies. Scaling rare earth production and processing outside China, without parallel investments in wastewater treatment, monitoring, and environmental safeguards, could amplify these impacts. While the Zagreb study does not directly assess mining or refining operations, it provides a valuable environmental lens for understanding how expanded rare earth use—and future processing decentralization—may introduce new regulatory and ecological challenges.

Controversial and Unresolved Issues

The findings raise several questions regulators have yet to fully address:

• Are gadolinium-based medical contrast agents adequately regulated given their persistence in waterways?
• Do rare earth nanoparticles pose long-term ecological or human health risks? Current data remain limited.
• Who bears responsibility—farmers, hospitals, manufacturers, or governments—when rare earth contamination arises indirectly from essential services?

Study Limitations

The research focused on a single urban area and a limited number of streams sampled during one season. While the analytical methods are robust, broader geographic coverage and multi-season sampling are needed. The study also does not directly assess biological uptake or toxicity, meaning ecological risks are inferred rather than measured.

The Bigger Picture

This work underscores a central paradox of the energy transition: rare earth elements enable cleaner technologies, yet their lifecycle introduces new environmental risks. As governments seek to reduce dependence on China’s rare earth processing dominance, understanding and managing these downstream environmental effects will be essential. Zagreb’s urban streams may serve as an early warning of what lies ahead if rare earth expansion outpaces environmental governance.

Citation: Kiralj Z. et al. (2025). Dissolved Rare Earth Elements in Water of Zagreb Urban Streams: EUS-Normalization, Gd-anomaly and Selected Nanoparticles. Book of Abstracts, 25th European Meeting on Environmental Chemistry (peer-reviewed conference), Chania, Greece, p. 134.

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