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Polylactic acid (PLA) is the most commonly used biodegradable plastic with rapid growth in recent years. This leads to predictable increased pollution of PLA microplastics (MPs) in the environment. However, quantification methods for the PLA MPs are still lacking. In this study, a method based on alkali-assisted thermal depolymerization and liquid chromatography–tandem mass spectrometry (LC–MS/MS) analysis was developed to quantify PLA MPs. After the background monomer compound was removed, PLA MPs were efficiently depolymerized to lactic acid and detected by LC–MS/MS with a limit of quantification of 18.7 ng/g. The ideal recovery of spiked PLA MPs of 93% was obtained, and the PLA MPs did not need to be separated or extracted in advance from the environmental samples. Using this method, PLA MPs were detected in all the sediment samples of a reservoir at a range of 53.5–491 ng/g dw, and the concentrations decreased with the sediment depth. In addition, after soaking in water at 95 °C for 30 min, approximately 12 μg of PLA MPs was released from a single teabag.

A landfill is an important sink of plastic waste and potential sources of microplastics (MPs) when mineralized refuse is reused. However, limitations are still present in quantifying MPs in mineralized refuse and assessing their degradation degree. In this study, laser direct infrared spectroscopy and liquid chromatography-tandem mass spectrometry (LC-MS/MS) were used to identify MPs of mineralized refuse from a landfill. Although 25–113 items/g MPs were detected in particles subjected to flotation, 37.9–674 μg/g polyethylene terephthalate (PET) and 0.0716–1.01 μg/g polycarbonate (PC) were detected in the residual solids by LC-MS/MS, indicating a great amount of plastic polymers still presented in the residue. This suggests that the commonly used flotation-counting method will lead to significant underestimation of MP pollution in mineralized refuse, which might be due to the aging and aggregation process caused by the long-term landfill process. The ratio of “bisphenol A/PC” and “plasticizer/MPs” was found to be positively correlated and negatively correlated with the landfill age, respectively. Therefore, in addition to the spectral index such as the carbonyl index, new indexes based on the concentrations of polymers, free monomers, and plasticizers were proposed to characterize the degradation degree of MPs in a landfill.

Coal and gas outburst is a dynamic phenomenon in underground mining engineering that is often accompanied by the throwing and breakage of large amounts of coal. To study the crushing effect and its evolution during outbursts, coal samples with different initial particle sizes were evaluated using a coal and gas outburst testing device. Three basic particle sizes, 5–10 mesh, 10–40 mesh, and 40–80 mesh, as well as some mixed particle size coal samples were used in tests. The coal particles were pre-compacted at a pressure of 4 MPa before the tests. The vertical ground stress (4 MPa) and the horizontal ground stress (2.4 MPa) were initially simulated by the hydraulic system and maintained throughout. During the tests, the samples were first placed in a vacuum for 3 h, and the coal was filled with gas (CH4) for an adsorption time of approximately 5 h. Finally, the gas valve was shut off and the coal and gas outburst was induced by quickly opening the outburst hole. The coal particles that were thrown out by the outburst test device were collected and screened based on the particle size. The results show the following. (1) Smaller particle sizes have a worse crushing effect than larger sizes. Furthermore, the well-graded coal particles are weakly broken during the outburst process. (2) As the number of repeated tests increases, the relative breakage index grows; however, the increment of growth decreases after each test, showing that further fragmentation becomes increasingly difficult.

Microplastics (MPs) in soils may be ingested by terrestrial animals. While the application of bioplastics is increasing, the ingestion and excretion characteristics of bio-MPs by terrestrial animals are poorly understood as compared to fossil-MPs. Here, the approach–avoidance behavior of adult earthworms Eisenia fetidato MP-contaminated soil was assessed. Fossil-based poly(ethylene terephthalate) (PET) and bio-based poly(lactic acid) (PLA) MPs were found to be preferred by the earthworms, which might be due to the odor of polymer monomers. MPs in earthworm casts were analyzed by microscopy counting and liquid chromatography–tandem mass spectrometry. The amount of microscopically recognizable excreted PET and PLA was 553 and 261 items/g, respectively, while a higher proportion of smaller PLA particles also presented. Bio-based PLA is much easy to break down by earthworms than fossil-based PET. Submicron and nanocron PLA accounted for 57 and 13% of the excreted PLA on the 10th day of excretion. MP excretion was well described with the first-order kinetic model, and the elimination half-life was 9.3 (for PET) and 45 h (for PLA). A longer excretion period of PLA may be related to its potential to break down in the earthworms’ digestive tract. This not only promotes the environmental degradation of PLA but also suggests the ecological risk caused by nanoparticles.