Effect of Global Warming with Arsenic Mobilization in Sediments of the River Padma

in Bangladesh

Dr. A. M. Shafiqul AlamProfessor

Department of Chemistry

University of Dhaka

E-mail:amsalam2004@yahoo.com

International Symposium On Climate Change & Food Security In South Asia

2

Arsenic mobilization from aquatic sediments is an issue of concern, as water-borne arsenic can migrate into sediments to tube well water, endangering aquatic organisms and people.

The occurrence, origin and mobility of arsenic in ground water is influenced by local geology, geochemistry, bio-geochemical transformation and hydrology of the alluvial aquifers as well as the temperature of earth.

Arsenic solubility in sediments increased greatly with diminishing redox potential, with arsenic in ground water predominantly as As(III).

INTRODUCTION

The redox potential decreases with increase of temperature in sediments. Therefore the conc. of As(III) would be higher in the sediments.

Since the mobility of As(III) is faster than As(V), the concentration of As (III) would be higher in the downstream than the upper stream of the river sediments.

Moreover, now a days, the temperature of earth is increasing significantly with time.

Therefore, it is very important to study the mobilization of the arsenic, iron and manganese with temperature from upper stream to down stream sediment in the river Padma.

Sampling areasThe sediment of the Padma river was collected by borehole technique. The sampling points are as follows:1. Rajshahi:

(A) Godagari

(B) Rajshahi City

(C) Ishardi

2. Manikgonj

(A) Confluence of Padma-Jumuna river

3. Munshigonj

(A) Mowaghat

4. Chandpur

(A) Confluence of the Padma-Meghna River

Godagari

Rajshahi

Ishardi

Manikgonj

Mowaghat

Chandpur

6

Borehole Technique

Sediment sampling

7

Sediments were collected at several depths ranging from 1 meter to 5 meters.

Sediments were collected by digging 1.5 inches (diameter) pipe through normal digging procedure.

The sediment samples were digested with HNO3 and HClO4 (3:2 ratio) in Teflon acid digestion bomb.

Methodology

8

Arsenic was analyzed using the Hydride Vapor Generator (HVG) attached with Atomic Absorption Spectrophotometer (AAS-680, Shimadzu, Japan.).

Fe & Mn were analyzed using Flame Atomic Absorption Spectrophotometer using air-acetylene flame.

Results & Discussion

Variation of arsenic from upper stream sediment to down stream in the river Padma

84.0

1

53.8

1

27.7

4

2.54

-20

0

20

40

60

80

100

Manikgonj Rajshahi Mowyaghat Chandpur

Sampling locations

Conc

of A

s m

g/K

g

Figure -1

Variation of iron from upper stream sediment to down stream in the river Padma

3314

0

2614

0

1697

0

1501

0

05000

10000150002000025000300003500040000

Manikgonj Rajshahi Mowyaghat Chandpur

Sampling locations

Co

nc

of F

e m

g/K

g

Figure -2

Variation of Mn from upper stream sediment to down stream in the river Padma

580

330

310

220

0100200300400500600700

Manikgonj Rajshahi Mowyaghat ChandpurSampling locations

Co

nc

of M

n m

g/K

g

Figure -3

13

Arsenic concentration was varied from upper, middle and lower Arsenic concentration was varied from upper, middle and lower stream in different depth of every location due to the geochemicstream in different depth of every location due to the geochemical, al, biogeochemical transformation with temperature in sediments, biogeochemical transformation with temperature in sediments, rocks and different ores present in soilrocks and different ores present in soil..

14

Lower amount of As was found in Manikgonj region due to strong current might swift As from the Padma-Jumuna confluence and high amount of As was found in Chandpur because this region was received As from the next upstream Padma-Jumuna confluence.

Figure -4

Variation of As with depth of the sediments

0

20

40

60

1m 2m 3m 4m 5m

Depth (m)

Con

c of

As

mg/

Kg

Chandpur

Rajshahi

Manikgonj

Variation of Fe w ith depth of the sediments

0

10000

20000

30000

40000

1m 2m 3m 4m 5m

Depths (m)

Co

nc

of

Fe

mg

/Kg

Manikgonj

Rajshahi

Chandpur

Figure -5

Variation of Mn with depth of the sediments

0

500

1000

1500

2000

2500

1m 2m 3m 4m 5m

Depth (m)

Co

nc

of

Mn

mg

/Kg

Chandpur

Rajshahi

Manikgonj

Figure -6

It was observed that the total arsenic concentration was higher in deeper depth than the upper part of the sediments.

Generally, the temperature increases with going down to the earth. Therefore, the higher concentration of arsenic found at the lower part of sediment was a direct consequences of the increased temperature.

Table: Average concentration of arsenic at different locations of

the river Padma

84.25 ±4.2130.11 ±2.454.14 ±2.5Chandpur

2.57 ±0.021.05 ±0.021.52 ±0.01Manikgonj

12.43 ±0.034.85 ±.017.58±0.02Rajshahi

Total As mg/Kg

As (V) mg/Kg

As (III) mg/Kg

Sampling Area

0

5

10

15

20

25

Rajshahi Manikgonj Chandpur

Locations

Co

nc.

of

As

(pp

b)

Variation of As in surface water of the river Padma

Figure -7

God

agar

i

Raj

shah

i

Isw

ardi

Man

ikgo

nj

Mow

yagh

at

Cha

ndpu

r

1m 2m 3m 4m 5m

020406080

100120140160180200

As conc mg/Kg

Locations

Depth (m)

