The bioaccumulation potential of heavy metals by Gliricidia sepium (Fabaceae) in mine tailings.

As a result of mining activities, waste of different types is generated. One example is mine tailings that contain potentially toxic elements such as heavy metals that negatively impact the environment and human health. Hence, developing treatments to guarantee its efficient elimination from the environment is necessary. Among these treatments, phytoremediation takes advantage of the potential of different plant species, to remove heavy metals from polluted sites. Gliricidia sepium is a tree that grows up to 15 m high and distributed from southern Mexico to Central America. This study evaluates the heavy metal bioaccumulation capacity in roots and leaves, and the effect of such bioaccumulation on fifteen macro- and one micro-morphological characters of G. sepium growing during 360 days in control, and in mine tailing substrates. G. sepium individuals growing on the exposed substrate registered the following average heavy metal bioaccumulation pattern in the roots: Fe > Pb > Zn > Cu, while in the leaf tissue, the bioaccumulation pattern was Cu > Fe > Pb > Zn. Macro- and micro-morphological characters evaluated in G. sepium decreased in plants exposed to metals. The translocation factor showed that Cu and Pb registered average values greater than 1. In conclusion, G. sepium is a species with potential for the phytoremediation of soils contaminated with Fe, Cu, and Pb, and for phytostabilizing soils polluted with Fe, Pb, Zn, and Cu, along with its ability to establish itself and turn into an abundant plant species in polluted sites, its capacity to bioaccumulate heavy metals in roots and leaves, and its high rate of HM translocation.

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.