Influence of Natural Organic Matter on As Transport and Retention

Abstract

Natural organic matter (NOM) can affect the behavior of arsenic within surface and subsurface environments. We used batch and column experiments to determine the effect of peat humic acids (PHA), groundwater fulvic acids (GFA), and a soil organic matter (SOM) extract on As sorption/transport in ferrihydrite-coated sand columns. A reactive transport model was used to quantitatively interpret the transport of As in flow-through column (breakthrough) experiments. We found that As(III) breakthrough was faster than As(V) by up to 18% (with OM) and 14% (without OM). The most rapid breakthrough occurred in systems containing SOM and GFA. Dialysis and ultrafiltration of samples from breakthrough experiments showed that in OM-containing systems, As was transported mostly as free (noncomplexed) dissolved As but also as ternary As-Fe-OM colloids and dissolved complexes. In OM-free systems, As was transported in colloidal form or as a free ion. During desorption, more As(III) desorbed (23-37%) than As(V) (10-16%), and SOM resulted in the highest and OM-free systems the lowest amount of desorption. Overall, our experiments reveal that (i) NOM can enhance transport/mobilization of As, (ii) different fractions of NOM are capable of As mobilization, and (iii) freshly extracted SOM (from a forest soil) had greater impact on As transport than purified GFA/PHA.

Solid-solution partitioning and thionation of diphenylarsinic acid in a flooded soil under the impact of sulfate and iron reduction

“…At the initial incubation stages (0-4 weeks) DPAA in sulfide soil was mobilized primarily due to sodium lactate addition since sodium lactate may mobilize DPAA by covering adsorption sites on Fe(III) (hydr)oxides and/or competitive adsorption (Polizzotto et al, 2006;Sharma et al, 2010;Sharma et al, 2011). At later incubation stages (4-8 weeks) DPAA was almost completely released into the solution in sulfide soil while associated with the solid-phase in anoxic soil (Fig.1A and B), which is likely due to the near-complete reductive dissolution of Fe(III) (hydr)oxides in sulfide soil.…”

Arsenic retention and transport behavior in the presence of typical anionic and nonionic surfactants

“…FH used in this study was synthesized according to Schwertmann's method (Sharma et al, 2011). Under continuous stirring, a solution of 1.0 mol/L KOH was added to a 500 mL solution of 0.2 mol/L Fe(NO 3 ) 3 ·9H 2 O at a rate of approximately 50 mL/min, till the pH of the solution reached 7.5.…”

“…Transport of arsenic through sediment is an important process governing arsenic concentrations in groundwater (Sharma et al, 2011). Based on the batch tests discussed above, surfactants had the potential to affect arsenic adsorption onto FH by competing for adsorption sites and electrostatic repulsion.…”

“…4, As(V) and As(III) had similar transport behavior in FH-sand columns. The PV when the concentration of arsenic in the effluent reached 50% of the influx concentration was employed to compare the breakthrough of arsenic in the absence or presence of SDBS (Sharma et al, 2011). Thus, breakthrough of As(III) occurred at 227.2 PV, more rapidly than As(V) breakthrough, which occurred at 298.2 PV, indicating the greater mobility of As(III).…”

“…In natural environments, there could be three scenarios in which surfactants influence arsenic adsorption and mobilization (Sharma et al, 2011). The first scenario represents water environments where surfactants coexist with arsenic.…”