Influence of calcium, magnesium, sodium, potassium and pH on copper toxicity to barley (Hordeum vulgare)

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 EC 5 0 Cu 2 + values, while a positive relationship between the cation activity and the EC50 was expected. Increased Mg 2+ activity resulted in a twofold increase in EC 5 0 Cu 2 + 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.