A review of sources, status, and risks of microplastics in the largest semi-enclosed sea of China, the Bohai Sea

Occurrence, trophic transfer and risk assessment of microplastics in fishery organisms from the Bohai Sea, China

Marine microplastic (MP) pollution has emerged as a critical environmental issue, posing significant risks to a wide range of marine organisms. However, the trophic transfer of MPs with different characteristics among marine species remain poorly understood. This study investigated the abundances and characteristics of MPs in various fishery organisms from the Bohai Sea, China, and evaluated the influencing factors, trophic transfer and associated risks. Results showed that MP abundances ranged from 0.50 ± 0.52-2.38 ± 1.41 items per individual. Most MPs were smaller than 1 mm (74.6 %), with fiber being the most common shape (80.8 %), and transparent being the dominant color (75.3 %). Among the 13 identified polymer types, cellophane was the most prevalent. MP ingestion by fishery organisms was significantly influenced by body size, biological taxa, and habitat, while showing no correlation with feeding habits. Notably, the trophic transfer and significant biomagnification of MPs occurred through the marine food chain. Specially, MPs within the size ranges from 30 to 500 µm, in fibrous shape, transparent color, and composed of cellophane, PET, PP, and PA polymers, demonstrated enhanced potential for trophic transfer. PHI-based quantitative risk assessment revealed a medium to danger risk of MPs to marine fishery organisms, with hazard indices spanning medium to danger risk levels. These findings provide new insights into the bioaccumulation and risk of MPs across different trophic levels in marine organisms.

Spatiotemporal distribution and fate of typical pesticides in the Bohai Sea and surrounding rivers, China

Pesticide leakage has lasting and profound effects on the stability and health of marine ecosystems. To explore the occurrence, distribution, and fate of typical pesticides in marine environments, three sampling campaigns were conducted in the Bohai Sea and surrounding rivers. Atrazine was the most pronounced pesticide, with a high concentration and detection frequency in both seawater and sediment. The presence of typical organophosphorus pesticides (OPs) was significantly lower than historical levels. Pesticide concentrations decreased from inshore to offshore. Furthermore, the spatiotemporal distribution characteristics of the pesticides highlighted the agricultural patterns and differences in pesticide use. Environmental factors and physicochemical properties jointly determined the behaviors and fates of pesticides in the marine environment. Sediment served as both a sink for widely used atrazine and a source of restricted OPs. Although some pesticides have been restricted or banned, such as dimethoate and chlorpyrifos, the risks caused by their long-term use and environmental accumulation cannot be ignored and the normalized monitoring of typical pesticides is necessary in the marine environment.

Oxidative stress dynamics in Hyalella azteca under sub-chronic exposure to naturally aged polypropylene microplastics

Microplastics (MPs) pollution has revealed a serious environmental issue, demonstrating chronic consequences for the affected environments and organisms. Although these plastic particles, pristine and aged, can circulate in different environmental matrices, their actual impacts on aquatic ecosystems are still under investigation. Here, we studied the toxicity of naturally aged secondary polypropylene (PP) MPs after constant exposure to ultraviolet radiation (26 µm) to the freshwater amphipod Hyalella azteca. The concentrations tested were 135, 1350, and 13,500 items/L. H. azteca was investigated for mortality and changes in enzyme markers after 7 and 14 days of exposure followed by a further 7 days of depuration. The results show that mortality was only significant at the highest concentration tested. The concentration of 13,500 items induced oxidative stress after 7 days of exposure only at the MDA levels and CAT activity, while the concentrations of 1350 and 13,500 items/L induced oxidative stress in all tested markers (SOD, CAT, GST and MDA after 14 days. After 7 days of depuration, the levels of biochemical damage were reduced, demonstrating the ability of the species to recover as they are isolated from this pollutant.

