Introduction
Many countries across the world are faced with the problem of water and soil contamination. The contaminations are caused by industrial effluents, military actions and agricultural activities among others. Human carelessness and ignorance also contribute significantly to water contamination. As a result, new biological, chemical and natural activities have been invented in order to control water contamination. One of the most successful measures used in control of water contamination is phytoremediation. It involves the use of plants to absorb pollutants from contaminated water found on the surface of the land and in the soil. This paper discusses the biological process that aids in the process of phytoremediation.
Discussion
Phytoremediation removes, destroys and stabilizes the contaminants in the soil or stagnant water. Many biological processes and mechanisms are involved in phytoremediation. These mechanisms are basically used to facilitate the uptake of pollutants by plants from the soil water making it clean and fresh (Wang, Li, Okazaki & Sugisaki 114). The mechanisms include biodegradation enhancement phytoremediation, phyto-degradation and phytostabalisation.
Usually, plants depend on microorganisms in the soil to enhance the nitrogen fixation process. Microorganisms mutually benefit from natural substances released by the plant to the soil to facilitate the internal biological activities. The underground microorganisms then die and live behind loosened soil that permits aeration and leaves a path for upward movement of soil water close to root hairs of the plants (Palmer 24). This process of phytoremediation is called rhizosphere biodegradation.
Secondly, phytostabalisation is also process of phytoremediation. It involves the concentration of pollutants released by plants and microorganisms close to the root hairs and makes them immobile. The pollutants do not move nor degrade but rather remain static around the roots of the plants. On the other hand, phytoaccumulation is the process by which the plants roots absorbs contaminants from the soil together with water and other dissolved substances and transport them to the shoots and the leaves. The contaminants consisting of metal elements such as cadmium, nickel, zinc, arsenic and copper are stored in the plants aerial shoots where they are collected for recycling and proper disposal (Marchiol, Fellet , Perosa & Zerbi 382).
Phytoremediation is the process in which the plants destroys the absorbed contaminants through metabolism and incorporate them into the body tissues. The plants tissues develop counter contaminants activities that ensure the conversion of contaminated materials in food products used in the plants body system (Larson, Sims & Marley 219). Contaminants are removed from some products through internal plant processes and transported to the storage organs of the plants. Additionally, they can absorb contaminated substances from the soil, incorporate them into the transport system and release the contaminants from the leaves into the air. The process that entails release of contaminated substances from the plants leaves into the air is referred to as phytovolatilisation (Wang, Li, Okazaki & Sugisaki 221).
Phytoextraction is a biological process of phytoremediatiom that involves the removal of soil contaminants and water pollutants by plants’ roots. Heavy metal substances are absorbed by the plants root hairs transported to the stem and finally to the leaves (Palmer 24). Ideally, the plants that are involved in this process take large amount of metal nutrients than required and accumulate them in the leaves and other storage organs in a way that they can be harvested. The plants that take in excess salt from the soil are called hyperaccumulators. Algae also play important role in phytoextraction process. The algae species can take large quantity of metallic substances found in water. They survive well on stagnant water and can comparatively take larger quantity of pollutants. The idea of plant absorption of metal substances from the soil is applied in phytomining (Wang, Li, Okazaki & Sugisaki 215). This is whereby the plants absorb metallic substances from the soil and store them in the root biomass. The plants are harvested and minerals substances extracted from them.
The biological phytoextraction process is categorized into two versions namely; the induced or assisted hyperaccumulation and natural hyperaccumulation. Induced hyperaccumulation is whereby an agent that increases the solubility of the metals is added in the soil. In most cases, a chelator is added to the soil. It increases the solubility and mobilization of minerals thus making the plants to absorb them easily (Wang, Li, Okazaki & Sugisaki 221). On the other hand, natural hyperaccumulation involves the absorption of minerals from the soil without the stimulation by any agent.
Another important mechanism in phytoremediation process is phytotransformation. The transformation of toxic substances to nontoxic substances through body metabolism is crucial in elimination of contaminants from the soil (Larson, Sims & Marley 220). Pollutants such as pesticides, explosives, solvents and industrial chemicals are eliminated from the soil through plants metabolism. In addition, microorganisms significantly contribute to elimination of pollutants from underground water. Ideally, they metabolize harmful substances into the soil water (Marchiol et al. 382). The complex substances such as recalcitrant compounds that do not break down by plant molecules go under the process of phytotransformation. Basically, the chemical structure of the molecules is changed without undergoing complete breakdown. This process is also called green liver.
The phytotransformation in plants basically consists of the three phases. In phase one, the plants uptake the xenobiotic compounds and after that, the polarity of the xenobiotic substances increases by addition of hydroxyl ions (Marchiol et al. 385). The second stage, also referred to phase two metabolisms, is characterized by addition of biomolecules substances such as amino acids and glucose to polarized xenobiotic substances. This results into increase in polarity and reduction in the toxicity concentration of the compounds thus increasing the rate of transportation of xenobiotic substances along the aqueous channels. The final stage is the phase III metabolism. The sequestration of the xenobiotic substances occurs in plants. The xenobiotic polymerized to form lignin-like structures that are sequestered in the plant. As a result, the possible harmful effects to plants functioning organs is reduced to zero (Larson, Sims & Marley 219). However, research has revealed that the plants containing polymerized xenobiotic substances may be harmful to the body.
Finally, the plants assist in controlling the movement of groundwater. The roots of the trees penetrates down the soil to the water table and form a network of roots hairs that take large quantity of water from the soil, a process known as hydraulic control. After the water surrounding the roots is absorbed, contaminants at the same time get into the plants and can as well remains stagnant not able to sessile (Wang, Li, Okazaki & Sugisaki 223).
Conclusion
In conclusion, the phytoremediation biological processes result to adequate control of contamination of water. These processes ensure that contaminants in water are eliminated through various methods. These include the release of the contaminants into air, incorporation in the body metabolism, concentration around the roots hairs and through soil loosening thus permitting aeration and upward movement of soil water. In addition, phytotransformation and phytoextraction contribute significantly in the elimination of contaminants. The water in the environment is made safe through simple absorption by plants.
Works cited
Amy Donovan Palmer. “Phytoremediation of Leeds in Residential Soils in Dorchester, MA.” Boston Public Health Commission (2002).
Marchiol L, Fellet G, Perosa D, Zerbi G. Removal of metals by sorghum bicolor and Helianthus annuus in a site polluted by industrial wastes: A field experience, Plant Physiology and Biochemistry (2007): 379-387.
Rupassara S I, Larson R A, Sims G. K. & Marley K. A. “Degradation of Atrazine by Hornwort in Aquatic Systems.” Bioremediation Journal (2002): 217-224.
X.J. Wang, F. Y. Li, M. Okazaki & M. Sugisaki, Phytoremediation of Contaminated Soil; Annual Report CESS (2003): vol.3 pp. 114-123.
