Effect Of On The Environmental Behavior And Phytotoxicity Of Oxytetracycline By Dissolved Organic Matter In Tropical Paddy Soil

In this paper,three kinds of Biochar were prepared by using cassava peel at 350 ??550 ? and 750 ?.The Dissolved Organic Matter(DOM)was extracted from these three kinds of Biochar.Oxytetracycline(OTC)as a contaminant,to study the effect of DOM on Adsorption-Desorption and Degradation Behavior of OTC in tropical soil system.At the same time,to study the effect of DOM on cabbage seed germination under OTC stress.The overarching objectives of this paper were to explore how DOM affects the environmental behavior and bioavailability of OTC in tropical soils,which provide a scientific basis for the environment behavior,fate and its integrated pollution prevention and control of OTC in tropical soil.The man conclusions were shown as follows:(1)After DOM addition,the adsorption process of OTC in soil mainly includes three pHases:rapid adsorption,slow adsorption and equilibrium adsorption.In the first 4 hours(rapid adsorption pHase),the Adsorption capacity of OTC in the soil increased dramatically;After a slow adsorption rate and finally reached the equilibrium until after 24 h.The pseudo-second-order kinetic model can better fit the dynamic process of OTC in soil after DOM addition.(2)The DOM can inhibit the adsorption of OTC in the soil.When the carbonization temperature of biochar is the same,with the concentration of DOM increases,the Adsorption capacity of OTC in the soil gradually decreased;When the concentration of DOM is the same,with the carbonization temperature of biochar increases,the Adsorption capacity of OTC in the soil gradually decreased;When the carbonization temperature of biochar and the concentration of DOM are the same,with the outside temperature decreases,the Adsorption capacity of OTC in the soil gradually decreased.Freundlich model,Langmuir model and Tekmin model all can better simulate the adsorption process of OTC in soil,the Freundlich model fits best.(3)DOM can promote the desorption of OTC in the soil,and with the concentration of DOM increases,the carbonization temperature of biochar and the outside temperature increases,this promotion will also be enhanced,OTC more easily desorbed from the soil.After addition of DOM,the adsorption and desoiption isotherms of OTC in soil are quite different,the Linear trend of desorption isothermal than the adsorption isothermal to be more obvious,this indicates that the adsorption and desorption process of OTC in soil after the addition of DOM were not reversible,and there is a clear hysteresis effect.The DOM can significantly reduce the hysteresis effect of OTC in the soil,and the hysteresis effect decreases with the increase of the concentration of DOM,the carbonization temperature of biochar and the outside temperature.(4)DOM can accelerate the degradation of OTC in soil.The half-life of OTC degradation in soil is related to the type and concentration of DOM.When the carbonization temperature of biochar is the same,with the concentration of DOM increases,the half-life of OTC degradation in soil gradually decreased,which showed as T1/2(1/16)>T1/2(1/4)>T1/2(1/2);When the concentration of DOM is the same,with the carbonization temperature of biochar increases,the half-life of OTC degradation in soil gradually decreased,which showed as T1/2(MS750)>T1/2.(MS550)>T1/2(MS350);The degradation effect of OTC in soils was best When added MS350-1/16,and the half-life of OTC degradation was reduced from 14.56d to 10.39d,and the degradation rates of 14th and 60th day were increased from 38.20%and 92.10%to 84.10%and 96.90%.In general,with the concentration of DOM increase and the carbonization temperature of biochar decrease,the degradation rates of OTC was accelerated,the half-life was decreased,and the degradation was more complete.(5)DOM,OTC and the combination of the two had no significant effect on the germination rate of cabbage seeds.DOM promotes root elongation and shoot elongation of cabbage seeds,with the concentration of DOM increases,this promotion will gradually increase.The effects of OTC on root elongation and shoot elongation of cabbage seeds were significantly different,OTC will inhibit the root elongation of cabbage seeds,the higher the concentration,the stronger the inhibitory effect;OTC promoted the shoot elongation of cabbage seeds at low concentrations(<100 mg/L),and inhibited the shoot elongation of cabbage seeds at high concentrations(>100 mg/L).DOM will promote the toxic effects of OTC to the root elongation of cabbage seeds,with the concentration of DOM increases,The toxic effect is also gradually increases.OTC can promote the shoot elongation of cabbage seeds when added DOM,and with the concentration of DOM increases,the promotion effect of OTC on he shoot elongation of cabbage seeds was gradually enhanced.