Characterization of microplastic distribution, sources and potential ecological risk assessment of domestic sewage from ships

Shipboard domestic sewage, encompassing both black water and gray water, has the potential to transport significant quantities of environmentally harmful microplastics, a concern that has garnered increasing global attention. In this study, Fourier infrared (FTIR) detection was used to detect microplastics in marine domestic wastewater. The primary objective was to evaluate the abundance and characteristics of microplastics present in ship domestic sewage, investigate potential sources and influencing factors, and assess the ecological risks associated with ship sewage through analyses of microplastic abundance and hazard indices. The findings revealed that the mean abundance of microplastics in ship domestic sewage are 50.82 particles per liter(n/L), with gray water exhibiting significantly higher levels at 167 n/L compared to black water at 36.96 n/L and mixed sewage at 46.57 n/L. Fiber microplastics constituted a predominant 95% of all samples collected from ships, followed by film microplastics. In terms of color distribution, transparent and blue microplastics were the most prevalent, with the majority measuring between 100 and 1000 μm in size. Polyethylene terephthalate (PET) emerged as the most common polymer type, followed by polypropylene (PP). The risk assessment highlighted that microplastics in domestic wastewater pose significant ecological risks to aquatic organisms, with pollution load indices consistently reaching Class IV levels. Correlation analyses between microplastic abundance and the physicochemical properties of sewage demonstrated a significant relationship between microplastic levels and the concentration of suspended solids in ship sewage. This study provides essential data to inform the development of regulatory policies aimed at managing the discharge of black water and gray water discharges from both domestic and international vessels.

Microplastic occurrence and hydrodynamic-sedimentary driving effects in the Bohai Strait region of China

The ubiquity of microplastics in oceans has led to an increased interest in microplastics in society. The Bohai Strait is in a key position in the Yellow and Bohai Seas and plays a key role in the exchange of materials and environmental changes in these waters. In this study, seawater, surface sediments, and column sediments, were collected from the Bohai Strait region. Among all seawater samples, the abundance of microplastics in the Bohai Strait region ranged between 0.38 and 3.20 items/L, and that of microplastics in surface sediments was between 15.80 and 94.41 items/kg d.w.. The average microplastics abundance in columnar sediments was 72.62 ± 29.86 items/kg d.w., which provided key information on the spatial distribution of microplastics and sedimentation phenomena in the Bohai Strait region. The abundance of microplastics was higher in regions where currents flowed more slowly, which suggests that ocean currents exert a crucial effect on microplastic distribution. In addition, the abundance of microplastics in sediments showed a close relation to the deposition rate, which implies that the deposition rate contribute to the deposition process of microplastics on the seafloor. The type of microplastics in seawater influences the kind of microplastics in sediments, which further emphasizes the importance of microplastics in seawater during microplastic transport and the deposition process. The results of this research contribute to the in-depth understanding of the behavior and propagation pathways of microplastics in oceans and provide a valuable reference for the reduction of microplastic pollution.

Multigenerational effects of combined exposure of triphenyltin and micro/nanoplastics on marine medaka (Oryzias melastigma): From molecular levels to behavioral response

In natural environments, micro/nanoplastics (MNP) inevitably coexist with various pollutants, making it essential to examine their combined toxicity and intergenerational effects on marine organisms. This study investigated the combined toxicity and intergenerational effects of exposure to triphenyltin (T), microplastics (M), nanoplastics (N), a combination of microplastics and triphenyltin (MT), and a combination of nanoplastics and triphenyltin (NT) on marine medaka. The results showed that all treatments had adverse and intergenerational effects on marine medaka. Regarding oxidative stress and energy metabolism, smaller sized plastic particles caused more significant damage to the organisms. However, MT inflicted greater gonadal system damage than NT, leading to imbalanced sex hormone levels. Additionally, T induced hyperactivity in fish, whereas MNP tended to induce behavioral depression. Notably, large plastic particles in the F0 generation had a more pronounced impact on depressive behaviors compared to smaller particles. These findings suggest that both individual and combined exposures to TPT and MNP can detrimentally affect marine medaka from the molecular to behavioral levels, posing risks to population sustainability. This study provided a robust theoretical foundation and deeper insights into the ecotoxicological impacts and risk assessments of coexisting pollutants.

