Heavy Metal Content in Paddy Soils of Ketara ... - Semantic Scholar

World Applied Sciences Journal 19 (2): 183-191, 2012 ISSN 1818-4952; © IDOSI Publications, 2012 DOI: 10.5829/idosi.wasj.2012.19.02.3687

Heavy Metal Content in Paddy Soils of Ketara, Besut, Terengganu, Malaysia J. Khairiah, M.S.M. Tharmendren, J. Habibah, H. Zulkefly, W.I. Wan Kamal and B.S. Ismail School of Environmental and Natural Resource Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia Abstract: A study to determine the heavy metal content in paddy soils was carried out at KETARA, Besut, Terengganu, Malaysia. The objective of the study was to determine the heavy metal content of the soil types in the study area. The heavy metals studied were Pb, Cd, Cu, Zn, Fe, Mn and Cr. Heavy metals in the soil were extracted using the sequential extraction method, which consists of four fractions namely the easily leachable and ion exchange (EFLE), acid reducible (AR), oxidizable organic (OO) and resistant (RR). Heavy metals were detected using an inductively coupled plasma mass spectrometer (ICP-MS). The study showed that the highest concentration of heavy metals was found in the resistant fraction (RR) for all the studied soils. Fe was the most dominant metal whereas Cd had the lowest concentration for all studied soil types. With the exception of Fe and Mn, the soils were naturally low in the respective heavy metals (Zn, Cu, Cr, Pb, Cd). The high amount of soil Fe and Mn in the studied soils could be attributed to the occurrence of Fe-Mn hydrous-oxide mottles. Meanwhile, the higher levels of Mn in the ELFE and AR fractions suggest that the continuous usage of agrochemical materials for paddy cultivation activities, rendered high bioavailable Mn in the soils. The elevated levels of Pb and Cd in the soils could possibly be attributed to anthropogenic sources. Key words: Heavy metal

Paddy

Soil

INTRODUCTION

showed an increase in the levels of Cd, Cu, Pb and Zn in the paddy and forest soil at the vicinity of the tailings (by surface erosion). Metals from both natural and pollutant sources have the potential to be assimilated by the plant through foliar or root absorption processes [3]. The heavy metals in the plant or crop may enter the food chain and later pose a risk to human health. Heavy metals which are easily taken up by plants occur in the available form in the soil. But not all metals in the soil are in the available form and some are strongly bound to various components in the soil. The bioavailability of elements in the soil to plants is controlled by many factors associated with soil and climatic conditions, plant genotype and agronomic management including: active/passive transfer processes, sequestrian and speciation, redox state, the type of plant root system and the response of plants to elements in relation to seasonal cycles [4]. Most metals that are available to plants come mainly from anthropogenic sources. The objective of this study was to determine the

Paddy is one of the most important economic crops grown in Malaysia. In order to increase the crop yield, various types of fertilizers have been used. Furthermore many types of herbicides, insecticides and fungicides have also been applied as crop control measures to protect the crop from weeds, pests and diseases. These activities have been reported as contributors to heavy metal pollution in many agricultural areas and may also cause chemical degradation of the soil, as a result of accumulation of compounds at undesirable levels. Because fertilizers are not sufficiently purified during the process of manufacture, for economic reasons, they usually contain several impurities and among them are heavy metals. Furthermore, heavy metals often constitute the active ingredients of pesticides [1]. Another source reported to contribute to heavy metal pollution in the paddy field is mining activities. The mining and milling activities of the Daduk mine (Au-Ag-Pb-Zn) in Korea [2]

Corresponding Author: Dr. B.S. Ismail, School of Environmental and Natural Resource Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM, Bangi, Selangor, Malaysia. Tel: +60389214183.

