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).
Two methods that can be used to monitor the emission of heavy metals are by dispersion method (biomonitoring) and by field measurements (direct measurements) (Wolterbeek, 2002). However, biomonitoring is more applicable compare to direct measurements because in biomonitoring method, 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 basics criteria for choosing the species to be used as biomonitor such as the selected species should be the dominant species in that particular area, the sampling should be easy and it is to identify the selected species (Hale et., al. 1998).
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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 root of plant was chose. On the other hand, although some metals are essential plant micronutrients, 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). There are various methods to determine the enrichment factor and this study 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. Enrichment factor, EF = (x/y)air/(x/y)crust where x is the enrichment factor species and y is the reference material (Quiterio et., al. 2004)..
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). On the other hand, Standard Reference Material (SRM) of soil (SRM1646a) and Plant (SRM1515) are used to validate the methods mention above as well as to obtain a rapid, safe and best sample preparation method. Hence, due to the high impact of heavy metal to the environment, the objective of this study to determine and quantify the concentration of heavy metal (Cadmium, Copper, Cobalt, Lead and Nickel) in soil and root of Eupatorium odoratum and its potential as phytoremediation species, to identify the possible sources of heavy metal near cement plant by enrichment factor, and to determine the optimum condition for digestion method.
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, 37% HCl, 70% HClO4 and 35% H2O2. 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.
2.1 Sampling Location and Pretreatment
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 25.146' N and 99O 45.850' E.
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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.
Figure 1: Location sampling sites of Root and Soil.
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.
Root sample were collected at the same sampling location where the soil sample were taken. The roots were carefully handpicked from the plant species Eupatorium odorata (Pokok Kapal Terbang). The existence of this plant species at all the sampling point is the key point of its selection as a plant to be selected as a bio-monitor. All the samples is 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 and transferred into pre-cleaned polyethylene bottle until analysis. On the other hand, root samples were cleaned using deionised water to remove soil, litter and unwanted coarse materials. Root samples are then dried in oven at 60OC, ground to pass 63Âµm stainless steel sieve and transferred into pre-cleaned polyethylene bottle until analysis.
2.2 Microwave Digestion
0.5gram of sample and standard reference material (SRM1646a - Estuarine Sediment for soil sample and SRM1515 - Apple Leaves for root sample) were weighed directly into a pre-cleaned Teflon microwave vessel and various combinations 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.
The operating condition for microwave procedures is summarized in the Table 1. Method A-C is for soil sample while Method D is for root sample.
Table 1: Operating condition for microwave digestion procedures
After 24hours, the digest were then transferred into a pre-cleaned 15ml polyethylene centrifuge tube, sealed, centrifuged and stored in 4OC fridge before ICP-MS analysis.
The instrument used in this analysis was Perkin-Elmer NexION 300 ICP-MS. The operating conditions are summarized in the Table 2.
Table 2: ICP-MS operating conditions
Plasma argon (L min-1)
Nebulizer flow (L min-1)
Dwell time (ms)
Number of replicates
1.00 mL of the digested sample and standard reference material (SRM) were 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 is then introduced to the nebulizer of ICP-MS.
All statistical analyses were processes using Microsoft Office Excel 2007.
3.0 Results and Discussion
The validation was done by similar treatment of SRM with the soil sample. After the analyses, it is found out that the highest percentage recovery is 73.28%.
Table 3: Percentage Recovery for SRM 1646a and SRM1515
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*Below detection limit
According to Sucharova and Suchara (2006), the use of nitric acid and hydrogen peroxide is widely used for the determination of metals in plants because both of these acids mineralize organic matter effectively. However in the presence of some matrices (rocks, soils, sediments) which have a high contain of silicon, it may reduce the recovery of some elements which is experienced in this study. In order to eliminate this silicon, hydrofluoric acid can be added to the digestion mixture but another crucial step needs to be taken to remove the tetrafluoride formed in the digests.
Unfortunately, the usage of hydrofluoric acid can result in the torch damage in ICP-MS (Melaku et., al. 2005) and operator safety is at high priority and the usage of hydrofluoric acid is not applicable in this study. For Cobalt, Copper and Nickel, it was found out that the usage of Nitric Acid and Perchloric Acid have the highest percentage recovery, where else, for Cadmium and Lead, the usage of Nitric Acid only produce the highest percentage recovery of SRM1646a.
