1. International Conference on Sustainability Science in Asia (ICSS-Asia), 2009 Arsenic in Irrigated Soil and Food Chain Dr. M. Ashraf Ali Professor of Civil Engineering Bangladesh University of Engineering and Technology, BUET Bangkok, Thailand, 23 November 2009 1

2. Presentation Outline Background Presence of As in Irrigation water and Irrigated Soil Arsenic in Food Chain (Rice, Vegetables) Conclusions 2

3. BACKGROUND: As Contamination and GW Irrigation in Bangladesh 3

4. Arsenic Contamination of Groundwater in Bangladesh: Shallow aquifer (< 100 m) primarily affected, which is widely used for domestic purpose through use of hand tubewells as well as for irrigation Out of 465 upazilas (sub- districts), 270 seriously affected Over 30 million people exposed to As above 50 ppb

5. Groundwater is widely used for irrigation during dry season (December-May), primarily for growing dry season paddy, called boro; some vegetables also receive groundwater irrigation. Groundwater irrigation covers about 79% of the total irrigated area (over 5 million ha in 2007-08); shallow irrigation wells covers about 63% of total irrigated area. In 2007-08, over 1.3 million shallow tubewells were used to irrigate about 3.2 million ha of land. An estimated 1360 tons of As is added to arable soils each year in Bangladesh Widespread groundwater irrigation suggests that ingestion of irrigated crops could be a major exposure route for As, along with drinking water. Groundwater Irrigation in Bangladesh

6. Surface water irrigation: almost unchanged since 80s Groundwater irrigation:5 fold increase (mainly STW) Source of water, irrigation equipment and irrigated area in Bangladesh

7. Distribution Of Shallow Irrigation Wells In Bangladesh High concentration of irrigation wells in N and NW regions of Bangladesh. Whereas higher As concentration in S, SC, NE regions.

8. ARSENIC IN IRRIGATION WATER AND IRRIGATED SOIL o EAWAG-ETH-BUET joint research 8

9. Data on As in soils in Bangladesh indicate that 5–10 mg/kg is the background level. Reports indicate that soil concentrations are increasing because of As input via irrigation water. Available data suggest significant accumulation of As in top layer of irrigated soil; reported soil As concentrations vary from about 10 to 70 mg/kg. Our research revealed significant spatial and temporal variation of As concentration in irrigated soil Arsenic in Irrigated Soil

10. Fe(III) oxides present in soil and those produced by oxidation of Fe(II) in irrigation water promote adsorption and retention of As in soil. However, desorption and dissolution of Fe-solids (e.g., during flooding) may reduce As accumulation in soil. The conditions under which As is building up in the soil and the time frame involved are not certain. Recent findings from a field trial demonstrated that increasing soil As levels resulted in a decrease in rice yield. Arsenic in Irrigated Soil

11. Distribution and Variability of Arsenic in Irrigated Rice Field EAWAG-ETH-BUET Joint Research on Arsenic in Irrigated Land and in Food Chain, funded by Swiss National Foundation Spatial distribution and temporal variability of Arsenic in Irrigation water and paddy soil Arsenic mobilization from paddy soil Dynamics and trends of Arsenic Accumulation in paddy soil 11

12. Field Site: Sreenagar, Munshiganj 12 18 paddy fields Total area: 3.16 ha Total irrigation:  1 m/season Irrigation Water: As (total): 397 ± 7  g/L As(III): 332 ± 27  g/L Fe: 10.9 ± 0.2 mg/L P: 1.92 ± 0.07 mg/L

13. Field site located at Munshiganj, about 30 km south of Dhaka Field exclusively used for cultivation of boro rice, since 1990s, when local irrigation well was constructed. The irrigation well extracts groundwater from a depth of 30-60 m, with a pumping rate of approximately 19 L s -1 Fields are irrigated 18-21 times between early January and late April. Local boro rice production requires 1 m of irrigation water per season. Fields are irrigated for 2-4 h at a time until covered by 3- 10 cm of water. Field Site and Irrigation Practice

