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Herein, a novel FeCoNi(b)-800 ternary metal nanoalloy was uniformly mixed with reduced graphene oxide (RGO) to synthesize the FeCoNi(b)-800@RGO(2:1) composite. The addition of RGO not only stopped the accumulation of FeCoNi(b)-800 alloy, but also heightened the electrocatalytic activity of composite. Particularly, the FeCoNi(b)-800@RGO(2:1) composite displayed the significantly strong electrocatalytic capacity for the reduction of roxarsone (ROX). Furthermore, the FeCoNi(b)-800@RGO(2:1) composite possessed enough porosity and metal catalytic sites, facilitating the transport and electrochemical reduction of the ROX. Thus, the FeCoNi(b)-800@RGO(2:1) composite modified glassy carbon electrode (FeCoNi(b)-800@RGO(2:1)/GCE) showed the superb electrochemical detection effect for ROX with relatively wide working range (0.1-1500 μM) and low detection limit (0.013 μM). Importantly, the FeCoNi(b)-800@RGO(2:1)/GCE sensor could accurately determine the contents of ROX in actual pork, chicken, duck and egg samples, indicating that it had good suitability in food safety monitoring., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Contamination of rice by arsenic represents a significant human health risk. Roxarsone -bearing poultry manure is a major pollution source of arsenic to paddy soils. A mesocosm experiment plus a laboratory experiment was conducted to reveal the role of rainwater-borne H 2 O 2 in the degradation of roxarsone in paddy rice soils. While roxarsone could be degraded via chemical oxidation by Fenton reaction-derived hydroxyl radical, microbially mediated decomposition was the major mechanism. The input of H 2 O 2 into the paddy soils created a higher redox potential, which favored certain roxarsone-degrading and As(III)-oxidizing bacterial strains and disfavored certain As(V)-reducing bacterial strains. This was likely to be responsible for the enhanced roxarsone degradation and transformation of As(III) to As(V). Fenton-like reaction also tended to enhance the formation of Fe plaque on the root surface, which acted as a filter to retain As. The dominance of As(V) in porewater, combined with the filtering effect of Fe plaque significantly reduced the uptake of inorganic As by the rice plants and consequently its accumulation in the rice grains. The findings have implications for developing management strategies to minimize the negative impacts from the application of roxarsone-containing manure for fertilization of paddy rice soils., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Water contamination is a serious environmental issue posing a significant global challenge. Roxarsone (ROX), a widely used anticoccidial drug is excreted in urine and feces, potentially disrupting natural habitats. Therefore, rapid and cost-effective ROX detection is essential. In this study, we developed a 2D sheet structure of zinc molybdate decorated on MXene (ZnMoO 4 /MXene) for detecting ROX using electrochemical methods. The materials were characterized using appropriate spectrophotometric and voltammetric techniques. The ZnMoO 4 /MXene hybrid exhibited excellent electrocatalytic performance due to its rapid electron transfer rate and higher electrical conductivity. The ZnMoO 4 /MXene-modified GCE (ZnMoO 4 /MXene/GCE) showed a broad linear range with high sensitivity (10.413 μA μМ -1 cm -2 ) and appreciable limit of detection (LOD) as low as 0.0081 μM. It also demonstrated significant anti-interference capabilities, excellent storage stability, and remarkable reproducibility. Furthermore, the feasibility of utilizing ZnMoO 4 /MXene/GCE for monitoring ROX in water samples was confirmed, achieving satisfactory recoveries., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Heavy metals are crucial carcinogenic agents threatening the environment and living habituates. Among them, arsenic (As) is an important metalloid that is categorized as a group I toxic carcinogen. Roxarsone (RX) is an organoarsenic antibiotic compound primarily used as a veterinarian drug and growth promoter for poultry animals. The extensive usage of RX increased the accumulation of As in living beings and the ecosystem. Therefore, we have prepared an electrochemical sensor based on 3D bismuth oxybromide with 2D selenium-doped graphitic carbon nitride (BOB/SCN) electrocatalyst for the rapid detection of RX. The elemental and structural details were thoroughly investigated with several spectroscopic techniques. The electrochemical properties were measured by impedance and voltammetric measurements. The electrocatalytic behavior toward the RX was estimated with different voltammetric methods. Therefore, our BOB/SCN-based electrochemical sensor demonstrated a low detection limit (2.3 nM), low quantification value (7.7 nM), optimal sensitivity (0.675 μA μM -1 cm -2 ), and good linear ranges (0.01-77 and 77-857 μM). Additionally, this sensor showed good electrochemical performance and was applied to monitor the RX in various real samples with remarkable recoveries. Based on these results, our BOB/SCN sensor is a promising electrochemical platform for determining RX.

An alarming increase in the use of pesticides and organoarsenic compounds and their toxic impacts on the environment have inspired us to develop a selective and highly sensitive sensor for the detection of these pollutants. Herein, a bio-friendly, low-cost Al-based luminescent metal-organic framework ( 1' )-based fluorescent material is demonstrated that helps in sustaining water quality by rapid monitoring and quantification of a long-established pesticide (pendimethalin) and a widely employed organoarsenic feed additive (roxarsone). A pyridine-functionalized porous aluminum-based metal-organic framework (Al-MOF) was solvothermally synthesized. After activation, it was used for fast (<10 s) and selective turn-off detection of roxarsone and pendimethalin over other competitive analytes. This is the first MOF-based recyclable sensor for pendimethalin with a remarkably low limit of detection (LOD, 14.4 nM). Real-time effectiveness in detection of pendimethalin in various vegetable and food extracts was successfully verified. Moreover, the aqueous-phase recyclable detection of roxarsone with an ultralow detection limit (13.1 nM) makes it a potential candidate for real-time application. The detection limits for roxarsone and pendimethalin are lower than the existing luminescent material based sensors. Furthermore, the detection of roxarsone in different environmental water and a wide pH range with a good recovery percentage was demonstrated. In addition, a cheap and bio-friendly 1'@chitosan@paper strip composite was prepared and successfully employed for the hands-on detection of pendimethalin and roxarsone. The turn-off behavior of 1' in the presence of pendimethalin and roxarsone was examined systematically, and plausible mechanistic pathways were proposed with the help of multiple experimental evidences.

The pentavalent arsenic compound roxarsone (RSN) is used as a feed additive in poultry for rapid growth, eventually ending up in poultry litter. Poultry litter contains chicken manure, which plays a vital role as an affordable fertilizer by providing rich nutrients to agricultural land. Consequently, the extensive use of poultry droppings serves as a conduit for the spread of toxic forms of arsenic in the soil and surface water. RSN can be easily oxidized to release highly carcinogenic As(III) and As(IV) species. Thus, investigations were conducted for the sensitive detection of RSN electrochemically by developing a sensor material based on lanthanum manganese oxide (LMO) and functionalized carbon nanofibers (f-CNFs). The successfully synthesised LMO/f-CNF composite was confirmed by chemical, compositional, and morphological studies. The electrochemical activity of the prepared composite material was examined using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The obtained results confirmed that LMO/f-CNF showed enhanced electrocatalytic activity and improved current response with a good linear range (0.01-0.78 μM and 2.08-497 μM, respectively), exhibiting a low limit of detection (LOD) of 0.004 μM with a high sensitivity of 13.24 μA μM -1 cm -2 towards the detection of RSN. The noteworthy features of LMO/f-CNF composite with its superior electrochemical performance enabled reliable reproducibility, exceptional stability and reliable practical application in the analysis of tap water and food sample, affording a recovery range of 86.1-98.87%.

