Environmental stressors, such as contaminants and physical factors, rarely act in isolation, and studying their joint effects provides a more accurate reflection of real-world scenarios. To capture these interactions and disentangle the direct and indirect influences on algal responses, we applied partial least squares structural equation modeling (PLS-SEM), allowing us to reveal the hierarchical relationships among stressors and their cumulative impact on algal physiology. We examined combined effects of microplastics (MP; presence/absence), polycyclic aromatic hydrocarbons (PAHs; a mixture of acenaphthene, fluorene, phenanthrene, and fluoranthene at a total chemical activity in the sediment of 0 or 0.14), and sediment resuspension (turbidity: 0.8–3.9 NTU) on Ceramium tenuicorne, a coastal macroalga that is likely to encounter all these stressors in its natural habitats. Mechanical mixing at two intensities (low and high) was applied as an experimental treatment to induce resuspension. The analysis separated the effects of mechanical mixing and turbidity, given their nonlinear relationship, as stronger mechanical mixing did not consistently result in proportional turbidity increases. The algal physiological responses were evaluated using changes in pigment composition (Chl a, Chl c, and carotenoids), photosystem II (PSII) performance, total antioxidant capacity, and algal stoichiometry measured as elemental (%C, %N, %H, and C/N) ratios. We found that PAH exposure was the main suppressor of pigment concentrations and PSII performance, underscoring the mechanisms of its adverse effects on the photosynthetic machinery and nutrient assimilation. Moreover, stronger turbulence further decreased pigment concentrations, while sediment resuspension increased antioxidant capacity in algae, possibly due to physical damage from abrasion and scouring. We also found that MP addition significantly increased turbidity, thus aggravating the effects of the sediment resuspension. In conclusion, we provide a mechanistic explanation of how the combined exposure to MPs, PAHs, and sediment resuspension can impact pigment composition, photosynthesis, and stoichiometry of the algae, leading to decreased productivity.

Macrophytes are essential primary producers in coastal ecosystems, significantly shaping food webs and providing critical ecosystem services. However, their habitats are increasingly becoming hotspots for plastic pollution due to their efficiency in trapping plastic particles from terrestrial runoff. This review explores the complex interactions between plastic litter and macrophyte systems, focusing on four main areas: (1) physical interference and habitat alterations due to particle retention by macrophytes; (2) chemical contamination and ecotoxicity; (3) nutrient dynamics affecting productivity; and (4) impacts on microbial communities associated with environmental compartments and plant microbiomes. Plastic debris can physically obstruct light and gas exchange, alter sediment properties, and leach toxic chemicals, adversely affecting macrophyte physiology and growth. These impacts can cascade through the ecosystem, disrupting habitat structure, food webs, and biogeochemical processes, ultimately threatening biodiversity and ecosystem stability. We highlight the necessity for a unified research approach to deepen our understanding of these interactions and advocate for leveraging macrophytes in bioremediation efforts and as indicators of plastic pollution in environmental management strategies. Understanding these often-overlooked interactions is crucial for assessing the environmental impact of plastic pollution and for the development of effective conservation and remediation policies.

The COVID-19 pandemic has resulted in unprecedented plastic pollution from single-used personal protective equipment (PPE), especially face masks, in coastal and marine environments. The secondary pollutants, microplastics from face masks (mask MP), rise concern about their detrimental effects on marine organisms, terrestrial organisms and even human. Using a mouse model, oral exposure to mask MP at two doses, 0.1 and 1 mg MP/day for 21 days, caused no change in animal locomotion, total weight, or sperm counts, but caused damage to sperm motility with increased curvilinear velocity (VCL). The high-dose mask MP exposure caused a significant decrease in linearity (LIN) of sperm motility. Further testicular transcriptomic analysis revealed perturbed pathways related to spermatogenesis, oxidative stress, inflammation, metabolism and energy production. Collectively, our findings substantiate that microplastics from face masks yield adverse effects on mammalian reproductive capacity, highlighting the need for improved plastic waste management and development of environmentally friendly materials.

