Arch Environ Contam Toxicol (2009) 56:693–706 DOI 10.1007/s00244-008-9239-x
Sources of Arsenic and Fluoride in Highly Contaminated Soils Causing Groundwater Contamination in Punjab, Pakistan Abida Farooqi Æ Harue Masuda Æ Rehan Siddiqui Æ Muhammad Naseem
Received: 13 May 2008 / Accepted: 8 September 2008 / Published online: 21 October 2008 Ó Springer Science+Business Media, LLC 2008
Abstract Highly contaminated groundwater, with arsenic (As) and fluoride (F-) concentrations of up to 2.4 and 22.8 mg/L, respectively, has been traced to anthropogenic inputs to the soil. In the present study, samples collected from the soil surface and sediments from the most heavily polluted area of Punjab were analyzed to determine the Fand As distribution in the soil. The surface soils mainly comprise permeable aeolian sediment on a Pleistocene terrace and layers of sand and silt on an alluvial flood plain. Although the alluvial sediments contain low levels of F, the terrace soils contain high concentrations of soluble F(maximum, 16 mg/kg; mean, 4 mg/kg; pH [ 8.0). Three anthropogenic sources were identified as fertilizers, combusted coal, and industrial waste, with phosphate fertilizer being the most significance source of F- accumulated in the soil. The mean concentration of As in the surface soil samples was 10.2 mg/kg, with the highest concentration being 35 mg/kg. The presence of high levels of As in the surface soil implies the contribution of air pollutants derived from coal combustion and the use of fertilizers. Intensive mineral weathering under oxidizing conditions produces highly alkaline water that dissolves the F- and As adsorbed on the soil, thus releasing it into the local groundwater.
A. Farooqi (&) Department of Environmental Sciences, Fatima Jinnah Women University, The Mall, Rawalpindi, Pakistan e-mail:
[email protected] H. Masuda Department of Geosciences, Osaka City University, 3-3-138, Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan R. Siddiqui M. Naseem Geosciences Laboratory, Geological Survey of Pakistan, Chak Shehzad, Islamabad, Pakistan
The degradation of groundwater quality arising from urbanization, industrialization, and agricultural activity is a serious global problem. In terms of contamination of groundwater and soil, arsenic and fluoride are the most critical elements due to their high toxicity (Smedley and Kinniburgh 2002). Arsenic is a mobile element that circulates in various forms through the atmosphere, water, and soil before ending up in the natural sink, viz., bottom sediments (Peterson et al. 1981; Savory and Wills 1984). Arsenic originates from both natural and anthropogenic sources, viz., industry, mining, farming, weathering of rocks, and atmospheric deposition (Smith et al. 1998; Patel et al. 2005). Even at low concentrations As is of particular concern because of its toxicity, its status as a carcinogen, and its potential impact on surface and ground waters and soil–plant ecosystems (WHO 2003). High levels of Ascontaminated groundwater ([10 lg/L) and soils ([5 mg/ kg) have been reported in many parts of the world, including Argentina, Bangladesh, Chile, China, Hungary, parts of India, Mexico, Taiwan, Vietnam, and many parts of the United States (Smedley and Kinniburgh 2002). Fluoride is a common constituent in rocks and soils. The major sources of high F- in soils include weathering of fluorine-rich minerals in country rocks (Tripathy et al. 2005), as well as various anthropogenic sources. The primary F- sources include the manufacture of bricks, iron, fertilizers, and glass and the operation of coal-fired power stations and aluminum smelters (Israel 1974; Polomiski et al. 1982; Gritsan et al. 1995). Contamination of air and groundwater by F- and As, arising from the combustion of coal, have been implicated in serious diseases over large areas of southern China (Zheng et al. 1996; Finkelman et al. 2002) and Inner Mongolia (Wang et al. 1999).
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Pakistan is strongly dependent on agriculture, which contributes about 24% of the Gross Domestic Product (GDP), accounting for nearly half of the employed labor force, and is the largest source of foreign exchange earnings. Although agricultural activity occurs in all areas of Pakistan, most crops are grown in Punjab and Sindh, along the plains of the Indus River. Punjab has the largest agricultural area and, therefore, accounts for the highest consumption of fertilizers (Food and Agriculture Organization 2004). Phosphate fertilizers were introduced in Pakistan in 1959/1960. Fertilizer consumption has increased threefold over the past 30 years, reaching 1 million nutrient tons in 1980/1981, 2 million tons in 1992/ 1993, and 3 million tons in 2002/2003. It is projected that over the next 10 years the consumption of fertilizer nutrients will increase at 2–3% per annum (Food and Agriculture Organization 2004). Contamination of groundwater As and F- in Punjab (Lahore and Kasur), Pakistan, has been reported (Farooqi et al. 2007a, b), where we demonstrated that groundwater in a shallow aquifer at 20- to 27-m depth is heavily polluted (maximum As and F- concentrations of 2.4 and 22.8 mg/L, respectively). A deeper aquifer also contained high
Arch Environ Contam Toxicol (2009) 56:693–706
concentrations of As and F-. Samples of rainwater and locally consumed coal and fertilizer also contained As and F-, indicating that these were the sources of groundwater pollutants in the area, entering the groundwater via contaminated soil (Farooqi et al. 2007a, b). To understand the entire process of groundwater contamination, it is important to determine the distribution of As and F- in the soil, as well as its geochemical properties. This article aims to describe the spatial distribution of As and Fin the soils and estimate their sources in the soil that ultimately contaminates the groundwater in the studied area.
