Soil variables that determine lead accumulation in Bidens pilosa L. and Tagetes minuta L. growing in polluted soils

- Lead concentration in Asteraceae roots depends on Pb and Cu bioavailability in soils.
- Pb translocation depends on Pb, Zn and Cu bioavailability in soils and their concentrations in plant.
- Total Transfer Factor for Pb is an optimal indicator for phytoremediator species selection.

Toxic metal soil pollution is one of the most serious environmental problems, with phytoextraction being an ecological and inexpensive potential solution to recuperate soil functionality. This emergent technology has produced good results for many elements, but phytoextraction has not been as successful for lead as for other pollutants. This research aimed to evaluate several factors that could be determinant on Pb uptake by the accumulator plants Bidens pilosa and Tagetes minuta. Topsoils (bulk and ryzospheric) and plants were collected around a former Pb smelter, and sequential extractions of Pb, Cu and Zn, organic matter content, electrical conductivity, pH, and texture were measured in soils. Also, bacterial diversity in soil was determined by the denaturing gradient gel electrophoresis (DGGE) technique. The Pb, Cu, and Zn concentrations in soil extractions and plants (leaves, stem, and root) were quantified by T-XRF in Synchrotron, Brazil. Our results demonstrated that Pb uptake from polluted soils and translocation to aerial tissues by two Asteraceae species are related not only to the traditional soil parameters, but even more importantly to the Zn and Cu concentrations in plant and soils. In addition, the soil bacterial biodiversity also affects the Pb uptake by plants. In this study, we propose the total translocation factor (TTF) to evaluate the phytoextraction efficiency, which is given by the ratio of total extraction of Pb in aerial organs and roots, instead of using the Pb concentrations alone.

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