John Hollerung Term Paper Phytoremediation: A General Overview John Hollerung Abstract Phytoremediation is the use of specific species of plants for the remediation of site contaminants. Attention has been drawn to this idea with the indication of cost savings when compared to conventional treatment technologies. This overview is designed to supply an analysis of the technology of phytoremediation today by providing an understanding of the basic concepts in the use of plants for treatment of soils and waters: degradation, extraction, and containment. Along with these three pillars of phytoremediation are experimental limitations preventing successful remediation. Examples of all three types of phytoremediation are explored and one case study is shown. By comparing documation, it was resolved that phytoremediation is still in its infancy and that more laboratory and field studies are needed before industrial application can begin to take hold. Understanding of the subject has increased exponentially since the incept of the idea, and new tools in the analysis of biochemistry and chemical mechanisms are achieving an unprecedented look into the mechanisms occurring within plants and the possibilities they hold for contaminant control. Keywords Phytoremediation, Phytoextraction, Phytodegredation, Phytostabalization, Chelating agent, Hyperaccumulate, Rhizodegredation, Phytotoxic, evapotranspirate Introduction to Phytoremediation Plants have long been adapting to survive in a variety of stressful environments. This uncanny ability to live in areas of high salinity, extreme heat, drought, or freezing temperatures, exemplifies the tolerance various plant species can have. Phytoremediation is a term coined in 1991 (EPA, 2000). Basic information came from previous research in constructed wetlands, oil spills, and heavy metal accumulation. Research methods can be categorized into to areas: exploration of mechanisms and evaluation of claims. Laboratory experiments are primarily used to understand observations in the field and to gain knowledge on the biochemistry occurring. With recent advancements in genetic modification, scientists have been able to create plants for specific environmental uses. Plants can be enhanced with qualities that allow them to be used in the effort to relieve environmental stresses and assist in the restoration of polluted soils. There are four characteristics preferred in a plant for phytoremediation techniques. The first is that the plant should be able to accumulate the pollutants to be extracted. Second, the plantsshould have enough tolerance to be able to not only survive in polluted soils, but to carry pollutants within their shoots. Third, the species should be fast growing with an amplified ability to accumulate toxins. Lastly, the plant should be easily harvestable for simple disposal (Kärenlampi et al., 2000). The three general techniques used in phytoremediation are degradation, extraction, and stabalization. These methods, used in conjunction with recent advancements in biochemistry, are improving the appeal and overall ability of phytoremediation to treat current issues. Experimental Factors Climate/Soil. Climate plays a significant role when it comes to phytoremediation. Although there are over 400 species of plants known to date which could be used for site cleanup, only a small fraction would be able to survive in the temperate zone of the specific region needing remediation. Not only would the plant have to be compatible with local weather and seasonal patterns, but also be able to adapt to the local ground soil composition. This includes porosity, pH, and moisture content among others. Most research focus has been on the ability for a plant to hyperaccumulate contaminants under specific and constant surroundings. Experimentally this allows for an accurate analysis of the plants peak capability, but if used in the field, results would tend to vary, but by how much? Yu (et al., 2005) performed an experiment to attempt to quantify the effect temperature has on phytoremediation efforts. Using fresh leaf samples from a weeping willow (Salix babylonica) and Chinese elder (Sambucus chinensis), Yu and his colleagues placed the leaves in containers with 0.95 g/L potassium cyanide solution for up to twenty eight hours using temperatures from 11ºC to 32ºC and monitored the disappearance of cyanide (CN) (Yu et al., 2005). The graph in Figure 1 shows the individual plant results. It is clear from this that increasing the temperature also increased the overall metabolism of CN. Figure 1: The rate of CN disappearance vp (mg kg−1 h−1) of Chinese elder and weeping willow leaves as a function of temperature (Yu et al., 2005). Although this experiment showed higher conversion associated with higher temperatures, other phytoremediation efforts may differ. The toxin CN is metabolized in vascular plants which possess the enzymes necessary to convert CN into asparagine by a reaction that obeys the Michaelis-Menten enzymatic kinetics. Under more complex reactions with various intermediates and larger contaminant compounds, the relationships become harder to generalize and model (Sung et al., 2001).Root depth. A limiting factor in the containment, degradation, or extraction of pollutants is root depth. Since the actual processes can only take place within a specified distance from the root structure, it is important to consider the extent of the pollution in choosing which species of plants to use. Soil carries the complexity of different contaminant concentrations and environmental properties at various depths (Sung et al., 2001). The plant chosen for the project has to be able to reach and tolerate the chemical in its various concentrations throughout the soil. Contaminant uptake/growth factor. Another aspect of phytoremediation is the ability for the plant to grow and take in contaminants. The speed at which a plant is able to develop new leaves and roots is directly related to the amount of contaminants that a plant is able to metabolize within a specific time period. Therefore, quick growth is a desirable characteristic if a plant is to be used for phytoremediation. In fact, a plant with accelerated growth is more desirable even if it may metabolize contaminants at a slower rate than a plant that could metabolize more but grew slower because the ability to harvest on a more frequent basis and