Materials and Methods Description of Study Area The present study area is situated 40–45 km south of Lahore, the primary city in Punjab, Pakistan, along the east bank of River Ravi (Fig. 1). The Punjab Province occupies part of the Indus Plain, located on a fluvial plain made up of sediments derived from the Ravi and Satluj rivers, as well as Pleistocene aeolian terrace deposits. The surface
Fig. 1 Index map showing the location of the study area and sampling points. White area represents the terrace
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soils consist mainly of permeable, organic-poor aeolian sediment on the terraces and layers of sand and silt on the alluvial flood plain. The alluvial sediments occasionally reach several thousand feet in thickness (Greenman et al. 1967). In many aspects, the terrace soils are largely homogeneous throughout the area, being reddish-brown to grayishbrown in color, and mostly moderately coarse- and medium-grained, and containing a high percentage of fine to very fine sand and silt. Most of the soils are moderately to highly permeable, are rich in lime, are depleted in phosphorus, have a pH of C8.5, and are at least 75 cm in depth (Greenman et al. 1967). The Lahore district is drained by the Ravi and Satluj rivers, which flow into Pakistan from India (Fig. 1). These rivers have a recharge source, however, and recharge has diminished since canal irrigation began in the 17th century (Greenman et al. 1967). Seepage from the canals has also led to an increase in the water table in areas of shallow groundwater, in which the salt concentration has became extremely high ([2000 ppm); deeper groundwater remains relatively unaffected (salt content, \1000 ppm [Israel 1974]). Groundwater is an important water source in the study area: [80% of the village water supply is obtained via hand pumps installed by private households in areas of shallow groundwater. Sampling and Analytical Methods We analyzed three types of soil samples: (a) 42 samples of surface soil; (b) 41 samples of soils taken from a depth of *30 cm at the same locations as the surface soils (both a and b) formed on aeolian sediments); and (c) 3 samples of surface sediments and 26 sediments taken from four excavations (outcrops) up to 500 cm deep from the surface of the river banks of the alluvial plain. The sampling was carried out in April 2005, at the end of the dry season. Soil samples were grabbed from the area. Soil and sediment samples were dried in an oven at 110–120°C, crushed, and sieved in the laboratory to remove materials [2 mm in size. The pH of the soil samples, mixed with water at the ratio of 1:5 after shaking, was measured using a pH meter (Horiba, Japan). Soil samples were powdered and processed for the determination of bulk mineralogy by X-ray diffractometry (XRD; RAD-1A; Rigaku). The major-element composition of bulk soil samples was determined quantitatively using Xray fluorescence photometry (VXQ-160S; Shimadzu). Xray fluorescence photometry uses glass beads for the determination of major-element composition. Glass beads were prepared by fusion in a platinum crucible, with 1.8 g of sample powder mixed with 3.6 g of lithium borate and a pinch of lithium iodide. For calibration curves glass beads of standard rock samples were prepared following the same
695
procedure as described above (sedimentary rock series JSd1, JSd-2, JSd-3, JLK-1, JSI-1, and JLs-1; distributed by the Geological Survey of Japan; http://www.aist.go.jp/RIODB/ geostand/semiment.html). The analytical error for analyses of major elements was estimated to be 2–3% on the basis of separately prepared standard samples. The minimum detection limit for major elements by XRF was 0.001%. The grain-size distribution of soil/sediment samples was analyzed using laser diffraction spectroscopy (SLAD3000S; Shimadzu) following dispersion of the samples in sodium hexametaphosphate solution. Reproducibility of the analytical results for duplicate samples was within ±3%. Water-soluble F- in the samples was extracted in pure water. Five-gram samples of soil were sieved through a 60mesh sieve (250 lm), to which 25 mL of distilled water was added. This was placed in polyethylene bottles, shaken for 0.5 h on an end-over-end shaker, and centrifuged to separate the aqueous fraction. The F- ion concentration of the aqueous fraction was analyzed using an ion selective electrode (Orion A920). This extract was also used to determine pH. Total As was analyzed by Hydride generation atomic absorption spectroscopy (SAS7000; Seiko Instruments). For analysis of total As, the bulk soil sample was fused with sodium carbonate, and the resultant cake was digested in dilute hydrochloric acid. Standard solutions were prepared using standard sediment samples (the same as those used for X-ray fluorescence photometry). These were then analyzed in an atomic absorption spectroscopy following the same procedure as used for the other samples. The minimum detection limit for As quantification was 1 ppb. The reproducibility of analytical values for duplicate samples was within ±5%, and the analytical error for total As was \10%, as estimated from analyses of the standard rock samples. Statistical analysis of the data was done using the Statistical Package for the Social Sciences (SPSS, version 13.1).
