Arsenic Metabolites, Including N-Acetyl-4-hydroxy-m-arsanilic Acid, in Chicken Litter from a Roxarsone-Feeding Study Involving 1600 Chickens

Arsenic speciation in freshwater fish using high performance liquid chromatography and inductively coupled plasma mass spectrometry

Arsenic speciation in freshwater fish is crucial for providing meaningful consumption guidelines that allow the public to make informed decisions regarding its consumption. While marine fish have attracted much research interest due to their higher arsenic content, research on freshwater fish is limited due to the challenges in quantifying and identifying arsenic species present at trace levels. We describe here a sensitive method and its application to the quantification of arsenic species in freshwater fish. Arsenic species from fish tissues were extracted using a methanol/water mixture (1:1 vol. ratio) and ultrasound sonication. Anion-exchange high-performance liquid chromatography (HPLC) enabled separation of arsenobetaine (AsB), inorganic arsenite (iAsIII), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), inorganic arsenate (iAsV), and three new arsenic species. Inductively coupled plasma mass spectrometry (ICPMS) provided highly sensitive and specific detection of arsenic. A limit of detection of 0.25 µg/kg (wet weight fish tissue) was achieved for the five target arsenic species: AsB, iAsIII, DMA, MMA, and iAsV. A series of experiments were conducted to ensure the accuracy and validity of the analytical method. The method was successfully applied to the determination of arsenic species in lake whitefish, northern pike, and walleye, with AsB, DMA, and iAsV being frequently detected. Three new arsenic species were detected, but their chromatographic retention times did not match with those of any available arsenic standards. Future research is necessary to elucidate the identity of these new arsenic species detected in freshwater fish.

Comparative Analysis of pK a Predictions for Arsonic Acids Using Density Functional Theory-Based and Machine Learning Approaches

Arsonic acids (RAsO(OH)2), prevalent in contaminated food, water, air, and soil, pose significant environmental and health risks due to their variable ionization states, which influence key properties such as lipophilicity, solubility, and membrane permeability. Accurate pK a prediction for these compounds is critical yet challenging, as existing models often exhibit limitations across diverse chemical spaces. This study presents a comparative analysis of pK a predictions for arsonic acids using a support vector machine-based machine learning (ML) approach and three density functional theory (DFT)-based models. The DFT models evaluated include correlations to the maximum surface electrostatic potential (V S,max), atomic charges derived from a solvation model (solvation model based on density), and a scaled solvent-accessible surface method. Results indicate that the scaled solvent-accessible surface approach yielded high mean unsigned errors, rendering it less effective. In contrast, the atomic charge-based method on the conjugated arsonate base provided the most accurate predictions. The ML-based approach demonstrated strong predictive performance, suggesting its potential utility in broader chemical spaces. The obtained values for pK a from V S,max show a weak prediction level, because the way of predicting pK a is related only to the electrostatic character of the molecule. However, pK a is influenced by many factors, including the molecular structure, solvation, resonance, inductive effects, and local atomic environments. V S,max cannot fully capture these different interactions, as it gives a simplistic view of the overall molecular potential field.

A reduction-secretion system contributes to roxarsone (V) degradation and efflux in Brevundimonas sp. M20

Roxarsone (V) (Rox(V)) is an organoarsenical compound that poses significant risks to aquatic ecosystems and various diseases. Reducing trivalent 3-amino-4-hydroxyphenylarsonic acid (HAPA(III)) offers a competitive advantage; however, it leads to localized arsenic contamination, which can disrupt the soil microbiome and impede plant growth. Three genes, BsntrA, arsC2, and BsexpA, encoding nitroreductase, arsenate reductase, and MFS transporter, respectively, were identified in the Rox(V)-resistant strain Brevundimonas sp. M20. A three-step approach, including nitroreduction, As(V) reduction, and HAPA(III) secretion, which is responsible for roxarsone(V) resistance, was subsequently confirmed. Moreover, the flavonoid compound baicalin occupied the HAPA(III) delivery space and grabbed the R127 residues via stronger interactions. This steric hindrance prevented the transportation of HAPA(III) by BsexpA to the extracellular space. These results demonstrate a new Rox(V) reduction pathway, providing a potential efflux pump inhibitor to trap more toxins.

Mo-doped Co LDHs as Raman enhanced substrate for detection of roxarsine

BACKGROUND

Roxarsone (ROX) is widely used as a feed additive, which is indigestible after ingestion by poultry, and most of it can only be excreted into the natural environment and degraded into highly toxic and carcinogenic inorganic arsenic compounds, which pose a hazard to the ecosystem and human health. However, for roxarsone, traditional detection methods require complex and time-consuming procedures, so it is urgent to find a new fast detection method for detection of ROX.

RESULTS

In this work, we developed a novel Raman enhancement material and utilized the Surface-enhanced Raman scattering (SERS) technique to achieve rapid and sensitive detection of roxarsone. Specifically, Mo-doped cobalt layered double hydroxides (Co-LDHs) semiconductor material (abbreviated as CMM-100) was prepared by a simple method of using ion-assisted MOF etching. Under laser excitation at a wavelength of 532 nm, the CMM-100 showed excellent SERS property to various organic dye molecules such as methylene blue (MB), Toluidine Blue(TB), and Crystal Violet (CV). Especially, an enhancement factor (EF) of 1.4 × 106 was achieved for MB. Compared with the traditional method, this work utilized the fast and non-destructive SERS technology, which achieved a rapid detection of ROX. The detection limit was as low as 9.73 × 10-10 M, and the detection range was from 10-9 M to 10-3 M.

SIGNIFICANCE

In this work, SERS technology was adopted for the rapid and sensitive detection of ROX. This study provides a Raman-enhanced substrate named CMMs for detection of food additives, pesticides, biomolecules, etc., which also broadens the application areas of SERS materials.

Influence of dissolved organic matter on the anaerobic biotransformation of roxarsone accompanying microbial community response

Roxarsone (ROX), commonly employed as a livestock feed additive, largely remains unmetabolized and is subsequently excreted via feces. ROX could cause serious environmental risks due to its rapid transformation and high mobility in the anaerobic subsurface environment. Dissolved organic matter (DOM) is an important constituent of fecal organics in livestock waste and could affect the ROX biotransformation. Nonetheless, the underlying mechanisms governing the interaction between DOM and ROX biotransformation have not yet been elucidated in the anaerobic environment. In this study, the changes of ROX, metabolites, and microbial biomass in the solutions with varying DOM concentrations (0, 50, 100, 200, and 400 mg/L) under anaerobic environments were investigated during the ROX (200 mg/L) degradation. EEM-PARAFAC and metagenomic sequencing were combined to identify the dynamic shifts of DOM components and the functional microbial populations responsible for ROX degradation. Results indicated that DOM facilitated the anaerobic biotransformation of ROX and 200 mg/L ROX could be degraded completely in 28 h. The tryptophan-like within DOM functioned as a carbon source to promote the growth of microorganisms, thus accelerating the degradation of ROX. The mixed microflora involved in ROX anaerobic degrading contained genes associated with arsenic metabolism (arsR, arsC, acr3, arsA, nfnB, and arsB), and arsR, arsC, acr3 exhibited high microbial diversity. Variations in DOM concentrations significantly impacted the population dynamics of microorganisms involved in arsenic metabolism (Proteiniclasticum, Exiguobacterium, Clostridium, Proteiniphilum, Alkaliphilus, and Corynebacterium spp.), which in turn affected the transformation of ROX and its derivatives. This study reveals the mechanism of ROX degradation influenced by the varying concentrations of DOM under anaerobic environments, which is important for the prevention of arsenic contamination with elevated levels of organic matter.