3.2 Heavy metal in soil
The analytical results (as shown in Table 4) show that there are big differences in the concentration of each element in soil and root. In this study, the soil sample has been grouped into three classes; 0.5 to 2km (1-4) which is close to cement plant and 2 to 6km (5-10) which is far 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).
Table 4: total concentration (mg/kg) in soil and root of Eupatorium odoratum
*Below detection limit
It was found out that the highest concentration of Cobalt is near the cement plant (3.8 mg/kg) and the lowest concentration was 1.517 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). Since the concentration of cobalt is high near the cement plant, the possible source of this cobalt might be from the cement plant activity. However, cobalt may occur naturally in the soil and its concentration depends on the pH, amount and composition of organic matter, clay etc (Hamilton 1994). In this study, 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. The concentration of cobalt in this study is lower compared to study reported in Belgium (Melaku et al. 2002) because the possible source may only come from cement plant while in Melaku et al. study the sources may come from the massive agricultural activities.
Meanwhile, the highest concentration of cadmium is near the cement plant with 0.066 mg/kg and while the lowest was 0.0014 mg/kg, 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 in soil may occurs naturally 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 in this study. The comparison with those from other country showed that the concentration of cadmium in this study was lower than the measured in Belgium (Melaku et al. 2005), Southern Jordan (Al-Khashman and Shawabkeh, 2006) and Central Jordan (Banat et al. 2005). 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.
On the other hand, the concentration of copper was high near the cement plant with 13.287 mg/kg and at approximately 5km away from the cement plant, the lowest concentration of copper was observed with 3.879 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) are high with 15.694 mg/kg and 15.887 mg/kg respectively. This is maybe because at this sampling site, it is near to the residential area where automobile activity is very high. 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 concentration in this study is lower compared with the concentration reported in Belgium (Melaku et al. 2002) and Spain (Mingorance et al. 2007) but higher compared to the concentration reported in Southern Jordan ( Al-Khashman and Shawabkeh, 2006). This is maybe because the rapid antropogenic activities in Belgium and Spain such as factories and coal power plant in the study area. As in this study, the copper is higher than the concentration reported in Southern Jordan because this element is released in large amount by the cement plant and enriched in soil.
The highest concentration of lead in soil was 11.741 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. The possible sources of high concentration of lead in this study is the cement plant activity but lead may enters the terrestrial environment through paint, recycling, disposal as well as the combustion of leaded gasoline and petrol 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). Compared to previous study in Belgium (Melaku et al. 2005), Spain (Mingorance et al. 2007), Southern Jordan (Al-Khashman and Shawabkeh, 2006) and Central Jordan (Banat et al. (2005), it was found out that the concentration of lead in this study is lower and this is maybe due to the antropogenic activities such as cement plant, mining, coal power plant, agricultural and factories near their study area.
Nickel concentration in soil ranged between 16.132 and 76.930 mg/kg. The highest concentration of nickel was observed near the cement plant with 76.930 mg/kg and the lowest concentration of nickel was 16.132 mg/kg located approximately 4km away from the cement plant. On the other hand, 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). The occurrences of Nickel in soil is normally as a result of 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 is might be the possible source of its high concentration in soil.
The comparison of the concentration of nickel in this study with the study in Belgium (Melaku et al. 2005) 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.
Table 5: Comparison of total mean concentrations (mg/kg) of metal in soils
aBanat et al. (2005). bAl-Khashman &Shawabkeh (2006). cMingorance et al. (2007). dMelaku et al. (2005)
Generally, in this study, it was found out that the concentration of each heavy metals are higher near the cement plant and as the distance farther, the concentration is decreased. Since heavy metals are 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 3.3.
3.3 Enrichment Factor
Enrichment factor can be calculated by comparing to the relative abundance respect to local control site (Mingorance et., al. 2007), based on the background value of metal taken as a world average of the metal in soil (Kaushik et., al. 2009), by comparing the concentration of elements in a certain period of time (Ramos et., al. 2009), compared with normalizing element such as Scandium or Lanthanum which assumed to be uniquely characteristics of the background (Bergamaschi et., al. 2002) and compared the concentration of each element with its concentration in the earth crust (Fang et., al. 2006).
In this study, 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.
