Plastic is a polymer that has high chemical stability and plasticity. As a result, it is widely used in many fields of industry and life. (Andrady, 2011). In the previous 60 years, plastic manufacturing has grown 622-fold, from 500,000 to 311 million tons (Thompson et al., 2009). Polyethylene accounts for most synthetic resin plastics worldwide, i.e., 36% of the total production (Geyer et al., 2017). Biodegradable plastics were developed to minimize the environmental damage caused by traditional plastics. Furthermore, the annual biodegradable plastic production is gradually increasing. In 2025, it was predicted to reach 2.4 million tons (Polman et al., 2021). PLA is the most common biodegradability plastic used in industry. Its output will rise from 30×104t per year to 95×104t per year over the next ten years (Shruti and Kutralam-Muniasamy, 2019). However, degradable plastics can only be completely degraded under special conditions. And degradable plastics are more likely to produce microplastics and adsorb other pollutants, which may have a bigger negative impact on the environment.
Previous research has revealed that only a small proportion (6 to 26%) of plastic trash gets recycled. As a result, a considerable amount of plastic waste leads to environmental pollution (Alimi et al., 2018). According to some researchers, if the production of plastics continues to rise and plastic trash is not effectively treated, by the middle of the twenty-first century, approximately 12 billion tons of plastic trash will have stored up in the natural environment (Jambeck et al., 2015). Plastic debris is generated in the environment by abrasion, oxidation, hydrolysis, photo-aging, and biological action of traditional and biodegradable plastic waste (Horton et al., 2017). Plastic fragments smaller than 5 mm are usually referred to as MPs internationally in order to unify the definition. (Bakir et al., 2014). Microplastic pollution in oceans, lakes, and rivers has become more widespread (Campanale et al., 2020; Ding et al., 2019; Sighicelli et al., 2018). The main source of microplastics in the environment is the crushing process of large plastic products. Furthermore, microplastics released into the environment by industrial and domestic wastewater should not be overlooked. Microplastic bioaccumulation along the food chain can occur in aquatic systems, affecting individuals and populations (Lonnstedt and Eklov, 2016). Microplastics have the potential to cause a wide range of toxicological reactions in organisms, including lethality, reduced feeding activity, growth and development inhibition, endocrine disruption, disruption of energy metabolism, oxidative stress, immune and neurotransmission dysfunction, and even genotoxicity (Lu et al., 2016). Because of their large specific area, hydrophobicity, and mobility, microplastics can accumulate various chemical contaminants and act as carriers for long-distance transportation (Guo et al., 2012). (Frias et al., 2010) reported that microplastic particles from two beaches in Portugal were contaminated with persistent organic pollutants, including polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and dichlorodiphenyltrichloroethane. (Gao et al., 2019) dispersed microplastics along the Chinese coastline in various locations. Six months later, heavy metals such as chromium, lead, and manganese were discovered on these microplastics. (Qiao et al., 2019) demonstrated that the presence of MPs can extend other pollutants' half-lives, enhance their bioavailability, and increase toxicity to organisms. Hence, it is crucial to comprehend the mechanisms and processes involved in MPs' pollutant adsorption.
As a new category of pollutants, antibiotics have attracted considerable interest due to their impact on biology and the generation of medicine-resistance genes (Yang et al., 2017). From 2000 to 2015, the total global antibiotic consumption grew by 69% (Klein et al., 2018). The intestines of humans and animals are not very efficient in absorbing antibiotics. As a result, most antibiotics are excreted directly into the environment as prodrugs (Danner et al., 2019). Li et al. (2018) examined 27 antibiotic residues in the Pearl River coastal area, among which macrolides were the most abundant, with 217 ng/L in river water and 232 ng/L in seawater. Sulfonamide antibiotics are extremely stable and do not degrade easily in the environment. Aquatic organisms exhibit chronic toxicity as a result of long-term antibiotic contamination (Wang et al., 2019). Studies have revealed that antibiotics can change the structure and variety of microbial communities by impeding processes like enzyme activity and food uptake. Additionally, antibiotics in the environment can result in the development of antibiotic resistance genes (ARGs) and resistant flora, and the presence of ARGs can render antibiotics useless, impair their ability to effectively treat disease, and endanger human health (Grenni et al., 2018). If antibiotics were enriched on microplastics, producing combined pollution, they might cause greater harm to the environment and organisms. It has been demonstrated that when aquatic organisms are exposed to a combination of antibiotics and microplastics, their bodies become enriched with microplastics. Antibiotics are transported from microplastics to organisms via desorption in the organisms' intestines, causing harm to the organisms (Razanajatovo et al., 2018). Understanding the interactions between microplastics and CIP can thus aid in the investigation of the environmental impact of multiple pollutant contamination.
Plastic aging can cause changes in the physicochemical properties of plastics, affecting their ability to adsorb other contaminants. Degradable microplastics and non-degradable microplastics differ significantly in composition, structure, and properties. As a result, Degradable microplastics and non-degradable microplastics interactions with co-existing contaminants in the aqueous environment may differ. Furthermore, complex environmental factors may have a significant impact on the interaction of MPs with other contaminants. A review of the literature revealed that the interaction between antibiotics and aged degradable microplastics has received little attention.
PLA is a new biodegradable plastic, while PE is a traditional plastic. These two types of plastic are commonly found in everyday life. Aged and new PLA / PE were used in our experiments. CIP was selected as an example to investigate the adsorption on microplastics. The objectives of this research were to investigate (1) how aging affects microplastic characteristics and adsorption performance, (2) the adsorption mechanisms of CIP on PLA and PE using the kinetic model, isotherm models, and thermodynamics, and (3) the effects of temperature, pH, ionic strength, fulvic acid, and norfloxacin (NOR) on the adsorption.