Jun 30, 2010 - members in a family of this village were showing arsenical skin lesions except a ... Bangladesh was first identified in 1992 (Dhar et al., 1997), detailed ...... concentrations of arsenic and other toxic elements in. Bangladesh's ...
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Status of groundwater arsenic contamination in Bangladesh: A 14-year study report Dipankar Chakraborti a,*, Mohammad Mahmudur Rahman a,b, Bhaskar Das a, Matthew Murrill a, Sankar Dey a, Subhas Chandra Mukherjee c, Ratan Kumar Dhar a, Bhajan Kumar Biswas a, Uttam Kumar Chowdhury a, Shibtosh Roy d, Shahariar Sorif d, Mohammad Selim d, Mahmuder Rahman d, Quazi Quamruzzaman d a
School of Environmental Studies (SOES), Jadavpur University, Kolkata 700 032, India Centre for Environmental Risk Assessment and Remediation (CERAR), University of South Australia, Mawson Lakes Campus, SA 5095, Australia c Medical College, Kolkata, India d Dhaka Community Hospital (DCH), Dhaka 1217, Bangladesh b
article info
abstract
Article history:
Since 1996, 52,202 water samples from hand tubewells were analyzed for arsenic (As) by
Received 28 December 2009
flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS) from all 64
Received in revised form
districts of Bangladesh; 27.2% and 42.1% of the tubewells had As above 50 and 10 mg/l,
15 June 2010
respectively; 7.5% contained As above 300 mg/l, the concentration predicting overt arsenical
Accepted 21 June 2010
skin lesions. The groundwater of 50 districts contained As above the Bangladesh standard
Available online 30 June 2010
for As in drinking water (50 mg/l), and 59 districts had As above the WHO guideline value (10 mg/l). Water analyses from the four principal geomorphological regions of Bangladesh
Keywords:
showed that hand tubewells of the Tableland and Hill tract regions are primarily free from
Bangladesh
As contamination, while the Flood plain and Deltaic region, including the Coastal region,
Arsenic
are highly As-contaminated. Arsenic concentration was usually observed to decrease with
Hand tubewell
increasing tubewell depth; however, 16% of tubewells deeper than 100 m, which is often
Groundwater
considered to be a safe depth, contained As above 50 mg/l. In tubewells deeper than 350 m,
Deep tubewells
As >50 mg/l has not been found. The estimated number of tubewells in 50 As-affected
Geomorphological regions
districts was 4.3 million. Based on the analysis of 52,202 hand tubewell water samples
Number of hand tubewells
during the last 14 years, we estimate that around 36 million and 22 million people could be
Population at risk
drinking As-contaminated water above 10 and 50 mg/l, respectively. However for roughly
Approach for mitigation
the last 5 years due to mitigation efforts by the government, non-governmental organizations and international aid agencies, many individuals living in these contaminated areas have been drinking As-safe water. From 50 contaminated districts with tubewell As concentrations >50 mg/l, 52% of sampled hand tubewells contained As 50 mg/l) (www.unicef.org/bangladesh/ Arsenic.pdf). Several articles have already been published on the various aspects of groundwater As contamination in Bangladesh, including the extent and magnitude of contamination, human health effects, source and mobilization of As, contamination
w a t e r r e s e a r c h 4 4 ( 2 0 1 0 ) 5 7 8 9 e5 8 0 2
of the food chain, social and socioeconomic aspects of arsenicosis as well as mitigation options and strategies. Compilations of information and references can be found at the following websites (SOES website: http://www.soesju.org; Lex van Geen, Lamont-Doherty Earth Observatory, Columbia University: http://www.ldeo.columbia.edu/wavangeen/; Richard Wilson, Department of Physics, Harvard University: http://phys4. harvard.edu/wwilson/arsenic/arsenic_project_introduction.html; Dhaka Community Hospital: http://dchtrust.org/; Andrew Meharg: http://www.abdn.ac.uk/biologicalsci/staff/details/a.meharg). This paper combines a large amount of unpublished and previously published data in order to provide an in-depth distribution of district-wise groundwater As contamination across Bangladesh. Locations of As-safe groundwater within these districts have also been identified. We present (i) the status of groundwater As contamination in all 64 districts of Bangladesh, based on 52,202 hand tubewell water sample analyses, (ii) the status of groundwater As contamination in the four principal geomorphological regions of Bangladesh, the locations in Bangladesh where groundwater is not As contaminated and the possibility of using both shallow and deep hand tubewells as potential groundwater resources for drinking water supply, (iii) an analysis of the relationship between As concentration, iron (Fe) concentration and tubewell depth, (iv) an estimation of the number of hand tubewells in As-affected districts as well as nationwide, (v) the status of As in tubewells deeper than 100 m depth in the four principal geomorphological regions of Bangladesh, (vi) an estimation of the population that could be drinking contaminated water at various As concentrations, (vii) a comparison of hand tubewell As concentrations in Bangladesh and West Bengal, (viii) the future danger of arsenic-related health effects and (ix) finally an approach for mitigation in Bangladesh.
