S Nayek paper 2013

International Journal of Chemoinformatics and Chemical Engineering, 3(2), 117-124, July-December 2013 117

Dynamics of Metal Distribution in Cultivated Soil and Vegetables in Vicinity to Industrial Deposition: An Inference to Chemical Contamination of Food Chain

Sumanta Nayek, Basic Science Department, EIILM University, Sikkim, India Suprakash Roy, Department of Chemistry, Malda Govt. Polytechnic College, Malda, West Bengal, India Suvanka Dutta, Department of Chemistry, National Institute of Technology, Durgapur, India Rajnarayan Saha, Department of Chemistry, National Institute of Technology, Durgapur, India Tanmoy Chakraborty, Department of Chemistry, Manipal University Jaipur, Rajasthan, India

ABSTRACT The present study demonstrates accumulation and distribution of heavy metals (Fe, Cr, Cd, Pb & Cu) in cultivated soil and vegetables, and its potential implication to health risk via consumption of contaminated vegetables. Deposition of atmospheric metals results significant enrichment of metal contents (Pb=1.6, Cu=1.4 & Cd=15.9) in cultivated soil. Elevated metal content in soil facilitate higher metal accumulation in growing vegetables through root uptake and also by leaf absorption. Results show noticeably higher metal translocation (>1) from soil to roots (TFr) and shoots (TFs), followed by higher metal accumulation in leafy shoots (except R. sativa). In sampled vegetables, estimated hazard quotient (HQ) for individual metal does not exceed the safe limit, but integrated hazard quotient (IHQ) in L. esculanta is above the safe limit (1.33) and incredibly close in R. sativa (0.97) and S. oleracia 0.93) to cause health hazard. Keywords:

Atmospheric Heavy Metals, Consumable Vegetables, Health Risk, Soil Contamination, Translocation Factor

DOI: 10.4018/ijcce.2013070109

118 International Journal of Chemoinformatics and Chemical Engineering, 3(2), 117-124, July-December 2013

1. INTRODUCTION

1.1. Study Area

The accumulation of heavy metals in agricultural soil and plants is of increasing concern due to food safety issues and potential health risk to local inhabitants (khan et al., 2008). Anthropogenic sources of heavy metals are associated with industrial activity and urbanization such as atmospheric deposition, waste disposal, industrial/urban effluents, vehicular exhaust and long term application of wastewater and sewage sludge in agricultural field (Bilos et al., 2001; Cui et al., 2005). Accumulation of heavy metals in consumable vegetables has been well linked with soil heavy metal and irrigation water from long back; atmospheric deposition has now been identified as one of the principal source of heavy metals entering into plants and soil especially around urban-industrial areas (Pandey et al., 2009). Atmospheric heavy metals may deposit by rain and dust, and contributed to elevated metal concentrations in surface layer of soil (Sharma et al., 2008). Heavy metals are extremely persistent in the environment; which in-turn absorbed by plant roots and subsequently mobilized to above ground vegetative parts. Leafy vegetables are known to accumulate sizable amounts of airborne metals (Voutsa et al., 1996; Pandey et al., 2009). Atmospheric metals may be absorbed directly on leafy surface, or entered through stomatal openings and accumulated within plant tissue. Metal accumulation in different plant parts depends on chemical form of metals, their translocation potential, individual species with their stage of maturity (Sinha et al., 2006). Heavy metal contamination in agricultural soil and vegetables through industrial wastewater and atmospheric source are of great concern because of metal translocation in soil-plant system and ultimately to the food chain (khan et al., 2008; Rattan et al., 2005). Thus accumulation of heavy metals in the edible parts of vegetables represents a direct pathway for their incorporation into the human food chain (Florijin et al., 1993); and therefore has drawn the attention of researchers to health risk assessment of population exposed to contaminated foodstuffs.

