Bioconcentration of Heavy Metals in Alfalfa (Medicago sativa) from Farm Soils around Sohar Industrial Area in Oman

APCBEE Procedia 5 ( 2013 ) 271 – 278

2212-6708 © 2013 The Authors. Published by Elsevier B.V.Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Societydoi: 10.1016/j.apcbee.2013.05.047

ICESD 2013: January 19-20, Dubai, UAE

Bioconcentration of Heavy Metals in Alfalfa (Medicago sativa) from Farm Soils around Sohar Industrial Area in Oman.

Tahra Talib Al-Rashdia and Hameed Sulaimanb a,b Biology Department, College of Science, P.O. Box 36, Sultan Qaboos University, Alkhod 123, Sultanate of Oman.

Abstract

Heavy metal accumulation in soils caused by industrialization has become a potential threat due to its availability to crops and their subsequent transformation in the food chain. Sohar Industrial Area in Oman has large number of industries operating in a confined area closer to agriculture farms which cultivates alfalfa as fodder for their livestock. This study assessed the presence of selected heavy metals in farm soils and alfalfa. Samples were collected from 8 farms, four each from two sites (2 and 4 km from the industry). Results show that the soil metal concentration are found to be in the order of Fe >Al> Ni> Zn>Cr> Co>Cu>Pb. There is no difference in concentration of metals between the distances. Most of the farm soils are saline in nature. In general, the metals bioaccumulate more in the root than in the shoot. Interestingly, the Pb which recorded the least concentration in soil has translocated the most to the edible shoot. © 2013 Published by Elsevier B.V. Selection and/or peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society Keywords: Heavy metals; Alfalfa; Industrial area; Bioconcentration.

1. Introduction

For the past 30 years the sultanate of Oman relied on oil as primary source to support the economy and the revenues from the petroleum products have enabled it to develop dramatically. In its vision 2020 there is a plan to move from dependence on the oil production by dropping the about 9% and aimed to move towards industrial growth to increase its GDP share to 29% in 2020.For this purpose, the sultanate steps forward to develop industrial estates managed by public establishment of

Corresponding author. Tel.: +968 24142303; fax: +968 24141437. E-mail address: [email protected]

Available online at www.sciencedirect.com

© 2013 The Authors. Published by Elsevier B.V.Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society

272 Tahra Talib Al-Rashdi and Hameed Sulaiman / APCBEE Procedia 5 ( 2013 ) 271 – 278

industrial estates (PEIE). There are eight estates in different governorate , Alrusial, Sohar, Raysut, Nizwa, Sur, Alburaimi, the information technology industry estate, Knowledge Oasis Muscat (KOM) and Almazyanah free zone. This required growth is expected to have negative impact on the environment in terms of its pollution and degradation. Rapid industrialization gave rise to such problem even though it promoted the development of socio-economy [1],[2].

Environmental pollution caused by heavy metals discharged from industrial area will end up in one of the environmental segments such as air, water , soil and vegetation mainly through pathways of solid wastes, wastewater and waste gases [3].Although the soil pollution usually may not be as apparent as that of the air or water, since the late 20th century, the influence of urbanization on the accumulation of heavy metals in soil has aroused more and more concern from scientists all over the world[4], [5], [6], [7], [8], [9].The deterioration of the environment quality from heavy metal contamination raising serious concerns which are being not degradable materials, in long term can accumulate in toxic level at higher concentration and their biotransformation in food chain. Many studies on this issue were done earlier in India [10] China [3], [2], [11], [12], [1], Poland [13], Turkey [14], Zimbabwe [15], Nigeria [16] focused on the impact of heavy metals on the soil-plant system.

The general objective of the study is to investigate the influence of industrial development on the agriculture farms in the vicinity of Sohar Industrial Area. The specific objective is to measure the heavy metals status in the farm soils growing Alfalfa and their biotransformation.

