Selenite enhances arsenate toxicity in Thunbergia alata
Katharina Bluemlein A , Elizabeth Klimm A , Andrea Raab A and Jörg Feldmann A BA University of Aberdeen, College of Physical Sciences, TESLA (Trace Element Speciation Laboratory), Meston Walk, Aberdeen AB24 3UE, Scotland, UK.
B Corresponding author. Email: j.feldmann@abdn.ac.uk
Environmental Chemistry 6(6) 486-494 https://doi.org/10.1071/EN09101
Submitted: 6 August 2009 Accepted: 10 November 2009 Published: 18 December 2009
Environmental context. Arsenic and selenium are two elements ubiquitously distributed in our environment. While selenium is not known to be essential to plants, it is certainly toxic as is arsenic. On the other hand selenium is known to be essential for mammals and an increase in selenium concentration in plants when used as feed or food may be beneficial for mammals in regions of low selenium concentration. The wide distribution of these two elements in the soil might result in elevated co-exposure of plants. So far no interactions of those elements in plants have ever been studied, although this might be mandatory when nutritionists would like to increase the selenium concentrations in crops, which are already challenged by elevated levels of arsenic.
Abstract. The suspected antagonism between selenite and arsenite in various mammalian species gave reason to investigate the effect of selenite on arsenate toxicity in higher plants using Thunbergia alata as a model plant. Here, we present a study involving (1) toxicity tests, (2) uptake and translocation experiments as well as (3) selenium–sulfur–arsenic speciation analysis by HPLC-ESMS-ICP-MS (oxygen) of selected plant tissues. The EC50 (effective concentration that inhibits growth by 50%) values, as a result of the toxicity studies, showed that selenite co-exposure enhances arsenate toxicity. The detection of two selenium species, SeII-PC2 complex and Se-cysteinylserine glutathione, suggested that the increased toxicity symptoms might have been a result of the competition of SeII with AsIII for sulfhydryl groups (crucial for arsenite detoxification in plant cells) as binding partners.
Additional keywords: ESMS, ICP-MS, phytochelatins.
Acknowledgements
K. Bluemlein thanks the College of Physical Sciences of the University of Aberdeen for a Ph.D. scholarship and E. Klimm thanks the Erasmus Program.
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A In this study the term antagonism refers to a decreased overall toxicity when selenium and arsenic are supplied simultaneously. Accordingly the term synergism refers to an increased overall toxicity.
B The oxidation state noted as +II for Se is a matter of definition. According to Pauling and Mulliken’s electronegativity (EN), Se is actually +II but since the EN of Se and S are similar, it may be assigned as 0.
C Arsenate was supplied only during the last 24 h before analysis.
