Outlines

2. Outlines • 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）

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5. 台灣地區高砷含量之地下水區

6. Abstract • Arsenic contaminated groundwater is used extensively in Bangladesh to irrigate the staple food of the region, paddyrice. • 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 arsenicin 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, 200,000-270,000people 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.

12. 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)

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 42.5μg g-1 ‧the age and depth of the tube-wells need to be considered as arsenic will accumulatein 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 Regression equation Scatter plot

17. Results and Discussion (4/9) • tube-well depth and arsenic concentrations in the well water were not significantly well depth(m)25-50 Arsenic levels(GW)50-250

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 0.092μg 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 1.83μg g-1 arsenic levels within the same range as the field trials at Gazipur

20. Results and Discussion (7/9) • 113.5 mg╱kg(as soil), 0.074 mg╱kg(rice grain),at Guandu,

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-1of 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

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.

23. 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.

24. Thanks for your attention!!