Results Particle-Size Distribution and Mineral Composition Results of fraction analyses and F-, As, pH, and P2O5 concentrations in soil samples taken from the surface and at a 30-cm depth and in alluvial sediments are summarized in Table 1, while Table 2 reports the results of sediments taken from four excavations. Surface and deep soils from the same location contain abundant silt and very fine sand, with minor clay. The soils are silty rather than sandy, with silt contents of 59.2–73.3% (average, 65.5%) and sand contents of 0.8–22.8% (average, 10.1%). The clay content
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Table 1 Particle size and F-, As, pH, and P2O5 concentrations of soil samples taken in Punjab, Pakistan Sample
Depth (cm)
Particle size distribution (%)
pH
Clay
Silt
Sand
As (mg/kg)
F- (mg/kg)
P2O5 (%)
KLW-2B
0
7.1
70.0
22.8
8.1
10
0.4
0.23
KLW-2A
30
16.3
68.6
15.1
7.9
10
0.6
0.21
KLW-3B
0
17.6
68.5
13.9
7.6
10
0.7
0.20
KLW-3A
30
18.5
68.6
12.8
8.5
8
1.4
0.20
KLW-4B
0
19.2
70.7
10.1
7.8
12
0.3
0.21
KLW-4A
30
17.8
68.6
13.7
8.2
10
1.5
0.18
KLW-5B KLW-5A
0 30
21.1 19.5
68.7 65.3
10.3 15.2
8.2 8.2
13 11
1.0 1.2
0.25 0.19
KLW-6B
0
19.4
69.4
11.1
8.7
15
1.4
0.12
KLW-6A
30
21.4
66.4
12.1
8.7
12
2.1
0.12
KLW-7B
0
18.1
71.9
10.0
8.9
13
2.1
0.31
KLW-7A
30
18.8
70.0
11.2
9.1
12
2.5
0.35
KLW-8B
0
17.7
70.1
12.2
8.2
14
0.9
0.22
KLW-8A
30
19.1
66.7
14.2
8.8
10
2.1
1.14
KLW-9B
0
15.5
66.4
18.1
8.8
15
1.9
0.22
KLW-9A
30
16.7
65.5
17.7
8.8
10
2.0
0.18
KLW-10B
0
17.4
72.4
10.1
9.4
10
1.4
0.17
KLW-10A
30
13.6
68.1
18.3
8.2
8
3.2
0.50
KLW-11B
0
16.8
65.1
18.0
8.8
12
1.7
0.21
KLW-11A
30
18.9
67.4
13.7
9.0
9
2.5
0.17
WP-1B
0
19.0
71.0
10.0
8.7
12
1.9
0.13
WP-1A WP-2B
30 0
18.0 14.2
68.4 70.2
13.6 15.6
8.7 8.2
10 12
2.5 1.2
0.15 0.16
WP-2A
30
18.3
67.7
14.1
8.3
11
1.4
0.26
WP-3B
0
12.1
69.2
18.7
7.6
19
0.1
0.18
WP-3A
30
15.1
70.9
14.0
7.7
17
0.2
0.17
WP-4B
0
16.6
65.1
18.2
8.3
10
0.6
0.19
WP-4A
30
16.4
66.1
17.4
8.3
7
0.6
0.19
WP-5B
0
15.4
71.9
12.7
8.6
9
1.1
0.23
WP-5A
30
16.4
71.5
12.1
8.8
9
1.9
0.16
WP-6B
0
15.1
73.3
11.6
8.3
10
0.9
0.19
WP-6A
30
15.2
69.0
15.8
8.3
9
1.3
0.18
WP-7B
0
16.9
69.6
13.6
8.0
8
0.7
0.17
WP-7A
30
16.9
69.6
13.6
8.2
8
1.2
0.18
WP-8B
0
15.9
65.8
18.2
8.1
7
0.8
0.26
WP-8A
30
16.3
63.8
20.2
8.2
6
1.1
0.26
WP-9B
0
11.1
63.9
24.8
8.0
8
0.4
0.16
WP-9A WP-10B
30 0
8.3 12.2
59.2 65.7
32.1 19.6
8.1 7.9
7 16
0.9 0.4
0.17 0.19
WP-10A
30
11.3
63.3
21.3
8.0
14
0.5
0.19
WP-11B
0
13.4
64.3
17.3
8.2
8
0.8
0.19
WP-11A
30
16.8
66.3
18.6
8.2
7
1.0
0.26
WP-12B
0
18.6
69.4
12.1
8.1
10
0.7
0.18
WP-12A
30
17.6
68.3
14.1
8.2
9
1.0
0.18
MM-1B
0
17.0
71.3
11.7
9.4
15
0.6
0.26
MM-1A
30
16.2
65.6
18.2
8.0
7
5.2
0.65
MM-2B
0
21.6
65.1
13.4
8.2
8
0.5
0.23
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Table 1 continued Sample
Depth (cm)
Particle size distribution (%)
pH
Clay
Silt
Sand
As (mg/kg)
F- (mg/kg)
P2O5 (%)
MM-2A
30
17.7
70.2
12.1
8.3
10
0.7
0.23
MM-3B
0
18.2
67.2
14.3
8.3
11
0.6
0.25
MM-3A
30
17.4
68.6
14.3
8.2
10
1.2
0.25
MM-4B
0
18.5
67.3
14.2
8.1
10
0.6
0.20
MM-4A
30
17.6
66.2
16.2
8.2
9
1.2
0.20
MM-5B
0
16.3
66.3
17.4
8.1
10
0.5
0.20
MM-5A
30
16.3
65.0
18.7
8.1
9
0.5
0.20
MM-9B
0
13.7
71.8
14.5
8.0
7
0.2
0.10
MM-9A MM-10B
30 0
14.4 18.5
69.8 67.5
16.5 14.0
8.0 8.1
6 10
0.3 0.7
0.21 0.21
MM-10A
30
16.1
67.0
16.9
8.2
12
1.1
0.20
MM-11B
0
17.3
62.9
13.8
9.3
10
4.3
0.55
MM-11A
30
18.0
61.3
14.9
9.3
11
4.8
0.58
MM-12B
0
18.1
67.3
14.6
8.2
9
0.8
0.13
MM-12A
30
13.0
71.7
15.3
8.2
9
1.0
0.13
MM-13B
0
17.8
63.9
18.3
8.2
8
0.4
0.22
MM-13A
30
17.4
63.9
18.6
8.2
9
0.8
0.25
MM-14B
0
14.7
63.7
21.6
8.4
8
1.6
0.22
MM-14A
30
17.7
64.7
17.6
8.4
7
1.7
0.22
RWR-1B
0
14.0
66.1
19.9
8.2
7
0.3
0.29
RWR-1A
30
18.1
67.4
14.5
8.2
7
0.5
0.15
RWR-2B
0
16.9
70.2
12.9
8.2
10
0.3
0.20
RWR-2A
30
16.0
67.1
16.9
8.2
13
0.5
0.26
RWR-3B RWR-3A
0 30
23.2 16.4
67.6 67.0
9.2 16.7
8.3 8.3
11 10
0.5 0.5
0.27 0.23
RWR-4B
0
18.7
65.7
15.7
8.3
7
0.6
0.21
RWR-4A
30
23.4
70.5
6.2
8.3
9
0.6
0.18
RWR-6B
0
15.2
73.4
11.4
8.3
6
0.8
0.18
RWR-6A
30
14.8
76.7
8.5
8.3
10
0.9
0.18
RWR-7B
0
24.0
75.1
0.8
10.0
35
16
0.24
RWR-8B
0
14.7
63.0
22.2
8.3
10
0.5
0.24
RWR-8A
30
15.4
64.9
19.7
8.4
7
1.5
0.23
RWR-9B
0
22.0
68.8
9.1
9.2
12
2.3
0.33
RWR-9A
30
22.3
70.1
7.6
9.2
9
3.5
0.34
RWR-10B
0
18.6
67.6
14.8
8.4
12
1.0
0.25
RWR-10A