Average arsenic conc. at 1-5 m depth of different sites

1m

2m

3m

4m

5m

Figure -8

22

God

agar

i

Raj

shah

i

Isw

ardi

Man

ikgo

nj

Mou

yagh

at

Cha

ndpu

r

1m

2m3m

4m5m

0

100

200

300

400

500

600

700

800

Mn conc mg/Kg

Locations

Depth (m)

Average Mn conc. at 1-5 m depth of different sites

1m

2m

3m

4m

5m

Figure -9

23

God

agar

i

Raj

shah

i

Isw

ardi

Man

ikgo

nj

Mou

yagh

at

Cha

ndpu

r

1m2m

3m4m

5m

0

10000

20000

30000

40000

50000

60000

Fe conc mg/Kg

Locations

Depth (m)

Average Fe conc. at 1-5 m depth of different sites

1m

2m

3m

4m

5m

Figure -10

24

0

1000

2000

3000

4000

5000

6000

7000

8000

0 200 400 600 800

Conc. of arsenic (mg/Kg)

Con

c. o

f Fe m

g/Kg

The correlation factor is poor which indicates there is slight relation

between iron concentration with arsenic contamination

Scattered diagram for comparison between As and Fe in

borehole sediments

Figure -11

25

Scattered diagram for comparison between As and Mn in

borehole sediments

010002000

3000400050006000

70008000

0 200 400 600 800

Conc. of arsenic mg/kg

Conc.

of M

n (m

g/K

g)

The correlation factor is poor which indicates there is slight relation between Mn

concentration with arsenic contamination

Figure -12

• The result shows arsenic was mobilized from upper stream Godagari-Rajshahi to down stream Mouyaghat- Chandpur.

Average percentage of arsenic in up, down and middle stream of the river Padma

41

6

53

Up Stream Godagari-Rajshahi

Middle Stream Ishwardi-Manikgonj

Down stream Moyaghat-Chandpur

Figure -13

•

Among the six locations of the Padma River, high amount of arsenic( 84.65 mg Kg-1) was found at Padma River near Chandpur and low amount was found (2.57 mg Kg-1) at Manikgonj near Padma-Jamuna confluence.

When the strong current of the river carries sediment particles,larger particles of the sediment settles and finely grained sediment particles are transported further distance. Finally, it stored to downstream region. As a result, arsenic concentration at the downstream region is higher.

Temperature/°C

24 25 26 27 28 29 30 31

Dis

solv

ed O

xyge

n (m

g/L)

4.8

5.0

5.2

5.4

5.6

5.8

6.0

6.2

6.4

Rajshahi

Manikgonj

Chandpur

Fig.-14.Variation of dissolved oxygen with temperature at different sampling places in Bangladesh.

Increasing of temperature, dissolved oxygen (DO) decreases in water. Therefore, redox potential of water containing sediments of Rajshahi is much decreased than Manikgonj and Chandpur area.

Due to lowering of redox potential of water inside the sediments layer, As (III) would be predominant species in sediments.

From the figure-14, it is found that the temperature at Rajshai is higher than the other two places.

As a consequence, the dissolved oxygen of the river water become higher at Manikgong and Chandpur areas compared to Rajshahiarea.

Therefore, the redox potential of the water also lowered at Rajshahi area. Due to the lowering of the redox potential of the water, As(III) would be the predominant species in the sediments.

Since the mobility of the As(III) is higher than the As(V), therefore, total As conc. at Chandpur area (downstream) was found to be higher.

This results imply that there is a direct relation of arsenic mobilization with temperature. Moreover, 35 years back, arsenic was not found in the ground water of Bangladesh. However, now arsenic is found in the ground water due to the change of global temperature which affects our soil, water environment and our health as well.

Year

2000 2001 2002 2003 2004 2005 2006 2007 2008

Te

mpe

ratu

re/0 C

31

32

33

34

35

36

37

Fig-15:Changing of temperature with time in Bangladesh

Rajshahi

Chandpur

Manikgonj

• Change of temperature with time of different sampling areas has been presented in Figure-15. These data was supplied by the Bangladesh Meteorological Department, Dhaka. From the Figure, it is observed that the average temperature of Bangladesh increased with time from 2000 to 2007. Temperature at Rajshahi, Manikgonj and Chandpur increased gradually with time. This effect arises due to the effect of Global Warming in the world.

• It is also clear that the temperature of Bangladesh increased within seven years. At Rajshahi, higher temperature was observed with respect to Manikgonj and Chandpur in Bangladesh. This increased temperature reduced the redox potential of water which helped to produce more As(III) from arsenic containing pyrites in sediments. Since the temperature of Rajshahi was higher than Manikgonj and Chandpur, more As(III) was produced at Rajshahi. Finally, it moved from Rajshahi to Chandpur in the sediments along the river Padma.

Conclusion

• The conc. of arsenic is found to be higher at the down stream of the Padma river.

• There is slight correlation found with the iron and manganese movement with arsenic in the sediment.

• Dissolved oxygen is lower at Rajshahi than Manikgonj and Chandpur because of the different temperature at these places.

• The arsenic is mobilized from upper stream at Godagari to down stream at chandpurwhich is higher than the guideline value.

• This effect arises due to the increase of temperature on earth (Effect of global warming).

• This higher conc. of arsenic in sediment would increase the arsenic conc. in ground water at Chandpur (Hajigonj area is the most endemic area of Bangladesh).

• Therefore, awareness should be increased to the people of developed countries so that they can protect the air environment from excess emission of carbon dioxide which is directly related to the global warming to the developing countries.