9
Micronutrient Fractionation in Coal Mine-Affected Agricultural Soils, India Rahul Agrawal 1 Bijendra Kumar 1 Kumari Priyanka 1 Chandravir Narayan 1 Kriti Shukla 1 Jhuma Sarkar 1 Anshumali 1 Received: 10 April 2015 / Accepted: 1 February 2016 Ó Springer Science+Business Media New York 2016 Abstract Assessment of the anthropogenic impacts on bioavailability, mobility, immobility and toxicity of four micronutrients (Cu, Fe, Mn, and Zn) were carried out by Community Bureau of Reference (BCR) fractionation scheme in agricultural soils (n = 10) around Jharia coal- field, eastern India. The relative abundance of micronutri- ents was as follows: Fe [ Mn [ Zn [ Cu. The enrichment factor was [ 1 for Zn (6.1) and Cu (1.8) near coal mining area indicated toward soil pollution due to coal mining activities and application of inorganic fertilizers. The I geo values of micronutrients were \ 0 suggest no pollution with respect to Cu, Fe, Mn and Zn. Correlation analysis showed geogenic origin of soil micronutrients and derived mainly from weathering of minerals present in the parent rock. The mean values of Cu, Mn and Zn were less than certified reference material indicating highly leached agricultural soils in the study region. BCR fractionation of micronu- trients showed that a single element could not reveal all types of chemical reactions occurring in soil consortium. Keywords Acid digestion Sequential extraction Soil Coalfield Coal plays an important role in energy generation and approximately 27 % of the world’s energy consumption originates from the incineration of coal (Bhuiyan et al. 2010). In India, coal based energy generation accounts for 55 % of country energy needs and open cast mines produced 91.65 % of total coal production (463 MT) dur- ing 2012–2013 (Ministry of Coal 2013). It is reported that 4m 3 of overburden produced per ton of mined coal (Juwarkar and Jambhulkar 2008) and the production of 463 MT of coal through opencast mining will result in 1850 Mm 3 overburdens. For producing this much amount of coal it is estimated that land at the rate of about 60 km 2 is degraded in direct mining and approximately 75 km 2 per year for external overburden and spoil dumps (Kundu and Ghose 1997). The Jharia Coal Field (JCF) is located in the eastern India, has the potential of contributing significantly to resolving the current energy crisis in the subcontinent. The expected production target during 2014–2015 for JCF is 35 MT. The cumulative effects of exploration activities at multiple sites have the potential to drive environmental change, particularly from a larger regional perspective. A report on Indian opencast mine showed dust emission from haul, transport, and communication roads was 78–124.5, 48–98.2, and 38.7–50.3 t/km 2 /month, respectively (Chau- lya et al. 2011). Mandal et al. (2012) reported higher dust deposition in summer (26.56 t/km 2 /month) than monsoon (12.68 t/km 2 /month). Some of the trace elements present in coal are of health concern (Masto et al. 2011) and they may be enriched in the coal dusts. Understanding the risk of agricultural soil pollution due to enrichment of trace ele- ments around coal mining areas is of utmost importance in view of implications for environmental health. Soil is a prominent sink for trace elements originated from geogenic and anthropogenic sources. Trace metals in the soil derived from weathering of country rock and, in some cases, anthropogenic inputs from industrial process (Kersten and Forstner 1989). Rout et al. (2013) reported higher con- centrations of Cu, Pb, and Zn in dust samples around the JCF. Recent studies on ecological risk assessment of soil & Rahul Agrawal [email protected] 1 Laboratory of Biogeochemistry, Department of Environmental Science and Engineering, Indian School of Mines, Dhanbad, Jharkhand 826004, India 123 Bull Environ Contam Toxicol DOI 10.1007/s00128-016-1745-3

Micronutrient Fractionation in Coal Mine-Affected Agricultural Soils, India

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Micronutrient Fractionation in Coal Mine-Affected AgriculturalSoils, India

