Considerations for conducting incubations to study the mechanisms of As release in reducing groundwater aquifers

Abstract

Microbial Fe reduction is widely believed to be the primary mechanism of As release from aquifer sands in Bangladesh, but alternative explanations have been proposed. Long-term incubation studies using natural aquifer material are one way to address such divergent views. This study addresses two issues related to this approach: (1) the need for suitable abiotic controls and (2) the spatial variability of the composition of aquifer sands. Four sterilization techniques were examined using orange-colored Pleistocene sediment from Bangladesh and artificial groundwater over 8 months. Acetate (10 mM) was added to sacrificial vials before sterilization using either (1) 25 kGy of gamma irradiation, (2) three 1-h autoclave cycles, (3) a single addition of an antibiotic mixture at 1x or (4) 10x the typical dose, and (5) a 10 mM addition of azide. The effectiveness of sterilization was evaluated using two indicators of microbial Fe reduction, changes in diffuse spectral reflectance and leachable Fe(II)/Fe ratios, as well as changes in P-extractable As concentrations in the solid phase. A low dose of antibiotics was ineffective after 70 days, whereas autoclaving significantly altered groundwater composition. Gamma irradiation, a high dose of antibiotics, and azide were effective for the duration of the experiment.

Reversible adsorption and flushing of arsenic in a shallow, Holocene aquifer of Bangladesh

“…Sediment incubation experiments were previously conducted using material from the site (Radloff et al, 2008). The land surface of the site is characterized by a sandy, raised area in the village with a gradually thickening silty-clay layer extending beneath the adjacent agricultural fields, which are bordered by a small stream (Fig.…”

Dissolved Organic Matter Quality in a Shallow Aquifer of Bangladesh: Implications for Arsenic Mobility

“…The study area was chosen because the redox condition of the shallow Holocene aquifer and in turn, groundwater As level and age, spans nearly the entire range found in Bangladesh 37–41 . Groundwater samples were collected from monitoring wells installed at Site K described in Radloff et al (2008) and Radloff (2010) 42, 43 and Site B described in Zheng et al (2005) 44 . The two sites are approximately 2 km apart and are in a primarily rural setting with numerous ponds and irrigated rice and vegetable fields.…”

An improved datalogger and novel probes for continuous redox measurements in wetlands

“…First, the HYPNOS datalogger was installed at site KW12 at the Araihazar village in Bangladesh [13]. This site (previously described by Radloff et al [14] as site K240) has a sandy aquifer with a fluctuating groundwater table. The groundwater table can be as low as 6 m below surface, or reach surface level during storm events.…”