Comparative study of Fe(II)/sulfite, Fe(II)/PDS and Fe(II)/PMS for p-arsanilic acid treatment: Efficient organic arsenic degradation and contrasting total arsenic removal.

As a widely used feed additives, p-arsanilic acid (p-AsA) frequently detected in the environment poses serious threats to aquatic ecology and water security due to its potential in releasing more toxic inorganic arsenic. In this work, the efficiency of Fe(II)/sulfite, Fe(II)/PDS and Fe(II)/PMS systems in p-AsA degradation and simultaneous arsenic removal was comparatively investigated for the first time. Efficient p-AsA abatement was achieved in theses Fe-based systems, while notable discrepancy in total arsenic removal was observed under identical acidic condition. By using chemical probing method, quenching experiments, isotopically labeled water experiments, p-AsA degradation was ascribed to the combined contribution of high-valent Fe(IV) and SO4•-in these Fe(II)-based system. In particular, the relative contribution of Fe(IV) and SO4•- in the Fe(II)/sulfite system was highly dependent on the molar ratio of [Fe(II)] and [sulfite]. Negligible arsenic removal was observed in the Fe(II)/sulfite and Fe(II)/PDS systems, while ∼80% arsenic was removed in the Fe(II)/PMS system under identical acidic condition. This interesting phenomenon was due to that ferric precipitation only occurred in the Fe(II)/PMS system. As(V) was further removed via adsorption onto the iron precipitate or the formation of ferric arsenate-sulfate compounds, which was confirmed by particle diameter measurements, fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Through tuning solution pH, complete removal of total arsenic could achieve in all three systems. Among these three Fe-based technologies, the hybrid oxidation-coagulation Fe(II)/PMS system demonstrated potential superiority for arsenic immobilization by not requiring pH adjustment for coagulation and facilitating the in-situ generation of ferric arsenate-sulfate compounds with comparably low solubility levels like scorodite. These findings would deepen the understanding of these three Fe-based Fenton-like technologies for decontamination in water treatment.

Iron-doped carbon nanotubes with magnetic enhanced Fe(VI) degradation of arsanilic acid and inorganic arsenic: Role of intermediate iron species and electron transfer.

Arsanilic acid (p-AsA), a prevalently used feed additive, is frequently detected in environment posing a great threat to humans. Potassium ferrate (Fe(VI)) was an efficient way to tackle arsenic contamination under acid and neutral conditions. However, Fe(VI) showed a noneffective removal of p-AsA under alkaline conditions due to its oxidation capacity attenuation. Herein, a magnetic iron-doped carbon nanotubes (F-CNT) was successfully prepared and further catalyzed Fe(VI) to remove p-AsA and total As species. The Fe(VI)/F-CNT system showed an excellent capability to oxidize p-AsA and adsorb total As species over an environment-related pH range of 6-9. The high-valent iron intermediates Fe(V)/Fe(IV) and the mediated electron-transfer played a significant part in the degradation of p-AsA according to the probes/scavengers experiments and galvanic oxidation process. Moreover, the situ formed iron hydroxide oxide and F-CNT significantly improved the adsorption capacity for total As species. The electron-donating groups (semiquinone and hydroquinone) and high graphitization of F-CNT were responsible for activating Fe(VI) based on the analysis of X-ray photoelectron spectroscopy (XPS). Density functional theory calculations and the detected degradation products both indicated that the amino group and the C-As bond of p-AsA were main reactive sites. Notably, Fe(VI)/F-CNT system was resistant to the interference from Cl-, SO42-, and HCO3-, and could effectively remove p-AsA and total As species even in the presence of complex water matrix. In summary, this work proposed an efficient method to use Fe(VI) for degrading pollutants under alkaline conditions and explore a new technology for livestock wastewater advanced treatment.

Efficient removal of p-arsanilic acid and arsenite by Fe(II)/peracetic acid (Fe(II)/PAA) and PAA processes.