In environmental systems, the soil is a principal route of contamination by various potentially toxic species. Roxarsone (RX) is an arsenic (V) organic compound used to treat parasitic diseases and as an additive for animal fattening. When the animal excretes RX, the residues may lead to environmental contamination. Due to their physicochemical properties, the soil's humic substances (HS) are important in species distribution in the environment and are involved in various specific interaction/adsorption processes. Since RX, an arsenic (V) compound, is considered an emerging contaminant, its interaction with HS was evaluated in simulated environmental conditions. The HS-RX interaction was analyzed by monitoring intrinsic HS fluorescence intensity variations caused by complexation with RX, forming non-fluorescent supramolecular complexes that yielded a binding constant K b (on the order of 10 3 ). The HS-RX interaction occurred through static quenching due to complex formation in the ground state, which was confirmed by spectrophotometry. The process was spontaneous (ΔG < 0), and the predominant interaction forces were van der Waals and hydrogen bonding (ΔH < 0 and ΔS < 0), with an electrostatic component evidenced by the influence of ionic strength in the interaction process. Structural changes in the HS were verified by synchronized and 3D fluorescence, with higher variation in the region referring to the protein-like fraction. In addition, metal ions (except ions Cu(II)) favored HS-RX interaction. When interacting with HS, the RX epitope was suggested by 1 H NMR, which indicated that the entire molecule interacts with the superstructure. An enzyme inhibition assay verified the ability to reduce the alkaline phosphatase activity of free and complexed RX (RX-HS). Finally, this work revealed the main parameters associated with HS and RX interaction in simulated environmental conditions, thus, providing data that may help our understanding of the dynamics of organic arsenic-influenced soils., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, Rox(V)), an extensively used organoarsenical feed additive, enters soils through the application of Rox(V)-containing manure and further degrades to highly toxic arsenicals. Microplastics, as emerging contaminants, are also frequently detected in soils. However, the effects of microplastics on soil Rox(V) degradation are unknown. A microcosm experiment was conducted to investigate soil Rox(V) degradation responses to polyethylene (PE) microplastics and the underlying mechanisms. PE microplastics inhibited soil Rox(V) degradation, with the main products being 3-amino-4-hydroxyphenylarsonic acid [3-AHPAA(V)], N-acetyl-4-hydroxy-m-arsanilic acid [N-AHPAA(V)], arsenate [As(V)], and arsenite [As(III)]. This inhibition was likely driven by the decline in soil pH by PE microplastic addition, which may directly enhance Rox(V) sorption in soils. The decreased soil pH further suppressed the nfnB gene related to nitroreduction of Rox(V) to 3-AHPAA(V) and nhoA gene associated with acetylation of 3-AHPAA(V) to N-AHPAA(V), accompanied by a decrease in the relative abundance of possible Rox(V)-degrading bacteria (e.g., Pseudomonadales), although the diversity, composition, network complexity, and assembly of soil bacterial communities were largely influenced by Rox(V) rather than PE microplastics. Our study emphasizes microplastic-induced inhibition of Rox(V) degradation in soils and the need to consider the role of microplastics in better risk assessment and remediation of Rox(V)-contaminated soils., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The retention and fate of Roxarsone (ROX) onto typical reactive soil minerals were crucial for evaluating its potential environmental risk. However, the behavior and molecular-level reaction mechanism of ROX and its substituents with iron (hydr)oxides remains unclear. Herein, the binding behavior of ROX on ferrihydrite (Fh) was investigated through batch experiments and in-situ ATR-FTIR techniques. Our results demonstrated that Fh is an effective geo-sorbent for the retention of ROX. The pseudo-second-order kinetic and the Langmuir model successfully described the sorption process. The driving force for the binding of ROX on Fh was ascribed to the chemical adsorption, and the rate-limiting step is simultaneously dominated by intraparticle and film diffusion. Isotherms results revealed that the sorption of ROX onto Fh appeared in uniformly distributed monolayer adsorption sites. The two-dimensional correlation spectroscopy and XPS results implied that the nitro, hydroxyl, and arsenate moiety of ROX molecules have participated in binding ROX onto Fh, signifying that the predominated mechanisms were attributed to the hydrogen bonding and surface complexation. Our results can help to better understand the ROX-mineral interactions at the molecular level and lay the foundation for exploring the degradation, transformation, and remediation technologies of ROX and structural analog pollutants in the environment., Competing Interests: Declaration of Competing Interest The authors declared that they have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted., (Copyright © 2022. Published by Elsevier B.V.)

The influence of Fe(III) on the interaction between roxarsone (ROX) and humic acid (HA) was investigated by multi-spectroscopic techniques. The fluorescence quenching experiment indicated that the fluorescence intensity of HA-ROX was quenched by Fe(III) through a static quenching process. Synchronous fluorescence spectra provided further information concerning the competitive combination between ROX and Fe(III) for HA. The results of the dialysis equilibrium experiment confirmed the existence of Fe(III) (0.05-0.1 mmol/L) promotes the combination of HA and ROX. Binding mechanisms were further characterized by FTIR spectroscopy, and the carboxyl functional group is involved in the binding process of HA/Fe/ROX. In addition, acidic and neutral conditions are more conducive to the combination of ROX and HA/Fe than alkaline conditions. The above discussion is of great significance in understanding the environmental fate of ROX under the coexistence of Fe(III) and HA., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The contamination of organoarsenic is becoming increasingly prominent while SR-AOPs were confirmed to be valid for their remediation. This study has found that the novel metal/carbon catalyst (Fe/C-Mn) prepared by solid waste with hierarchical pores could simultaneously degrade roxarsone (ROX) and remove As(V). A total of 95.6% of ROX (20 mg/L) could be removed at the concentration of 1.0 g/L of catalyst and 0.4 g/L of oxidant in the Fe/C-Mn/PMS system within 90 min. The scavenging experiment and electrochemical test revealed that both single-electron and two-electron pathways contributed to the ROX decomposition. Spectroscopic analysis suggested the ROX has been successfully mineralized while As(V) was fixed with the surface Fe and Mn. Density functional theory (DFT) calculation and chromatographic analysis indicated that the As7, N8, O9 and O10 sites of ROX molecule were vulnerable to being attacked by nucleophilic, electrophilic and radical, resulting in the formation of several intermediates such as phenolic compounds. Additionally, the low metal leaching concentration during recycling and high anti-interference ability in various water matrices manifested the practicability of Fe/C-Mn/PMS system., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Organoarsenical antibiotics pose a severe threat to the environment and human health. In aquatic environment, dissolved organic matter (DOM)-mediated photochemical transformation is one of the main processes in the fate of organoarsenics. Dicarbonyl is a typical redox-active moiety in DOM. However, the knowledge on the photoconversion of organoarsenics by DOM, especially the contributions of dicarbonyl moieties is still limited. Here, we systematically investigated the photochemical transformation of three organoarsenics with the simplest β-diketone, acetylacetone (AcAc), as a model dicarbonyl moiety of DOM. The presence of AcAc significantly enhanced the photochemical conversion of roxarsone (ROX), whereas only minor effects were observed for 3-amino-4-hydroxyphenylarsonic acid (HAPA) and arsanilic acid (ASA), because the latter two (with an amino (-NH 2 ) group) are more photoactive than ROX (with a nitro (-NO 2 ) group). The results demonstrate that AcAc was a potent photo-activator and the reduction of -NO 2 to -NH 2 might be a rate-limiting step in the phototransformation of ROX. At a 1:1 M ratio of AcAc to ROX, the photochemical transformation rate of ROX was increased by 7 folds. In O 2 -rich environment, singlet oxygen, peroxide radicals, and ·OH were the main reactive species that led to the breakage of the C-As bond in ROX and the oxidation of the released arsono group to arsenate, whereas the triplet-excited state of AcAc ( 3 AcAc*) and carbon-centered radicals from the photolysis of AcAc dominated in the reductive transformation of ROX. In anoxic environment, 3-amino-4-hydroxyphenylarsonic acid was one of the main reductive transformation intermediates of ROX, whose photolysis rate was about 35 times that of ROX. The knowledge obtained here is of great significance to better understand the fate of organoarsenics in natural environment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Nanomaterials have versatile properties owing to their high surface-to-volume ratio and can thus be used in a variety of applications. This work focused on applying a facile hydrothermal strategy to prepare praseodymium vanadate nanoparticles due to the importance of nanoparticles in today's society and the fact that their synthesis might be a challenging endeavor. The structural and morphological characterizations were carried out to confirm the influence of the optimizations on the reaction's outcomes, which revealed praseodymium vanadate (PrVO 4 ) with a tetragonal crystal system. In this regard, the proposed development of electrochemical sensors based on the PrVO 4 nanocatalyst for the real-time detection of arsenic drug roxarsone (RXS) is a primary concern. The detection was measured by amperometric ( i - t ) signals where PrVO 4 /SPCE, as a new electrochemical sensing medium for RXS detection, increased the sensitivity of the sensor to about ∼2.5 folds compared to the previously reported ones. In the concentration range of 0.001-551.78 μM, the suggested PrVO 4 /SPCE sensor has a high sensitivity for RXS, with a detection limit of 0.4 nM. Furthermore, the impact of several selected potential interferences, operational stability (2000 s), and reproducibility measurements have no discernible effect on RXS sensing, making it the ideal sensing device feasible for technical analysis. The real-time analysis reveals the excellent efficiency and reliability of the prosed sensor toward RXS detection with favorable recovery ranges between ±97.00-99.66% for chicken, egg, water, and urine samples.

