Modelling metal-metal interactions and metal toxicity to lettuce Lactuca sativa following mixture exposure (Cu2+-Zn2+ and Cu2+-Ag+)

Metal toxicity to lettuce Lactuca sativa was determined following mixture exposure based on the concepts of concentration addition (CA) and response addition (RA). On the basis of conventional models assuming no interaction between mixture components, Ag+ was the most toxic, followed by Cu2+ and Zn2+. Furthermore, ion ion interactions were included in quantitatively estimating toxicity of interactive mixtures of Cu2+-Zn2+ and Cu2+-Ag+ by linearly expanding the CA and RA models. About 80-92% of the variability in the root growth could be explained by this approach. Estimates by the extended models indicate significant alleviative effects of Zn2+ on Cu2+ toxicity whereas Cu2+ did not significantly affect Zn2+ toxicity. According to the extended CA model, Cu2+ significantly reduced Ag+ toxicity while Ag+ enhanced Cu2+ toxicity. Similar effects were not found by the extended RA model. These interactions might result from their individual uptake mechanisms and toxic actions as published in literature. (C) 2013 Elsevier Ltd. All rights reserved.