Interaction between roxarsone, an organic arsenic compound, with humic substances in the soil simulating environmental conditions.

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 Kb (on the order of 103). 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 1H 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.

Biodegradation of roxarsone by a bacterial community of underground water and its toxic impact.

Roxarsone is included in chicken food as anticoccidial and mainly excreted unchanged in faeces. Microorganisms biotransform roxarsone into toxic compounds that leach and contaminate underground waters used for human consumption. This study evaluated roxarsone biotransformation by underground water microorganisms and the toxicity of the resulting compounds. Underground water from an agricultural field was used to prepare microcosms, containing 0.05 mM roxarsone, and cultured under aerobic or anaerobic conditions. Bacterial communities of microcosms were characterized by PCR-DGGE. Roxarsone degradation was measured by HPLC/HG/AAS. Toxicity was evaluated using HUVEC cells and the Toxi-ChromoTest kit. Roxarsone degradation analysis, after 15 days, showed that microcosms of underground water with nutrients degraded 90 and 83.3% of roxarsone under anaerobic and aerobic conditions, respectively. Microcosms without nutrients degraded 50 and 33.1% under anaerobic and aerobic conditions, respectively. Microcosms including nutrients showed more roxarsone conversion into toxic inorganic arsenic species. DGGE analyses showed the presence of Proteobacteria, Firmicutes, Actinobacteria, Planctomycetes and Spirochaetes. Toxicity assays showed that roxarsone biotransformation by underground water microorganisms in all microcosms generated degradation products toxic for eukaryotic and prokaryotic cells. Furthermore, toxicity increased when roxarsone leached though a soil column and was further transformed by the bacterial community present in underground water. Therefore, using underground water from areas where roxarsone containing manure is used as fertilizer might be a health risk.

Retention of phenylarsenicals in soils derived from volcanic materials.

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.

Alterações histopatológicas em músculos e nervos de aves causadas por Monensina e Roxarsona / Microscopic changes in muscles and peripheral nerves of broiler chickens caused by Monensin and Roxarsone

Rações comerciais para frangos de corte geralmente contêm coccidiostáticos na sua fórmula. Um deles, a Monensina, é amplamente utilizado, e quando administrado em doses tóxicas pode levar a lesões nas musculaturas cardíaca e esquelética. A Roxarsona muitas vezes é adicionada à Monensina para potencializá-la, causando lesões em nervos periféricos de aves submetidas ao estresse. Os objetivos desse estudo foram conhecer os efeitos tóxicos da associação das drogas Monensina e Roxarsona em frangos de corte e desenvolver um modelo experimental que permita estudo das lesões macro e microscópicas das musculaturas esquelética e cardíaca e de nervos periféricos. Frangos de corte, pelo seu rápido crescimento e desenvolvimento, foram os animais de escolha. Para tanto, 360 frangos de corte foram divididos em seis grupos experimentais, com três repetições. Diferentes grupos foram tratados com doses crescentes de Monensina, associada ou não à Roxarsona, durante 35 dias. Após esse período as aves foram abatidas e foram colhidos fragmentos das musculaturas cardíaca e esquelética e também nervos periféricos para exame histopatológico. Músculos e nervos de animais tratados com ambas as drogas apresentaram lesões inflamatórias e degenerativas. A intoxicação por Monensina e Roxarsona mostrou ser eficaz como modelo experimental para lesões musculares e nervosas.

Anticoccidial agents are commonly used in the poultry industry. One of them, Monensin, is widely used, and in toxic levels can induce lesions in cardiac and skeletal muscle. Roxarsone can be used in addition to Monensin, increasing its efficacy. Peripheral neuropathy has been shown in chickens that were fed roxarsone supplemented diets and subjected to stress. This paper shows the effects of Monensin in association with Roxarsone in broiler chicken to develop an experimental model that concerns gross and microscopic study of lesions in peripheral nerves and cardiac and skeletal muscle. Broiler chickens are select due to fast growing and developing. 360 chickens distribute in six grups (three repetitions) were fed either with Monensin and/or Roxarsona for a period of thirty five days. The groups were Monensin Oppm/Roxarsone Oppm, Monensin Oppm/Roxarsone 80ppm, Monensin 150ppm/Roxarsone Oppm, Monensin 150ppm Roxarsone 80ppm, Monensin 300ppm/Roxarsone Oppm, Monensin 300ppm /Roxarsone 80ppm. Clinical signs were observed and recorded. After this period, birds were euthanatized and muscles and nerves were removed and submitted to microscopic examination. No gross lesions were observed. The histopathologic findings showed necrosis and myodegeneration in cardiac and skeletal muscle, and macrophages between the fibers. Microscopic lesions were observed in peripheral nerves and cardiac and skeletal muscles consisting in degeneration of and infiltration of inflammatory cells. The use of the association of these drugs in broilers showed to be adequate as a model for nerve and muscle lesions.