Rahul Agrawal1 • Bijendra Kumar1 • Kumari Priyanka1 • Chandravir Narayan1 •

Kriti Shukla1 • Jhuma Sarkar1 • Anshumali1

Received: 10 April 2015 / Accepted: 1 February 2016

� Springer Science+Business Media New York 2016

Abstract Assessment of the anthropogenic impacts on

bioavailability, mobility, immobility and toxicity of four

micronutrients (Cu, Fe, Mn, and Zn) were carried out by

Community Bureau of Reference (BCR) fractionation

scheme in agricultural soils (n = 10) around Jharia coal-

field, eastern India. The relative abundance of micronutri-

ents was as follows: Fe[Mn[Zn[Cu. The enrichment

factor was[1 for Zn (6.1) and Cu (1.8) near coal mining

area indicated toward soil pollution due to coal mining

activities and application of inorganic fertilizers. The Igeovalues of micronutrients were\0 suggest no pollution with

respect to Cu, Fe, Mn and Zn. Correlation analysis showed

geogenic origin of soil micronutrients and derived mainly

from weathering of minerals present in the parent rock. The

mean values of Cu, Mn and Zn were less than certified

reference material indicating highly leached agricultural

soils in the study region. BCR fractionation of micronu-

trients showed that a single element could not reveal all

types of chemical reactions occurring in soil consortium.

Keywords Acid digestion � Sequential extraction � Soil �Coalfield

Coal plays an important role in energy generation and

approximately 27 % of the world’s energy consumption

originates from the incineration of coal (Bhuiyan et al.

2010). In India, coal based energy generation accounts for

55 % of country energy needs and open cast mines

produced 91.65 % of total coal production (463 MT) dur-

ing 2012–2013 (Ministry of Coal 2013). It is reported that

4 m3 of overburden produced per ton of mined coal

(Juwarkar and Jambhulkar 2008) and the production of 463

MT of coal through opencast mining will result in

1850 Mm3 overburdens. For producing this much amount

of coal it is estimated that land at the rate of about 60 km2

is degraded in direct mining and approximately 75 km2 per

year for external overburden and spoil dumps (Kundu and

Ghose 1997).

The Jharia Coal Field (JCF) is located in the eastern

India, has the potential of contributing significantly to

resolving the current energy crisis in the subcontinent. The

expected production target during 2014–2015 for JCF is 35

MT. The cumulative effects of exploration activities at

multiple sites have the potential to drive environmental

change, particularly from a larger regional perspective. A

report on Indian opencast mine showed dust emission from

haul, transport, and communication roads was 78–124.5,

48–98.2, and 38.7–50.3 t/km2/month, respectively (Chau-

lya et al. 2011). Mandal et al. (2012) reported higher dust

deposition in summer (26.56 t/km2/month) than monsoon

(12.68 t/km2/month). Some of the trace elements present in

coal are of health concern (Masto et al. 2011) and they may

be enriched in the coal dusts. Understanding the risk of

agricultural soil pollution due to enrichment of trace ele-

ments around coal mining areas is of utmost importance in

view of implications for environmental health. Soil is a

prominent sink for trace elements originated from geogenic

and anthropogenic sources. Trace metals in the soil derived

from weathering of country rock and, in some cases,

anthropogenic inputs from industrial process (Kersten and

Forstner 1989). Rout et al. (2013) reported higher con-

centrations of Cu, Pb, and Zn in dust samples around the

JCF. Recent studies on ecological risk assessment of soil

& Rahul Agrawal

[email protected]

1 Laboratory of Biogeochemistry, Department of

Environmental Science and Engineering, Indian School of

Mines, Dhanbad, Jharkhand 826004, India

123

Bull Environ Contam Toxicol

DOI 10.1007/s00128-016-1745-3

contamination by trace elements in the vicinity of JCF

reveal pollution load due to coal mining activities, mine

fires, windblown dust, dumping of crust materials etc.

