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MA4 Biotic Ligand Model
(032) Development and validation of Biotic Ligand Model with nickel for the algae Pseudokirchneriella subcapitata.
Heijerick, D1, Deleebeeck, N2, De Schamphelaere, K2, Van Sprang, P1, Janssen, C2, 1 EURAS, Gent-Zwijnaarde, Belgium2 Laboratory of Environmental Toxicology, Ghent University, Gent, Belgium
ABSTRACT- Recently, biotic ligand models have been developed for various metals (e.g. Cu, Ag, Zn) and organisms (fish, algae, invertebrates). These models allow to predict the effect of major cations (e.g. Ca, Mg, and Na) and physico-chemical water characteristics (pH, dissolved organic carbon) on metal bioavailability and toxicity. In this study, the individual effects of calcium, magnesium, potassium, sodium and pH on nickel toxicity to the green alga Pseudokirchneriella subcapitata was studied. Based on toxicity data, stability constants for the binding of Ni2+ and those cations affecting Ni-toxicity were derived using the mathematical approach that was proposed by De Schamphelaere and Janssen (2002). Potassium proved to be the only cation tested that did not significantly change nickel toxicity. The amount of KOH added for pH-adjustments also did not affect the sensitivity of algal cells to Ni-toxicity. Magnesium seemed to be the main cation that reduced Ni-toxicity. Addition of 4 mM Mg to the standard test medium reduced total Ni-toxicity (72h-EbC50) with approximately one order of magnitude. Other cations like calcium and sodium had less effect on Ni-toxicity (approximately a factor of 2). The results of the toxicity tests performed at different pH-levels (5.5 to 8.0) indicate that competition between H+ and Ni2+ reduces nickel toxicity to same extent as calcium and sodium did. Based on the results of the tests performed at different pH-levels it was concluded that there is no linear relationship between (H+) and the 72h-EbC50 (expressed as M (Ni2+)). This finding is similar to what has been found for copper and zinc (De Schamphelaere et al., 2003, Heijerick et al., 2002), and may suggest the existence of more than one type of metal binding site and/or physiological alterations of the cell wall upon pH-changes. Further experiments were carried out to assess the effect of pH on the Ni-toxicity modifying effects of Ca, Mg and Na and these effects were incorporated into the algal Ni-BLM. Finally, the potential use of the developed algal model for predicting Ni-toxicity in natural surface waters is investigated in a series of tests using waters form different European eco-regions. The outcome of these validation experiments demonstrates the potential use of this type of models in a regulatory framework.
Key words: algae, BLM, nickel , bioavailability
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