Effects Of Organic Fertilizer And Biochar On The Forms Of Antibiotics During Saline-alkali Soil Improvement

The contamination of antibiotics in soil has become a hot issue in the environmental field,but there is little research on the occurrence and bioavailability of antibiotics in saline-alkali soil.In the process of improving saline-alkali soil,the addition of external modifier can affect the occurrence of antibiotics by changing the physical and chemical properties of soil,and then affect the bioavailability and ecological risk of antibiotics in soil,but the research has not attracted much attention.In this paper,the common organic manure(pig manure)and biochar(corn straw)were used as representatives of saline-alkali soil amendments,and the common tetracycline(OTC)and Sulfamethoxazole(SMX)in soil were used as representatives of antibiotics.This paper studied the effects of modifiers on the form and bioavailability of antibiotics in the process of improving saline-alkali soil,and got the following conclusions:(1)The amount of biochar and pig manure had different effects on the forms of OTC and SMX in saline-alkali soil.The increase of amendments dosage is not conducive to the formation of organic acid-soluble fraction for OTC,but is conducive to the formation of water-soluble fraction and bound fraction.However,for SMX,the formation of its water-soluble fraction is unfavorable,and the change of its organic acid-soluble fraction and bound fraction content is small.The changes of water-soluble fraction and organic acid-soluble contents of antibiotics in soil affects the bioavailability of antibiotics in soil.The biologically effective fraction content of OTC gradually decreased,and it was the lowest(decreased by 50.34%)when the amount of biochar applied was 2%,and the bioavailability of OTC was increased when the amount of biochar applied was increased,the biologically effective fraction content of SMX decreased with the increase of the amount of biochar applied(decreased by 35.91%),and the bioavailability of OTC decreased after the application of pig manure,but there was no obvious rule in the range of change and the amount of biochar applied,the biologically effective fraction content of SMX decreased with the increase of pig manure(decreased by 36.25%).On the one hand,the addition of biochar and pig manure will change the soil p H,so that the charge of OTC and SMX in the soil will change,which will further affect the adsorption capacity of the soil to antibiotics.On the other hand,the addition of biochar and pig manure will change the soil specific surface area,porosity,etc.,and these changes will have an impact on the adsorption of OTC and SMX in the soil.(2)The addition of biochar and pig manure(2%)had significant impacts in the forms of OTC and SMX in different degrees of salinization soil,and the bioavailability of OTC and SMX gradually increased with the deepening of salinization,but the addition of biochar and pig manure could significantly hinder this trend.Biochar was more effective in reducing OTC bioavailability in saline-alkaline soils,while pig manure was more effective in reducing SMX bioavailability in saline-alkaline soils.When biochar was added,with the increase of soil salinization,the acid-soluble fraction content of OTC decreased significantly,while the water-soluble fraction content and bound fraction content increased gradually;the water-soluble fraction of SMX increased gradually,while the organic acid-soluble fraction content and the bound fraction content of SMX decreased gradually.When pig manure was added,with the increase of soil salinization,the acid-soluble fraction content of OTC increased first and then decreased,the water-soluble fraction content didn’t change much,and the bound fraction content decreased gradually,and the water-soluble content of SMX decreased obviously,the organic acid-soluble fraction content and the bound fraction content also decreased slowly.After the addition of biochar,the content of OTC biologically effective fraction decreased with the deepening of soil salinization(decreased by 39.40%),and the content of SMX biologically effective fraction increased slowly(increased by 3.83%).After the addition of pig manure,the content of OTC biologically effective fraction increased first and then decreased,while the content of SMX biologically effective fraction decreased significantly(decreased by 32.06%).Biochar and pig manure interact with Na~+in salinized soil,such as generating electrostatic attraction with Na~+,thereby reducing the competitive adsorption of Na~+and antibiotics,providing more adsorption sites for the adsorption of antibiotics,and significantly reducing the bioavailability of antibiotics in salinized soil.Or through the formation of"Ion Bridge"by Na~+,the adsorption of OTC and SMX in the soil is increased,thereby reducing its bioavailability.(3)The period in which the amendments stay in the soil(improvement time)had a significant effect on the forms of OTC and SMX in saline soil.The water-soluble fraction content of OTC and SMX in soil with different contents of biochar and pig manure added showed an overall downward trend with the change of improvement time.The water-soluble fraction content of OTC and SMX decreased significantly in the early stage of improvement(7-30 days),and gradually flattened out in the later stage.The organic acid-soluble fraction content of OTC and SMX showed a decreasing trend with the improvement time,and the effect of pig manure on the organic acid-soluble fraction content of OTC showed a large difference in the rate of decline at different time stages.The small increase of water-soluble fraction and organic acid-soluble fraction content OTC and SMX at individual time stages during the improvement period is related to the change of soil and the physical and chemical properties of the soil and amendments caused by aging,indicating that the aging effect is reversible,and aging not only promotes the transformation of antibiotics to a more stable form,but also makes it transform from a more stable form to a bioavailable form when the environmental conditions change.The content of bound fraction OTC showed a trend of gradual decrease,and the content of bound fraction SMX increased overall.The addition of the two amendments significantly reduced the content of OTC and SMX biologically effective fraction in soil,and promoted the transformation of OTC and SMX to abiotic active states,and reduced ecological risk of antibiotics in saline soils.