2. Materials and Methods

Sohar industrial port area is located in Sohar (24° 22 N, 56° 45 E) in Albatina region. The site occupies an area of approximately 7.5 Km in a north-south direction by 1.85 km in an east-west direction. This study focuses on the impact of heavy metals emerging from the industrial area on the farms surrounding the area from the western direction. Therefore, two sites were selected based on the distance from the middle of the industrial area. The first site is within 2 km (24°28'6.29"N; 56°36'32.07"E) while the second site is 4 km away (24°27'44.31"N; 56°35'43.04"E). From each site, four farms were selected and soil and alfalfa samples were collected in triplicate

Composite soil samples were collected with shovel forced into the soil to a depth of approximately 15 cm. Then, soil samples were dried at 70 °C and sieved through 2mm sieve. Heavy metals, pH, Conductivity, organic matter, soil texture were analyzed using standard methods. Alfalfa seedlings were removed as whole and later separated into root and shoot. Alfalfa forage tissue was left unwashed to reflect animal feed condition and air dried for 72 hrs. Acid digestion method was used to analyze heavy metal and then their concentration were measured using Inductively Coupled Plasma mass spectroscopy(ICP).Bioconcentration and transformation factors were calculated following the estimates used by Lotfinasabasl [17].

3. Results and Discussion

3.1. Metals in soil

The mean concentration of the heavy metals in soil varies widely in the two studied sites (Table 1). General metal concentration is found to be in the order of Fe >Al> Ni> Zn>Cr> Co>Cu>Pb. Iron is the dominant element in both studied sites. The difference in the concentration is not significant with distance.

(USEPA) Maximum Permissible limits. Most of the studies which have been done on the accumulation of the heavy metals around industrial areas confirmed that with time the soil become contaminated with metals [12], [2],


[10]. Therefore, in our study area it is necessary to monitor in order to prevent soil contamination since the industrial operation has been going on more than a decade now.

Table 1.The mean heavy metal concentration (mg/kg) of soil sample.

Sites Zn Al Co Cu Ni Pb Cr Cd Fe

Site 1 (2km)

Farm 1 0.22 4.75 0.03 BDL 0.31 BDL BDL BDL 6.61

Farm 2 0.03 BDL BDL BDL BDL 0.01 BDL BDL 0.48

Farm 3 1.04 9.1 0.4 0.323 7.68 BDL 1.113 BDL 20.9


Site 2 (4km)

Farm 5 0.07 BDL BDL BDL BDL BDL BDL BDL 0.12


Farm 7 1.15 8.51 0.45 0.43 8.72 0.12 1.331 BDL 20.68

Farm 8 0.04 0.16 BDL BDL BDL 0.25 BDL BDL 1.31

BDL: Below Detection Limit

3.1.1. Soil properties and heavy metals Soil physico-chemical variables such as pH, electronic conductivity, total dissolved solid, sodium

adsorption ratio, organic matter, cations and anions were examined (Table 2). The texture of the soil is sandy loam. Sandy loam soil in general will not increase the probability of heavy metal adsorption because it has no charge and the space between the particles is large .On the other hand it allows the pollutants to percolate causing groundwater pollution. The pH was ranging from 7.26 to 8.09. According to Food and Agriculture Organisation, the soil is saline when the pH is less than 8.2 and more often near neutrality[18]. Organic matter was recorded in all soils, although the amount and type vary considerably. It plays role in the maintenance as well as improvement of many soil properties. Qishlaqi and Moore carried out statistical analysis of the sources and accumulation of heavy metal in agricultural soils and noticed that soil organic matter was the most important factor controlling their distribution[19].Electronic conductivity and total dissolved solid are higher in site 1 especially in the two first farms compared with site 2. Sodium Adsorption Ratio (SAR) of soil ranges from 0.42 to 6.96. Since the electronic conductivity is higher than 4 and the sodium adsorption ration is <13 the soil falls into the category of saline soil [18]. The sultanate is characterized by high temperature and low rainfall where the mean annual rainfall does not exceed 100 mm [20]. The annual potential evaporation is significantly greater than annual precipitation. Because of high evaporation there is a need to conserve the soil moisture for long period thus plants can use it efficiently. In addition to that, water used for irrigation is saline which subsequently will enhance the salt accumulations. All these reasons would result in soil salinity problem. The consequences associated with it are threefold: a low soil water potential, giving rise to symptoms similar to those of water stress, high levels of NaCl may give rise to an ion imbalance and lead to deficiency symptoms and cause plant toxicity [21]. Plants do not respond to salinity in a similar manner; some crops can produce acceptable yields at much greater soil salinity than others. It is a major concern among the farmers since the alfalfa is the fodder crop in the study area.


