Hg, Cu, Pb, Cd, and Zn accumulation in macrophytes growing in tropical wetlands

Abstract

The concentrations of Hg, Cu, Pb, Cd, and Zn accumulated by regional macrophytes were investigated in three tropical wetlands in Colombia. The studied wetlands presented different degrees of metal contamination. Cu and Zn presented the highest concentrations in sediment. Metal accumulation by plants differed among species, sites, and tissues. Metals accumulated in macrophytes were mostly accumulated in root tissues, suggesting an exclusion strategy for metal tolerance. An exception was Hg, which was accumulated mainly in leaves. The ranges of mean metal concentrations were 0.035-0.953 mg g -1 Hg, 6.5-250.3 mg g -1 Cu, 0.059-0.245 mg g -1 Pb, 0.004-0.066 mg g -1 Cd, and 31.8-363.1 mg g -1 Zn in roots and 0.033-0.888 mg g -1 Hg, 2.2-70.7 mg g -1 Cu, 0.005-0.086 mg g -1 Pb, 0.001-0.03 mg g -1 Cd, and 12.6-140.4 mg g -1 Zn in leaves. The scarce correlations registered between metal concentration in sediment and plant tissues indicate that metal concentrations in plants depend on several factors rather than on sediment concentration only. However, when Cu and Zn sediment concentrations increased, these metal concentrations in tissues also increased in Eichhornia crassipes, Ludwigia helminthorriza, and Polygonum punctatum. These species could be proposed as Cu and Zn phytoremediators. Even though macrophytes are important metal accumulators in wetlands, sediment is the main metal compartment due to the fact that its total mass is greater than the corresponding plant biomass in a given area.