Roxarsone biotransformation by a nitroreductase and an acetyltransferase in Pseudomonas chlororaphis, a bacterium isolated from soil

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, Rox), a widely used organoarsenical feed additive, can enter soils and be further biotransformed into various arsenic species that pose human health and ecological risks. However, the pathway and molecular mechanism of Rox biotransformation by soil microbes are not well studied. Therefore, in this study, we isolated a Rox-transforming bacterium from manure-fertilized soil and identified it as Pseudomonas chlororaphis through morphological analysis and 16S rRNA gene sequencing. Pseudomonas chlororaphis was able to biotransform Rox to 3-amino-4-hydroxyphenylarsonic acid (3-AHPAA), N-acetyl-4-hydroxy-m-arsanilic acid (N-AHPAA), arsenate [As(V)], arsenite [As(III)], and dimethylarsenate [DMAs(V)]. The complete genome of Pseudomonas chlororaphis was sequenced. PcmdaB, encoding a nitroreductase, and PcnhoA, encoding an acetyltransferase, were identified in the genome of Pseudomonas chlororaphis. Expression of PcmdaB and PcnhoA in E. coli Rosetta was shown to confer Rox(III) and 3-AHPAA(III) resistance through Rox nitroreduction and 3-AHPAA acetylation, respectively. The PcMdaB and PcNhoA enzymes were further purified and functionally characterized in vitro. The kinetic data of both PcMdaB and PcNhoA were well fit to the Michaelis-Menten equation, and nitroreduction catalyzed by PcMdaB is the rate-limiting step for Rox transformation. Our results provide new insights into the environmental risk assessment and bioremediation of Rox(V)-contaminated soils.

Enhanced adsorption of roxarsone on iron-nitrogen co-doped biochar from peanut shell: Synthesis, performance and mechanism

Efficient removal of organic arsenic (roxarsone, ROX) from wastewater is highly demanded on the purpose of human health and environmental protection. This work aims to prepare Fe-N co-doped biochar (Fe-N-BC) via one-pot hydrothermal method using waste peanut shell, FeCl3·6H2O and urea, followed by pyrolysis. The effect of Fe-N co-doping on biochar's physicochemical properties, and adsorption performance for ROX were systematically investigated. At the pyrolysis temperature of 650 °C, Fe-N-BC-650 shows a significantly increased specific surface area of 358.53 m2/g with well-developed micro-mesoporous structure. Its adsorption capacity for ROX reaches as high as 197.32 mg/g at 25 °C, with > 90 % regeneration efficiency after multiple adsorption-desorption cycles. Correlation and spectral analysis revealed that the pore filling, π-π interactions, as well as hydrogen bonding play the dominant role in ROX adsorption. These results suggest that the Fe-N co-doped biochar shows great potential in the ROX removal from wastewater with high efficiency.

Arsenic speciation in freshwater fish: challenges and research needs

Food and water are the main sources of human exposure to arsenic. It is important to determine arsenic species in food because the toxicities of arsenic vary greatly with its chemical speciation. Extensive research has focused on high concentrations of arsenic species in marine organisms. The concentrations of arsenic species in freshwater fish are much lower, and their determination presents analytical challenges. In this review, we summarize the current state of knowledge on arsenic speciation in freshwater fish and discuss challenges and research needs. Fish samples are typically homogenized, and arsenic species are extracted using water/methanol with the assistance of sonication and enzyme treatment. Arsenic species in the extracts are commonly separated using high-performance liquid chromatography (HPLC) and detected using inductively coupled plasma mass spectrometry (ICPMS). Electrospray ionization tandem mass spectrometry, used in combination with HPLC and ICPMS, provides complementary information for the identification and characterization of arsenic species. The methods and perspectives discussed in this review, covering sample preparation, chromatography separation, and mass spectrometry detection, are directed to arsenic speciation in freshwater fish and applicable to studies of other food items. Despite progress made in arsenic speciation analysis, a large fraction of the total arsenic in freshwater fish remains unidentified. It is challenging to identify and quantify arsenic species present in complex sample matrices at very low concentrations. Further research is needed to improve the extraction efficiency, chromatographic resolution, detection sensitivity, and characterization capability.

Inhibitory effect of polyethylene microplastics on roxarsone degradation in soils

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.

Effects of dissolved organic matter derived from chicken manure on the biotransformation of roxarsone in soil

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, ROX), widely used as a livestock feed additive, is excreted untransformed in large concentrations. Accumulation of this manure in the open environment increases dissolved organic matter (DOM) and ROX in soil within the aeration zone. And microbial action plays a dominant role in the transformation of ROX. However, the specific effect of DOM on the biotransformation of ROX is not known. In this paper, we investigated the transformation rate, metabolite content, and microbial community response of ROX in soils with different DOM concentrations (71.61, 100, 200, 500, and 800 mg L-1). The transformation of ROX was consistent with first-order transformation kinetics. DOM promoted the transformation of ROX, and with high DOM (DOM ≥200 mg L-1), ROX was transformed almost completely within two days. In this case, DOM provided nutrients to microorganisms and promoted their growth, accelerating the transformation of ROX. Also, the solubility of ROX was enhanced by DOM to increase its bioavailability. The microbial diversity was negatively correlated with DOM concentration and ROX transformation time; during the transformation of ROX, Bacillus, Arthrobacter, Enterococcus, Acinetobacter, and Pseudomonas became dominant in the soil with anomalously high levels of DOM. This study demonstrates the transformation process of ROX under actual environmental conditions where organic matter coexists with ROX, and this understanding is important for the prevention and control of arsenic pollution in soil within the aeration zone with anomalously high levels of DOM.

