Cistus ladanifer phytostabilizing soils contaminated with non-essential chemical elements

Cistus ladanifer L. is one of the spontaneous species from Iberian Pyrite Belt (IPB) considered promising for phytostabilisation of mining areas. Although the plant–soil relationships of some potentially hazardous elements (e.g. As, Pb, Cu and Zn) are known, for other elements also potentially hazardous and non-essential this information is scarce. However, in soils with multielemental contamination and for landscape rehabilitation processes, these elements should also be considered. The aim of this investigation was to evaluate the potential of C. ladanifer in the phytostabilisation of the soils, developed on different contaminated substrata (e.g. mine wastes, schists and greywackes or their mixtures) and containing non-essential elements (Al, Ag, Ba, Bi, Cd, Sb and Sr), from three Portuguese IPB mining areas (Caveira, Lousal and São Domingos). The uptake, accumulation and translocation of these non-essential elements and their influence on the concentrations of beneficial elements (Co, Na and Se) and major nutrients were studied.Multielemental contaminated soils from the three mining areas had high total concentrations of some non-essential elements (Ba and Sb for the three mines and Se for Caveira and São Domingos). Soil available fraction of the studied elements were usually small (<8.6% of the total concentration) except for Cd whose available fraction was between 10 and 100% of the total concentration (<0.3–1.3mg Cd/kg). In general, C. ladanifer showed significant uptake (biological absorption coefficients indicating strong and intensive uptake) and translocation (translocation coefficients >1) of the studied elements (even the non-essentials), but small accumulation in the shoots (mg/kg−Ag, Bi, Sb and Se: <1.6; Ba, Cd, Co and Sr: 0.05–37.8; Al and Na: 49–2503), independently of the mine area. Elemental concentrations in the shoots were below the limit values indicated for phytotoxicity and toxicity for domestic animals intake. Although the statistical negative influence of Ag, Sb and Sr on the concentrations of the beneficial elements (Na) and nutrients (Ca and Fe) in roots or shoots had been obtained, no visual symptoms was observed in the plants. Cistus ladanifer plants from the studied populations can be considered non-accumulators and excluders of Al, Ag, Ba, Bi, Sr and Sb (soil-plant transfer coefficient≪1) and beneficial elements. Although plants from São Domingos and, in some cases, from Caveira can be accumulators of Cd, the concentrations of Cd in the shoots were small (<0.2mg/kg) and did not represent any environmental risk. Due to its adaptability, tolerance and standard plant behaviours in the three mining areas, C. ladanifer will be a good choice for phytostabilisation of soils contaminated with non-essential elements.