30
16.6
69.6
13.8
8.3
16
0.6
0.19
MM-8B
Alluvial, 0
5.0
36.2
50.7
7.7
10
0.2
0.10
MM-8A
Alluvial, 30
5.2
36.7
51.2
7.5
9
bdl
0.10
BRB-1B BRB-1A
Alluvial, 0 Alluvial, 30
4.9 4.6
45.2 47.3
55.4 53.2
7.8 7.8
10 9
0.2 bdl
0.18 0.17
BRB-2B
Alluvial, 0
2.0
37.6
54.1
7.6
10
0.2
0.11
BRB-2A
Alluvial, 30
2.4
38.0
52.9
7.6
9
bdl
0.13
-
Note: bdl, below detection limit. Detection limit for F is 0.1 mg/kg
is higher, with values of 7.1–24.0%. The alluvial sediments contain 50.7–55.4% fine sand (average, 52.7%), 36.2– 47.3% silt (average, 38.0%), and 1–5% clay. Sediments
taken from the excavations contain 7.1–81.6% silt (average, 48%). These results show that the alluvial sediments are more permeable than the aeolian soils.
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Table 2 Particle size and F-, As, pH, and P2O5 concentrations of sediment samples taken from excavations in Punjab, Pakistan Sample
Depth (cm)
Particle size distribution (%) Clay
Silt
Sand
pH
As (mg/kg)
F- (mg/kg)
P2O5(%)
Excavation 1 KLW-1A
0
13.2
67.7
19.1
8.2
16.0
1.10
2.630
KLW-1B
50
15.1
69.4
15.6
8.1
17.0
0.35
0.108
KLW-1C
100
18.3
61.6
20.0
8.3
6.0
1.00
0.217
KLW-1D
150
20.4
70.7
8.9
8.2
14.0
0.48
0.163
KLW-1E
200
22.3
66.8
10.9
8.3
8.0
1.03
0.100
KLW-1F KLW-1G
250 300
1.0 0.0
21.9 7.1
70.6 87.4
8.1 8.1
4.0 8.0
0.26 0.28
0.172 0.124
KLW-1H
350
0.2
31.5
62.0
8.1
4.0
0.17
0.142
KLW-1I
400
0.4
33.2
61.4
8.1
4.0
0.33
0.131
MM-6A
0
17.9
68.1
14.0
8.1
5.0
0.34
0.174
MM-6B
100
17.5
68.5
14.1
8.3
6.0
2.55
0.148
MM-6C
200
12.5
80.6
6.8
8.6
19.0
4.17
0.133
MM-6D
300
10.0
76.1
13.9
8.5
19.0
2.88
0.156
MM-6E
400
3.7
69.0
27.2
8.2
5.0
0.62
0.149
MM-6F
500
0.5
18.1
76.0
8.3
9.0
0.74
0.111
0
6.9
64.1
28.6
8.3
9.0
1.53
0.263
MM-7B
50
7.5
81.6
10.8
8.2
8.0
0.55
0.176
MM-7C
100
1.2
41.0
57.3
8.2
8.0
0.35
0.160
MM-7D MM-7E
150 200
3.6 5.5
58.2 81.6
37.3 12.8
8.1 8.1
6.0 7.0
0.30 0.27
0.080 0.129
BRB-3A
100
1.1
30.3
68.0
8.2
6.0
0.54
0.216
BRB-3B
110
5.5
72.5
22.1
8.2
7.0
1.30
0.141
BRB-3C
120
0.9
18.8
81.0
8.1
4.0
0.39
0.222
BRB-3D
130
0.9
54.6
44.3
8.3
10.0
1.07
0.119
BRB-3E
140
0.0
18.0
81.2
8.1
4.0
0.62
0.180
BRB-3F
200
1.1
42.7
52.3
8.0
1.0
0.63
0.133
Excavation 2
Excavation 3 MM-7A
Excavation 4
The results of XRD analyses reveal that the soil samples from a depth of 0–30 cm contain abundant quartz, moderate amounts of muscovite and feldspar, and minor clay minerals (chlorite and kaolinite); in contrast, the alluvial sediments contain greater amounts of quartz and lack clay minerals (not shown). Major-Element Chemistry Determined by XRF The mean and standard deviation values for all major elements show no distinct difference in composition from the surface to a 30-cm depth (Table 3). Silica (SiO2) concentrations are 61.2–74.5% (average, 67.80%) and 61.2– 80.0% (average, 68.0%) in surface and deep soil samples, respectively. Such a high SiO2 concentration attests to the quartz-rich nature of the soils. Al2O3 is the second-most-
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abundant major element, ranging in concentration from 10.3 to 15.7% (average, 13.0%) and fro 7.6 to 15.7% (average, 12.7%) in surface and deep soils, respectively. Fe2O3 has average concentrations of 5.0 and 4.7% in surface and deep soil samples, respectively. The alluvial sediments taken from the surface and excavations show similar major-element compositions, which are listed in Table 4. As and F- Concentrations As concentrations of soil samples are relatively higher in surface soils than in deep soils from the same location, the mean value of As from the surface is 11.09 mg/kg, while that from 30 cm is 9.56 mg/kg (Table 1). In excavations the As concentrations show inconsistency with the depth,
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Table 3 Descriptive statistics for soil samples from the surface and a 30-cm depth (N = 45 throughout) Depth
Mean
SD
Correlation F-
Clay
As
Surface
16.03
4.53
0.356*
0.260
30 cm
15.96
4.10
0.4**
0.351*
Silt
Surface 30 cm
66.30 65.58
7.86 7.47
0.225 0.232
0.207 0.124
Sand
Surface
17.17
10.73
-0.319
-0.252
30 cm
18.07
10.16
-0.344
-0.128
Surface
8.34
0.510
0.67**
0.482**
30 cm
8.31
0.380
0.68**
0.491**
pH As FSiO2 TiO2
Surface
4.5268
0.732**
1.000
30 cm
11.08889 9.56
2.32
0.791**
1.000
Surface
0.80
2.374
1.000