Response of Antibiotic Resistance Genes and Related Microorganisms to Arsenic during Vermicomposting of Cow Dung

Antibiotic resistance pollution in livestock manure is a persistent issue that has drawn public attention. Vermicomposting is an ecofriendly biological process that can render livestock manure harmless and resourceful. However, little is known about the impact of vermicomposting on antibiotic resistance in livestock manure under stress caused by potentially toxic arsenic levels. Herein, lab-scale vermicomposting was performed to comprehensively evaluate the shift in antibiotic resistance genes (ARGs) and related microorganisms in fresh earthworm casts as well as vermicompost product health (i.e., nutrient availability and enzyme activity) when they were fed on arsenic-contaminated cow manure. The results showed that the earthworms' interaction with cow dung led to a significant reduction in ARG concentrations, especially for tetracycline ARGs (tet-ARGs), β-lactam ARGs (bla-ARGs), and quinolone ARGs (qnr-ARGs). However, arsenic significantly enhanced ARG accumulation in earthworm casts in a dose-dependent manner. Moreover, vermicomposting increased the percentage of Bacteroidota in the converted products. Furthermore, arsenic exposure at low concentrations promoted the proliferation of Proteobacteria, whereas high concentrations had little effect on Proteobacteria. Our study provides valuable insight into the changes in the antibiotic resistome and related microorganisms during vermicomposting of arsenic-amended cow manure, and it is crucial to explain the environmental impact of earthworms and improve our understanding of the reciprocal benefits of soil invertebrates.

A Highly Selective and Sensitive Fluorescent Sensor Based on Molecularly Imprinted Polymer-Functionalized Mn-Doped ZnS Quantum Dots for Detection of Roxarsone in Feeds

Roxarsone (ROX) as an organoarsenic feed additive has been widely used in livestock breeding and poultry industry, but ROX can degrade into highly toxic inorganic arsenic species in natural environments to threaten to the environment and human health. Therefore, there is a considerable interest in developing convenient, selective and sensitive methods for the detection of ROX in livestock breeding and poultry industry. In this work, a fluorescent molecularly imprinted polymer (MIPs) probe based on amino-modified Mn-ZnS quantum dots (QDs) has been developed by sol-gel polymerization for specific recognition of ROX. The synthesized MIPs-coated Mn-ZnS QDs (MIPs@Mn-ZnS QDs) have highly selective recognition sites to ROX because there are multi-interactions among the template ROX, functional monomer phenyltrimethoxysilane and the amino-functionalized QDs such as the π-π conjugating effect, hydrogen bonds. Under the optimal conditions, an obvious fluorescence quenching was observed when ROX was added to the solution, and the quenching mechanism could be explained as the photo-induced electron transfer. The MIPs@Mn-ZnS QDs sensor exhibited sensitive response to ROX in the linear range from 3.75 × 10^-8 M to 6.25 × 10^-7 M (R² = 0.9985) and the limit of detection down to 4.34 nM. Moreover, the fluorescence probe has been applied to the quantitative detection of ROX in feed samples, and the recovery was in the range of 91.9% to 108.0%. The work demonstrated that the prepared MIPs@Mn-ZnS QDs probe has a good potential for rapid and sensitive determination of ROX in complicated samples.

Environmental Behavior and Remediation Methods of Roxarsone

Roxarsone (ROX) is used extensively in the broiler chicken industry, and most is excreted in poultry litter. ROX degradation produces inorganic arsenic, which causes arsenic contamination of soil and aquatic environment. Furthermore, elevated arsenic concentrations are found in livers of chickens fed ROX. Microorganisms, light, and ions are the main factors that promote ROX degradation in the environment. The adsorption of ROX on different substances and its influencing factors have also been studied extensively. Additionally, the remediation method, combining adsorption and degradation, can effectively restore ROX contamination. Based on this, the review reports the ecological hazards, discussed the transformation and adsorption of ROX in environmental systems, documents the biological response to ROX, and summarizes the remediation methods of ROX contamination. Most previous studies of ROX have been focused on identifying the mechanisms involved under theoretical conditions, but more attention should be paid to the behavior of ROX under real environmental conditions, including the fate and transport of ROX in the real environment. ROX remediation methods at real contaminated sites should also be assessed and verified. The summary of previous studies on the environmental behavior and remediation methods of ROX is helpful for further research in the future.

Phenylarsonics in concentrated animal feeding operations: Fate, associated risk, and treatment approaches

Phenylarsonics are present as additives in animal feed in some countries. As only a small fraction of these additives is metabolized in animals, they mostly end up in the environment. A comprehensive investigation of the fate of these additives is crucial for evaluating their risks. This review aims to provide a clear understanding of the transformation mechanism of phenylarsonics in vivo and in vitro and to evaluate their fate and associated risks. Degradation of phenylarsonics releases toxic As species (mainly as inorganic arsenic (iAs)). Trivalent phenylarsonics are the metabolites or biotic degradation intermediates of phenylarsonics. The cleavage of As groups from trivalent phenylarsonics catalyzed by C-As lyase or other unknown pathways generates arsenite (As(III)). As(III) can be further oxidized to arsenate (As(V)) and methylated to methyl-arsenic species. The half-lives associated with abiotic degradation of phenylarsonics ranged from a few minutes to tens of hours, while those associated with biotic degradation ranged from several days to hundreds of days. Abiotic degradation resulted in a higher yield of iAs than biotic degradation. The use of phenylarsonics led to elevated total As and iAs levels in animal products and environmental matrices, resulting in As exposure risk to humans. The oxidation of phenylarsonics to As(V) facilitated the sorptive removal of As, which provides a general approach for treating these compounds. This review provides solid evidence that the use of phenylarsonics has adverse effects on both human health and environmental safety, and therefore, supports their withdrawal from the global market.

Comparative Study of Roxarsone Reduction by Shewanella oneidensis MR-1 and Cellulomonas sp. Strain Cellu-2a

Roxarsone, an organoarsenic compound, has been used extensively as an additive in poultry feed to promote animal growth. Although roxarsone is moderately toxic, it can be converted into more toxic compounds upon exposure to the environment, resulting in human health risks. This article reports on a comparative study of roxarsone reduction by fermentative, anaerobic Cellulomonas sp. Cellu-2a and a widely distributed metal-reducing bacterium, Shewanella oneidensis MR-1. The strain Cellu-2a showed a faster roxarsone reduction capability by fermentative growth than by MR-1 in anaerobic respiration. With an environmentally relevant mineral, hydrous ferric oxide (HFO) included in the incubations, there was a rather rapid abiotic (indirect, heterogeneous) reduction of roxarsone by the solid phase Fe(II) in HFO generated by reduction of Fe(III) of HFO by MR-1, while still direct reduction was major reaction by Cellu-2a even with HFO. This study provides evidence of direct and/or indirect bacterial reduction of roxarsone in fermentative conditions as well as in anaerobic respiration conditions, at exposure to the environment, which would assist understanding of environmental behaviors of roxarsone in biological settings with HFO, a naturally occurring ubiquitous mineral class.

