Distribution Characteristics Of Microplastics In Typical Farmland Soils And Their Effects On The Environmental Behavior Of Estroge

Microplastics（MPs）,one of the most concerning new pollutants,are distinguished by their small size and high hydrophobicity.It is very easy to absorb organic pollutants and transport them to areas with less human activity,causing compound pollution,and it can also enter the human body through food chains.Because China is an agricultural country,the health of the soil environment has a direct impact on food security.At the same time,our country is a major producer of plastic products,and because of the irrational use of plastic products and the low recovery rate,soil has become a source and sink of MPs,posing significant pollution risks.Estrogen,a type of Endocrine Disrupting Chemicals,is commonly found in environmental media such as soil and etc.,where it not only affects reproductive organs function and normal sexual differentiation of organisms,even causes the"triple"effect,and MPs,as estrogens carriers,have more toxic effects on environmental organisms.In this study,typical agricultural land（paddy field and dry land）in Jiangmen City,Guangdong Province,was selected to conduct field research,analyze the distribution characteristics of MPs in agricultural land,and evaluate its ecological risk and pollution load.The adsorption characteristics of estrone（E1）,17α-estradiol（17α-E2）,17β-estradiol（17β-E2）,estriol（E3）,diethylenol（DES）and 17α-eylestradiol（17α-EE2）on MPs were studied.The adsorption kinetics,isothermal adsorption mechanism and site energy of estrogen on MPs were analyzed.In addition,the difference of estrogen degradation in soil before and after the presence of MPs was compared,which provided theoretical basis and data support for scientific assessment of the ecological and environmental risk of compound pollution of estrogen and MPs in environment.Findings are as follows:（1）Polyvinyl chloride（PVC-MPs）accounted for the largest proportion of all point samples in this survey area,followed by polyethylene terephthylate（PET-MPs）and polyurethane（PU-MPs）.The distribution of PVC-MPs was the widest（detection rate>95%）and the abundance was the highest(60-4872 particle·kg^-1)in the agricultural soil of Jiangmen City.The abundance of MPs in paddy soil was higher than that in dryland soil,and small size MPs（20-100μm）were more widely distributed and more abundant in soil.The proportion of MPs risk Index（PRI）level IV risk in the region reached 82.9%,and PVC-MPs was the main contributor due to its extremely high hazard coefficient.According to the MPs pollution load index（PLI）of the soil,the PLI value of this area is between 2and 11,which belongs to class I pollution,and the overall pollution is light.（2）According to the adsorption behavior of polyethylene（PE-MPs）on six typical estrogens,the experimental results show that the kinetic adsorption process is more consistent with the quasi-second-order kinetic model,and the increase of the initial concentration will affect the adsorption equilibrium time and the proportion of estrogen adsorption.The adsorption of estrogen on PE-MPs was more consistent with Freundlich model（R²>0.94）in the single system and the composite system.Isothermal adsorption experiments,XPS and FTIR characterization results show that the adsorption process of estrogen by MPs is mainly affected by van der Waals force and hydrophobic partition,and chemical bonding cooperation has a certain effect on the adsorption of synthetic estrogen on PE-MPs.Compared with the single system,the adsorption site energy of each estrogen in the complex system shifted to the high energy region as a whole,and the six estrogens showed competitive adsorption on PE-MPs.（3）The experimental results of estrogen degradation by PE-MPs showed that the degradation of E1 and 17α-EE2 by PE-MPs had a delayed effect in soil,resulting in a greater estrogen equivalent concentration（ΣEEQ）in soil and an increased environmental risk.The first order exponential degradation kinetic model and the second order degradation kinetic model can better simulate the degradation process of estrogen in soil,and the half-life of six estrogens basically conforms to E1>17α-EE2>17α-E2>17β-E2>E3≈DES.（4）There are two main reasons for the prolongation of estrogens half-life caused by PE-MPs:on the one hand,the growth and diversity of microorganisms were relatively more stable after the addition of PE-MPs to the soil,but species richness and species diversity were reduced.The dominant phylum was consistent in soil samples treated with CK and 0.5%PE and was dominated by Actinobacteria,Chloroflexi and Proteobacteria.The degradation of estrogens in soil were mainly the effect of Altererythrobacter,Bacillus,Nocardioides and Sphingomonas,with Bacillus and Nocardioides being most significantly affected by PE-MPs.While the effect of PE-MPs on microorganisms led to the slowdown of E1 and 17α-EE2 degradation.PE-MPs exposed to soil showed surface aging,and the change of surface structure made more spots of PE-MPs to attach microorganisms,and microorganisms on the surface of PE-MPs led to the decrease of abundance in soil leading to pore water,thus the relative decrease of bacterial genera involved in estrogens degradation and decrease of the rate and amount of estrogens degradation.On the other hand,the FTIR and XPS maps revealed that new functional groups（carbonyl groups and esters）appeared on the surface of PE-MPs,and these oxygen-containing functional groups（carbonyl groups and esters）also indicated that PE-MPs were oxidized by active free radicals in the soil,which indirectly indicated that PE-MPs competed with estrogens for oxidation sites in the soil,which could be one of the reasons for estrogens of slow degradation.