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Gd in wastewater from MRI

The article about gadolinium contrast agents (Anthony King) reminded me of the case of Harold McCluskey who after an accident at Hanford absorbed a large amount of americium and was treated with DTPA. This case from the 1970s is interesting to compare to the contemporary gadolinium cases. One common Gd contrast agent is the Gd complex of DTPA which is known as gadopentetate. 

While many of the documents regarding gadolinium I have read have concentrated on bone and brain, I know that after a large intake of americium that it is important to prevent the americium depositing into both the liver and the bones. It would be interesting to find out if any studies on Gd in the liver have been conducted. While americium will deliver a dose of alpha radiation to the liver the action of the gadolinium will be purely chemical, this change of element and properties may alter the list of organs which are of interest after an intake of Gd.

I saw an interesting paper by F.G. Shellock and E. Kanal which included the idea of zinc displacing the gadolinium from things like diethylenetriaminepentacetate (DTPA), others have worked further on this issue. I know that after an intake of either americium or plutonium into a cut that the treatment is injections of calcium diethylenetriaminepentacetate in the first days, after a while it is normal to change to zinc diethylenetriaminepentacetate as treatment with the calcium salt tends to strip zinc out of the person.

One interesting thing, the chemistry world article considered in a very shallow way the form of the gadolinium. As the gadolinium in the DTPA complex will tend to exchange with zinc the gadolinium will be released from the ligand. When I checked the f1 value for gadolinium is very low (0.0005) when I checked a ICRP document (ICRP PUBLICATION 119 Compendium of Dose Coefficients based on ICRP Publication 60). The F1 value is the fraction of an element which will be absorbed into the blood stream if it is swallowed. It is a measure of how bioavailable an element is. It is important to understand that some variation of F1 fraction will occur from person to person and it will also change when the chemical form of an element is altered. But it is an important thing to be aware of.

For example the F1 value for cesium is 1.0, for copper and zinc is 0.5 while the value for gallium is 0.001. The value for the elements which form the more highly charged ions tends to be lower. If we consider the series cesium (F1 =1), barium (F1 = 0.2) and lanthanum (F1 = 0.0005) we can see that F1 decreases as the charge of the cation increases. There are some elements which buck the trend such as germanium (F1 = 1.0) but in general the elements which form highly charged cations are poorly absorbed by humans. In particular plutonium (F1 = 0.0005) is very poorly absorbed by adults. For small children the F1 value is slightly larger at 0.005).

As a result I do not expect the gadolinium to pass into humans as a result of eating fish or other things which live in the water.


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