Phytoremediation Potential of Crotalaria pumila (Fabaceae) in Soils Polluted with Heavy Metals: Evidence from Field and Controlled Experiments

Abstract

Phytoremediation is a useful, low-cost, and environmentally friendly alternative for the rehabilitation of heavy-metal-contaminated (HM) soils. This technology takes advantage of the ability of certain plant species to accumulate HMs in their tissues. Crotalaria pumila is a herbaceous plant with a wide geographical distribution that grows naturally in environments polluted with HMs. In this work, the bioaccumulation capacity of roots and leaves in relation to five HMs (Cr, Cu, Fe, Pb, and Zn) was evaluated, as well as the morphological changes presented in C. pumila growing in control substrate (without HMs) and mine-tailing substrate (with HMs) under greenhouse conditions for 150 days. Four metals with the following concentration pattern were detected in both tissues and substrates: Fe > Pb > Cu > Zn. Fe, Pb, and Zn concentrations were significantly higher in the roots and leaves of individuals growing on mine-tailing substrate compared to the control substrate. In contrast, Cu concentration increased over time in the exposed individuals. The bioconcentration factor showed a similar pattern in root and leaf: Cu > Fe > Pb > Zn. Around 87.5% of the morphological characters evaluated in this species decreased significantly in individuals exposed to HMs. The bioconcentration factor shows that C. pumila is efficient at absorbing Cu, Fe, and Pb from the mine-tailing substrate, in the root and leaf tissue, and the translocation factor shows its efficiency in translocating Cu from the roots to the leaves. Therefore, C. pumila may be considered as a HM accumulator plant with potential for phytoremediation of polluted soils with Cu, Pb, and Fe, along with the ability to establish itself naturally in contaminated environments, without affecting its germination rates. Also, it exhibits wide geographical distribution, it has a short life cycle, exhibits rapid growth, and can retain the mine-tailing substrate, extracting HMs in a short time.