copper

[jimmy 22]

if you test for copper and it shows zero does that mean its safe? or could it still kill if its been used 2 years before and was drained and running w/saltwater fish.now is a octo tank or is it still in the silicone even though it reads zero? i hope that makes sence? thanks

 

[esquid]

As I have already posted, the copper ions work their way into the substance to the silicone sealant. The copper is not just sitting on the outside of the sealant, but is under the surface. The ions can then work their way out over time. How much time they can stay inside the silicone before coming back out, I don't think anyone knows. So, yes you can have a copper test give a negative result and then later have copper appear in the tank. The test only measures the copper content of the sample of water. They only way to know it is safe it to know the history of the tank.

erin

 

[Thales]

Hey Erin,

I am suspicious of the idea that enough copper can work its way into silicone, and enough work its way back out again to be toxic. Do you have any thoughts?

RR

 

[Jean]

from Carlo Colombo and Constant M. G. van den Berg 1998, In-line deoxygenation for flow analysis with voltammetric detection, Analytica Chimica Acta, vol 377


"A drawback of using in-line deoxygenation could be due to possible interaction (chemical or physical) of the samples with the tubing. In particular silicone tubing appeared to be prone to adsorbing copper complexes, whereas the Poreflon tubing did not appear to be subject to this drawback. A change in response due to a changed metal concentration was completed within 5 scans (ca. 5 min) for cobalt using either silicone or Poreflon (Fig. 6(A) and (B)), so carry-over effects were minor with both types of tubing for this metal. However, a greater carry-over effect occurred when copper was determined using silicone tubing than using Poreflon tubing (Fig. 6(C) and (D)) indicating that the metal complexes were adsorbing on the silicone tubing, desorbing again when the concentrations were lowered. A longer flushing time (ca. 20 scans) was therefore required using silicone tubing to obtain a stable response for copper (Fig. 6(C) and (D)). On the other hand the change in response due to a changed copper concentration was completed within 5 scans (ca. 5 min) using Poreflon tubing. This comparison showed that the copper–oxine complex was interacting with the silicone tubing. For this reason chemically inert tubing as Poreflon is preferable." plus the attached.

I'm just not prepared to risk it!

J

 

[esquid]

sorry, just walked in the door from having been at a seaside class for a week and Rosie is trying to eat the sugarglider. I've been trying to write up an explanation of how copper acts in polymers, but work and school keep sucking up my time.

Anyway, it depends on what the LD50 of copper is for cephalopods, which i'm having trouble finding. This document:
http://www.napa-sonoma-marsh.org/documents/DEIR/text/apps/AppC-ContaminantsToxictoWildlife.pdf
gives a LC50 range of 28-39 ug/L (0.028-0.039 ppm) and sub-lethal effects happening at 10 ug/L (0.01 ppm). But that is for mollusks and crustations in general, so for cephs it could be at lower concentrations.

The other thing is what concentration of copper medication was used. It looks like copper sulphate is used in a range of 0.2-500 ppm depending on how long the treatment lasts. Also how much of the copper is actually sequestered. If only 1% is sequestered (number made up for example), then from a 2 ppm dose there could be 0.02 ppm of copper in the sealant vs if the dose is 200 ppm then you could have 2 ppm copper in the sealant.

anyway... I guess a shorter answer is it depends on a lot of things, but is it really worth the risk. I'll keep trying to dig things up, but it looks like this in an area that has a lot of opportunities for research.

erin

 

[DWhatley]

Erin,
Thanks for the research and posting what you are finding.

 

[Joe-Ceph]

Does acrylic absorb copper? Or to put it another way: are used acrylic tanks dangerous to use for cephs?

 

[esquid]

The acrylic most likely can absorb copper ions also. The side chains of PMMA, acrylic, have oxygen atoms with partial negative charges that the copper would be temporarily attracted to. I ran this by a friend who is a doctor of chemistry and he said this sounds accurate, but also because of the shape of the side chain the acrylic may chelate the copper ions. This is a form of cross bonding that holds metal ions in place, like the iron in the center of heme rings, think blood. Chelated metal ions is actually a form of medication used on humans and fish. Because of the chelation the copper may be less likely to come back out of the acrylic. But, again somebody is going to have to run an experiment to get a better answer. I love how the more I learn, the more wishy-washy it all becomes.

I'm curious, what is the low end of the detection range on the copper tests you all are using? And if you have used copper med's what kind did you use?

erin

 

[Jean]

I don't know about octopus but the LD50 for L. vulgaris exposed to copper is 25 ug/L

D'Aniello et al., 1990. Italian Journal of Biochemistry 39(2) p 130-132.

J

 

[esquid]

I was trying to get at that paper, but for some reason UMaine doesn't subscribe to Italian Journal of Biochemistry. does it say what time period that LD50 is for?

erin