The widespread occurrence of p-arsanilic acid (p-ASA) in natural environments poses big threats to the biosphere due to the generation of toxic inorganic arsenic (i.e., As(III) and As(V), especially As(III) with higher toxicity and mobility). Oxidation of p-ASA or As(III) to As(V) followed by precipitation of total arsenic using Fe-based advanced oxidation processes demonstrated to be a promising approach for the treatment of arsenic contamination. This study for the first time investigated the efficiency and inherent mechanism of p-ASA and As(III) oxidation by Fe(II)/peracetic acid (Fe(II)/PAA) and PAA processes. p-ASA was rapidly degraded by the Fe(II)/PAA process within 20 s at neutral to acidic pHs under different conditions, while it was insignificantly degraded by PAA oxidation alone. Lines of evidence suggested that hydroxyl radicals and organic radicals generated from the homolytic OO bond cleavage of PAA contributed to the degradation of p-ASA in the Fe(II)/PAA process. p-ASA was mainly oxidized to As (V), NH4+, and p-aminophenol by the Fe(II)/PAA process, wherein the aniline group and its para position were the most vulnerable sites. As(III) of concern was likely generated as an intermediate during p-ASA oxidation and it could be readily oxidized to As(V) by the Fe(II)/PAA process as well as PAA alone. The in-depth investigation demonstrated that PAA alone was effective in the oxidation of As(III) under varied conditions with a stoichiometric molar ratio of 1:1. Efficient removal (> 80%) of total arsenic during p-ASA oxidation by Fe(II)/PAA process or during As(III) oxidation by PAA process with additional Fe(III) in synthetic or real waters were observed, mainly due to the adsorptive interactions of amorphous ferric (oxy)hydroxide precipitates. This study systematically investigates the oxidation of p-ASA and As(III) by the Fe(II)/PAA and PAA processes, which is instructive for the future development of arsenic remediation technology.

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.

Insight into UV-LED/PS/Fe(â ¢) and UV-LED/PMS/Fe(â ¢) for p-arsanilic acid degradation and simultaneous arsenate immobilization.

As a feed additive, p-arsanilic acid (p-ASA) is hardly metabolized in animal bodies and is excreted chemically unchanged via feces and urine, which can be transformed into more toxic inorganic arsenic species and other organic by-products upon degradation in the aquatic environment. In this study, UV-LED/persulfate (PS)/Fe(Ⅲ) and UV-LED/peroxymonosulfate (PMS)/Fe(Ⅲ) processes were developed to remove p-ASA and immobilize the formed inorganic arsenic via tuning solution pH. UV-LED/PMS/Fe(Ⅲ) (90.8%) presented the best performance for p-ASA degradation at pH 3.0, and the p-ASA degradation in these processes both followed the pseudo-first-order kinetics. The ∙OH played the major role in UV-LED/PS/Fe(Ⅲ) and UV-LED/PMS/Fe(Ⅲ) systems. Solution pH greatly affected the p-ASA degradation and the maximum removal can be achieved at pH 3.0 due to the presence of more Fe(OH)(H2O)52+. The dosages of Fe(III) and PMS (PS), SO42- and HCO3- significantly influenced the performance of p-ASA oxidation, while HA, Cl- and NO3- slightly affected the p-ASA degradation. According to quantum chemical calculation, radical addition on the C atom in the C-As bond of p-ASA was corroborated to be the dominant reaction pathway by SO4∙- and ∙OH. Additionally, the reactive sites and reasonable degradation pathways of p-ASA were proposed based on DFT calculation and HPLC/MS analysis. The release of inorganic arsenic in both processes can be effectively immobilized and the toxicity of the reaction solution dramatically reduced by adjusting solution pH to 6.0. UV-LED/PMS/Fe(Ⅲ) process was found to be more cost-effective than UV-LED/PS/Fe(Ⅲ) process at the low oxidant dosages.

Lignin-based magnetic activated carbon for p-arsanilic acid removal: Applications and absorption mechanisms.

It is crucial for water environment security to remove its p-arsanilic acid (p-ASA) efficiently. Namely, removing p-arsanilic acid from aqueous media through magnetic separation, has become a novel method of removing toxic pollutants from water. Batch adsorption experiments demonstrated a higher adsorption of lignin-based magnetic activated carbon (201.64 mg g-1) toward p-ASA. In addition, LMAC nanoparticles exhibited typical magnetism (35.63 emu g-1 of saturation magnetization) and could be easily separated from the aqueous solution. Meanwhile, the endothermic adsorption of p-ASA over LMAC could spontaneously proceed and be well described by the pseudo-first-order and pseudo-second-order model as well as the intra-particle diffusion model. Moreover, the mechanisms during p-ASA adsorption over LMAC included the electrostatic attraction, surface complexation, π-π stacking and hydrogen bonding interaction. Importantly, lignin-based magnetic activated carbon has high absorbability and preferable reusability in real water samples. Consequently, this paper provides insights into preparation of the lignin-based magnetic activated carbon may be potential adsorbents for the remediation of organoarsenic compounds.

