Sensor-based investigation of biogeochemical controls on arsenic mobilization in rural Bangladesh

1. Sensor-based investigation of biogeochemical controls on arsenic mobilization in rural Bangladesh Nithya Ramanathan, Christine Lee, Tiffany Lin, Rebecca Neumann, Sarah Rothenberg, Charlie Harvey, Thomas Harmon, Eddie Kohler, Deborah Estrin, Jenny Jay

2. Tufts (Medford, Massachusetts) Shafiqul Islam UBC (Vancouver, British Columbia) Roger Beckie UCLA (Los Angeles, California) Jenny Jay Christine Lee Tiffany Lin Nithya Ramanathan Sarah Rothenberg UC Merced (Merced, California) Tom Harmon BUET (Dhaka, Bangladesh) Ashraf Ali Borhan Badruzzaman Sajib Sha alom ETH (Zurich, Switzerland) Stephan Hug Linda Roberts MIT (Boston, Massachusetts) Ashfaque Kandakher Charlie Harvey Rebecca Neumann Stanford (Palo Alto, California Scott Fendorf Matt Polizotto

4. WHO LIMIT IN DRINKING WATER: 0.01 mg/L (10 ppb)** • Guideline is restricted by measurement limitations. Based on health criteria, the guideline value for arsenic in drinking-water would be less than 0.01mg/L. **Taken from WHO arsenic reference: http://www.who.int/mediacentre/factsheets/fs210/en/

5. 0 C o r e Surface Clay 20 40 60 80 100 120 140 160 Solid phase Arsenic Dissolved As (ppb) ug/g or ppm 15 Piezometers 0 2 4 6 8 10 400 0 800 Depth (m) Sand Clay Sand Swartz et al. 2002. Geochim. Cosmochim. Acta

6. (Dittmar et al, 2007 Environmental Science & Technology, Roberts et al, 2007 Environmental Science & Technology) Diagram based on that in (Polizotto et al, 2006 Chemical Geology) Oxidation => As Immobilization (Dry Season) As(III)-sulfide minerals As(III) Fe(III) hydroxides As(III) Aqueous As(III) Mobilized to Depth (Polizotto et al, 2006 Chemical Geology) (Harvey 2006) Reduction => As Mobilization (Monsoon Season) microbial respiration, driven by organic carbon from ponds (Harvey et al, 2006 Chemical Geology)

7. Goal: robust wireless sensing system for groundwater chemistry studies

8. DEPLOYMENT: Wireless sensing system, Feb 2006Deployed 48 sensors over 12 DaysCollected 25,000 measurements Image Courtesy: Charlie Harvey, MIT / Jason Fisher, UC Merced

9. Daily trends were observable in several redox active geochemical parameters Goal: Temporally dense investigation of seasonal oxidation-reduction processes leading to arsenic mobilization at a field site in Munshiganj, Bangladesh

10. DATA QUALITY: Examples of Faulty Data

11. DEPLOYMENT: Wired sensing system, Mar 2007Deployed 21 sensors over 2 MonthsCollected 220,000 measurements Dissolved Oxygen (Bund) 1’,1.5’,3.5’ Dissolved Oxygen 1’,1.5’,3.5’ Dissolved Oxygen 1’,1.5’,3.5’ Goal: Investigate diurnal oxidation-reduction cycling processes in Munshiganj, Bangladesh 52.5’ 34’ Tower 20’ High

12. Dissolved Oxygen NH4+, NO3- / CO3- 1’,3’ NH4+, NO3- (Bund) 1’,3’ 28’ Tower

13. Dissolved Oxygen at 1’First Week April, 2007

14. Ammonium [M] 1’ In Bund Nitrate [M] 1’ In Bund Carbonate [M] 1’ in Paddy

15. DATA: Diurnal Cycles in Data Collected During Field Campaign, Mar 2007 Date (2007)

16. Diurnal in addition to Seasonal Redox Cycles? Oxidation => As Immobilization As(III)-sulfide minerals As(III) Fe(III) hydroxides As(III) Aqueous As(III) Mobilized to Depth Reduction => As Mobilization microbial respiration, driven by organic carbon from ponds

17. DATA QUALITY 2007: Improved but still problematic ** Replaced 1 broken nitrate sensor in the field in the first couple days with a carbonate sensor

18. Deployed (2007) Focus for Robust Sensing System Design on Improving Data Integrity: Implemented Solutions Being Tested Javelin Protects Sensors (Harmon et. al.) Image Courtesy Jason Fisher, UC Merced In-Field Sample Validation (Hach) • Hobo U-12 Logger • Limited to positive readings • Wired communication MDA2400 Custom designed board by Atla labs, provides high quality sensor interface. Enables wireless communication Confidence In-situ fault detection enables fixing faults and validating data in the field. In-Situ Calibration (Harmon et. al)

19. Thank you!!

20. DATA: Diurnal Cycles in Data Collected During Field Campaign, Mar 2007

21. DATA: Diurnal Cycles in Data Collected During Field Campaign, Mar 2007

22. Two In-Situ Sensor Deployments to Study Arsenic Mobilization • 20 Minute sampling period • Battery powered operation • Lifetime limited by sensor maintenance!

23. Daily trends were observable in several redox active geochemical parameters

24. Pylon 1 Pylon 2 Pylon 3 20 feet 30 feet 1 foot 3 feet 5 feet DEPLOYMENT: Wireless sensing system, Feb 2006Deployed 48 sensors over 12 DaysCollected 25,000 measurements 6 ISE Suites - Ammonium, pH, Redox, Nitrate, Chloride, Calcium, Carbonate (Sentek) 3 Suites – Temperature, Moisture (Decagon Echo 20)

25. 1’ In Bund Ammonium [M] In-Field Physical Sample Measurement Nitrate [M]

26. 3’ In Bund Ammonium [M] Nitrate [M]

27. 1’ In Paddy Ammonium [M] Carbonate [M]

28. 3’ In Paddy Ammonium [M] Nitrate [M]

29. DATA: Diurnal Cycles in Data Collected During Field Campaign, Feb 2006 Image Courtesy: Jason Fisher, UC Merced