Phytoremediation of Cadmium-contaminated agricultural land using indigenous plants
Abstract
The content of the heavy metal cadmium (Cd) which is excessive in the soil could affects on the soil and plants health. The aim of this descriptive study was to investigate the ability of selected indigenous plants in stabilizing Cd. The study was conducted at an agricultural production center in Batu City, East Java, Indonesia. There were two stages of this study, namely: (1) analysis of nutrient and heavy metal contamination, and (2) phytoremediation experiment by using five types of indigenous plants. The experiment was arranged in completely randomized design (CRD) with three replications. Once the plants were harvested, the plant materials then were analyzed the heavy metal content remaining in the soil and absorbed by the plants. The heavy metal content analysis used AAS (Atomic Absorption Spectrometry). Subsequently, the analysis result data were calculated for the bio-concentration factor (BCF) and heavy metal reduction. The initial content of heavy metal Cd in the soil prior phytoremediation had passed the threshold value (2.26 mg kg-1). The five indigenous plants tested on the contaminated soil showed a good growth pattern, especially in the fourth week after planting. The average ability of this selected plant to reduce heavy metals Cd was up to 71.2%. The reductions of heavy metals Cd obtained by each plant were Vetiveria zizanioides (71.2%), Eleusine indica, L. (58.9%), Ageratum conyzoides L. (52.2%), Euphorbia hirta (51.8%) and Chromolaena odorata (22.1%).
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Introduction
Cadmium (Cd) pollution in the soil environment has been rapidly increasing in recent years, as a result of the use of agrochemicals such as fertilizers and herbicide. Phosphatic fertilizers are widely regarded as being the major sources of Cd contamination to the agricultural soil (Gray et al., 1999). Phosphate fertilizer contains a relatively high amount of Cd (up to 500 mg kg-1 ) as a trace element from its manufacturing process (Loganathan et al., 2003). Hence, the intensive usage of phosphate fertilizer could result in the high Cd contamination in the soil (Tijani et al., 2008; Zeng et al., 2007). The use of organic fertilizer, such as farmyard manure also considered as the source of Cd contamination to the soil. Alloway (1995) reported that farmyard manure typically contains 0.3 - 1.8 mg kg-1 of Cd. Large annual application of farmyard manure (35 Mg of fresh manure ha-1 ) were significant as Cd source to contaminate the soils (Alloway, 1995).
The intensification of agricultural activities in the city of Batu – Indonesia has led to the high usage of agrochemical products to increase the plant yields. However, the extensive usage of agrochemical is likely to pollute the soil by trace elements, and heavy metals originated from the agrochemical (Alloway, 1995). The usage of pesticides and phosphate fertilizers is a common agricultural method by farmers in the city of Batu. Recent soil analysis from the initial study of this experiment in Batu showed that the soil Cd concentration has passed the threshold value of 2.26 mg kg-1 . The high concentration of Cd in soils not only toxic to plants but also could generate secondary problems of acidifying the soil (Loganathan, 2003).
Looking at the potential soil contamination of Cd, it is important that farmers are starting to apply the appropriate soil remediation techniques to minimize the damage to plant and soil. One of the proposed soil remediation techniques is phytoremediation of Cd by using the indigenous hyperaccumulator plants. The phytoremediation technique by using indigenous hyperaccumulator plants is considered as the most inexpensive technology, compared to the other physical or chemical soil remediation techniques (McMohan, 2000). The indigenous hyperaccumulator plants could reduce the migration of Cd through the soil medium, also known as the phytostabilisation mechanism (Ogundiran and Osibanjo, 2008; Robinson et al., 2009). A study by Hamzah et al. (2012) also reported the potential of using indigenous hyperaccumulator plants to stabilize heavy metals and remediate contaminated soil to be used as agricultural soil again. The objective of this study is to describe the potential ability of selected indigenous plants in stabilizing Cd from contaminated agricultural soils in the city of Batu - Indonesia.
Conclusion
Soil in the research site of Bumiaji Vilage of Batu regency, Indonesia had a low fertility levels and the soil available Cd was higher than the permitted concentration for agriculture. Three indigenous plant (Eleusine indica L., Ageratum conyzoides, L and Euphorbia hirta, L.) have been tested for the ability in stabilizing Cd from the contaminated agricultural soil. Eleusine indica L. has shown the ability of accumulating Cd in its roots, while both of Ageratum conyzoides, L and Euphorbia hirta, L. accumulate Cd in its stalks and leaves. Of the three indigenous plants tested in this experiment, Eleusine indica L. was the most tolerant plants against Cd contamination, and also proven to be the suitable plants in reducing soil available Cd.
