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Arsenic Contamination ofBangladesh Paddy Field Soils:Implications for Rice Contribution toArsenic Consumption

Professor： Pao-Nuan Hsieh ,Ph.D.

Reporter： Tzu-Hui Ho(何姿慧 )

Nov 19th, 2009

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OutlinesOutlines

• Abstract

• Introduction

• Materials and Methods

• Results and Discussion

• References

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• 世界各地砷污染之分佈（ Smedley and kinniburgh, 2002 ）世界各地砷污染之分佈 （ Smedley and kinniburgh, 2002 ）

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台灣地區高砷含量之地下水區

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AbstractAbstract

• Arsenic contaminated groundwater is used extensively in Bangladesh to irrigate the staple food of the region, paddy rice.

• A survey of arsenic levels in paddy soils and rice grain was undertaken.

• Regression of soil arsenic levels with tube-well age was significant.

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IntroductionIntroduction(1(1/4/4))

• The digging of tube-wells for drinking water supply into aquifers elevated in arsenic in Bangladesh and West Bengal has been described as the greatest mass poisoning in human history. ---36 million people exposed

• Groundwater arsenic concentrations approaches 2mg L-1, 200,000-270,000 people will die of cancer from drinking arsenic contaminated drinking water

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Introduction Introduction (2(2/4/4))

• Arsenic contaminated groundwater is not just used for drinking water but is also widely used for irrigation of crops,and particularly for the staple food paddy rice,~provides 73% of calorific intake

• Groundwater is used extensively to irrigate rice crops in Bangladesh, particularly during the dry season with 75% of the total cropped area given over to rice cultivation and 83% of the total irrigated area used for rice cultivation.

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Introduction Introduction (3(3/4/4))

• Levels of arsenic in rice grain are typically 0.05-0.4 μg g-1 for North America, Europe, and Taiwan(0.074 μg g-1 ).

• Arsenic levels in rice grain reached 0.7 μg g-1 in rice grown on paddy soils containing 68 μg g-1 arsenic in China , showing the potential for arsenic contamination of rice grain from contaminated paddy soils.

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Introduction Introduction (4(4/4/4))

• Contamination of soil was related to tube-well arsenic levels, depth, and age to understand the mechanism of soil contamination by arsenic.

• Arsenic levels in Bangladesh produced rice, were determined to calculate baseline exposure of the population to rice derived arsenic.

• Dietary arsenic exposure was then modeled using these data.

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Materials and Methods Materials and Methods (1(1/3/3))

• Collection of Soil and Rice Grain Samples：Soil and rice samples were collected during the period of January-February, 2001.

Soil samples were collected from 27 administrative districts of Bangladesh, and a total of 71 samples were obtained.

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Materials and Methods Materials and Methods (2(2/3/3))

• Analysis ： soil and rice grain(husk)→oven dry(70 ºC)→grinding

→digested→nitric acid-hydrogen peroxide

→heating block(60 ºC)→cooled →diluted in deionized water

→filtered(Whatman no. 42 filter paper)

→soil(Perkin-Elmer 3300)

→rice grain(Perkin-Elmer Aanalyst 300 、 FIAS 100 hydride generator)

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Materials and Methods Materials and Methods (3(3/3/3))

• Tube-Well Data： year constructed, depth, arsenic levels obtain from the British Geological Survey (BGS) web-site.

• The BGS tube-well data was similarly averaged per district for comparison with the soils data.

• Statistics：Minitab v.13

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Results and Discussion Results and Discussion (1(1/9/9))

• Arsenic in Paddy Soils： ‧surface paddy soils 3.1 to 42.5 μg g-1

‧ the age and depth of the tube-wells need to be

considered as arsenic will accumulate in the

soil with long period of time

‧ the soils had become contaminated through

irrigation with arsenic contaminated water

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Results and Discussion Results and Discussion (2(2/9/9))

well age vs arsenic levels(soil)

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Results and Discussion Results and Discussion (3(3/9/9))

• Continuous variable

• Two continuous variable →covariance

• Linear regression • Linear regression of tube-well age against paddy

soil arsenic levels was significant (P=.048) 〈 .05

• Similar regressions with tube-well depth (P=.505) 〉 .05 and

tube-well arsenic levels (P =.684) 〉 .05 were not significant

Scatter plot

Regression equation

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Results and Discussion Results and Discussion (4(4/9/9))

• tube-well depth and arsenic concentrations in the well water were not significantly

Arsenic levels(GW)50-250

well depth(m)25-50

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Results and Discussion Results and Discussion (5(5/9/9))

• Arsenic Levels in Rice ： Samples collected from Gazipur District at the Ba

ngladesh Rice Research Institute had an average level of

0.092 μg g-1 dry wt, highest 0.21 μg g-1

Arsenic content

10.9,14.6 μg g-1

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Results and Discussion Results and Discussion (6(6/9/9))

• Western Bangladesh Districts arsenic levels ranging from 0.058 to 1.83 μg g-1

arsenic levels within the same range as the

field trials at Gazipur

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Results and Discussion Results and Discussion (7(7/9/9))

• 113.5 mg kg(as soil), 0.074 mg kg(rice grain),at Guandu,╱ ╱

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Results and Discussion Results and Discussion (8(8/9/9))

• calculate daily human intake of arsenic from rice.• With a drinking water intake of 0.1 mg L-1, arsenic

intake from rice will account for 17.3 and 29.6% of arsenic consumption if rice contained 0.1 and 0.2 μg g-1 of arsenic, respectively.

• These grain values are typical of what has been observed in a range of studies in Asia, Europe, and N. America

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0.1

0.01

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Results and Discussion Results and Discussion (9(9/9/9))

• the bioavailability of arsenic in rice • arsenic in rice grain →inorganic arsenic→toxic

and readily assimilated into the blood stream

• provide a safe water source

• decrease dietary exposure from arsenic still exists.

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ReferencesReferences

Meharg, A. A., and Rahman A. A., 2003. “Arsenic Contamination of Bangladesh Paddy Field Soils: Implications for Rice Contribution to Arsenic Consumption,” Environmental Science Technnology, 37(2)： 229-334.

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Thanks for your attention!!