The masking phenomenon of microplastics additives on oxidative stress responses in freshwater food chains.

The variability and intrinsic mechanisms of oxidative stress induced by microplastics at different trophic levels in freshwater food chains are not well understood. To comprehensively assess the oxidative stress induced by polystyrene microplastics (PS-MPs) in freshwater food chains, the present study first quantified the oxidative stress induced by PS-MPs in organisms at different trophic levels using factorial experimental design and molecular dynamics methods. Then focuses on analyzing the variability of these responses across different trophic levels using mathematical statistical analysis. Notably, higher trophic level organisms exhibit diminished responses under PS-MPs exposure. Furthermore, the coexistence of multiple additives was found to mask these responses, with antioxidant plastic additives significantly influencing oxidative stress responses. Mechanism analysis using computational chemistry simulation determines that protein structure and amino acid characteristics are key factors driving PS-MPs induced oxidative stress variation in freshwater organisms at different nutrient levels. Increased hydrophobic additives induce protein helicalization and amino acid residue aggregation. This study systematically reveals the variability of biological oxidative stress response under different nutrient levels, emphasizing the pivotal role of chemical additives. Overall, this study offers crucial insights into PS-MPs' impact on oxidative stress responses in freshwater ecosystems, informing future environmental risk assessment.

Potential thyroid hormone disorder risks of tire antioxidants to aquatic food chain organisms after absorbing free radicals in marine and freshwater environments.

Tire antioxidants are essential functional chemical additives in tire rubber production. Because of the characteristic easy precipitation in the water environment, the environmental pollution problem caused by tire antioxidants is concerning. To reveal the mechanism by which tire antioxidants reduce common oxidative factors (free radicals) in the environment and to control the potential biological thyroid hormone disorder risk of tire antioxidant derivatives, eight commonly used antioxidants in tire production were selected for analysis. Firstly, the ability of tire antioxidants to reduce three different free radicals was quantitatively characterized based on Gaussian calculation method and inferring the radical reduction mechanism of tire antioxidants. Moreover, using the PaDEL-Descriptor software and random forest algorithm found that the N-octanol/water partition coefficient, a structure descriptor of tire antioxidant molecules, significantly correlated with their reducing ability. Second, molecular docking and molecular dynamics methods were used to assess the thyroid hormone disorder risk to aquatic organisms of eight antioxidants after reducing three free radicals. And this is the first study to construct an assessment score list of potential thyroid hormone disorder risk of the derivatives of tire antioxidants after reducing free radicals to marine and freshwater aquatic organisms based on the risk entropy method. Through the screening of this list, it was found that the derivative of the antioxidant 2,2,4-trimethyl-1,2-dihydroquinoline oxidized by free radicals had the highest risk of thyroid hormone disorder. In addition, the top organism in the aquatic food chain was the most affected. This study also revealed that van der Waals interactions and hydrogen bonding were the main influencing factors of thyroid hormone disorder risk to aquatic organisms of the derivatives of tire antioxidants that reduce free radicals based on amino acid residue analysis. Overall, the results provide theoretical support for the selection of antioxidants and the avoidance and control of environmental risks in the tire rubber production process.

Microplastics in cultivated soil environment: Construction of toxicity grading evaluation system, development of priority control checklist, and toxicity mechanism analysis.

The present study aimed to comprehensively evaluate the toxicological effects of microplastics (MPs) on cultivated soil quality. Based on improved G1 evaluation method, we first constructed a grading evaluation system comprising of the indicators of toxicological effects of cultivated soil quality under MPs exposure, while focusing on types of MPs that had significant/non-significant toxicity effects. Furthermore, we verified reliability of screening results of significance-links at each level, using several data processing methods. Then, using natural breakpoint classification method, a priority control checklist of toxicological effects of 18 types of MPs on cultivated soil was developed to determine the types of MPs having significant toxicity risks and cultivated soil quality links significantly affected by the toxicity of MPs exposure. Finally, quantum-mechanics/molecular-mechanics (QM/MM) methods were used to carry out the differential toxicity mechanism analysis. The results showed that MPs with higher non-polar surface area may lead to stronger toxicity effect to the cultivated soil quality. Notably, the MPs that have abundant binding sites enhance the binding affinity, and less polar MPs bind more strongly to the non-polar amino acids of target receptors. Our study provides a new theoretical perspective for multi-dimensional analysis toxicological effects of different MPs exposure on cultivated soil quality.