172-6 Sourcing and Monitoring of Heavy Metals using Nontraditional Isotopes in the Hyperaccumulator Brassica juncea

Session: Environmental Geochemistry and Health (Part II)

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Given rising national and global demands for metals, developing cost-effective methods for identifying new deposits and passively monitoring metal mobility throughout the natural environment are of high priority for societal advancement. Some metal isotope systems have shown great promise in helping to identify the provenance of either valuable metal resources or environmental contaminants, even within plant biomass. Thallium (Tl), which is a highly toxic heavy metal and an emerging environmental pollutant, is one such element that has been shown to accumulate or even hyperaccumulate in a number of plant species, including Brassica juncea (B. juncea – brown mustard). Thallium in B. juncea has shown evidence of reflecting inherited geogenic signatures from the underlying soil, providing a non-invasive means of understanding metal provenance and changes in sourcing or availability over time. However, to ensure that geogenic signatures within biomass can serve as a tool for differentiating background soil metals from anthropogenic metals arising from industrial processes such as smelting and coal combustion, consistent and persistent reproducibility of original metal signatures within plant material must be established. 

To determine how well distinct soil-based Tl isotopic compositions and variable metal concentrations are reflected in plant signatures, four greenhouse trials of B. juncea grown in distinct Tl-bearing soils along with a control were grown in triplicate in the IU Botany Greenhouse. For each trial, the soil was spiked with either USGS Nod-P-1 or USGS Nod-A-1 at 2 mg/kg Tl or 10 mg/kg Tl. Plants were harvested and separated into individual parts (i.e., roots, stem, leaves, etc.), dried, ground, and digested in preparation for metal concentration and Tl isotopic analysis via Q-ICPMS and MC-ICPMS. As expected, higher soil metal concentrations resulted in higher plant metal concentrations and, regardless of soil composition, metal distribution trends within tissues were consistent: the majority of Tl (and several other metals) was sequestered within the leaves, accounting for ~35-45% of all plant-based Tl. This translocation of Tl and other metals can be both beneficial, for phytoremediation, or detrimental, as B. juncea leaves are commonly consumed globally. Ongoing Tl isotopic analysis aims to further refine the applicability of Tl biogeochemical signatures as a tool to assess and monitor metal remediation and fingerprint Tl sources.

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