title: Mixture toxicity and interactions of copper, nickel, cadmium, and zinc to barley at low effect levels: Something from nothing?
abstract: Metal contamination is mostly a mixture of different metals, and these multicomponent mixtures can produce significant mixture effects. The present study was set up to investigate the 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 of 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 IA 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 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, the present study shows that the CA model can be used as a conservative model to predict metal mixture toxicity to barley. Environ Toxicol Chem 2016;35:2483-2492. © 2016 SETAC.
authors.affiliation: Division of Soil and Water Management, KU Leuven, Leuven, Belgium. liske.versieren@ees.kuleuven.be.
authors.forename: Liske
authors.initials: L
authors.lastname: Versieren
authors.affiliation: Division of Soil and Water Management, KU Leuven, Leuven, Belgium.
authors.forename: Steffie
authors.initials: S
authors.lastname: Evers
authors.affiliation: Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, Ghent, Belgium.
authors.forename: Karel
authors.initials: K
authors.lastname: De Schamphelaere
authors.affiliation: Department of Biology (SPHERE Group), University of Antwerp, Antwerp, Belgium.
authors.forename: Ronny
authors.initials: R
authors.lastname: Blust
authors.affiliation: Division of Soil and Water Management, KU Leuven, Leuven, Belgium.
authors.forename: Erik
authors.initials: E
authors.lastname: Smolders
mesh_terms: D002104:Cadmium / Q000633:toxicity*; D003300:Copper / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D001467:Hordeum / Q000187:drug effects* / Q000378:metabolism; D008962:Models, Theoretical; D009532:Nickel / Q000633:toxicity*; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D018675:Toxicity Tests; D015032:Zinc / Q000633:toxicity*
chemical_list: D002104:Cadmium; D003300:Copper; D009532:Nickel; D015032:Zinc
keywords: Antagonism; Metals; Mixture toxicity; Root elongation; Synergism