Comparative accumulation and root-to-leaf partitioning of arsenic, lead, cadmium and mercury in indigenous and exotic tree species on a rehabilitated gold-mine landscape at Ayanfuri, Ghana

Trees are widely planted on rehabilitated gold-mine waste to stabilise degraded land, but species are usually chosen for growth performance, with little attention to how they take up and distribute potentially toxic elements (PTEs). We screened arsenic (As), lead (Pb), cadmium (Cd) and mercury (Hg) in the roots and leaves of 19 trees of 17 species, five indigenous to West Africa and twelve introduced, growing on three reclaimed waste dumps and in two reference forests at the Edikan concession, Ayanfuri, Ghana. On a whole-plant basis, indigenous trees had higher median concentrations than exotic trees of As (0.82 versus 0.22 mg kg − 1 ), Pb (0.61 versus 0.25 mg kg − 1 ) and Cd (0.52 versus 0.27 mg kg − 1 ) (Mann–Whitney U test; p = 0.022, 0.018 and 0.009; q = 0.029 for each after false discovery rate adjustment). Hg did not differ between the groups (p = 0.106). Median leaf-to-root translocation factors were 0.95–0.99 for all four elements, so leaf concentrations were close to, and in most trees slightly below, root concentrations. Ceiba pentandra had the highest As and Pb, Terminalia superba and Triplochiton scleroxylon the highest Cd, and the exotic Tectona grandis the highest Hg, with about twice as much in its leaves as in its roots. Indigenous species thus accumulated more As, Pb and Cd without concentrating them in foliage, making them candidates for phytostabilisation trials. The study is exploratory: no soil was analysed, so soil-to-plant transfer factors could not be calculated, and most species are represented by one tree.