Ecotoxicology and Environmental Safety ] (]]]]) ]]]–]]] Influence of calcium, magnesium, sodium, potassium and pH on copper toxicity to barley (Hordeum vulgare) K. Lock à , P. Criel, K.A.C. De Schamphelaere, H. Van Eeckhout, C.R. Janssen Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, J. Plateaustraat 22, 9000 Ghent, Belgium Received 14 February 2006; received in revised form 24 August 2006; accepted 18 November 2006 Abstract The extent to which Ca 2+ , Mg 2+ , Na + ,K + ions and pH independently influence copper toxicity to barley (Hordeum vulgare) was assessed by measuring root growth in nutrient solutions. Increased Ca 2+ activity resulted in a sixfold decrease in EC50 Cu 2þ values, while a positive relationship between the cation activity and the EC50 was expected. Increased Mg 2+ activity resulted in a twofold increase in EC50 Cu 2þ values. Na + ,K + and H + activities did not significantly affect Cu 2+ toxicity. The obtained results indicated that competition for binding sites between Cu 2+ and cations such as Ca 2+ , Mg 2+ , Na + ,K + and H + is not an important factor in determining Cu 2+ toxicity to H. vulgare. However, the EC50s could, with one exception, be predicted within a factor three based on the free Cu 2+ activity, indicating that the free Cu 2+ activity cannot only be used to predict metal toxicity to aquatic, but also to terrestrial organisms. r 2006 Elsevier Inc. All rights reserved. Keywords: Bioavailability; Metal speciation; Plants; Risk assessment 1. Introduction Copper has many industrial uses including wires and cables for transmission of electricity, water pipes and tubing, roofing and facing materials on buildings and linings in brakes of vehicles, all of which results in distribution of copper into the environment. Copper is also used as a constituent of some fungicides used in vineyards. Metals such as copper may cause environmental risks when occurring at elevated concentrations. Therefore, environmental quality criteria and standards are devel- oped. Recently it has been recognized that standard procedures for deriving environmental quality criteria for chemical substances are inadequate for metals because they are not able to predict the potential impact on ecosystems (Fairbrother et al., 1999; Janssen et al., 2000). This is caused by the fact that current environmental quality criteria and risk assessment procedures for metals are predominantly based on total metal concentrations. How- ever, there is increasing evidence that total metal concen- trations do not predict metal bioavailability and toxicity very well. To account for the observed variability in total copper toxicity, many authors have suggested that free copper ion activity is—at least in aquatic environment—a better predictor of biological response (e.g. reproduction, growth, uptake) than total copper concentration (review by Camp- bell, 1995). However, a considerable number of authors have concluded that free copper ion activity does not always accurately predict copper toxicity due to competi- tion effects by other cations such as Ca, Mg and Na or bioavailability of inorganic and organic copper complexes (e.g. Pagenkopf, 1983; Blust et al., 1991; Campbell, 1995; De Schamphelaere and Janssen, 2002). The Biotic Ligand Model concept (BLM) (Di Toro et al., 2001; De Schamphelaere and Janssen, 2002) is now considered to be the state-of-the-science metal bioavail- ability model/concept, because it incorporates both metal complexation and speciation in the solution surrounding the organism and interactions between metal ions and competing cations at binding sites on the organism–water interface. The main assumption of the BLM is that metal toxicity occurs as a result of free metal ions (or other ARTICLE IN PRESS www.elsevier.com/locate/ecoenv 0147-6513/$ - see front matter r 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.ecoenv.2006.11.014 à Corresponding author. Fax: +32 9 264 37 66. E-mail address: Koen_Lock@hotmail.com (K. Lock). Please cite this article as: Lock, K., et al., Influence of calcium, magnesium, sodium, potassium and pH on copper toxicity to barley (Hordeum vulgare). Ecotoxicology and Environmental Safety (2007), doi:10.1016/j.ecoenv.2006.11.014