Lead Translocation\nand Isotopic Fractionation after\nUptake by Brassica juncea (Brown Mustard)

The behavior of lead (Pb) during plant uptake is poorly\nunderstood,\nparticularly as it pertains to plant isotopic fractionation patterns\nand whether they can accurately reflect unique geogenic or anthropogenic\nsources of contamination. Here, we characterize concentrations and\nchanges in plant Pb ratios during uptake to determine the feasibility\nof bioremediation and isotopic fingerprinting for Pb sourcing in Brassica juncea (B. juncea), a known Pb-tolerant species, which was grown in a controlled greenhouse\nenvironment. Twenty individuals were cultivated from three trials\nusing substrates amended with Pb from different sources (natural ore,\nanthropogenic, and mixed) and a control with no Pb amendment. After\nmaturation, plants were harvested, split into individual parts, and\nanalyzed for both Pb concentrations and isotopic composition. Results\ndemonstrate significant translocation of Pb from the roots to the\nleaves, showing an average leaf translocation factor of 3.6. Other\nabove-ground parts’ translocation factors were consistently\nbelow 1 (TF = 0.4, on average). Results also show no preferential\nuptake of any given Pb isotope into the plants, resulting in similar\nisotopic compositions throughout. Above-ground plant part, <sup>206</sup>Pb/<sup>207</sup>Pb (1.17–1.19) were within the range of initial\nsubstrate values (1.14–1.18), though the roots did show a significant\nincrease in <sup>206</sup>Pb/<sup>207</sup>Pb (1.21–1.22).\nWe were unable to differentiate plants grown from each treated substrate,\nmaking them unreliable for isotopic fingerprinting of substrate Pb\nsources. This confirms the limitations of B. juncea as a potential biomonitoring apparatus but demonstrates a greater\nthan expected ability to translocate Pb to its above-ground parts,\nwhich may indicate some useful and significant phytoextraction potential\nduring phytostabilization projects and subsequent health concerns\nfor those consuming the plant when grown in low [Pb] soils.