Photodegradation of para-arsanilic acid mediated by photolysis of iron(III) oxalate complexes.

Organic arsenicals are important environment pollutants due to wide use in livestock and toxicity of degradation products. In this work we report about the efficient photodegradation of the p-arsanilic acid (p-ASA) and its decomposition products in the Fe(III)-oxalate assisted approach under nature-relevant conditions. At neutral pH under near-visible UV irradiation the Fe(III) oxalate complexes generate the primary oxidizing intermediate, OH radical (the quantum yield of ϕOH âˆ¼ 0.06), which rapidly reacts with p-ASA with high rate constant, (8.6 ± 0.5) × 109 M-1s-1. Subsequent radical reactions result in the complete photooxidation of both p-ASA and basic aromatic photoproducts with the predominant formation of inorganic arsenic species, mainly As(V), under optimal conditions. Comparing with the direct UV photolysis, the presented Fe(III)-oxalate mediated degradation of p-ASA has several advantages: higher efficiency at low p-ASA concentration and complete degradation of organic arsenic by-products without use of short-wavelength UV radiation. The obtained results illustrate that the Fe(III)-oxalate complexes are promising natural photosensitizers for the removal of arsenic pollutants from contaminated waters.

Making Weak Antigens Strong: Modifying Antigens by Dinitrophenol or Arsynyl Coupling.

Many compounds on their own do not have all of the properties needed to induce a strong antibody response. However, small changes in the structure of an antigen can often greatly alter the immunogenicity of a compound. Common methods for doing so include the addition of small modifying groups such as dinitrophenol or arsenate to the molecules. These techniques either alter regions of the immunogen to provide better sites for T-cell binding or expose new epitopes for B-cell binding. The techniques are rapid and easy, and have been used extensively as a general procedure to increase the chances of raising antisera, particularly against well-conserved antigens.

Arsanilic acid modified superparamagnetic iron oxide nanoparticles for Purification of alkaline phosphatase from hen's egg yolk.

Recent studies of magnetic carrier technology have focused on its applications in separation and purification technologies, due to easy separation of the target from the reaction medium by applying an external magnetic field. In the present study, Fe3O4 superparamagnetic nanoparticles were prepared to utilize a chemical co-precipitation method, then the surfaces of the nanoparticles were modified with arsanilic acid derivatives which were used as the specific nanocarriers for the affinity purification of alkaline phosphatase from the hen's egg yolk. The six different types of magnetic nanocarriers with varied lengths of the linkers were obtained. All samples were characterized step by step and validated using FTIR, SEM, EDX, VSM and XRD analysis methods As the results were shown, the use of inflexible tags with long linkers on the surface of the nanocarrier could lead to better results for separation of alkaline phosphatase from the hen's egg yolk with 76.2% recovery and 1361.7-fold purification. The molecular weight of the purified alkaline phosphatase was estimated to be 68kDa by SDS-PAGE. The results of this study showed that the novel magnetic nanocarriers were capable of purifying alkaline phosphatase in a practically time and cost effective way.

Transformation of para arsanilic acid by manganese oxide: Adsorption, oxidation, and influencing factors.

Aromatic organoarsenic compounds tend to transform into more mobile toxic inorganic arsenic via several processes, and can inadvertently spread toxic inorganic arsenic through the environment to water sources. To gain insight into the transformation mechanisms, we herein investigated how the process of para arsanilic acid (p-ASA) transformation works in detail on the surface of adsorbents by comparing it with phenylarsonic acid (PA) and aniline, which have similar chemical structures. In contrast to the values of 0.23 mmol g-1 and 0.68 mmol g-1 for PA and aniline, the maximum adsorption capacity was determined to be 0.40 mmol g-1 for p-ASA at pH 4.0. The results of FTIR and XPS spectra supported the presence of a protonated amine, resulting in a suitable condition for the oxidation of p-ASA. Based on the combined results of UV-spectra and UPLC-Q-TOF-MS, we confirmed that the adsorbed p-ASA was first oxidized through the transfer of one electron from p-ASA on MnO2 surface to form a radical intermediate, which through further hydrolysis and coupling led to formation of benzoquinone and azophenylarsonic acid, which was identified as a major intermediate. After that, p-ASA radical intermediate was cleaved to form arsenite (III), and then further oxidized into arsenate (V) with the release of manganese (Mn) into solution, indicating a heterogeneous oxidation process.