2.
Materials and methods
2.1.
Study area and sampling
Chittagong district is primarily in the Hill tract region, but a few thanas such as Sitakundu, Mirsharai, Anowara and Banskhali are also partially in the Flood plain region. In the Hill tract areas, tubewells are substantially fewer in number, and tubewells deeper than 200 m are usually available. During the past 14 years, 52,202 hand tubewell water samples were collected altogether and analyzed from all 64 districts covering the four principal geomorphological regions of Bangladesh; however, about 95% of the samples were collected and analyzed between 1996 and 2002. During epidemiological work from 2003 to 2009, additional hand tubewell samples were collected from affected villages. The details of the sample collection procedure are provided in the Supplementary Information. More than 5000 water samples were analyzed for both As and Fe from Bangladesh, including almost all tubewells from a single village (n ¼ 547). In this article, the relation between As and Fe is provided based on these 547 data.
2.2.
Instrumentation
FI-HG-AAS method was utilized for the analysis of As in groundwater. Details of the AAS instrument, the FI system and reagents used have been described elsewhere (Rahman et al., 2002). For Fe analysis, the 1,10-phenanthroline method was performed with a UVevis Spectrophotometer.
2.3.
Quality control analysis
For quality control, inter-laboratory tests were performed for As in water samples as reported elsewhere (Rahman et al., 2002). EPA water standards were also analyzed to check the accuracy of the FI-HG-AAS method (Rahman et al., 2002).
3.
Bangladesh is a small country (144,000 km2) with a population of around 153 million (http://www.intute.ac.uk/sciences/ worldguide/html/823.html). It is divided into 64 total districts that comprise 6 divisions: Dhaka, Chittagong, Rajshahi, Khulna, Barisal and Sylhet. Each district contains several thanas, a total of 508 nationwide, which are composed of large clusters of villages known as Unions that are further divided into small groups of villages. The population of each thana was obtained from the national Census of 2001 (http://www.bbs.gov.bd) and utilized for estimates of the number of individuals exposed to various concentrations of As through drinking water. Geomorphologically, Bangladesh comprises four main regions: Tableland, Flood plain, Deltaic region including the Coastal region, and Hill tract (Fig. 1). We have combined Deltaic and Coastal regions as there is no clear geological demarcation. Interestingly, due to salinity in shallow tubewells in the Coastal region, people drink primarily deep tubewell water. Samples were collected from 117 deep hand tubewells of 5 thanas along the Coastal region. Four districts (Panchagarh, Thakurgaon, Dinajpur and Joypurhat) are exclusively in the Tableland region while 13 districts are composed of both the Tableland and Flood plain regions. The
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Results and discussion
3.1. Arsenic contamination of groundwater in all 64 districts of Bangladesh The distribution of As concentration in all 64 districts of Bangladesh is presented in Table 1. In summary, 52,202 water samples were collected from 3600 villages of 338 thanas. Groundwater from 2500 villages of 59 districts and 2000 villages of 50 districts was found to contain As above 10 mg/l and 50 mg/l, respectively. Out of 338 surveyed thanas, As concentrations above 50 mg/l were found in 197 thanas. Furthermore, 42.1% of the hand tubewell water samples contained As above 10 mg/l, and 27.2% contained As above 50 mg/l. Surprisingly, 7.5% of the analyzed tubewells had As concentrations above 300 mg/l, the threshold concentration associated with arsenical skin lesions (Chakraborti et al., 2004). A total of 301 (0.6%) hand tubewells were found with As above 1000 mg/l, mainly in the Lakshmipur and Noakhali districts. The maximum As concentration detected in a hand tubewell was 4730 mg/l of the village Chiladi in Noakhali district. Many villages in the As-affected areas of Bangladesh surveyed over the past 14 years were found to have 70e100% of the hand tubewells contaminated with As above 50 mg/l. It is possible that Chiladi (Thana: Senbagh, District: Noakhali) is the village
5792
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Fig. 1 e Four geomorphological regions of Bangladesh and the status of As contamination in groundwater in 64 districts of Bangladesh.
