Field sampling protocol

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FIELD WATER COLLECTION for later Arsenic Bioreporter Analysis

Reference

Trang, P. T. K., Berg, M., Viet, P. H., Van Mui, N., & van der Meer, J. R. (2005). Bacterial bioassay for rapid and accurate analysis of arsenic in highly variable groundwater samples. Environmental Science & Technology, 39(19), 7625–7630. doi:10.1021/es050992e pdf

Concept

Arsenic contaminated groundwater is often iron (Fe) -rich.
Acids or complexing agents need to be added

  • to prevent co-precipitation of arsenic onto FeOOH particles, which form when anoxic groundwater is exposed to oxygen in air
  • to preserve the sample arsenic composition


Water must be collected to minimize oxygen-exposure = deep and not surface water

Reagents

  • 7.5M HNO3 (Merck) !!! to dilute acid. !!! ATTENTION: add acid TO water (and not the reverse)
  • Arsenic (III) stock solution (As(III) 1000mg/L, AAAS grade, Fluka, Switzerland)

Materials

  • plastic bottles
  • water resistant pens for labeling
  • 0.45µm filters
  • Pipette capable of introducing 1ml of acid solution
  • Measuring cup capable of measuring 50ml

Methods

IN THE LAB

  1. Prepare for plastic bottles for water collection
    1. Mark the outside the volume for 50ml
    2. Wash the bottles with diluted 0.015mM HNO3 acid
  2. Prepare a 0.75M HNO3 stock to bring to the field

IN THE FIELD

  1. Pump water from the well for 10 minutes
    1. Oxygen concentration in water must reach a stable value – preferably, measure oxygen levels with a dissolved oxygen electrode to see that it stabilizes
  2. Immediately filter through 0.45µm filters
  3. Fill sample bottle to the line marked previously = 50ml
  4. Add 1ml of 0.75M HNO3 (Acidify the solution) to make 0.015mM final concentration
  5. Keep at 4oC in the laboratory
  6. Analyze within 2 weeks