Utilization of Plant Refuses as Component of Heavy Metal Ion Sensors in Water Samples

Waste materials like fruit and vegetable refuses were utilized as component of sensors capable of detecting heavy metals like lead ions and mercury ions by electrochemical method. The ability of the fabricated sensors to detect the presence of heavy metals was analyzed using electrochemical methods like cyclic voltammetry and differential pulse anodic stripping voltammetry. Results showed that the fabricated electrode were able to detect the presence of mercury and lead ions in aqueous solutions. @JASEM Several heavy metals coming mostly from mining wastes and industrial discharges have been found to contaminate our natural waters (Schalcsha et al., 1998). Both the chemically combined forms as well as the elemental form of these metals are toxic (Manahan, 1993). Acute lead, mercury, cadmium, chromium, and copper poisoning in humans causes severe dysfunction in the renal, reproductive, and nervous systems (Berman, 1980). In addition, chronic exposure to these contaminants present even at low concentrations in the environment can prove to be harmful to the human health (Wyatt et al., 1998). There are several methods used to detect these metals, of which atomic absorption spectrometry (AAS) is the most popular. However, the cost of analysis, the unavailability of equipment, maintenance, sample pre-treatment and large concentrations of solutions limit their application. An alternative method for the detection of these metals is the use of chemically modified carbon paste electrodes (CMCPE). The CMCPE are a class of metal sensors which are relatively easy to prepare and gives a stable response. The concept of chemically modified carbon paste electrodes was a product out of the desire to manipulate the chemical nature of the electrode surface by incorporating a modifying agent. Through this, the electrode assumes the desirable properties of the modifier in binding metals wherein enhanced selectivity, sensitivity and over-all stability is achieved. Fruits and vegetable refuse (part of plants which have no economic use) like peelings from banana, apple and potato and cabbage and kangkong stems are waste materials which are readily available and of no use except as source of organic matter when left to decay in soil. Plant parts which are of no economical use also contain the materials responsible for the binding of heavy metals. Previous studies have proved that plants are capable of binding heavy metals (Velasco-Alinsug et al 2005; Yang et al 2005). The discovery of metal hyper-accumulating properties in certain plants made way for the potential of using plant based system for treatment of wastes containing metals (Ensley, 2000). It has been shown that some plant species have the ability to accumulate elevated amounts of toxic heavy metals (Blaylock and Huang, 2000; Reeves and Baker, 2000). Some varieties of Thlaspi and ecotypes of Silene vulgaris have been found to accumulate cadmium (Ernst et al., 2000; Brown et al., 1994). Larrea tridentata, a desert inhabitant shrub (creosote bush) accumulates copper (Gardea-Torredey 2001) and species of alfalfa plants (Medicago sativa L.) and Euryale ferox Salisb. accumulates cadmium, chromium, and copper (Rai et al., 2002; Peralta et al., 2001; Peralta-Videa et al., 2002). The use of plant refuses as modifiers in CMCPE is due to the fact that they possess an electrochemically or chemically active moiety. These moieties could be any of the following: redox or ligand sites, ionexchange sites, enzyme active sites; all of which possesses certain functionalities or donor groups. Pineapple peelings were successfully used as a modifier of a voltammetric sensor for lead ions (Mojica et al 2006). The purpose of this study is to utilize plant waste materials as components of metal sensors. Sensors were fabricated utilizing these waste materials and their performances were characterized by electrochemical method in terms of cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV). MATERIALS AND METHODS Different waste products from various sources were collected. Waste materials such as peelings from, apple (Malus domestica), banana (Musa sapientum L.) and potato (Solanum tuberosum) and stems from cabbage (Brassica oleracea L. var capitata) and kangkong (Ipomoea aquatica Forsk) were sliced into small sizes and freeze dried. Powdered forms of these waste materials were collected and kept on freezer. Each product from waste material was then thoroughly mixed with graphite powder and mineral oil. A 100 mg mixture of graphite (Sigma) powder and the different modifiers were mixed with Utilization of Plant Refuses as Component... ELMER-RICO E. MOJICA; JOSE RENE L. MICOR 70 approximately 20 uL of Nujol oil to form a paste. A portion of the paste was packed into the end of hard plastic tube where a copper rod was inserted to establish electrical contact (Figure 1). The fabricated electrodes were then used as the working electrode. Fig 1. A diagram of modified carbon paste electrode. This modified electrode contains carbon powder, mineral oil and modifiers from plant