Microplastics in ecosystems: Critical review of occurrence, distribution, toxicity, fate, transport, and advances in experimental and computational studies in surface and subsurface water

Microplastics (MPs), particles under 5 mm, pervade water, soil, sediment, and air due to increased plastic production and improper disposal, posing global environmental and health risks. Examining their distribution, quantities, fate, and transport is crucial for effective management. Several studies have explored MPs' sources, distribution, transport, and biological impacts, primarily focusing on the marine environment. However, there is a need for a comprehensive review of all environmental systems together for enhanced pollution control. This review critically examines the occurrence, distribution, fate, and transport of MPs in the following environments: freshwater, marine, and terrestrial ecosystems. The concentration of MPs is highly variable in the environment, ranging from negligible to significant amounts (0.003-519.223 items/liter in water and 0-18,000 items/kg dry weight sediment, respectively). Predominantly, these MPs manifest as fibers and fragments, with primary polymer types including polypropylene, polystyrene, polyethylene, and polyethylene terephthalate. A complex interplay of natural and anthropogenic actions, including wastewater treatment plant discharges, precipitation, stormwater runoff, inadequate plastic waste management, and biosolid applications, influences MPs' presence and distribution. Our critical synthesis of existing literature underscores the significance of factors such as wind, water flow rates, settling velocities, wave characteristics, plastic morphology, density, and size in determining MPs' transport dynamics in surface and subsurface waters. Furthermore, this review identifies research gaps, both in experimental and simulation, and outlines pivotal avenues for future exploration in the realm of MPs.

Bio-based microplastic polylactic acid exerts the similar toxic effects to traditional petroleum-based microplastic polystyrene in mussels

Microplastics (MPs) have accumulated in the oceans, causing adverse effects on marine organisms and the environment. Biodegradable polylactic acid (PLA) is considered as an excellent substitute for traditional petroleum-based plastics, but it is difficult to degrade completely and easily become MPs in the marine environment. To test the ecological risk of bio-based PLA, we exposed thick-shelled mussels (Mytilus coruscus) to bio-based PLA and petroleum-based polystyrene (PS) (at 102, 104, and 106 particles/L) for 14 days. The significant increase in enzyme activities related to oxidative stress and immune response showed that mussels were under physiological stress after MP ingestion. While enzyme activities of nerve conduction and energy metabolism were significantly disturbed after exposure. Meanwhile, normal physiological activities in respiration, ingestion and assimilation were also suppressed in association with enzyme changes. The negative effects of PS and PLA in mussels were not differentiated, and further integration analysis of integrated biomarker response (IBR) and principal component analysis (PCA) also showed that PLA would induce adverse effects in mussels and ecological risks as PS, especially at environmental concentrations. Therefore, it is necessary to pay more attention to the environmental and ecological risk of bio-based MP PLA accumulating in the marine environment.

Distribution characteristics and ecological risk analysis of microplastics in sediments and effluents related to offshore oil and gas activities in the Bohai Sea, China

Oil and gas activities are sources of marine microplastics (MPs) but have received less attention globally. This study assessed the distribution characteristics and ecological risks of MPs in 31 sediment samples and effluent samples of 5 oil and gas platforms related to offshore oil and gas activities in the Bohai Sea. The results showed that the mean abundance of MPs in sediment, produced water, and domestic sewage was 205.7 ± 151.5 items/kg d.w., 18 ± 11 items/L, and 26 ± 39 items/L, respectively. The MPs in sediments and effluents were dominated by transparent, rayon, and fibers <1 mm. Oil and gas activities may influence the abundance of MPs in the sediments. The sediments in the area were at a low level of risk, but some samples exhibited indexes beyond low levels. The mass of MPs carried by the effluents from oil and gas platforms in the Bohai Sea was less than that of other sources.