0.791**
30 cm
1.90
1.130
1.000
Surface
67.80
1.130
-0.066
0.152
30 cm
68.00
2.923
-0.067
-0.012
-0.115
Surface
0.709
0.062
-0.027
-0.063
30 cm
0.722
0.081
-0.037
-0.153
AL2O3
Surface
13.00
1.092
0.063
-0.074
Fe2O3
30 cm Surface
12.70 5.00
1.440 0.843
0.042 -0.009
0.053 -0.056
30 cm
4.71
0.740
0.272
0.023
Surface
0.084
0.011
-0.011
-0.054
30 cm
0.084
0.011
0.227
0.000
Surface
2.251
0.366
0.089
0.017
30 cm
2.140
0.428
-0.004
0.127
Surface
3.160
1.387
-0.064
-0.204
30 cm
3.240
1.450
0.086
Na2O
Surface
1.557
0.327
0.083
30 cm
1.600
0.450
0.193
0.126
K2O
Surface
2.736
0.325
-0.047
0.082
30 cm
2.650
0.350
-0.018
0.061
Surface
0.212
0.072
0.251
30 cm
0.240
0.173
0.518**
MnO MgO CaO
P2O5
-0.06 0.117
0.065 -0.041
Note: Correlation significant at the * 0.05 and ** 0.01 level
e.g., from excavations 1 and 3 a high concentration of As is shown in the surface samples, while in excavations 2 and 4 this is not the trend. Samples of alluvial sediments from the surface and excavations contain As concentrations in the range of 9–10 mg/kg (mean, 9.2 mg/kg). A trial bore was carried out to obtain soil samples at Nazir Ahmed, district Rahim Yarr Khan, Sindh Province, Pakistan, where arsenic contamination was 100 lg/L (Haq 2007). The average As concentrations reported in the present study are higher than those reported previously; e.g., studies undertaken around the world show average surface soil concentrations of 0.1– 4.0 mg/kg (Allaway 1970), 7.5 mg/kg (Adriano 1986), and 3.6–8.8 mg/kg (Pais and Jones 1997).
The statistical analysis of soil samples collected from the surface and a 30-cm depth presented in Table 3 shows that the concentrations of soluble F- are higher in the deep soil samples (0.1–5.2 mg/kg; mean, 1.9 mg/kg) than the surface soils from the same localities (0.1–2.1 mg/kg; mean, 0.8 mg/kg). A statistically significant difference is observed between the two estimates at 95% confidence intervals in F- concentrations from the surface and a 30cm depth. The soluble F- content in the alluvial sediments is from 0 to 4.7 mg/kg, with a mean value of 0.62 mg/kg. Sample RWR-7 was collected only from the surface, and it shows the highest concentrations of F- (16.0 mg/kg) and As (35.0 mg/kg). Samples high in As concentration also show a high F- concentration; a significant positive correlation is observed between As and F- concentrations from the surface (r2 = 0.732; n = 45) as well from a 30cm depth (r2 = 0.791; n = 45), as reported in Table 3. Except for excavation 1, the other three also show a significant positive correlation between F- and As as reported in Table 4. Major-Element Compositions and Relationships Among F-, As, and P The major-element compositions of the analyzed soils and sediment samples fail to show any positive correlation with concentrations of As and soluble F-. The correlations of major constituents with As and soluble F- are presented in Table 3. The concentrations of soluble F- (surface, 30-cm, and alluvial sediments) show a positive correlation with the proportion of clay fraction (Fig. 2a; r2 = 0.356; n = 45), for surface samples and (Fig. 2a; r2 = 0.40; n = 45) for soil samples from a 30-cm depth; however, As concentrations show a positive correlation with clay fraction only at a 30-cm depth (Fig. 2b; r2 = 0.351; n = 45). The relationships among soluble F-, total As, and P (as P2O5) are shown in Fig. 3a–c. At least four soil endmembers were identified in the study area. Background soil, i.e., Endmember A (MM-9) was collected from a site about 1000 m away from the contaminated lands. Endmember A contains the lowest concentrations of F-, As, and P2O5, implying background soil concentrations for the area. Endmember B contains extremely high F- and As concentrations, 16 and 35 mg/kg, respectively, with low P2O5 concentrations, *2.4 g/kg. Endmember C is characterized by moderate F- (2 mg/kg), high As (10 mg/kg), and high P2O5 (11.5 g/kg) concentrations. The As and P2O5 concentrations within the studied soils and sediments are plotted in the triangle A–B–C in Fig. 3c. The relationship between F- and P2O5 clearly indicates another endmember, endmember D, which contains high F- (5.2 mg/kg), low As (7 mg/kg), and high P2O5 (6.5 g/kg) concentrations. Endmember E is potentially an additional
