title: Application of the biotic ligand model to explain potassium interaction with thallium uptake and toxicity to plankton.
abstract: Competitive interaction between TI(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 T1(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 T1(I) toxic effects on Chlorella sp., regardless of [T1(I)] in solution. Similar excess of K is required to suppress T1(I) toxicity to Synechococcus leopoliensis (Cyanobacteria; University of Texas Culture Collection strain 625) and Brachionus calyciflorus (Rotifera; strain AB-RIF). The mechanism for the mitigating effect of K on T1(I) toxicity was investigated by measuring 204T1(I) cellular uptake flux and efflux in Chlorella sp. Potassium shows a competitive effect on T1(I) uptake fluxes that could be modeled using the BLM-derived stability constants and a Michaelis-Menten relationship. A strong T1 efflux dependent only on the cellular T1 concentration was measured. Although T1 efflux does not explain the effect of K on T1(I) toxicity and uptake, it is responsible for a high turnover of the cellular T1 pool (intracellular half-life = 12-13.5 min). No effect of Na+, Mg2+, or Ca2+ was observed on T1+ uptake, whereas the absence of trace metals (Cu, Co, Mo, Mn, Fe, and Zn) significantly increased T1 uptake and decreased the mitigating effect of K+. The importance of K+ in determining the aquatic toxicity of T1+ underscores the use of ambient K+ concentration in the establishment of T1 water-quality guidelines and the need to consider K in predicting biogeochemical fates of T1 in the aquatic environment.
authors.affiliation: Department of Biology/Clarkson Center for the Environment, Clarkson University, Potsdam, New York 13699, USA. mtwiss@clarkson.edu
authors.forename: Christel S
authors.initials: CS
authors.lastname: Hassler
authors.forename: Ryan D
authors.initials: RD
authors.lastname: Chafin
authors.forename: Mary Beth
authors.initials: MB
authors.lastname: Klinger
authors.forename: Michael R
authors.initials: MR
authors.lastname: Twiss
mesh_terms: D052918:Environmental Restoration and Remediation; D008024:Ligands; D010933:Plankton / Q000187:drug effects*; D011188:Potassium / Q000378:metabolism*; D013793:Thallium / Q000378:metabolism* / Q000633:toxicity*
chemical_list: D008024:Ligands; D013793:Thallium; D011188:Potassium