Microplastic abundance in the semi-enclosed Osaka Bay, Japan

Anthropogenic particles in sea surface water of the semi-enclosed Osaka Bay were identified using stereomicroscopy, classified according to polymer type using Fourier-transform infrared spectroscopy (FTIR), and categorized according to their physical characteristics. A total of 565.1 particles were detected in the water samples. However, plastic particles accounted for only 22.4% of the particles. Microplastic abundance in Osaka Bay showed seasonal variance from 8.9 ± 1.4 (in May) to 22.8 ± 6.5 particles/L (in July), which is consistent with previous reports in other semi-enclosed bays. Microplastics were mainly fragmented and fiber shaped, with gray and colorless/white coloration. The dominant polymer types were polypropylene, poly(methylmethacrylate), polyester, polyethylene, and polyethylene terephthalate. Generally, there were considerably higher abundances of microplastics at offshore sites compared with nearshore sites. The results of this study suggest that local river effluents and marine-related activities are probable sources of microplastics in Osaka Bay.

Effects of COVID-19 on coastal and marine environments: Aggravated microplastic pollution, improved air quality, and future perspective

The COVID-19 pandemic during 2020-2023 has wrought adverse impacts on coastal and marine environments. This study conducts a comprehensive review of the collateral effects of COVID-19 on these ecosystems through literature review and bibliometric analysis. According to the output and citation analysis of these publications, researchers from the coastal countries in Asia, Europe, and America payed more attentions to this environmental issue than other continents. Specifically, India, China, and USA were the top three countries in the publications, with the proportion of 19.55%, 18.99%, and 12.01%, respectively. The COVID-19 pandemic significantly aggravated the plastic and microplastic pollution in coastal and marine environments by explosive production and unproper management of personal protective equipment (PPE). During the pandemic, the estimated mismanaged PPE waste ranged from 16.50 t/yr in Sweden to 250,371.39 t/yr in Indonesia. In addition, the PPE density ranged from 1.13 × 10-5 item/m2 to 2.79 item/m2 in the coastal regions worldwide, showing significant geographical variations. Besides, the emerging contaminants released from PPE into the coastal and marine environments cannot be neglected. The positive influence was that the COVID-19 lockdown worldwide reduced the release of air pollutants (e.g., fine particulate matter, NO2, CO, and SO2) and improved the air quality. The study also analyzed the relationships between sustainable development goals (SDGs) and the publications and revealed the dynamic changes of SDGs in different periods the COVID-19 pandemic. In conclusion, the air was cleaner due to the lockdown, but the coastal and marine contamination of plastic, microplastic, and emerging contaminants got worse during the COVID-19 pandemic. Last but not least, the study proposed four strategies to deal with the coastal and marine pollution caused by COVID-19, which were regular marine monitoring, performance of risk assessment, effective regulation of plastic wastes, and close international cooperation.

Impacts of autochthonous dissolved organic matter on the accumulation of methylmercury by phytoplankton and zooplankton in a eutrophic coastal ecosystem

The bioaccumulation of methylmercury (MeHg) within the pelagic food webs is a crucial determinant of the MeHg concentration in the organisms at higher trophic levels. Dissolved organic matter (DOM) is recognized for its influence on mercury (Hg) cycling in the aquatic environment because of its role in providing metabolic substrate for heterotrophic organism and serving as a strong ligand for MeHg. However, the impact of DOM on MeHg bioaccumulation in pelagic food chains remain controversial. Here, we explored MeHg bioaccumulation within a pelagic food web in China, in the eutrophic Bohai Sea and adjacent seas, covering a range of DOM concentrations and compositions. Our findings show that elevated concentrations of dissolved organic carbon (DOC) and phytoplankton biomass may contribute to a reduction in MeHg uptake by phytoplankton. Moreover, we observe that a higher level of autochthonous DOM in the water may result in more significant MeHg biomagnification in zooplankton. This can be explained by alterations in the structure of pelagic food webs and/or an increase in the direct consumption of DOM and particulate organic matter (POM) containing MeHg. Our study offers direct field monitoring evidence of dual roles played by DOM in regulating MeHg transfers from water to phytoplankton and zooplankton in coastal pelagic food webs. A thorough understanding of the intricate interactions is essential for a more comprehensive evaluation of ecological risks associated with MeHg exposure in coastal ecosystems.

