Changes of arsenic fractionation and bioaccessibility in wastewater-irrigated soils as a function of aging: Influence of redox condition and arsenic load

Impact of Redox Condition on Fractionation and Bioaccessibility of Arsenic in Arsenic-Contaminated Soils Remediated by Iron Amendments: A Long-Term Experiment

“…This indicates that effect of redox conditions on the tendency of 4 in iron-amended soils is negligible. The decomposition of organic matter and the increase of crystallization of Fe oxides with the contact time may be responsible for the decrease of 4 in iron-amended soils [10,22,23]. In addition, the proportion of 4 in S IN was significantly higher than that in S IA during the whole incubation period.…”

“…Moreover, in the whole incubation period, the proportion of 1 in S IN was higher than that in S IA , indicating that more soluble As in iron-amended soils transformed into less mobilizable fractions under aerobic condition in comparison with under anoxic condition. This is likely to be attribute to the ongoing reduction of As(V) to As(III) in soils under anoxic condition and the higher adsorption of As(V) than As(III) onto soil components [10,11,17,18]. Different from 1, there was no significant difference of 2 in both S IA and S IN , and the proportion of 2 exhibited a negligible level during the whole incubation time (Figure 3).…”

“…The reason for the increase of 3 in S IN within the first 3 d may be as follows: on the one hand, pH in S IN may increase within the first 3 d, because soil pH increased slightly after the flood while pH in nonflooded soil showed little change [20]; on the other hand, the reduction of As(V) to As(III) often occurs in soils under anoxic conditions [12], both leading to the increase of 3 in S IN within the first 3 d, because As(III) is preferentially nonspecific adsorbed to Fe-hydroxides at alkaline condition [2]. As on external surface of soil minerals gradually diffuses into inner surface and mineral lattice and forms relatively immobilizable surface complexes and insoluble secondary solid phases [10,21], which may be responsible for the decrease of 3 in iron-amended soils with the contact time. The change of 3 in S IA ended in the first 10 d while in S IN it ended within 60 d, indicating that the transformation of 3 into other fractions in iron-amended soils under the anoxic condition is more lasting than that under the aerobic condition.…”

“…Thus, it is essential to understand the stabilization/aging processes of As related to the change of As fractions in soils. And the stabilization/aging processes of As in soils not only depended on the properties of amendments but also were affected by some environmental conditions, such as temperature and redox conditions [5,[8][9][10]. For instance, the crystallization of Fe (hydr)oxides and the diffusion of As in micropores from the outer layers into the inner complex are accelerated after the temperature elevated, resulting in the transformation of labile fractions of As into unlabile fractions [5,9].…”

“…For instance, the crystallization of Fe (hydr)oxides and the diffusion of As in micropores from the outer layers into the inner complex are accelerated after the temperature elevated, resulting in the transformation of labile fractions of As into unlabile fractions [5,9]. The forms of As and Fe-hydroxides in soils are commonly affected by the redox conditions [10,11]. However, the effect of redox condition on the stabilization processes and bioaccessibility of As in soils amended by iron grit are little known.…”