Potential for the phytoremediation by Pteris vittata of an arsenic contaminated site in Venice (Italy)

The fern Pteris vittata, recently identified as a arsenic hyperaccumulator, has rapid biomass growth and is able to translocate efficiently arsenic to the aerial biomass. The suitability of P. vittata for the in situ phytoremediation of a site near Venice (Italy) was evaluated in a field study. Originally a marshy land, and filled in the past with various materials, the site currently shows a diffuse, moderate contamination by arsenic. After fern transplantation, arsenic was measured in fronds at regular intervals. Soil was analyzed for arsenic and metal content, and phytoavailability was estimated by sequential selective extractions. In the first trial (summer-autumn 2007) P. vittata showed a high extraction efficiency: after about 100 days, frond arsenic concentrations were between 200-900 mg kg-1 dw, with bioaccumulation factors (BAF) between 4.8-20. However, plant growth and survival were severely affected by the adverse pedoclimatic conditions. Thus, in the second trial (spring-winter 2008) older and more resistant plants were used, and manure was applied to increase organic carbon content in soil. Moreover, some plants were inoculated with arbuscural mycorrhizzae. Soil fertilization had a positive effect on both plant growth and phytoextraction efficiency. Conversely, it was not possible to demonstrate any influence of mycorrhization. After about 120 days, arsenic concentration in fronds were between 200-600 mg/kg dw; in dead fronds collected in winter, arsenic concentrations were drastically reduced. The lower concentration in the second trial, probably associated to a dilution effect due to the increased plant growth, is nonetheless counterbalanced by the highest biomass production