| Roxarsone(Roxarsone,4-hydroxy-3-nitrophenylarsinic acid)has antibacterial,anticoccidial,growth-promoting and feed conversion efficiency improvements,and is therefore widely used as an organic arsine feed additive in the livestock and poultry industry.However,it is difficult to degrade and transform in the animal body,and most of it will be discharged into the environmental water body and soil through the animal feces in its original form,thereby causing the risk of arsenic environmental pollution.Understanding the degradation and transformation pathways of Roxarsone in the soil environment and its impact on the activities of various enzymes in the soil is of great significance for solving the potential risks of environmental arsenic pollution.In this paper,indoor simulation culture experiments were used to study the degradation and transformation pathways of Roxarsone under different water treatments(60% WHC and 130% WHC)in three soils(red soil,paddy soil and vegetable garden soil).The activities of various enzymes(fluorescein diethyl ester(FDA)hydrolase,?-hydroglucosidase,phosphatase and urease)were evaluated.The specific main research contents and results are as follows:In this study,laboratory simulated culture experiments are used to study the degradation kinetics characteristics,the change in the concentration of degradation products,the combined form of arsenic in the degradation products,and the degradation of roxarsone in three types of soils and two types of water.The effect of the process on soil fluorescent diethylglycolate(FDA)hydrolase,?-glucosidase,phosphatase and urease activities.The main research contents and results of this paper are as follows:1.A high performance liquid chromatography-inductively coupled plasma tandem mass spectrometry(HPLC-ICP-MS/MS)method was developed for thesimultaneous determination of p-arsanilic acid(p-ASA),roxarsone(ROX),and arsenic acid(As V)in soil.Methods for the analysis of arsenic compounds such as arsenite(As III),monomethylated arsenic(MMA)and dimethylated arsenic(DMA).A Hamilton PRP-X100 anion exchange column was used,with 60 mmol/L malonate-0.1% TFA(p H = 6)and water as the mobile phase at p H=6 to achieve the good separation of six arsenic species within 12 min.0.1 M Na H2PO4-0.1 M H3PO4(9:1,V:V)was selected as the extractant,and the microwave-assisted extraction conditions(80°C,30 min)were optimized.The recoveries of various forms of arsenic were verified by standard recovery experiments,accuracy and precision.2.The changes of the binding form of arsenic in the soil during the degradation of roxarsone and the two moisture conditions(60% WHC and 130% WHC)of roxarsone(50 mg / kg)in red soil,paddy soil and vegetable garden soil were studied.Degradation,and established the main pathway for the degradation and transformation of roxarsone.The results showed that with the degradation of roxarsone and the degradation and transformation of roxarsone in the three types of soil,the non-specific adsorption of arsenic in the soil gradually decreased.At low moisture(60% WHC),red soil and rice The soil and vegetable garden soil decreased from 8.95%,42.57%,and 28.53% to 0.75%,12.89%,and 6.34%,respectively,and the high soil(130%WHC)red soil,paddy soil,and vegetable garden soil decreased from 8.32%,35.01%,and 27/98% fell to 0.57%,1.94% and 0.32%.The content of arsenic in the bound form of amorphous iron-aluminum oxide and crystalline form of iron-aluminum oxide gradually increased.21.0%,12.46% and 18.70% rose to 29.30%,29.47% and 29.48%,crystalline iron-aluminum oxide combined arsenic rose from 20.82%,3.53% and6.55% to 26.49%,9.17% and 12.0%;At moisture(130% WHC),the amorphous iron-aluminum oxide bound arsenic in red soil,paddy soil and vegetable garden soil rose from 22.22%,17.34% and 18.42% to 29.98%,49.70% and 35.88%,respectively.The compound-bound arsenic rose from 22.10%,5.64%,and 7.85% to 35.71%,10.56%,and 11.68%,respectively.A kinetic model was used to fit the degradation curve of roxarsone.The results showed that the degradation rate of roxarsone under low water content was vegetable garden soil> paddy soil> red soil.Under high watercontent conditions,the degradation of roxarsone The rate is vegetable garden soil ?paddy soil >> red soil,and the degradation rate of roxarsone in the three soils under low moisture content conditions is significantly lower than that under high moisture content conditions.The degradation products of roxarsone in soil include3-amino-4-hydroxyphenylarsinic acid(HAPA),As(III)and As(V)and a small amount of DMA and MMA,and with the extension of cultivation time,the three soils The final arsenic forms are mainly As(V).3.The response of soil FDA hydrolase,?-glucosidase,phosphatase and urease activities during the degradation of roxarsone was studied.During this process,despite the differences in the response of various enzyme activities in the three types of soil,Roxarsone inhibited the FDA hydrolase,?-glucosidase,and phosphate in most soils in the short term(1-15 days)Enzyme and urease activities,at low moisture(60%WHC),the maximum inhibition rates of FDA hydrolase and phosphatase in red soil were 33.67% and 27.34%,respectively,and that of FDA hydrolase,phosphatase and?-glucosidase in paddy soil The maximum inhibition rates were 26.69%,16.10% and25.22%,respectively.The maximum inhibition rates of FDA hydrolase and urease in vegetable garden soil were 10.82 and 9.67%,respectively;at high moisture(130%WHC),FDA hydrolase and phosphatase in red soil The maximum inhibition rates were 50.50% and 22.42%,respectively,and the maximum inhibition rates of FDA hydrolase,urease,and ?-glucosidase in paddy soil were 38.18%,30.89%,and 55.40%;occurred in the late period(30-90 days)The activation trend may be related to the change of the chemical form and binding form of arsenic in the soil.. |
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