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bioavailability of heavy metals, (from fertilizers and pesticides applied) in the paddy soil from KETARA, Besut, Terengganu.

rpm for ½ hr after which the samples were filtered through 0.45 µm milipore filter paper and made up to 50 ml with distilled water. The samples were washed with 50 ml distilled water, followed by further shaking and centrifuging as described previously. For the metals in the organic oxidation fraction, extraction was carried out by first adding 15 ml of H2O2 to the samples in the water bath (1-1 ½ hrs), followed by of 50 ml of NH 4CH3OO (pH 3.5). The samples were then digested using HNO 3:HClO4 at 25: 10 ratio on a sand bath until the samples changed to a whitish colour. The determination of heavy metals was done using the ICP-MASS Spectrometer Elan 9000. Other parameters carried out included organic carbon analysis (Walkey-Black method [6], soil pH [7] method) and grain size (according to Badri [5]). All analyses were carried out in triplicate.

MATERIALS AND METHODS Studies were carried out at IADA and KETARA paddy cultivation areas of Besut, Terengganu, which are located at the East Coast of Peninsular Malaysia. In the study, soil samples were collected from six stations with different types of soil and different history of previous activities that took place prior to the paddy cultivation activities by KETARA. The soil at station 1 (undisturbed soils) constituted soil from the middle sub-terrace, upper sub-terrace and edge of the levee areas that were inadequately to moderately well and well drained. Station 2 (flooded area) soil came from the lower sub-terrace area, contained high amounts of organic matter and had poor drainage. The soil at station 3 (peat area) was rich in organic matter and had poor drainage. The soil at station 4 (leveled area) was mixed due to the leveling of the edge of the levee and the upper sub-terrace soils into the back swamp area. This station had a mixture of the moderately well and very poorly drained soil. Station 5 (highland area) had soil obtained from the upper sub-terrace and middle sub-terraced areas that were inadequately to moderately well drained. The soil at station 6 (normal area) came from the upper sub-terrace that was moderately well drained. At each station, the soil samples were randomly taken from three different areas, from the 0-30 cm depth. The soil samples were air-dried in the laboratory before being ground and passed through a 250 µm sieve. The heavy metals were extracted from the soil by the sequential extraction method according to Badri [5]. This method was used to extract metals from the four fractions namely the easily leachable and ion exchange fraction (EFLE), acid reducible fraction (AR), organic oxidation (OO) and resistant fraction (RR). The EFLE fraction extracts metals loosely bound to various components in the soil. The acid reduction fraction collects metals strongly bound to secondary minerals in the soil and metals that aggregate with the organic matter are extracted in the organic oxidation fraction. Metals inherent in the soil are present in the resistant fraction. To extract heavy metals from the soil, each 10 gram soil sample was weighed then placed into a kartell bottle and 50 ml 1.0 M NH4CH3OO (pH7) were added for extraction of metals from the EFLE fraction. The sample was shaken for 1 ½ hrs, followed by centrifugation at 3000

RESULTS AND DISCUSSION The study showed that paddy soils of IADA KETARA, Terengganu were slightly acidic (pH 5.4 to 6.12) and dominated by fine grained sediments (Table 1). This finding is in line with other reports on the fluviatile, alluvial deposits of the East Coast of Peninsular Malaysia [8, 9]. Geologically, the study area constituted unconsolidated Quaternary alluvial deposits, underlain with metasediment and intermediate intrusive igneous rocks [10]. The alluvial deposits were formed as a result of sea-level fluctuation and sedimentation throughout the Quaternary period (approximately of 2 million years ago) along the East Coast of Peninsular Malaysia. According to Anizan [8], fluviatile, alluvial soils vary from clay to clay loam, to sandy clay loam. The soils were strongly gleyed and speckled with rusty or reddish brown mottles. Paramananthan [9] reported that the soil in the neighbouring paddy area (Kemubu Plain, Kelantan) was also derived from the fluviatile alluvial deposits. The soils in the Kemubu Plain were made up predominantly of fine grained (clay and silt) sediments, that were slightly acidic (pH 4.7-5.7) and contained very low organic carbon (0.280.46%). Most of the soils from the study area contained a fair to high percentage of organic carbon (1.46-9.85%). The higher amount of organic carbon in the soils was attributed to the provenance of the sediments. The paddy cultivation area of IADA KETARA, Besut was surrounded by phyllite, slate, shale and sandstone in which the argillaceous rocks were commonly carbonaceous [11]. Upon weathering, the organic carbon 184

