Contamination of coastal wetlands with heavy metals: factors affecting uptake of heavy metals by salt marsh plants

Abstract

In this paper, the factors affecting uptake of heavy metals by salt marsh plants from contaminated salt marsh soils are discussed. Three routes of uptake can be distinguished: from the soil through the roots, from the water through the shoots during flooding and from atmospheric deposits through the shoots. The first route is considered most important. In the soil, the mobility and availability of the metals is determined by their chemical speciation. One of the most important factors determining the chemical speciation of the metals in salt marsh soils is the oxidation state of the soil. Due to the oxidative activity of the roots, plants are capable of changing the oxidation state of the soil in the rhizosphere. The resulting increase of the redox potential of the soil may strongly influence the mobility and availability of heavy metals to salt marsh plants. Apart from the chemical speciation of heavy metals in salt marsh soils, other factors, like interactions with micro-organisms, inter- and intra-specific differences in uptake systems of the plants and (micro-)climatic characteristics, may strongly determine uptake of heavy metals by salt marsh plants. It is discussed that in future research these factors should get more attention. The concept of biomonitoring may prove a helpful tool for this purpose.