Numerous studies have shown evidence of gadolinium (Gd) retention in the brains of contrast MRI patients, leaving many the imaging industry to believe the use of certain contrast agents should be reevaluated and potentially stopped altogether. Now, according to a new study published by Environmental Science & Technology, Gd is showing up in the San Francisco Bay, particularly in an area immediately surrounded by hospitals and other facilities that use Gd-based contrast agents.

“The contrast agents are injected into the human bloodstream and excreted via the kidneys,” Vanessa Hatje, Federal University of Bahia in Bahia, Brazil, and colleagues wrote. “Due to the high stability of these compounds, they readily pass through humans bodies and then through conventional wastewater treatment plants, resulting in positive Gd anomalies in aquatic systems that receive treated effluents.”

The San Francisco Bay Regional Monitoring Program began collecting and analyzing water samples from the San Francisco Bay in 1993. The program tracked numerous rare earth elements (REEs), including Gd, during that time. In 1993, the concentration of Gd was 23.3 pmol kg^-1; that doubled by 2000 (49.1 pmol kg^-1) and then reached its maximum in the 2013 measurement (171 pmol kg^-1). The authors added that Gd concentrations are expected to increase as time goes on.

San Francisco Bay’s growing concentration of Gd was attributed to elevated MRI use. However, with that in mind, Hatje and colleagues noted that the amount of Gd in the water samples has not increased nearly as much over the years as one might think.

“The high increase in MRI units and applications observed for the United States, in general, has also occurred in the Bay area, but surprisingly, the data does not reflect such a high increase,” the authors wrote. “The anthropogenic anomaly of Gd is possibly a common feature of the REE distribution of other coastal systems along the coast of the United States that are subject to receiving wastewater enriched in Gd due to high-tech industrial and, especially, medical applications.”

Hatje et al. explained that there is still “relatively little knowledge” of what happens to Gd and other REE in the environment, but they did note that concentrations are “well below the threshold of ecotoxicological effects” for now.

“There are currently substantial gaps in our knowledge of REE, from their anthropogenic levels and fate to their biogeochemical or anthropogenic cycling and their individual and additive toxicological effects,” the authors wrote.

Hatje and colleagues concluded that as researchers try to learn more about the impact of Gd and other REEs on the environment, it’s important for both the government and wastewater treatment industry to respond to the current situation.

“Consequently, the adoption of new public policies and the development of more effective treatment technologies will determine the future adverse impacts of REE in aquatic systems,” the authors wrote.

The full text of this study from Environmental Science & Technology is available to read online, and it covers other REEs besides Gd at great length.

Previous coverage of Gd and its potential effects use can be found here, here, and here.