Anthropogenic gadolinium as a tracer of raw sewage in surface water
2021
De Paula Marteleto, Thaís | Enzweiler, Jacinta
Anthropogenic gadolinium (Gdₐₙₜₕ) 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 Gdₐₙₜₕ in surface water of a small drainage area (circa 4 km²), which does not receive WWT effluents. The unexpected Gdₐₙₜₕ 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 Gdₐₙₜₕ 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 Gdₐₙₜₕ, because of the input of distinct anthropogenic sources in the study area.
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