Microplastics (≤ 10 μm) bioaccumulation in marine sponges along the Moroccan Mediterranean coast: Insights into species-specific distribution and potential bioindication

Microplastics (MPs) are pervasive in marine environments and widely recognized as emerging environmental pollutants due to the multifaceted risks they exert on living organisms and ecosystems. Sponges (Phylum Porifera) are essential suspension-feeding organisms that may be highly susceptible to MPs uptake due to their global distribution, unique feeding behavior, and sedentary lifestyle. However, the role of sponges in MP research remains largely underexplored. In the present study, we investigate the presence and abundance of MPs (≤10 μm size) in four sponge species, namely Chondrosia reniformis, Ircinia variabilis, Petrosia ficiformis, and Sarcotragus spinosulus collected from four sites along the Mediterranean coast of Morocco, as well as their spatial distribution. MPs analysis was conducted using an innovative Italian patented extraction methodology coupled with SEM-EDX detection. Our findings reveal the presence of MPs in all collected sponge specimens, indicating a pollution rate of 100%. The abundance of MPs in the four sponge species ranged from 3.95×105 to 1.05×106 particles per gram dry weight of sponge tissue, with significant differences observed among sampling sites but no species-specific differences. These results imply that the uptake of MPs by sponges is likely influenced by aquatic environmental pollution rather than the sponge species themselves. The smallest and largest MPs were identified in C. reniformis and P. ficiformis, with median diameters of 1.84 μm and 2.57 μm, respectively. Overall, this study provides the first evidence and an important baseline for the ingestion of small MP particles in Mediterranean sponges, introducing the hypothesis that they may serve as valuable bioindicators of MP pollution in the near future.

Spatial distribution of polystyrene nanoplastics and small microplastics in the Bohai Sea, China

Micro- and nano-plastic (MNP) pollution has attracted public concerns. Currently, most environmental researches focus on large microplastics (MPs), while small MNPs that have great impacts on marine ecosystems are rarely reported. Understanding the pollution levels and distribution patterns of small MNPs could help assess their potential impacts on the ecosystem. Polystyrene (PS) MNPs were often used as models to assess their toxicity, hence, we collected 21 sites in a Chinese sea area (the Bohai Sea) to analyze their pollution level and horizontal distribution in surface water samples, and vertical distributions in five sites with the water depth >25 m. Samples were filtered by glass membranes (1 μm) to trap MPs, which were frozen, ground, dried, and detected by pyrolysis-gas chromatography-mass spectrometry (pyGC-MS); while the nanoplastics (NPs) in the filtrate were captured with alkylated ferroferric oxide (Fe₃O₄) to form aggregates, which were separated by glass membrane (300 nm) filtration for pyGC-MS determination. Small PS MPs (1-100 μm) and NPs (<1 μm) were detected in 18 samples with the mass concentrations ranging from <0.015 to 0.41 μg/L, indicating that PS MNPs are widely present in Bohai Sea. Our study contributes to understanding the pollution levels and distribution patterns of MNPs (<100 μm) in the marine system and provides valuable data for their further risk assessment.

N6-methyladenosine methylation mediates non-coding RNAs modification in microplastic-induced cardiac injury

