Uptake, Translocation, and Transformation of Arsenic by Four Fern Species in Arsenic-Spiked Soils

Arsenic (As) toxicity has become a global concern because of the ever-increasing contamination of water, soil, and crops in many regions of the world. Although most plants are susceptible to As, some ferns are resistant to it and can accumulate As. In this study, four species of ferns, Asplenium nidus (AN), Pteris umbrosia (PU), Polypodium vulgare (PV), and Pteris cretica (PC), were screened for their ability to tolerate and hyperaccumulate As. Ferns were exposed to 120mg As kg-1 as sodium arsenate (Na2HAsO4) for 50 days under natural sunlight in greenhouse conditions, and the fronds and roots were analyzed for As speciation and selected macronutrients [potassium (K) and phosphorus (P)]. The species of ferns varied widely in their abilities to transport As to the fronds (ranged from 164 to 4820mgkg-1 DW) with the greatest frond As concentration found in PU (4820mgkg-1). The distribution of soil As fractions indicated that As was mostly bound carbonate (carb) (32.4%) and in the residual fractions (45.1%). Chemical fractionation of As-spiked soil indicated that the greatest reduction in soil As after growing was in carb As form. Arsenic speciation analysis shows that 82% of the total As in the aboveground biomass is present as the reduced form of As, arsenite [As(III)], which is considered to be the more toxic form. However, in roots, only 60% of the As is present as As(III). Furthermore, among the four species of ferns, PU is the most promising to be used in the remediation of the affected area. Therefore, it is possible to use PU to remediate As-contaminated soils by repeatedly harvesting its fronds.