Photodegradation of roxarsone in the aquatic environment: influencing factors, mechanisms, and artificial neural network modeling

Roxarsone (ROX), an organoarsenic feed additive, can be discharged into aquatic environment and photodegraded into more toxic inorganic arsenics. However, the photodegradation behavior of ROX in aquatic environment is still unclear. To better understand ROX photodegradation behavior, the influencing factors, photodegradation mechanism, and process modelling of ROX photodegradation were investigated in this study. The results showed that ROX in the aquatic environment was degraded to inorganic As(III) and As(V) under light irradiation. The degradation efficiency was enhanced by 25% with the increase of light intensity from 300 to 800 μW/cm² via indirect photolysis. The photodegradation was temperature dependence, but was only slightly affected by pH. Nitrate ion (NO₃^-) had an obvious influence, but sulfate, carbonate, and chlorate ions had a negligible effect on ROX degradation. Dissolved organic matter (DOM) in the solution inhibited the photodegradation. ROX photodegradation was mainly mediated by reactive oxygen species (in the form of single oxygen ¹O₂) generated through ROX self-sensitization under irradiation. Based on the data of factors affecting ROX photodegradation, ROX photodegradation model was built and trained by an artificial neural network (ANN), and the predicted degradation rate was in good agreement with the real values with a root mean square error of 1.008. This study improved the understanding of ROX photodegradation behavior and provided a basis for controlling the pollution from ROX photodegradation.

Pollution characteristics and health risk assessment of arsenic transformed from feed additive organoarsenicals around chicken farms on the North China Plain

Arsenic is frequently found in poultry waste, most of which is transformed from feed additive organoarsenicals, resulting in arsenic pollution of soils and water around poultry farms. The North China Plain, an important area for livestock breeding of China, was chosen to investigate the pollution characteristics and assess the health risk of arsenic around chicken farms. Among the 138 chicken farms sampled, almost no roxarsone, a common organoarsenical, was detected in chicken feeds, manure, and surface soils, while the detectable rate of other arsenic species was high. Because of long-term enrichment, the concentrations of arsenic species in manure were generally higher than that in feed. As(III) was the main inorganic arsenic species in the manure, where is reducing environment. In surface soils beneath the accumulated manure, As(V) was the predominant arsenic species with 100% detectable rate. The detectable rate and average concentrations at 0 cm were generally higher than those at 25 cm depth, indicating that arsenic accumulated in the surface soils. In addition, a typical conceptual diagram of arsenic was developed to clarify the pollution process from feed to soil. Through health risk assessment of inorganic arsenic, the carcinogenic risk (CR) and non-carcinogenic risk (non-CR) were both negligible. The city of Jiaozuo had the highest CR and non-CR, which was 11 times higher than that of the city with the lowest risks. This study presents a clear picture and evaluation of arsenic pollution on chicken farms, inspiring future studies assessing arsenic pollution after the ban of organoarsenicals.

Antimicrobial Activity of Metals and Metalloids

Competition shapes evolution. Toxic metals and metalloids have exerted selective pressure on life since the rise of the first organisms on the Earth, which has led to the evolution and acquisition of resistance mechanisms against them, as well as mechanisms to weaponize them. Microorganisms exploit antimicrobial metals and metalloids to gain competitive advantage over other members of microbial communities. This exerts a strong selective pressure that drives evolution of resistance. This review describes, with a focus on arsenic and copper, how microorganisms exploit metals and metalloids for predation and how metal- and metalloid-dependent predation may have been a driving force for evolution of microbial resistance against metals and metalloids. Expected final online publication date for the Annual Review of Microbiology, Volume 75 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Quantum dot-labelled antibody based on fluorescence immunoassays for the determination of arsanilic acid in edible pork and liver

Arsanilic acid (ASA) residue, which is the most common contaminant in edible animal tissues such as pork and liver, has caused environmental and food-safety concerns. In this study, direct and indirect competitive fluorescence-linked immunosorbent assays (dc-FLISA and ic-FLISA) incorporating quantum dots (QDs) as the fluorescent label were developed for the first time to detect ASA residues in edible pork and animal liver. Monoclonal antibodies against ASA and rabbit anti-mouse antibody were conjugated to orange QDs with excitation wavelengths at 450 nm, and the QD-Abs served as detection probes. The limits of detection for dc-FLISA and ic-FLISA were 0.11 ng/mL and 0.001 ng/mL, respectively. QD-FLISA was used to analyse spiked samples; recoveries ranged from 80.2%-91.2% in dc-FLISA and 82.5%-91.2% in ic-FLISA, and the coefficients of variations (CV) were less than 12%. Compared with conventional indirect competitive enzyme-linked immunosorbent assay (ic-ELISA), the QD-FLISA described here was more sensitive and accurate in the analysis of ASA residues in animal tissues. Moreover, the results of QD-FLISA correlated well with HPLC. These results indicate that dc-FLISA and ic-FLISA are sensitive and reliable for detection of ASA residues in edible animal tissues.

The Pseudomonas putida NfnB nitroreductase confers resistance to roxarsone

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, Rox) has been used for decades as an antimicrobial growth promoter for poultry and swine. Roxarsone is excreted in chicken manure unchanged and can be microbially transformed into a variety of arsenic-containing compounds such as 3-amino-4-hydroxyphenylarsonic acid (HAPA(V)) that contaminate the environment and present a potential health hazard. To cope with arsenic toxicity, nearly every prokaryote has an ars (arsenic resistance) operon, some of which confer resistance to roxarsone. Pseudomonas putida KT2440 is a robust environmental isolate capable of metabolizing many aromatic compounds and is used as a model organism for biodegradation of aromatic compounds. Here we report that P. putida KT2440 (ΔΔars) in which the two ars operons had been deleted retains resistance to highly toxic trivalent Rox(III), the likely active form of roxarsone. In this study, a genomic library constructed from P. putida KT2440 (ΔΔars) was used to screen for resistance to Rox(III) in Escherichia coli. One gene, termed, PpnfnB, was identified that encodes a putative 6,7-dihydropteridine reductase. Cells expressing PpnfnB reduce the nitro group of Rox(III), and purified NfnB catalyzes FMN-NADPH-dependent nitroreduction of Rox(III) to less toxic HAPA(III). This identifies a key step in the breakdown of synthetic aromatic arsenicals.

Bacterial Community Dynamics Distinguish Poultry Compost from Dairy Compost and Non-Amended Soils Planted with Spinach

The aim of this study was to determine whether and how poultry litter compost and dairy manure compost alter the microbial communities within field soils planted with spinach. In three successive years, separate experimental plots on two fields received randomly assigned compost treatments varying in animal origin: dairy manure (DMC), poultry litter (PLC), or neither (NoC). The composition and function of bacterial and fungal communities were characterized by the amplicon sequencing of marker genes and by the ecoenzyme activity, respectively. The temporal autocorrelation within and among years was adjusted by principal response curves (PRC) to analyze the effect of compost on community composition among treatments. Bacteria in the phylum Bacteriodetes, classes Flavobacteriia and Spingobacteriales (Fluviicola, Flavobacteriia, and Pedobacter), were two to four times more abundant in soils amended with PLC than DMC or NoC consistently among fields and years. Fungi in the phylum Ascomycota were relatively abundant, but their composition was field-specific and without treatment differences. The ecoenzyme data verify that the effects of PLC and DMC on soil communities are based on their microbial composition and not a response to the C source or nutrient content of the compost.