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Table 4 Descriptive statistics for sediments collected from four excavations at different depths Excavation
Depth (cm)
Average
SD
Correlation F-
Clay
pH
As
F-
SiO2
TiO2
AL2O3
Fe2O3
MnO
MgO
CaO
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1
0–400
10.10
9.58
0.72**
2
0–500
10.35
7.13
0.32*
3
0–200
4.94
2.57
4
100–200
1.583
1.96
1
0–400
8.17
2
0–500
3 4
0–200 100–200
N As 0.57**
9
-0.03
6
0.51**
0.34
5
0.74**
0.26
6
0.09
0.89**
0.11
9
8.33
0.19
0.94**
0.94**
6
8.18 8.15
0.08 0.10
0.88** 0.59**
0.94** 0.99**
5 6
9
1
0–400
5.29
0.30*
1.00
9
2
0–500
10.50
6.75
0.81**
1.00
6
3
0–200
7.60
1.14
0.77**
1.00
5
4
100–200
5.33
3.08
0.64**
1.00
6
1
0–400
0.53
0.361
1.00
0.30*
9
2
0–500
1.88
1.55
1.00
0.81**
6
3
0–200
0.60
0.53
1.00
0.77**
5
4
100–200
0.76
0.35
1.00
0.64**
6
1
0–400
70.20
5.42
–0.35
0.18
9
2
0–500
62.86
3.60
–0.62
–0.28
6
3
0–200
73.62
7.21
–0.32
–0.58
5
4
100–200
68.55
7.33
0.07
1
0–400
0.68
0.10
–0.19
–0.18
9
2 3
0–500 0–200
0.65 0.79
0.05 0.32
-0.44 0.07
-0.22 0.31*
6 5
4
100–200
0.73
0.07
-0.04
0.62**
0.69**
1
0–400
11.45
1.79
0.28
2
0–500
12.48
0.79
0.67**
0.50**
3
0–200
10.46
2.24
0.21
0.40*
4
100–200
11.30
2.93
-0.20
1
0–400
4.08
0.84
0.48*
2
0–500
4.80
0.58
0.69**
0.58**
3
0–200
4.19
1.07
0.52**
0.77**
4
100–200
4.29
1.23
-0.21
-0.37
6
6 9 6 5
-0.72
6
-0.26
9
-0.73
6 5 6
1
0–400
0.08
0.01
0.19
-0.33
9
2
0–500
0.08
0.01
0.08
-0.03
6
3
0–200
0.08
0.02
4
100–200
0.08
0.01
1
0–400
1.93
0.50
0.31*
2 3
0–500 0–200
2.79 1.78
0.75 0.79
0.94** 0.46**
4
100–200
2.07
1.00
-0.12
-0.71
1
0–400
3.41
1.28
0.21
-0.22
9
2
0–500
5.74
1.37
0.18
-0.31
6
3
0–200
2.40
1.26
4
100–200
4.40
1.80
0.53** -0.37
0.45** -0.23
0.94**
5
-0.50
6
-0.40
9
0.74** 0.63**
0.67** -0.75
6 5 6
5 6
Arch Environ Contam Toxicol (2009) 56:693–706
701
Table 4 continued Excavation
Depth (cm)
Average
SD
Correlation -
F Na2O
K2O
P2O5
Depth
N As
1
0–400
1.60
0.17
0.10
2
0–500
2.59
0.81
0.53**
3
0–200
1.44
0.18
4
100–200
2.41
1.33
1
0–400
2.42
0.49
0.41*
2
0–500
2.56
0.21
0.66**
0.59**
6
3
0–200
2.21
0.62
0.46*
0.46**
5
4
100–200
2.62
0.65
1 2
0–400 0–500
0.40 0.15
0.79 0.01
0.56** 0.26
3
0–200
0.16
0.07
0.90**
4
100–200
0.17
0.04
0.76**
-0.26
6
1
0–400
0.56**
-0.80
9
2
0–500
0.26
0.13
6
3
0–200
0.90**
-0.83
5
4
100–200
0.76**
-0.65
6
0.32* -0.23
–0.26
-0.12
9
0.14
6
0.26
5
-0.61
6
-0.38
9
-0.64
6
0.48** -0.21
9 6
0.97**
5
Note: Correlation significant at the * 0.05 and ** 0.01 level
Fig. 2 Relationships of F- (a) and As (b) to the clay fraction within samples. Solid triangles represent surface samples, open triangles represent samples from a 30-cm depth, open circles represent surficial alluvial sediments, and filled circles represent alluvial sediments from a 30-cm depth
Fig. 3 Relationships between F- and As (a), F- and P2O5 (b), and As and P2O5 (c) within soil samples. Symbols are the same as those used in Fig. 2
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702
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Fig. 4 Relationship between F- and pH (a) for samples from the surface, a 30-cm depth, and alluvial sediments. Symbols are the same as those used in Fig. 2 Relationships between F- and pH (b) and between As and pH (c) for samples from excavations. Filled
rectangles represent outcrop 1 (KLW-1), open rectangles represent outcrop 2 (MM-6), filled diamonds represent outcrop 3 (MM-7), and plus symbols represent outcrop 4 (BRB-3)
endmember, containing high As (19 mg/kg), low F(0.1 mg/kg), and low P2O5 (1.8 g/kg) concentrations; however, this endmember is considered to be a mixture of endmembers A and B.
therefore, it is likely that dry deposition via coal is a source of As in the studied soils and sediments. Area 2 includes Waran Piran Wala (WP-3, WP-10, and WP-13) and Raiwind Road, where maximum concentrations of 35 mg/kg were detected in soil (RWR-7B) from the eastern part of the study area. The distribution of areas with high F- concentrations is similar to that for As, although less extensive (Zones 1’ and 2’ in Fig 5b), and the maximum concentrations of soluble F- are observed in the same soils that contain the maximum As concentrations. These observations indicate that F- and As may have different sources but similar polluting paths.
