US EPA

1018736 

Journal Article 

Accumulation of arsenic and zinc in the rhizosphere of wetland plants 

Otte, ML; Kearns, CC; Doyle, MO 

1995 

Yes 

Bulletin of Environmental Contamination and Toxicology
ISSN: 0007-4861
EISSN: 1432-0800 

55 

1 

154-161 

English 

7663086 

10.1007/BF00212403 

WOS:A1995QY38200023 

Oxidation of the rhizosphere by wetland plants leads to precipitation of iron oxyhydroxides in the rhizosphere and on the root surface of the plants. These precipitates are also known as ironplaque. Arsenic and zinc have a high binding affinity for iron oxyhydroxides (Padmanabham 1983; Belzile and Tessier 1990; Gerth et al. 1993) and were found to accumulate in ironplaque on roots of Aster tripolium L. (Otte et al. 1989; 1991). It was argued that rhizosphere oxidation and formation of an ironplaque would favor the accumulation of iron, arsenic and zinc in the rhizosphere (Otte et al. 1991; Otte and Ernst 1994). Oxidation of ferrous iron to its ferric form would lead to precipitation of iron oxyhydroxides in the rhizosphere, which in turn would lead to a decreasing concentration gradient of dissolved iron towards the plant roots. The iron oxyhydroxides in turn would bind arsenic and zinc, again creating a decreasing concentration gradient of both elements towards the roots. These gradients would lead to the diffusion of iron, arsenic and zinc in the direction of the roots. Assuming that uptake of the elements by the roots is slower than supply through diffusion, an increase in concentrations of all three elements would be expected to occur in the solid phase of the rhizosphere. Similar processes, but induced by changes in pH rather than Eh, occur in the rhizosphere of upland plants like soybean (Glycine max L.) and barley (Hordeum vulgare L.) as described by Youssef and Chino (1991). Already, Otte et al. (1991) found indications that arsenic accumulated in soil immediately adjacent to the roots ('rhizosphere soil').

These plant-induced processes in wetland soils may not only affect availability of zinc and arsenic to the plants, but may also play an important role in the sink function of wetlands for metals and metalloids. Knowledge of these processes is important for our understanding of the functioning of wetland ecosystems, as well as for the utilization of wetlands as so-called helophyte filters (Gersberg et al. 1986; Brix and Schierup 1989; Mickle 1993).

A research project was started to study the impact of rhizosphere oxidation and ironplaque formation on the distribution of arsenic and zinc in salt marsh soils. Here we report on the results of a pilot field study which compared concentrations of the metals in ironplaque, rhizosphere soil and bulk soil under Spartina anglica Hubbard and Halimione portulacoides (L.) Aellen. It was hypothesized that iron, zinc, and arsenic concentrations in the soil would increase from the bulk soil towards the roots. 

Cytology and Cytochemistry-Plant; Biochemical Studies-Minerals; Toxicology-General; Toxicology-Environmental and Industrial Toxicology; Plant Physiology; Gramineae; Leguminosae