Present investigation is carried out in Durgapur industrial zone (Lat long) of state West Bengal, India. This industrial region is heavily dense with a number of industries viz. Iron & Steel plants, Thermal power plants, Chemical factory and Sponge iron & Ferro alloy industries. Field sampling has been performed from cultivated fields in vicinity to Durgapur Steel Plants (DSP) and Alloy Steel plants (ASP). Although these cultivated fields are irrigated by ground water (considered the as safest source) through submarshal pump, but heavily contaminated by the deposition of atmospheric heavy metals on soil as well as on plant surfaces from surrounding industrial sources. Mostly garden vegetables (viz. tomato, spinach, radish etc) are produced in these contaminated fields by farmers and sell it to local market/residents. This present investigation is seek to satisfy the following objectives: i) accumulation of heavy metals in cultivated soil and vegetables, ii) metal translocation in soil–plant system, iii) and health risk assessment of heavy metals in consumable vegetables.

2. METHODOLOGY 2.1. Sample Collection and Preparation Atmospheric heavy metal concentrations were estimated by using high volume sampler (NPM-HVS). Monitoring was performed for 12 hr duration, and sampling sites were also free from overhead obstacles which may interfere in deposition of atmospheric metals. High volume sampler was kept at 2m high to avoid ground level particles. Immediately after collection, air particulate matter was acidified with 70% HNO3 and stored in dark at room temperature (28 ºC). Cultivated soil and vegetable samples were collected following randomize block design method. Surface soil (0-10 cm) were collected from root zone of cultivated vegetables with the help of plastic spatula, and kept in zipped plastic bag. In laboratory, soil samples were air dried,

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pulverized and sieved through 2mm screen. Vegetables namely tomato (Lycopercicum esculatum), spinach (Spinacia oleratia), radish (Raphanus sativa) and amaranth (Amaranthus viridis) were collected randomly from cultivated field. Only healthy/uninfected samples were collected at their mature stage. Plant species were kept separately in polythene bags, and taken to the laboratory as soon as possible. In laboratory, sampled species were cleaned with tap water followed by distilled water, and separated into roots and leafy vegetative parts. Plant samples were dried in room temperature, and then oven dried (80 ºC) to a constant weight.

2.2. Analytical Methods Soil pH and EC was analyzed by preparing soil water suspension (1:5, w/v) with distilled water (Rhoades et al., 1982). Organic matter (OM) content in soil was determined by wet dichromate oxidization method (Walkley & Black et al., 1934). Cation exchange capacity (CEC) of soil (1g dry weight) was determined in flame photometer by extracting exchangeable sodium with ammonium acetate solution (1 mol L-1) (Reeuwijk et al., 1995). Metal concentrations in cultivated soil and plant samples were analyzed by microwave digestion using HNO3 (65%) and HClO4 (70%) acids (Suprapur quality, Merk). Soil samples (1g of air dried) were analyzed for heavy metals by digesting with 3:1 HNO3 and HClO4 acids in microwave (600 watt, 6 min). Plant samples (1g dry-weight) were digested with HNO3 and HClO4 (5:1) in microwave (480 watt, 3 min) until a transparent solution was obtained. Digested samples were brought to room temperature, filtered with GF/C filter paper, and diluted to 25 mL in volumetric flask. Total metal concentrations in sampled plants and soil were determined in atomic absorption spectrophotometer (GBC Avanta, USA).

2.3. Quality Control AR grade reagents were used during experimental process, and analysis of water/soil samples

were triplicated to ensure the reliability of results. E-mark (AR grade, Germany) standard solutions (1000 mg mL-1) were used to calibrate the instrument for metal analysis. Ultrapure water (Milli Q) was used to run blanks, and prepare intermediate standards. Each analytical setup was consisting of a method blank, and standard solutions were analyzed after every 25 sample to check instrument performance. Pb and Cd content in examined samples were determined by using Graphite furnace. Standard reference materials (NIST-SRM 2709 for soil, NIST-SRM 1570 for water, and NBS-SRM 1573 for plants) were used to check the analytical precision. Reproducibility of analytical data was within 2.5% standard error (SE) level of certified value for every heavy metal.

2.4 Indices Used Metal contamination in water and soil is calculated by using enrichment factor respectively, to quantify degree of metal contamination in cultivated soil with respect to control/recommended standards (Barman et al., 2000). Enrichment factor (EFsoil) = Metal concentrations incontaminated soil Metal standards in uncontaminated soil (Kabata Pendiasand Pendias,1992) Translocation factor (TF) is a ration of metal concentrations in plants with bio-available metal fractions in medium where the plant grows (Cui et al., 2004). Metal translocation form soil to plant roots (TFr) and roots to vegetative shoots (TFs) is calculated as:

TFr =

Metal concentrations in plant roots Exchangeablemetal content insoil

120 International Journal of Chemoinformatics and Chemical Engineering, 3(2), 117-124, July-December 2013

and

density of vehicles/road traffic (Voutsa et al., 1996; Jassir et al., 2005).