Multiple transformation pathways of p-arsanilic acid to inorganic arsenic species in water during UV disinfection.

p-Arsanilic acid (p-ASA) is widely used in China as livestock and poultry feed additive for promoting animal growth. The use of organoarsenics poses a potential threat to the environment because it is mostly excreted by animals in its original form and can be transformed by UV-Vis light excitation. This work examined the initial rate and efficiency of p-ASA phototransformation under UV-C disinfection lamp. Several factors influencing p-ASA phototransformation, namely, pH, initial concentration, temperature, as well as the presence of NaCl, NH4(+), and humic acid, were investigated. Quenching experiments and LC-MS were performed to investigate the mechanism of p-ASA phototransformation. Results show that p-ASA was decomposed to inorganic arsenic (including As(III) and As(V)) and aromatic products by UV-C light through direct photolysis and indirect oxidation. The oxidation efficency of p-ASA by direct photosis was about 32%, and those by HO and (1)O2 were 19% and 49%, respectively. Cleavage of the arsenic-benzene bond through direct photolysis, HO oxidation or (1)O2 oxidation results in simultaneous formation of inorganic As(III), As(IV), and As(V). Inorganic As(III) is oxidized to As(IV) and then to As(V) by (1)O2 or HO. As(IV) can undergo dismutation or simply react with oxygen to produce As(V) as well. Reactions of the organic moieties of p-ASA produce aniline, aminophenol and azobenzene derivatives as main products. The photoconvertible property of p-ASA implies that UV disinfection of wastewaters from poultry and swine farms containing p-ASA poses a potential threat to the ecosystem, especially agricultural environments.

[Photocatalytic Oxidation of p-arsanilic Acid by TiO2].

The p-arsanilic acid (ASA) is an important organoarsenical compound and its removal is more difficult compared to inorganic arsenic, however, little attention has been paid to the removal of ASA in aqueous environment. The influence of P25 on the adsorption of ASA, effect of P25 dosage, pH and illumination intensity on the photo-catalysis, the production analysis and main mechanism of photo-degradation were investigated in this study. The results showed that in the P25 catalysis process, simulated natural light could degrade ASA into As (V) by oxidation. The total As was reduced to about 0.34 mg x L(-1) within 0.5 h under the following condition: the initial concentration of ASA was 2 mg x L(-1) and the dosage of TiO2 was 1 g x L(-1). The result showed that the removal rate of ASA in acidic conditions was much higher than that in alkaline conditions. The optimal strength of light was 68.5 mW x Cm(-2). Hydroxide radical played a major role in photocatalytic oxidation of ASA by P25.

Rapid degradation of p-arsanilic acid with simultaneous arsenic removal from aqueous solution using Fenton process.

Although banned in some developed countries, p-arsanilic acid (p-ASA) is still used widely as a feed additive for swine production in many countries. With little uptake and transformation in animal bodies, nearly all the p-ASA administered to animals is excreted chemically unchanged in animal wastes, which can subsequently release the more toxic inorganic arsenic species upon degradation in the environment. For safe disposal of the animal wastes laden with p-ASA, we proposed a method of leaching the highly water-soluble p-ASA out of the manure first, followed by treatment of the leachate using the Fenton process to achieve fast oxidation of p-ASA and removal of the inorganic arsenic species released (predominantly arsenate) from solution simultaneously. The effects of solution pH, dosages of H2O2 and Fe(2+), and the presence of dissolved organic matter (DOM) on the treatment efficiency were systematically investigated. Under the optimum treatment conditions (0.53 mmol L(-1) Fe(2+), 2.12 mmol L(-1) H2O2, and initial pH of 3.0), p-ASA (10 mg-As L(-1)) could be completely oxidized to As(V) within 30 min in pure water and 4 natural water samples, and at the final pH of 4.0, the residual arsenic levels in solution phase were as low as 1.1 and 20.1-43.4 µg L(-1) in the two types of water matrixes, respectively. The presence of humic acid significantly retarded the oxidation of p-ASA by scavenging HO, and inhibited the As(V) removal through competitive adsorption on ferric hydroxide. Due to the high contents of DOM in the swine manure leachate samples (TOC at ∼500 mg L(-1)), much higher dosages of Fe(2+) (10.0 mmol L(-1)) and H2O2 (40.0 mmol L(-1)) and a longer treatment time (120 min) were required to achieve near complete oxidation of p-ASA (98.0%), while maintaining the levels of residual arsenic in the solution at <70.0 µg L(-1). The degradation pathway of p-ASA in the Fenton process was proposed based on the major degradation products detected. Together, the results demonstrate that the Fenton process is promising as an efficient, robust, and low-cost treatment method for controlling the risk of p-ASA in the animal wastes generated at factory farms.

