Effects Of Different Kinds Of Microplastics Bioaccumulation And Dissipation Of Phenanthrene And Atrazine In Soils

Due to the characteristics of small particle size and large specific surface area,microplastics have strong adsorption capacity for organic pollutants in soil.Organic pollutants can enter the food chain with microplastics and affect the ecosystem.However,the research on the effect of microplastics on the migration and transformation of organic pollutants in soil is still relatively lacking.In addition,most of the existing studies focus on non-degradable microplastics and lack of research on the impact of degradable microplastics.In this study,we selected the newly made and aged polyethylene（PE and APE）and degradable butanediol adipate and butanediol terephthalate（PBAT）microplastics with diameters of 100～180μm,and studied the adsorption characteristics of these three microplastics for phenanthrene and atrazine.The effects of microplastics on soil physicochemical properties and soil microbial community structure were investigated with or without earthworms.The effects of microplastics on microflora structure and pollutant accumulation in earthworms were investigated.On this basis,the effects and mechanisms of these three microplastics on soil phenanthrene and atrazine depletion were investigated.The main research achievements of this paper are as follows:（1）Compared with PE,the surface of APE has more polar functional groups and pore structure,and higher crystallinity.PBAT had no obvious crystallization peak and its polarity was significantly higher than PE and APE.The adsorption isotherms of phenanthrene and atrazine for the three microplastics conform to Freundlich model（R₂=0.93～0.99）.The order of adsorption capacity for phenanthrene and atrazine（lg K_f）was PBAT（2.94 and 2.09）>APE（1.86 and 1.29）>PE（1.73 and1.27）,which was related to the crystallinity of microplastics.The adsorption capacity of phenanthrene was stronger than that of atrazine,which was related to the water solubility of these two pollutants.（2）The bacterial community structure in soil and earthworm was determined by16Sr DNA.The results showed that soil microbial community structure was significantly different with and without earthworms.The effect of earthworms on soil available nitrogen concentration was the main factor to change soil microbial community structure（contribution rate was 91.70%）.The relative abundance of phenanthrene and atrazine degrading bacteria in soil with earthworms was 1.70～2.42and1.08～2.71 times of that without earthworms,respectively.The degradation genera phenanthrene and atrazine were also detected in earthworms,of which two species（Bacillus and Sphingomonas）were common to soil.（3）Microplastics can significantly reduce the concentration of soil pore water.Correlation analysis showed that lg K_f was the main controlling factor affecting the concentrations of phenanthrene and atrazine in pore water and earthworm.Microbial degradation is the main way of phenanthrene depletion in soil,while chemical hydrolysis and biodegradation are the main ways of atrazine depletion in soil.Microplastics inhibited the degradation of phenanthrene（by 11%～80%）,while earthworms promoted the degradation of phenanthrene（by 18%～106%）.Similarly,microplastics inhibited atrazine degradation（by 10%～67%）,while earthworms promoted atrazine degradation（by 28%～61%）and increased the proportion of biodegradation.The results of material conservation showed that the contribution of earthworm enrichment to the reduction increase was less than 0.64%.The increase of relative abundance of soil degrading bacteria was the main factor that earthworm promoted phenanthrene degradation and atrazine degradation in soil.