Evaluating the Risk Posed by Gadolinium in the Grand River Watershed
Bibliographic record
Abstract
Gadolinium (Gd) is a rare earth element (REE), primarily used in contrast agents for magnetic resonance imaging (MRI), with additional applications in metallurgy, phosphors, neutron shielding, and other niche applications. Both Gd and Gd-based contrast agents (GBCAs, the form used for MRIs) have been detected downstream of wastewater effluent discharges and there is currently little research into the risk this poses to aquatic ecosystems. This study investigated the potential environmental risks of Gd and GBCAs using the Grand River watershed (GRW) in southwestern Ontario as a model ecosystem due to it containing a variety of land uses (urban, industrial, agricultural) and multiple MRI facilities using GBCAs. Total and dissolved REE concentrations were measured throughout the GRW with a focus on potential sources of contamination such as wastewater treatment plants. Sampling results showed low but measurable levels of multiple REEs in the watershed, with Gd anomalies downstream of wastewater discharge points with concentrations up to 9 times the watershed average (176 ng/L at outflow & 19 ng/L in GRW). The potential for adverse effects of inorganic Gd and GBCAs were assessed using standard toxicity test methods with Daphnia magna as well as tissue bioaccumulation studies with fathead minnows. We determined an acute EC50 of 231 µg Gddissolved/L of inorganic Gd for D. magna in a soft water media, but were unable to calculate an EC50 for GBCAs due to insufficient mortalities at the tested concentrations, concluding than it would be >2.5 mg Gddissolved/L of GBCA. Chronic 21d reproduction tests with D. magna, in the same soft water media showed no significant effect on survival or reproduction in concentrations up to 200 μg Gdnominal/L inorganic Gd, however this test was limited by low dissolved concentrations (<20% of nominal). Bioaccumulation tests showed that dissolved organic carbon (DOC) reduced the accumulation of Gd into gill tissues (32% decrease at highest tested concentration), while Ca and Na did not. When combining our environmental Gd and D. magna results into a risk assessment, we found risk quotients below 1, indicating minimal risk, even before considering mitigating conditions such as protective DOC being present or less toxic GBCAs composing some of the Gd present.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".