with the most severe As contamination in the world where people were drinking from contaminated sources for extended periods of time. Out of 73 hand tubewells analyzed from Chiladi, only one tubewell contained As between 10 and
50 mg/l (depth of this tubewell is 190 m) and the remaining 72 tubewells contained As above 100 mg/l. It was also found that 21 tubewells from this village had As above 1000 mg/l. During our surveys in both Bangladesh and several states of India
Table 1 e Distribution of hand tubewells against concentration ranges (mg/l) of As in all 64 districts of Bangladesh. Division
Rajshahi
District
Area (km2)
Population Total no. No. of No. of No. of of thana surveyed thana As samples thana >50 mg/l analyzed
Distribution of total samples in different As concentration (mg/l) ranges 1000
Maximum concentration detected (mg/l)
e e e e e e e e 12 e 25 e e 2 e e
1 e e e e e e e 10 e 16 e e e e e
1040 77 512 32 50 50 22 63 1600 50 2108 15 524 939 216 130
79 11 457 27 138 168 95 33 164 236
67 11 105 6 39 42 27 5 20 133
17 13 76 4 6 33 5 e e 1
12 2 32 e 5 13 4 e e 1
e e 3 e 6 16 1 3 e e
958 841 1120 592 3143 2190 1230 1050 375 750
e 40 e 3 e 8
e 227 e 5 e 24
e 106 e 1 e 8
e 75 e e e e
e 47 e e e 1
e 16 e e e e
15 1770 50 310 10 731
6 12 29 14
1 3 17 2
e e
e e e e
e e e e
e e e e
100 133 302 177
2898.25 3437.98 2179.27 965.44 2296.10 1241.46 3435.67 1896.05 1702.56 1580.85 2371.50 1404.63 2407.01 2370.45 2497.92 1809.52
3013056 2642850 2138181 846696 1792073 1109343 2391355 1521336 1425322 1571690 2176270 836196 2286874 2542441 2693814 1214376
11 13 7 5 9 5 11 6 5 6 9 5 13 8 9 5
11 13 7 5 7 5 10 3 5 6 9 5 10 8 4 5
4 e 5 e e e e 2 4 e 7 e 7 2 3 2
767 2641 1233 398 539 464 537 117 1902 523 5117 462 2698 464 278 461
607 2612 863 388 467 434 527 91 920 505 1595 458 2197 285 187 416
125 28 308 10 72 30 10 22 434 18 1807 4 266 114 79 38
17 1 40 e e e e 4 173 e 807 e 105 19 8 6
16 e 17 e e e e e 273 e 691 e 121 20 4 1
Khulna
Bagherhat Chuadanga Jessore Jhenaidaha Khulna Kushtia Meherpur Magura Narail Satkhira
3959.11 1177.40 2570.42 1949.62 4394.46 1621.15 716.08 1048.61 990.23 3858.33
1549031 1007130 2471554 1579490 2378971 1740155 591436 824311 698447 1864704
9 4 8 6 14 6 3 4 3 7
3 4 6 3 12 6 3 4 3 5
3 4 6 3 9 5 3 3 3 5
371 457 5465 388 1000 2065 1024 496 371 532
90 124 4227 185 518 1082 526 243 96 32
72 223 248 142 233 557 271 168 56 73
34 73 317 24 55 154 95 44 35 56
Barisal
Barguna Barisal Bhola Jhalakati Patuakhali Pirojpur
1831.31 2790.51 3737.21 758.06 3220.15 1307.61
848554 2355967 1703117 694231 1460781 1111068
5 10 7 4 7 6
2 6 3 3 1 4
e 6 e 2 e 4
43 803 74 42 15 124
35 179 57 17 13 42
8 113 17 16 2 41
Sylhet
Habiganj Moulavi Bazar Sunamganj Sylhet
2636.58 2799.39 3669.58 3490.40
1757665 1612374 2013738 2555566
8 6 10 11
2 5 2 5
2 2 2 1
103 152 89 391
59 72 6 331
