Copper toxicity, humic acids, and toxicity

[randy holmes-farley]

Since Ron Shimek is proceeding to measure toxicity of tank water on sea urchins, I thought it would be useful for people to see this abstract. Humic acids apparently eliminate the toxicity of copper which is bound to it, and only the free copper is toxic:

Effect of humic acids on speciation and toxicity of copper to Paracentrotus lividus larvae in seawater. Lorenzo, J. I.; Nieto, O.; Beiras, R. Departamento de Ecoloxia e Bioloxia Animal, Universidade de Vigo, Vigo, Galicia, Spain. Aquatic Toxicology (2002), 58(1-2), 27-41.

Abstract

The effects of humic acid (HA) on the toxicity of copper to sea urchin P. lividus larvae were studied in chem. defined seawater. Square Wave Anodic Stripping Voltammetry (SWASV) was employed to study the complexation of copper in seawater medium. A simple complexation model assuming one ligand type and a 1:1 reaction stoichiometry successfully explained the inverse titrn. expts. A conditional stability const. of 6.53 ± 0.05 and a complexating capacity of 230 ± 7 mmol Cu/g HA were obtained. Sea urchin bioassay tests with 2 endpoints, embryogenesis success and larval growth, were carried out in order to study the toxicity of dissolved copper in both the presence and absence of HA. The toxicity data obtained fitted well into a logistic model, and the high sensitivity of both endpoints (EC50 were 41.1 mg Cu/L and 32.9 mg Cu/L, resp.) encourages their use for biomonitoring. The HA had a clearly protective effect, reducing the toxicity of Cu to the sea urchin larvae. The labile copper, rather than the total copper concns., explained the toxicity of the Cu-HA solns., and the Cu-HA complexes appeared as non-toxic forms. These results are in agreement with the Free Ion Activity Model, because the labile Cu concns. in this buffered and chem. defined medium covary with the free ion activity of the Cu, validating the model to naturally occurring HA in the marine environment.

 

[jamesw]

Very interesting Randy - maybe I should pull that carbon bag out of my sump...

Cheers
James Wiseman

 

[randy holmes-farley]

Maybe

As a follow up, this article shows that the free copper concentration in normal seawater is more than 100,000 times lower in concentration than the total copper concentration. Consequently, it is not unreasonable to consider the possibility that the free copper in our tanks is very low (despite elevated total copper concentrations), and may not present a toxicity problem:

http://www.sciencedirect.com/science?_o ... 5e9319cf92

Intercomparison of voltammetric techniques to determine the chemical speciation of dissolved copper in a coastal seawater sample. Bruland, Kenneth W.; Rue, Eden L.; Donat, John R.; Skrabal, Stephen A.; Moffett, James W. Institute of Marine Sciences, University of California at Santa Cruz, Santa Cruz, CA, USA. Analytica Chimica Acta (2000), 405(1-2), 99-113.

Abstract

The chem. speciation of dissolved copper in a coastal seawater sample was detd. using a variety of voltammetric methods by three different research groups. This intercomparison study was performed on a sample from near the mouth of Narragansett Bay, Rhode Island, chosen to be representative of coastal seawater from the East Coast of North America. Three research groups used distinct methods of competitive ligand equilibration/adsorptive cathodic stripping voltammetry (CLE-ACSV) with different competing ligands (salicylaldoxime, benzoylacetone and 8-hydroxyquinoline), two of which employed a range of added ligand concns. Two groups used anodic stripping voltammetry (ASV) with a thin mercury film (TMF) rotating glassy carbon disk electrode (RGCDE). Combining these various approaches, resulted in anal. competition strengths (aCu(AL)2) ranging from 102.7 to 106.5 for the CLE-ACSV approaches and 101.3 (aCu) for the ASV methods. As the value of the anal. competition strength for the added competing ligand increased, the value detd. for the natural Cu-binding ligand concn. decreased, while its conditional stability const., KCuLi.Cu2+cond, increased. This type of behavior is consistent with the natural Cu-binding ligands consisting of a continuum of Cu-binding ligands with increasingly smaller concns. of increasingly stronger ligands. Results from the different approaches carried out at similar anal. competition strengths compared very favorably. All of the approaches detd. that dissolved copper in this sample was overwhelmingly chelated with strong Cu-binding ligands (>99.97%). Thus, although the total dissolved copper concn. was 12.7 nM (107.9 M), the Cu-binding ligands lowered the free cupric ion concn., [Cu2+], to .apprx.10-13.0 M, a concn. that is non-toxic to even the most sensitive marine microorganisms.

 

[jamesw]

I'm sorry Randy - this research just doesn't count and I'm not willing to even read it. You should do the research yourself like a real scientist.

/sarcasm

Cheers
James Wiseman

 

[Louis Z]

Now I can dump my phyto cultured with the Guillard formula freely into my tank knowing that all copper will be chelated. Err how long does it take to chelate copper? On contact? I guess to keep my sump as dirty as possible for here is where it will go.

 

[randy holmes-farley]

I'm sorry Randy - this research just doesn't count and I'm not willing to even read it. You should do the research yourself like a real scientist.


Don't remind me :lol: