chapter materials d methods -...

CHAPTER -III

MATERIALS d METHODS

CHAPTER-3

MATERIALS AND METHODS

3.1 Study area

3.1.1. Bihar

Study site description

The study was carried out in two rural residential areas referred to as Semaria Ojha Patti

and Kastulia in Northern Bhojpur district of Bihar (Figure 3.1 & 3.2). Bhojpur district lies

between 25° 10' to 25° 40' Nand from 83° 45' to 84° 45' E inhabiting population of 22,

33415 with population density 903 km-2• The study area is located in the middle-Gangetic

alluvial plain amid the flood-prone belt of Sone-Ganga interfluve region at about 8 km

south of the Ganga River. Son River, a right-hand perennial tributary of the Ganga, flows

along the eastern boundary of the study area whereas the northern, southern and western

boundaries are marked by the Ganga course (Saha et al., 2010). This region has some of

the most fertile soil found in the country as new silt is continually laid down by the rivers

every year. The Gangetic alluvial plains are the most thickly populated region of India.

The middle-Gangetic plain (MGP), covering about 89% geographical area of Bihar

( -94,000 km2), holds potential alluvial aquifers. The tract is known for surplus food

production and intensive groundwater extraction for drinking, irrigation, and industrial

uses. The period of general rains (southwest monsoon) usually starts in third week of June

with a sudden rise of relative humidity to over 70% and a fall in temperature of between

about 5 and 8°C from about 35°C. The rainfall continues with intermissions till the end of

September or the early part of October. Annual normal rainfall in this part of MGP is

1 ,061 mm and nearly 88% of which is contributed during monsoon season (Saha et al.,

2010).

The northern part is flood-prone as the Ganga remains in high spate during monsoon

(Second Irrigation Commission Report, 1994). The region represents an agrarian economy

with a cropping intensity of 176%. Groundwater caters to the entire domestic need and

more than 80% of the irrigation requirement (Saha et al., 2010). Industrial demand for

Chapter- 3: Materials and methods

water is insignificant, as the study area is devoid of any manufacturing units. Recent

estimation by CGWB and GWD (2007) indicates groundwater extraction as 1.0 x 105 m3

km-2, against a replenishable resource of 3.21 x 105 m3 km-2, indicating large untapped

resource within the shallow aquifer system.

Semaria Ojha Patti ( -4 km2 in area) and Kastulia ( -3 km2 in area), with population of

3500 inhabitants and 1500 inhabitants respectively, are remote agricultural regions located

at nearly 30 km from Ara, the district's headquarter, lying between two major important

cities Patna and Buxar in the MGP in Bihar. Important land uses for economic activities to

the local people in the study area are subsistence agriculture and pastoral production.

Numerous mechanical bore wells were found in the area drilled by farmers for irrigation.

The depth of these wells ranges from 30 m to 60 m yielding few litres to 30 1 s·1 of water.

The main cultivation for livelihood sustenance is focused on paddy, wheat, maize, pulses,

and some cash crops (e.g. sugarcane) which are water intensive. The irrigation demand is

largely met by the extraction from shallow aquifers in the area. There are no potable water

supply networks in these rural localities; hence people rely mostly on groundwater

extracted through hand-pumps and dug-wells.

In Bihar, mining activities are limited to sand mining in Sone River. About 40 km length

of Sone River forms the part of southern and eastern boundary of the Bhojpur district. The

only managed sand-collecting centre is Koilwar (near Ara), which is about 5 km strips.

About 35 km length is not properly managed to gather the sand.

Hydrogeological settings

The MGP is predominantly alluvial deposits of Quaternary age. Most parts of the MGP

are characterized by a rapidly filling and aggradational regime. The channels are not

deeply incised in this area, and exposed bank sediments are those of the recent, aggrading

floodplain system and the alluvial sequences in this area range in age from Middle

Pleistocene to Holocene. The sedimentation in the narrow and entrenched Sone-Ganga

interfluve region of the active middle-Gangetic flood plain was influenced by sea level

fluctuation during the Holocene, causing increased aggradations and formation of large

fluvial lakes and swamps (Singh, 2001). A higher sediment supply in the MGP may be a

function of, apart from its greater proximity to the Himalayan front in the north, a higher

crustal shortening rate and a higher average Holocene uplift rate (Lave and Avouac, 2000).

47


These alluvial deposits are conventionally divided into the older alluvium (Pleistocene)

and the newer alluvium (Holocene) [Singh, 2001]. The older alluvium is present in the

ground above the flood level of the rivers whereas newer alluvium is confined to the river

channels and their floodplains. The newer alluvium, as distinct from the older unit, is

characteristically unoxidised and consists of sand and silt-clay, which were mainly

deposited in a fluvial and fluvio-lacustrine setting (Acharyya, 2005). The upper succession

of the newer alluvium is predominantly argillaceous (silty clay or sandy clay), followed by

fine to medium sand with occasional clay lenses forming the shallow aquifer (Saha et al.,

2010). The As is generally associated with many types of mineral deposits and in

particular those containing sulphide minerals such as arsenopyrite. However, elevated

concentrations are sometimes found in fine grained argillaceous sediments and

phosphorites. X-ray Diffractrometry results of As-safe older alluvial and As-contaminated

newer alluvial soil samples from the MGP reveals presence of minerals such as quartz,

muscovite, chlorite, kaolinite, feldspar, amphibole, and goethite (Shah, 2008).

The study area is confined within newer alluvium entrenched channel and floodplain of

the Ganga River (Figure 3.2). The area is underlain by a multi-layer sequence of sand

(aquifer) alternating with aquitards like sandy-clay and clay, down to depth of 300 m. In

the Sane-Ganga interfluves region, the Quaternary deposits within 300 m below ground

exhibit two-tier aquifer system. The shallow aquifer system is confined within 120-130 m

depth, followed by a laterally continuous 20-30 m thick clay/sandy-clay zone forming the

aquitard. The deeper aquifer system exists below this aquitard, which continues down to

240-260 m below ground (Saba, 2009). The shallow aquifer system is referred as active

channel deposit and marked as newer alluvium. The groundwater in deep aquifer remains

under confined to semi-confined condition in the affected Bhojpur district as revealed by

the pumping test carried out by Saha (2009). The deep aquifer can, therefore, be developed

for safe community based drinking water supply in the area.

48

Chapter- 3: Materials and methotb

84"0'0"E 85"0'0"E 86"0'0"E 87"0'0"E OO"''O"E

-- r;Mr J :::: ! ~ S-Grarite CJ Fe-CXe CJ C.GraJitic c001pex - R-Basalt - Mica Belt - Oi-GP - Gorowana CJ Allt.Mlnl

Siwalik - Vlnctly

• We~LO


gardening), and for very limited industrial uses. Smelting and mining activities use surface

water (mainly river water).

In hardrock states like Jharkhand, occurrences of groundwater are limited to weathered

and fractured zones. Since most of the area in this region is occupied by hardrock terrains,

limited availability of groundwater has resulted in growing number of over-exploited

blocks/mandals/taluks (Chatterjee and Purohit, 2009). In these rocks, the groundwater

occurs in shallow unconfined aquifers in the weathered residuum and under semi-confined

conditions in deeper fracture and joints. The presence of unsaturated fractures has been

detected down to 285 m depth but the unsaturated fractures are either non-productive or

completely dry (Dev Burman and Das, 1990). Thus the presence of groundwater is subject

to availability of secondary porosity i.e. joints, fractures, fissures and weathered residuum.

As per the report of CGWB (2006), many districts are facing falling levels of groundwater

in Jharkhand (Dhanbad, Dumka, Lohardaga, East-Singhbhum, West-Singhbhum, Giridih,

Palamu, Hazaribagh and Ranchi). Average annual rainfall varies from 1300 mm to 1400

mm, nearly 80% of which is received during the South-West Monsoon (June to

September).

Dhanbad district

Dhanbad and ]haria

Dhanbad is the most industrialised district in the State of Jharkhand with intense coal

mining activities and perhaps one of the most polluted Coalfields in the country. Dhanbad

district lies between 23°37' 3" Nand 24°04' 00" N latitudes and between 86°06' 30" E and

86° 50' 00" E longitudes. The district is bounded on the west by Giridih and Bokaro, on the

north by Giridih and Jamtara and on the east and south by Purulia district of West Bengal.

Dhanbad district covers an area of 2509.5 km2 with population density 510 km-2 (NATMO

maps, Survey of India, 1997). The district is drained by the rivers Damodar, Barakar,

Khudia and Kartri Nadi.

About 200 coal mines of Jharia coal fields, which produce prime cooking coal are located

around Dhanbad township. The large scale industries like coal washing, coke making, iron

and steel, fertilizer, cement and lead smelter are located nearby. Population here is

depended mainly on groundwater resources. Jharia coalfield, located in Dhanbad district

of Jharkhand state, is one of the single largest coalfields in India that has been actively

51


associated with coal mining activities for more than a century. The study area lies in the

heart of Damodar valley along the north of Damodar River. The coal basin extends for

about 38 km in the east-west direction and a maximum of 18 km in the north-south

direction covering an area of about 450 km2 (Sarkar et al., 2007). In view of large

population and unhygienic condition around Jharia coal belt, active population of the

Jharia coalfield faces acute shortage of clean drinking water. The coalfield covers a semi-

arid tract. The climate of the district is tropical in nature and experiences hot summer with

dry and cold winter. The mean maximum and minimum temperature is 31 °C and 20°C,

respectively. The average annual rainfall of 1280 mm is recorded for the Dhanbad district.

The south-west monsoon lasts from July to October and the area gets more than 85% of

the annual rainfall during these four monsoon months (Singh et al., 2007). Major

cultivation in 71127.88 ha agricultural land of the district is paddy, wheat, pulses and

vegetables etc.

Geological settings

Geological formations of Dhanbad district are composed of crystalline rocks which

belongs to Dharwar system (Archean) and southern half is occupied by great coal basin of

Jharia. Major rock groups are sandstone shale, limestone and gneisses, coal, fireclay and

china clay. Soils of the district have two broad categories: alfisols and ultisols comprising

red sandy soils, and red and yellow soils. The former is found in north western part,

mainly in forest area, and later is in the remaining portion of the district. The sedimentary

sequence in coal mining area of Dhanbad district is composed of 50% sandstone, 20%

shales, 25% intercalation of shale and sandstone, and 5% coal (Central Mine Planning &

Design Institute Ltd., 1981).

In the Jharia region, Precambrian basement metamorphic rocks (Granite, granite-gneisses,

quartzites, mica schists and amphibolites) are overlain by Talchir Formation (Greenish

shale and fine-grained sandstones) and are followed upward by Barakar Formation (Buff-

coloured coarse and medium-grained feldspathic sandstones, grits, shales, carbonaceous

shales and coal seams) which is the main coal bearing horizon. This in turn is overlain by

Barren Measures (Buff-coloured sandstones, shales and carbonaceous shales) and

followed upward by Raniganj Formation (Fine-grained feldspathic sandstones, shales with

coal seams), which is the second coal-bearing horizon in the coalfield (Sarkar et al., 2007).

52

fU'OU'E B5'0U"E 86'0U'E

26'0U'N

25'0U"N

JHAR'KHAN D 24'0U'N

23'0U"N

22'0U"N

--21'0U"N

fU'OU'E B5'0U'E 86'0U"E

Figure 3.3: Map depicting study sites in Jharkhand.

Ranchi district

Ranchi and Muri


87'0U'E

N

+ 26'0U"N 25'0U'N

24'0U"N

23'0U'N

22'0U'N

21'0'0'N

87'0U'E

Ranchi, one of the oldest districts of Jharkhand, lies between 23° 21' N and 23° 43' N

latitudes and 84° 00' E and 84° 54' E longitudes. The district has an area of 7,593 km2 with

53


a population density of -290 km-2• The annual average temperature is about 24°C and the

annual average rainfall varies from 1400 to 1600 mm (NATMO maps, CGWB & Survey

of India, 1997). Out of total geographical area, net shown area is -33%. The major crops

grown in the district are paddy (82.5%), wheat (1.6%), pulses (9.19%), oil seeds (3.14%),

maize (1.97%), and potato (1.6%) of the net shown area of the district. Groundwater

accounts for -60% of 25720.5 ha area under irrigation. The district has 16 big industrial

estates of which Heavy Engineering Corporation, Associated Cement Company Ltd.,

Electric Equipment Factory, High Tension Insulator Factory and Auxiliary Factories

comprising of thousands of small scale and cottage industries are important.

Geological settings

Physiographycally, the district comprises of three broad divisions: (a) the North western

part region, (b) the lower Chotanagpur plateau, and (c) the Ranchi plateau. Geologically

the district is underlain by Pre-cambrian metamorphic rocks e.g., Chotanagpur granites,

gneisses and schists. The district has variety of soils, such as red, yellow and sandy soils,

while red gravelly and older alluvium occurs occasionally. Recent alluvium occurs along

the river channels.

East Singhbhum district

The Singhbhum district is located in the state of Jharkhand between 86° 03' N and 86° 52'

N latitudes and between 22° 14' E and 22° 55' E longitudes. Area of the district is 5567.03

km2 with a total population of 16,12,411 having density of 290 km-2• The district forms a

part of northern fringe of the Chotanagpur plateau. Hills are alternating with valleys and

river basins. The northern part of the district is occupied by the Dalma range. The central

strip on either side of the Subarnarekha and its tributaries is plain land and flanked on the

north by mountain chain and on the south by a rugged mass of hills in which numerous

feeder streams take their rise. The district has dry climate with high day temperature

reaching up to 48°C and the mean temperature is 11 °C in winter. The average monsoon

rainfall is about 1400 mm (CGWB, NATMO, 2000).

The total cultivated area of the district amounts only 20% and forest covers an area of

22%. The remaining area being rocky or otherwise unsuitable for cultivation. The

principle food crop is paddy followed by maize, pulses etc. The East Singhbhum is one of

54


the most industrially developed district of Jharkhand. The major group of industries in the

district include metallurgical, automobile, chemical wires and cabel units. They are

concentrated in Tatanagar and Ghatsila. In addition to large scale industries, there are

many other small scale industries such as, khadi and village industries and cement based

industries.

Geological settings

The geological formation of the district consists largely of metamorphosed basic igneous

rocks of Archaean age. The significant formation i.e. the series of basic lavas flows of

Dalma hills, north of Jamshedpur (Tatanagar). Other rocks are schists, mica schists,

quartzite, pegmatite and conglomerate. The igneous rocks are generally altered to

epidiorite, copper, kyanite, iron ore, mica, atomic minerals as main minerals of the district.

The soils of the district have two broad categories: alfisol and ultisol comprising red

gravely, red sandy, red loamy, mixed red and black soil, red and yellow soil and lateritic

soil.

West Singhbhum district

Geographically, West Singhbhum district is located in the state of Jharkhand between 22°

01' N to 23° 1 0' N latitudes and between 85° 09' E to 86° 15' E longitudes. It covers an

area of 7834.84 km2 with population density of 228 km-1• The district forms part of the

southern fringe of the Chhotanagpur plateau and is highly mountainous tract, high hills

alternating steep valleys. The plain land in the district is largely confined to the valleys of

south Koel River and the Kharkhai River. Other rivers are Karo and tributaries of the

Subarnarekah and the Baitarni rivers. The climate is tropical in nature and experiences hot

summer with dry and cold winter with quite high day temperature generally -43°C in

summer and mean winter temperature-!! °C. The annual rainfall varies from 1400 mm to

1500 mm (CGWB, NATMO, 2000). Relative humidity remains high throughout the year.

There are hills alternating with plains, steep mountains, and deep forests on the mountain

slope. Agriculture is the main stay of the economy of the district. However, the agriculture

is mainly for subsistence and it is yet to be taken up on a commercial basis due to lack of

irrigation and other infrastructure bottlenecks. The district is endowed with abundant

mineral and forest resources. Net cultivated area in the district amounts to about 31% and

55


substantial part (22%) under forest cover. Paddy is the main crop followed by oilseeds,

maize and pulses. The district occupies a significant place in the industrial map of

Jharkhand due to its mineral resources. Iron ore mines are located in Noamundi,

Manoharpur blocks. Other minerals those are available in the district include limestone,

china clay, Manganese, soapstones etc.

Geological settings

The geological features of the district are composed of granites and gneisses of Archaean

age intrusive into the oldest sedimentary rocks now highly metamorphosed. Iron ore series

are originated from igneous rocks and equivalent to a larger part of Dharwar system. The

volcanic lava from Dalma hills is spreaded over north of the district. Major rock groups

are granite, diorite, pegmatite, shale, phyllite, quartzite, schists and epidiorite. In addition

to large iron ore deposites, manganese, limestone, mica, china clays etc. are also found in

the district. The soils of the district have two broad categories: alfisol and ultisol

comprising red gravely, red sandy, red loamy, red earth, red and yellow soils. The former

is found in the forested area and the latter is in the remaining portion of the district.

River basins

The numerous subsidiary divides radiating the Palamu-Ranchi uplands give rise to a

landscape, where there are a large number of small but youthful independent river basins,

the main streams emerging from which either merge to form larger more mature rivers or

themselves mature as they rich the plain. This is indicated by the change in the steepness

of slopes and increasing sinuosity of the rivers. Two major rivers, Damodar and

Subarnarekha, passing through the study area in Jharkhand have been investigated with

respect to their hydrogeochemical characteristics and quality aspects.

Damodar River Basin


The Damodar River basin extends from 21° 45' N to 23° 30' Nand 84° 45' E to 88° 20'E

(Figure 3.4) circumscribing parts of Jharkhand and West Bengal, which is about 11.7%

and 8.5% of the total geographical area of these two states, respectively (Singh et al.,

2005). It is a small-rain fed river (541 km long), originating from Khamerpet Hill (elev.

1068 m), near the tri-junction of Palamu, Ranchi and Hazaribag districts of Jharkhand. It

flows through the cities of Ramgarh, Bokaro, Dhanbad, Asansol, Durgapur, Bard wan and

56


Hawrah and joins the lower Ganga (Hooghly estuary) at Shayampur, 55 km downstream

of Hawrah. The river is fed by a number of tributaries at different reaches, the major ones

being the Bokaro, Konar, Jamunia and Barakar. The total catchment area of the basin is

about 23,170 km2, of this about three quarters of the total basin area lies in Jharkhand and

one quarter in West Bengal. The basin is characterized by a tropical climate with an

annual rainfall of about 1200 mm. The major part of the rainfall (82%) occurs in the

monsoon season (June-October) with a few sporadic rains in winter (Singh and Hasnain,

1999).

Hydrgeological settings

The Damodar River flows through variable topography and geology. The upland

catchment area in Jharkhand comprises highly dissected with deep ravines and bare hills

and the lower catchment area is within the delta plains of West Bengal. The basin geology

is characterized by rocks consisting of granites and granitic gneisses of Archean age,

sandstones and shales of the Gondwana age and the recent alluvials (Singh et al., 2005). In

the lower part of the basin, rocks of Tertiary age are covered by a thick veneer of

alluvium. The upland area of the basin is occupied by rocks of the Archean crystalline

complex and basic intrusives. The bulk of the crystalline complex consists of Late-

Precambrian gneisses and granites of batholithic dimension. The gneisses are non-uniform

in character and mostly granitic in composition (Singh and Hasnain, 1999). The lithology

of the reservoirs is dominated by the quartzites, quartz-mica-schists, biotite-gneiss, biotite-

schist, garnetiferous gneiss and schist, acid granulites with hornblend and amphibolites of

Archean age (Ghose, 1983). Gondwana rocks consisting of sandstones, shales and fire

clays with coal seams are forming the part of the catchments of Tenughat, Panchet and

Durgapur Barrage. Though not rich in metallic minerals, the Damodar basin is the

storehouse of Indian coal. Other than coal, fire clay, bauxite, mica, limestones are

associated with the geological formation of the basin. Besides domestic effluents, these

reservoirs receive the pollution load from the various sources like coal washeries, coal

mining effluent, mining dumps, coke industries, thermal power plants, mining machineries

and vehicular sources. These point and non-point sources of pollution severely affected the

quality of the water and sediments.

57

Subarnarekha River Basin



The Subarnarekha river flows eastwards through the Singhbhum copper mining region.

Continuing eastwards, it enters the Bay of Bengal after a 470 km course (Figure 3.4). The

longest river in South Bihar (now Jharkhand state, after administrative division of Bihar

state), the Subarnarekha originates from the eastern slopes of the Ranchi uplands and

flows eastwards up to Muri, galloping down the Hirni, Dasam, Johna and Hundru falls. It

then takes a sharp tum to the south and flows into the gap between the Ajodya

(Bhagmundi) hills on the east and the Ranchi uplands in the west. South of Chandil, the

river cuts through the Dalma range and turns south-east and flows along the valleys

between the Dalma and Dhanjori ranges towards Bahargora. Here it leaves the State,

meanders eastwards and takes an arcuate course to join the Bay of Bengal near

Nangaleshwar. Several tributaries of the river like the Sapghara, Gurma, Bhagalduba,

Dimnajhore, the Garra nadi, the upper parts of the Sanjai, the Kharkhai and other

tributaries in the Porahat-Dalma areas show evidences of headward erosion and river

capture. The course of Subamarekha cutting across the Dalma range gives the impression

of an antecedent drainage and erosion (Mahadevan, 2002).

The south-westernmost zone is a hilly area belonging to the Singhbhum belt, reaching an

altitude of 450-500 m. This area is covered by a fairly dense forest with scattered small

settlements in the valleys and small paddy fields close to the settlements. The area

between the bottom of the hills and right bank of the Subarnarekha River (e.g. the bank

located right downstream) is a strip 17 km long and 1.5 to 3.5 km wide. This area is

almost flat with paddy fields, small forested areas, barren land on rock outcrops, and with

important settlements in relation to the Cu or U mining sites. The left bank (e.g. the bank

located left downstream) of the Subarnarekha River is similar to the right bank, but it does

not bear any mining activity. The Cu smelter was built close to the main agglomeration of

the area (Ghatsila).

Total annual rainfall is nearly I ,300 mm, with around 300 mm per month during the

monsoon season between mid-June and mid-September. The temperature varies between

7°C and 36°C in winter and between 22°C and 45°C in summer. The Subarnarekha River

discharge has a steep increase in response to monsoon rains (increases by 2-3 m). This is

enhanced because the upper catchment dams are cleared at the beginning of rains for

58


safety. However, monsoon rains do not cause an immediate increase in the tributary

(hereafter referred to as nallah) flow rates, early precipitation being collected and stored in

the paddy fields, or recharging the shallow aquifers (Negrel et al., 2007).

94"0"U'E B5"0'!J"E 86"0'(J"E 87"0'U'E OO"O'O"E 27"0'(J"N-.-----.L------'------L------'------L----r-27"0'(J'N

26"0"()'

25"0'0'

JHARKHAND

23"0"()'

22"0"()'

ORISSA

N

+

BAY OF

BENGAL

26"0'U'N

25"0"0''N

24"0'U'N

23"0"U'N

22"0"0"N

21"0"0" 21"0"U'N

.a. Sampling locations

20"0'0' --River 20"0"0"N

94"0"U'E B5"0'0"E 86"0'!J"E 87"0'U'E OO"O'O'E

Figure 3.4: Map showing Subarnarekha and Damodar rivers with sampling locations for water and sediments.

59


Hydrgeological settings

It is underlain by folded and fractured Pre-Cambrian metasediments, mainly mica schists,

locally with quartzite and hornblende schists (Ghosh et al., 2002) and shows dominant

vertical fracturation. Mineral resources, mainly copper (Cu) but also uranium (U), are

associated with a Precambrian shear zone. Frequent quartzite outcrops in the river bed

imply that alluvial formations are discontinuous and cannot host continuous alluvial

aquifers. Only fissured aquifers were identified (Negrel et al., 2007).

3.2. Sampling and analysis

3.2.1. Sampling events and techniques

In order to quantify the nature of metal contamination, a survey of arsenic (As) and heavy

metals (cadmium, chromium, copper, lead, nickel, zinc etc.) in the waters, soils and stream

sediments was conducted in the state of Bihar and Jharkhand. Groundwater, surface water,

soil, and stream sediment samples were collected from the study area during the

investigation period. Sediment samples were collected from river systems presumably

impacted by mine tailings and smelting processes. Sediments were sampled at the water

sampling points along the waterways of river basins undertaken for the study (Figure 3.5).

A total of 340 water samples (313 of groundwater and 27 of surface water) were collected

for three seasons during the study period (2006-2009). Among these, 60 groundwater

samples (20 samples in each season) were collected from 20 shallow wells (15.24- 54.86

m depth) located in residential houses within the study areas in Bhojpur district of Bihar

based on general survey of water quality from the occupants of the respective houses. Rest

of the groundwater samples were collected from four districts viz., Dhanbad, Ranchi, East

Singbbhum and West Singhbhum district in Jharkhand state.

Seven sampling sites were established on the Subamarekha river system covering the four

investigated districts of Jharkhand and two on the Damodar river system (at Dhanbad,

Jharkhand). The sampling locations along the rivers are shown in Figure 3.4.

60


ojpur Bihar

Orissa

r:::=:::c==:r:::=;:=:::::::::~·.Kilometers · 250 . . 0 62iS 125

Figure 3.5: Map showing sampling locations for soils in Bihar and Jharkhand regions.

The sampling campaigns were realized in the monsoon season (August, 2006), winter

season (January, 2007) and summer season (May, 2009). The groundwater samples were

collected from hand-pumps. First, the water was left to run from the sampling source

(hand-pump) for 4-6 minutes to pump out the volume of water standing in the casing

before taking the final sample and then water samples were collected in pre-cleaned, acid

sterilized high density 250 ml polypropylene bottles. Surface water samples were collected

from Damodar and Subamarekha rivers passing through the study areas in Jharkhand at a

61


depth of 15 em below the surface. Additional water samples were collected in chromic-

acid-washed brown glass bottles and filtered with glass-fibre (GF/C) fllter papers for the

analysis of dissolved organic carbon (DOC).

A total of 28 soil samples (4 from the study sites in Bihar and 24 from Jharkhand) in

August, 2006 were collected from selected sites at a depth of about 10 em below the

surface after removing the top soil cover. A total of 9 Bed surficial sediment samples (2

from Damodar River and 7 from Subarnarekha River) were also collected along with

water from the river courses in August, 2006 with a plastic spade by scooping from the

upper 3-5 em of river bed representing contemporary deposits at a water depth of about 50

em. The soils and sediments were packed and sealed in clean wide mouth capped

polyethylene bags and brought to the laboratory, where they were dried at room

temperature (25-30°C), properly mixed and powdered and were kept in cold room at 4°C.

Plate 2: Affluents coming into Subarnarekha River from HINDALCO factory near Muri.

62

Chapter- 3: Ma1erials and metfwds

Plate 3: Collecting samples from a Mining site in Dhanbad region

Plate 4: A child from Kastulia (Bhojpur district, Bihar) having skin manifestations of Arsenic

3.2.2. Analytical methods

In the present work, an integrated analysis of four different environmental compartments -

gr-m:rndwater, surface water, sediment and soil - applying various Geostatistical tools is

carried out during the three sampling campaigns (between year 2006-2009) at various

locations distributed within the entire study areas.

Water

Hydrogeochemical parameters (major ions, trace elements, pH, Eh etc.) were monitored

periodically in the wells to investigate the temporal variations of the water quality. The

physical parameters namely pH, Eh, EC and TDS were measured in-situ by portable

corresponding digital instruments. Speciation of inorganic As in the groundwater samples

was performed in the field following the methodology described by Meng et al. , (2001).

The Asm and As v in water samples were separated using disposable anion exchange

63


cartridges (MetalSoft Center, NJ, USA), stuffed with aluminosilicate adsorbent, which

selectively adsorb As v but allow Asm to pass through in a pH range 4 to 9. Further, all

types of samples were immediately preserved in portable ice-box to minimize chemical

alteration until they were brought at the earliest possible to the laboratory where the

samples were kept at 4 oc in a thermostatic cold chamber until further processing and analyses. Water samples were filtered through 0.45flm Millipore membrane filter papers in

the laboratory. About 100 ml of sample was acidified with ultrapure HN03 (2% v/v) to pH

-2 to stabilize the dissolved metals and rest of the portion was kept unacjdified. Cations

were analyzed in the acidified fraction, whereas the unacidified fraction was used for the

analysis of anions.

Bicarbonate content was determined following the potentiometric titration method

(Clescerl et al., 1998). Anions and cation (NH/) were analyzed by Dionex ICS-90 Ion

Chromatography System using the specific analytical columns "IonPac AS 12A (4 x 200

mm)" for anions and "IonPac CS12A (4 x 250 mm)" for cations. Dissolved silica (~Si04)

and DOC were determined from the unacidified water samples by the molybdosilicate

method (Clescerl et al., 1998) and the vial digestion method using COD reactor

respectively; finally, absorbance measurements were carried out using a Varian UV-

Visible Spectrophotometer (CARRY 100 Bio) for both the parameters. Metals such as Na,

K, Ca, Mg, Fe and Mn were measured by Atomic Absorption Spectrophotometer (Thermo

Scientific M Series) in flame mode of analysis, whereas total dissolved As (AsT) and Asm

were quantified using AAS coupled with on-line hydride generator. The Asm was

measured in eluted fractions, whereas AsT was quantified using separate filtered acidified

samples. The total inorganic As content detection is normally based on the concentration

of Asm after converting all As species in the sample to the Asm form, as As v is

electroinactive (Greschonig and Irgolic, 1992). Samples were added with 20% (w/v) KI (2

ml in 20 ml sample) and kept for 15 min reaction period for the reduction of As v to Asm

prior to the analysis. Further, As111 was reduced to arsine(AsH3) by on-line hydride

generation (HG) using 1% (w/v) NaB~ in 0.1% (w/v) NaOH and 5M HCl as buffer

solution. The concentration of As v was subsequently calculated by subtracting Asm from

the AsT.

Merck-certified standard solutions and AnalR grade chemicals were used for quality

control during analyses. Milli-Q water was used during processing and analyses of the

64


samples. Standards for major and trace elements were analyzed as unknown intermittently

to check precision as well as accuracy of the analysis and the precision was :::;5%. The

AAS was programmed to perform analyses in triplicates and RSD was found within ±3%

in most of the cases reflecting the precision of the analysis. The analytical precision for the

measurement of cations and anions, indicated by the ionic balance error (IBE), was

computed on the basis of measured ions expressed in milliequivalent per liter. The values

were observed within a standard limit of ±5% (Domenico and Schwartz, 1998) with very

few exceptions coming beyond the limit but within ±10%, which attests the good quality

of the data.

Soils/Sediments

The major and trace elements in soils and sediments were determined by wavelength

dispersive X-ray fluorescence (WD-XRF) Spectrometry and energy dispersive X-ray

fluorescence (ED-XRF) spectrometry, respectively. The Canadian soil standards (SO-l,

S0-2, S0-3, and S0-4) were analyzed as unknown samples for major and trace elements,

and the reproducibility was found in the range of 90-95%. The physical parameters

namely pH, Eh and EC were measured in aqueous suspensions of soils and sediments in

the ratio 1:2.5 (solid:liquid), in deionized water. Sequential loss on ignition (LOI) method

was used to estimate the organic and carbonate content of soils and sediments (Heiri et al.,

2001 ). The elemental C, H, N and S were measured using CHNS-0 Analyzer (EURO EA

Elemental analyzer). BCR extraction method was followed for the sequential extraction of

As and other heavy metals in soils and sediments. The semi quantitative mineralogical

analysis of soils/sediments was carried out using Philips X'Pert X-ray Diffraction System.

The details of analytical techniques and analytical instruments used in the analyses are

given below.

Water analysis

pH, Redox potential (Eh), Conductivity(EC) and TDS

The pH, Eh, EC and TDS were measured in unfiltered water samples using respective

digital probes (HACH). The pH and Eh probes were calibrated with buffer solution of pH

4, 7 and 9.2. The samples were stirred continuously in order to maintain homogeneity

before noting down the pH. The EC probe was calibrated and set for O.OlM KCl solution

(1.413J.LS cm-1 at 25°C).

65


Bicarbonate (HCOJ)

The HC03- content was determined following the potentiometric titration method

(Clescerl et al., 1998). Bicarbonate standards ranging between 100-1000 ppm were

prepared from NaHC03. 50 ml sample and a series of bicarbonate standards were titrated

against 0.02N HCl. The end point was noted at pH 4.5. A standard graph was plotted

between HC03- standards and volume of the acid consumed during titration. The

concentration of HC03- in the samples was calculated using linear regression equation of

the standard plot.

Dissolved silica (IL!Si04)

The ~Si04 content was determined by the Molybdo-silicate method (Clescerl et al.,

1998). Silica standards were prepared, ranging between 5-20 ppm from natrium silicate

(Na2Si03). 20 ml each of sample and standard was pipetted out in 50 ml volumetric flask

and 10 ml of ammonium molybdate solution (prepared by dissolving 2 gm ammonium

molybdate in 10 ml of distilled water; 6 ml of concentrated HCl was added and final

volume was raised to 100 ml by distilled water) and 15 ml of reducing reagent (prepared

by mixing 100 ml metol sulphite solution, 60 ml 10% oxalic acid and 120 ml 25%

sulphuric acid, and making the total volume 300 ml by adding distilled water) was added

and mixed well. Metol sulphite solution was prepared by dissolving 5 gm metol in 210 ml

distilled water and 3 gm sodium sulphite was added and the volume was made up to 250

ml by adding distilled water. The samples was stirred properly and kept for 3 hours to

complete the reaction. The optical density was measured at 650 nm using Varian UV-

Visible Spectrophotometer (CARRY 100 Bio). A Graph between standard concentration

and optical density was drawn and concentrations of samples were recorded from it.

Dissolved Organic Carbon (DOC)

The 100-ppm stock solution was prepared from potassium perpthalate (C8H50 4) salt.

Standards ranging between 5-25 ppm were prepared by serial dilution of the stock

solution. 10 ml of sample and standard were added to Erlenmeyer flask; 0.4 ml of buffer

solution of pH was added and stirred at a moderate speed for 10 minutes. Persulphate

powder pillow was added to sample and reagent blank vial. Then 0.3 ml deionized water

was added to the reagent and 0.3 ml prepared sample was added to sample vial and stirred

to mix. Blue indicator ample was inserted in each vial. The vial assemblies were capped

66


tightly and placed in the COD reactor for 2 hours at 103-105°C. The vial assemblies were

removed carefully from the reactor and placed them in a test tube rack. The vials were

allowed to cool for 1 hour for accurate results. The optical density was taken at 430 nm

using Varian UV- Visible Spectrophotometer (CARRY 100 Bio ). The concentration of DOC

was obtained using linear regression equation of the standard plot.

Analysis using Ion-Chromatograph

Anions (F, cr, N03-, Poi-, and SOl) and cation (N~ l were analyzed by Dionex ICS-90 Ion Chromatography System using the specific analytical columns "IonPac AS12A (4 x

200 mm)" for anions and "IonPac CS12A (4 x 250 mm)" for cations. The samples were

filtered with 0.22 mm nylon filter paper at the time of analysis. Mixed standard solutions

(Merk) were used for calibration. The stock standard solution was diluted to 1 ppm, 5ppm

and 10 ppm and calibration was made with the diluted range of mixed standards. The

standards were also run intermittently to check the precision of the analysis which was

::::95%.

Dionex ICS-90 Ion Chromatography System

An ion chromatography system typically consists of a liquid eluent, a high-pressure pump,

a sample injector, a separator column, a chemical suppressor, and a conductivity cell.

Before running a sample, the system is calibrated using a standard solution. By comparing

the data obtained from a sample to that obtained from the standard, sample ions can be

identified and quantified. A computer running chromatography software automatically

converts each peak in a chromatogram to a sample concentration and produces a tabulated

printout of the results.

The system has incorporated resin based column chemistries and innovative conductivity

detection with programmable solvent delivery, for sensitive and accurate analysis of

inorganic ions. Ion-chromatography depends upon the separation of anions on anion-

exchange resin column, according to their size and charge by elution with dil.

NazC03/NaHC03 solution. The separated anions are then converted to the corresponding

free acids by passing the eluent through the column of cation exchanger (W-form). The

presence of free mineral acids, even at very low concentrations, causes a change in the

conductivity of the final eluent, which may be readily measured. Such a methods using

suitable standards provide a measure of the concentrations of individual ions.

67


Eluent preparation

The eluent for anion was prepared by pipetting 5.4 ml of 0.5 M Na2C03 plus 0.6 ml of 0.5

M NaHC03 into a 1 1 volumetric flask. Milli-Q water with a specific resistance of 18.2

megohm-em was used to dilute the concentrate to a final volume of 1 1. For cations, 10.0

ml of 1.0N Methanesulphonic acid (MSA) eluent concentrate was pipette into a 1 1

volumetric flask and diluted to 1 1 using milli-Q water with a specific resistance 18.2

megaohm-cm.

Regenerant preparation

A dilute sulfuric acid regenerant is used for anion analyses and a tetrabutylammonium

hydroxide (TBAOH) regenerant is used for cation analyses.

Atomic absorption Spectrophotometer

Atomic absorption spectrophotometry is based on the measurement of the decrease in light

intensity from a source (hollow cathode lamp) when it passes through a vapour layer of the

atoms of the analytic element. The hollow cathode lamp produces intense electromagnetic

radiation with a wavelength exactly the same as that absorbed by the atoms, leading to

high selectivity. The radiation from the hallow cathode lamp passes through a flame into

which the sample is aspirated. Consequently the metallic compounds are decomposed in

the flame and metal is reduced to the elemental state, forming a cloud of atoms. These

atoms absorb a fraction of radiation in the flame. The decrease in radiant energy increases

with the concentration of the sort-for element in the sample, according to Beer's law. The

resultant radiant energy passes to a monochromatic light to eliminate extraneous light

resulting from the flame and finally to a detector and recorder (read-out system).

Graphite Furnace (GF)

Graphite furnace is the replacement of flame as an atomizer and sample holder for some

element existing at low concentrations in the samples. The furnace consists of a hallow

graphite cylinder placed so that the light beam passes through it. A small sample of up to

100 J.d volume is placed in the tube through in the tip. An electrical current is passed

through the tube for heating-slowly at first to dry the sample and then rapidly

incandescence. The volatile metals are vaporized in the hollow portion of the tube and the

68

Chapter- 3: Materials arui methods

absorption of the metal atoms is recorded as a spiked-shaped signal. The detection limits

with the graphite furnace are -100 times better than those from a conventional lamp.

Hydride Generator (HG)

This is an addendum to Atomic Absorption Spectrophotometer (AAS) which forms

arsenic hydride by the reaction with alkaline sodium tetrahydroborate (NaB.f-4) with

acidified samples. The inclusion of on-line HG generally increases the sensitivity of

detection and reduces the possible interferences from the sample matrix.

Soil analysis

pH, ECandEh

Aqueous suspensions were prepared from the materials in the ratio 1:2.5 (solid:liquid), in

deionized water. The suspensions were stirred for 5 minutes, left to rest for 30 min. and

stirred again for 2 min. Finally pH of soil suspension was measured. The aqueous

suspensions were allowed to settle for 1 hour and then conductivity (EC) of the

supernatant liquid was measured.

Redox potential (Eh) is an electrical measurement that shows the tendency of a soil

solution to transfer electrons to or from a reference electrode. It is a reading of voltage

difference between a working electrode such as a Pt electrode and a reference electrode

inserted into the soil. From this measurement we can estimate whether the soil is aerobic,

anaerobic, and whether chemical compounds such as Fe oxides or nitrate have been

chemically reduced or are present in their oxidized forms. The pH, EC and Eh

measurement in the aqueous suspension of soils and stream sediments was made by the

soil and water analysis kit in the laboratory.

Total Organic Matter and Carbonate

The weight percentage of organic matter and carbonate content in soils and sediments was

measured by means of Loss on Ignition (LOI) method, which is based on sequential

heating of the samples in muffle furnace. After oven-drying of the samples of constant

weight in ceramic crucible overnight at -1 05°C, organic matter was combusted in a first

step to ash and carbon dioxide at a temperature between 500-550°C. The LOI was then

calculated using the following equation:

69

Clulpter- 3: Materials and methods

LOI55o = ((DWw5-DW55o)IDWw5)*lOO

where LOI550 represents LOI at 550°C (as a percentage), DW105 represents the dry weight

of the sample before combustion and DW 550, the dry weight of the sample after heating to

550°C (both in gm). The weight loss during the reactions is measured by weighing the

samples before and after heating. The weight loss is proportional to the amount of organic

carbon contained in the sample.

In the second step, the same samples were heated at 950°C resulting in evolution of carbon

dioxide from carbonate, leaving oxide and LOI was calculated as:

LOI95o = {(DW55o-DW95o)IDWw5}*lOO

where LOI950 is the LOI at 950°C (as a percentage), DW550 is the dry weight of the sample

after combustion of organic matter at 550°C, DW950 represents the dry weight of the

sample after heating to 950°C, and DW 105 is again the initial dry weight of the sample

before the organic carbon combustion (all in gm). Assuming a weight of 44 g mor1 for

carbon dioxide and 60 g mor' for carbonate (C032-), the weight loss by LOI at 950°C

multiplied by 1.36. The resultant value refers to the weight of the carbonate in the original

sample.

X-ray Fluorescence (XRF)

X-ray Fluorescence (XRF) IS a multi-elemental analytical technique that uses the

interaction of X-rays with a material to determine its elemental composition. XRF is

suitable for solids, liquids and powders, and is non-destructive in most circumstances.

There are two main XRF methodologies - energy dispersive (EDXRF) and wavelength

dispersive (WDXRF). Typically EDXRF covers all elements from sodium (Na) to

uranium (U), whilst WDXRF can extend this down to beryllium (Be). Concentrations can

range from 100% down to ppm and in some cases sub-ppm levels. Limits of detection

depend upon the specific element and the sample matrix, but as a general rule, heavier

elements will have better detection limits.

70


Interaction of X-rays with Matter

The interaction of X-rays with matter is more complex than simply 'passing through'. On

reaching a material, some of the X-rays will be absorbed, and some scattered- if neither

process occurs, the X-rays will be transmitted through the material. When absorption

occurs, the X-Rays interact with the material at the atomic level, and can cause subsequent

fluorescence- it is this X-ray Fluorescence which forms the basis of XRF spectroscopy.

The technique is based on the principle that when a sample is bombarded with energetic

X-rays, gamma radiation or photons, it gives rise to secondary radiation as electron drops

into vacant positions in the inner orbitals. The emitted X-rays have energies (energy

difference between the knocked out and the replacement elelctron) characteristics of the

particular atom. Thus, the energy of the emitted fluorescent X-ray is directly linked to a

specific element being analyzed. It is this key feature which makes XRF such a fast

analytical tool for elemental composition. In general, the energy of the emitted X-ray for a

particular element is independent of the chemistry of the material. The energy

(wavelength) of the emitted radiation yields a qualitative analysis of the elements, while

the intensity of the radiation provides a quantitative ananlysis with reference to a standard

samples.

Energy Dispersive XRF (ED-XRF)

An energy dispersive detection system directly measures the different energies of the

emitted X-Rays from the sample. By counting and plotting the relative numbers ofX-Rays

at each energy, an XRF spectrum is generated.

Working principle: The principle of the energy dispersive (ED) detector is based on the

generation of electron-hole pairs in a semiconductor material (often silicon). An incident

X-Ray is absorbed by the detector material, and will cause one or more electron-hole pairs

to form. Once this has occurred, the electrons are pulled off the detector, and the resulting

current is proportional to the number of electron-hole pairs, which in itself is directly

related to the X-ray energy. This analysis process is repeated at a very high rate, and the

results sorted into energy channels. With an ED-XRF system, an entire spectrum is

acquired virtually simultaneously, so that elements from across most of the periodic table

can be detected within a few seconds.

71


Wavelength Dispersive XRF (WD-XRF)

A wavelength dispersive detection system physically separates the X-rays according to

their wavelengths. The X-rays are directed to a crystal, which diffracts the X-rays in

different directions according to their wavelengths (energies). On a sequential system, a

detector is placed at a fixed position, and the crystal is rotated so that different

wavelengths are picked up by the detector. The XRF spectrum is built up point by point.

Working principle: An excitation source, generally an X-ray tube, while emitting X-rays

produces a primary beam of energetic radiation which excites fluorescent X-rays in the

sample. Alternative excitation sources are radioactive source emitting gamma rays or

photons from accelerator. The sample is mounted as a pellet which was made by mixing

with boric acid. The resultant fluorescent X-rays are passed through a collimator to select

a parallel secondary beam, which is dispersed according to wavelength by diffraction with

a crystal monochromator. The monochromatic X-rays in the secondary beam are counted

by the detector, which rotate at the rate twice that of the crystal to scan the spectrum of

emitted radiation.

Pressed pellets were prepared by using aluminum cups. These cups were filled with boric

acid and 1 g of the finely powdered sample was put on the top of the boric acid and

pressed under a hydraulic press at 20 tons of pressure to get a pellet for XRF spectrometry.

CHNS-0 Analyzer

CHNS-0 is an elemental analyzer dedicated to the simultaneous determination of amount

(%) of carbon (C), Hydrogen (H), Nitrogen (N), Sulfur (S) and Oxygen (0) contained in

inorganic, organic and polymeric materials and in substances of different nature and origin

i.e. solid, liquid and gaseous samples. The functional principle involves dynamic,

spontaneous combustion with subsequent chromatographic separation.

