Overview/CYU
What is gadolinium (Gd)?
A malleable silvery-white metal with atomic number 64 belonging to the lanthanide series.
What are the predominant forms of Gd in Lake Michigan?
According to Visual MINTEQ 86.747% to TOTGd is present in the form of GdPO4 (aq) next followed by GdOH2+ at 7.199%.
Screenshots of the output screen and species distribution screen from Visual MINTEQ can be viewed in supplemental.
By what routes can gadolinium enter the environment?
Glass additives, automobile catalysts, and the most common route, contrast media used in MRIs. After patients are dosed with a Gd based contrast agent it is excreted through urine. Most wastewater treatment plants are not equipped to remove gadolinium from water (studies have shown only up to 10% is removed), this is how it is released into surface waters. This is why we've seen an uptick in gadolinium in cities that have hospitals that perform a large number of MRIs, however, we've also seen elevated Gd levels in rural areas due to outpatient MRIs.
What is the biggest roadblock to measuring Gd in aqueous systems?
Low concentrations. While it's true that larger amounts of Gd is entering the environment, when it is dispersed in water, samples still contain very small amounts. Thus methods used and developed need to be highly sensitive.
What are some effects of exposure to gadolinium?
Possible neuropathy and nephrogenic systemic fibrosis can occur in patients receiving a Gd-based contrast for medical imaging, this is rare but more likely to occur if the patient has inhibited renal function. Exposure to unchelated Gd is highly toxic and seen to cause hepatocellular and splenic toxicity in animals.
What are the main kinds of Gd-ligand complexes?
Lanthanides, including Gd usually have large coordination numbers. In complexes used for MRIs it is common to use a ligand with 8 donor atoms leaving 1 water molecule in the inner sphere. These donor ligands can either be linear or cyclic. Linear complexes are formed relatively quickly where as cyclic complexes are more rigid and form more slowly.
What are the predominant forms of Gd in seawater?
According to Visual MINTEQ 45.785% to TOTGd is present in the form of GdSO4+ next followed by Gd3+ at 31.250%.
Screenshots of the output screen and species distribution screen from Visual MINTEQ can be viewed in supplemental.
What is transmetallation?
The transfer of ligands from one metal to another. This is the mechanism most likely to release toxic Gd3+. Iron, zinc, and copper are possible substituents in Gd complexes due to their similar thermodynamic stability. These ions are also easily available in the environment or body.
Gd complexes can also dissociate where more competitive ligands are present.
What are some common measurement methods for Gd in water?
Ion chromatography (IC), high performance liquid chromatography (HPLC), size exclusion chromatography (SEC).
Where gadolinium has been seen to be retained in the body?
The liver, kidneys, brain, and spleen.
This retention is based on the body's pH which makes the Gd ion precipitate as gadolinium phosphate in blood and tissues.
CYU. Out of the following kinds of Gd complexes, order them from which you expect to be least stable to most stable: linear ionic, macrocyclic, linear non-ionic
linear non-ionic < linear ionic < macrocyclic
What are the predominant forms of Gd in the Ogallala Aquifer?
According to Visual MINTEQ 59.944% to TOTGd is present in the form of GdSO4+ next followed by Gd3+ at 28.302%.
Screenshots of the output screen and species distribution screen from Visual MINTEQ can be viewed in supplemental.
One form of Gd contrast agent that seemed to be more studied than others was Gd-DTPA which is linear and di-ionic. Describe the stability of this chelate.
Gd-DTPA is relatively inert. Very slow transmetallation can occur over long periods of time with other lanthanides, iron, zinc, and copper. High concentrations of Ca and Mg found in seawater can destabilize it. This is particularly prevalent in estuarial mixing of seawater and riverwater, one study stated that up to 15% of Gd can be released from its ligand.
What method has proven to be more effective that common chromatographic methods?
Hydrophilic interaction liquid chromatography (HILIC) with inductively coupled plasma-mass spectrometry (ICP-MS). This method has shown to have high sensitivity and element selectivity.
What can add to bioaccumulation of Gd in an organism?
Exposure through the environment or diet.
What makes the possibility of Gd retention additionally concerning is not only can humans retain Gd from medical procedures, but studies have shown organisms lower on the food chain retain Gd which can effect higher up organisms through diet.
What are the possible precipitates for each water sample?
Lake Michigan: GdPO4 x H2O (s), GdPO4 (s)
Seawater: NA
Ogallala Aquifer: GdPO4 x H2O (s), GdPO4 (s)
See supplemental for more info
What happens when chelated Gd enters a wastewater treatment plant?
A study in 2020 by Liu noted unidentified Gd species in water samples at a treatment plant suggesting that Gd-chelate complexes can be destabilized by bacterial attack, UV photo-oxidation, and transmetallation during water treatment.
Fun Fact
While our goal is not to place gadolinium in water on purpose the accidental release has allowed some scientists to track groundwater movement rates. However, this isn't entirely reliable as we can only follow relatively stable compounds until they transform, one study said they were able to track water movement for a few months at most.
What is another way Gd is a danger to organisms?
Free Gd and Ca have similarly sized radii causing Gd to inhibit processes relying on calcium.