Laboratory-Simulated Photoirradiation Reveals Strong Resistance of Primary Macroplastics to Weathering.

The photodegradation of macroplastics in the marine environment remains poorly understood. Here, we investigated the weathering of commercially available plastics (tabs 1.3 × 4.4 × 0.16 cm), including high-density polyethylene, low-density polyethylene, polypropylene, polystyrene, and polycarbonate, in seawater under laboratory-simulated ultraviolet A radiation for 3-9 months, equivalent to 25-75 years of natural sunlight exposure without considering other confounding factors. After the exposure, the physical integrity and thermal stability of the tabs remained relatively intact, suggesting that the bulk polymer chains were not severely altered despite strong irradiation, likely due to their low specific surface area. In contrast, the surface layer (∼1 µm) of the tabs was highly oxidized and eroded after 9 months of accelerated weathering. Several antioxidant additives were identified in the plastics through low temperature pyrolysis coupled with gas chromatography/mass spectrometry (Pyr-GC/MS) analysis. The Pyr-GC/MS results also revealed many new oxygen-containing compounds formed during photodegradation, and these compounds indicated the dominance of chain scission reactions during weathering. These findings highlight the strong resistance of industrial macroplastics to weathering, emphasizing the need for a broader range of plastics with varying properties and sizes to accurately estimate plastic degradation in the marine environment.

Insights into the controlling factors of the transport of tire wear particles in saturated porous media: The facilitative role of aging and fulvic acid.

The widespread distribution and potential adverse effects of tire wear particles (TWPs) on soil and groundwater quality pose a growing environmental concern. This study investigated the transport behavior of TWPs in saturated porous media and elucidated the underlying mechanisms influenced by environmental factors. Additionally, the effects of key environmental factors, such as aging, ionic strength, cation species, medium type, and natural organic matter (NOM), on the transport of TWPs were evaluated. The results showed that aging processes simulated through O3 and UV irradiation altered the physicochemical properties of TWPs, increased the mobility of TWPs at low ionic strengths. However, the high ionic strengths and the presence of Ca2+ significantly inhibited the mobility of TWPs due to enhanced aggregation. The transport mechanism of the original and aged TWPs shifted from blocking to ripening under favorable retention conditions (i.e., high ionic strengths, divalent cations, and fine sands). Interestingly, the presence of fulvic acid (FA) inhibited the ripening of the three TWPs, significantly promoting their transport through a spatial site resistance mechanism. The two-site kinetic attachment model (TSKAM), extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, and colloid filtration theory (CFT) were applied to describe the transport behavior of the TWPs. The study provided a comprehensive understanding of the transport behavior of TWPs in groundwater environments, highlighting the environmental risks associated with their widespread distribution.

Bioinspired Bidirectional Stiffening Soft Actuators Enable Versatile and Robust Grasping.

The bending stiffness modulation mechanism for soft grippers has gained considerable attention to improve grasping versatility, capacity, and stability. However, lateral stability is usually ignored or hard to achieve at the same time with good bending stiffness modulation performance. Therefore, this article presents a bioinspired bidirectional stiffening soft actuator (BISA), enabling compliant and stable performance. BISA combines the air tendon actuation (ATA) and a bone-like structure (BLS). The ATA is the main actuation of the BISA, and the bending stiffness can be modulated with a maximum stiffness of about 0.7 N/mm and a maximum magnification of three times when the bending angle is 45°. Inspired by the morphological structure of the phalanx, the lateral stiffness can be modulated by changing the pulling force of the BLS. The actuator with BLSs can improve the lateral stiffness by about 3.9 times compared to the one without BLSs. The maximum lateral stiffness can reach 0.46 N/mm. And the lateral stiffness can be modulated by decoupling about 1.3 times (e.g., from 0.35 to 0.46 N/mm when the bending angle is 45°). The test results show that the influence of the rigid structures on bending is small with about 1.5 mm maximum position errors of the distal point of the actuator in different pulling forces. The advantages brought by the proposed method enable versatile four-finger grasping. The performance of this gripper is characterized and demonstrated on multiscale, multiweight, and multimodal grasping tasks.

A multi-scale approach to detecting standing dead trees in UAV RGB images based on improved faster R-CNN.