Relation of As and F-to Soil pH Correlations of soil pH with As and F- concentrations are presented in Tables 3 and 4. A significant positive correlation is observed between soluble F- and pH for soils from the surface and a 30-cm depth (Fig. 4a; r2 = 0.654; n = 45). Similarly excavations also show a significant positive correlation with pH (Fig. 4b; r2 = 0.877; n = 26). Figure 4c shows a significant positive correlation between As and pH for excavation sediments (r2 = 0.92; n = 17), except for samples taken from excavation KLW-1. A linear positive correlation was observed between the As concentration and the pH of the soil samples from the surface (r2 = 0.482; n = 45) as well as from a 30-cm depth (r2 = 0.491; n = 45). This significant correlation of As and F- with pH shows that the enrichment of F- and As in the studied area is associated with alkalinization of the soil and shows that the soil pH is controls the behavior of these elements. Spatial Distribution of As and FThe spatial distribution of As and F- is shown in Fig. 5a and b. Arsenic is unevenly distributed in the soils of the study area. Highly contaminated soils are concentrated in areas 1 and 2 (shaded areas in Fig. 5a); area 1 includes the southern part of Manga Mandi and Kalalanwala, where the soil contains As concentrations [15 mg/kg. A sample collected close to brick kilns, MM-1, also contains high amounts of As (15.0 mg/kg). As stated above, the As concentration of coals used by brick factories in this area ranges from 4 to 12 mg/kg (Farooqi et al. 2007a, b);
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Discussion Chemical Constraints on F- and As Concentrations The statistical analysis of the data presented in Table 3 shows the lack of significant positive correlation between major-element compositions and F- and As concentrations of the samples collected from the surface and a 30-cm depth. The lack of a positive correlation between major constituents and As and F- concentrations suggests that the As and F- concentrations are not related to the chemistry and mineralogy of the local soils; i.e., anthropogenic sources have a greater influence than natural sources. While in the case of excavations this trend is not consistent, excavation 2 shows a significant positive correlation of Fwith Al2O3, Fe2O3, Na2O, K2O, and MgO, and excavation 3 shows a significant positive correlation of As with Fe2O3 and MnO (Table 4). This trend of correlation in excavations shows that, along with the anthropogenic sources in the study area, high As and F- concentrations are also being controlled by natural sources. Further studies on cored sediments from the study area are needed to verify this phenomenon.
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703
Fig. 5 Geographic distribution of As (a) and F- (b) throughout the study area
Only the clay fraction is positively correlated with As and F- concentrations (Fig. 2a and b), suggesting that clay minerals, which occur at low concentrations in the alluvial sediments, adsorb As and F-; the F- ion substitutes for the hydroxyl ion (OH-) in amorphous aluminum hydroxides (Al[OH] 3) (Bower and Hatcher 1967; Fluhler et al. 1982). Soil pH is an important factor in controlling F- concentrations (McLaughin et al. 2001; Loganathan et al. 2003); indeed, in the present study the pH of the soils appears to control the As and F- concentrations. Fluoride concentrations increase with increasing pH of the soils and alluvial sediments from the excavation (Fig. 4a and b). Similar observations have been reported for soils in the United Kingdom (Larsen and Widdowoson 1971), where F- is desorbed under alkaline conditions as a result of repulsion by negatively charged surfaces. Like F-, As concentration also shows a positive relationship with pH (Fig. 4c). In the studied area As speciation of groundwater samples shows that As is present in the form of AsV (Farooqi et al. 2007a, b). AsV is the form most effectively adsorbed onto Fe-oxyhydroxide/ oxide under weakly acid to neutral pH conditions; it is released into solution with increasing pH and alkaline conditions (Anderson et al. 1976; Gustafsson and Jacks 1995). Given that an alkaline solution effectively dissolves F- and As, enrichment in As and F- occurs with the formation of highly alkaline soil. It is plausible that the release of As and F- into a groundwater aquifer occurs in
association with the infiltration of dilute surface water that is alkalized by soils. Soil alkalinization is a naturally occurring phenomenon, although it is intensified by human activity. Soils in arid and semiarid areas are characterized by excess evaporation over rainfall, leading to the accumulation of salts derived from rainfall and irrigation water. Alkalinization can be induced by the application of ammonium fertilizers and high-pH irrigation water that contains a high content of sodium bicarbonate (Vanlenza et al. 2000). Extensive areas of alkaline soil arising from waterlogging and evaporation have been reported in the Indus Plain and many other arid and semiarid regions (Shahid and Jenkins 1994; Sharma et al. 2000). The present study area is mostly agricultural land. In the research area, pesticides and fertilizers are being used on wheat, rice, and sugarcane crops. The use of fertilizers enhances the process of soil alkalinization. In Pakistan the annual consumption of fertilizers in 1999 was 2824 thousands metric tons for 129 kg/ha cropland in Pakistan and, mostly, in Punjab (http://earthtrends.wri.org). Phosphatic fertilizers are extensively used in the area. In many studies, elevated arsenic concentrations in groundwater have been found due to application of phosphate fertilizers (Davenport and Peryea 1991; Campos 2002). In addition to canal water, groundwater is an important source of irrigation, contributing 30–40% of the total irrigation load (Nespak 1991). Extensive irrigation and
123
704