Organoarsenicals enter the environment from biogenic and anthropogenic sources. Trivalent inorganic arsenite (As(III)) is microbially methylated to more toxic methylarsenite (MAs(III)) and dimethylarsenite (DMAs(III)) that oxidize in air to MAs(V) and DMAs(V). Sources include the herbicide monosodium methylarsenate (MSMA or MAs(V)), which is microbially reduced to MAs(III), and the aromatic arsenical roxarsone (3-nitro-4-hydroxybenzenearsonic acid or Rox), an antimicrobial growth promoter for poultry and swine. Here we show that Sphingobacterium wenxiniae LQY-18 T , isolated from activated sludge, is resistant to trivalent MAs(III) and Rox(III). Sphingobacterium wenxiniae detoxifies MAs(III) and Rox(III) by oxidation to MAs(V) and Rox(V). Sphingobacterium wenxiniae has a novel chromosomal gene, termed arsU1. Expressed in Escherichia coli arsU1 confers resistance to MAs(III) and Rox(III) but not As(III) or pentavalent organoarsenicals. Purified ArsU1 catalyses oxidation of trivalent methylarsenite and roxarsone. ArsU1 has six conserved cysteine residues. The DNA sequence for the three C-terminal cysteines was deleted, and the other three were mutated to serines. Only C45S and C122S lost activity, suggesting that Cys45 and Cys122 play a role in ArsU1 function. ArsU1 requires neither FMN nor FAD for activity. These results demonstrate that ArsU1 is a novel MAs(III) oxidase that contributes to S. wenxiniae tolerance to organoarsenicals., (© 2021 Society for Applied Microbiology and John Wiley & Sons Ltd.)

Roxarsone is a phenyl-substituted arsonic acid comprising both arsenate and benzene rings. Few adsorbents are designed for the effective capture of both the organic and inorganic moieties of ROX molecules. Herein, nano zerovalent iron (nZVI) particles were incorporated on the surface of sludge-based biochar (SBC) to fabricate a dual-affinity sorbent that attracts both the arsenate and benzene rings of ROX. The incorporation of nZVI particles significantly increased the binding affinity and sorption capacity for ROX molecules compared to pristine SBC and pure nZVI. The enhanced elimination of ROX molecules was ascribed to synergetic adsorption and degradation reactions, through π-π* electron donor/acceptor interactions, H-bonding, and As-O-Fe coordination. Among these, the predominate adsorption force was As-O-Fe coordination. During the sorption process, some ROX molecules were decomposed into inorganic arsenic and organic metabolites by the reactive oxygen species (ROS) generated during the early stages of the reaction. The degradation pathways of ROX were proposed according to the oxidation intermediates. This work provides a theoretical and experimental basis for the design of adsorbents according to the structure of the target pollutant., Competing Interests: Declaration of Competing Interest There are no conflicts to declare., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The transformation of roxarsone (ROX) during UV disinfection with Fe(III) has been investigated. Fe(OH) 2+ , as the main Fe(III) species at pH = 3, produces HO under UV irradiation leading to the oxidation of ROX. Dissolved oxygen plays a very important role in the continuous conversion of generated Fe 2+ to Fe 3+ , which ensures a Fe(III)-Fe(II) cycle in the system. The presence of Cl - /HCO 3 - /NO 3 - has little influence on the ROX transformation, whereas PO 4 3- achieves an obvious inhibitory effect. The transformation of ROX leads to the formation of inorganic arsenic consisting of a much higher amount of As(V) than As(III). LC-MS analysis shows that phenol, o-nitrophenol and arsenic acid were the main transformation products. Both the radical scavenger experiment and electron spin resonance data confirm that the HO is responsible for ROX transformation. The toxic transformation products are found to have potential environmental risks for the natural environment, organisms and human beings., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

We report a facile and ultrasound assisted sonochemical synthesis of a Tungsten disulfide nanorods decorated nitrogen-doped reduced graphene oxide based nanocomposite. The WS 2 NRs/N-rGOs nanocomposite was characterized by FESEM, HRTEM, XRD, XPS and electrochemical methods and its application towards the electrochemical detection of organo-arsenic drug (coccidiostat). The WS 2 NRs/N-rGOs modified SPCE was used for the electrochemical reduction of roxarsone (ROX) and it showed superior electrocatalytic performance in terms of reduction peak current and shift in overpotential when compared to those of WS 2 NRs/SPCE, N-rGOs/SPCE and based SPCE. The WS 2 NRs/N-rGOs modified SPCE showed an excellent sensing ability towards ROX in nitrogen saturated phosphate buffer (PB) then the other controlled modified and unmodified electrodes. The WS 2 NRs/N-rGOs/SPCE displays high sensitive response towards ROX and gives wide linearity in the range of 0.1-442.6 µM ROX in neutral phosphate buffer (pH 7.0) and the sensitivity of the sensor is calculated as 14.733 µA µM -1  cm -2 . The WS 2 NRs/N-rGOs nanocomposite modified sensor also exhibits valuable ability of anti-interference to electroactive analytes. Furthermore, the as-prepared WS 2 NRs/N-rGOs/SPCE has been applied to the determination of ROX in biological and pharmaceutical samples., (Copyright © 2019 Elsevier B.V. All rights reserved.)