World Appl. Sci. J., 19 (2): 183-191, 2012 Table 1: The pH, organic carbon and grain size of the paddy soils from KETARA, Besut, Terengganu Location

pH

Station 1

5.84 ± 0.25

Percentage organic carbon 1.58 ± 0.31

Percentage grain size (Mn>Zn>Cu>Cr>Pb>Cd. 185

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The high amount of total Fe and Mn in the study area could be attributed to the occurrence of iron and manganese mottles in the paddy soils as described by previous researchers [8, 9, 12]. In addition to the mottles, the elevated levels of Mn in the AR and ELFE fractions were attributed to the fertilizers applied to the paddy soils. It is a known fact that impure phosphate fertilizers contain high amounts of heavy metals such as Mn (40-200 mg/kg), Zn (50-1450 mg/kg), Pb (7-225 mg/kg), Cu (1-300 mg/kg), Cd (0.1-170 mg/kg) and Ni (7-38 mg/kg) [1, 13]. Most of the heavy metals studied were concentrated in the resistant (RR) and oxidizable-organic (OO) fractions. On the other hand, heavy metal concentration in the easily leacheable and ion exchange (ELFE) and acid reducible (AR) fractions were low. According to Chaney and Hornick [14] and Chaudri et al. [15], the clayey soils allow lower metal bioavailability than the sandy soils. In the current study, the findings suggest that the heavy metal affinity to the unavailable forms was influenced by the soil composition, pH and the amount of organic carbon in the soils. The low bioavailable heavy metals in the soils suggest that heavy metal pollution in the study area was negligible.

Most of the soil Fe was found to be in the unavailable form in the soil fractions following decreasing order of RR>OO>RA, suggesting the accumulation of Fe in the resistant form and in association with organic matter (Fig. 1a). Low amount of ELFE Fe (OO>AR>ELFE. In the current study, the soil Zn in the RR fraction was very low (1.441.86 mg/kg) compared to that in the paddy soils of Kedah (12.95-17.96 mg/kg), suggesting the naturally low amount of Zn in fluviatile, alluvial deposits. Manceau et al. [12] reported that in acidic to near-neutral, aluminium-rich clayey paddy soils, Zn was predominantly bound to the hydroxyl-Al interlayers in the fine soil matrix. Based on the mineralogical study of the Kemubu Plain, the clay fraction from the fluviatile alluvial deposits was composed mainly of kaolinite, mica and small amounts of quartz, gibbsite and goethite. Meanwhile, the silt fraction was predominantly kaolinite, mica and quartz [9]. Similarly, paddy soils from KETARA, Besut were slightly acidic and comprised mainly of clay and silt. Such soils could provide a good binder for Zn accumulation, thus increasing the unavailable forms of Zn in the soils. The concentration of Zn in the ELFE fraction was very low (10% of the total Pb respectively (Fig. 3b). On the other hand, its concentration in the AR and ELFE fractions was low, indicating the low level of bioavailable Pb in the soils. The result suggests that the concentration of Pb was naturally low in the fluviatile, alluvial deposits and most of the metal occurred in the unavailable form. This finding is in agreement with the general findings, that Pb is highly immobile in soils and has high affinity for soil organic matter [19, 24, 25]. According to Adriano [19], organic matter and clay were the dominant constituents that contributed to Pb adsorption. Besides, Pb was also scavenged by iron oxides present in soils [25]. The clayey nature of the studied soils, their high organic carbon content and high Fe and Mn concentration might have possibly been responsible for the fixation of Pb into the unavailable form. In station 4, the total Pb concentration was elevated and stood at 19.09 mg/kg, which is comparable to that of the paddy soils of Kedah [16]. More than 98% of the soil Pb in the above mentioned station was concentrated in the acid reducible (AR) fraction. The cause of the elevated Pb concentration in this station was inadequately investigated except that the area was leveled prior to paddy cultivation. Anthropogenic Pb usually, originates from industrial activities or automobile exhausts which could partially be responsible for the elevated Pb levels in agricultural areas [26]. Located at rural areas and away from industrial activities, the paddy soils in the study area were unlikely to have received anthropogenic Pb. However, the elevated Pb levels could possibly be attributable to the sampling location, whereby soil samples were taken from a site near a busy road. The leveling activities and soil modification that took place in station 4 prior to paddy cultivation could also be a

