Phytoremediation of nitrate contamination using two halophytic species, Portulaca oleracea and Salicornia europaea

Nitrate is a common form of nitrogen fertilizer, and its excess application combined with easy leaching from agricultural fields causes water and soil contamination, hazards on human health, and eutrophication of aquatic ecosystems. Compared to other pollutants, the application of phytoremediation technology for nitrate-contaminated sites has received less attention. Nitrophilous halophyte species are suitable candidates for this purpose particularly by application of additional treatments for assisting nitrate accumulation. In this work, two annual halophyte species, Portulaca oleracea and Salicornia europaea were studied for their phytoremediation capacity of nitrate-contaminated water and soils. Plants were treated with three nitrate levels (2, 14, and 50 mM) combined with either selenium (10 µM as Na₂SeO₄) or salt (100 mM NaCl) in the hydroponics and sand culture medium, respectively. A fast growth and production of higher biomass enables P. oleracea for higher nitrate removal compared with S. europaea in both experiments. In S. europaea, both selenium and salt treatments enhanced nitrate removal competence through increasing the biomass and nitrate uptake or assimilation capacity. Salt treatment, however, reduced these parameters in P. oleracea. Based on data, selenium-assisted phytoremediation of nitrate contamination is a feasible strategy for both species and S. europaea is better suited to nitrate-contaminated saline water and soils. Nitrate accumulation in both species, however, exceeds that of the permitted nitrate level in the forage crops suggesting that the phytoremediation byproducts could not be consumed and other management strategies should be applied to the residual biomass.