# Environmental Behavior and Remediation Methods of Roxarsone
## 1 Introduction  
Roxarsone (3-nitro-4-hydroxyphenylarsone acid; ROX) is a low-toxic form of an organoarsenical, that has been widely used as an additive in livestock feed to control coccidiosis, improve feed efficiency, and promote weight gain [1]. Their disease prevention and growth accelerative effects were first observed in the 1940s and 1950s. It was later approved for use in poultry and pig production [2, 3]. However, almost all of the ROX consumed by poultry is excreted in feces and urine chemically unchanged because ROX is not metabolized by animals [4]. Around the world, thousands of tons of poultry waste are used on land every year. This treatment is economical because poultry waste is rich in nutrients and is an effective fertilizer. In any case, repeated use of poultry waste on land introduces organoarsenicals into the environment and increases arsenic levels in the soil [5, 6]. Figure 1 illustrates the environmental behavior of ROX. ROX that enters the environment can quickly and completely be transformed on soil surfaces through biological and abiotic processes [7]. The catabolites of ROX include 3-amino-4-hydroxyphenylarsine acid (HAPA) [8, 9, 10], monomethylarsine acid (MMA), dimethylarsine acid (DMA), As(III), As(V), and other arsenic-containing compounds [11]. Inorganic arsenic species (As(III) and As(V)) more readily migrate and are more toxic than organoarsenic compounds, and inorganic arsenic species can be adsorbed to and accumulated in soil. This can lead to higharsenic concentrations in soil, surface water, and groundwater [12; 13] that can pose risks to human and environmental health. Concern about arsenic pollution in environmental media and arsenic residues in chickens has led to arylarsenic feed additives, including ROX, to be banned in China, the European Union, and the USA [14; 15]. However, ROX has already accumulated in the environment after decades of use. And ROX is still used in many countries, including Australia, Brazil, and India [16; 17].  
ROX degradation, conversion, migration, and the effects of ROX on organisms are currently receiving attention around the world. In order to comprehensively master the research progress of ROX on environmental behavior and remediation, the existing literature were fully reviewed. In the Web of Science Core Collection, we searched for \"roxarsone\"environment\" and \"roxarsone\"remediation\" and 235 and 38 records were obtained, respectively. After removing the literature with weak correlation, the keywords of all downloaded articles were analyzed, and the correlation diagram between ROX and the keywords was drawn (Figure 2). Keywords \"degradation\" and \"adsorption\" appeared most frequently, 9 times and 11 times, respectively, and other keywords appeared 2\(\sim\)3 times. Keywords that appeared only once were not plotted. These keywords have been completely covered in this review. The aim of this review is to compile and analyze currently available information about the environmental behavior and remediation methods of ROX, including ecological hazards, transformation, adsorption, biological response, and remediation methods.  
Figure 1: Environmental behavior of ROX used as feed additives.