(Masto et al. 2011; Pandey et al. 2015a, b). But, these

studies were mainly focused on total metal concentrations

in airborne particulate matter and soils. Previous studies do

not highlight that what happens with micronutrients in soil

system contributed by anthropogenic sources. Answer to

this question basically reveals the fate of micronutrients in

the agricultural soils, especially in the vicinity of mining

facilities. The optimum plant growth and crop yield

depends not only on the total amount of micronutrients

present in the soil at a particular time but also on their

chemical forms that may influence their environmental

mobility and availability to organisms. The biogeochemi-

cal reactions of micronutrients depend on their different

chemical forms in soil consortium and sensitive to soil

texture, organic matter, pH, electrical conductivity etc. To

address this, selective chemical extraction methods can be

used to estimate the concentrations of micronutrients

bound to particular soil phases (Rao et al. 2008). The

modified version of the three-steps Community Bureau of

Reference (BCR) procedure (Ure et al. 1993; Sahuquillo

et al. 1999) was used for trace metal fractionation and

assess the spatial variation in the concentrations of differ-

ent chemical forms of micronutrients in agricultural soils

around JCF. Exchangeable fraction involves weakly

adsorbed trace metals retained on the solid surface by

relatively weak electrostatic interaction and can be released

by ion-exchangeable processes etc. Remobilization of

metals can occur in this fraction due to adsorption des-

orption reactions and lowering of pH (Narwal et al. 1999).

Reducible fraction involves trace metals that are released in

reducible conditions such as those bound to hydrous oxides

of Mn and Fe. The fraction obtained when trace metals

bound to iron and manganese oxides, a reducing solution is

used as the extractant (Gleyzes et al. 2002). The informa-

tion obtained with the analysis of soil after sequential

chemical extraction may be useful to better understand the

mobility/immobility, adsorption/desorption, bioavailability

and finally origin of metal contamination in agricultural

soils of the JCF region.

Materials and Methods

Jharia Coal Field (JCF) is one of the most important coal

mining areas in India containing proven coal reserves of

approximately one billion tones in a crescent-shaped basin

of approximately 400 km2. It is roughly elliptical or sickles

– shaped, located in Dhanbad district of Jharkhand lies

between 23�390N to 23�500N latitudes and 86�050E to

86�300E longitudes (Fig. 1). The main natural drainage is

the Damodar River, which is supplemented by perennial

streams (e.g. Tisra, Chatkari, Katri, Khudia, Jamuniya,

Kumari and Bansjora). The region is important for its large

reserves of lower gondwana coal distributed in the JCF.

The average elevation of the area is 201 m above msl.

Climatically the JCF is of tropical monsoonal nature with

its hot summer, dry and cold winter. The annual average

temperature is about 25�C and it receives annually about

900–1300 mm of rainfall. The total land covered in the JCF

is 392.85 Km2 in which the agricultural land area is

10.08 %. From the cropping area data, it can be inferred

that the unirrigated kharif (monsoon) crops continue to

cover 95 % of the total cropped area. Rabi (winter) irri-

gated crops cover only 3 % of the total cropped area.

Summer irrigated crops are only 1 %. Rabi crops and

summer crops are not popular in the district due to lack of

irrigation facilities (CGWB 2013). Agriculture is mostly

rain fed and comprises Kharif crop, while Rice is the main

crop. Maize, gram, wheat, oil seeds, vegetables, etc. are the

main food crops in the district. Guava, papaya and jack

fruit are the main horticultural crops. The agricultural

activities are concentrated in the eastern and western

regions of JCF. The agricultural soils are red (mostly of the

residual type is known as lateritic soils are formed at high

temperature and high rainfall) and sandy intertwined with

rolling undulation. The entire Jharia is drained by two

small streams Ekra Nala and Kori Jore River. Water bodies

in Jharia region are not perennial and become dry during

the hot seasons and filled during monsoon seasons. The

surface drainage pattern and its surrounding area in the

coalfield have undergone a major change due to mining and

other anthropogenic activities, resulting in low irrigation

facility on the one hand and poor ground water recharge on

the other. The whole study area is under direct/indirect

impact of the coal mining activities, therefore the selection

of control site is not possible for the comparison of the

data, if we select control site in outside the study area then

there is chances of changes in geological formations.