The soils contain in general, magnesium and chloride as predominant cation and anion respectively. Sensitivity to high chloride concentration shows a discrepancy between plant species and cultivar [21]. Generally most woody crop tolerate excessive levels of Cl where as some woody plant species and beans are susceptible to Cl toxicity [22] The critical toxicity concentration is about 4-7 and 15-50 mg/g for Cl sensitive and Cl tolerant plant species respectively. Roseberg and co-workers reported the relative inhibition of ammonium chloride nitrification was attributed to difference in osmotic potential under different saline condition or to a direct effect of Cl [23]. There is very week correlation between the physio- chemical properties and the heavy metals concentartionin the soil (Table 3).

Table 2. The mean ± SD, Min, Max of the physicochemical parameters in Site 1 and Site 2.

Site 1 Site 2

Variables Mean ± SD Min Max Mean ± SD Min Max

pH 7.35 ± 0.08 7.26 7.46 7.80 ±0.21 7.50 8.00

EC(ds/m) 12.46 ± 4.65 8.13 17.09 5.39 ± 1.80 3.91 7.77

TDS(mg/l) 7976 ± 2978 5203.00 10943.00 3450 ± 1149 2502.00 4972.00

SAR 5.04 ± 1.82 2.84 6.96 2.18 ± 1.62 0.42 4.27

OM % 2.79 ± 1.08 1.20 3.45 1.55 ± 0.29 1.16 1.87

Cations(mg/l)

K+ 58.59 ± 25.89 32.16 92.84 27.06 ± 14.71 16.11 48.57

Na+ 408.58 ±192.60 295.00 696.80 215.55± 59.99 160.30 282.90

Mg+2 828± 426.45 420.00 1345.00 272.68 ± 128.23 195.50 464.00

Ca+2 933.05 ± 303.91 583.00 1278.00 351 ± 184.13 146.00 583.00

Anions(mg/l)

Cl- 3883 ± 1815.13 2133.00 5633.00 1357 ± 712 815.00 2321.00

NO3- 10.65 ± 9.14 2.54 23.77 246.07 ± 115.88 92.78 371.33

SO4-2 776.41 ± 297.04 381.00 1082.00 361.72 ± 261.06 146.62 738.21

Table 3. Correlation between some of the heavy metals and physicochemical parameters (p < 0.05)

Parameter R Zn Al Co Cu Ni Cr Pb Fe

pH 0.35 0.25 0.38 0.33 0.41 0.50 0.53 0.31 EC (ds/m) -0.26 -0.08 -0.29 -0.29 -0.35 -0.35 -0.57 -0.19 TDS -0.26 -0.08 -0.29 -0.29 -0.35 -0.35 -0.57 -0.19 SAR 0.12 0.30 0.11 0.06 0.12 0.12 -0.52 0.18 Organic matter % 0.28 0.40 0.25 0.17 0.24 0.24 0.31 0.34

3.2. Metals in Alfalfa

Table 4 represents the variation of bioconcentration factors (BCF) of heavy metals in root and shoot of the studied sites. In site 1 the root showed the highest BCF (11.66, 10.63, 9.89 for Fe, Al and Zn respectively)


whereas for the site 2 only Zn and Al are the highest in root (Figure 1, 2). Generally, bioconcentration factorof root is higher than shoot which means the root accumulates more heavy metals. Among the metals Pb recorded the highest translocation factor which is indicative of higher mobility Pb which is translocated from the root to the aerial part of plant (Table 5, Figure 3).

