title: Oxidation of thallium by freshwater plankton communities.
abstract: Thallium is a toxic metal that is of emerlI(I) or Tl(III), and its oxidation state affects its complexation and subsequent bioavailability and toxicity. We conducted lab and field incubations with 204Tl(I) and natural plankton assemblages to study the occurrence and mechanism of Tl oxidation. We observed that Tl(III) comprised 74% of total dissolved Tl after a 60 h incubation in surface waters from Lake Ontario, revealing a maximum specific oxidation rate of 0.014 h(-1). No Tl(I) oxidation was observed in sterile-filtered control treatments, indicating that solar radiation alone does not oxidize Tl(I) to Tl(III). Additional incubations with pond water revealed that Tl(I) oxidation is mediated by microbial activity and is not related to the presence of abiotic particles or phytoplankton or protozoa. We also identified a minor fraction (5-13%) of nonion-exchangeable (Chelex-100 resin; pH 1.5) Tl that may represent dimethylthallium or complexed thallium. This study demonstrates that planktonic bacteria are responsible for oxidizing the thermodynamically stable Tl(I) to the more abundant Tl(III).
authors.affiliation: Marine Sciences Research Center, Stony Brook University, Stony Brook, New York 11794-5000, USA.
authors.forename: Benjamin S
authors.initials: BS
authors.lastname: Twining
authors.forename: Michael R
authors.initials: MR
authors.lastname: Twiss
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Fisher
mesh_terms: D000818:Animals; D001682:Biological Availability; D056890:Eukaryota; D020387:Food Chain; D005618:Fresh Water / Q000032:analysis*; D006114:Great Lakes Region; D007474:Ion Exchange; D007700:Kinetics; D010084:Oxidation-Reduction; D010839:Phytoplankton / Q000737:chemistry*; D010933:Plankton / Q000737:chemistry*; D013793:Thallium / Q000737:chemistry* / Q000633:toxicity; D013794:Thallium Radioisotopes / Q000737:chemistry* / Q000633:toxicity; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000633:toxicity
chemical_list: D013794:Thallium Radioisotopes; D014874:Water Pollutants, Chemical; D013793:Thallium