Natural aging and Cu(II) coexistence synergistically promote nonylphenol adsorption by degradable PLA microplastics in aquatic environments

This paper first studied the adsorption of the endocrine disruptor nonylphenol on degradable polylactic acid (PLA) microplastics under natural aging and Cu(II) coexistence. It is shown that the kinetics of nonylphenol adsorption conformed to the second-order kinetic equation, meaning chemisorption controlled the adsorption rate. Natural aging increased the adsorption rate by 45.8 %. The Henry and Freundlich models fitted the adsorption isotherm well. Natural aging increased the adsorption ability (parameter of the Freundlich model K F represented) by 41.4 %, and the presence of Cu(II) promoted 86.6 %. It was proved that natural aging and the presence of Cu(II) facilitated the adsorption synergistically. The characterizations showed that aging promoted nonylphenol adsorption by increasing the specific surface area and the number of oxidative functional groups of microplastics, favoring hydrogen bonding between oxygen-containing functional groups and nonylphenol. Cu(II) promoted the adsorption by forming a ternary complex of nonylphenol, microplastics and copper. However, the complexity of the ternary complex formation, particularly stronger in aged PLA due to enhanced Cu(II) complexation, resulted in a more significant decrease in the nonylphenol adsorption rate. Cu(II) decreased the adsorption rate by 70.83 % (pristine) and 74.29 % (aged). Acidic or alkaline conditions inhibited the adsorption due to electrostatic effects, and Cu(II) reduced this inhibitory effect. Fulvic acid inhibited the adsorption through competitive adsorption and enhanced the adsorption by forming a ternary complex of nonylphenol, fulvic acid and copper when coexisting with Cu(II). The results provide a theoretical basis for understanding interaction and ecological risk between microplastics and nonylphenol in the actual complex environment. • Aging promoted nonylphenol adsorption by affecting surface property of microplastics. • Cu(II) enhanced adsorption by complex of nonylphenol, microplastics and copper. • Natural aging and Cu(II) facilitated the adsorption synergistically. • Cu(II) reduced the inhibitory effect of acidity and alkalinity on adsorption. • The complex of nonylphenol, fulvic acid and copper promoted adsorption.