Hence, in this study we could not select any control site.

Ten soil samples were collected in the monsoon (August

2014) from agricultural fields located in the eastern (four

sampling sites) and western regions (six sampling sites)

around JCF. In each site, a plot of one hectare was selected

and five soil cores (5 cm inner diameter each) of 0–15 cm

depth were randomly sampled from five points (north,

south, east, west and central) and mixed to obtain a com-

posite sample. The soil samples were stored in acid-cleaned

HDPE bottles in frozen state using portable ice box to

minimize the biogeochemical alterations and transported to

the laboratory for analytical processing. In laboratory, the

bulk soil samples air-dried, broken into pieces, grinded well

in the mortar and pestle to crush the aggregate particles for

further physico-chemical and metal extraction analysis.

Bull Environ Contam Toxicol

123

The pH and electrical conductivity (EC) were measured

on a 1:2.5 soil: water (w/v) ratio (Tan 2005); water holding

capacity (WHC) was determined by keeping fresh soil

overnight with water at a 1:2 ratio (Harding and Ross

1964); bulk density (BD) by Core method (Blake 1965);

soil organic carbon (SOC) and soil organic matter (SOM)

by using the Walkley and Black dichromate oxidation

method (1934). The total concentration of micronutrients

was determined by digestion with aqua regia

(HCl:HNO3 = 3:1), according to the ISO 11466 (ISO

1995).

Micronutrient fractionation in soil samples were ana-

lyzed with the modified version of the BCR three-steps

sequential extraction procedure (Rauret et al. 1999): First

step (Exchangeable and weak acid soluble fraction, F1-

Exc): 1 g of soil sample was extracted with 40 mL of

0.11 mol/L acetic acid solution by shaking in a mechanical,

end-over-end shaker at 30 ± 10 rpm at 22 ± 5�C for 16 h.

The extract was separated by centrifugation at 30009g for

20 min, collected in polyethylene bottles and stored at 4�Cuntil analysis. The residue was washed by shaking for

15 min with 20 mL of doubly deionised water and then

centrifuged, discarding the supernatant. Second step (Re-

ducible fraction, F2-Reduc): 40 mL of 0.5 mol/L hydrox-

ylammonium chloride solution was added to the residue

from the first step, and the mixture was shaken

30 ± 10 rpm at 22 ± 5�C for 16 h. The acidification of

this reagent is by the addition of a 2.5 % (v/v) 2 mol/L

HNO3 solution. The extract was separated and the residue

was washed as in the first step. Third step (Oxidizable

fraction, F3-Oxi): 10 mL of 8.8 mol/L hydrogen peroxide

solution was carefully added to the residue from the second

step. The mixture was digested for 1 h at 22 ± 5�C and for

1 h at 85 ± 2�C, and the volume was reduced to less than

3 mL. A second aliquot of 10 mL of H2O2 was added, the

mixture was digested for 1 h at 85 ± 2�C, and the volume

was reduced to about 1 mL. The residue was extracted with

50 mL of 1 mol/L ammonium acetate solution, adjusted to

pH 2.0, at 30 ± 10 rpm and 22 ± 5�C for 16 h. The

extract was separated and the residue was washed as in

previous steps. Residue from the third step (Residual

fraction, F4-Res): the residue from step 3 was digested with

aqua regia, following the ISO 11466 (ISO 1995). In this

case, the amount of acid used to attack 1 g of sample was

reduced to keep the same volume/mass ratio: 7.0 mL of

HCl (37 %) and 2.3 mL of HNO3 (70 %) were added.

Three independent replicates were performed for each

sample and blanks were measured in parallel for each set of

analysis using aqua regia extraction and BCR procedure,

respectively. Micronutrients concentrations in the extracts

obtained at each step were determined by using an atomic

absorption spectrophotometer (GBC Avanta PM).