Introduction: Growing concerns regarding the reproductive toxicity associated with daily life exposure to micro-/nano-plastics (abbreviated as MNPs) have become increasingly prevalent. In reality, MNPs exposure involves a heterogeneous mixture of MNPs of different sizes rather than a single size. Methods: In this study, an oral exposure mouse model was used to evaluate the effects of MNPs of four size ranges: 25–30 nm, 1–5 µm, 20–27 µm, and 125–150 µm. Adult male C57BL/6 J mice were administered environmentally relevant concentrations of 0.1 mg MNPs/day for 21 days. After that, open field test and computer assisted sperm assessment (CASA) were conducted. Immunohistochemical analyses of organ and cell type localization of MNPs were evaluated. Testicular transcriptome analysis was carried out to understand the molecular mechanisms. Results: Our result showed that MNPs of different size ranges all impaired sperm motility, with a decrease in progressive sperm motility, linearity and straight-line velocity of sperm movement. Alterations did not manifest in animal locomotion, body weight, or sperm count. Noteworthy effects were most pronounced in the smaller MNPs size ranges (25–30 nm and 1–5 µm). Linear regression analysis substantiated a negative correlation between the size of MNPs and sperm curvilinear activity. Immunohistochemical analysis unveiled the intrusions of 1–5 µm MNPs, but not 20–27 µm and 125–150 µm MNPs, into Leydig cells and testicular macrophages. Further testicular transcriptomic analysis revealed perturbations in pathways related to spermatogenesis, oxidative stress, and inflammation. Particularly within the 1–5 µm MNPs group, a heightened perturbation in pathways linked to spermatogenesis and oxidative stress was observed. Conclusions: Our data support the size-dependent impairment of MNPs on sperm functionality, underscoring the pressing need for apprehensions about and interventions against the escalation of environmental micro-/nano-plastics contamination. This urgency is especially pertinent to small-sized MNPs.

The prevalence of microplastics in the marine environment poses potential health risks to humans through seafood consumption. Relevant data are available but the diverse analytical approaches adopted to characterise microplastics have hampered data comparison among studies. Here, the techniques for extraction and identification of microplastics are summarised among studies of marine mussels and fish, two major groups of seafood. Among the reviewed papers published in 2018-2021, the most common practice to extract microplastics was through tissue digestion in alkaline chemicals (46 % for mussels, 56 % for fish) and oxidative chemicals (28 % for mussels, 12 % for fish). High-density solutions such as sodium chloride could be used to isolate microplastics from other undigested residues by flotation. Polymer analysis of microplastics was mainly carried out with Fourier-transform infrared (FTIR) spectroscopy (58 % for both mussels and fish) and Raman spectroscopy (14 % for mussels, 8 % for fish). Among these methods, we recommend alkaline digestion for microplastic extraction, and the automated mapping approach of FTIR or Raman spectroscopy for microplastic identification. Overall, this study highlights the need for a standard protocol for characterising microplastics in seafood samples.

The spatial distribution and abundance of suspected microplastics (SMPs) in the surface water of a metropolitan city, as represented by four Hong Kong rivers, was studied during the dry season. Shing Mun River (SM), Lam Tsuen River (LT), and Tuen Mun River (TM) are located in urbanized areas, and SM and TM are tidal rivers. The fourth river, Silver River (SR) is situated in a rural area. TM had a significantly higher SMP abundance (53.80 ± 20.67 n/L) than the other rivers. The SMP abundance increased from upstream to downstream in non-tidal rivers (LT and SR), but not in tidal rivers (TM and SM), probably due to the tidal influence and a more homogeneous urban development along the tidal rivers. Inter-site differences in the SMP abundance were strongly correlated with the built area ratio (defined as the percentage of surrounding developed land area), human activities, and the nature of the river. About half (48.72 %) of the SMPs were <250 μm. Fibers and fragments were most abundant (>98 %), with most of them being transparent (58.54 %), black (14.68 %), or blue (12.12 %). Polyethylene terephthalate (26.96 %) and polyethylene (20.70 %) were the most common polymers. However, the MP abundance could be overestimated due to the presence of natural fibers. By contrast, an underestimation of the MP abundance could result from a smaller volume of water samples collected, due to a low filtration efficiency caused by high organic content and particle concentrations in the water. A more effective solid waste management strategy and upgrading of the sewage treatment facilities for removing microplastics are recommended to ameliorate the microplastic pollution in local rivers.

