Heavy metal bioaccumulation and morphological changes in Vachellia campechiana (Fabaceae) reveal its potential for phytoextraction of Cr, Cu, and Pb in mine tailings

Vachellia campechiana (Mill Seigler & Ebinger) is widely distributed in Mexico and is a dominant species of tailings in Huautla, in the state of Morelos, Mexico. Mining activities carried out in this region generated about 780 thousand tons of bioavailable heavy metal waste (HMs) that were deposited in the environment without any treatment. This study evaluates the bioaccumulation capacity and morphological changes of V. campechiana growing during 1 year in control or tailing substrates (treatments) under greenhouse conditions. The concentration of six HMs was also measured in roots, leaves, and seeds by atomic absorption spectrophotometry. Five metals showed a similar bioaccumulation pattern in the roots and leaves of V. campechiana grown in both substrates: Pb > Fe > Cr > Cu > Zn. The concentrations of Cr, Cu, and Pb were significantly higher in the roots and leaves of individuals growing on the exposed substrate. The presence of essential metals (Cu, Fe, Zn) was only recorded in the seeds, with similar concentrations in both treatments. Seventeen of 18 morphological characters evaluated in V. campechiana decreased in plants exposed to metals. Pb, Cu, and Fe showed a bioconcentration factor greater than one in roots and leaves. The translocation factor showed the following pattern: Cr > Cu = Pb. In conclusion, V. campechiana is a candidate species to phytoremediate environments contaminated with Pb, Cr, and Cu due to its ability to establish itself and turn into the dominant plant species in polluted sites, its ability to bioaccumulate non-essential metals in roots and leaves, and its high rate of HMs translocation.