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.
Organoarsenicals such as roxarsone (ROX) are extensively utilized in the poultry industry, and land application of poultry litter is an important route by which arsenics are introduced into the environment. In the present study, degradation of ROX and structurally related nitrophenols by a heat activated persulfate (PS) oxidation process, one in situ chemical oxidation process (ISCO), was systematically explored. The effects of temperature, PS dosage, pH and natural water constituents (i.e., fulvic acid, Cl−) on the degradation of ROX were investigated. Products analysis by solid phase extraction (SPE) and liquid chromatography-electrospray ionization-triple quadrupole mass spectrometry (LC-ESI-MS/MS) revealed that 2,4-dinitrophenol (2,4-DNP) and 2,4,6-trinitrophenol (2,4,6-TNP) were generated as major intermediate products, suggesting denitration–renitration process occurred during SO4˙−-based oxidation of ROX. Interestingly, the formation of polynitration by-products was further confirmed in heat activated persulfate oxidation of nitrophenols. Formation of inorganic arsenics during ROX degradation was measured by inductively coupled plasma-mass spectrometry (ICP-MS). It was evident that the arsenic substituent of ROX was converted to As(V). On the basis of the intermediate products identified, detailed mechanisms and transformation pathways for ROX oxidation were proposed. Results manifest that heat activated PS oxidation could be an efficient approach to treat ROX contamination. However, post-treatment is necessary for complete removal of As(V) to minimize ecotoxicological risks.
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