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Air pollution can be define as the presence of air contaminants in outdoor atmosphere in the form of dust, fumes, gas, mist and others which may threaten or injurious to human, property, plant or animal life (Peavy, pp417). Nowadays a rapid industrial activity such as cement plant has added loads of pollutants to environment (CPCB India, 2004; Melaku et al, 2005; Kansal et al, 2009).
In cement industry, huge amount of heavy metals are emitted from handling, spillage and leaking (Abdul-Wahab 2006). This antropogenic activity emits metals to the atmosphere and will be deposited to the soil through wet and dry deposition which may affect the air quality (Al-Khashman and Shawabkeh, 2006). The most common heavy metals that are emitted from cement plant are zinc, cadmium, lead, nickel, copper and chromium (El-Awady and Sami, 1997).
Biomonitoring of heavy metal is still new in Malaysia and have its own advantages such as sampling is available for all year, easy to identify and sample, abundant, long-lived, have a wide geographical distribution and be relatively tolerant to pollutants (Wittig, 1993).There are several organs of plant can be used as biomonitor such as roots, leaves, barks, stems and fruits (Ahmad et al. 2007) and in this study soil was chose. The increasing of level metals in soil lead to uptake by plants which will affect the quality of agricultural product. For this reason, soil can also act as biomonitoring agent of heavy metal (Melaku et., al. 2005).
Enrichment factor is widely used to identify the possible sources of the antropogenic pollutants of the metallic elements (Fang et., al. 2006). The EF is calculated by comparing the concentration of respective metal with standard value of earth crust element (Kansal et., al 2009) and the formula is as followed.
ICP-MS was chose because of its multi-element capability, low sampling consumption and high detection but the disadvantages if this technique is that it requires a solid sample to be changed to liquid form (Melaku et., al. 2005). Here, microwave digestion technique is the most acceptable method to be adapted where the digestion time of sample can be reduced, the amount of solvent used is very small, low contamination and operator safety is confirmed (Melaku et., al. 2005).
Due to the high impact of heavy metal to the environment, the objective of this study to quantify and determine the concentration of heavy metal (cobalt, cadmium, copper, lead and nickel) in soil using microwave digestion and to identify the possible sources of heavy metal near cement plant by enrichment factor.
The reagents used in this study were all reagent grade. Water was distilled and deionised water. All the acids are stock solution of acids which consists of 65% HNO3 and 70% HClO4. Multi-element Calibration Standard 3 (Matrix per volume: 5% HNO3 per 100ml) was used to prepare the analytical multi-element standard solutions to obtained the calibration curve for ICP-MS.
The methodology of this research can be explained in 4 stages which are sampling location and pretreatment, digestion technique, ICP-MS analysis and data analysis.
Sampling Location and Pre-Treatment
The sampling location was located near the Lafarge Cement Plant in Teluk Ewa, Langkawi. This site was selected because there are cement and boat activity such as fishermen and eco-tourism purposes (located near to Black Sand Beach, Langkawi). All samples were taken on 12 December 2010. Cement plant is located at 6O 25.146ââ‚¬â„¢ N and 99O 45.850ââ‚¬â„¢ E. The sampling locations are in the directions of North, South, South-East and South-West. Samples 1-4 are located near to cement plant (0.5-2km) while samples 5-10 located far from the cement plant (2-6km) as shown in Figure 1.
10 sampling locations were selected and at each sampling location 1 composite soil sample of 4-5 sub-samples were taken about 0-25cm depth using a hand-held stainless steel shovel that had been pre-cleaned in the laboratory using 5% Nitric acid. Each sub-sample is approximately 20-25 gram
and total composite sample soil sample was approximately 100 gram. All the samples then transferred into a pre-cleaned polyethylene plastic, sealed, preserved at 4OC in Coldman Box using ice cubes and transported to the Chemistry Laboratory at Universiti Teknologi MARA Arau Perlis.
In the laboratory, soil samples were dried in oven at 60OC, ground to pass 63Âµm stainless steel sieve, transferred into pre-cleaned polyethylene bottle and stored at 4OC until analysis.
0.5gram of soil sample were weighed directly into a pre-cleaned Teflon microwave vessel and combination of acid were added, the vessels was place inside the rotor of the microwave digestion system, sealed, tighten using a torque wrench and finally submitted to a microwave dissolution program according to the operating condition in table 1.
Hold time (min)
Table 1: Operating Condition for Microwave Digestion Procedures
After 24hours, the digested sample were then transferred into a pre-cleaned 15ml polyethylene centrifuge tube, sealed, centrifuged and stored in 4OC before ICP-MS analysis.
The instrument used in this analysis was Perkin-Elmer NexION 300 ICP-MS. The operating conditions are summarized in table 2.