A sensitive electrochemical (voltammetric; DPV) sensor has been developed for the determination of coccidiostat drug (roxarsone) based on the use of an SPCE (screen-printed carbon electrode) modified with tungsten disulfide nanosheets (WS 2 NSs). The electrochemical detection of roxarsone on the WS 2 -modified SPCE was examined by electrochemical strategies. XPS, XRD, Raman, SEM, TEM, EDS and EIS were used to characterize the nanosheets. The effects of scan rate, pH values (phosphate buffer) and buffer concentration were optimized. A selective roxarsone sensor was developed that works best at -0.64 V (vs. Ag/AgCl) and performs much better than the bare SPCE. Features include (a) a wider linear range (0.05 to 490 μM), (b) a nanomolar detection limit (0.03 μM) and (c) high sensitivity (29 μA·μM -1 ·cm -2 ). The modified SPCEs have been successfully applied to the determination of roxarsone in spiked meat samples where they gave high accuracy and good recoveries. Graphical abstract Synthesis of WS 2 nanosheets and electrochemical detection of roxarsone.

In order to evaluate the influence of roxarsone (ROX) on the livestock wastewater treatment, a lab-scale pilot employing an anoxic-oxic (A-O) process was investigated by adding different concentrations of ROX at different periods. The mass balance of arsenic (As) in the A-O system was established through the analysis of As speciation and As migration in the gas, liquid and solid phases. The results showed that around 80% of total ROX (initial concentration was 50mgROXL -1 ) was eliminated in the anoxic reactor (R1) in which at least about 11% of total ROX was transformed to inorganic As v (iAs v ) due to the direct breaking of the C-As bond of ROX. Inorganic As III (iAs III ) and arsine (AsH 3 ) were produced in R1, while the generated iAs III in the effluent of R1 was almost completely oxidized to iAs V in the aerobic reactor (R2). However, the concentration of ROX in the effluent of R2 was almost the same as that in the effluent of R1. After 85days operation, iAs V and residual ROX as the main forms of As were observed after the A-O process. Furthermore, the mass balance of As at steady state revealed that around 0.08%, 3.91% and 96.01% of total As was transformed into gas (biogas), solid (excess sludge) and liquid (effluent). Additionally, the 16S rRNA analysis demonstrated that the existence of ROX in livestock wastewater may play a crucial role in the diversity of bacterial community in the A-O system., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Roxarsone, one of feed add drugs containing arsenic, has been most widely used in poultry and swine industry. Roxarsone discharged into the environment has caused serious pollution problem. Herein, a reusable functional material for selective recognition and adsorption of roxarsone and its derivatives were designed and synthesized. The interaction mechanism is based on acid-base interaction and surface molecular imprinting. Dual functionalized core-shell structure with silica gel as the core was prepared to use as carrier for surface molecularly imprinted polymers. Surface molecularly imprinted polymers for roxarsone was successfully designed and synthesized using 3-aminopropyltriethoxysilane and methyl acryloyloxypropyltriethoxy silane as functional monomers, Ethylene glycol dimethacrylate as crosslinker, Azobisisobutyronitrile as initiator, acetonitrile as solvent. Binding study showed that the recognition selectivity for roxarsone and its derivatives can be significantly improved (3.5-4 folds) with molecular imprinting. Moreover, the prepared functional material for selective recognition and adsorption of Roxarsone was reusable for multiple times without significant decreasing their adsorption capacities., (Copyright © 2017 John Wiley & Sons, Ltd.)

The extensive use of roxarsone (3-nitro-4-hydroxyphenylarsonic acid) as a feed additive in the broiler poultry industry can lead to environmental arsenic contamination. This study was conducted to reveal the response of soil microbial communities to roxarsone pollution along a concentration gradient. To explore the degradation process and degradation kinetics of roxarsone concentration gradients in soil, the concentration shift of roxarsone at initial concentrations of 0, 50, 100, and 200 mg/kg, as well as that of the arsenic derivatives, was detected. The soil microbial community composition and structure accompanying roxarsone degradation were investigated by high-throughput sequencing. The results showed that roxarsone degradation was inhibited by a biological inhibitor, confirming that soil microbes were absolutely essential to its degradation. Moreover, soil microbes had considerable potential to degrade roxarsone, as a high initial concentration of roxarsone resulted in a substantially increased degradation rate. The concentrations of the degradation products HAPA (3-amino-4-hydroxyphenylarsonic acid), AS(III), and AS(V) in soils were significantly positively correlated. The soil microbial community composition and structure changed significantly across the roxarsone contamination gradient, and the addition of roxarsone decreased the microbial diversity. Some bacteria tended to be inhibited by roxarsone, while Bacillus, Paenibacillus, Arthrobacter, Lysobacter, and Alkaliphilus played important roles in roxarsone degradation. Moreover, HAPA, AS(III), and AS(V) were significantly positively correlated with Symbiobacterium, which dominated soils containing roxarsone, and their abundance increased with increasing initial roxarsone concentration. Accordingly, Symbiobacterium could serve as indicator of arsenic derivatives released by roxarsone as well as the initial roxarsone concentration. This is the first investigation of microbes closely related to roxarsone degradation.

Roxarsone (Rox), an organoarsenic compound, served as a feed additive in the poultry industry for more than 60 years. Residual amounts of Rox present in chicken meat could give rise to potential human exposure to Rox. However, studies on the bioavailability of Rox in humans are scarce. We report here the accumulation and transepithelial transport of Rox using the human colon-derived adenocarcinoma cell line (Caco-2) model. The cellular accumulation and transepithelial passage of Rox in Caco-2 cells were evaluated and compared to those of arsenobetaine (AsB), arsenite (As III ), and arsenate (As V ). When Caco-2 cells were exposed to 3 μM Rox, AsB, and As III separately for 24 h, the maximum accumulation was reached at 12 h. After 24-h exposure, the accumulated Rox was 6-20 times less than AsB and As III . The permeability of Rox from the apical to basolateral side of Caco-2 monolayers was similar to As V but less than As III and AsB. The results of lower bioavailability of Rox are consistent with previous observations of relatively lower amounts of Rox retained in the breast meat of Rox-fed chickens. These data provide useful information for assessing human exposure to and intestinal bioavailability of Roxarsone.

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., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Microbes play a critical role in the global arsenic biogeocycle. Most studies have focused on redox cycling of inorganic arsenic in bacteria and archaea. The parallel cycles of organoarsenical biotransformations are less well characterized. Here we describe organoarsenical biotransformations in the environmental microbe Shewanella putrefaciens. Under aerobic growth conditions, S. putrefaciens reduced the herbicide MSMA (methylarsenate or MAs(V)) to methylarsenite (MAs(III)). Even though it does not contain an arsI gene, which encodes the ArsI C-As lyase, S. putrefaciens demethylated MAs(III) to As(III). It cleaved the C-As bond in aromatic arsenicals such as the trivalent forms of the antimicrobial agents roxarsone (Rox(III)), nitarsone (Nit(III)) and phenylarsenite (PhAs(III)), which have been used as growth promoters for poultry and swine. S. putrefaciens thiolated methylated arsenicals, converting MAs(V) into the more toxic metabolite monomethyl monothioarsenate (MMMTAs(V)), and transformed dimethylarsenate (DMAs(V)) into dimethylmonothioarsenate (DMMTAs(V)). It also reduced the nitro groups of Nit(V), forming p-aminophenyl arsenate (p-arsanilic acid or p-AsA(V)), and Rox(III), forming 3-amino-4-hydroxybenzylarsonate (3A4HBzAs(V)). Elucidation of organoarsenical biotransformations by S. putrefaciens provides a holistic appreciation of how these environmental pollutants are degraded.