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.

Birnessite (δ-MnO2) mediated degradation of organoarsenic feed additive p-arsanilic acid.

p-Arsanilic acid (p-ASA), is a widely used animal feed additive in many developing countries, and is often introduced to agricultural soils with animal wastes. A common soil metal oxide, birnessite (δ-MnO2), was found to mediate its degradation with fast rates under acidic conditions. Experimental results indicate that adsorption and degradation of p-ASA on the surface of δ-MnO2 were highly pH dependent, and the overall kinetics for p-ASA degradation and formation of precursor complex could be described by a retarded first-order rate model. For the reaction occurring between pH 4.0 and 6.2, the initial rate equation was determined to be rinit=2.36×10(-5)[ASA]0.8[MnO2]0.9[H+]0.7. p-ASA first forms a surface precursor complex on δ-MnO2 during degradation, followed by formation of p-ASA radicals through single-electron transfer to δ-MnO2. The p-ASA radicals subsequently undergo cleavage of arsenite group (which is further oxidized to arsenate) or radical-radical self-coupling. Instead of full mineralization (with respect to arsenic only), about one-fifth of the p-ASA "couples" to form an arsenic-bearing azo compound that binds strongly on δ-MnO2. The fast transformation of p-ASA to arsenite and arsenate mediated by δ-MnO2 significantly increases the risk of soil arsenic pollution and deserves significant attention in the animal farming zones still using this feed additive.

Effect of central metal ions of analogous metal-organic frameworks on adsorption of organoarsenic compounds from water: plausible mechanism of adsorption and water purification.

The adsorptive removal of organoarsenic compounds such as p-arsanilic acid (ASA) and roxarsone (ROX) from water using metal-organic frameworks (MOFs) has been investigated for the first time. A MOF, iron benzenetricarboxylate (also called MIL-100-Fe) exhibits a much higher adsorption capacity for ASA and ROX than activated carbon, zeolite (HY), goethite, and other MOFs. The adsorption of ASA and ROX over MIL-100-Fe is also much more rapid than that over activated carbon. Moreover, the used MIL-100-Fe can be recycled by simply washing with acidic ethanol. Therefore, it is determined that a MOF such as MIL-100-Fe can be used to remove organoarsenic compounds from contaminated water because of its high adsorption capacity, rapid adsorption, and ready regeneration. Moreover, only one of three analogous MIL-100 species (MIL-100-Fe, rather than MIL-100-Al or MIL-100-Cr) can effectively remove the organoarsenic compounds. This selective and high adsorption over MIL-100-Fe, different from other analogous MIL-100 species, can be explained (through calculations) by the facile desorption of water from MIL-100-Fe as well as the large (absolute value) replacement energy (difference between the adsorption energies of the organoarsenic compounds and water) exhibited by MIL-100-Fe. A plausible adsorption/desorption mechanism is proposed based on the surface charge of the MOFs, FTIR results, calculations, and the reactivation results with respect to the solvents used in the experiments.

Density functional theory calculations on the complexation of p-arsanilic acid with hydrated iron oxide clusters: structures, reaction energies, and transition states.

