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Application of the biotic ligand model to explain potassium interaction with thallium uptake and toxicity to plankton

Chafin, Ryan D.
Klinger, Mary Beth
Twiss, Michael R.
Published in Environmental Toxicology & Chemistry. 2007, vol. 26, no. 6, p. 1139
Abstract Competitive interaction between Tl(I) and K was successfully predicted by the biotic ligand model (BLM) for the microalga Chlorella sp. (Chlorophyta; University of Toronto Culture Collection strain 522) during 96-h toxicity tests. Because of a greater affinity of Tl(I) (log K = 7.3–7.4) as compared to K (log K = 5.3–6.3) for biologically sensitive sites, an excess of 40-to 160-fold of K is required to suppress Tl(I) toxic effects on Chlorella sp., regardless of [Tl(I)] in solution. Similar excess of K is required to suppress Tl(I) toxicity to Synechococcus leopoliensis (Cyanobacteria; University of Texas Culture Collection strain 625) and Brachionus calyciflorus (Rotifera; strain AB-R1F). The mechanism for the mitigating effect of K on Tl(I) toxicity was investigated by measuring 204Tl(I) cellular uptake flux and efflux in Chlorella sp. Potassium shows a competitive effect on Tl(I) uptake fluxes that could be modeled using the BLM-derived stability constants and a Michaelis—Menten relationship. A strong Tl efflux dependent only on the cellular Tl concentration was measured. Although Tl efflux does not explain the effect of K on Tl(I) toxicity and uptake, it is responsible for a high turnover of the cellular Tl pool (intracellular half-life = 12–13.5 min). No effect of Na+, Mg2+, or Ca2+ was observed on Tl+ uptake, whereas the absence of trace metals (Cu, Co, Mo, Mn, Fe, and Zn) significantly increased Tl uptake and decreased the mitigating effect of K+. The importance of K+ in determining the aquatic toxicity of Tl+ underscores the use of ambient K+ concentration in the establishment of Tl water-quality guidelines and the need to consider K in predicting biogeochemical fates of Tl in the aquatic environment.
Keywords AlgaeBiotic ligand modelCyanobacteriaGrowth rateWater-quality guidelines
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HASSLER, Christel et al. Application of the biotic ligand model to explain potassium interaction with thallium uptake and toxicity to plankton. In: Environmental Toxicology & Chemistry, 2007, vol. 26, n° 6, p. 1139.

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Deposited on : 2013-02-20

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