Prevalence of Arsenic in chicken feed and its contamination pattern in different parts of chicken flesh: a market basket study

Organoarsenic compounds are widely used in chicken feed for control of coccidial parasite, quick weight gain, and for imparting attractive color to the chicken flesh. A study was conducted to assess the level of arsenic in both chicken feed and flesh. Chicken feed was collected from 10 farm houses and total arsenic was estimated. The quantitative estimation suggests that the four levels of chicken feed contain different quantities of arsenic load. The results demonstrated that feed at stages III and IV levels contain 0.01 mg/g and 0.018 mg/g of arsenic respectively. However, at stages I and II levels, the feed contains 0.005 mg/g and 0.0052 mg/g of arsenic respectively. Proceeding similarly, chicken flesh was collected from ten vendors in the local markets of Burdwan. The experimental results revealed that deposition of arsenic in different parts of chicken body is not same. The highest accumulation was recorded in the flesh of chest followed by stomach, whereas flesh of the legs and heart showed lower levels of arsenic accumulation. A comprehensive calculation was thereafter done to assess the total amount of arsenic ingestion through consumption of chicken. If a person takes 60.0 g of chicken flesh (leg, breast, muscles, and stomach) everyday, then the person may consume 0.186-0.372 μg of arsenic per day. This study therefore clearly suggests that excessive consumption of poultry chicken may prove to be fatal. However, further research is necessary to confirm the present findings. To the best of our knowledge, this is probably the first report on the likelihood of arsenic contamination in the flesh of different body parts of poultry chicken from Eastern India.

Identification of an anaerobic bacterial consortium that degrades roxarsone

The degradation of roxarsone, an extensively used organoarsenic feed additive, occurs quickly under anaerobic conditions with microorganisms playing an important role in its degradation. Here, an anaerobic bacterial consortium that effectively degraded roxarsone was isolated, and its degradation efficiency and community changes along a roxarsone concentration gradient under anaerobic conditions were assessed. We used batch experiments to determine the roxarsone degradation rates, as well as the bacterial community structure and diversity, at initial roxarsone concentrations of 50, 100, 200, and 400 mg/kg. The results showed that roxarsone was degraded completely within 28, 28, 36, and 44 hr at concentrations of 50, 100, 200, and 400 mg/kg, respectively. The anaerobic bacterial consortium displayed considerable potential to degrade roxarsone, as the degradation rate increased with increasing roxarsone concentrations. Roxarsone promoted microbial growth, and in turn, the microorganisms degraded the organoarsenic compound, with the functional bacterial community varying between different roxarsone concentrations. Lysinibacillus, Alkaliphilus, and Proteiniclasticum were the main genera composing the roxarsone‐degrading bacterial community.

Arsanilic acid contributes more to total arsenic than roxarsone in chicken meat from Chinese markets

Organoarsenicals have been used in poultry production for years, however, studies focused on roxarsone (ROX), with little attention to p-arsanilic acid (ASA). We assessed arsenic (As) concentration and speciation in chicken meat collected from 10 cities in China. The geometric mean for total As in 249 paired raw and cooked samples was 4.85 and 7.27 μg kg^-1 fw, respectively. Among 81 paired raw and cooked samples, ASA and ROX were detected in >90% samples, suggesting the prevalence of organoarsenical use in China. ASA contributed the most (45% on average) to total As in cooked samples, followed by As(V), DMA, As(III), and ROX (7.2-22%). ASA was found to contribute more to total As in chicken meat compared to ROX for the first time. Arsenic in chicken meat showed considerable geographic variation, with higher inorganic arsenic (iAs) being detected from cities with higher ROX and ASA, indicating that organoarsenical use increased iAs concentration in chicken meat. When health risk was estimated, dietary exposure to iAs would result in an increase of 3.2 bladder and lung cancer cases per 100,000 adults. The result supports the removal of organoarsenicals in poultry production from Chinese market and further supports its removal from the global markets.

N-Hydroxyarylamine O-Acetyltransferases Catalyze Acetylation of 3-Amino-4-Hydroxyphenylarsonic Acid in the 4-Hydroxy-3-Nitrobenzenearsonic Acid Transformation Pathway of Enterobacter sp. Strain CZ-1

The organoarsenical feed additive 4-hydroxy-3-nitrobenzenearsonic acid (roxarsone [ROX]) is widely used and released into the environment. We previously showed a two-step pathway of ROX transformation by Enterobacter sp. strain CZ-1 involving the reduction of ROX to 3-amino-4-hydroxyphenylarsonic acid (3-AHPAA) and the acetylation of 3-AHPAA to N-acetyl-4-hydroxy-m-arsanilic acid (N-AHPAA) (K. Huang, H. Peng, F. Gao, Q. Liu, et al., Environ Pollut 247:482-487, 2019, https://doi.org/10.1016/j.envpol.2019.01.076). In this study, we identified two nhoA genes (nhoA1 and nhoA2), encoding N-hydroxyarylamine O-acetyltransferases, as responsible for 3-AHPAA acetylation in Enterobacter sp. strain CZ-1. The results of genetic disruption and complementation showed that both nhoA genes are involved in ROX biotransformation and that nhoA1 is the major 3-AHPAA acetyltransferase gene. Quantitative reverse transcription-PCR analysis showed that the relative expression level of nhoA1 was 3-fold higher than that of nhoA2 Each of the recombinant NhoAs was overexpressed in Escherichia coli BL21 and homogenously purified as a dimer by affinity chromatography. Both purified NhoAs catalyzed acetyl coenzyme A-dependent 3-AHPAA acetylation. The K_m values of 3-AHPAA for NhoA1 and NhoA2 were 151.5 and 428.3 μM, respectively. Site-directed mutagenesis experiments indicated that two conserved arginine and cysteine residues of each NhoA were necessary for their enzyme activities.IMPORTANCE Roxarsone (ROX) is an organoarsenic feed additive that has been widely used in poultry industries for growth promotion, coccidiosis control, and meat pigmentation improvement for more than 70 years. Most ROX is excreted in the litter and dispersed into the environment, where it is transformed by microbes into different arsenic-containing compounds. A major product of ROX transformation is N-acetyl-4-hydroxy-m-arsanilic acid (N-AHPAA), which is also used as a clinical drug for treating refractory bacterial vaginosis. Here, we report the cloning and functional characterization of two genes encoding N-hydroxyarylamine O-acetyltransferases, NhoA1 and NhoA2, in Enterobacter sp. strain CZ-1, which catalyze the acetylation of 3-amino-4-hydroxyphenylarsonic acid (3-AHPAA) formed by the reduction of ROX to N-AHPAA. This study provides new insights into the function of N-hydroxyarylamine O-acetyltransferase in the transformation of an important organoarsenic compound.

Soil attribute regulates assimilation of roxarsone metabolites by rice (Oryza sativa L.)

