In vivo synchrotron study of thallium speciation and compartmentation in Iberis intermedia

Thallium (TI) is a metal of great toxicological concern and its prevalence in the natural environment has steadily increased as a result of manufacturing and combustion practices. Due to its low natural abundance and increasing demand, TI is the fourth most expensive metal, thus, recovery and reuse could be a profitable endeavor. The hyperaccumulator Iberis intermedia was examined via in vivo micro-X-ray absorption near edge (micro-XANES) and micro-X-ray fluorescence (micro-XRF) spectroscopies to determine the speciation and distribution of TI within leaves of the plant. I. intermedia plants were cultivated under controlled conditions in 0, 10, and 20 mg TI kg(-1) soil leading to a shoot concentration of up to 13 430 mg TI kg(-1) dry weight plant mass during 10 weeks of growth. Live plant leaves were examined by micro-XANES and micro-XRF which determined aqueous TI(I) to be the model species distributed primarily throughout the vascular network. A direct relationship of vein size to TI concentration was observed. The high uptake of TI and high potential biomass of I. intermedia, combined with knowledge of TI speciation and compartmentation within the plant, are discussed in terms of accumulation/tolerance mechanisms, consequences for potential food chain contamination, and phytomining strategies to reclaim TI-contaminated soils, sediments, and waters.