The use of macrophytes for heavy metal pollution control in urban wetlands

A literature survey has been undertaken to identify the role and function of aquatic macrophytes in the removal of contaminants from polluted surface waters. The survey focussed primarily on heavy metals, however nitrate, phosphate and hydrocarbon removal are also discussed and the application of aquatic macrophytes in wastewater treatment systems is also described. The objectives of the research are: To determine heavy metal variations in water, sediment and plant tissues in both field and greenhouse conditions and to assess the management implications of macrophytes for heavy metal pollution control in urban wetlands. The sampling sites and the methods selected for the determination of heavy metal levels in water column, sediment and plant tissues are also discussed. Heavy metal (Cu, Pb, Zn and Cd) uptake rates and the maximum storage capabilities by sediment and plant have been investigated in controlled greenhouse-based phytoassay experiments. Typha latifolia heavy metal uptake ability is in the order of Cd>Cu>Zn>Pb. Temporal variations of Cu, Pb, Zn and Cd in urban stormwater runoff, sediment and Typha latifolia tissues at the selected field sites have also been investigated. An increase in sediment and Typha tissue levels is observed from rural to urban sites. Field samples from all sites show a progressive decrease in metal levels from sediment to root to rhizome to leaf. All metals show temporal variability in Typha tissues. Typha latifolia biomass and plant metal distributions have also been investigated. The rhizome of Typha can store 54 - 61 % and the leaves 32 - 40 % of the total meta s found accumulated in the plant. An annual crop of leaf biomass can remove up to Cu 525, Pb 415, Zn 680 and Cd 59 g/ha. Leaf harvesting could provide a useful method of heavy metal removal from recently constructed wetlands