Table 4. Bioconcentration factor of heavy metals in sites 1 and 2

Study sites Bioconcentration factor of heavy metalsZn Al Co Cu Ni Pb Cr Fe

Site 1(root) 9.89 10.63 0.82 5.66 0.84 1.63 2.71 11.66Site 1 (shoot) 8.88 9.25 0.94 4.04 0.97 2.13 1.89 9.20Site 2 (root) 11.84 3.84 0.18 3.70 0.24 0.27 0.80 3.14Site 2 (shoot) 4.92 2.56 1.86 1.96 0.18 0.58 0.57 2.80

Table 5. Translocation factor of heavy metals in sites 1 and 2

Study site Translocation factor of heavy metalsZn Al Co Cu Ni Pb Cr Fe

Site 1 0.89 0.87 1.14 0.71 1.14 1.31 0.70 0.79Site 2 0.39 0.67 0. 60 0.53 0.74 2.17 0.71 0.89

Fig. 1. Bioconcentration factor of heavy metals in root and shoot of site 1.


Fig. 2. Bioconcentration factor of heavy metals in root and shoot of site 2.

Fig. 3. Translocation factor of heavy metal in the studied sites.

Alfalfa is an important perennial fodder crop in the Sultanate which account for about 10% of the totalcropped area [24]. It is used as main fodder for the cattle. The bioconcentration of metal in soil is higher thanbiotransformation within the plant (Figures 1, 2 and 3). The analysis of the roots may indicate the degree of heavy metal accumulation in the polluted soil and offers clues on the degree of soil pollution. The metal


immobilization in plant roots determines the recuperation of a high proportion of metals in roots (80 90 %) [25].The bioaccumulation capability depends not only on the total concentration of the respective metal in the soil but also on its availability to roots and transfer across the soil-root inter phase and the type of plants as well [17].

4. Conclusion

Farms in the study area have been cultivating Alfalfa for years and considered by the farmers as an economically important crop. The heavy metal content in the soil were not very high and were well within the permissible limits of the USEPA standards. This might be due to the recent history of industrial development closer to the farms. The heavy metal did not show any apparent correlation with soil physico-chemical properties.Also,the poor quality of the arid soil might not have favoured the metal bioavailability to the crop. Although the metals in the soil and its transformation to the crop are not alarming, earlier studies have confirmed that the soils around the industrial area with time will slowly get contaminated by metals. Hence the metal emission from Sohar industrial area has to be constantly monitored to control emissions and prevent further damage in the surrounding farms.

References

[1] Wu S, Zhou S, Li X. Determining the anthropogenic contribution of heavy metal accumulation around a typical industrial town: Xushe China. J of Geochem Explor 2011 ; 110: 92-97.

[2] Yan-Feng Z, Xue-Zheng S, Biao H, Dong-Sheng Y, Hong-Jie W, Wei-Xia S, Öboern I, Blomb ck K. Spatial Distribution of Heavy metals in Agricultueral soils of an industry-based peri-urban area in Wuxi, China. Pedosphere 2007; 17 :44-51.

[3] Haiyan W, Stuanes AO. Heavy metal pollution in air-water-soil-plant system of Zhuzhoucity, Hunan province. China. Water, Air & Soil poll 2003; 147: 79-107.