14. Fe Concentration in Irrigation Channel Water 14 Dissolved Fe concentrations decreased by 76% along the channel, indicating that most Fe was oxidized and formed HFO colloids. Roberts et al., 2007

15. As Concentration in Irrigation Channel Water 15 Total As input to any field within the irrigation area is virtually unaffected by the length of channel stretch between well and field inlet. Roberts et al., 2007

16. Fe Concentration in Rice Field Water 16 All Fe(II) was oxidized and formed HFO colloids within a distance of 20 m from the field inlet. Shortly (0-2 hr) after irrigation Roberts et al., 2007

17. As Concentration in Rice Field Water 17 As input to soil decreased strongly with increasing distance from the inlet. 2.75 hr after irrigation Shortly (0-2 hr) after irrigation Roberts et al., 2007

18. As Concentration in Field Water at Different Times 18 As concentrations in the stagnating field water decreased strongly, indicating transfer of As to soil. Roberts et al., 2007

19. Major Findings Total As input to a rice field was independent of the length of the irrigation channel. But within each field As input to soil decreased strongly with increasing distance from the inlet. The pattern of As distribution and extent of lateral heterogeneity would depend both on the composition of the irrigation water (As/P, Fe/As ratios) and on the type of irrigation system used Passage of the irrigation water through a designated treatment field or pond prior to its distribution might offer a simple means for reducing As input to soils used for crop production.. Within the top 40 cm of soil, the mean As 19

20. Arsenic in Paddy Soil 20 Soil Sample Collection : December 2004: before rice transplantation May 2005: After harvest December 2005: After monsoon flooding

21. Distribution of As in topsoil (0-10 cm) in December 2004 21 Median (12 fields) As in topsoil (0-10 cm): 12.5 – 18 mg kg -1 Median (12 fields) As in subsoil (30-40 cm): 7 – 14 mg kg -1 Dittmar et al., 2007

22. Total and Oxalate-extractable As in topsoil (0-10 cm) as a function of distance from Inlet 22 Peak Soil-As concentration in May 2005, after harvest As concentration reduced in December 2005, suggesting remobilization during monsoon due to reduction of submerges soil Dittmar et al., 2007

23. Total and Oxalate-extractable As as a function of depth 23 Peak Soil-As concentration in May 2005, after harvest As concentration reduced in December 2005, suggesting remobilization during monsoon due to reduction of submerges soil Dittmar et al., 2007

24. Difference in Soil As (in mg kg -1 ) in topsoil (0-10 cm) between Dec. 2007 and Dec. 2004 24 Dittmar et al., 2009, Submitted

25. Area-weighted Soil As Concentration between December 2004 – December 2007 25 Dittmar et al., 2009, Submitted

26. Soil As Mass at different depth ranges between December 2004 – December 2007 26 Dittmar et al., 2009, Submitted

27. Major Findings Annual As input with irrigation water equaled 4.4±0.4 kg ha -1 a -1. Within the top 40 cm of soil, the mean As accumulation over three years amounted to 2.4±0.4 kg ha -1 a -1, implying that on average 2.0 kg ha -1 a -1 were lost from the soil. Estimated 1.05-2.1 kg As ha -1 a -1 were lost by diffusion into monsoon floodwater The remaining As-loss (up to 0.95 kg ha -1 a -1 was attributed to leaching with percolating irrigation water. 27

28. Estimated changes in soil As (0 – 40 cm) according to three scenarios 28 Significant risk of high long-term accumulation of As in soil Dittmar et al., 2009, Submitted

29. ARSENIC IN FOOD CHAIN o EAWAG-ETH-BUET joint research o BUET study 29

30. Rice mainly contains As(V), As(III) and DMA. Reported As concentrations in rice range from 0.03 to 1.24 mg/kg; percentage of inorganic As ranged from 11 to 94%. Compared to other countries, rice from Bangladesh (and India) had the highest percentage of inorganic As (80 percent), against 42 percent in rice from the USA. All As present in vegetables, pulses and spices is reported to be present in inorganic form Limited data on water-soil-crop (rice/vegetable) transfer of As Arsenic in Rice and Food Items