Metal content  in vegetativeshoots  TFs = s in plant roots Metal concentrations 

3.2. Concentrations of Heavy Metals in Cultivated Soil and Vegetables and Metal Translocation in Soil-Plant System

2.5. Statistical Applications Pearson correlations were performed between atmospheric metal concentrations with metal content in plants (dry weight) and also between exchangeable metal concentrations in soil with plant metal content (dry weight). All statistical applications were performed in Microsoft excel, by suing XL stat, version 10.

3. RESULTS AND DISCUSSION 3.1. Concentrations of Air Borne Heavy Metals in Sampling Site The industrial atmosphere is highly enriched in heavy metals discharged through the emission from surrounding industries; in addition, aerosol deposition has also been recognized as major source of airborne heavy metals (Singh & Agarwal et al., 2005; Pandey et al., 2009). Atmospheric metal concentrations (µg m-3) in sampled area vicinity to industrial zone are Fe (2.15 – 4.98) > Pb (1.65 – 3.96) > Cr (1.04 – 3.82) > Cd (0.36 – 0.58) > Cu (0.34 – 2.86). Results of present study are compared with metal content in nearby unpolluted location reported by (Gupta et al., 2011) (Fe=0.37±0.03, Cr= 0.12±0.01, Pb=0.63±0.04 and Cd=0.07±0.01 µg m-3). Concentrations of airborne Fe and Cr in industrial surrounding area are noticeably higher (10.41 and 18.23 folds) than unpolluted site; while rest of the metals (viz. Cd, Pb and Cu) exhibit their relatively higher abundance in comparison to control site. The extent of atmospheric metal concentrations in industrial surrounding areas are very much comparable and consistent with earlier findings (Pandey & Pandey et al., 2009; Gupta et al., 2011). Build up metal concentrations in atmosphere of sampled area can be attributed to discharge of particulate metals through industrial emissions, and higher

Soil represents an excellent media to monitor heavy metal contamination from anthropogenic sources. Several physicochemical of soil (viz. pH, CEC, OM content) are known to affect the bioavailability and plant uptake of metals (Adriano et al., 2001). Cultivated soil shows neutral pH (7.12±0.3); with EC value of 2.22± 0.8 ms at 25 C. Organic matter (OM) of cultivated soil is in moderate range (4.3±0.2), with CEC value of 12.18± 0.4 meq of Na/100 g soil. Mobilization of heavy metal from soil to plants is known to increase with increase CEC with decrease/less alkaline condition. Presence of OM in excess also retard root uptake of metals by forming insoluble complex with metal ions. Determination of bio-available metals in soil environment is very useful, as only the exchangeable-soluble fractions of metals are readily available for plant uptake. Extents of bio-available metal fractions in cultivated soil are much less in comparison to total metal content (Table 1). Rests of the metal fractions are in insoluble complex form, chelated with organic matter or as lithogenic fractions. The degree of soil pollution is estimated by enrichment factor (EF), indicating enchantment in metal concentrations with respect to recommended standards in unpolluted surface soil (Kabata Pendian & Pendias et al., 1992). Significant enrichment factor (>1) is observed for Cd and Pb (Table 1). Elevated concentration of heavy metal in cultivated soil signifies deposition of substantial atmospheric heavy metals which in turn increase accumulation of toxic metals in standing crops/vegetables. Potential health risks to humans and animals from consumption of crops can be due to heavy metal uptake from contaminated soils via plant roots as well as direct deposition of

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Table 1. Heavy metal concentrations in cultivated soil vicinity to industrial areas Heavy metals (mg kg-1)

Total metal concentrations in cultivated soil*

Bio-available metal fractions in cultivated soil

Enrichment factor (EF)

