Mixture toxicity and interactions of Cu, Ni, Cd and Zn to barley at low effect levels: Something from nothing?
Metal contamination is mostly a mixture of different metals and these multi‐component mixtures can produce significant mixture effects. This study was set up to investigate toxicity of multiple metal mixtures of Cu, Ni, Cd and Zn to plants at metal doses individually causing low level phytotoxic effects. Barley (Hordeum vulgare L.) root elongation toxicity tests were performed in resin buffered nutrient solutions to control metal speciation. Treatments included single metal concentrations and binary, ternary and quaternary mixtures. Mixtures of different metals at free ion concentrations each causing <10% inhibition on root elongation, yielded significant mixture effects, with inhibition reaching up to 50%. The independent action (IA) model predicted mixture toxicity statistically better than the concentration addition (CA) model, but some synergisms relative to the independent action model were observed. These synergisms relative to IA were most pronounced in quaternary mixtures and when the dose response curves had steep slopes. Generally, antagonistic interactions relative to the concentration addition (CA) model were observed. Increasing solution Zn concentrations shifted metal interactions (CA based) from additive or slightly synergistic at background Zn concentrations to antagonistic at higher Zn concentrations, suggesting a protective effect of Zn. Overall, this study shows that the CA model can be used as a conservative model to predict metal mixture toxicity to barley. This article is protected by copyright. All rights reserved