Adsorption Behavior And Mecanism Of Imidacloprid On Typical Polar Microplastics

With the production and use of industrial chemicals,the hazards of new pollutants to public health and the ecological environment have gradually emerged.The control of new pollutants is an important strategic task during the"14th Five-Year Plan"period.Microplastics are a new pollutant formed by the degradation of plastic wastes under the action of environmental physicochemical mechanisms.Their environmental behavior in freshwater ecosystems is a global ecological issue that has received increasing attention.Most studies have focused on the pollution,fate and transformation of non-polar microplastics and organic pollutants in the aquatic environment.Less attention has been paid to the photo-aging behavior of polar microplastics,biodegradable microplastics,and microplastics derived from everyday plastic products and its interaction between with organic pollutants.Based on this,in this research,two typical polar microplastics（polyamide and polylactic acid）were selected as non-biodegradable and biodegradable representatives,and the neonicotinoid insecticide imidacloprid was used as the target pollutant.The adsorption behavior and the influence of environmental factors（p H,inorganic ions and humic acid）were explored,and the ultraviolet light aging mechanism of polar microplastics and the adsorption mechanism of imidacloprid were revealed.In addition,the adsorption behavior of imidacloprid with different shapes of polylactic acid plastic products（powder,film,and fragments）was also studied,and the aging mechanism of microplastics derived from plastic products was explored.The main conclusions of this research are as follows:（1）UV photo-aging had opposite effects on the adsorption of imidacloprid on PA microplastics and polylactic acid microplastics.The adsorption capacity of PA microplastics to imidacloprid decreased by 19.22%after UV photo-aging,while the adsorption capacity of polylactic acid microplastics to imidacloprid increased by 41.18%after UV photo-aging.This depends on the natural structure of polar microplastics and their ability to absorb UV light.Electrostatic interaction,hydrogen bonding,van der Waals interaction and polar-polar interaction are the main mechanisms for the adsorption of imidacloprid by polar microplastics.High p H value and low ionic strength favor the adsorption of imidacloprid by polar microplastics by changing the charge distribution on the polar microplastic surface.Humic acid is easy to form complexes with imidacloprid,which reduces the adsorption capacity of imidacloprid on microplastics.（2）The adsorption capacity of polylactic acid microplastics derived from plastic products to imidacloprid is smaller than that of commercial pure polylactic acid microplastics.Microplastics derived from plastic products age in the environment much slower than commercially pure microplastics.The aging rate of polylactic acid powder microplastics is higher than that of the others.The polymer skeleton of polylactic acid powder microplastics was fractured at the early stage of UV/H₂O₂ aging,while the polymer skeletons of polylactic acid film microplastics and polylactic acid fragment microplastics were fractured after oxidation,which may be related to the oxygen content of the original samples.After three months of aging,the adsorption capacity of the three polylactic acid microplastics followed polylactic acid powder microplastics>polylactic acid film microplastics>polylactic acid fragment microplastics,which was mainly related to the aging process of microplastics.In conclusion,microplastics and neonicotinoid insecticides present in the aquatic environment can alter their environmental behaviors through the interactions between them,causing negatively affecting the aquatic environment.This research has implications for scientific understanding of the environmental behavior of polar microplastics and neonicotinoid insecticides.