To determine the deficiency or enrichment of micronu-

trients, comparisons are made to background concentration

in the Earth’s crust. The enrichment factor (EF) was cal-

culated with respect to Fe according to the following

equation: EF = (Cx/CFe)Soil/(Cx/CFe)Earth’s crust where (Cx/

CFe)Soil is the ratio of concentration of the element being

determined (Cx) to that of Fe (CFe) in the soil sample and

(Cx/CFe)Earth’s crust is the ratio in the reference Earth’s crust

(Atgin et al. 2000). Iron was selected as a reference ele-

ment because it is a major sorbent phase for trace metals,

and is a quasi conservative tracer of the natural metal-

bearing phases in environmental components (Schiff and

Fig. 1 Study area of Jharia coalfield (ten sampling sites)

Bull Environ Contam Toxicol

123

Weisberg 1999; Turner and Millward 2000). Contamina-

tion factor (CF) was calculated by dividing the concen-

tration of examined element (Ci) by geochemical

background value (Bi) of that element (Hakanson 1980):

CF = Ci/Bi. Pollution Load Index (PLI) was calculated by

the expression given by Tomlinson et al. (1980):

PLI = (CF1 9 CF2 9 CF3 9 ��� 9 CFn)1/n where n is set

of polluting elements. The geoaccumulation index (Igeo)

for the metals was determined using Muller’s expression

(1979): Igeo = Log2 (Cn)/1.5(Bn) where Cn is the concen-

tration of metals examined in soil samples and Bn is the

geochemical background concentration of the metal,

average shale (Turekian et al. 1961). The factor analysis of

BCR fractions was carried out by using ‘‘Statistical

Package for Social Sciences (SPSS), version 16.0.’’ The

‘‘principal component analysis’’ and ‘‘Varimax rotation’’

were used for extracting and deriving factors, respectively.

Results and Discussion

Physico-chemical properties of the agricultural soils are

presented in Table 1. The soil pH ranged from 6.3 to 7.8.

The electrical conductivity varied from 49.6 to 1295 lS/cm. The water holding capacity showed variation from

20.5 % to 51.5 %. Bulk Density of soils varied from 1.3 to

1.6 gm/cc. Soil organic matter (SOM) varied from 1.2 %

to 6.1 %. The mean value of SOM is high (3.8 %) indi-

cating deposition of orthodox (simple) organic carbon in

form of coal dust.

Based on aqua regia acid digestion for pseudo-total

metal contents in soils, the descending order of micronu-

trients was Fe[Mn[Zn[Cu. The mean concentrations

of Cu, Fe, Mn and Zn were 31.2, 19,786.2, 215.0 and

126.7 mg/kg, respectively. The Cu and Zn showed high

values than the world normal limit and less than the critical

soil concentration. Critical soil concentrations of trace

elements are the threshold concentrations in the soil

beyond which detrimental effects on vegetations are evi-

dent (Alloway 2013). The EF value between 0 and 1

suggest that the element is completely from crustal sources

or natural process, while the EF values [1 suggest

anthropogenic origin of trace elements (Zsefer et al. 1996).

The EF value of Fe and Mn indicates weathering of coarser

quartzitic sandstone and grits in the study area (Table 1).

The EF value of Mn (0.7) shows its conservative behavior

in the agricultural soils. Higher enrichment values of Zn

(6.1) and Cu (1.8) in mining areas with negligible Igeovalues indicating anthropogenic factors increasing pollu-

tion of soils due to coal mining activities. Bhuiyan et al.