31. Arsenic in Rice 31 Plant Sample Collection : May 2005 May 2006 May 2007 Dittmar et al., in preparation

32. Variation of Soil As with Distance from Inlet 32 Dittmar et al., in preparation

33. Variation of Straw-As with distance from Inlet 33 Dittmar et al., in preparation

34. Variation of Grain-As with distance from Inlet 34 Dittmar et al., in preparation

35. Variation of Grain-As with Soil-As (Pot Study) 35 Dittmar et al., in preparation

36. Major Findings As concentrations in straw and grain of rice appear to be strongly correlated with As in soil As. Arsenic concentration in both straw and grain could vary over a wide range within a paddy field Increasing soil As could result in significantly elevated concentrations of As in straw and grain of rice 36

37. As in Vegetables Three areas selected: Two As affected areas:  Sonargaon, Narayangonj  Kachua, Chandpur One unaffected area:  Sherpur, Bogra Selected Vegetables : Potato, Tomato, Stem Amaranth, Red Amaranth, Cabbage and Cauliflower (grown the both As-affected groundwater and As-free surface water)

38. Study involved collection of irrigation water (both surface water and groundwater) soil core samples and vegetable plants samples Analysis of As concentration in irrigation water, soil and plant (root, stem, leaf, edible part) samples As in groundwater used for irrigation: Borga: < 1 ppb Chandpur: 73 to 132 ppb Narayanganj: 63 to 266 ppb As in surface water used for irrigation: Bogra: < 1 ppb Chandpur: up to 6.7 ppb Narayanganj: up to 25.3 ppb Arsenic in Vegetables

39. Arsenic in Vegetable Samples: Potato Groundwater Irrigation Sampling Location As in Water (mg/l) As in Root Soil Mean ± SD (mg/kg) As in Root Mean ± SD (mg/kg) As in Stem Mean ± SD (mg/kg) As in Leaf Mean ± SD (mg/kg) As in Edible Part Mean ± SD (mg/kg) Bogra (n=6)< 1.02.55 ± 0.280.16 ± 0.040.09 ± 0.030.07 ± 0.030.02 ± 0.01 Chandpur (n=6)95 – 1324.09 ± 0.231.78 ± 0.570.34 ± 0.150.25 ± 0.100.23 ± 0.12 Narayanganj (n=6)214 - 2435.82 ± 0.932.62 ± 0.601.45 ± 0.322.06 ± 0.411.15 ± 0.31 Surface Water Irrigation Sampling Location As in Water (mg/l) As in Root soil Mean ± SD (mg/kg) As in Root Mean ± SD (mg/kg) As in Stem Mean ± SD (mg/kg) As in Leaf Mean ± SD (mg/kg) As in Edible Part Mean ± SD (mg/kg) Bogra (n=3)< 1.02.59 ± 0.510.35 ± 0.120.12 ± 0.050.25 ± 0.110.04 ± 0.01 Chandpur (n=3)1.63.12 ± 1.080.45 ± 0.090.24 ± 0.100.25 ± 0.080.10 ± 0.03 Narayanganj (n=3)25.34.90 ± 1.671.58 ± 0.460.85 ± 0.251.03 ± 0.450.51 ± 0.20

40. Arsenic in Vegetable Samples: Tomato Groundwater Irrigation Sampling Location As in Water (mg/l) As in Root Soil Mean ± SD (mg/kg) As in Root Mean ± SD (mg/kg) As in Stem Mean ± SD (mg/kg) As in Leaf Mean ± SD (mg/kg) As in Edible Part Mean ± SD (mg/kg) Bogra (n=6)<1.03.03 ± 0.570.33 ± 0.280.13 ± 0.040.39 ± 0.160.27 ± 0.05 Chandpur (n=3)734.53 ± 0.511.69 ± 0.470.99 ± 0.240.85 ± 0.211.05 ± 0.29 Narayanganj (n=6) 63 - 1665.63 ± 1.681.99 ± 0.111.15 ± 0.352.82 ± 0.231.70 ± 0.15 Surface Water Irrigation Sampling Location As in Water (mg/l) As in Root soil Mean ± SD (mg/kg) As in Root Mean ± SD (mg/kg) As in Stem Mean ± SD (mg/kg) As in Leaf Mean ± SD (mg/kg) As in Edible Part Mean ± SD (mg/kg) Bogra (n=3)2.53.67 ± 0.761.72 ± 0360.55 ± 0. 130.33 ± 0.090.47 ±0.08 Chandpur (n=6)2.0 - 3.23.53 ± 1.460.48 ± 0.160.23 ± 0.080.36 ± 0.070.78 ± 0.31 Narayanganj (n=3) 18.22.21 ± 0.511.03 ± 0.381.09 ± 0.270.93 ± 0.350.99 ± 0.25