Metal standards in unpolluted surface soil1

Fe

178.4±9.4

56.74± 3.6

0.18

1000.0

Cr

66.2±8.4

21.46±2.8

0.66

100.0

Pb

79.2±6.7

15.82±2.3

1.6

50.0

Cd

15.9±3.8

3.54±0.9

15.9

1.0

Cu

43.5±5.2

18±1.4

1.4

30.0

* Metal content expressed as mean value ± SD, (n = 16) 1 Metal standards in unpolluted surface soil (Kabata Pendias & Pendias et al., 1992)

contaminants from the atmosphere onto plant surfaces (McBride et al., 2003). Partitioning of heavy metals in different plant parts is a common strategy to prevent toxicity; and interactions among the metals are also responsible for their varied accumulation within the plants (Sinha et al., 2006). Present investigation shows that Fe is the most abundant in sampled vegetables, and accumulates more in leafy vegetative parts (Table 2). Highest Fe concentration is noted in shoots of S. oleracia (308-342 mg g-1), while roots of R. sativa also show considerable amount of Fe accumulation (178.6-196.3 mg g-1). Cr concentrations in sampled vegetables are notably high

(Table 2), and its highest accumulation noticed in S. oleracia (38.6-52.8 mg g-1). The roots of L. esculenta also show higher Cr contents (23.8-27.3 mg g-1). Pb is known as least bioavailable metal in the soil environment, but present investigation shows higher concentrations of Pb in shoots than roots (Table 2). This situation can be explained by deposition of air borne Pb on leafy surface from industrial & atmospheric sources. Among the studied metals, Cd shows lowest abundance in cultivated soil followed by its least accumulation in plants. L. esculenta exhibits enhanced accumulation of Pb and Cd in comparison to other species. Cu is an essential micronutrients required for

Table 2. Heavy metal concentrations in shoots and roots of cultivated vegetables Cultivated species

Fe

Cr

Pb

Cd

Cu

Lycopercicum esculatum

Shoot

298.2 ± 15.7

36.6 ± 5.3

26.8 ± 3.4

12.4 ± 1.7

42.1 ± 3.8

Root

137.8 ± 6.8

25.4 ± 1.5

15.3 ± 1.1

7.2 ± 0.2

17.6 ± 1.8

Amaranthus viridis

Shoot

227.6 ± 12.6

24 ± 4.1

11.3 ± 1.2

4.8 ± 0.8

51.2 ± 5.3

Root

116.4 ± 4.7

14.8 ± 1.2

6.5 ± 0.4

1.4 ± 0.06

22.5 ± 2.1

Spenacia oleracia

Shoot

326.4 ± 14.1

44.5 ± 6.4

17.4 ± 2.4

7.5 ± 1.6

31.8 ± 5.0

Root

78.6 ± 2.9

18.6 ± 1.1

8.4 ± 0.5

2.6 ± 0.2

14.7 ± 0.6

Shoot

264 ± 9.6

32.8 ± 5.4

20.6 ± 3.1

9.6 ± 1.4

88.2 ± 6.9

Root

189.2 ± 8.3

21.8 ± 1.5

12.8 ± 0.7

5.8 ± 0.05

56.1 ± 2.3

Edible parts

450.0

5.0

5.0

0.3

40.0

Raphanus sativa WHO/FAO metal standards1

* Metal content in plants (dry weight DW) expressed as mean value ± SD, (n=16). 1 WHO/FAO metal standards for consumable vegetables (1999)

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Table 3. Translocation factor (TFr & TFs) of heavy metals in examined plant species Heavy metals

L. esculatum TFr

TFs

A. viridis TFr

S. oleracia

TFs

TFr

R. sativa

TFs

TFr

TFs

Fe

2.4

2.2

2.0

1.9

1.4

4.1

3.3

1.4

Cr

1.2

1.4

0.7

1.6

0.9

2.4

1.0

1.5

Cd

2.1

1.7

0.4

3.3

0.7

2.9

1.6

1.7

Pb

0.96

1.8

0.4

1.7

0.5

2.0

0.8

1.6

Cu

0.97

2.4

1.2

2.3

0.8

2.1

3.0

1.6

* TFr - transfer factor from soil – root and TFs – transfer factor form root – shoot