RF Power (W)
Plasma argon (L min-1)
Nebulizer flow (L min-1)
Number of replicates
Table 2: ICP-MS operating conditions
1.00 ml of the digested sample was filtered using Whatman 13mm Syringe Filter 0.45Âµm to remove silica content and other fine materials that may present after the digestion. The 1.00ml filtered sample was then transferred into a pre-cleaned centrifuge tube and adjusted to 10ml with 0.14M nitric acid. Sample was then introduced to the nebulizer of ICP-MS.
All statistical analyses were processes using Microsoft Office Excel 2007.
Results and Discussion
The analytical results (as shown in Table 4) showed that there are slightly differences in the concentration of each element. In this study, the soil sample has been grouped into two classes; 0.5 to 2km (sample no. 1-4) and 2 to 6km (sample no. 5-10) from cement plant (Mingorance et., al. 2007). These heavy metals are released from cement plant in the form of particulate matter, PM2.5 and PM10 (Fang et., al. 2006; El-Awady and Sami. 1997).
Result showed that the highest concentration of cobalt is near the cement plant with 3.8 mg/kg and the lowest concentration was 1.52 mg/kg, located approximately 4km away from the cement plant. This concentration is lower compare to the general critical soil concentration which is 40 mg/kg (Smith and Carson, 1981). The concentration of cobalt is higher near the cement plant and the possible source of this cobalt might be from the cement plant activity. Besides that, cobalt may occur naturally in the soil and its concentration depends on the pH, amount and composition of organic matter, clay etc (Hamilton 1994). Since the sampling location is near
to beach area and the high level of clay might be a possible reason of the high concentration of cobalt.
Meanwhile, the highest concentration of cadmium was near the cement plant with 0.066 mg/kg and the lowest was 0.0014 mg/kg, located 6km away from the cement plant. The concentration of cadmium in this study is less than general critical soil concentration which is 8 mg/kg (Alloways, 1990). Cadmium occurs naturally in soil due to the chemical weathering of parent material (Chen et al. 2010) but cement plant might be also the possible sources of cadmium in soil.
On the other hand, the concentration of copper was higher near the cement plant with 13.3 mg/kg and at approximately 5km away from the cement plant, the lowest concentration of copper was observed with 3.88 mg/kg. However, the concentration of copper in this study is still below the general critical soil concentration which is 125 mg/kg (Alloway, 1990). Cement plant activity might be the possible source of this copper but it may also occur naturally in soil from the weathering of bedrock or parent rock geology (Martley et al. 2004). As an addition, it was found out that the concentration of copper at sampling site 7 and 9 (far from industrial activities) were high with 15.69 mg/kg and 15.89 mg/kg respectively. This is maybe because there were automobile activity at this sampling site such as residential area (Kg Ayer Hangat), tourism activity (Black Sand Beach) and boating activity (parking for fishing boat). Davis et., al. (2001) reported that the high concentration of Copper at the residential area is linked to the usage of copper in brake particles which contribute the metal to environment.
The highest concentration of lead in soil was 11.74 mg/kg which is located approximately 0.5km from the cement plant and the lowest concentration of lead was observed at 5km away from the cement plant with 3.8 mg/kg. The possible sources of high concentration of lead is due the cement plant activity but lead may also enters the terrestrial environment through paint, recycling, disposal as well as the combustion of leaded gasoline and petrol and its deposition to atmosphere ended up to be accumulated in soil (Dudka et al. 1994). However, the concentration of lead in this study is also lower compared to the general critical soil concentration which is 400 mg/kg (Alloway, 1990).
Table 4: total concentration (mg/kg) in soil.
Nickel concentration in soil ranged between 16.1 and 76.9 mg/kg. The highest concentration of nickel was observed near the cement plant with 76.9 mg/kg and the lowest concentration of nickel was 16.1 mg/kg located approximately 4km away from the cement plant. The concentration of nickel in this study is lower than the general critical soil concentration which is 140 mg/kg (Soil Guideline Values, Environment Agency). Besides that, the occurrences of Nickel in soil is due to the weathering phenomena of clay mineral and ultramafic rocks (such as peridotite and pyroxenite) and its formation in topsoil commonly ranges from 0-100 mg/kg depending on the amount of clay mineral and ultramafic rocks present (Quantin et., al. 2008). However, cement plant activity might be the possible source of its high concentration in soil.
The result from this research was compared with some location in the world as shown in table 5 below. The concentration of cobalt in this study is lower compared to study reported in Belgium (Melaku et al. 2002) because the possible sources may come from the massive agricultural activities.
aBanat et al. (2005). bAl-Khashman &Shawabkeh (2006). cMingorance et al. (2007). dMelaku et al. (2005)
Table 5: Comparison of total mean concentrations (mg/kg) of metal in soils
The comparison with those from other country showed that the concentration of cadmium in this study was lower than the measured in Belgium, Southern Jordan and Central Jordan. This is maybe due to antropogenic activities such as agricultural, factories and coal power plant in the particular country that enhanced the concentration of cadmium in soil.
