Arsenic Contamination

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					Arsenic Contamination of
Bangladesh Paddy Field Soils:
Implications for Rice Contribution to
Arsenic Consumption



    Professor:Pao-Nuan Hsieh ,Ph.D.
    Reporter:Tzu-Hui Ho(何姿慧)
    Nov 19th, 2009


                                        1
Outlines

•   Abstract
•   Introduction
•   Materials and Methods
•   Results and Discussion
•   References




                             2
• 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)
                                                  3
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    4
台灣地區高砷含量之地下水區

            5
Abstract

• 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.



                                                  6
Introduction(1/4)

• 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

                                                 7
Introduction (2/4)
• 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.


                                                            8
Introduction (3/4)

• 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.


                                                    9
Introduction (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.
                                                10
Materials and Methods (1/3)

• 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.




                                                                11
Materials and Methods (2/3)

• 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)




                                                                 12
Materials and Methods (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



                                                  13
Results and Discussion (1/9)

• 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


                                                     14
Results and Discussion (2/9)

         well age   vs arsenic levels(soil)




                                              15
Results and Discussion (3/9)

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


                                                                        Scatter plot



                                                                                  16
Results and Discussion (4/9)

• tube-well depth and arsenic concentrations in the
  well water were not significantly
                                            well
  Arsenic                                   depth(m
  levels(GW                                 )25-50
  )50-250




                                                      17
Results and Discussion (5/9)

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



                                                   18
Results and Discussion (6/9)

• 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




                                                19
Results and Discussion (7/9)




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


                                                             20
Results and Discussion (8/9)
• 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
                                                   0.01
                                                   0.1

                                                    1


                                                          21
Results and Discussion (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.




                                                     22
References

 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.




                                         23
Thanks for your attention!!



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