Retention of phenylarsenicals in soils derived from volcanic materials

The adsorption of arsenate and p-arsanilic acid onto ferrihydrite and subsequent desorption by sulfate and artificial seawater: Future implications of sea level rise

Sea level rise (SLR) is estimated to impact 25% of the world's population along coastal areas leading to an increase in saltwater intrusion. Consequently, changes in the soil biogeochemistry of currently non-saline and/or well-drained soils due to saltwater intrusion are of major concern. Saltwater intrusion is expected to affect farmland across large broiler producer regions, where large amounts of manure containing organic arsenicals were applied over the past decades. To determine how SLR may impact the speciation and mobility of adsorbed inorganic and organic As, we used in situ real-time attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) to determine the adsorption and desorption mechanisms of As(V) and 4-aminophenylarsonic (p-ASA, a poultry feed additive) on ferrihydrite (Fh) in the presence of sulfate at varying pH. The adsorption of As(V) and p-ASA increased at lower pH, with As(V) showing IR features consistent with the formation of inner-sphere of As-Fh surface complexes, while p-ASA also formed others structures as H-bonded As-surface complexes, likely mediated by outer-sphere complexes, based on our FTIR and batch experiments data. No observable As(V) or p-ASA desorption from the Fh surface was promoted by sulfate, however sulfate adsorption on the Fh surface was remarkably larger for p-ASA than for As(V). Complimentary, we carried out batch studies of As(V) and p-ASA desorption by Fh, using artificial seawater (ASW) at varying concentrations. The 1% ASW desorbed ∼10% of initially sorbed p-ASA, while at 100% ASW desorbed ∼40%. However, <1% of As(V) was desorbed by 1% ASW solution and only ∼7.9% were desorbed at 100% ASW. The spectroscopic data support the more extensive desorption of p-ASA compared to As(V) observed in batch experiments, suggesting that organoarsenicals may be easily desorbed and, after conversion to inorganic forms, pose a risk to water supplies.

Natural degradation of roxarsone in contrasting soils: Degradation kinetics and transformation products

Roxarsone (ROX) is transformed to more toxic arsenicals after land application of ROX-containing poultry litter to agricultural soils. To date, no reports have compared ROX degradation in soils with contrasting properties. In this study, the impact of different incubation conditions on ROX degradation was investigated in red (C-Soil) and yellow-brown (H-Soil) soils. The degradation half-lives of extractable ROX in C-Soil and H-Soil were found to be 130-394d and 4-94d, respectively, indicating that the extractable ROX degraded faster in H-Soil. This result stems from the higher organic matter content, more abundant soil microbes, and lower ROX sorption capacity of H-Soil compared to C-Soil. Degradation of extractable ROX in both C-Soil and H-Soil was significantly promoted by soil moisture and exogenous glucose. Exogenous P(V) facilitated degradation of extractable ROX in C-Soil, but limited effects were observed for H-Soil. HPLC-ICP-MS analysis confirmed that ROX and dimethylarsinic acid were the predominant As species in soil extracts from 119-day incubated C-Soil and H-Soil, respectively. Ultimately, minimal transformation of extractable ROX was observed in C-Soil, but the majority of extractable ROX in H-Soil was biologically transformed. The differences in degradation of extractable ROX in C-Soil and H-Soil highlight the key roles of soil properties on the environmental fate of ROX and associated arsenicals. Results from this study inform the need for comprehensive evaluation of the ecological risks in organoarsenical-contaminated soils.

Sorption of roxarsone onto soils with different physicochemical properties

Elevated roxarsone (ROX) concentrations in soils, caused by land application of ROX-bearing poultry litter, mandate investigation of ROX sorption onto soils. Equilibrium and kinetic studies of ROX sorption onto five soils were carried out to explore the relationship between sorption parameters and soil properties, and to reveal the effects of coexisting humic acid (HA), P(V), As(V), and As(III) on ROX transport. Experimental results indicated that ROX sorption reached equilibrium within 24 h, with pseudo-second order rate constants of 5.74-5.26 × 10(2) g/(mg h); film and intra-particle diffusion were the rate-limiting processes. ROX sorption to soils involved partitioning and adsorption phenomena; however, their relative contributions varied for different soils. The maximum ROX sorption varied with soil type, ranging from 0.59 to 4.12 mg/g. Results from correlation analysis and multiple linear regressions revealed that the maximum sorption capacities, partition coefficients, and desorption percentages were correlated with soil properties, especially iron content, total organic carbon, and dissolved organic carbon. ROX sorption to soils was affected more by soil pH than the initial pH of ROX-containing solutions. Carboxylic and amide functional groups were determined to be responsible for ROX sorption to soils. ROX sorption capacities decreased in the presence of HA, P(V), As(V), and As(III), indicating that ROX mobility in soils was facilitated by dissolved organic matter (DOM) and competing anions.

Study of photodegradation and photooxidation of p-arsanilic acid in water solutions at pH = 7: kinetics and by-products

The paper presents the kinetics and proposed pathways photodegradation and photooxidation of p-arsanilic acid, in a neutral environment by ozone and hydrogen peroxide. The results showed that in a neutral environment, photoozonation process was characterized by the highest decomposition rate constant (k) (k = 31.8 × 10(-3) min(-1)). The rate constants decreased in the order UV/O3 > O3 > UV/H2O2 > H2O2 > UV. It was also found that under pH = 7, decomposition of p-arsanilic acid leads mainly to the formation of aniline, which undergoes secondary reactions. Intermediate products of oxidation and photooxidation by hydrogen peroxide like nitrobenzene, nitrophenol, azobenzenes, and phenylazophenol were identified depending on processes. However, in the photodegradation process, formation of nitrasone as a reaction product of p-arsanilic acid with oxygen in the singlet state was observed. In the case of ozonation and photoozonation, in addition, aniline formation of carboxylic acids was observed.