Presentation on theme: "1 Arsenic Contamination of Bangladesh Paddy Field Soils: Implications for Rice Contribution to Arsenic Consumption Professor ： Pao-Nuan Hsieh,Ph.D. Reporter."— Presentation transcript:
1 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 19 th, 2009
2Outlines Abstract Introduction Materials and Methods Results and Discussion References
3 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 ）
6Abstract 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.
7 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
8 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.
9 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.
10 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.
11 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.
13 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
14 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
15 Results and Discussion (2/9) well age vs arsenic levels(soil)
16 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 tube-well arsenic levels (P =.684) 〉.05 were not significant Scatter plot Regressio n equation
17 Results and Discussion (4/9) tube-well depth and arsenic concentrations in the well water were not significantly Arsenic levels(GW )50-250 well depth(m )25-50
18 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
19 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
21 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 1 0.1 0.01
22 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.
23References 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.