The dried grinded samples weighed in milligrams housed in a tin capsule are dropped into

a quartz tube at 1000°C with constant flow of helium (carrier gas). A few seconds before

the samples drops into the combustion tube, the steam is enriched with a major amount of

high purity oxygen to achieve a strong oxidizing environment for complete

combustion/oxidation of substances. The combustion gas mixture is driven through an

72


oxidation catalyst (W03) zone, then through a subsequent copper zone which reduces

nitrogen oxides and sulphuric anhydride (S03) eventually formed during combustion on

catalyst reduction to elemental nitrogen and sulphurous anhydride (S02) and retains the

excess oxygen. The resulting four components of the combustion mixture are detected by

a Thermal Conductivity Detector in the sequence N2, C02, H20 and S02. In case of

Oxygen which is analyzed separately, the sample undergoes immediate pyrolysis in a

helium steam which ensures quantitative conversion of organic oxygen into carbon

monoxide separated on a GC column packed with molecular sieves. The measuring range is

0.01- 100%.

X-ray diffraction (XRD)

X-ray diffraction (XRD) is a versatile, non-destructive technique that examines the

deflection of X-ray beams by crystal lattices and reveals detailed information about the

mineral composition and crystallographic structure of natural and manufactured materials.

X-rays can be diffracted from the repeating patterns of atoms that are characteristic of

crystalline materials. The constructed diffraction patterns give evidence for the

periodically repeating arrangement of atoms in the crystal.

In order to determine the major mineralogical components of soil and sediment samples,

an X-ray diffraction (XRD) analysis was performed on representative samples. Samples

were carefully prepared, mounted and aligned, prior to the measurements. This analysis

was performed with Philips X' Pert X-ray Diffraction System using Cu-Ka radiation. XRD

analysis was carried out from 5 to 90°28 and a step scan of 2.4° min-1•

Sequential extraction of arsenic and heavy metals in soils/sediments

Sequential extractions provide semi-quantitative information on element distribution

between operationally defined geochemical fractions in soils, sediments and waste

materials (Cappuyns et al., 2007). Sequential extractions can give an indication of the

'pools' or 'sinks' of heavy metals that are potentially available under changing

environmental conditions. In addition to total concentrations, the mobility and availability

of arsenic and other potentially toxic elements must be assessed in order to elucidate their

behaviour in soils and prevent possible toxic hazards (Banat et al., 2005). The importance

of metal mobility and bioavailability in the environmental risk assessment of contaminated

soils is widely recognized (Samsoe-Petersen et al., 2002).

73


Mobility and bioavailability of heavy metals in soil depends on their speciation or

fractionation. The Community Bureau of Reference (BCR) method has been widely used

in the fractionation of heavy metals including arsenic for both soil and sediment

(Quevauiller et al., 1993; Fernandez et al., 2004; Cappuyns et al., 2007).

The BCR extraction procedure is an operationally defined speciation sequential scheme

developed under the auspices of the European Bureau Communautaire de R 'ef'erence,

used to study the fractionation of trace elements and heavy metals in environmental solid

samples (sediments, soils, waste residues, etc.), which are sequentially extracted with three

reagents of increasing reactivity giving four fractions ( 1, 2, 3 and residual). The

philosophy behind sequential procedures is that each successive reagent will dissolve

different components, so from the study of fractionation patterns of the elements one can

infer information (1) about the mobility, pathways or bioavailability of the studied

chemical element or (2) to assess the potential hazard that the samples can pose to the

environment (Pardo et al., 2004). According to the method, metal is divided into acid

soluble/exchangeable, reducible, oxidisable and residual fractions. The exchangeable

fraction is considered readily mobile and bioavailable, whereas the residual fraction

appears to incorporate into crystalline lattice of soil and becomes relatively inactive.

Reducible and oxidisable fractions could be relatively active depending on soil properties.

The methods of sequential extraction of soils were developed in order to more precisely

define the single fractions of elements in a soil. Sequential extraction usually necessitates

from three to seven steps. Unlike sequential extraction, single extraction method only

focuses on the metal bioavailable fraction.

To examine the fractionation and mobilization potential of As and other heavy metals, a

sequential extraction procedure (SEP), consisting of four steps, was applied for 24 soil

samples ( 4 from Bihar and 20 from Jharhand). The principle is to expose the pulverized

sample to different solvents, each of which is able to extract mainly one specific fraction.

BCR Scheme of extraction

The sequential extraction was performed by sequentially extracting 1 gm of the soil

samples in a 100 ml centrifuge tube at room temperature using a mechanical shaker. After

shaking, the soil suspension was centrifuged at 3000 rpm at each step and the supernatant

74


solution was decanted, filtered through a Millipore filter (pore size 0.45 mm) and put aside

for analysis. After each of the first two steps, the soil residue was washed every time with

10 ml H20 (15 min centrifuge). After centrifuging, the washing solution was carefully

decanted and discarded.

For elemental analysis, the solid residue fraction samples (av. 0.5 g) was transferred to the

Teflon crucible and 2 ml of aqua regia [3HC1 (37%):1 HN03 (65%)]. Additionally 5 ml

hydrofluoric acid (HF) was added to dissolve the very stable silicate minerals that could

also carry As and other heavy metals load. The crucible was heated for 1.5 hrs at 100°C

and then allowed to cool down to room temperature. 5.6gm of Boric acid crystal (H3B03)

was dissolved in 20 ml distilled water and then added to the crucible content that was

made up to 100 ml. The solution was transferred to polypropylene bottles for storage. The

sample was left undisturbed overnight to allow the formation and setting of borosilicate

from the solution. The gelatinous precipitate is separated by centrifugation. The solutions

thus obtained were analyzed by AAS (Thermo Scientific M Series AA Spectrophotometer)

in graphite furnace mode for As, Fe, Mn, Cu, Zn, Pb, Ni and Cr. The highly volatile AsF3

and AsPs might be produced during digestion and lead to a loss of As from the sample.

The detailed flow chart of the procedure for sequential extraction method is given below:

75


[ 1 gm oven dried sample J

Add 40 mL OJ 1 M Acetic acid -(CH3COOH)

- Shake for 16 hours luble fraction Acid so

(Exchan

I geable) - Centrifuge at 3000 rpm for 20 min.

Remove the supernatant, filter and -preserve at 4°C for analysis

l Residues ] - Add 40 mL OJ M NH20H.HC1

Reducible fraction _, Adjust at pH-2 with cone. HN03

r-1 Repeat the above steps (*) \

l Residues ] f-1 Add 10 mL 8.8 M HzOz (>30% w/v) H Keep at room temperature for 1 hour r- Heat in Water-Bath at 85°C for 1 hour

Oxidizable fra ction Until reduces to near dryness (

chapter materials d methods -...

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