Owing to their potential adverse health effects, global contamination by microplastics (MPs) has attracted increased scientific and societal concerns. However, in vivo studies on MP toxicity, along with its effects and underlying mechanisms, remain limited. We recently found that non-coding RNA (ncRNAs) contribute to MP-mediated vascular toxicity. Moreover, previous studies have identified N6-methyladenosine (m6A) modifications in ncRNAs as influencing factors in cardiovascular disease. However, whether and how m6A modifications in ncRNAs are affected by MP-induced cardiotoxicity remain unknown. Herein, we profiled differentially expressed ncRNAs and their related m6A modification profiles in MP-exposed myocardial tissue using RNA sequencing (RNA-seq) and methylated RNA immunoprecipitation sequencing (MeRIP-seq). First, we observed that MPs accumulated in different organs and upregulated apoptosis in the heart, liver, spleen, and kidney cells. Furthermore, total m6A and METTL3 levels increased in the myocardium after exposure to MPs. RNA-seq results revealed that 392 lncRNAs and 302 circRNAs were differentially expressed in MP-treated mouse myocardium compared to the control group. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses showed that these altered lncRNAs and circRNAs were closely associated with endocytosis, cellular senescence, and cell cycle signaling pathways, which may cause cardiotoxicity. Furthermore, MeRIP-seq data showed different distributions and abundances of m6A modifications in lncRNAs and circRNAs. Additionally, we identified differentially m6A methylated lncRNAs and circRNAs through conjoint analysis of the two high-throughput sequencing datasets and found that both m6A modifications and the expression of circ-Arfgef2 and lncG3bp2 were upregulated after exposure to MPs. This suggests that MP-induced m6A modifications in ncRNAs are involved in cardiotoxicity. Our findings contribute to a better understanding of MP-induced cardiotoxicity and new molecular targets for treating cardiac injury.

Recent trends on microplastics abundance and risk assessment in coastal Antarctica: Regional meta-analysis

We investigated sources, abundance and risk of microplastics (MPs) in water, sediments and biota around Antarctica. The concentration of MPs in Southern Ocean (SO) ranged from 0 to 0.56 items/m³ (mean = 0.01 items/m³) and 0-1.96 items/m³ (mean = 0.13 items/m³) in surface and sub-surface water. The distribution of fibers in water was 50%, sediments were 61%, and biota had 43%, which were followed by fragments in the water (42%), sediments (26%), and biota (28%). Shapes of film had lowest concentrations in water (2%), sediments 13%), and biota (3%). Ship traffic, drift of MPs by currents, and untreated waste water discharge contributed to the variety of MPs. The degree of pollution in all matrices was evaluated using the pollution load index (PLI), polymer hazard index (PHI), and potential ecological risk index (PERI). PLI at about 90.3% of locations were at category I followed by 5.9% at category II, 1.6% at category III, and 2.2% at category IV. Average PLI for water (3.14), sediments (6.6), and biota (2.72) had low pollution load (<10). Mean PHI for water, sediments, and biota showed hazards level V with a higher percentage of 84.6% (>1000) and 63.9% (PHI:0-1) in sediments and water, respectively. PERI for water showed 63.9% minor risk, and 36.1% extreme risk. Around 84.6% of sediments were at extreme risk, 7.7% faced minor risk, and 7.7% were at high risk. While 20% of marine organisms living in cold environments experienced minor risk, 20% were in high risk, and 60% were in extreme risk. Highest PERI was found in the water, sediments, and biota in Ross Sea, due to high hazardous polymer composition of polyvinylchloride (PVC) in the water and sediments due to human activity, particularly use of personnel care products and waste water discharge from research stations.

Transcriptome-wide m6A modification mediates cardiotoxicity in mice after chronic exposure to microplastics

