Dunzhu Li

Micro- and nanoplastics (MNPs) are pervasive micropollutants in aquatic environments and along shorelines. Their release is predominantly attributed to mechanical abrasion or ultraviolet exposure, both requiring substantial external energy inputs. The role of aquatic factors (e.g., air bubbles) in the generation of MNPs is poorly understood. Here we show microbubbles that spontaneously form on seven typical plastics across a wide temperature range (25° to 95°C) and in various water types (deionized, tap, river, and marine water) can erode plastic surfaces and drive MNP release. Nucleation, expansion, and movement of microbubbles generate shear stresses capable of dislodging polymer protrusions at surface defect sites. This sweeping action, combined with the unbalanced surface tension forces at the three-phase contact line, generates O-shaped ring structures composed of accumulated polymers, which ultimately fragment leading to the release of MNPs into the aquatic environment. Our findings demonstrate that microbubble-induced erosion represents a low-energy pathway for micropollutant release.

Soil microbial communities are important for nutrient cycling regulation in forest ecosystems. However, limited knowledge exists regarding the characteristics of these microbial communities in Masson pine (Pinus massoniana Lamb.) plantations of different stand ages. In this study, four planted Masson pine stands (8-year-old, 12-year-old, 22-year-old, and 38-year-old stands) and one natural broadleaved forest stand (as a control) with three replications, were selected in the Laoshan Forest Farm, Qiandao Lake Town, Zhejiang Province, China. Soil physicochemical properties were measured and their effects on soil microbial communities were studied. Amplicon-based high-throughput sequencing was employed to process raw sequence data for soil microbes. It is worth noting that significant differences (p < 0.05) in soil bacterial genera were observed among different stand age groups. Total nitrogen (TN), total phosphorus (TP), total potassium (TK), available potassium (AK), soil organic carbon (SOC), and soil bulk density (BD) were identified as the primary factors influencing bacterial community distribution (p < 0.05). Available nitrogen (AN), SOC, TN, and TK showed significant correlations with soil fungal communities (p < 0.05). These findings underscore the crucial role of soil physicochemical properties in shaping soil microbial community composition in Masson pine plantations.

Residual stress is an intrinsic property of semicrystalline plastics such as polypropylene and polyethylene. However, there is no fundamental understanding of the role intrinsic residual stress plays in the generation of plastic pollutants that threaten the environment and human health. Here, we show that the processing-induced compressive residual stress typically found in polypropylene and polyethylene plastics forces internal nano and microscale segregation of low molecular weight (MW) amorphous polymer droplets onto the plastic’s surface. Squeeze flow simulations reveal this stress-driven volumetric flow is consistent with that of a Bingham plastic material, with a temperature-dependent threshold yield stress. We confirm that flow is thermally activated and stress dependent, with a reduced energy barrier at higher compressive stresses. Transfer of surface segregated droplets into water generates amorphous polymer micropollutants (APMPs) that are denatured, with structure and composition different from that of traditional polycrystalline microplastics. Studies with water-containing plastic bottles show that the highly compressed bottle neck and mouth regions are predominantly responsible for the release of APMPs. Our findings reveal a stress-induced mechanism of plastic degradation and underscore the need to modify current plastic processing technologies to reduce residual stress levels and suppress phase separation of low MW APMPs in plastics.

Plastics are an essential commodity due to their superior engineering properties, durability and low cost for utilization in various commercial products. However, the degradation of plastics due to several environmental stresses has led to the formation of microplastics (MPs). MPs have risen to the top of environmental concerns due to their affinity to pollute the environment and to pass it to the food chain, threatening human health. In this context, attempts have been made to extract and characterise MPs from aqueous and solid matrices. A problem that not only hampers research but also regulatory decisions is the variety of methods used for the extraction and characterisation of MPs, especially in organic solid matrices (OSMs) with organic matter >5%, making the comparison of results difficult. This paper aims to address this by critically assessing the methodologies used for the extraction and qualitative and quantitative characterisation of MPs in OSMs. Further, the current impediments in the accurate characterisation of MPs in OSMs are identified, along with recommendations for future research. Finally, recent efforts by various countries to legislate against certain sources of MPs, as well as issues and novel techniques to remediate MPs from the soil, and wastewater have been highlighted.