Characterizing the binding interactions between virgin/aged microplastics and catalase in vitro.

Microplastics (MPs) undergo physical, chemical, and biological aging in the environment, leading to changes in their physicochemical properties, affecting migration characteristics and toxicity. Oxidative stress effects induced by MPs in vivo have been extensively studied, but the toxicity difference between virgin and aged MPs and the interactions between antioxidant enzymes and MPs in vitro have not been reported yet. This study investigated the structural and functional changes of catalase (CAT) induced by virgin and aged PVC-MPs. It was shown that light irradiation aged the PVC-MPs, and the aging mechanism was photooxidation, resulting in a rough surface and appearing holes and pits. Because of the changes in physicochemical properties, aged MPs had more binding sites than virgin MPs. Fluorescence and synchronous fluorescence spectra results suggested that MPs quenched the endogenous fluorescence of CAT and interacted with tryptophane and tyrosine residues. The virgin MPs had no significant effect on the skeleton of CAT, while the skeleton and the polypeptide chains of CAT became loosened and unfolded after binding with the aged MPs. Moreover, the interactions of CAT with virgin/aged MPs increased the α-helix and decreased the ß-sheet contents, destroyed the solvent shell, and resulted in a dispersion of CAT. Due to the large size, MPs cannot enter the interior of CAT and have no effects on the heme groups and activity of CAT. The interaction mechanism between MPs and CAT may be that MPs adsorb CAT to form the protein corona, and aged MPs had more binding sites. This study is the first comprehensive investigation of the effect of aging on the interaction between MPs and biomacromolecules and highlights the potential negative effects of MPs on antioxidant enzymes.

Study on the binding of polystyrene microplastics with superoxide dismutase at the molecular level by multi-spectroscopy methods.

Microplastics are harmful pollutants that widely exist worldwide and pose a severe threat to all types of organisms. The effects of polystyrene microplastics (PS-MPs) on organisms have been extensively studied, but the interaction mechanism between PS-MPs and superoxide dismutase (SOD) at the molecular level has not been reported yet. Therefore, based on multiple spectroscopic methods and enzyme activity measurements, the molecular mechanism of the interaction between PS-MPs and SOD was investigated. The multispectral results showed that the protein skeleton and secondary structure of SOD were altered by PS-MPs, resulting in decreased α-helix and ß-sheet content. After PS-MPs exposure, fluorescence sensitization occurred, and micelles were formed, along with the enhanced hydrophobicity of aromatic amino acids in SOD. Moreover, the resonance light scattering (RLS) spectra result suggested that the PS-MPs and SOD combined to form a larger complex. Eventually, the activity of SOD was increased due to these structural changes, and the concentration of PS-MPs is positively correlated with SOD activity. This study can provide experimental support for studying the toxicological effects of PS-MPs.

Probing the molecular mechanism of interaction between polystyrene nanoplastics and catalase by multispectroscopic techniques.

Nanoplastics are emerging pollutants that pose a potential threat to the environment and organisms and are widely distributed in environmental samples and food chains. The accumulation of polystyrene nanoplastics (PS-NPs) in an organism can cause oxidative stress. Currently, toxicity studies of PS-NPs mainly focus on the individual and cellular levels, whereas few studies have been conducted on the molecular mechanisms of the interaction between PS-NPs and catalase (CAT). Based on this, CAT was chosen as the target receptor for molecular toxicity research to reveal the interaction mechanism at the molecular level between PS-NPs and CAT by using various spectroscopic means and enzyme activity detection methods. The results indicated that PS-NPs destroyed the secondary structure of CAT, causing its protein skeleton to loosen and unfold, increasing the content of α-helices, decreasing the content of ß-sheets, and exposing the position of the heme group. After exposure to PS-NPs, the internal fluorophore of CAT underwent fluorescence sensitization, resulting in a micelle-like structure, which enhanced the hydrophobicity of aromatic amino acids but did not change their polarity. In addition, the aggregation state of CAT was altered upon binding to PS-NPs, and the volume was further increased. Finally, these structural changes led to a gradual decrease in CAT activity. This study presents a comprehensive assessment of the toxicity of PS-NPs at the molecular level, which can provide more experimental support for the study of the biotoxicological efficacy of PS-NPs.

Impact of light-aged microplastic on microalgal production of dissolved organic matter.

Microplastics (MPs) can affect phytoplankton and its photosynthetic performance in many but often in negative ways. Phytoplankton is an important source of dissolved organic matter (DOM) in aquatic ecosystems, but the impact of MPs on the algal production of DOM is poorly known. We investigated the impacts of polyvinyl chloride MPs on the growth and DOM production by Chlamydomonas reinhardtii microalgae in a 28-day-long experiment. During the exponential growth phase of C. reinhardtii, MPs slightly affected algal growth and DOM production. At the end of experiment, MPs decreased the biomass of C. reinhardtii by 43 % in the treatment with MPs exposed to simulated solar radiation prior the experiment (light-aged) and more than in the treatment with virgin MPs. The light-aged MPs decreased algal DOM production by 38 % and modified the chemical composition of DOM. According to spectroscopic analyses, the light-aged MPs increased aromaticity, average molecular weight and fluorescence of DOM produced by C. reinhardtii. The elevated fluorescence was associated with humic-like components identified by a 5-component parallel factor analysis (PARAFAC) from the excitation-emission matrices. We conclude that although MPs can leach DOM to aquatic ecosystems, they potentially modify the aquatic DOM more by interfering with the algal production of DOM and changing the composition of produced DOM.

Adsorption of inorganic and organic phosphorus onto polypyrrole modified red mud: Evidence from batch and column experiments.

The ubiquitous presence of inorganic and organic phosphorus in wastewater and natural water bodies has deteriorated the water environment qualities and exerted significant influences on ecosystems. In this study, an effective polypyrrole modified red mud adsorbent (PRM) was optimized for the adsorptive removal of inorganic and organic phosphorus from aqueous solutions. The addition of ferric chloride and pyrrole was optimized for complete oxidation and modification of polypyrrole onto red mud. Kinetic studies illustrated that the adsorption progress was accomplished by physical and chemical adsorption. The experimental data of the optimized PRM were described well by Langmuir isotherm, and the equilibrium adsorption capacity was 32.9 and 54.7 mg/g for inorganic and organic phosphorus, respectively. The PRM showed commendable adsorption performance despite the pH conditions ranging from 3 to 11. From the effect of ion strength and X-ray photoelectron spectroscopy (XPS) tests, we found that ligand exchange is the main mechanism of orthophosphate adsorption onto PRM, while electrostatic attraction played an important role in organic phosphorus adsorption. The adsorption performance from column studies showed that the velocity of flow influenced the breakthrough time of the column but the initial concentration had minor impacts. This study would extend the potential application of polypyrrole modified red mud, acting as an efficient adsorbent for inorganic and organic phosphorus adsorption in water treatment.