Meanwhile, the concentration of copper in this study was lower compared with the concentration reported in Belgium and Spain but higher compared to the concentration reported in Southern Jordan. This is maybe because the rapid antropogenic activities in Belgium and Spain such as factories and coal power plant in the study area. On the other hand, copper was higher than the concentration reported in Southern Jordan maybe because this element is released in large amount by the cement plant activity in Teluk Ewa and accumulated in soil.
Besides that, compared to previous study in Belgium, Spain, Southern Jordan and Central Jordan, it was found out that the concentration of lead in this study is lower and this is maybe due to the antropogenic activities present at their sampling sites such as cement plant, mining, coal power plant, agricultural and factories.
On the other hand, the comparison of the concentration of nickel in this study with the study in Belgium showed that the concentration of nickel is lower and this is maybe due to the massive agricultural activities in the sampling site of the study.
Background concentration, mg/kg
a Hamilton E.I (1994), b Kaushik et., al. (2009), c Quynh and Ba (2000)
Table 6: Enrichment factor of different element in soil
Generally, it was found out that the concentration of each heavy metal was higher near the cement plant and as the distance farther the concentration was decreased. Since heavy metals were emitted from the cement plant in the form of particulate matter, its distribution and dispersion strongly influenced by wet and dry deposition (Al-Khashman and Shawabkeh, 2006) as well as the wind direction of a particular area (Mingorance et., al. 2007). Langkawi Island is located near the equator and observed an average temperature of 24OC to 33OC. This island observed two different seasons during the year; dry season in the month of November to March and the wet seasons prevail in the month of April to October. As an addition, Langkawi receives rainfall about 2500mm per annum and humidity level remains 80% throughout the year (Ministry of Tourism Malaysia). These characteristics might be the possible reason of the distribution pattern of heavy metals that was observed in this study.
The possible sources of heavy metal in soils can be determined by calculating the enrichment factor for each heavy metal which discussed in section 3.1.
3.1 Enrichment Factor
Enrichment factor (EF) for each element was evaluated by comparing the concentration of particular element with the background value of metal taken as a world average of metal in soil and the result is shown in Table 6.
It was found out that the enrichment factor value for cobalt ranged between 5.06 and 12.7 and similar observation was observed for nickel where the enrichment factor ranged between 3.22 and 15.4. The highest enrichment factor was observed near the cement plant and as the distance farther the enrichment factor is lowered. The possible source of the enrichment for cobalt and nickel in soil is cement plant activity near the sampling area. On the other hand, the enrichment factor for cadmium, copper and lead were ranged between 0.047-0.163, 0.028-0.113 and 0.109-0.335. The enrichment factor for these elements was <1 and it can be said that these elements were naturally enriched in the soil as a result of the weathering of the parent rock (Quantin et al.2008).
The enrichment factor from this study was compared with some places in the world as shown in table 7 below.
aGallorini et al. (2002). bFang et al. (2006). cKansal et al. (2009)
Table 7: Comparison of Enrichment Factor of different heavy metal in soils.
Kansal et al (2009) and Fang et al. (2006) reported that the enrichment factor for nickel was 9.8 and 44.4 respectively (Table 7). The value is higher compared to this study because there are rapid industrial activities such as agricultural activity, foam eutrophications, wheat productions and wastewater disposal area in their sampling site as compared with study where only cement plant activity is the possible sources of enrichment of nickel in soil.
From table 7, cadmium, copper and lead were said to be enriched naturally in soil. However, Kansal et al. (2009) reported that the concentration of Cadmium was 15.3, Fang et al. (2006) reported the concentration for Copper and Lead was 40.8 and 314.4 respectively and Gallorini et al. (2002) reported the enrichment factor for Cadmium, Copper and Lead was 13.5, 6.1 and 7.5 respectively.
The high concentration of enrichment factor value was a result of rapid industrial activities within the sampling area such as agricultural activity, foam eutrophications, wheat productions and wastewater disposal area at their sampling site.
The concentration of cobalt, cadmium, copper, lead and nickel in soil were ranged between 1.5 and 3.8 mg/kg, 0.014 and 0.066 mg/kg, 3.88 and 15.9 mg/kg, 3.80 and 11.7 mg/kg and 16.13 and 76.9 respectively. It was found out that the level of heavy metal in soil near cement plant is lower compared to general critical soil concentration. Cobalt and Nickel show EF>1 which indicates that both of this element enriched in the soil as a result of in the cement plant area the sampling site. It is advisable that in the future study the use of supra-pure acids is crucial because normal acids sometimes contain higher concentration of elements than the sample itself. As an addition, biomonitoring technique is not well known in Malaysia and the use of biomonitors (such as roots, soil, tree bark, leaves, lichen etc) with some advantages (such as cheap, sample availability, sample abundant and wide geographical distribution) strengthen its application in this country to monitor pollutant is applicable..