The widespread presence of microplastics (MPs) has garnered attention owing to their possible adverse effects. However, the cardiotoxicity of MPs and their underlying mechanism remains unclear. N6-methyladenosine (m6A) modification contributes to post-transcriptional modulation of gene expression, but whether this modification is relevant to MP-induced cardiotoxicity is unknown. First, we detected damage to the myocardial tissue among MP-exposed and -unexposed (control) mice by staining them with hematoxylin and eosin, Masson trichrome, and Oil Red O. Then, we comprehensively measured the transcriptome-wide m6A methylome and m6A-altered genes using high-throughput sequencing assays, such as methylated RNA immunoprecipitation sequencing and RNA sequencing. Our data indicated MP-induced myocardial inflammatory injury and histological alterations in vivo, evidenced by the severity of cardiac fibrosis and increased lipid accumulation. We found 878 increased and 316 decreased methylation peaks mostly distributed in the 3' UTR among the MP-exposed group compared with the control group. We found 779 upregulated and 340 downregulated genes in the MP-exposed group. In addition, conjoint analysis of results from the two high-throughput sequencings showed that 109 and 11 hypermethylated genes were upregulated and downregulated, respectively; 12 and 21 hypomethylated genes were upregulated and downregulated, respectively. Results of the cross-link analysis showed that several potential signals, such as ECM-receptor interactions, cell adhesion molecules, cytokine-cytokine receptor interactions, and NF-κB signaling, contributed to MP-induced cardiotoxicity. Our findings indicated that m6A modifications of genes were involved in MP-induced cardiotoxicity and reported new information regarding the chronic cardiotoxicity caused by MP exposure in mice.

Occurrence, geochemical characteristics, enrichment, and ecological risks of rare earth elements in sediments of "the Yellow river-Estuary-bay" system

Recent studies have suggested that rare earth elements (REEs) are contaminants of emerging concern. Moreover, the understanding of the occurrence and risks of REEs in river-estuary-bay systems is limited. The present study investigated the distributions, geochemical characteristics, and ecological risks of Y and 14 REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) in sediments from the Yellow River to its estuary and adjacent Laizhou Bay. The average total concentrations of Y and REEs in the sediments generally increased from the Yellow River (149 mg/kg) to the estuary (165 mg/kg) and Laizhou Bay (173 mg/kg). In the estuarine core sediments, the concentrations of Y, light REEs (LREEs), and heavy REEs (HREEs) were in the ranges of 19.5-31.4 mg/kg, 58.6-156 mg/kg, and 12.3-19.1 mg/kg, respectively, from the 1700s to 2018, showing no obvious increasing or decreasing trends. The surface and core sediments from the river to the bay were characterized by obvious fractionation between LREEs and HREEs. In sediments, Fe minerals and clay are believed to promote the accumulation of REEs, especially HREEs. The enrichment levels of REEs generally increased from the middle reaches of the Yellow River to the bay, and Gd, Tb, Dy, Ho, Yb, and Lu were the most enriched elements in the sediments. Lu had moderate potential ecological risks in sediments of "the Yellow River-estuary-bay" system, and other REEs had relatively low ecological risks. The potential ecological risk indices of Y and REEs ranged from 78.7 to 144, showing increasing trends from the Yellow River to its estuary and adjacent bay, which should raise concerns regarding emerging contaminant management around estuarine and coastal regions.

The occurrence, speciation, and ecological effect of plastic pollution in the bay ecosystems

Bay is a unique part of the ecosystem, acting as the intersection for marine and terrestrial systems and hosting diverse biological organisms. The ubiquitous application of plastics has resulted in a massive amount of plastic waste released and accumulated in the bay ecosystem, posing significant ecological effects. Thus, thoroughly understanding plastic pollution's occurrence, speciation, and ecological effect in the bay ecosystems is of vital importance. We conducted a comprehensive review on the sources and distribution of plastics in the bay ecosystem, and the associate ecological effects, from individual toxicity to trophic transfer in ecosystems. Among bay areas around the world, the concentrations of microplastics vary from 0.01 to 3.62 × 10⁵ item/m³ in seawater and 0 to 6.75 × 10⁵ item/kg in sediment. Small-sized plastic particles (mostly <2 mm) were widely reported in bay organisms with the concentration range of 0 to 22.5 item/ind. Besides, the toxicity of plastics on marine organisms has been documented in terms of mortality, growth, development, reproduction, enzyme activity and transcription. Since abundance of small plastic particles (e.g., micro- and nano-scale) is far greater than large plastic debris in the bay ecosystems, in-depth risk assessment of small-sized plastics needs to be conducted under environmentally realistic conditions. Our review could provide a better understanding on the occurrence, speciation, and ecological effect of plastic pollution in the bay ecosystems.