Investigation on Phytoremediation Capability of Artiplex (Atriplex sp.) and Oleander (Nerium oleander) in Aradkooh Landfill for Cadmium and Lead

Intruduction:

Increasing industrial activities with the production of pollutants, including heavy metals, is one of the serious problems of modern communities, which has led to their accumulation in the environment. Heavy metals are also one of the important pollutants in landfill leachate. Plants and soil near the landfill may be contaminated by the leachate. Landfilling is the oldest method of solid waste disposal which can be a threat to the environment and health. Due to its easy operation and cost-effective, landfill is the most widely used method of municipal solid waste disposal in the world. Pollution cleaning technologies to reduce the harmful effects in the locations contaminated with heavy metals can be done by physical, chemical and biological methods. Phytoremediation, as a biological method, uses the green plants to extract, sequester, and detoxify pollutants. This method is a low-cost technique, environmentally friendly, and due to the non-production of by-products, is non-destructive for natural ecosystems. Considering the high moisture of wastes in Iran and their potential to produce leachate, as well as the possibility of contamination of water and soil in the landfill, especially with heavy metals, this study was conducted with the aim of evaluating the accumulation of lead (Pb) and cadmium (Cd) heavy metals in the soil, shoots and roots of artiplex (Atriplex sp.) and oleander (Nerium olander) plants in Aradkooh landfill of Tehran.

This study was conducted in Aradkooh landfill which is located in the south of Tehran in the Kahrizak region. About 5200 tons of municipal solid waste were sent to this landfill every day. A part of the solid waste in Aradkoh was placed in various processes to energy and compost, and about 2500 tons of the solid waste was landfilled. According to previous reports, it is estimated that 250 cubic meters of leachate are produced daily in the Aradkoh landfill. In the studied landfill, there is an atriplex plant in four areas and a hand-planted oleander in one area. Ten samples of soil, root, and shoot, totaling 120 total were randomly selected from each growing area of the atriplex plant. Oleander shoots and soil were also tested from 10 different plants for a total of 40 samples. Then the levels of Cd and Pb in the soil, roots, and shoots were assessed. In this study, the outcomes were analyzed employing four key indices: the bioconcentration factor (BCF), the translocation factor (TF), the pollution index (PI), and PINemerow. The BCF and TF indices were employed to assess the phytoextraction and phytostabilization capabilities of plants, while the PI and PINemerow methods were used to pinpoint the most environmentally hazardous heavy metal in the soil.

 According to the results, the concentration of Pb and Cd in  shoots of atriplex  area 2 (with an average of 19.7 and 5.75 mg/kg, respectively) were significantly higher than in other areas, while the concentration of these metals in root of oleander (with an average of 8.17 and 1.06 for Pb and Cd, respectively) were higher than the shoot. The amount of Pb element in soil of the oleander plant (with an average of 35.13 mg/kg) and Cd in soil of the atriplex area 2 (with an average of 3.78 mg/kg) were significantly higher than other areas. Additionally, the levels of heavy metals in the soil of two plants were higher than the Nemerow index, which indicated high levels of pollution in the sampling areas, but still below the safe levels that was set by national standards (3.9 and 300 mg/kg for Cd and Pb respectively) and the World Health Organization (5 and 40 mg/kg for Cd and Pb, respectively). In addition, bioaccumulation factor of shoot in all growth atriplex areas for Pb and Cd (with an average of 1.44 and 1.3, respectively) were higher than 1.0 while, the root bioaccumulation factors of this plant in any of the growth areas, were not higher than 1.0. In the case of oleander, the shoot and root bioconcentration factors  for Pb and Cd were not reported more than one.

In general, it appears that atriplex, a native plant in the Aradkooh landfill, exhibits superior capabilities for absorbing heavy elements compared to oleander. Therefore, atriplex seems well-suited for the extraction of Pb and Cd from the soil, as it can accumulate these metals in its shoots. In contrast, oleander is not well-suited for phytostabilization or phytoextraction of these elements, as it exhibits limited ability to accumulate these heavy metals in its roots and shoots. Consequently, atriplex can be a valuable choice as a resilient species for phytoremediation projects in landfills and areas near mines. It is worth noting that the Pb content in the soil is higher than that of Cd. Although both metals fall within the permissible limits of national and WHO standards, the soil in the Aradkooh landfill is considered to be significantly polluted based on the Nemerow index.