Removing copper from reefs, How about calciumethylenediaminetetraacetate ([CaEDTA])?

[jamiep]

OK so I'm not sire if this should be in the chemistry forum or in here but just in passing in one of my lectures this week, there was a discussion on Wilsons disease which is accumulation of copper in tissues. Which got me thinking about the accumulation of cooper in some of our reef tanks!

There are several different drug used to help treat Wilsons disease, all of which remove heavy metals of any sort from our bodys. One of these is the Calcium complex of EDTA which has a reason in itself.

EDTA being a very strong ligand would bind to Calcuim in the body an errode the bones so when the calcium complex is added, the calcium is displaced by the copper and adds calcium to the body...:eek2: hey it would add calcium to our tanks aswell!

So I know that there are many chemists on this board and would like your input into thinking reasons why this wouldnt work, or if it has ever been tried before!

 

[Randy Holmes-Farley]

EDTA is known to natural waters chemists and biologists as a way to reduce potentially toxic metal availability to levels where they can be studied.

What is it that you want to accomplish? Copper and iron and certain other metals do need to be bioavailable. It is not apparent to me that it is present at excessively high levels in my tank, at 0.01 ppm copper. Adding a lot of EDTA might not be a good idea if it reduced bioavailability a lot.

Also, we have magnesium and calcium at vastly higher concentrations than copper. For magnesium, it is 340,000 times as concentrated as copper. I'm not sure the equilibrium binding of copper to EDTA is enough stronger than to magnesium and calcium to allow all that much copper binding (but this could be looked up), especially if the copper is already bound to organics (as it is in seawater).

 

[Randy Holmes-Farley]

Assuming you could get around some of these issues, I think the biggest problem would be the fine balancing act of dosing enough to be beneficial by limiting metal bioavailability and not dosing so much it was a toxicity concern by limiting metal bioavailability too much, assuming such a balance is even possible (since there are several critical metals, such a balance may not actually be possible, even if perfectly done).

 

[jamiep]

My thought was for any acidental contamination that ever happened in our reefs. If copper gets in, alot of things are stuffed and live rock can be considered useless unless being used in a FO tank.

Calcium is displaced by copper in EDTA so I would struggle to think other wise that its wouldn't displace magnesium, both being very similar except in size and the fact the Mg's electronic configuration is further from d subshells.

The other thing we have to take into account is that these complex's are in equlibrium, so how much do we have to worry about Calcium in some tanks, primarly those not containing any SPS or LPS corals, clams or other Calarific species.

I will try and check when I am on university computers the binding energys of EDTA to a few ion's in our reefs (Ca, Mg, Sr and Cu)

 

[Randy Holmes-Farley]

How do you propose to remove the copper EDTA from the tank?
A water change? Wouldn't a water change remove the unbound copper just as well? I suppose as an emergency measure it might be useful if you could not do rapid water changes, but I'm not convinced it is as useful as binding the copper to a material that actually removes it, like cuprisorb or a polyfilter.

Calcium is displaced by copper in EDTA so I would struggle to think other wise that its wouldn't displace magnesium, both being very similar except in size and the fact the Mg's electronic configuration is further from d subshells.

I am very familiar with the chemistry involved. My job as a chemist often involves designing organic materials to bind various ions out of water, and I have filed patents on materials that would bind copper and potentially treat Wilson's disease, that you mentioned. The balance in such a binding situation is always driven by the relative amounts of the two ions, not just the binding strength. Knowing the exact constants, especially in seawater, however, would be useful.

Don't forget the concern about the ions we want: iron, manganese, etc. They bind very strongly to EDTA.

 

[Randy Holmes-Farley]

This article suggests that the binding of calcium is significant in the presence of low levels of ions such as copper:

http://findarticles.com/p/articles/mi_m0FDN/is_2_7/ai_85523010

from it:

EDTA chelation effects on urinary losses of cadmium, calcium, chromium, cobalt, copper, lead, magnesium, and zinc - ethylenediaminetetraacetic acid

"There were significant increases in lead, zinc, cadmium, and calcium, and these increases roughly corresponded to the expected relative increases predicted by the EDTA-metal-binding constants as measured in vitro. There were no significant increases in urinary cobalt, chromium, or copper as a result of EDTA infusion."



This article gives the constants:

http://jn.nutrition.org/cgi/reprint/112/4/652.pdf

It is pretty specific for copper over some of the other metals mentioned, specifically Ca++ and Mg++.

Overall, however, I'm not sure how you'd know how much to add to not overdose and bind other things, while binding enough to be useful.

 

[tydtran]

It seems like it probably wouldn't work because as Randy points out, competing ions like Ca and Mg are in such vast molar excess over copper. Therapeutic copper in a reef aquarium would be <0.18mg/L whereas calcium is 400mg/L; Ca would be in 3500X molar excess over coppper. As Randy has pointed out, the molar excess of Mg over copper would be even higher. Under these conditions, the binding constant for EDTA-Cu versus EDTA-Ca complexes would have to be 3-4 order of magnitude higher in order for you to get significant chelation of Cu.

The other issue of course is getting the stuff out. Chelated copper is still in the tank.