37 65 34 44
1 e
3 e
w a t e r r e s e a r c h 4 4 ( 2 0 1 0 ) 5 7 8 9 e5 8 0 2
4 e e e e e 57 e 124 e 8 15 e e
e e 1 e e e e e 23 e 52 e 1 9 e e
Bogra Dinajpur Gaibanda Joypurhat Kurigram Lalmanirhat Naogaon Natore Nawabganj Nilphamari Pabna Panchagarh Rajshahi Rangpur Sirajganj Thakurgaon
(continued on next page)
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Division
District
Area (km2)
Population Total no. No. of No. of No. of of thana surveyed thana As samples thana >50 mg/l analyzed
Distribution of total samples in different As concentration (mg/l) ranges 1000
Maximum concentration detected (mg/l)
Dhakaa Faridpur Gazipur Gopalganj Jamalpur Kishoreganj Madaripur Manikganj Munshiganj Mymensingh Narayanganj Narshingdi Netrokona Rajbari Shariatpur Sherpur Tangail
1459.56 2072.72 1741.53 1489.92 2031.98 2731.21 1144.96 1383.06 954.96 4363.48 687.76 1140.76 2747.91 1118.80 1181.53 1363.76 3375.00
8511228 1756470 2031891 1165273 2107209 2594954 1146349 1285080 1293972 4489726 2173948 1895984 1988188 951906 1082300 1279542 3290696
27(6) 8 5 5 7 13 4 7 6 12 5 6 10 4 6 5 11
6 5 4 5 2 12 4 3 5 9 3 5 10 3 3 5 11
3 5 1 5 1 11 4 3 5 6 2 3 10 2 3 3 4
574 707 3386 384 144 1328 2309 282 151 1825 412 336 533 174 152 303 597
449 243 3312 86 89 527 453 79 10 1705 54 252 201 79 63 191 443
29 171 33 74 30 429 480 101 6 101 42 16 180 72 29 100 131
26 67 8 55 7 238 336 44 12 12 34 7 84 5 20 7 21
63 142 16 146 6 133 622 55 80 6 147 23 49 15 26 5 2
7 40 16 19 2 1 316 2 36 1 68 24 13 1 12 e e
e 24 1 2 2 e 76 1 7 e 36 10 6 e 2 e e
e 12 e 2 6 e 21 e e e 26 4 e 2 e e e
e 8 e e 2 e 5 e e e 5 e e e e e e
352 1630 533 920 1172 365 1200 586 529 330 1750 1000 580 714 580 275 224
Chittagong
Bandarban Brahmanbaria Chandpur Chittagong Comilla Cox’s Bazar Feni Khagrachari Lakshmipur Noakhali Rangamati
4479.03 1927.21 1704.06 5282.98 3085.17 2491.86 928.34 2699.55 1455.96 3600.99 6116.13
298120 2398254 2271229 6612140 4595557 1773709 1240384 525654 1489901 2577244 508182
7 8 8 26 13 7 5 8 4 6 10
2 2 7 14 6 2 2 3 4 4 2
e 2 7 2 6 e 2 e 4 4 e
41 47 1165 366 545 58 186 39 2662 843 47
41 12 50 319 113 58 58 39 304 5 47
e
e
9 36 26 26 e 53 e 235 36 e
9 30 13 29 e 40 e 339 92 e
e 17 675 8 128 e 28 e 852 413 e
e e 294 e 123 e 5 e 421 80 e
e e 54 e 75 e 1 e 246 79 e
e e 21 e 25 e 1 e 177 48 e
e e 5 e 26 e e e 88 90 e
e 210 1318 275 1769 e 1000 e 2030 4730 e
124355263
508 (486)
338
197
52202
29768
8230
3714
6487
2263
938
501
301
e
57.0
15.8
7.1
12.4
4.3
1.8
1.0
0.6
Total
147570
Percentage (%) a Dhaka city has 22 thanas and we consider Dhaka city as a thana.
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Dhaka
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Table 1 (continued ).
Total
a Districts are in mixed geomorphological region. Dhaka city has 22 thanas and we consider Dhaka city as a thana.