The health of the trees in the forest affects the ecological environment, so timely detection of Standing Dead Trees (SDTs) plays an important role in forest management. However, due to the large spatial scope of forests, it is difficult to find SDTs through conventional approaches such as field inventories. In recent years, the development of deep learning and Unmanned Aerial Vehicle (UAV) has provided technical support for low-cost real-time monitoring of SDTs, but the inability to fully utilize global features and the difficulty of small-scale SDTs detection have brought challenges to the detection of SDTs in visible light images. Therefore, this paper proposes a multi-scale attention mechanism detection method for identifying SDTs in UAV RGB images. This method takes Faster-RCNN as the basic framework and uses Swin-Transformer as the backbone network for feature extraction, which can effectively obtain global information. Then, features of different scales are extracted through the feature pyramid structure and feature balance enhancement module. Finally, dynamic training is used to improve the quality of the model. The experimental results show that the algorithm proposed in this paper can effectively identify the SDTs in the visible light image of the UAV with an accuracy of 95.9%. This method of SDTs identification can not only improve the efficiency of SDTs exploration, but also help relevant departments to explore other forest species in the future.

Hitchhiking into the Deep: How Microplastic Particles are Exported through the Biological Carbon Pump in the North Atlantic Ocean.

Understanding residence times of plastic in the ocean is a major knowledge gap in plastic pollution studies. Observations report a large mismatch between plastic load estimates from worldwide production and disposal and actual plastics floating at the sea surface. Surveys of the water column, from the surface to the deep sea, are rare. Most recent work, therefore, addressed the "missing plastic" question using modeling or laboratory approaches proposing biofouling and degradation as the main removal processes in the ocean. Through organic matrices, plastic can affect the biogeochemical and microbial cycling of carbon and nutrients. For the first time, we provide in situ measured vertical fluxes of microplastics deploying drifting sediment traps in the North Atlantic Gyre from 50 m down to 600 m depth, showing that through biogenic polymers plastic can be embedded into rapidly sinking particles also known as marine snow. We furthermore show that the carbon contained in plastic can represent up to 3.8% of the total downward flux of particulate organic carbon. Our results shed light on important pathways regulating the transport of microplastics in marine systems and on potential interactions with the marine carbon cycle, suggesting microplastic removal through the "biological plastic pump".

Occurrence, distribution, and associated pollutants of plastic pellets (nurdles) in coastal areas of South Texas.

Nurdles, also known as plastic resin pellets, are now a major source of plastic pollution on beaches globally, thus it is important to elucidate their weathering patterns and environmental fates as well as the associated pollutants. In this study we collected nurdles from 24 sites in the coastal bend region of south Texas, covering areas from the near shore railway stations to the adjacent bays and barrier islands. The morphologies of nurdles and associated pollutants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and mercury, were investigated. The results showed that the nurdles varied greatly in color, shape, polymer composition, and oxidation degree. More than 80 % of the nurdles were made with polyethylene, and the rest with polypropylene, polyester, polystyrene, polyethylene-vinyl acetate, and polyvinyl chloride based on Fourier Transform Infrared Spectroscopy (FTIR) analysis. PCBs were not detected on nurdles. PAHs and mercury on nurdles were detected at 12 % and 20 % of the sampling sites. The total concentrations of detectable PAHs ranged from 92.59 to 1787.23 ng/g-nurdle, and the detectable mercury concentrations ranged from 1.23 to 22.25 ng/g-nurdle. Although the concentrations of these pollutants were not at the acute toxic effect level, the presence of PAHs and mercury suggested the potential risk of pollutant exposure to marine organisms in ecosystems, given the fact that nurdles are persistent in the environment.

Effects of nano- and microplastics on the bioaccumulation and distribution of phenanthrene in the soil feeding earthworm Metaphire guillelmi.

Microplastics (MPs) and nanoplastics (NPs), are collectively referred to as fine plastic particles (FPs), have been reported for both the "vector" effect and "dilution" effect which alters the bioaccumulation of organic contaminants. However, which effect plays a dominant role, especially in terrestrial ecosystems, remains unknown. In the present study, we used 14C-radioactive labeling tracing technique to assess the sorption of a typical polycyclic aromatic hydrocarbon, phenanthrene on soil particles and FPs, as well as the contribution of vector effects of FPs on the bioaccumulation and distribution of phenanthrene by the geophagous earthworm Metaphire guillelmi. The results showed that the presence of FPs in soil decreased the bioaccumulation of 14C-Phenanthrene in M. guillelmi by decreasing the bioavailable fraction of phenanthrene in soil, and the decreasing effect was more dramatic for NPs treatments. In all cases, bioaccumulation of 14C-Phenanthrene in M. guillelmi was still determined by the free concentration of 14C-Phenanthrene in soil and limited vector effects was observed. Moreover, the different correlation coefficients between the free concentration of 14C-Phe in two soils and bioaccumulated 14C-Phenanthrene in earthworms indicated that soil properties remained a dominant factor that determines the bioaccumulation efficiency of 14C-Phenanthrene in the FPs-soil system. Although the total 14C-Phenanthrene bioaccumulation in earthworms did not increase, vector effects may be responsible for the increased relative distribution of 14C-phenanthrene in the organ region, compared with skin and gut regions, leading to unknown risks to organs that are sensitive to these contaminants.