several physiological processes of plants. Cu concentration in sampled vegetables found to be more in shoots (Table 2); however roots of R. sativa contains noticeably higher amount of Cu (308-342.2 mg g-1). Correlation study between atmospheric metals with plant metal content and soil metals with plant metal content is found to be insignificant; but significant correlations (p1) from soil to plant roots is observed in R. sativa (Fe, Cr, Cd, Cu), L. esculenta (Fe, Cr, Cd), A. viridis (Fe, Cu), and S. oleracia (Fe). Heavy metal mobilization from soil to plant roots did not follow any particular pattern (Table 3), which can be explained by varying mobility of individual metals, and also plant’s inherent capacity to absorb metal ions. The studied heavy metals in sampled vegetables exhibit higher TFs value (Table 3) indicating their higher affinity towards leafy vegetative parts, consistent with earlier workers (Barman et al., 2000; Bose et al., 2007). Metal concentrations in edible plant parts (mostly vegetative body and below ground parts for R. sativa) are also compared with FAO/WHO standards for metal content in consumable vegetables (Table 2). Concentrations of most of the studied metals (viz. Cr, Cd,

Pb and Cu) in cultivated vegetables are much higher than recommended permissible limits, which can be linked to potential health risk of local inhabitants.

3.3. Health Risk Assessment of Heavy Metals in Consumable Vegetables Prolonged human consumption of unsafe concentrations of heavy metals in foodstuffs may lead to the disruption of numerous biological and biochemical processes in the human body (Amune et al., 2012). Health risk assessment of contaminant essentially requires quantification of level of exposure of particular contaminant (or in combination with other elements) to the organisms. Hazard Quotient (HQ) is often used by the researchers for assessment of potential health hazards due to consumption of metal contaminated vegetables (Wang et al., 2005; Qishlaqi et al., 2008). HQ is a ratio of measured dose to the reference dose (RfD), and HQ value ≥ 1 indicates high risk to the exposed population. HQ = [Wplant] × [Mplant] / RfD × B Where [Wplant] = dry weight of contaminated plant materials consumed per day (mg d-1), [Mplant] = concentration of metal in dry plant materials (mg kg-1), RfD = food reference dose for metals (mg d-1), and B = body weight of consumer (kg). A conversion factor of 0.085 was used to convert fresh green vegetable weight to dry weight (Rattan et al., 2005). Estimated

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daily intakes of vegetables were considered to be: A. viridis 200 g, L. esculenta 300 g, S. oleracia 250g and R. sativa 250-300 g. The RfD is an estimate of a daily exposure to the human population that is likely to be without an appreciable risk of deleterious effects during life time (US-EPA, IRIS 2006). The RfD value for heavy metals are adopted from US EPA safe limit of oral/dietary metal exposure (Fe: 3E-01, Cr: 1.5E-0, Cd: 1E-03, Pb: 3.5E-03, and Cu: 4E-02 mg kg-1 day-1). Average estimated body weights of adult local inhabitant are 60 kg, which is obtained through survey. In this study estimated HQ value of individual metal for sampled vegetables did not exceed the permissible limit of 1. But integrated hazard quotient (IHQ) of examined metals (∑HQ of Fe, Cr, Cd, Pb, Cu) is significantly high in L. esculenta (1.33), and in R. sativa and S. oleracia IHQ value is incredibly close to permissible limit (0.97 and 0.93 respectively), therefore can be linked with potential health hazards in long run. Negligible IHQ is observed in A. virides (0.51).

4. CONCLUSION Enrichment in metal content in cultivated soil and vegetables can be attributed to industrial emission and atmospheric deposition of air borne metals. However root absorption of soil metals suppose to be dominant over leaf absorption of atmospheric metals, and also major reason for buildup metal concentrations in cultivated vegetables. Cr, Pb, and Cd content in examined species are above the permissible limits of consumption standards. Calculated hazard quotient (HQ) of individual heavy metals in individual species do not exceed the safe limit, but integrated hazard quotient (IHQ) of examined heavy metals (Fe, Cr, Cd, Pb and Cu) in tomato is noticeably high (>1), and also of serious concern for radish and spinach. Therefore consumption of these metal contaminated vegetables in excess or through long run can be the reason for health hazard to exposed community.

5. ACKNOWLEDGMENT The authors wish to thank Mr K. Pobi and Ms P. Sen for their technical support during this research work.

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