52202 486 (508)
338
29768
8230
3714
6487
2263
938
501
301
e e e e e e e e e 489 5a
54a
19
e
489
134 4730 3143 e 227 74 e 322 179 e 552 386 e 1181 1082 2 3179 3306 15 1471 2228 204 3153 4873 9534 9760 9985 0.2 34.9 32.8 2.1 50.8 54.7 9755 19845 22113 64 158 97 64 (86) 229 139 17a 34a 22
Tableland Flood Plain Deltaic region including Coastal belt Hill tract
10e50 51e99 100e299 300e499 500e699 700e1000 >1000 10 mg/l As > 50 mg/l surveyed analyzed No. of thanas within region GeoNo. of morphological districts region within region
Table 2 e Distribution of hand tubewells against concentration (mg/l) ranges of As in four principal geomorphological regions of Bangladesh.
Maximum Concentration found (mg/l)
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(West Bengal, Bihar, Jharkhand, Uttar Pradesh, Assam and Manipur), we have not encountered a village with such widespread and severe As contamination. In contrast, we found many villages and thanas in As-affected districts of Bangladesh where As concentration in many hand tubewells was less than 10 mg/l. Fig. 1 shows the groundwater As contamination status in all 64 districts and the four principal geomorphological regions of Bangladesh. Table 1 (Supplementary information) shows a summary of the present status of As contamination and its associated health effects in Bangladesh. Table 1 also shows a comparison of the present status of As contamination as of 2009 and the initial survey results published in 1997, illustrating the changing arsenic situation over the past 14 years. All the samples collected from four districts (Rangamati, Khagrachari, Bandarban and Cox’s Bazar) out of 64 were found to have groundwater As levels less than 10 mg/l. Based on this, we can assume that the groundwater of these four districts is predominantly free from As contamination. In Patuakhali district, the highest concentration detected was 10 mg/l, however the number of tubewells sampled in this district was rather small. Interestingly, As above 50 mg/l was found in only 1 sample (concentration 77 mg/l) in Dinajpur district out of 2647 samples. Furthermore, only 28 samples from this district contained As between 10 and 50 mg/l. Usually small invisible As-rich particles are present in tubewell water which dissolved when preservative (nitric acid) was added during the collection of water samples. Roychowdhury (2008) reported that a significant amount of As was being released from a large number of small particles, containing mainly colloidal iron hydroxides from newly installed tubewells. The presence of these particles was found to increase the As level of samples not filtered through a Millipore filter by 12% (Roychowdhury, 2008). Most probably due to this reason, we detected a sample with As above 50 mg/l in Dinajpur district. In this study, we do not consider Dinajpur district as As contaminated above 50 mg/l. Of 46,321 hand tubewells from 50 As-contaminated districts of Bangladesh, 48.1% and 30.9% were found to have As above 10 mg/l and 50 mg/l, respectively. Based on these groundwater surveying efforts, we have classified the districts of Bangladesh into five categories: highly affected (As > 300 mg/l), moderately affected (As ¼ 100e300 mg/l), mildly affected (As ¼ 50e100 mg/l), very mildly affected (As ¼ 10e50 mg/l) and unaffected/As-safe (As < 10 mg/l) (Supplementary Information).