Aromatic organoarsenicals, such as p-arsanilic acid (pAsA), are still used today as feed additives in the poultry and swine industries in developing countries. Through the application of contaminated litter as a fertilizer, these compounds enter the environment and interact with reactive soil components such as iron and aluminum oxides. Little is known about these surface interactions at the molecular level. We report density functional theory (DFT) calculations on the energies, optimal geometries, and vibrational frequencies for hydrated pAsA/iron oxide complexes, as well as changes in Gibbs free energy, enthalpy, and entropy for various types of ligand exchange reactions leading to both inner- and outer-sphere complexes. Similar calculations using arsenate are also shown for comparison, along with activation barriers and transition state geometries between inner-sphere complexes. Minimum energy calculations show that the formation of inner- and outer-sphere pAsA/iron oxide complexes is thermodynamically favorable, with the monodentate mononuclear complexes being the most favorable. Interatomic As-Fe distances are calculated to be between 3.3 and 3.5 Å for inner-sphere complexes and between 5.2 and 5.6 Å for outer-sphere complexes. In addition, transition state calculations show that activation energies greater than 23 kJ/mol are required to form the bidentate binuclear pAsA/iron oxide complexes, and that formation of arsenate bidentate binuclear complexes is thermodynamically -rather than kinetically- driven. Desorption thermodynamics using phosphate ions show that reactions are most favorable using HPO4(2-) species. The significance of our results for the overall surface complexation mechanism of pAsA and arsenate is discussed.

Kinetics, intermediates and acute toxicity of arsanilic acid photolysis.

Arsanilic acid (4-amino phenyl arsenic acid, ASA) is widely used in poultry production as feed additives, while most of ASA in the feed is excreted in the animal manure and released into the environment. However, the environmental behaviors of ASA were not well understood. In the present study, the photolysis behaviors of ASA and the toxicity of its metabolites to luminescent bacterium were studied. The results showed that ASA could be photodegraded and this process was strongly affected by solution pH, humic acid and dissolved oxygen. Upon UV irradiation for 360 min, ASA could be completely eliminated, but the reduction of total organic carbon (TOC) was not significant. In addition, NH4(+) ions and inorganic arsenic including arsenite and arsenate were identified as the predominant end-products. The conversion of ASA included both direct and indirect photolysis involving radicals, and its possible photolysis pathways were proposed on the basis of the identified intermediates. Unfortunately, higher adverse effects of the conversion products of ASA on bacteria were observed during the photolysis reaction. The results of present study might be helpful for assessing the environmental persistence and risks of ASA.

Occurrence of arsenic impurities in organoarsenics and animal feeds.

Organoarsenics are widely used as excellent feed additives in animal production in the world. Roxarsone (ROX) and arsanilic acid (ASA) are two organoarsenics permitted to be used in China. We collected 146 animal feed samples to investigate the appearance of ROX, ASA, and potential metabolites, including 3-amino-4-hydroxyphenylarsonic acid (3-A-HPA), 4-hydroxyphenylarsonic acid (4-HPA), As(V), As(III), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) in feeds. The stability of ROX in both ROX additives and animal feeds was also examined. The results show that 25.4% of the 146 animal feeds contained organoarsenics, with average contents of ROX and ASA as 7.0 and 21.2 mg of As/kg, respectively. Unexpectedly, As(III) and MMA frequently occurred as As impurities in feeds bearing organoarsenics, with higher contents than organoarsenics in some samples. 3-A-HPA, 4-HPA, and DMA were not detected in all samples. ROX and As impurities in both ROX additives and feeds stayed unchanged in the shelf life. It suggests that As impurities in animal feeds bearing organoarsenics should generate from the use of organoarsenics containing As impurities. This constitutes the first report of As impurities in organoarsenics.

Identification of degradation products of phenylarsonic acid and o-arsanilic acid in contact with suspensions of soils of volcanic origin.

A set of organoarsenicals were identified in aqueous phenylarsonic acid (PA) and o-arsanilic acid (AA) solutions treated with soil of volcanic origin in batch systems. The transformation products were separated by liquid chromatography (RP-LC) and identified with element selective inductively coupled plasma-mass spectrometry (ICP-MS) as well as molecular selective electrospray ionization-mass spectrometry (ESI-MS) detection after their HPLC separation. The identification of the main degradation products by means of ESI-MS, ESI-MS/MS and ESI-TOF-MS showed the occurrence of nitrophenylarsonic acid and methylphenylarsinic acid in the solutions containing AA and PA in contact with soils, respectively. Using irradiation of PA solution with visible light, new compounds related from PA appeared with increasing irradiation times which were identified as 4-hydroxyphenylarsonic acid, 3-hydroxyphenylarsonic acid and 2-hydroxyphenylarsonic acid. Additionally, a dihydroxyphenylarsonic compound was identified as impurity of PA.