Uptake of lead and zinc from soil by blackberry plants (Rubus fruticosus L. agg.) and translocation from roots to leaves

Abstract

• Pb and Zn in soil ofa the Innerste floodplain exceed precautionary limits. • Concentrations of Pb and Zn in soils and blackberries are positively correlated. • Uptake and translocation of Pb and Zn are reduced at higher soil levels. • R. fruticosus is a useful bioindicator but unsuited for phytoremediation. Heavy metals transported by rivers are deposited in sediments and floodplains, and floodplain soils act as both sinks and sources of these metals. The Innerste River is contaminated by historical metal ore mining, processing, and smelting in the Harz Mountains (Germany). Our study compared the uptake of lead (Pb) and zinc (Zn) in wild blackberries ( Rubus fruticosus L. agg.) growing within and outside the Innerste floodplain in a downstream area. The potential of blackberries as bioindicators and for phytoremediation of soils polluted by Pb and Zn was assessed based on bioconcentration factors (BCF) and the intra-plant mobility of the two metals based on translocation (TF) factors. Concentrations of Pb and Zn were significantly higher in soils and blackberry plants from the Innerste floodplain compared to adjacent non-flooded area, while soil pH and organic matter content did not differ significantly between the two zones. Mean concentrations (mg/kg d.w.) of Pb (1457.2) and Zn (1365.2) in the regularly flooded soils far exceeded the precautionary limits of the German Federal Soil Protection and Contaminated Sites Ordinance. Concentrations of both heavy metals in blackberry roots and leaves increased with their levels in soil. Except for BCF Root Pb, BCFs and TFs decreased exponentially with increasing heavy metal concentration in soil and roots, respectively. This indicates that the uptake of Pb and Zn by R. fruticosus and their translocation within the plant are reduced at higher soil levels of both heavy metals. BCF < 1 were determined for both heavy metals and a TF < 1 for Pb. Only blackberries growing outside the floodplain showed a TF > 1 for Zn. Our results indicate that blackberries can be used as bioindicators of soil contamination by Pb and Zn. Regarding their uptake characteristics, blackberries constitute excluders rather than accumulators, and are thus unsuited for phytoremediation.