Distribution and biotransfer of potentially toxic elements in a terrestrial ecosystem from an abandoned realgar mine

The present study was conducted to examine the trophic transfer of potentially toxic elements (PTEs) in a closed arsenic mine. Eight PTEs in a soil-plant-leaf litter-earthworm-top predators (free-range local chicken and wild passerine bird) system were analyzed for nitrogen and carbon stable isotopes, PTE concentrations, bioaccumulation factors (BAFs), and transfer factors (TFs). The PTE concentrations in soils from mining areas were generally higher than a adjacent controlled area, with As and Cd in soils showing the prominent compared to other six PTEs, as seen for the indices of geo-accumulation index (I_geo), pollution index (PI) and potential ecological risk index (RI). The relatively high BAF and TF values suggested a distinct biotransfer of PTEs along the soil-plant-leaf litter-earthworm system. BAFs were mostly <1 except in earthworms, indicating that earthworms had a strong capacity to take up these metals. The TFs varied both among PTEs and organism's species, e.g., the transfer capacities of As in Pteris vittata and Pteris cretica, Cd in Miscanthus sinensis, and Pb, Cr and Mn in moss were the highest. For local free-range chicken and wild passerine bird, the concentrations of PTEs were higher in gastric contents and feather than in internal tissue (stomach, liver and heart), with lower contents in muscle and egg. Bioaccumulation of PTEs generally decreased from decomposer earthworms, to primary producer plants, to top predator, indicating a potential bio-dilution tendency in higher trophic levels in the terrestrial food chain.