Characterization of Fe Plaque and Associated Metals on the Roots of Mine-Waste Impacted Aquatic Plants

Abstract

Iron plaque on aquatic plant roots are ubiquitous and sequester metals in wetland soils; however, the mechanisms of metal sequestration are unresolved. Thus, characterizing the Fe plaque and associated metals will aid in understanding and predicting metal cycling in wetland ecosystems. Accordingly, microscopic and spectroscopic techniques were utilized to identify the spatial distributions, associations, and chemical environments of Fe, Mn, Pb, and Zn on the roots of a common, indigenous wetland plant (Phalaris arundinacea). Iron forms a continuous precipitate on the root surface, which is composed dominantly of ferrihydrite (ca. 63%) with lesser amounts of goethite (32%) and minor levels of siderite (5%). Although Pb is juxtaposed with Fe on the root surface, it is complexed to organic functional groups, consistent with those of bacterial biofilms. In contrast, Mn and Zn exist as discrete, isolated mixed-metal carbonate (rhodochrosite/hydrozincite) nodules on the root surface. Accordingly, the soil-root interface appears to be a complex biochemical environment, containing both reduced and oxidized mineral species, as well as bacterial-induced organic-metal complexes. As such, hydrated iron oxides, bacterial biofilms, and metal carbonates will influence the availability and mobility of metals within the rhizosphere of aquatic plants.

Excessive sulfur supply reduces arsenic accumulation in brown rice

“…Thus, As uptake by rice plants is recognized as a major route of As transfer into food chain which has the potential to become a new disaster for population in Southeast Asia (Heikens et al 2007). Therefore, it is crucial to understand the mechanism of As uptake by rice and to find strategies for reducing As accumulation in grain for enhanced food safety.Paddy rice (Oryza sativa L.) oxygenates its rhizosphere, resulting in the formation of an iron oxyhydroxide plaque (Hansel et al 2001 …”

Influence of chromium in Laguncularia racemosa (L). Gaertn f. physiology

“…This behavior is itself an efficient mechanism of tolerance in environments contaminated by heavy metals. The formation of iron plaque on roots that can diminish the loss of oxygen is common in aquatic and wetland plants (Møller and SandJensen, 2008) and may influence the availability and mobility of metals in the rhizosphere of aquatic plants (Hansel et. al, 2001).…”

Influence of external zinc and phosphorus supply on Cd uptake by rice (Oryza sativa L.) seedlings with root surface iron plaque

“…The formation of iron plaque on the root surfaces of rice and other wetland plants is due to the release of oxygen and oxidants in the rhizosphere and the subsequent oxidation of ferrous to ferric iron and the precipitation of iron oxide or hydroxide on the root surface (Armstrong 1967;Chen et al 1980b;Taylor et al 1984). Mineralogical investigations in wetland fields have shown that the composition of iron plaque in Phalaris arundinacea is mainly ferrihydrite (∼63%) with smaller amounts of goethite (32%) and minor amounts of siderite (5%; Hansel et al 2001), or predominately goethite in Juncus bulbosus (Chabbi 1999) and rice (Chen et al 1980a). Iron plaque therefore has chemical properties similar to those of iron oxides in the soil and can thus sequester both cations and anions and alter the uptake and accumulation of elements by plants.…”