Batch and greenhouse experiments were conducted to examine the effects of Fenton process on transformation of roxarsone in soils and its resulting impacts on the growth of and As uptake by a rice plant cultivar. The results show that addition of Fenton reagent markedly accelerated the degradation of roxarsone and produced arsenite, which was otherwise absent in the soil without added Fenton reagent. Methylation of arsenate was also enhanced by Fenton process in the earlier part of the experiment due to abundant supply of arsenate from Roxarsone degradation. Overall, addition of Fenton reagent resulted in the predominant presence of arsenate in the soils. Fenton process significantly improved the growth of rice in the maturity stage of the first crop, The concentration of methylated As species in the rice plant tissues among the different growth stages was highly variable. Addition of Fenton reagent into the soils led to reduced uptake of soil-borne As by the rice plants and this had a significant effect on reducing the accumulation of As in rice grains. The findings have implications for understanding As biogeochemistry in paddy rice field receiving rainwater-borne H2O2 and for development of mitigation strategies to reduce accumulation of As in rice grains., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The fate and transport of roxarsone (ROX), a widely used organoarsenic feed additive, in soil is significantly influenced by the ubiquitous presence of soil-derived dissolved organic matter (DOM). In this study, fluorescence quenching titration and two-dimensional correlation spectroscopy (2D-COS) were employed to study ROX binding to DOM. Binding mechanisms were revealed by fluorescence lifetime measurement and Fourier transform infrared spectroscopy (FTIR). Humic- and protein-like fluorophores were identified in the excitation-emission matrix and synchronous fluorescence spectra of DOM. The conditional stability constant (log KC) for ROX binding to DOM was found to be 5.06, indicating that ROX was strongly bound to DOM. The binding order of ROX to DOM fluorophores revealed by 2D-COS followed the sequence of protein-like fluorophore ≈ the longer wavelength excited humic-like (L-humic-like) fluorophore > the shorter wavelength excited humic-like (S-humic-like) fluorophore. 2D-COS resolved issues with peak overlapping and allowed further exploration of the interaction between ROX and DOM. Results of fluorescence lifetime and FTIR spectra demonstrated that ROX interacted with DOM through the hydroxyl, amide II, carboxyl, aliphatic CH, and NO2 groups, yielding stable DOM-ROX complexes. The strong interaction between ROX and DOM implies that DOM plays an important role in the environmental fate of ROX in soil., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Aromatic organoarsenical roxarsone (ROX) is a common additive for livestock feed. This arsenic containing pollutant could be discharged into the environment through agricultural application of animal manure, and pose potential threats to both humans and the wider environment. In this study, the influence of pH, competing anions and metal ions on the adsorption and desorption of ROX on goethite were investigated in order to understand their mobility in the environment. Both hydroxide ions and phosphate are common substances in the environment, and both are potential competing anions for ROX. Our results showed the addition of phosphate desorbed more ROX than the addition of hydroxide ions. As pH increased, the effect of phosphate did not show much difference to that of hydroxide ion. The results indicate that the presence of phosphate will greatly increase the mobility of ROX at low pH. Six common metal ions, including Zn(2+), Cu(2+), Fe(3+), Mn(2+), Mg(2+), and Ca(2+), were tested and all spiked metal ions enhanced the stability of ROX adsorption on the surface of goethite, and led to less desorption when phosphate was added. The results demonstrate that metal ions may form complex/surface precipitation with ROX to enhance its adsorption. The effect from Fe(3+), Zn(2+) and Cu(2+) was more pronounced than other metal ions, which might result from the fact that these three metal ions tend to associate with hydroxide ions and decrease the pH. The results of this research may shed light on the environmental fate and transportation of aromatic organoarsenicals in soil., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Trivalent organoarsenic compounds are far more toxic than either pentavalent organoarsenicals or inorganic arsenite. Many microbes methylate inorganic arsenite (As(III)) to more toxic and carcinogenic methylarsenite (MAs(III)). Additionally, monosodium methylarsenate (MSMA or MAs(V)) has been used widely as an herbicide and is reduced by microbial communities to MAs(III). Roxarsone (3-nitro-4-hydroxybenzenearsonic acid) is a pentavalent aromatic arsenical that is used as antimicrobial growth promoter for poultry and swine, and its active form is the trivalent species Rox(III). A bacterial permease, ArsP, from Campylobacter jejuni, was recently shown to confer resistance to roxarsone. In this study, C. jejuni arsP was expressed in Escherichia coli and shown to confer resistance to MAs(III) and Rox(III) but not to inorganic As(III) or pentavalent organoarsenicals. Cells of E. coli expressing arsP did not accumulate trivalent organoarsenicals. Everted membrane vesicles from those cells accumulated MAs(III) > Rox(III) with energy supplied by NADH oxidation, reflecting efflux from cells. The vesicles did not transport As(III), MAs(V) or pentavalent roxarsone. Mutation or modification of the two conserved cysteine residues resulted in loss of transport activity, suggesting that they play a role in ArsP function. Thus, ArsP is the first identified efflux system specific for trivalent organoarsenicals., (© 2015 John Wiley & Sons Ltd.)

Roxarsone (ROX) remains to be as an organoarsenical feed additive used widely in developing countries. However, most of the ROX is excreted unchanged in manure, which could be readily photodegraded into inorganic arsenic derivatives. In this study, the comparative cytotoxicity and arsenic accumulation were evaluated after the exposure of Tetrahymenathermophila (T. thermophila) cell model to ROX and its photodegradates. The cytotoxic effects were estimated according to the relevant cell growth curves, morphologies and MTT assays. The 36 h median effective concentrations for ROX and its photodegradates at various photolysis times (10, 20, and 30 min) are 39.0, 2.08, 1.88, and 1.82 mg (total arsenic) L(-1), respectively. In parallel, the cellular arsenic uptakes were determined by hydride generation-atomic fluorescence spectrometry. Phospholipid layer as basic membrane structure was mimicked to assess the correlation between membrane permeability and cytotoxicity. The biocompatibility of ROX was dependent on its tendency to interact with cell membrane while the cytotoxicity was induced by the trans-membrane of the inorganic arsenic species present in the photodegradates of ROX. Furthermore, the photodegradates of ROX-associated alterations of intracellular protein profiles were analyzed using a proteomic approach. Overall, the significance was clarified that the control of arsenic emission caused by the application of ROX needs to be imposed., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Roxarsone (ROX) and nitarsone (NIT) are used as additives in animal feeding operations and have been detected in animal manure, agricultural retention ponds, and adjacent surface waters. This work investigates treatment of organoarsenicals using UV-based treatment processes, namely UV irradiation at 253.7 nm and the UV-H2O2 advanced oxidation process. The apparent molar absorptivity was mapped for ROX and NIT across pH and wavelength. For UV irradiation at 253.7 nm, the fluence-based pseudo-first order rate constant (kp(')) and effective quantum yield (Φ) for ROX were 8.10-29.7 × 10(-5) cm(2)/mJ and 2.34-8.37 × 10(-3) mol/E, respectively; the corresponding constants were slightly lower for NIT. The observed rate constants are higher during advanced oxidation (e.g., kp,ROX(')=3.92(±0.19)-217(±48) × 10(-4) cm(2)/mJ). Second order rate constants for organoarsenical transformation by hydroxyl radicals were determined to be 3.40(±0.45) × 10(9) and 8.28(±0.49) × 10(8) M(-1)s(-1) for ROX and NIT, respectively. Solution pH and nitrate concentration did not significantly impact ROX transformation during advanced oxidation; however, bicarbonate and dissolved organic matter from chicken litter reduced ROX transformation through hydroxyl radical scavenging. Inorganic arsenic was the predominant transformation product of ROX during UV-H2O2 treatment., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