Roxarsone (ROX), an organoarsenic feed additive, and its metabolites, can be present in animal manure used to fertilize rice. Rice is prone to absorb arsenic, and is subject to straighthead disorder, which reduces rice yield and is linked with organic arsenic compounds. This study aims to elucidate how soil property affect arsenic accumulation in rice plants fertilized with chicken manure containing ROX metabolites. Manures of chickens fed without or with ROX, designated as control manure and ROX treated manure (ROXCM), respectively, were applied in eight paddy soils of different origins, to investigate the assimilation of arsenic species in rice plants. The results show that inorganic arsenic (arsenate and arsenite), monomethylarsonic acid and dimethylarsinic acid (DMA) were detected in all brown rice and husk, trace tetramethylarsonium and trimethylarsine oxide were occasionally found in these both parts, whereas all these arsenic species were determined in straw, irrespective of manure type. ROXCM application specifically and significantly increased brown rice DMA (P = 0.002), which remarkably enhanced the risk of straighthead disease in rice. Although soil total As impacted grain biomass, soil free-iron oxides and pH dominated arsenic accumulation by rice plants. The significantly increased grain DMA suggests manure bearing ROX metabolites is not suitable to be used in soils with abundant free-iron oxides and/or high pH, if straighthead disorder is to be avoided in rice.

China's Ban on Phenylarsonic Feed Additives, A Major Step toward Reducing the Human and Ecosystem Health Risk from Arsenic

Phenylarsonic feed additives were once widely used in poultry and swine production around the world, which brought significant and unnecessary health risk to consumers due to elevated residues of arsenic species in animal tissues. They also increased the risk to ecosystems via releases of inorganic arsenic through their environmental transformation. Out of concern for the negative impacts on human and ecosystem health, China, one of the world's largest poultry and swine producing countries, recently banned the use of phenylarsonic feed additives in food animal production. This ban, if fully enforced, will result in reduction of approximately 1160 cancer cases per year from the consumption of chicken meat alone, and avoid an annual economic loss of nearly 0.6 billion CNY according to our risk analysis. Furthermore, the inventory of anthropogenic arsenic emissions in China will be cut by approximately one-third with the phase-out of phenylarsonic feed additives. This ban is also expected to lead to significant reduction in the accumulation of arsenic in the soils of farmlands fertilized by poultry and swine wastes and, consequently, lower the accumulation of arsenic in food crops grown on them, which could have even greater public health benefits. But effective enforcement of the ban is crucial, and it will require detailed supervision of veterinary drug production and distribution, and enhanced surveillance of animal feeds and food products. Furthermore, control of other major anthropogenic sources of arsenic is also necessary to better protect human health and the environment.

Facile synthesis of mesoporous WS2 nanorods decorated N-doped RGO network modified electrode as portable electrochemical sensing platform for sensitive detection of toxic antibiotic in biological and pharmaceutical samples

We report a facile and ultrasound assisted sonochemical synthesis of a Tungsten disulfide nanorods decorated nitrogen-doped reduced graphene oxide based nanocomposite. The WS₂ 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 WS₂ 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 WS₂ NRs/SPCE, N-rGOs/SPCE and based SPCE. The WS₂ 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 WS₂ 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 WS₂ NRs/N-rGOs nanocomposite modified sensor also exhibits valuable ability of anti-interference to electroactive analytes. Furthermore, the as-prepared WS₂ NRs/N-rGOs/SPCE has been applied to the determination of ROX in biological and pharmaceutical samples.

Role of ArsEFG in Roxarsone and Nitarsone Detoxification and Resistance

Organoarsenical biotransformations are important components of the global cycling of arsenic. Roxarsone (3-nitro-4-hydroxybenzenearsenate or Rox(V)) and nitarsone (4-nitrobenzene arsenate or Nit(V)) are synthetic aromatic organoarsenicals used in the poultry industry as additives to prevent coccidiosis and improve feed efficiency. Here, we describe a novel pathway of resistance to roxarsone and nitarsone involving biotransformation of their trivalent forms (Rox(III)) and (Nit(III)) to the trivalent organoarsenicals HAPA(III) and pAsA(III), coupled to active extrusion of the aromatic aminobenezylarsenicals from the cells. The arsE, arsF, and arsG were cloned from the arsenic island in the chromosome of Shewanella putrefaciens 200. When expressed in Escherichia coli together, but not alone, arsEFG conferred resistance to Rox(III) and Nit(III) and decreased the accumulation of both. The cells transformed Rox(III) or Nit(III) to HAPA(III) or pAsA(III) by reducing the nitro group to an amine. Everted membrane vesicles from cells expressing arsG accumulated HAPA(III) or pAsA(III). Our data indicate that ArsE and ArsF together reduce Rox(III) or Nit(III) to HAPA(III) or pAsA(III), which are extruded from the cells by the efflux permease ArsG. Identification of the coupled pathway of ArsE, ArsF, and ArsG catalysis is a molecular description of a novel pathway for resistance to roxarsone and nitarsone.

Effect of roxarsone metabolites in chicken manure on soil biological property

Roxarsone (ROX), an organoarsenic feed additive, occurs as itself and its metabolites including As(V), As(III), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in animal manure. Animal manure improves soil biological property, whereas As compounds impact microorganisms. The integral influence of animal manure bearing ROX metabolites on soil biological quality is not clear yet. Herein, the effect of four chicken manures excreted by chickens fed with four diets containing 0, 40, 80 and 120 mg ROX kg^-1, on soil biological attributes. ROX addition in chicken diets increased total As and ROX metabolites in manures, but decreased manure total N, ammonium and nitrate. The elevated ROX metabolites in manures increased soil total As, As species and total N, and increased first and then decreased soil nitrate and nitrite, but did not affect soil ammonium in manure-applied soils. The promoting role of both soil As(III) and ammonium on soil microbial biomass carbon and nitrogen, respiration and saccharase activity, were exceeded or balanced by the inhibiting effect of soil nitrate. The suppression of soil catalase activity by soil As(V) was surpassed by the enhancement caused by soil nitrate and nitrite. Soil urease, acid phosphatase and polyphenol oxidase activities were not suitable bioindicators in the four manure-amended soils. Soil DMA did not affect soil biological properties, and MMA was not detectable in all manure-amended soils. The above highlights the complexity of joint influence of soil As and N on biological attributes. Totally, when ROX is used at allowable dose in chicken diet, soil biological quality would be suppressed in manure-amended soil.

