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Journal of Chemistry
Volume 2015 (2015), Article ID 274340, 12 pages
http://dx.doi.org/10.1155/2015/274340
Research Article

Evaluation of Heavy Metals Contamination from Environment to Food Matrix by TXRF: The Case of Rice and Rice Husk

Chemistry for Technologies Laboratory, Department of Mechanical and Industrial Engineering, University of Brescia, Via Branze 38, 25123 Brescia, Italy

Received 4 December 2014; Revised 2 March 2015; Accepted 3 March 2015

Academic Editor: Javier Hernandez-Borges

Copyright © 2015 Fabjola Bilo et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

This paper is devoted to the chemical analysis of contaminated soils of India and the rice grown in the same area. Total reflection X-ray fluorescence spectroscopy is a well-established technique for elemental chemical analysis of environmental samples, and it can be a useful tool to assess food safety. Metals uptake in rice crop grown in soils from different areas was studied. In this work soil, rice husk and rice samples were analyzed after complete solubilization of samples by microwave acid digestion. Heavy metals concentration detected in rice samples decreases in the following order: Mn > Zn > Cu > Ni > Pb > Cr. The metal content in rice husk was higher than in rice. This study suggests, for the first time, a possible role of heavy metals filter played by rice husk. The knowledge of metals sequestration capability of rice husk may promote some new management practices for rice cultivation to preserve it from pollution.

1. Introduction

Heavy-metal pollution of soil affects the quality of the environment leading to serious consequences. Heavy metals group includes Ag, Ba, Cd, Co, Cr, Mn, Hg, Mo, Ni, Pb, Cu, Sn, Tl, V, Zn, and some metalloids such as As, Sb, Bi, and Se. Arsenic, for example, is often considered as a heavy metal due to the similarity of its chemical properties and behavior with the other heavy metals. Heavy metals accumulation in soil, and in the environment in general, may be related to the phenomenon of bioaccumulation ability of living organisms, that is, increasing the concentration at human organism due to industrial activities and the food chain. The main sources of heavy-metal pollution in soil are irrigation, especially with sewage; solid-waste disposal, for example, sludge and compost refuse; the use of pesticides and fertilizers; and atmospheric deposition [1].

Plants acquire the necessary nutrients, such as N, P, and K, from the environment. However, they may also accumulate unnecessary and toxic metals, such as Pb and Cd. Several plants have the ability to accumulate high metal concentrations [2]. Many studies have reported data for the transfer of heavy metals from soil to plants and vegetables through roots and shoot [3]. Therefore, toxic metals such as As, Cd, and Pb can be taken up from cereal crops and transferred to their grains [4]. Toxic metals may be classified according to their capability of being transferred from soil to plants in mobile metals, such as Cd, and poorly mobile metals, such as Pb. This property may affect their bioaccumulation in plants [5].

Rice is one of the most important and widespread cereals in the world. It is the staff of life for 3 billion people, mainly in Asia [6], contributing over 70% of the energy and 50% of the protein provided by their daily food intake. In the last report of EU Commission, India was presented as the first country for rice production with 19% of export. India is followed by Cambodia and Thailand. United States and Vietnam are the countries with less amount of imported rice [7]. About 80% of the rice production of Europe takes place in Italy and Spain, with a further 12% in Greece and Portugal.

On this basis the presence of toxic heavy metals in rice, which may raise the metal daily intake, should be strongly avoided in order to prevent negative effects on human health. The following elements are considered macronutrients in rice and their content is usually in some %: P, S, K, Ca, and Mg. Other elements, like Mn, Fe, Cu, Zn, Se, and Ni, are classified as micronutrients and they are present in lower amount, while As, Cr, Pb, and Cd are undesirable elements because of their toxic effects even in very low quantity. As a consequence, it is crucially necessary to reduce possible accumulation effects in rice grains from the environment for safe food production. Great efforts are necessary to remediate polluted sites. Other approaches could be developed to reduce metals accumulation in edible parts of plants. For instance, favorable agronomic practices and chemical regulators may decrease plant heavy metals uptake. In this context it is important to identify which parts of the plant accumulate more toxic substances.

Rice husk (RH) is the external protecting covering of each rice grain. The chemical composition of RH varies from sample to sample depending on rice variety, climate, and origin. Organic compounds and water are the main components of RH (about 74%), followed by amorphous silica (between 15 and 22%) and other inorganic compounds (about 4%) such as Al2O3, Fe2O3, CaO, and MgO [8]. Omatola and Onojah [9] reported the following list of elements detected by X-ray fluorescence (XRF) in RH: K, Ca, Cr, Mn, Fe, Ni, Cu, Zn, Sr, Br, I, As, and Cl. These elements, owing to their low concentrations, are considered as impurities. Sun and Gong reported that the main application of RH [10] is the production of thermal energy, due to its high calorific value, about 13607 kJ/kg. Several other destinations of RH were reported, such as livestock for the cattle, agricultural fertilizer, ingredient for substrates in floriculture and horticulture, and simple fertilizer for plants. RH was also used for the production of biodegradable pots, instead of using oil.

It is also known that the produced byproduct of rice husk is called rice husk ash (RHA). RHA is widely used by the steel industry in the production of high quality flat steel for automotive body panels [11]. Owing to its insulating properties, RHA has been used in the manufacture of refractory bricks, which are exposed to extreme temperatures in furnaces, such as the blast furnaces employed for producing molten iron, and in the production of cement clinker. The Indian Space Research Organization has successfully developed the technology for producing high purity precipitated silica from RHA, which has a potential use in the computer industry [12, 13]. American and Brazilian scientists also developed new ways to extract and purify silicon from RHA to use it in semiconductor manufacture. Other uses have been explored. In the frame of the COSMOS-RICE project, RHA is employed as metals stabilizer for municipal solid waste incineration fly ash treatment [14, 15].

It is very interesting to verify the higher capability of heavy accumulation by RH with respect to rice. This can play a fundamental role in the management of rice cultivation.

Elemental chemical analysis of rice is usually performed by normative techniques such as FAAS [16]. In this study we used total reflection X-ray fluorescence (TXRF) to analyze the chemical composition of rice, RH, and soils of two different areas of India. The aim was the evaluation of metal uptake from soil to rice and the investigation of possible sources of environmental pollution in the studied areas. Moreover this work aims to highlight the possible role of RH in preserving rice from bioaccumulation of heavy metals.

2. Materials and Methods

2.1. Study Areas

Elemental chemical analysis of soils coming from the central-east area of India, where soil contains high concentration of heavy metals, was performed. The state of Chhattisgarh (India) is rich in minerals such as iron, limestone, dolomite, coal, bauxite, garnet, quartz, marble, alexandrite, and diamonds. Because of the huge production of rice, Chhattisgarh district nickname is “rice bowl of Central India.” Industrial activities in this area increased a lot in the last years. In fact, the construction of new coal-fired power plants has increased up to 50% the production of ashes, which exposes the human and the environment to high pollution risks. Therefore, Raipur and Korba were chosen as the target cities of this study. Raipur is located at 21° 13′ 60 N and 81° 37′ 60 E, and hundreds varieties of rice grow. Different studies have already confirmed the presence of heavy metals in soils from this area, demonstrating a degradation of the environmental quality [1719]. Meanwhile, Korba is located at 22° 21′ 0 N and 82° 40′ 60 E and, as well as Raipur, it is also a “victim” of the industrial growth, especially of cement industry. Soil and rice samples from each city region were collected in 5 different areas. Samples in Raipur were collected in duplicate to check the homogeneity of its composition. The two samples, named as A and B in Table 1, were collected in the same area at a distance less than 1 km from each other.
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