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., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Roxarsone (3-nitro-4-hydroxy benzene arsenic acid) is an organoarsenic feed additive and has been widely used in the poultry industry to prevent coccidiosis and improve feed efficiency. The presence of roxarsone and its degradation products results in the instability of the anaerobic methanogenic process. This study investigated the degradation and speciation of roxarsone in an anaerobic granular sludge (AGS) system and the impacts of roxarsone and its degradation products on the structure of AGS. Roxarsone inhibited methane production, and the added roxarsone was rapidly degraded into 3-amino-4-hydroxyphenylarsonic acid (HAPA). After 240 days of incubation, the distribution of arsenic differed between the aqueous solution and the AGS in the assays of 20 and 350mg/L roxarsone. Species analysis indicated that HAPA was completely degraded in all of the assays with roxarsone addition after 240 days of incubation. Species distribution was affected by the phases and the initial concentration of roxarsone added. The concentration of As(III) was higher than that of As(V) in both the aqueous solution and the AGS in all assays with roxarsone addition. The toxicity of roxarsone and its degradation products resulted in changes in the structure and the microorganism species in the AGS., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Roxarsone (4-hydroxy-3-nitrophenylarsonic acid) has been commonly used in animal feed as an organoarsenic additive, most of which is excreted in manure. Roxarsone is easily biodegraded to 4-hydroxy-3-aminophenylarsonic acid (HAPA) under anaerobic conditions, but HAPA persists for long periods in the environment, increasing the risk of arsenic contamination through diffusion. We investigated the electrochemical stimulation of the microbial degradation of roxarsone under anaerobic conditions. After the carbon sources in the substrate were depleted, HAPA was slowly degraded to form arsenite under anaerobic conditions. The degradation rate of HAPA was significantly increased when 0.5 V was applied without adding a carbon source. The two-cell membrane reactor assays reveal that the HAPA was degraded in the anode chambers, confirming that the anode enhanced the electron transfer process by acting as an electron acceptor. The degradation product formed with electrochemical stimulation was arsenate, which facilitates the removal of arsenic from wastewater. Based on the high performance liquid chromatography-ultraviolet-hydride generation-atomic fluorescence spectrometry (HPLC-UV-HG-AFS) and gas chromatography-mass spectrometry (GC-MS) data, the pathway for the biodegradation of roxarsone and the mechanisms for the electrochemically stimulated degradation are proposed. This method provides a potential solution for the removal of arsenic from organoarsenic-contaminated wastewater.

In this study, the methods of fluorescence spectroscopy and fluorescence quenching titration technique were used to identify the interactions between humic acid (HA) and roxarsone (ROX). Effects of HA concentration, pH and temperature on the bonding strength between HA and ROX were investigated. The results showed that the four fluorescence peaks (E(x)/E(m) = 300 nm/480 nm, 370 nm/480 nm, 420 nm/500 nm, 460 nm/520 nm, marked as peak A, B, C, D respectively) of HA could be quenched by ROX. The extent of decreases in fluorescence intensities of different peaks was different and followed the order of C > B > A > D. The common logarithm of association constants (lg K) between peak A and ROX increased slightly with the increase of HA concentration and were much larger than the bimolecular quenching constant of O2. It was confirmed that the carboxyl groups and the carboxide groups of HA were quenched statically by ROX. The lg K values fluctuated between 3.55 L x mol(-1) and 3.98 L x mol(-1) when pH ranged from 5.00 to 9.00, and the maximum value occurred at pH 6.00. It might be resulted from the fact that pH could change the formation of ROX and conformation of phenolic hydroxyl groups and carboxyl groups in HA. The lg K values decreased and fluctuated between 2.65 L x mol(-1) and 3.89 L x mol(-1) with temperature ranging from 25.0 degrees C to 55.0 degrees C, which further confirmed the static quenching interaction between HA and ROX. Transient-fluorescence spectrum analyses and liner model simulations revealed that single static quenching was the main mechanism between ROX and the functional groups of fluorescence peak A, B, D in HA, and combined dynamic and static quenching was the main mechanism between ROX and the functional groups of peak C in HA.

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid) has been widely used as organic arsenic additive in animal industry. In this study, the adsorption of roxarsone on TiO₂ under dark conditions, the photocatalytic decomposition of roxarsone under UV/TiO₂, and the possible photocatalytic pathway were investigated. At the initial concentration of 5-35 mg/L, the adsorption of roxarsone fitted well with the pseudo-second-order kinetics. The isotherms analysis showed that the Langmuir model was better than the Freundlich and Dubinin–Radushkevich models for describing the adsorption process. After 7 h of photocatalytic decomposition, a complete disappearance of roxarsone was achieved. The pH value has a significant effect on both adsorption and photocatalytic decomposition of roxarsone. The results of high-performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS) and gas chromatography-mass spectrometry (GC/MS) analyses proved the cleavage of the As-C bond during the photocatalytic decomposition process by TiO2 and the intermediates of the decomposition. Based on the results, a possible photocatalytic decomposition pathway was proposed.

Roxarsone has been extensively used in the feed of animals, which is usually excreted unchanged in the manure and eventually enter into animal wastewater, challenging the biological phosphorus removal processes. Knowledge of its inhibition effect is key for guiding treatment of roxarsone-contaminated wastewater, and is unfortunately keeping unclear. We study the inhibition of roxarsone on biological phosphorus removal processes for roxarsone-contaminated wastewater treatment, in terms of the removal and rates of chemical oxygen demand (COD), phosphate. Results showed that presence of roxarsone considerably limited the COD removals, especially at roxarsone concentration exceeding 40 mg L(-1). Additionally, roxarsone inhibited both phosphorus release and uptake processes, consistent with the phosphate profiles during the biological phosphorus removal processes; whereas, roxarsone is more toxic to phosphorus uptake process, than release function. The results indicated that it is roxarsone itself, rather than the inorganic arsenics, inhibit biological phosphorus removal processes within both aerobic and anaerobic roxarsone-contaminated wastewater treatment., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

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.

