John Wiley & Sons, Ltd.

Delineating ion‐ion interactions by electrostatic modelling for predicting rhizotoxicity of metal mixtures to lettuce Lactuca sativa

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Effects of ion‐ion interactions on metal toxicity to lettuce Lactuca sativa were studied based on the electrical potential at the plasma membrane (PM) surface (ψ0). Surface interactions at the proximate outside of the membrane influenced ion activities at the PM surface ({Mn+}0). At a given free Cu2+ activity in the bulk medium ({Cu2+}b), additions of Na+, K+, Ca2+, and Mg2+ resulted in substantial decreases in {Cu2+}0. Additions of Zn2+ led to declines in {Cu2+}0, but Cu2+ and Ag+ at the exposure levels tested had negligible effects on the PM surface activity of each other. Metal toxicity was expressed by the {Mn+}0–based strength coefficient, indicating a decrease of toxicity in the order: Ag+ > Cu2+ > Zn2+. Adsorbed Na+, K+, Ca2+, and Mg2+ had significant and dose‐dependent effects on Cu2+ toxicity in terms of osmolarity. Internal interactions between Cu2+ and Zn2+ and between Cu2+ and Ag+ were modelled by expanding the strength coefficients in concentration addition (CA) and response multiplication (RM) models. These extended models consistently indicated that Zn2+ significantly alleviated Cu2+ toxicity. According to the extended CA model, Ag+ significantly enhanced Cu2+ toxicity while Cu2+ reduced Ag+ toxicity. By contrast, the RM model predicted insignificant effects of adsorbed Cu2+ and Ag+ on the toxicity of each other. These interactions were interpreted using ψ0, demonstrating its influence on metal toxicity. Environ Toxicol Chem © 2014 SETAC

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