seepage from canals have led to a rise in the water table of shallow groundwater, leading in turn to high salt concentrations, [2000 ppm (Ghafoor et al 1991; Kahlown and Azam 2002). Given that the study area is located in a semiarid region, this rise in the groundwater table will inevitably result in the salinization and alkalinization of soils due to evaporation. Sources of As and F- and Topographic Constrains As noted above, four or five endmember soils were identified in the present study based on the concentrations of As, F-, and P (points A, B, C, D, and E in Figs. 3 and 5). Point A represents background soil, which is largely free of contamination, free of soluble F-, contains ca. 5 mg As/kg, and contains 1–2 mg P2O5/kg. Endmember B contains extremely high concentrations of As (35 mg/kg) and F(16 mg/kg) and low P2O5 (2.1 g/kg). This soil corresponds to the surface soil (RWR-7B) collected at the edge of a cultivated field situated along a canal that flows close to a prominent industrial zone that includes chemical plants. The factories in this zone do not possess waste-treatment plants; consequently, the waste material is dumped directly outside or drained from the premises. Thus, the high concentrations of As and F- recorded in endmember B are the result of industrial waste. Endmember C is a soil taken from a 30-cm depth in a cultivated area (KLW-8A). The soil contains high levels of P2O5 (11.4 g/kg) and moderate levels of F- (2.1 mg/kg) and high As (10 mg/kg). This endmember represents the contribution of the phosphate fertilizers applied in the area. We found previously that the locally applied fertilizers contain 55–265 mg F/kg and 5–10 mg As/kg (mean, 7.4 mg/kg) (Farooqi et al. 2007a, b). The F- concentration in agricultural soils is known to increase with the application of fertilizers (Pickering 1985; Skjelkvale 1994; McLaughin et al. 2001), as phosphate fertilizers commonly contain 1.3–3.0% F- as an impurity (Fluhler et al. 1982). Endmember D contains high P2O5 (6.50 mg/kg), high levels of F- (5.2 mg/kg), and low As (7.0 mg/kg). This soil was collected from agricultural land in the western part of the study area. The concentrations of P2O5 and As in this soil plotted on the line connecting soils A and C (Fig. 3c), indicating that these components are dominantly derived from fertilizers. There is an additional source of the F- found in endmember D. As described above, the highly Fcontaminated soils are distributed in two areas (areas 1’ and 2’ in Fig. 5b). Area 2’, which includes the soil sample with the highest concentrations of F- and As (RWF-7), is close to an industrial zone, meaning that industrial waste is likely the main source of F- and As in this soil. Area 1’ includes the southern part of the area of brick kilns and
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extends to the southwest. As stated in our previous paper, the locally consumed coals contain 5–20 mg F/kg (mean, 10 mg/kg) and 4–12 mg As/kg (mean, 8 mg/kg) (Gritsan and Miller1995). Although the extent of the area with high As concentrations (area 1 in Fig. 5-a) is smaller than the area with high F- concentrations (area 1’), area 1 is included within area 1’, indicating that the source of Fand As in this area can be attributed to the combustion of coal. Arsenic concentrations in ambient air in the Lahore district are 230–2230 ng/m3 (JICA and Pakistan EPA 2000), which is much higher than the values reported in other parts of the world; e.g., 91–512 ng/m3 in Calcutta, India (Chakraborti et al. 1992), 25 ng/m3 in Wuhan City, China (Waldman et al. 1991), and 1.2–44.0 ng/m3 in Los Angeles, USA (Rabano et al. 1989). In the present study area, the wind direction during the dry season, when the brick kilns are active, is dominantly toward the southwest (WASA 2004), thus the distribution of soils with high concentrations of F- and As is consistent with the likely extent of dry deposition. The elevation of the study area decreases gradually toward the southwest (not shown), however, the areas with high concentrations of F- and As (areas 1 and 1’ for Fand areas 2 and 2’ for As) are slightly lower (about 195 m above sea level) than the surrounding area ([200 m). This observation, combined with the fact that clay-rich soils contain higher F- and As concentrations, means that polluted surface soils are removed toward topographic lows. Possible Causes of Groundwater Pollution Based on the previous studies on groundwater in this studied area (Farooqi et al. 2007a, b), most groundwater seriously affected by F- and As appears at 20- to 30-mdepth wells, which is the shallowest aquifer just beneath the aeolian sediments. Also, the highly contaminated groundwaters appear unevenly. The most contaminated groundwater appears at the center of Kalalanwala village (Farooqi et al. 2007a, b), areas 1 and 1’ in the present study, and the second-most-contaminated groundwaters appear at Waran Piran Wala village (Farooqi et al. 2007a, b), just west of areas 2 and 2’. This means that the infiltration of water from the surface into the shallowest groundwater is the major cause of the contaminated groundwater. The structure of the aquifer could be another cause for the appearance of the locally contaminated groundwater, since the contaminated groundwater seems not to extend ubiquitously in the aquifer. Further study is needed to verify the aquifer structure, to measure the distribution of As and F- in cored sediments, and to determine the natural mechanism of As and Fdissolution along with the anthropogenic sources.
Arch Environ Contam Toxicol (2009) 56:693–706
Summary Three anthropogenic sources are identified: fertilizers, combusted coal, and industrial waste. A high concentration of As was detected in surface soil samples, the highest concentration being 35 mg/kg, while a high F- concentration was detected in subsurface soils except for that of RWR-7b (16 mg/kgfrom surface). The presence of high levels of As in the surface soil is due to the contribution of air pollutants by wet and dry deposition derived from coal combusted in brick factories, industrial waste from the factories, and the use of fertilizers. Use of phosphate fertilizers in the area is the major source of fluorine accumulated in the soil. Highly alkaline water, due to the use of fertilizers, acts to dissolve the F- and As adsorbed on the soil, thus releasing it into the local groundwater. Infiltration of water from the surface into the shallowest groundwater is the major cause of the contaminated groundwater in the area, while the structure of the aquifer could be another cause of the contaminated water in the area. Acknowledgments We are thankful to Mr. M. Sakhawat, Director of the Geoscience Laboratory, Geological Survey of Pakistan, Islamabad, for his cooperation and for provision of all of the necessary facilities for fieldwork and laboratory analyses. Technical support from Ms. K. Okazaki, Osaka City University, is also appreciated. We thank Dr. H. Chiba, Okayama University, for his guidance with fluoride analysis using an ion meter. This work was financially supported by the JSPS (Scientific Aid: Grant No. 12440145) and the Sumitomo Foundation.
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