Silica reduces the toxicity of aluminium to a tropical freshwater fish (Mogurnda mogurnda).

The toxicity of aluminium (Al) to fish in acidic waters has been well documented. It was therefore expected that Al toxicity would be significant in fish communities in Gadjarrigamarndah (Gadji) Creek, a seasonally flowing stream in tropical northern Australia. This creek receives acidic groundwater containing elevated concentrations of Al from earlier land irrigation of treated mine tailings water from the former Nabarlek uranium mine. It was hypothesised that Al toxicity was reduced by high levels of silica (Si) in the water, and the subsequent formation of Al-silicate complexes. This prompted a laboratory assessment of the toxicity of Gadji Creek water to sac-fry of the native fish, Mogurnda mogurnda, followed by more detailed investigation of the toxicity of Al and the influence of Si in reducing Al toxicity. No mortality of M. mogurnda sac-fry was observed in two toxicity tests using Gadji Creek water collected in August 1997 and September 1998. The majority of Al (80-95%) was calculated to be complexed with humic substances and sulfate, with < 1% being complexed with silicate. Assessment of the influence of silica on the acute toxicity of Al in the absence of natural organic complexants (i.e. in reconstituted freshwater, pH 5) revealed that Si reduced Al toxicity. As the molar ratio of Si:Al was increased, the percent survival of M. mogurnda sac-fry increased until there was no significant (P > 0.05) difference from the controls. However, speciation modelling again predicted that little (< 3%) Al complexed with silicate, with the speciation and bioavailability of Al remaining constant as the molar ratio of Si:Al increased. Therefore, the original hypothesis that Al-silicate complexes in solution reduced the toxicity of Al to M. mogurnda could not be supported. This potential mechanism, and an alternative hypothesis, that Si competes with Al for binding sites at the fish gill surface, requires further investigation.

[1]  Exley,et al.  Hydroxyaluminosilicates and acute aluminium toxicity in fish , 1997, Journal of Theoretical Biology.

[2]  D. Charles,et al.  Acidic Deposition and Aquatic Ecosystems: Regional Case Studies , 2011 .

[3]  J. Schott,et al.  The stability of aluminum silicate complexes in acidic solutions from 25 to 150°C , 1996 .

[4]  D. Schindler,et al.  Acidic deposition: Effects on aquatic ecosystems , 1984 .

[5]  David L. Parkhurst,et al.  Revised chemical equilibrium data for major water-mineral reactions and their limitations , 1990 .

[6]  J R Smith,et al.  Hydrogen ion buffers for biological research. , 1966, Analytical biochemistry.

[7]  N. Riethmuller.  The effect of true water hardness and alkalinity on the toxicity of Cu and U to two tropical Australian freshwater organisms , 2000 .

[8]  D. A. Palmer,et al.  Aluminum speciation and equilibria in aqueous solution: V. Gibbsite solubility at 50°C and pH 3–9 in 0.1 molal NaCl solutions (a general model for aluminum speciation; analytical methods) , 1994 .

[9]  E. Tipping,et al.  Humic substances in acid surface waters; modelling aluminium binding, contribution to ionic charge-balance, and control of pH , 1991 .

[10]  P. Campbell,et al.  Possible mechanisms of aluminum toxicity in a dilute, acidic environment to fingerlings and older life stages of salmonids , 1988 .

[11]  A. E. Greenberg,et al.  Standard methods for the examination of water and wastewater : supplement to the sixteenth edition , 1988 .

[12]  V. Farmer,et al.  An assessment of complex formation between aluminium and silicic acid in acidic solutions , 1994 .

[13]  J. Birchall,et al.  Acute toxicity of aluminium to fish eliminated in silicon-rich acid waters , 1989, Nature.

[14]  P. Campbell,et al.  Survival time modeling of exposure of juvenile atlantic salmon (Salmo salar) to mixtures of aluminum and zinc in soft water at low pH , 1995 .

[15]  J. E. Jensen,et al.  Log-Logistic Analysis of Herbicide Dose-Response Relationships , 1995, Weed Technology.

[16]  A. Wilson,et al.  The absorptiometric determination of aluminium in water. A comparison of some chromogenic reagents and the development of an improved method. , 1974, The Analyst.

[17]  G. Pokrovski.  Structure and Stability of Aluminum-Silica Complexes in Neutral to Basic Solutions. Experimental Study and Molecular Orbital Calculations , 1998 .

[18]  I. Grenthe,et al.  The temperature dependence of stability constants for the formation of polynuclear cationic complexes , 1994 .

[19]  D. Schindler.  Experimental studies of chemical stressors on whole lake ecosystems: With 11 figures and 6 tables in the text , 1988 .

[20]  R. Playle,et al.  The Bioavailability and Toxicity of Aluminum in Aquatic Environments , 1999 .

[21]  A. R. Williams,et al.  Sublethal effects and bioaccumulation of cadmium, chromium, copper and zinc in the marine amphipodAllorchestes compressa , 1991 .

[22]  F. James Rohlf,et al.  Biometry: The Principles and Practice of Statistics in Biological Research , 1969 .

[23]  J. Birchall,et al.  A mechanism of hydroxyaluminosilicate formation , 1993 .

[24]  S. Markich,et al.  Evaluation of the free ion activity model of metal-organism interaction: extension of the conceptual model. , 2000, Aquatic toxicology.

[25]  D. A. Palmer,et al.  Aluminum speciation and equilibria in aqueous solution: III. Potentiometric determination of the first hydrolysis constant of aluminum(III) in sodium chloride solutions to 125°C , 1993 .

[26]  C. Driscoll,et al.  pH-Dependent Binding of Aluminum by a Fulvic Acid , 1993 .

[27]  K. Wilkinson,et al.  Effect of Fluoride Complexation on Aluminum Toxicity Towards Juvenile Atlantic Salmon (Salmo salar) , 1990 .