Arsenic species in an arsenic hyperaccumulating fern, Pityrogramma calomelanos: a potential phytoremediator of arsenic-contaminated soils

The fern Pityrogramma calomelanos is a hyperaccumulator of arsenic that grows readily on arsenic-contaminated soils in the Ron Phibun district of southern Thailand. P. calomelanos accumulates arsenic mostly in the fronds Žup to 8350 g As g 1 dry mass. while the rhizoids contain the lowest concentrations of arsenic Ž88 310 g As g 1 dry mass.. The arsenic species in aqueous extracts of the fern and soil were determined by high performance liquid chromatography coupled to an inductively coupled plasma mass spectrometer ŽHPLC-ICPMS. which served as an arsenic specific detector. Only a small part of the arsenic Ž6.1 12%. in soil was extracted into water, and most of this arsenic Ž 97%. was present as arsenate. The arsenic in the fern rhizoids was approximately 60% water-extractable, 95% of which was present as arsenate. In contrast, arsenic in the fern fronds was readily extracted into water Ž86 93%. and was present mainly as arsenite Ž60 72%. with the remainder being arsenate. Methylarsonate and dimethylarsinate were detected as trace constituents in only two fern samples. Preliminary estimates of phytoremediation potential suggest that P. calomelanos might remove approximately 2% of the soil arsenic load per year. With due consideration to the type of arsenic compounds present in the fern, and their water-solubility, the option of disposing high arsenic ferns at sea is raised for discussion.