Jump to Main Content
Uptake and Fractionation of Thallium by Brassica juncea in a Geogenic Thallium-Amended Substrate
- Rader, Shelby T., Maier, Raina M., Barton, Mark D., Mazdab, Frank K.
- Environmental science & technology 2019 v.53 no.5 pp. 2441-2449
- Brassica juncea, bioavailability, feldspar, heavy metals, isotope fractionation, isotopes, leaves, manganese, mica, planning, plant growth, pods, stems, thallium
- This study shows thallium (Tl) concentrations in Brassica juncea (Indian mustard) tissue are more than an order of magnitude higher (3830 μg/kg) than that of the substrate (100 μg/kg) and are strongly influenced by the underlying mineralogy; i.e., Tl bioaccessibility depends on the mineral structure: K-feldspar > Mn nodule > hendricksite mica. The majority of Tl for all substrates is contained in edible parts of the plant, i.e., leaves (41% of total Tl, on average) ≥ flower stems (34%) > seed pods (11%) ≈ stems (10%) > flowers (3%). We also show that Tl isotope fractionation induced by B. juncea is substantial, at nearly 10 ε²⁰⁵Tl units, and generates systematic plant-specific patterns. Progressive plant growth strongly fractionates Tl isotopes, discriminating against ²⁰⁵Tl as the plant matures. Thus, ²⁰⁵Tl values are systematically higher in the early formed stem (ε²⁰⁵Tlₐᵥg = +2.5) than in plant elements formed later (ε²⁰⁵Tlₐᵥg = −2.5 to +0.1), which demonstrates the large degree of translocation and the associated effects during plant growth. This study establishes the potential of Tl isotopes as a new tool for understanding heavy metal (re)distribution during anthropogenic and geologic processes and the utility of such information in environmental and health-related planning and in phytomining or bioprospecting.