(2010) reported that the soil with higher Zn attributed to

the geochemical weathering of sulfide minerals derived

from mine drainage. Long-term coal mining activities, coal Table

1Summaryofphysico-chem

ical

param

etersandmicronutrients

Range/meanvalues

pH

EC(ls/

cm)

MC

(%)

WHC

(%)

BD

(g/

cc)

SOC

(%)

SOM

(%)

Cu(m

g/

kg)

Fe(m

g/kg)

Mn(m

g/

kg)

Zn(m

g/

kg)

PLI

Range

6.3–7.8

49.6–1295

2.0–5.6

20.5–51.5

1.3–1.6

0.8–3.5

1.2–6.1

22.5–42.6

9718–33,032

113–323.23

61.7–158.9

0.4–0.7

Mean

7.0

240

3.3

39

1.4

2.2

3.8

31.2

19,786.2

215.0

126.7

0.6

EF

1.8

10.7

6.1

CF

0.8

0.5

0.3

1.2

I geo

\0

\0

\0

\0

WorldNorm

al(Bhuiyan

etal.2010)

24

26,000

550

60

Indianstatus(Singh2009)

1.8–960

4000–273,000

37–11,500

7–2960

Criticalsoilconcentration(A

lloway

2013)

60

–1500

70

Bull Environ Contam Toxicol

123

burning, and mine fires have been primary contributors of

Cu. Oorts (2013) and Pandey et al. (2015a, b) also found

high concentrations of Cu in PM10 in coal mining and mine

fire affected areas. Mandal and Sengupta (2006) found that

the topsoils and the soils collected from the different depth

profiles surrounding a coal industries in India were enri-

ched in the trace elements. The mean CF values of Cu, Fe

and Mn showed medium contamination category (\1) for

while moderate ([1 to\2) for Zn in the JCF. Based on PLI

(0.6) agricultural soils were not polluted because greater

number of elements (Cu, Fe and Mn) in medium contam-

ination category than moderate polluting element (Zn).

Hence, the soils near coal mining area or distant from

mining activities were showing no pollution load. The Igeovalues of micronutrients were\0 suggest no pollution with

respect to Cu, Fe, Mn and Zn.

The agricultural sites in the vicinity of coal mining areas

showed higher concentrations of Cu and Fe, especially in

the western Jharia region (JCF 5, JCF 6, JCF 7, JCF 8, JCF

9 and JCF 10) (Fig. 2). The area under open cast mining is

greater in the western JCF than eastern JCF region.

Moreover, the distance between agriculture land and min-

ing areas are physically separated by geomorpholical bar-

riers in the eastern Jharia. This imparts greater degree of

remoteness in the eastern Jharia compared to the western

Jharia. Thus soil/coal soil sources seems reasonable, par-

ticularly in the light of the fact that large exposed surface

areas of earth and stockpiles of coal piled around the mines

and at railway sidings often serve as a source of fugitive

dust. Hence, the general tendency for the levels to decline

gradually towards the non-mining areas, especially in the

eastern JCF and clearly point towards mining operations as

the primary source of suspended particulate matter (SPM)

in the region. In the monsoon, the mean value of SPM was

135 and 110 lg/m3 in the western and eastern JCF,

respectively (Agrawal 2015). Singh et al. (2012) studied

the geogenic sources of Cu, Mn, Fe and Zn in the Damodar

basin. Banerjee (2000) reported high concentrations of

trace elements in coal of JCF.

Pearson correlation coefficient was analyzed to ascertain

the sources of micronutrients in agricultural soils (Table 2).

