Phyto-evaluation of Cd-Pb Using Tropical Plants in Soil-Leachate Conditions

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Leachate from landfills is produced as a by-product of the infiltration of precipitation and the continuous process of biochemical breakdown that often take place during the course of natural disintegration and degradation of waste materials underneath soil covers. The discharge of leachate consists of a myriad composition of organic compounds, inorganic ions, and heavy metals that are potentially detrimental to the environment.1,2 Heavy metals such as zinc (Zn), copper (Cu), iron (Fe), and nickel (Ni) are commonly referred to as trace metals and are essentially required by all living organisms in low concentrations for growth and development. However, other heavy metals such as lead (Pb), cadmium (Cd), mercury (Hg), and chromium (Cr) are nonessential metals that are not required for the growth of living organisms and are toxic at a certain concentration.3 Generally, the heavy metals found in a landfill leachate consist of Cd, Cu, Cr, Pb, Ni, and Zn.4 Among these metals, Cd and Pb are highly hazardous, even at a very low level of concentration compared with other heavy metals. Naturally occurring Cd and Pb in soils are often undetectable and extremely poisonous. Both Cd and Pb cannot be degraded or destroyed in the biological environment and are persistent in soils for a long period of time.5,6 Moreover, both metals can be easily bioaccumulated from one organism to another via the food chain. Furthermore, due to its harmful characteristics, both Cd and Pb are categorized among the 126 chemical pollutants of the Toxic and Priority Pollutants.7 The use of various tropical plants for heavy metal phytoremediation has been expansively studied over the years.8-13 Recent reports by previous works14-16 have revealed the phytoextraction properties of Cd and Pb in a few selected tropical plant species growing under conventional contaminated soil-based culture. However, all these studies were limited regarding the phytoassessment findings using different tropical plants growing under soil-leachate culture conditions. As a result, this article reports the use of landfill leachate (treated leachate) as the source of polluted material to (1) assess its effects on plant growth performance, (2) evaluate Cd and Pb accumulation and its tolerance level, and (3) determine the viability and phytoremediation potential of 3 different tropical plants growing under the soil-leachate conditions. The 3 tropical plants, arbitrarily selected in this study, based on their fundamental fast growing, nonsusceptibility to pest resistance and minimal maintenance characteristics were Acacia, Mucuna, and Vetiver.

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