Biotransformation of arsenic-containing roxarsone by an aerobic soil bacterium Enterobacter sp. CZ-1

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, ROX) is an arsenic-containing compound widely used as a feed additive in poultry industries. ROX excreted in chicken manure can be transformed by microbes to different arsenic species in the environment. To date, most of the studies on microbial transformation of ROX have focused on anaerobic microorganisms. Here, we isolated a pure cultured aerobic ROX-transforming bacterial strain, CZ-1, from an arsenic-contaminated paddy soil. On the basis of 16S rRNA gene sequence, strain CZ-1 was classified as a member of the genus Enterobacter. During ROX biotransformation by strain CZ-1, five metabolites including arsenate (As[V]), arsenite (As[III]), N-acetyl-4-hydroxy-m-arsanilic acid (N-AHPAA), 3-amino-4-hydroxyphenylarsonic acid (3-AHPAA) and a novel sulfur-containing arsenic species (AsC₉H₁₃N₂O₆S) were detected and identified based on high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS), HPLC-ICP-MS/electrospray ionization mass spectrometry (ESI-MS) and HPLC-electrospray ionization hybrid quadrupole time-of-flight mass spectrometry (ESI-qTOF-MS) analyses. N-AHPAA and 3-AHPAA were the main products, and 3-AHPAA could also be transformed to N-AHPAA. Based on the results, we propose a novel ROX biotransformation pathway by Enterobacter. sp CZ-1, in which the nitro group of ROX is first reduced to amino group (3-AHPAA) and then acetylated to N-AHPAA.

Arsenic Concentrations, Speciation, and Localization in 141 Cultivated Market Mushrooms: Implications for Arsenic Exposure to Humans

Mushrooms accumulate arsenic (As), yet As concentrations, speciation, and localization in cultivated mushrooms across a large geographic distribution are unknown. We characterized 141 samples of nine species from markets in nine capital cities in China, with samples of Lentinula edodes, Pleurotus ostreatus, and Agaricus bisporus being analyzed for As speciation and localization. Total As concentrations ranged from 0.01 to 8.31 mg kg^-1 dw, with A. bisporus (0.27-2.79 mg kg^-1) containing the most As followed by P. ostreatus and L. edodes (0.04-8.31 and 0.12-2.58 mg kg^-1). However, As in A. bisporus was mostly organic including nontoxic arsenobetaine, while P. ostreatus and L. edodes contained mainly inorganic As (iAs). On the basis of in situ imaging using LA-ICP-MS, As in L. edodes was localized to the surface coat of the cap, while As in P. ostreatus was localized to the junction of the pileus and stipe. When As speciation and daily mushroom consumption (1.37 g d^-1 dw) are considered, daily mushroom consumption may result in elevated iAs exposure, with increased bladder and lung cancer rates up to 387 cases per 100000. Our study showed that market mushrooms could be a health risk to the general public so its production should be monitored.

Aromatic organoarsenic compounds (AOCs) occurrence and remediation methods

Many researchers at home and abroad have made a body of researches and have gained great achievements on the environmental occurrence, fate, and toxicity of inorganic arsenic. But there is less research on the use of aromatic organoarsenic compounds (AOCs), which are common feed additives for livestock in the poultry industry. In this review, we outline the current state of knowledge acquired on the occurrence and remediation of AOCs, respectively. We also identify knowledge gaps and research needs, including the elucidation of the environmental fate of AOCs, metabolic pathway, the impact of metabolic modification on toxicity, and advanced analytical or repaired methods that allows for monitoring, identification or removal of the degradation products.

Transfer of arsenic from poultry feed to poultry litter: A mass balance study

Roxarsone (rox), an arsenic (As) containing organic compound, is a common feed additive used in poultry production. To determine if As present in rox is excreted into the poultry litter without any retention in chicken meat for safe human consumption, the transference of As from the feed to poultry excreta was assessed using two commercial chicken strains fed with and without dietary rox. The results revealed that both the strains had similar behaviour in growth (chicken weight; 2.17-2.25kg), feed consumption (282-300kgpen^-1 initially containing 102 chicken) and poultry litter production (73-81kgpen^-1) during the growth phase of 35days. Our mass balance calculations showed that chickens ingested 2669-2730mg As with the feed and excreted out 2362-2896mg As in poultry litter during the growth period of 28days when As containing feed was used, yielding As recovery between 86 and 108%. Though our complementary studies show that residual arsenic species in rox-fed chicken meat may have relevance to human exposure, insignificant retention of total As in the chicken meat substantiates our mass balance results. The results are important in evaluating the fate of feed additive used in poultry production and its potential environmental implications if As containing poultry litter is applied to soil for crop production.

Transformation of roxarsone in the anoxic-oxic process when treating the livestock wastewater

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 (AsH₃) 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.

Metabolism of a Phenylarsenical in Human Hepatic Cells and Identification of a New Arsenic Metabolite

Environmental contamination and human consumption of chickens could result in potential exposure to Roxarsone (3-nitro-4-hydroxyphenylarsonic acid), an organic arsenical that has been used as a chicken feed additive in many countries. However, little is known about the metabolism of Roxarsone in humans. The objective of this research was to investigate the metabolism of Roxarsone in human liver cells and to identify new arsenic metabolites of toxicological significance. Human primary hepatocytes and hepatocellular carcinoma HepG2 cells were treated with 20 or 100 μM Roxarsone. Arsenic species were characterized using a strategy of complementary chromatography and mass spectrometry. The results showed that Roxarsone was metabolized to more than 10 arsenic species in human hepatic cells. A new metabolite was identified as a thiolated Roxarsone. The 24 h IC₅₀ values of thiolated Roxarsone for A549 lung cancer cells and T24 bladder cancer cells were 380 ± 80 and 42 ± 10 μM, respectively, more toxic than Roxarsone, whose 24 h IC₅₀ values for A549 and T24 were 9300 ± 1600 and 6800 ± 740 μM, respectively. The identification and toxicological studies of the new arsenic metabolite are useful for understanding the fate of arsenic species and assessing the potential impact of human exposure to Roxarsone.

Biochemical Characterization of ArsI: A Novel C-As Lyase for Degradation of Environmental Organoarsenicals

Organoarsenicals such as the methylarsenical methylarsenate (MAs(V)) and aromatic arsenicals including roxarsone (4-hydroxy-3-nitrobenzenearsenate or Rox(V)) have been extensively used as an herbicide and growth enhancers in animal husbandry, respectively. They undergo environmental degradation to more toxic inorganic arsenite (As(III)) that contaminates crops and drinking water. We previously identified a bacterial gene (arsI) responsible for aerobic demethylation of methylarsenite (MAs(III)). The gene product, ArsI, is an Fe(II)-dependent extradiol dioxygenase that cleaves the carbon-arsenic (C-As) bond in MAs(III) and in trivalent aromatic arsenicals. The objective of this study was to elucidate the ArsI mechanism. Using isothermal titration calorimetry, we determined the dissociation constants and ligand-to-protein stoichiometry of ArsI for Fe(II), MAs(III), and aromatic phenylarsenite. Using a combination of methods including chemical modification, site-directed mutagenesis, and fluorescent spectroscopy, we demonstrated that amino acid residues predicted to participate in Fe(II)-binding (His5-His62-Glu115) and substrate binding (Cys96-Cys97) are involved in catalysis. Finally, the products of Rox(III) degradation were identified as As(III) and 2-nitrohydroquinone, demonstrating that ArsI is a dioxygenase that incorporates one oxygen atom from dioxygen into the carbon and the other to the arsenic to catalyze cleavage of the C-As bond. These results augment our understanding of the mechanism of this novel C-As lyase.