Fig. 4: Cd percentage in the four soil fractions of the study area contributory factor. Further studies are necessary to illustrate the reason why Pb in the leveled areas formed strong association in the acid reducible fraction, making it available rather than unavailable. Cadmium: The total Cd concentration in the soils of the study area was 0.06-2.54 mg/kg and this value is comparable to that of paddy soils in Kedah [16] (Fig. 4). The speciation of Cd in soils varied among the stations studied. A high concentration of total Cd was observed in station 4 and 6. In both the stations, the soil Cd was dominant in the acid reducible (AR fraction), which accounted for more than 90% of the total Cd. In the soil in station 5, Cd was dominant in the unavailable form (RR fraction) whereas certain amounts of the bioavailable Cd was observed in the soil of stations 1, 2 and 3. According to Adriano [19], the sorption capacity of soil increases approximately three times per unit increase of pH within the pH range of 4-7.7 and the low Cd concentration in the soils was because it was adsorbed and coprecipitated with the hydrous iron oxides. In the current study, the slightly acidic nature of the soils and the presence of hydrous iron oxides promoted the formation of the unavailable forms of Cd. The occurrence of bioavailable Cd in the study area could be attributed to the application of fertilizers and pesticides in the paddy cultivation activities. Khairiah et al. [16] reported that the bioavailable Cd in paddy soils of Kedah was attributed to the application of agrochemical fertilizers and pesticides over several years. It has been reported that the insufficiently purified phosphate fertilizers were contaminated with Cd [1, 27, 28]. Similarly, the application of impure fertilizers and pesticides in KETARA, Besut, could have been the cause of the 189

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increase in the concentration of Cd in the soils could increase. In the study, the Cd concentration in the ELFE fraction was low, suggesting low toxicity of Cd in the paddy soils studied.

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CONCLUSION

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Results on heavy metal speciation in the current study could provide a valuable insight of heavy metal distribution in paddy soils developed on fluviatile, alluvial deposits. With the exception of Fe and Mn, the paddy soils of KETARA, Besut were naturally low in heavy metals (Zn, Cu, Cr, Pb, Cd). The distribution of heavy metals in soils are influenced by soil composition, pH and organic carbon content. Most of the heavy metals studied were distributed mainly in the resistant (RR) and oxidizable organic (OO) fractions, suggesting their occurrence in the unavailable forms and their affinity to the organic matter respectively. The high amounts of soil Fe and Mn in the soils of the study area might be attributed to the occurrence of Fe-Mn hydrous-oxide mottles. Meanwhile, the higher levels of Mn in the ELFE and AR fractions suggest that the continuous usage of agrochemical materials for paddy cultivation activities, rendered high bioavailable Mn in the soils. The elevated levels of Pb and Cd in the soils could possibly be attributed to anthropogenic sources. However, the low concentration of heavy metals in the easily leacheable and ion exchange (ELFE) fraction implied that paddy soils in the study area were not contaminated with toxic heavy metals.

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ACKNOWLEDGMENT The authors would like to thank the officers from KETARA, namely Zulkefly Harun, Hj. Wan Kamal Wan Ibrahim, Mustaffa Othman and Shafee Abd Wahab for their technical help.

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