| Microplastics（MPs）are an emerging pollutant with a wide range of sources and distributions,and their environmental behaviors,such as migration,degradation,adsorption of pollutants and toxic organisms have far-reaching ecological and environmental risks,which has aroused more and more attention.Polybutylene succinate（PBS）and polybutylene adipate terephthalate（PBAT）are two typical biodegradable plastics with widely used in agriculture,industry and other fields.The exposure of PBS and PBAT to the environment constantly releases MPs that will undergo aging,adsorption of contaminants,and will directly or indirectly affect the migration and transformation of contaminants to some extent,which has an impact on the biological effectiveness of MPs or other contaminants.However,relevant MPs contamination and ecological risks need to be further explored due to the so-called“bio-degradability”of PBS and PBAT plastics.To study the environmental behavior characteristics of PBS and PBAT biodegradable microplastics,this paper prepared aged PBS and PBAT MPs and characterized their physicochemical properties.The adsorption characteristics of MPs to the representative pollutant pentachlorophenol（PCP）in water were investigated.The single and joint effects of MPs and PCP on lettuce seed germination were also further studied in order to provide basic data and theoretical basis for an in-depth understanding of the environmental behavior and risks of biodegradable MPs.The main contents and conclusions of this study are as follows:（1）Aged PBS and PBAT MPs were prepared by UVa,UV+H2O,UV+H2O2,and UV+K2S2O8,and the physicochemical properties of the MPs were characterized by SEM,BET,ATR-FT-IR,and DSC,et al.The results showed that PBS and PBAT MPs（before and after aging）are both rubbery polymers at room temperature,and the UVa aging method had the most obvious aging effect on the two MPs,with esterification reactions occurring during the aging process.Among them,the physical property changes of MPs mainly include:the surface of MPs yellowed,became rough,and formed cracks,holes,small particles or small fragments in different degrees.Compared with the pristine MPs,the specific surface area of UV-3d-aged PBS and PBAT MPs increased by 82.28%and 244.56%,the O/C ratio decreased by 3.22%and 34.92%,and the water contact angle also decreased by 31.95%and 43.75%,respectively.（2）The adsorption kinetics and adsorption isotherm of PCP adsorbed by MPs results showed that,after UVa aging for 3 days,the adsorption capacity of PBS and PBAT MPs on PCP increased by 45.00%and 177.97%,respectively,which was positively correlated with the BET sizes of MPs and negatively correlated with the water contact angles of MPs.Pristine and UVa-aged PBAT MPs was more likely to be a carrier for PCP than PBS MPs,and the adsorption process may form hydrogen bonding interaction.The main mechanisms of PCP adsorption by MPs were partitioning and multilayer adsorption on non-homogeneous surfaces.The adsorption of PCP by pristine PBS,UVa-aged PBS,and UVa-aged PBAT MPs increased under high salinity and weak alkaline conditions,while the adsorption of PCP by pristine and aged PBS and PBAT MPs decreased in the presence of humic acid.（3）Lettuce,a PCP-sensitive model specie,was selected as the test plant for the toxic effects of microplastics and PCP,and the results showed that the single/joint effects of MPs（100～1000 mg/L）and PCP（1～4 mg/L）on the lettuce seed germination were small,while the water uptake,fresh weight and root length of seedlings were inhibited to different degrees,which was basically positive with the pollutant concentration.Compared with the control groups,the relative water uptake of lettuce seedlings in MPs and PCP treated groups ranged from 15.72%～95.06%and51.60%～85.94%,fresh weight from 70.18～120.75 mg and 79.46～99.40 mg,and relative root lengths of 23.50%～93.38%and 17.83%～32.63%,respectively.PBS MPs was more toxic to lettuce seedlings than PBAT MPs,and the toxicity of 1000 mg/L PBS to lettuce seedlings was comparable to that of 2 mg/L PCP.The adsorption of PCP by MPs reduced the PCP toxicity to lettuce seedlings in the MPs-PCP complex solutions and increased the MPs toxicity,resulting in the toxicity of the complex solution to lettuce seedlings between the MPs and PCP single toxicity. |