Table 6: Enrichment factor of different element in soil
Background concentration, mg/kg
a Hamilton E.I (1994), b Kaushik et., al. (2009), c Quynh and Ba (2000)
If the value of EF is close to unity, it can be said that the element is naturally enriched in soil. However, if the EF is larger than unity, the metal is enriched as a result of antropogenic activities which in this study are the emission from cement plant.
Table 6 shows the enrichment factor of five different metals in soils. From this table it was found out that the enrichment factor value for Cobalt ranged between 5.056 and 12.665, said to be enriched as a result of cement plant activity. Similar observation was observed for Nickel where the enrichment factor ranged between 3.22 and 15.38 which also said to be enriched as a result of cement plant activity. Kansal et al (2009) and Fang et al. (2006) in their study reported that the enrichment factor for Nickel was 9.8 and 44.4 respectively (Table 7). The value is higher because the concentrations of these elements were high as result of rapid industrial activities such as agricultural activity, foam eutrophications, wheat productions and wastewater disposal area.
The enrichment factor for Cadmium, Copper and Lead were <0.2, <0.1 and <0.3 respectively and 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 (Table 7). 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
Table 7: Comparison of Enrichment Factor of different heavy metal in soils.
aGallorini et al. (2002). bFang et al. (2006). cKansal et al. (2009)
3.4 Heavy metal in root and the potential of Eupatorium odoratum as phytoremediation species
It was found out that the concentration of cobalt in root ranged between 0.036 and 0.86 mg/kg, cadmium ranged between 0.019 and 0.254 mg/kg, lead ranged between 0.249 and 11.606 mg/kg and nickel ranged between 0.619 and 35.962 mg/kg. Even though there was a big differences in the concentration of these elements in compare to soil but similar pattern was observed to that in soil. In plants, cobalt is classified as a beneficial elements and acts as micronutrient in plants which is required for the fixation of nitrogen in legumes (Hursthouse et al. 2008). Cadmium is non-essential in plant and at high concentration it can consider toxic to plant where metabolic activities such as photosynthesis and transpiration might be inhibited, but the critical concentration of cadmium to be toxic is different in regards to a plant species (Chen et al. 2003). Meanwhile, plants absorb lead mainly from root uptake and the presence of high concentration of lead may leads to growth inhibition of root (Kovalchuk et al. 2005). In plant, nickel may be a potentially toxic and will result in weak plant growth, reduced nutrient uptake and enhanced chlorosis (Poulik, 1997). In this study also, it was found out that the concentration of copper was higher compare to that in soil. The highest concentration of copper was 294.355 mg/kg and the lowest was 7.452 mg/kg. The pattern observed is different to the other element and indicates that this species can act as accumulator of copper. Hence, as a result of uptake mechanism, these heavy metals were present in root sample.
Table 6: Mobility ratio of different element
aBanat et al. (2005). bAl-Khashman &Shawabkeh (2006). cMingorance et al. (2007). dMelaku et al. (2005)
In order determine the transferring mechanism of element from soil-to-plant, mobility ratio can be calculated by the following formula, MR = Mplant / Msoil where Mplant is the concentration of element in root and Msoil is the concentration of element in soil. MR>1 indicates that the plant act as accumulator while MR<1 indicates that this plant is an excluder (Mingorance et al. 2007)
From this table, it was found out that Eupatorium odoratum can act as accumulator for copper and to certain extend can also act as accumulator for cadmium. As an addition, this finding also suggests that this plant species were tolerant to cobalt, lead and nickel by imparting the minimal value of MR.
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, 3.879 and 15.887 mg/kg, 3.802 and 11.741 mg/kg and 16.132 and 76.930 respectively while the concentration of Cobalt, Cadmium, Copper, Lead and Nickel in root were ranged between 0.036 and 0.84 mg/kg, 0.019 and 0.254 mg/kg, 7.452 - 294.355 mg/kg, 0.249 and 11.606 and 0.619 and 35.962 mg/kg respectively. In this study, it was found out that the level of heavy metal near cement plant is high in the soil compared to minimal risk level (MRL) and can be hazardous to the people in the residential area. 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. The mixture of acids (HNO3 + HClO4) shows the highest percentage followed by HNO3 only and mixture of HNO3 + HCl. 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. This study also showed that Eupatorium odoratum possess the capacity to take up selected heavy metal via its roots and this suggest the potential of Eupatorium odoratum as a phytoremediation species in polluted soil. 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.