3.2. Status of groundwater As contamination in the four geomorphological regions of Bangladesh The distribution of As concentration across the four geomorphological regions is presented in Table 2. In the Tableland areas, As greater than 50 mg/l was detected in only 17 (w0.2%) hand tubewells out of the 9755 analyzed. In 204 (2.1%) samples, As was found at concentrations between 10 and 50 mg/l (Table 2). We noticed that in the areas of the Hill tract and Tableland regions either eroded by Flood plain rivers or bordering the Flood plain region arsenic contamination was more likely; however, this could be a result of poorly delineated geomorphological boundaries. BGS-DPHE (1999) data
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reported that only 44 (1.7%) of the 2607 samples analyzed from Tableland region had As above 50 mg/l. So far 19,845 hand tubewell water samples have been analyzed from 158 of the total 229 thanas in the Flood plain region. Of these samples, 50.8% and 34.9% had As concentrations greater than 10 mg/l and 50 mg/l, respectively (Table 2). BGS-DPHE (1999) data indicated that 4587 (27.8%) out of 16,513 samples analyzed from this area had As above 50 mg/l. From the Deltaic region including Coastal belt, 22,113 hand tubewell water samples from 97 of the total 139 thanas have been analyzed. The results indicated that 54.7% of the samples had As above 10 mg/l and 32.8% above 50 mg/l (Table 2). BGSDPHE (1999) reported 12,245 water samples from 126 thanas of this region and 3344 (27.5%) samples had As above 50 mg/l. We have not identified any sample with As above 10 mg/l from the Hill tract regions (Table 2), a finding similar to that of the BGS-DPHE (1999) study which only analyzed samples from Chittagong and Cox’s Bazar districts. The results indicate that the groundwater of the Tableland and Hill tract regions are generally free from As contamination while that of the Flood plain and Deltaic region including Coastal belt are heavily As contaminated. The probable reason for contamination is heavy deposition of Holocene sediments on the Flood plain and Deltaic region. In the Coastal region, deep tubewells are available and As contamination of groundwater is less compared to the Deltaic region. The results in Table 2 also indicate that the Flood plain region is more As-affected than the Deltaic region. The percentage of samples having As above 1000 mg/l in the Flood plain (1.14%, 227 samples) are more than the Deltaic region (0.33%, 74 samples).
3.3. Why some areas of Tableland are to some extent Ascontaminated and some areas in Flood plain safe In 1999, BGS-DPHE reported the analytical results of 2607 tubewell samples from 64 thanas. According to our assessment and the BGS-DPHE map of Tableland, these results showed that 49 thanas are free from As contamination; however, 44 samples out of the 794 analyzed from 15 thanas showed contamination above 50 mg/l. Out of these 15 thanas, 11 border the Flood plain while the other 4 thanas appear to be strictly in Tableland. The areas of Tableland bordering the Flood plain might have become As-contaminated if some rivers passed through this region or if there is a history of erosion of Tableland by any of these rivers. Deposition of Holocene sediment due to the severe surface erosion of Tableland is the probable cause of As contamination. Again confusion arises when we try to find out the actual extent of Tableland from the BGS-DPHE (1999) map and the Bangladesh Physical Map (1996). These two maps differ to some extent mainly in the delineations of borders. Stratigraphically the Barind Tract, Madhupur Garh, and Lalmai Hills of Comilla are the same. These areas are collectively known as Tableland and geomorphologically consist of Pleistocene red clay, silt and sand. The Barind Tract and Madhupur Garh are marginally overlain by As bearing Holocene sediments (BGS-DPHE, 1999; PHED, 1991). Arsenic analysis reports in some geographical locations in the districts of Gazipur, Bogra, and Tangail, which are in Tableland but
partially overlain by Holocene Flood plain deposit, showed the presence of considerable groundwater As contamination. The possible reason of such contamination is due to Flood plain deposition on the eroded surface of Tableland. A unique example is Gazipur district, where 4 out of 5 thanas are in Tableland and free from As contamination; while Kapasia, an eroded area of Tableland filled up by Holocene Flood plain deposit, is found to be As contaminated. We analyzed 101 tubewell samples from Kapasia, and 41 (40.5%) samples had As above 50 mg/l with a maximum concentration of 533 mg/l. The districts Nawabganj, Rajshahi, Narayanganj and Narsingdi are mainly in the Flood plain region; however Nachole thana of Nawabganj, Tanore and Godagari thanas of Rajshahi, Rupganj thana of Narayanganj and Belaboo thana of Narsingdi are in the Tableland region. All these thanas situated in the Tableland region are almost free from As contamination. Only a single sample had As above 50 mg/l, and this could be the result of As-rich particles which dissolved when preservative (nitric acid) was added during water sample collection. According to the geomorphological map of Bangladesh, all 28 thanas except 5 (Domar, Patgram, Badarganj, Mithapukur and Pirganj, which are in Tableland) in the districts Nilphamari, Kurigram, Lalmonirhat and Rangpur in the northwest are in the Flood plain region. These 5 thanas should be Assafe and the results of our As analyses show that the groundwater of these 5 thanas in Tableland are almost free from As contamination. However, the other 23 thanas situated in the Flood plain should be As contaminated, but the results of As analyses show that except Prigacha (which is highly As contaminated) hand tubewells (n ¼ 1438) of all other 22 thanas had As concentration