41. Arsenic in Vegetables: Correlation with Water and Soil Arsenic Potato (p < 0.05)(p < 0.01)

42. MAJOR OBSERVATIONS The As concentrations in edible parts of the vegetables are strongly correlated with As concentrations in both irrigation water and root-soil. Among the selected vegetables, mean As concentrations have been found to be relatively higher for stem amaranth, red amaranth (both leafy vegetable) and tomato. Total As concentrations in most vegetables irrigated with As contaminated groundwater exceeded the Chinese food safety standard of 0.05 mg/kg inorganic As (wet weight basis) by a large margin.

43. Food Consumption Pattern Average food consumption in “g/capita/day” Hels et al. (2003) - Rice: 450 - Vegetables: 178 - Roots & Tubers: 61 - Fish: 39 - Other animal products: 31 In rural areas, the main meal usually consists of boiled rice served with cooked vegetables. Reported vegetable consumption varies from 130 to 500 g/capita/day (wet/fresh weight)

44. Exercise: Dietary Intake of Arsenic from Rice & Vegetables (  g/day) Vegetable Consumption (g/capita/day) Bogra Vegetable Mean As: 0.074 mg/kg Narayanganj Vegetable (SW irrigation) Mean As: 0.185 mg/kg Narayanganj Vegetable (GW irrigation) Mean As: 0.33 mg/kg 1309.62443 17813.23358 5003793165 WHO’s Provisional Maximum Tolerable Daily Intake: 126  g/day (60 kg adult) Intake from rice with As=0.2 to 0.5 mg/kg* (450 g/capita/day): 72-180  g /day Intake from vegetables: 24-165  g /day *80% inorganic As

45. Exercise: Dietary Intake of Arsenic from Drinking Water and Food Sources (  g/day) Source and Consumption (g/capita/day) Bogra Vegetable Mean As: 0.074 mg/kg Narayanganj Vegetable (SW irrigation) Mean As: 0.185 mg/kg Narayanganj Vegetable (GW irrigation) Mean As: 0.33 mg/kg Vegetables (178 g/capita/day) 13.23358 Rice (450 g/capita/day) As: 0.4 mg/kg* 144 Water from food (1.3 l/capita/day) As: 100 ppb --130 Drinking Water (3.0 l/capita/day) As: 100 ppb --300 As from Food 157307332 As from Drinking water --300 *80% inorganic As

46. Conclusions Presence of As in irrigation water leads to elevated levels of As in soil, with significant spatial and temporal variation. Areas without pronounced monsoon flooding may be at greater risk of soil As accumulation than seasonally flooded fields. Long-term accumulation of soil As will result in a concomitant long-term decline in rice yields on As- affected paddy fields. Because only about 21% of the total area of Bangladesh is annually flooded more deeply than 0.9 m and because less intensely flooded areas are often multiply cropped, As-related yield reductions in these areas could seriously affect national food security.

47. Conclusions Human As uptake via rice and vegetables may represent a major As uptake pathway, especially where As intake via drinking water is limited (by provision of low-As drinking water) Increasing soil As levels cause an increase in the As content of rice straw. Since rice straw is used to feed cattle, this may result in increasing human exposure to As via milk and meat products. Among other measures, efforts should be made to develop measures (e.g., water treatment) to reduce As input to agricultural land, and agricultural practices (e.g., raised bed cultivation, maintaining aerobic condition, use of silicon fertilizer) that reduces As uptake by plants. Efforts should also be made to develop rice varieties less susceptible to adverse effects of high soil As.

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