Aromatic organoarsenicals roxarsone (ROX) and p-arsanilic acid (ASA) are common feed additives for livestock and could be released into the environment via animal manure and agricultural runoff. To evaluate their environmental fate, the adsorption behavior of ROX and ASA was investigated with two common soil metal oxides, goethite (FeOOH) and aluminum oxide (Al(2)O(3)), under different reactant loading, water pH and competing ion conditions. ROX and ASA exhibit essentially identical adsorption characteristics. FeOOH and Al(2)O(3) exhibit similar adsorption trends for both organoarsenicals; however, the adsorption efficiency on the surface site basis was about three times lower for Al(2)O(3) than for FeOOH. The adsorption reaction is favorable at neutral and acidic pH. Phosphate and natural organic matter significantly interfere with aromatic arsenical adsorption on both metal oxides, whereas sulfate and nitrate do not. Pre-adsorbed aromatic arsenicals can be quickly but not completely displaced by phosphate, indicating that ion exchange is not the only mechanism governing the adsorption process. The adsorption envelope was successfully modeled by a diffuse double layer surface complexation model, identifying the critical role of di-anionic organoarsenic species in the adsorption. Results of this research can help predict and control the mobility of aromatic arsenicals in the environment., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Roxarsone, an organoarsenic compound serving as a common feeding additive in poultry industry, brings about potential risk of the toxic inorganic arsenate contamination in ambient environment. Current understanding in the dynamics of roxarsone removal and the determining environmental processes remains unclear, thus restricts the progress in roxarsone-contaminated wastewater treatment. In this study, the adsorption of roxarsone on multi-walled carbon nanotubes (MWCNTs) was investigated. The adsorption of roxarsone on MWCNTs decreased dramatically with increasing pH from 2.0 to 11.7 and decreased significantly with increasing ionic strength from 0 to 1.0 mol/L KCl. It was found that the sorption isotherms of roxarsone on MWCNTs were nonlinear, which can be well described according to the Freundlich and Polanyi-Manes models. Thermodynamic analysis indicates that the adsorption of roxarsone on MWCNTs is an exothermic and spontaneous process. Sorption site energy analysis reveals a distribution of sorption energy and the heterogeneous adsorption sites of roxarsone on MWCNTs. The dynamic adsorption with column shows the potential of the practical application for the roxarsone-contaminated wastewater treatment by MWCNTs. The FTIR analysis indicates that EDA interaction and electrostatic repulsion might be the dominant mechanisms for the adsorption of roxarsone on MWCNTs., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Roxarsone is a commonly used additive in chicken (Gallus gallus) industry. However, little is known on the intrinsic molecular mechanism via which the growth performance of birds improves. This study was therefore performed to investigate the expression profiles of genes induced by roxarsone. Fifty-six broiler chickens were divided into two groups, namely treated and untreated with roxarsone. The treated group was provided a diet of 45.4mg/kg roxarsone medication and the other group acted as control. Data analysis showed that roxarsone consistently and significantly (P<0.05) increased chicken growth performance. In addition to this a significant (P<0.05) increase of arsenic residue in liver has been seen. Microarray expression analysis of 8935 genes in liver showed that 22 genes (10 up- and 12 down-regulated) had altered expression throughout the experimental periods. Two novel genes (GenBank accession no. GU724343 and GU724344) were cloned through rapid amplification of cDNA ends (RACE). Gene GU724343 was predicted to encode an unidentified protein and the second gene GU724344 was presumed to encode a new member of immunoglobulin-like receptor (CHIR) family. Our results suggested for the first time that the role of roxarsone could be mainly to modify the expression levels of cell growth, immunity/defense and energy metabolism associated genes, as a result promoting animal growth. Further research on these genes should help to increase the knowledge of improving animal productivity safely and effectively., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Organoarsenic drugs such as roxarsone and 4-arsanilic acid are poultry feed additives widely used in US broilers to prevent coccidosis and to enhance growth and pigmentation. Despite their veterinary benefits there has been growing concern about their use because over 90% of these drugs are released intact into litter, which is often sold as a fertilizing supplement. The biochemical degradation of these antimicrobials in the litter matrix can release significant amounts of soluble As(III) and As(V) to the environment, representing a potential environmental risk. Silver/polydimethylsiloxane (Ag/PDMS) nanocomposites are a class of surfaceenhanced Raman scattering (SERS) substrates that have proven effective for the sensitive, reproducible, and field-adaptable detection of aromatic acids in water. The work presented herein uses for the first time Ag/PDMS nanocomposites as substrates for the detection and characterization of trace amounts of roxarsone, 4-arsanilic acid, and acetarsone in water. The results gathered in this study show that organoarsenic species are distributed into the PDMS surface where the arsonic acid binds onto the embedded silver nanoparticles, enhancing its characteristic 792 cm(-1) stretching band. The chemisorption of the drugs to the metal facilitates its detection and characterization in the parts per million to parts per billion range. An extensive analysis of the distinct spectroscopic features of each drug is presented with emphasis on the interactions of the arsonic acid, amino, and nitro groups with the metal surface. The benefits of SERS based methods for the study of arsenic drugs are also discussed., (© 2011 Society for Applied Spectroscopy)

Sorption of phenylarsenicals including 4-hydroxy-3-nitrophenylarsonic acid (roxarsone), an animal feed additive widely used for growth stimulation, on soils was investigated in batch systems. Phenylarsonic acid, o-arsanilic acid and roxarsone were retained differently by unpolluted, non-sterilized soils. Sorption isotherms were analyzed by the Henry, Tóth and Langmuir-Freundlich equations. The saturation capacity of the Acrisol soil was 3.4 for o-arsanilic acid, 10.9 for phenylarsonic acid and 1.9 g(As) kg(soil)(-1) (dry mass) for roxarsone. The iron content in the soil was not the only factor determining retention of the studied phenylarsenicals. The order of retention on the three soils after 24 h was: roxarsone>o-arsanilic acid>phenylarsonic acid. Besides arsenite and arsenate, new arsenic-containing compounds were detected., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Background, Aim, and Scope: Organoarsenical-containing animal feeds that promote growth and resistance to parasites are mostly excreted unchanged, ending up in nearby wastewater storage lagoons. Earlier work documented the partial transformation of organoarsenicals, such as, 3-nitro-4-hydroxyphenylarsonic acid (roxarsone) to the more toxic inorganic arsenate [As(V)] and 3-amino-4-hydroxyphenylarsonic acid (3-AHPAA). Unidentified roxarsone metabolites using liquid chromatography coupled to inductively coupled plasma mass spectrometry (LC/ICP-MS) were also inferred from the corresponding As mass balance. Earlier batch experiments in our laboratory suggested the presence of organometallic (Cu) complexes during relevant roxarsone degradation experiments. We hypothesized that organocopper compounds were complexed to roxarsone, mediating its degradation in field-collected swine wastewater samples from storage lagoons. The objective of this study was to investigate the role of organometallic (Cu) complexes during roxarsone degradation under aerobic conditions in swine wastewater suspensions, using electrospray ionization mass spectrometry (ES-MS)., Materials and Methods: Two swine wastewater samples differing in % solids content and total recoverable Cu concentrations were reacted with 500 ppb of roxarsone under aerobic conditions for 16 days. LC/ICP-MS and ES-MS were used for As speciation analyses, and characterization of metal-organoarsenical complexes in swine wastewater subsamples, respectively., Results and Discussion: An organocopper roxarsone metabolite was found only in the high-Cu wastewater sample, suggesting the role of Cu in roxarsone degradation under aerobic conditions. The organocopper metabolite was not found in the low-Cu wastewater sample, because roxarsone did not undergo degradation under aerobic conditions even after 16 days., Conclusions: Aerobic degradation of organoarsenicals (roxarsone) has not been documented before. Preliminary dataset from this study illustrates the direct and/or indirect association of particulate Cu in catalyzing roxarsone degradation under aerobic conditions in samples with high % solids content., Recommendations and Perspectives: Concerns regarding the degradation of roxarsone in wastewater to the more toxic inorganic As may be partially linked to the presence of particulate Cu. The presence of Cu in wastewater-suspended particle surfaces has never been coupled before to organoarsenicals degradation reactions, thus, further studies are needed to elucidate the related reaction mechanisms and pathways. Water depth-dependent solid particle distribution profiles in wastewater storage lagoons could provide empirical evidence towards the design of effective degradation practices for nitrophenol-containing compounds, such as, organoarsenical-containing antibiotics, or explosive munitions compounds.

