Anthropogenic gadolinium as a tracer of raw sewage in surface water

Anthropogenic gadolinium (Gd-anth) is a frequent contaminant in surface water that receives wastewater treatment (WWT) effluents due to the high stability of Gd-based contrast agents (Gd-CAs) used in magnetic resonance imaging (MRI) exams and excreted by patients. This study describes the presence of Gd-anth in surface water of a small drainage area (circa 4 km(2)), which does not receive WWT effluents. The unexpected Gd-anth anomalies were attributed to raw sewage leaking from underground effluent removal pipes. The study area is within a university campus with a hospital that regularly runs MRI exams employing Gd-CAs. Besides Gd, the whole lanthanide (Ln) series was measured and except for Gd, all remaining Ln data were correlated, implicating that besides the natural Gd, a distinct Gd species contributes up to 95% to its whole content in the water samples. Besides surface water, samples of the local sewage and pluvial water networks were collected and analyzed. The ratio between measured and expected Gd values (Gd/Gd*) in surface water samples ranged between 1 and 46, the first corresponding to pristine locations and absence of Gd anomaly and the second nearby the sewage and pluvial water networks. The Gd-anth anomalies presented transient values, probably associated with the application of the Gd-CAs to patients and their permanence in the hospital. Other proxies commonly associated to sewage discharge also presented transient values, not necessarily correlated Gd-anth, because of the input of distinct anthropogenic sources in the study area.

Automated summary

The presence of anthropogenic gadolinium in surface water of a small drainage area was attributed to leakage of raw sewage, likely from a hospital running MRI exams employing Gd-CAs. Apart from natural Gd, a distinct Gd species was found to contribute up to 95% to its whole content in the water samples.