The impacts of weathering on concentration and bioaccessibility of organic pollutants associated with plastic pellets (nurdles) in coastal environments.

Nurdles, the pre-production plastic pellets, are a major source of plastic pollution in marine environments due to unregulated spills during production and transportation. We analyzed the types of plastics and associated organic pollutants on nurdles collected along the shoreline of Gulf of Mexico in Texas. Our results showed that the nurdles were made from polyethylene (81.9%) and polypropylene (18.1%). Polycyclic aromatic hydrocarbons (PAHs, 16 US EPA priority) and polychlorinated biphenyls (PCBs, 7 commercial congeners) sorbed to the nurdles were in concentration ranges of 1.6-14,700 ng/ g and 0-642 ng/ g, respectively. Heavily weathered nurdles tended to have higher concentrations of PAHs and PCBs than lightly weathered ones. The bioaccessibility of sorbed contaminants was evaluated using a simulated intestinal fluid. The results showed that the associated PAHs were more bioaccessible in lightly weathered nurdles (13.1 ± 2.3%) than heavily weathered one (5.3 ± 0.1%), and that no PCBs were bioaccessible. These findings are informative for toxicity evaluation and resource management of plastic debris in coastal environments.

Eco-friendly and facile one-step synthesis of a three dimensional net-like magnetic mesoporous carbon derived from wastepaper as a renewable adsorbent.

Millions of tons of paper and its derivatives are annually wasted without being recycled and reused. To promote the comprehensive utilization of resources and eco-friendly preparation, waste filter paper, printer paper, and napkins were chosen as carbon sources to one-step synthesize three types of three dimensional (3D) net-like magnetic mesoporous carbon (MMC) by an eco-friendly and low-cost method. These mesoporous (3.90-7.68 nm) composites have a high specific surface area (287-423 m2 g-1), well-developed porosity (0.24-0.74 cm3 g-1) and abundant oxygen-containing functional groups. Compared to the other two composites, the adsorbent derived from filter paper showed the highest adsorption capacity towards methylene blue (MB) (q max = 332.03 mg g-1) and rhodamine B (RhB) (q max = 389.59 mg g-1) with a high adsorption rate (<5 min). According to the effect of pH value on adsorption capacity, and combining the analysis of Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy, the main adsorption mechanisms can be summarized as hydrogen bonds, electrostatic interactions, and π-π interaction. Besides, the occurrence of redox reactions between Fe2+/Fe0 and dye cannot be ignored. Finally, experiments on reusability were performed. They showed that the 3D net-like MMC could be easily regenerated and still maintained a removal efficiency of above 80% for RhB and 90% for MB after five cycles.

Quantifying the bioaccumulation of nanoplastics and PAHs in the clamworm Perinereis aibuhitensis.

The impact of nanometer-scale plastics (<1000 nm nanoplastics, NPs) on the bioaccumulation of hydrophobic organic pollutants, and especially polycyclic aromatic hydrocarbons (PAHs), in marine organisms has become of urgent concern. However, simultaneous determinations of the bioaccumulation of NPs and PAHs have been hindered by the lack of an efficient digestion method that removes background interference from the tissue without altering the surface properties of the plastic and destroying the PAHs. To solve this problem, an enzymatic digestion-based protocol using proteinase K and subsequent quantification methods were developed on a typical marine benthic invertebrate - the clamworm Perinereis aibuhitensis. Enzymatic digestion removed 91% of the biological tissues, comparable to the amount removed using 65% HNO3 (93% removed) and better than that removed using 30% H2O2 or 10% KOH digestion (76% and 66%, respectively). After enzymatic digestion, roughly 92% of the NPs and 88% of the amount of pyrene were recovered, without significant modification of the NPs or pyrene degradation. By contrast, the NP and pyrene recovery achieved with HNO3 digestion was only 1.4% and 0.1%, respectively. The newly developed protocol was successfully applied to a 96-h bioaccumulation study. The use of radioactively labeled 14C-pyrene and fluorescently labeled NPs allowed the simultaneous quantification of NPs and PAHs in the clamworm and revealed a bioconcentration factor (BCF) of 1.96 ±â€¯0.93 and 402.7 ±â€¯47.0, respectively. The quantification of NPs and pyrene indicated that NP-adsorbed pyrene accounted for <1% of the total pyrene accumulation in the clamworm body when the concentration of NPs in seawater was as low as 0.4 mg/L. Our enzymatic digestion and dual-labeling technique thus provides the first reported BCF value of NPs in a marine benthic organism and new insights into the vector effects of these particles on the bioaccumulation of organic contaminants in a marine ecosystem.