Modeling toxicity of binary metal mixtures (Cu²⁺–Ag⁺, Cu²⁺–Zn²⁺) to lettuce, Lactuca sativa, with the biotic ligand model

Abstract

Abstract-The biotic ligand model (BLM) was applied to predict metal toxicity to lettuce, Lactuca sativa. Cu 2þ had the lowest median effective activity (EA50 M ), compared with Ag þ and Zn 2þ (EA50 Cu ¼ 2.60 Â 10 À8 M, EA50 Ag ¼ 1.34 Â 10 À7 M, EA50 Zn ¼ 1.06 Â 10 À4 M). At the 50% response level, the fraction of the total number of biotic ligands occupied by ions ( f50 M ) was lowest for Ag þ among the metals ( f50 Ag ¼ 0.22, f50 Cu ¼ 0.36, f50 Zn ¼ 0.42). Cu 2þ had the highest affinity for biotic ligands compared with Ag þ and Zn 2þ , as shown by stability constants of the cation-biotic ligand binding, expressed as log K MBL (log K CuBL ¼ 7.40, log K AgBL ¼ 6.39, log K ZnBL ¼ 4.00). Furthermore, the BLM was combined with the toxic equivalency factor approach in predicting toxicity of mixtures of Cu 2þ -Zn 2þ and Cu 2þ -Ag þ . The fraction of biotic ligands occupied by ions was used to determine the relative toxic potency of metals and the toxic equivalency quotient (TEQ) of mixtures. This approach allowed for including interactions in estimating mixture toxicity and showed good predictive power (r 2 ¼ 0.64-0.84). The TEQ at the 50% response level (TEQ50, Cu 2þ equivalents) for Cu 2þ -Zn 2þ mixtures was significantly lower than the value for Cu 2þ -Ag þ mixtures. Joint toxicity depended on both TEQ and specific composition of the mixture. The present study supports the use of the accumulation of metal ions at the biotic ligands as a predictor of toxicity of single metals and mixtures. Environ. Toxicol. Chem. 2013;32:137-143. # 2012 SETAC

Evaluating the Combined Toxicity of Cu and ZnO Nanoparticles: Utility of the Concept of Additivity and a Nested Experimental Design

“…This suggests metal-specific responses of lettuce or different toxicokinetics of excess Cu and Zn in terrestrial plants. However, the EC 50 of dissolved Zn calculated in this study was significantly lower than the value predicted for Zn 2+ in the research of Le et al This difference can be the result of differences in the chemical composition of the background medium used and the subsequent variation in speciation as calculated by the Windermere humic–aqueous model VI. Additionally, the effects of Cu or Zn seemed to be associated with the form of the metal species that the relatively lower EC 50 values of nitrate salts were calculated in this study as compared to the corresponding nanoparticles.…”

“…Theoretically, if Cu NPs and ZnO NPs would act comparably to their metal salts, the existing models for predicting the combined effects of metals can be applied to predict the toxicity of mixtures of metal-based NPs. As shown in our previous studies, , Cu 2+ competed with Zn 2+ for binding to the biotic ligand of lettuce. However, this research is more complex than in case of mixtures of metal salts because suspensions of each type of metal-based NPs consist of a mixture mainly containing dissolved metal species and undissolved particles.…”

Predict Metal Toxicity and Water Quality Criteria of Different Types of Water Into Taihu Lake, China Using Biotic Ligand Model

“…The difference in the relative toxicity of zinc and copper was consistent with the finding in the study that gill binding constant for dissolved Zn was lower than that of dissolved Cu (Santore, 2001b). It was also consistent with the results of Galvez (1998) who had also measured a gill binding constant for zinc which was lower than the binding constants for copper as well (Yen, 2013).…”

Surface Electrical Potentials of Root Cell Plasma Membranes: Implications for Ion Interactions, Rhizotoxicity, and Uptake

“…Therefore, the essential scientific challenge is to further develop the traditional models for responses to multiple metals. Le et al , [ 43 ] introduced the traditional CA concept into the BLM model and successfully evaluated the effect of binary mixtures of Cu-Ag and Cu-Zn toxicity on lettuce, Lactuca sativa . However, these studies of metal mixtures are still based on free metal ion activities or concentrations in the external media rather than metal activities at PM surfaces.…”