The strong association corresponding to the couples Cu–

Zn, and Mn–Zn indicates geogenic origin of soil

micronutrients and derived mainly from weathering of

minerals present in the country rock. This also shows co-

precipitation of Cu with (hydro)oxides in soil material. The

positive correlation between Mn–pH and Mn–EC indicates

complex behavior of Mn in soils and is controlled by dif-

ferent environmental factors of which pH–EC conditions

are the most important (Kabata-Pendias 2000). These

chemical processes result into the formation of a large

number of oxides and hydroxides of Mn that reflect vari-

able stability and properties in agricultural soils around

JCF region. The oxides of Mn show large surface area,

which is not only important for soil reactions but also

highly associated with activities of microbes in agricultural

Fig. 2 Spatial variation in concentrations of a Cu, b Fe, c Mn, and d Zn

Bull Environ Contam Toxicol

123

soils (Kabata-Pendias 2011). The significant correlation

between Zn and organic matter (0.55) indicates biogenic

sources of Zn (Singh 2008). Correlation analysis by Pandey

et al. (2015a, b) shows natural and anthropogenic sources

of soil trace elements around JCF. Global comparison

shows higher concentrations of Fe, Mn and Zn in the coal

mine affected agricultural soils in northern Bangladesh

(Bhuiyan et al. 2010) and Gangreung coal field in South

Korea (Kim and Chon 2001).

In order to identify the fractions of micronutrients, the

results based on the three-step BCR fractionation proce-

dure is given in Table 3. The recovery of the BCR proce-

dure was calculated by dividing the sum of sequential

extractions of micronutrients with the values of micronu-

trients obtained by aqua regia digestion: Recovery

(%) = [(F1 ? F2 ? F3 ? F4)/(aqua regia diges-

tion)] 9 100. The mean recovery values indicate good

agreement between the total concentration and the sum of

BCR results. This shows that the precision and accuracy of

the sequential extraction procedure is inherently good, the

limiting factor being the inherent heterogeneity of the soil

samples (Tessier et al. 1979; Burt et al. 2003). In this study,

the mean values of Cu, Mn and Zn were less than certified

reference material indicating highly leached agricultural

soils in the JCF region.

The high concentrations of Exc and Reduc fractions of

micronutrients (Cu and Zn) were found in the soils around

western JCF region (Fig. 3). The Oxi fractions of Cu and

Zn showed less spatial variations in eastern and western

JCF region. The large spatial variation in the Res fraction

of Fe reveals loss of clay minerals in the agricultural soils

in JCF region. The fractions of Mn show some similarities

with that of Cu and Mn, thus, Mn shows higher availability

than Fe in most samples.

The descending order of Exc, Reduc and Oxi fraction are

as follows: Exc-Zn (44.1)[Mn (43.3)[Cu (14.6)[ Fe

(0.1); Reduc-Cu (48.2)[Mn (45.7)[Zn (31.7)[ Fe

(10.9); Oxi-Cu (18.6)[Zn (11.2)[Mn (2.5)[ Fe (1.4);

Res-Fe (87.7)[Cu (18.7)[Zn (12.9)[Mn (8.5). The

extraction of Zn was greater in the Exc fraction, while Cu

was dominantly extracted as Reduc fraction. The Mn was

more or less equally fractionated in Exc and Reduc frac-

tions. The percent values of micronutrients based on the

sums of the first three fractions (F1 ? F2 ? F3) show

following order: Mn (91.5 %)[Zn (87.1 %)[Cu

(81.3 %)[ Fe (12.4 %). The less concentration of

micronutrients in the Oxi fraction indicates highly oxidized

nature of soil microclimate and might be responsible for

the greater organic matter mineralization and insignificant

complexation of micronutrients in the soil organic residues

in the JCF region. The results show that the most mobile

and bioavailable micronutrient is Mn followed by Zn and

Cu, and least mobile and conservative element is Fe. The

Res fraction of Fe shows its strong affinity to minerals and

resistant components of the solid matrix, strongly bounded

to clay minerals and biologically unavailable (Kartal et al.

2006).

BCR fractionation of micronutrients reveals soil pollu-

tion in the JCF region. For example, anthropogenically

enriched Zn is dominantly found in the Exc and Reduc

fractions. Beckett (1989) showed that the Exc fraction

involves weak electrostatic interaction and ion-exchange-

able processes such as adsorption–desorption reactions and

lowering of pH. The micronutrients recovered in these

conditions may be thought to have been present as co-

precipitated with carbonate minerals but also as specifically

sorbed to some sites of the surface of clays, organic matter

Table 2 Summary of Pearson correlation matrix

Cu Fe Mn Zn pH EC OM

Cu 1

Fe -0.01 1

Mn 0.03 0.38 1

Zn 0.52 0.16 0.60 1

pH 0.43 -0.08 0.5 0.43 1

EC -0.03 0.36 0.7 0.15 0.58 1

OM 0.33 -0.43 0.17 0.55 0.12 -0.15 1

Table 3 Summary of comparative results of analysis of BCR fractions and the aqua regia digestion

