US EPA

1015679 

Journal Article 

Investigating arsenic speciation and mobilization in sediments with DGT and DET: a mesocosm evaluation of oxic-anoxic transitions 

Bennett, WW; Teasdale, PR; Panther, JG; Welsh, DT; Zhao, H; Jolley, DF 

2012 

1 

Environmental Science & Technology
ISSN: 0013-936X
EISSN: 1520-5851 

46 

7 

3981-3989 

English 

22397626 

10.1021/es204484k 

WOS:000302850400052 

Mobilization of arsenic from freshwater and estuarine sediments during the transition from oxic to anoxic conditions was investigated, using recently developed diffusive sampling techniques. Arsenic speciation and Fe(II) concentrations were measured at high resolution (1-3 mm) with in situ diffusive gradients in thin films (DGT) and diffusive equilibration in thin films (DET) techniques. Water column anoxia induced Fe(II) and As(III) fluxes from the sediment. A correlation between water column Fe(II) and As(III) concentrations was observed in both freshwater (rs=0.896, p<0.001) and estuarine (rs=0.557, p<0.001) mesocosms. Porewater sampling by DGT and DET techniques confirmed that arsenic mobilization was associated with the reductive dissolution of Fe(III) (hydr)oxides in the sub-oxic zone of the sediment; a relationship that was visible because of the ability to measure the co-incident profiles of these species using combined DGT and DET samplers. The selective measurement of As(III) and total inorganic arsenic by separate DGT samplers indicated that As(III) was the primary species mobilized from the solid phase to the porewater. This measurement approach effectively ruled out substantial As(V) mobilization from the freshwater and estuarine sediments in this experiment. This study demonstrates the capabilities of the DGT and DET techniques for investigating arsenic speciation and mobilization in a range of sediment conditions.