Phosphate regulates uranium(VI) toxicity to Lemna gibba L. G3

• Published in: Environmental toxicology 2007-02, Vol.22 (1), p.9-16
• Main Authors: Mkandawire, Martin, Vogel, Kerstin, Taubert, Barbara, Dudel, E. Gert
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Applied ecology; Araceae - drug effects; Araceae - growth & development; bioaccumulation; bioavailability; Biodegradation, Environmental; Biological and medical sciences; Biological Availability; Dose-Response Relationship, Drug; EC50; ecotoxicity; Ecotoxicology, biological effects of pollution; Environmental Monitoring; Fundamental and applied biological sciences. Psychology; General aspects; Germany; Hydrogen-Ion Concentration; Lemna gibba; Mining; Phosphates - metabolism; Phosphates - toxicity; Plant Leaves - chemistry; Plant Leaves - drug effects; Uranium - metabolism; Uranium - toxicity; Uranium Compounds - metabolism; Uranium Compounds - toxicity; uranium mining; uranium speciation; Water Pollutants, Radioactive - metabolism; Water Pollutants, Radioactive - toxicity
• ISSN: 1520-4081; 1522-7278
• DOI: 10.1002/tox.20228

The influence of phosphate on the toxicity of uranium to Lemna gibba G3 was tested in semicontinuous culture with synthetic mine water developed as an analogue of surface water of two abandoned uranium mining and ore processing sites in Saxony, Germany. Six concentrations of uranium were investigated under five different supply regimes of PO43− at constant pH (7.0 ± 0.5) and alkalinity (7.0 ± 1.6 mg L−1 total CO32−). The results showed significant inhibition of specific growth rates in cultures exposed to the highest uranium concentrations (3500 and 7000 μg U L−1) at lowest PO43− supply of 0.01 mg L−1. An increase of phosphate concentration from 0.01 to 8.0 mg L−1 resulted in an increase of EC50 from 0.9 ± 0.2 to 7.4 ± 1.9 mg L−1 (significant with Student's t test, P > 0.05). The accumulation of uranium in L. gibba increased exponentially with the increase in uranium concentration in cultures with 0.01 and 0.14 mg PO43− L−1. Accumulation also increased significantly when PO43− supply was increased from 0.14 to 1.36 mg PO43− L−1 for all uranium concentrations. However, as the supply of PO43− gradually increased from 1.36 to 8.0 mg PO43− L−1, uranium bioaccumulation increased slightly but insignificantly before leveling off. Uranium speciation modeling with PhreeqC geochemical code predicted increases in the proportions of uranyl phosphate species when PO43− concentrations increase in the media. Most of these uranyl phosphate species have a high probability of precipitation [saturation indices (SI) > 0.93]. Therefore, the alleviation of uranium toxicity to L. gibba with phosphates is due to interactions among components of the media, mainly uranyl and phosphate which results in precipitation. Consequently, bioavailable fractions of uranium to L. gibba are reduced. This might explain lack of consistent EC50 values for uranium to most aquatic organisms. © 2007 Wiley Periodicals, Inc. Environ Toxicol 22: 9–16, 2007.