Screening for natural manganese scavengers: Divergent phytoremediation potentials of wetland plants

Manganese is a potentially toxic micronutrient with great ecological risk. In wetland soils, Mn bioavailability increases sharply with contamination hazards. Wetland plants may have different effects on Mn mobility and reactivity in soils, affecting their phytoremediation potential. This study evaluated the role of three naturally occurring wetland plants (i.e., Hibiscus tiliaceus, Eleocharis acutangula, and Typha domingensis) in Mn biogeochemistry and screened their potential for phytoremediation in an Mn-contaminated estuary (Doce River estuary; SE-Brazil). Shoots, roots, and soils (0–40 cm) of each plant species were sampled. Soil physicochemical parameters (i.e., pH, rhizospheric pH, and redox potentials) were measured, and Mn concentrations were determined in the plant tissues, root iron plaques, and soils. In addition, Mn geochemical fractionation was performed on the studied soils. Our results reveal that T. domingensis is highly efficient at Mn phytoremediation. T. domingensis showed unprecedented Mn shoot concentrations (6858 mg kg−1), translocation (TF; 99.5), and bioconcentration factors (BCF; 11.7). We revealed that rhizospheric acidification promoted by T. domingensis significantly altered the soil Mn geochemistry, favoring its acquisition from iron plaques and short-range-ordered Mn oxides. In contrast, despite the high Mn bioavailability, E. acutangula and H. tiliaceus showed Mn concentrations 13- and 10-fold lower than those recorded for T. domingensis. Naturally growing T. domingensis is able to phytoextract 147 tons of Mn (∼19,000 m2), which represents a removal of 75.7 ton ha−1. The Mn phytoextraction potential of T. domingensis should be assessed in association with different phytotechnologies and agronomic practices to maximize its phytoextraction efficiency.