Elements Sum of Extraction fractions

(F1 ? F2 ? F3 ? F4)

Pseudo-total Digestion (aqua

regia)

Recovery

(%)

BCR-141 R BCR-

142

NIST

2711

Mean Mean Mean Mean Mean Mean

(Pueyo et al.

2008)

(Bakircioglu et al.

2011)

Cu 29.4 31.2 94.7 47 25.3 114

Fe 19,113 19,786 95.7 – – –

Mn 198.9 215 93.1 270 527 –

Zn 131.5 126.7 104.7 – 79.6 350.4

Bull Environ Contam Toxicol

123

and Fe/Mn oxyhydroxides. The Cu pollution in soils shows

its greater concentrations in Reduc and Oxi fractions and

indicates the prevalence of strong redox conditions in soils.

The Reduc fraction act as sink for heavy metals because Fe

and Mn oxyhydroxides present as coating on mineral sur-

faces or as fine discrete clay particles in soil matrix. This

may involve precipitation, adsorption, surface complex

formation and ion exchange. The amorphous Fe and Mn

oxide have greater potential to sink micronutrients than its

crystalline Fe/Mn oxyhydroxides (Dong et al. 2000). Low

concentrations of micronutrients in Res fraction, except Fe,

show presence of highly weathered secondary minerals in

agricultural soils. The high Res Fe shows crystalline

structures of minerals responsible for greater leaching of

Cu and Zn (Davidson et al. 1998; Kartal et al. 2006).

Leaching of micronutrients accounts for poor correlation

between BCR fractions and pH/organic carbon and

indicates their multiple sources in the soils (Table 4),

hence, increase the potential exposure risk associated with

anthropogenic enrichment of metals.

PCA analysis shows that the factor 1 (F1) of Reduc, Oxi

and Res fractions have positive loading on Cu, Mn and Zn

(Table 5). Hence, F1 may be classified as geogenic factor

due to crustal origin of micronutrients in these fractions

and the similar geology of the eastern and western JCF

regions. The F1 of Exc fraction shows negative loading on

Cu, Mn and Zn except Fe indicating greater variation in the

origin of readily extractable micronutrient in soil. Similar

trend is shown by the factor 2 (F2) of BCR fractions

highlights that anthropogenically contributed metals are

weakly bound to soil constituents. Thus results of PCA not

only substantiate the geologic origin, but also reveal

specific differences in the anthropogenic origin of

micronutrients in agricultural soils in the JCF region.

Fig. 3 BCR fractions of micronutrients: a Cu, b Fe, c Mn and d Zn

Table 4 Summary of Pearson

correlation matrix for BCR

fractions

Element Exch Reduc Oxi Res Total BCR

pH OC pH OC pH OC pH OC pH OC

Cu -0.15 -0.19 0.39 0.31 0.73 0.26 -0.33 0.31 0.50 0.24

Fe -0.69 -0.07 0.00 -0.33 0.15 -0.57 -0.10 -0.43 -0.09 -0.46

Mn 0.10 0.49 0.34 -0.01 -0.23 0.23 -0.33 0.31 0.24 0.24

Zn 0.18 0.42 0.47 0.31 -0.18 0.41 -0.17 -0.11 0.28 0.48

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123

Acknowledgment

Authors are grateful to Ministry of Human Resource

Development, Government of India for funding the

research project of Mr. Rahul Agrawal (2013MT0143) at

Indian School of Mines, Dhanbad, Jharkhand, India. We

appreciate the anonymous reviewers for their valuable

comments, criticisms, and suggestions.

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