Plant-Microbe Interactions Influencing Removal of Heavy Metals and Polycyclic Aromatic Hydrocarbons (PAHs) in Constructed Wetlands (pp. 151-165)
Authors: (He Chang, Zhenhua Zhang, Zed Rengel, Kathy Meney, School of Earth and Environment, The University of Western Australia, Australia, and others)
Abstract: Contamination with heavy metals and organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) is a serious issue all over the world. Frequently, metals and PAHs co-occur in the contaminated sites. The presence of co-contamination in waters and soils may have an exacerbated effect on biota. Phytoremediation is an environmental technology, in which plants are used for decontamination of soils and waters from organic and inorganic pollutants. In addition, rhizoremediation refers to interactions among plants, microbes and pollutants near the roots (i.e. in the rhizosphere). Root exudation of organic and inorganic compounds can influence microbes by either favouring or suppressing certain taxonomic groups, and the root systems themselves may facilitate microbial spread in the soil volume. The presence of microbes that can degrade pollutants can increase plant growth and nutrient uptake as well as improve pathogen resistance, thereby enhancing phytoremediation. Constructed wetlands have been used in treating wastewater and contaminated lands, including the removal of PAHs and heavy metals. The microbes are mostly responsible for the biodegradation of PAHs, whereas the wetland plants can stabilize and/or remove metals in/from the systems. The interaction between metals and PAHs can be independent, synergistic or antagonistic. The microbial community shift due to the presence of PAHs as well as PAH-stimulated root exudates may influence toxicity of heavy metals to wetland plants. The chemical forms of heavy metals may be modified by the presence of certain groups of bacteria. Microbes may also interact with roots and increase plants tolerance to pollutants. Other factors such as pH,
redox status and organic matter in the media (water/soil/sediment) may also contribute to the complicated interactions between heavy metals and organic pollutants. The mechanisms underlying the plant-microbe interactions regarding removal or detoxification of heavy metals such as Cd and PAHs in constructed wetlands are not fully understood. Future studies aimed at elucidating these mechanisms may result in improved rhizoremediation of combined pollutants in constructed wetlands.