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

Jizhong Meng,Shoujun Yuan,Juliang Jin,Arong Arong,Xinmin Zhan,Liwen Xiao,Zhen-Hu Hu,Wei Wang

doi:10.1007/s11356-021-16183-5

Abstract

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.

Highlights

Roxarsone (ROX, 4-hydroxy-3-nitrophenylarsonic acid) is an organoarsenical and widely used in the poultry industry as a feed additive to improve feed efficiency, prevent coccidial intestinal parasites and increase growth with the dosage of 20–50 mg/kg (Bednar et al, 2003; Shui et al, 2016; Zhao et al, 2020)
Inorganic arsenics were generated accompanying with ROX photodegradation
It was reported that As(III) was generated from ROX degradation and further oxidized to As(V) (Meng et al, 2019; Xie et al, 2016). Those results indicated that ROX in the aquatic environment was oxidized to inorganic arsenics under light irradiation

Summary

Introduction

Roxarsone (ROX, 4-hydroxy-3-nitrophenylarsonic acid) is an organoarsenical and widely used in the poultry industry as a feed additive to improve feed efficiency, prevent coccidial intestinal parasites and increase growth with the dosage of 20–50 mg/kg (Bednar et al, 2003; Shui et al, 2016; Zhao et al, 2020). Most of ROX in the feed is excreted to poultry litter. It has been reported that 29.8 mg/kg of total arsenic concentration was detected in the poultry litter (Fisher et al, 2015; Zhao et al, 2020).

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