Influence of Typha domingensis in the accumulation and speciation of high concentrations of Cr, Ni and Zn in the sediment of a constructed wetland.

DI LUCA, G. A.; MUFARREGE, M. M.; HADAD H. R.; MAINE, M. A.

Praga

Simposio; Joint Meeting of Society of Wetland Scientists, Wetpol and Wetland Biogeochemistry Symposium; 2011

Joint Meeting of Society of Wetland Scientists, Wetpol and Wetland Biogeochemistry

A free water surface wetland was built to treat wastewater containing metals (Cr, Ni, Zn) and nutrients from a tool factory in Argentina. Emergent and floating, locally abundant, macrophyte species were transplanted into the wetland at the beginning of the operation period, in 2003, but only Typha domingensis persisted. Although, it is widely recognized that contaminants accumulated mainly in sediment, there were opposite views about the macrophyte role in metal dynamics in these aquatic systems and the distribution of them in sediment. A greenhouse experiment was conducted in order to determine whether the presence of T. domingensis affects the accumulation and speciation of Cr, Ni and Zn in sediments of an aquatic system. Twenty plastic aquaria of 10 L capacity were used, in which were placed 4 kg of sediment and 2 rhizomes of T. domingensis. Twenty aquaria without plants were arranged. 5 L of solution 100 mg l-1 Cr + 100 mg l-1 Ni + 100 mg l-1 Zn was added. Two vegetated and two no vegetated aquaria were sampled periodically during 90 days. All the water, the total plant biomass and sediment were collected and the aquaria were discarded. In each sample, concentrations of metals in water, in plant tissues (leaves, roots and rhizomes) and in the sediment profile (0-3 cm, 3-7 cm and 7-10 cm), pH, redox potential, relative growth rates and chlorophyll concentration were measured. The fractionation of metals in the surface layer (0-3cm) (Tessier et al., 1979) was performed. The three metals were efficiently removed from the water. The pH was significantly higher and the redox potential was significantly lower in non-vegetated aquaria, compared to aquaria with vegetation. The sediment with plants accumulated significantly higher concentration of the three studied metals. The accumulation of metals was significantly higher in the superficial sediment (0-3 cm). In both treatments, Cr was mainly accumulated in the fraction bound to organic matter, Ni in the fraction of Fe-Mn oxides and Zn in Fe-Mn oxides and carbonates with no significant difference between both fractions. Leaves accumulated high metal concentrations in some samples exceeding those of roots. The chlorophyll concentrations decreased in all samples, except at 14 and 21 days, which coincided with an increase in metal concentration in leaves. Despite relative growth rates were positive; they were significantly lower than in the control. It can be concluded that in the case of an accidental dumping of high concentrations of Cr, Ni and Zn in constructed wetlands vegetated with T. domingensis, this species will survive and will enhance the accumulation but will not affect the speciation of these metals in the sediment