Given the potential risk to the ecosystem, attention has increased in recent decades to the contamination of the aquatic environment by microplastics (MPs). Due to the limitations of conventional analysis methods of MPs, little is known about the size distribution and abundance of a full-size MPs from 1 μm to 5 mm. The present study quantified MPs with size ranges of 50 μm – 5 mm and 1–50 μm in the coastal marine waters from twelve locations in Hong Kong using fluorescence microscopy and flow cytometry respectively, during the end of wet (September 2021) and dry (March 2022) seasons. The average abundance of MPs with size ranges of 50 μm – 5 mm and 1–50 μm from twelve sampling locations marine surface waters were found ranging from 27 to 104 particles L⁻¹ and 43,675–387,901 particles L⁻¹ in the wet season respectively, and 13–36 particles L⁻¹ and 23,178–338,604 particles L⁻¹ in the dry season respectively. Significant temporal and spatial variations of small MPs abundance might be observed at the sampling locations, which were contributed by the influences of the estuary of Pearl River, sewage discharge points, land structure, and other anthropogenic activities. Based on the MPs abundance information, ecological risk assessment was conducted and revealed that the small MPs (< 10 μm) in coastal marine surface waters may pose potential health risks to aquatic organisms. Additional risk assessments are needed in order to determine whether or not the MPs exposure would cause health risks to the public.

This study examined microplastic (MP) occurrence and abundance in marine fish collected from the western and eastern waters of Hong Kong during the wet and dry seasons. Over half (57.1%) of the fish had MP in their gastrointestinal (GI) tracts, with overall MP abundance ranging from not detected to 44.0 items per individual. Statistical analysis revealed significant spatial and temporal differences in MP occurrence, with fish from more polluted areas having a higher likelihood of MP ingestion. Additionally, fish collected in the west during the wet season had significantly higher MP abundance, likely due to influence from the Pearl River Estuary. Omnivorous fish had significantly higher MP counts than carnivorous fish, regardless of collection location or time. Body length and weight were not significant predictors of MP occurrence or abundance. Our study identified several ecological drivers that affect MP ingestion by fish, including spatial-temporal variation, feeding mode, and feeding range. These findings provide a foundation for future research to investigate the relative importance of these factors in governing MP ingestion by fish in different ecosystems and species.

Coastal wetlands trap plastics from terrestrial and marine sources, but the stocks of plastics and their impacts on coastal wetlands are poorly known. We evaluated the stocks, fate, and biological and biogeochemical effects of plastics in coastal wetlands with plastic abundance data from 112 studies. The representative abundance of plastics that occurs in coastal wetland sediments and is ingested by marine animals reaches 156.7 and 98.3 items kg^–1, respectively, 200 times higher than that (0.43 items kg^–1) in the water column. Plastics are more abundant in mangrove forests and tidal marshes than in tidal flats and seagrass meadows. The variation in plastic abundance is related to climatic and geographic zones, seasons, and population density or plastic waste management. The abundance of plastics ingested by pelagic and demersal fish increases with fish length and dry weight. The dominant characteristics of plastics ingested by marine animals are correlated with those found in coastal wetland sediments. Microplastics exert negative effects on biota abundance and mangrove survival but positive effects on sediment nutrients, leaf drop, and carbon emission. We highlight that plastic pollution is widespread in coastal wetlands and actions are urged to include microplastics in ecosystem health and degradation assessment.

The most frequently used method to quantify microplastics (MPs) visually by microscope is time consuming and labour intensive, where the method is also hindered by the size limitation at 10 µm or even higher. A method is proposed to perform pre-concentration of MPs by vacuum filtration, hydrogen peroxide wet digestion, fluorescent staining and flow cytometric determination to rapidly detect and quantify small MPs sized from 1–50 µm. The method performance was evaluated by the spiking of seven different types of polymer, including polystyrene (PS), low-density polyethylene (LDPE), polypropylene (PP), poly(methyl methacrylate) (PMMA), polyvinyl chloride (PVC), polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) at different levels (400, 4000, 40,000 particles mL−1), with a satisfactory overall % recoveries (101 ± 19.4%) observed, where in general no significant difference between the two methods was observed. Furthermore, a pre-concentration process by vacuum filtration was introduced to reduce the matrix effect. After pre-concentration, satisfactory % recoveries and accuracy in MP counts resulted from both ultrapure water (94.33 ± 11.16%) and sea water (103.17 ± 9.50%) samples. The validated method using flow cytometry can be used to quantify MPs in environmental water samples that can reduce time and human resources.