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

Abstract

• We first investigated the solid-solution partitioning of DPAA in a flooded soil.• We first examined the impacts of sulfate and iron reduction on DPAA partitioning.• Elevated DPAA mobilization and thionation was observed in sulfide soil.• DPAA mobilization associated with Fe(III) reductive dissolution was demonstrated.• Enhanced mobilization of DPAA and sulfate reduction promoted DPAA thionation. Editor: Jay Gan Diphenylarsinic acid (DPAA) is a major organic arsenic (As) compound derived from abandoned chemical weapons. The solid-solution partitioning and transformation of DPAA in flooded soils are poorly understood but are of great concern. The identification of the mechanisms responsible for the mobilization and transformation of DPAA may help to develop effective remediation strategies. Here, soil and Fe mineral incubation experiments were carried out to elucidate the partitioning and transformation of DPAA in anoxic (without addition of sulfate or sodium lactate) and sulfide (with the addition of sulfate and sodium lactate) soil and to examine the impact of sulfate and Fe(III) reduction on these processes. Results show that DPAA was more effectively mobilized and thionated in sulfide soil than in anoxic soil. At the initial incubation stages (0-4 weeks), 6.7-74.5% of the total DPAA in sulfide soil was mobilized likely by sorption competition with sodium lactate. At later incubation stage (4-8 weeks), DPAA was almost completely released into the solution likely due to the near-complete Fe(III) reduction. Scanning transmission X-ray microscopy (STXM) results provide further direct evidence of elevated DPAA release coupled with Fe(III) reduction in sulfide environments. The total DPAA fraction decreased significantly to 24.5% after two weeks and reached 3.4% after eight weeks in sulfide soil, whereas no obvious elimination of DPAA occurred in anoxic soil at the initial two weeks and the total DPAA fraction decreased to 10.9% after eight weeks. This can be explained in part by the enhanced mobilization of DPAA and sulfate reduction in G R A P H I C A L A B S T R A C T a b s t r a c t a r t i c l e i n f o Contents lists available at ScienceDirectScience of the Total Environment j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n v sulfide soil compared with anoxic soil. These results suggest that under flooded soil conditions, Fe(III) and sulfate reduction significantly promote DPAA mobilization and thionation, respectively, and we suggest that it is essential to consider both sulfate and Fe(III) reduction to further our understanding of the environmental fate of DPAA.

Speciation and sorption structure of diphenylarsinic acid in soil clay mineral fractions using sequential extraction and EXAFS spectroscopy

“…These results provide a means of estimating the DPAA sorption capacity of clay mineral fractions on the basis of DPAA fractions associated with amorphous, poorly crystalline, and well-crystallized Fe/Al (hydr)oxides. It should also be noted that DPAA extracted in steps iii-iv could be a potential source of DPAA contamination during the dissolution of Fe (hydr)oxides in flooded soils (Zhu et al 2016b). According to our SEP data, a substantial amount of DPAA in the clay mineral fractions from the Gleyic Acrisol soil (46.2%) was presented in this potentially available form (Fig.…”

Diphenylarsinic acid sorption mechanisms in soils using batch experiments and EXAFS spectroscopy

“…Concurrently, the K f values decreased for most soils deficient of amorphous and crystalline metal (hydr)oxides with the removal of SOM but increased slightly for those of S2, S7 and S10 (Table 2). Many discrepancies in the role of SOM in the sorption of phenyl As have been reported and factors related to the role of SOM, namely competitive sorption (Zhu et al, 2016a), covering sorption sites on Fe/Al (hydr) oxides (Maejima et al, 2011), forming SOM-Fe-As complexes (Fu et al, 2016) and hydrophobic interactions (Arroyo-Abad et al, 2011) should be considered, and the contribution of each factor to the sorption of phenyl As may depend on soil type.…”

Contrasting effects of iron reduction on thionation of diphenylarsinic acid in a biostimulated Acrisol

“…The soil incubation experiment was prepared using 100-mL serum bottles as described by Zhu et al (2016a). Soil cultures containing 20 g of the dried soil and 30 mL of the ultrapure water were prepared for anoxic and sulfide incubation.…”

“…These results demonstrate that DPAA sorption onto soils are due mainly to ligand exchange reactions with hydroxyl groups on Fe (hydr)oxides. Limited studies have found that DPAA mobilization in a biostimulated Phaeozem was due primarily to the addition of sodium lactate at early stages but due to the near-complete Fe(III) reduction at later stages of incubation (Zhu et al 2016a). Other studies propose that As mobilization is attributable mainly to Fe(III) reduction in carbon-limited environments (Masscheleyn et al 1991;Nickson et al 1998).…”

“…However, Fe(III)-reducing microorganisms are capable of utilizing organic carbon compounds as electron donors (Kulkarni et al 2018) and dissimilatory Fe(III) reduction was reported to proceed efficiently under carbon-rich conditions (Lovley and Phillips 1986a), which thereby enhance the effect of Fe(III) reduction on the mobilization of As (Eiche et al 2017). In contract to the Phaeozem, DPAA mobilization from goethite was due mainly to Fe(III) reduction even in the presence of high concentrations of DOM (Zhu et al 2016a). Accordingly, we hypothesized that DOM in Fe-rich soils may enhance DPAA mobilization primarily by creating reducing conditions that promote Fe(III) reduction.…”