Roxarsone (4-hydroxy-3-nitro-phenylarsonic acid) and p-arsanilic acid (4-aminophenylarsonic acid) are feed additives widely used in the broiler and swine industry. This study evaluated the inhibitory effect of roxarsone, p-arsanilic, and other phenylarsonic compounds on the activity of acetate- and H(2)-utilizing methanogenic microorganisms. Roxarsone, p-arsanilic, and 4-hydroxy-3-aminophenylarsonic acid (HAPA) inhibited acetoclastic and hydrogenotrophic methanogens when supplemented at concentrations of 1mM, and their inhibitory effect increased sharply with incubation time. Phenylarsonic acid (1mM) inhibited acetoclastic but not H(2)-utilizing methanogens. HAPA, a metabolite from the anaerobic biodegradation of roxarsone, was found to be sensitive to autooxidation by oxygen. The compound (2.6mM) caused low methanogenic inhibition (only 14.2%) in short-term assays of 12h when autooxidation was prevented by supplementing HAPA solutions with ascorbate. However, ascorbate-free HAPA solutions underwent spontaneous autooxidation in the presence of oxygen, leading to the formation of highly inhibitory compounds. These results confirm the microbial toxicity of organoarsenic compounds, and they indicate that biotic as well as abiotic transformations can potentially impact the fate and microbial toxicity of these contaminants in the environment., ((c) 2009 Elsevier B.V. All rights reserved.)

A novel, simple and sensitive liquid chromatography-hydride generation online coupled with atomic fluorescence spectrometry (LC-HG-AFS) method was developed for simultaneous determination of p-arsanilic acid (p-ASA) and roxarsone in feed. 20% Methanol aqueous was used as extraction reagent, after preprocessing samples by ultrasonic oscillation, then injected into the chromatography Waters symmetry shield RP18 analytical column (150mm x 4.6mm, 5 microm), finally detected by an atomic fluorescence spectrometer. The calibration curves of analyses were linear over a range of concentrations (0.2-4mg L-1 and the correlation coefficients were higher than 0.9990. The limits of detection were 0.2 mg L-1. The method has been validated by linearity, precision and recovery. p-ASA and roxarsone in feed can be successfully and simultaneously determined using the developed method without a tedious pretreatment procedure.

A growing body of literature reports 3-nitro-4-hydroxyphenylarsonic acid (roxarsone) degradation in poultry litter (PL) to the more toxic inorganic arsenic (As). Aluminum-based drinking-water treatment residuals (WTR) present a low-cost amendment technology to reduce As availability in PL, similar to the use of alum to reduce phosphorus availability. Batch experiments investigated the effectiveness of WTR in removing roxarsone and inorganic As species from PL aqueous suspensions. Incubation experiments with WTR-amended PL evaluated the effects of WTR application rates (2.5-15% by weight) and incubation time (up to 32 d) at two incubation temperatures (23 and 35 degrees C) on As availability in PL. Batch PL aqueous experiments showed the high affinity of As(V), As(III), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), and roxarsone for the WTR. The 10% WTR amendment rate decreased As availability in PL by half of that of the unamended (no WTR) PL-incubated samples. The reduction in dissolved As concentrations during incubation of WTR-amended PL samples was kinetically limited, being complete within 13 d. Parallel reductions in roxarsone, As(V), and DMA concentrations were observed with liquid chromatography-inductively coupled plasma mass spectrometry, whereas As(III) and MMA concentrations were always <5% of dissolved As. Incubation temperature did not significantly (p > 0.05) influence dissolved As concentrations in the WTR-amended PL. Potential formation of a copper-containing roxarsone metabolite was considered in PL aqueous suspensions with the aid of electrospray mass spectrometry. Further experiments in the field are necessary to ensure that sorbed As is stable in WTR-amended PL.

The extensive use of 3-nitro-4-hydroxybenzene arsonic acid (roxarsone) in the production of broiler chickens can lead to increased soil arsenic concentration and arsenic contaminated dust. While roxarsone is the dominant arsenic species in fresh litter, inorganic As (V) predominates in composted litter. Microbial activity has been implicated as the cause, but neither the specific processes nor the organisms have been identified. Here we demonstrate the rapid biotransformation of roxarsone under anaerobic conditions by Clostridium species in chicken litter enrichments and a pure culture of a fresh water arsenate respiring species (Clostridium sp. strain OhILAs). The main products were 3-amino-4-hydroxybenzene arsonic acid and inorganic arsenic. Growth experiments and genomic analysis indicate strain OhILAs may use roxarsone as a terminal electron acceptor for anaerobic respiration. Electronic structure analysis suggests that the reducing equivalents should go to the nitro group, while liberation of inorganic arsenic from the intact benzene ring by cleaving the C-As bond is unlikely. Clostridium and Lactobacillus species are common in the chicken cecum and litter. Thus, the organic-rich manure and anaerobic conditions typically associated with composting provide the conditions necessary for the native microbial populations to transform the roxarsone in the litter releasing the more toxic inorganic arsenic.

Poultry litter often contains arsenic as a result of organo-arsenical feed additives. When the poultry litter is applied to agricultural fields, the arsenic is released to the environment and may result in increased arsenic in surface and groundwater and increased uptake by plants. The release of arsenic from poultry litter, litter-amended soils, and soils without litter amendment was examined by extraction with water and strong acids (HCI and HNO3). The extracts were analyzed for As, C, P, Cu, Zn, and Fe. Copper, zinc, and iron are also poultry feed additives. Soils with a known history of litter application and controlled application rate of arsenic-containing poultry litter were obtained from the University of Maryland Agricultural Experiment Station. Soils from fields with long-term application of poultry litter were obtained from a tilled field on the Delmarva Peninsula (MD) and an untilled Oklahoma pasture. Samples from an adjacent forest or nearby pasture that had no history of litter application were used as controls. Depth profiles were sampled for the Oklahoma pasture soils. Analysis of the poultry litter showed that 75% of the arsenic was readily soluble in water. Extraction of soils shows that weakly bound arsenic mobilized by water correlates positively with C, P, Cu, and Zn in amended fields and appears to come primarily from the litter. Strongly bound arsenic correlates positively with Fe in amended fields and suggests sorption or coprecipitation of As and Fe in the soil column.

Arsenic compounds have been used extensively in agriculture in the US for applications ranging from cotton herbicides to animal feed supplements. Roxarsone (3-nitro-4-hydroxyphenylarsonic acid), in particular, is used widely in poultry production to control coccidial intestinal parasites. It is excreted unchanged in the manure and introduced into the environment when litter is applied to farmland as fertilizer. Although the toxicity of roxarsone is less than that of inorganic arsenic, roxarsone can degrade, biotically and abiotically, to produce more toxic inorganic forms of arsenic, such as arsenite and arsenate. Experiments were conducted on aqueous litter leachates to test the stability of roxarsone under different conditions. Laboratory experiments have shown that arsenite can be cleaved photolytically from the roxarsone moiety at pH 4-8 and that the degradation rate increases with increasing pH. Furthermore, the rate of photodegradation increases with nitrate and natural organic matter concentration, reactants that are commonly found in poultry-litter-water leachates. Additional photochemical reactions rapidly oxidize the cleaved arsenite to arsenate. The formation of arsenate is not entirely undesirable, because it is less mobile in soil systems and less toxic than arsenite. A possible mechanism for the degradation of roxarsone in poultry litter leachates is proposed. The results suggest that poultry litter storage and field application practices could affect the degradation of roxarsone and subsequent mobilization of inorganic arsenic species., (Copyright 2002 Elsevier Science B.V.)