[4] Nriagu JO, Pacyan JM. Quantitative assessment of worldwide contamination of air, water and soils by trace metals. Nature 1988; 333: 134-139

[5] Frangi JP, Richard D. Heavy metal soil pollution catography in northen France. The Sci of the Total Environ 1997; 205: 71-79. [6] Govil PK, Reddy GLN, Krishna AK . Contamination of soil due to heavy metals in the Parancheru industrial development area,

Andhra Pradesh, India. Environ Geol 2001; 41 : 461-469. [7] Wong SC, Li XD, Zhang G, Qi SH, Min YS. Heavy metals in agricultural soils of the Pearl River Delta, South China. Environ

poll 2002; 119: 33-44. [8] Romic M, Romic D. Heavy metals distribution in agricultural topsoils in urban area. Environ Geol 2003; 43: 795-805. [9] Pedosphere 2004; 14: 151-

158. [10] Sharma RK, Agrawal M, Marshall FM. Atmospheric deposition of heavy metals (Cu, Zn,Cd, pb) in Varanasi City, India.

Environ Monit Assess 2008; 142: 269-278. [11] Fu J, Zhou Q, Liu J, Liu W, Wang T, Zhang Q, Jiang G. High levels of heavy metals in rice (Oryza sativa L.) from a typical E-

waste recycling area in southeast China and its potential risk to human health. Chemosphere 2008; 71: 1269-1275. [12] Li F, Fan Z, Xiao P, Oh K, Ma Y, Wei H. Contamination, chemical speciation and vertical distribution of heavy metals in soils

of an old and large industrial zone in Northeast China. Environ Geol 2009; 57:1815-1823. [13] rna-Binkw A. Monitoring of selected heavy Poland.

Polish J of Environ Studies 2000; 9 :511-515. [14] Aydinalp C , Marinova S. Distribution and forms of heavy metals in some agricultural soils. Polish J of Environ Studies

2003 ;12 : 629-633.


[15] Muchuweti M, Birkett JW, Chinyanga E, Zvauya R, Scrimmshaw MD ,Lester JN. Heavy metal content of vegetables irrigated with mixtures of wastewater and sewage sludge in Zimbabwe:implication for human health. Agric Ecosys & Environ 2006; 112: 41-48

[16] James OK. Heavy metal contamination of plants and soil in itakpe iron ore deposit area of Kogi state, Nigeria. Environ Res J 2008; 2:122-124.

[17] Lotfinasabasl S. Studies on heavy metals bioaccumulation potential of Mangrove species, Avicennia Marina. Interna J of Eng Sci &Technol 2012; 4: 4411-4421.

[18] FAO. 1983. Guidelines: land evaluation for rainfed agriculture. Soils Bulletin 52. FAO, Rome. 249 P [19] Qishlaq A, Moore F. Statistical analysis of accumulation and sources of heavy metals occurrence in agricultural soils of Khoshk

River Banks, Shiraz, Iran. Am Euras J Agric Environ Sci 2007; 2: 565-573 [20] Al-Dhuhli HS, Al-Rawahy SA, Prathapar S. Effectiveness of mulches to control soil salinity in sorghum fields irrigated with

saline water. A monograph on management of salt-affected soil and water for sustainable agriculture 2010. 41-46 [21] Lambers H, Chapin FS, Pons TL. Plant physiological ecology. 2nd . New York: Springer: 2008 [22] Mass EV. Physiological response to chloride. In Special Bulletin on chloride and crop production (T.L. Jackson ed). Potash &

Phosphate institute Atlanta GA ; 2: 4-20. [23] Roseberg RJ, Christensen NW, Jackson TL. Chloride soil solution osmotic potential and soil pH effects on nitrification. Soil Sc

Am J; 50: 941-945. [24] Ministry of Agriculture and Fisheries (MAF). 2005 Agricultural Census 2004/2005. Directorate General of Planning and

Investing Promotion, Department of Statistics and Information. Oman. [25] Smical A, Hotea V, Oros V, Juhas ZJ, Pop E . Studies on transfer and bioaccumulation of heavy metals from soil into Lettuce.

Environ Eng &Mgt J 2008; 7: 609-615.

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Bioconcentration of Heavy Metals in Alfalfa (Medicago sativa) from Farm Soils around Sohar Industrial Area in Oman