Tracing heavy metals in 'swine manure - maggot - chicken' production chain

With the development of large-scale livestock farming, manure pollution has drawn much attention. Conversion by insects is a rapid and cost-effective new method for manure management. Swine manure conversion with maggots (Musca domestica larvae) has developed, and the harvested maggots are often used as animal feed. However, the flow of heavy metals from manure to downstream processes cannot be ignored, and therefore, heavy metal content was measured in untreated raw manure, maggot-treated manure, harvested maggots and maggot-eating chickens (chest muscle and liver) to evaluate potential heavy metal risks. The levels of zinc, copper, chromium, selenium, cadmium and lead had significant differences between untreated raw manure and maggot-treated manure. The concentrations of all detected heavy metals, except for cadmium and selenium, in maggots met the limits established by the feed or feed additive standards of many countries. The bioaccumulation factor (BAF) of heavy metals decreased with the increase of the maggot instar, indicating that heavy metals were discharged from the bodies of maggots with the growth of maggots. Also, the contents of overall heavy metals in chickens fed harvested maggots met the standards for food. In conclusion, regarding heavy metals, it is eco-safe to use maggots in manure management.

Methylated Phenylarsenical Metabolites Discovered in Chicken Liver

We report the discovery of three toxicologically relevant methylated phenylarsenical metabolites in the liver of chickens fed 3-nitro-4-hydroxyphenylarsonic acid (ROX), a feed additive in poultry production that is still in use in several countries. Methyl-3-nitro-4-hydroxyphenylarsonic acid (methyl-ROX), methyl-3-amino-4-hydroxyphenylarsonic acid (methyl-3-AHPAA), and methyl-3-acetamido-4-hydroxyphenylarsonic acid (or methyl-N-acetyl-ROX, methyl-N-AHPAA) were identified in such chicken livers, and the concentration of methyl-ROX was as high as 90 μg kg^-1 , even after a five-day clearance period. The formation of these newly discovered methylated metabolites from reactions involving trivalent phenylarsonous acid substrates, S-adenosylmethionine, and the arsenic (+3 oxidation state) methyltransferase enzyme As3MT suggests that these compounds are formed by addition of a methyl group to a trivalent phenylarsenical substrate in an enzymatic process. The IC₅₀ values of the trivalent phenylarsenical compounds were 300-30 000 times lower than those of the pentavalent phenylarsenicals.

Valorisation of post-sorption materials: Opportunities, strategies, and challenges

Adsorption is a facile, economic, eco-friendly and low-energy requiring technology that aims to separate diverse compounds (ions and molecules) from one phase to another using a wide variety of adsorbent materials. To date, this technology has been used most often for removal/recovery of pollutants from aqueous solutions; however, emerging post-sorption technologies are now enabling the manufacture of value-added key adsorption products that can subsequently be used for (i) fertilizers, (ii) catalysis, (iii) carbonaceous metal nanoparticle synthesis, (iv) feed additives, and (v) biologically active compounds. These new strategies ensure the sustainable valorisation of post-sorption materials as an economically viable alternative to the engineering of other green chemical products because of the ecological affability, biocompatibility, and widespread accessibility of post-sorption materials. Fertilizers and feed additives manufactured using sorption technology contain elements such as N, P, Cu, Mn, and Zn, which improve soil fertility and provide essential nutrients to animals and humans. This green and effective approach to managing post-sorption materials is an important step in reaching the global goals of sustainability and healthy human nutrition. Post-sorbents have also been utilized for the harvesting of metal nanoparticles via modern catalytic pyrolysis techniques. The resulting materials exhibited a high surface area (>1000m²/g) and are further used as catalysts and adsorbents. Together with the above possibilities, energy production from post-sorbents is under exploration. Many of the vital 3E (energy, environment, and economy) problems can be addressed using post-sorption materials. In this review, we summarize a new generation of applications of post-adsorbents as value-added green chemical products. At the end of each section, scientific challenges, further opportunities, and issues related to toxicity are discussed. We believe this critical evaluation not only delivers essential contextual information to researchers in the field but also stimulates new ideas and applications to further advance post-sorbent applications.

Public Health Risk of Arsenic Species in Chicken Tissues from Live Poultry Markets of Guangdong Province, China

Arsenic-based feed additives, such as roxarsone (ROX), are still legally and widely used in food animal production in many countries. This study was conducted to systematically characterize the content and speciation of arsenic in chicken tissues from live poultry markets and in commercial chicken feeds in Guangdong, a major poultry production and consumption province in China, and to assess the corresponding public health risk. The total arsenic contents in the commercial feeds could be modeled as a mixture of two log-normal distributions (geometric means: 0.66 and 17.5 mg/kg), and inorganic arsenic occurred at high levels (0.19-9.7 mg/kg) in those with ROX detected. In general, chicken livers had much higher contents of total arsenic compared to the muscle tissues (breast and drumstick), and chicken muscle from the urban markets contained arsenic at much higher levels than that from the rural markets. The incremental lifetime cancer risk (bladder and lung cancer) from dietary exposure to arsenic contained in chicken meat products on local markets was above the serious or priority level (10^-4) for 70% and 30% of the adult populations in Guangzhou and Lianzhou, respectively. These findings indicate the significant need to phase out the use of arsenic-based feed additives in China.

Response of microbial communities to roxarsone under different culture conditions

Roxarsone is a feed additive widely used in the broiler and swine industries that has the potential to contaminate the environment, mainly via the use of poultry manure as fertilizer, which results in release of inorganic arsenic to the soil and water. This study was conducted to investigate roxarsone degradation and the response of the microbial community under different culture conditions using high-throughput sequencing technology. Poultry litter was incubated for 288 h in the presence of roxarsone under light aerobic, dark aerobic, or dark anaerobic conditions. The results showed that roxarsone was completely degraded after 48 h of dark anaerobic incubation, while 79.9% and 94.5% of roxarsone was degraded after 288 h of dark aerobic and light aerobic incubation, respectively. Under dark aerobic conditions with microbial inhibitor sodium azide, roxarsone was rarely degraded during the 288 h of incubation, illustrating that microorganisms play an important role in roxarsone degradation. Microbial community structure was significantly different among various culture conditions. Olivibacter, Sphingobacterium, and Proteiniphilum were the top 3 genera in the control samples. Sphingobacterium and Alishewanella dominated the light aerobic samples, while the dominant microflora of the dark aerobic samples were Acinetobacter spp. Pseudomonas and Advenella were the predominant genera of dark anaerobic samples. This study emphasizes the potential importance of microbes in roxarsone degradation and expands our current understanding of microbial ecology during roxarsone degradation under different environmental conditions.

Accumulation and Transport of Roxarsone, Arsenobetaine, and Inorganic Arsenic Using the Human Immortalized Caco-2 Cell Line

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.