In-situ Phytoremediation of Arsenic from Contaminated Soil

Abstract

IntroductionSoil pollution is a major environmental problem faced by human and as such a great threat to human and environment. Previously, cases of rice Arsenic were reported in Asia. It has become a global concern like other environmental pollution issues, with implications ranges from effects to the ecosystems, ecology, human health etc. Due to the presence of heavy metals, other inorganic and organic contaminants heavy metal and its contamination in soil environment are usually related to human activities such as industrialization, applications of fertilizers and pesticides on farm land, generation of energy and production of fuels, mining and metallurgical processes and waste disposal which causes toxicity to all living organisms [1]. In China, it is estimated that more than 20 million hectares of land or soil environments have been contaminated, accounting for about 20% of the total land. Some of the major heavy metals that causes soil contamination and subsequent environmental pollution includes As, Cd, Cr, Cu, Co, Hg, Mn, Ni, Pb and Zn. Generally, heavy metal pollution is a combination of these several heavy metals [2]. Arsenic is a naturally occurring element widely distributed in the earth's crust. Arsenic is very toxic when found in large quantities in drinking water and food sources. In some part of India and Bangladesh, it is found that arsenic contaminates the groundwater supply. Arsenic is widely distributed in the biosphere. It occurs in sea water at a level of 2 μ/ kg [3]. The use of arsenic containing pesticides in the past has left large areas of agricultural land contaminated [4]. The use of arsenic in the preservation of timber has also led to contamination of the environment. Arsenic and its compounds are naturally present in low concentration at places with high geothermal activities [5].Phytoremediation can be defined as the removal of a substance from the air, soil or water via the natural ability of plants to take up metals as nutrients. Some of them are essential mineral nutrients needed for the growth and development such as Cu, Co, Fe, Mn and Zn whereas other heavy metals, like the Cd, As and Pb, have no physiological benefits. On the other hand, this natural potential of plants is a problem for human health when these elements are found in higher amount in food crops. Base on this findings, many researchers have taken to phytoremediation method. Phytoremediation includes several subsets such as phytoextraction, phytoming, phytostabilization, rhizofiltration and phytovolatilization.When plants are referred to as hyper accumulator, there must accumulate at least 100 mg/kg (0.01% dry weight) of As, Cd, in their root and particularly be able to translocate them to their shoots. Hyper accumulating plants include Pteris ferns, Pityrogramma calomelanos, Lemna gibba (duckweed), Lepidium sativum (watercress), Lupinus albus (white lupin), mustard plants [6]. Biomass producing plants are studied following the approach of assisted phytoremediation, in which plants have to be managed with practi...