Urban wetlands serve a variety of healthful roles in cities, including as 'sponges' that absorb potential flood waters, leisure spaces for people and habitat for many species. However, urban wetlands also receive contaminated surface runoff and may become reservoirs of harmful contaminants, including related to our earlier efforts to safeguard health. Antibiotics are a public health mainstay, but overuse has promoted the spread among bacteria of genes enabling them to survive treatment. Here, by collecting and analyzing samples from 17 urban wetlands across China and comparing them with global datasets from natural lakes and urban raw sewage, we find these urban wetlands to be hotspots of antibiotic resistance genes (ARGs), with average abundances about nine times higher than in natural lakes and comparable to that in raw urban sewage. We further discover both human bacterial pathogens and indicators of the potential transfer of ARGs among bacteria ('horizontal transfer'), suggesting viruses in urban wetlands carrying ARGs might facilitate their spread within bacterial communities there. We also find higher levels of economic development associated with lower ARG abundances, suggesting socioeconomic factors could also shape the geographical distribution of ARGs in urban wetlands, perhaps through associated improvements in sewer systems. These findings emphasize the importance of collecting and treating stormwater before its release into urban wetlands to safeguard wildlife and human health.

Retinoic acids (RAs) and their oxidative metabolites (i.e., 4-oxo-RAs) are teratogenic to aquatic animals at elevated levels, while their toxic mechanisms in invertebrates remain largely unknown. This study aimed to determine whether marine microalgae could release RAs and 4-oxo-RAs, and to elucidate their toxic mechanisms to the marine copepod Tigriopus japonicus using transcriptomics. We observed elevated levels of RAs and 4-oxo-RAs in natural coastal seawater during algal blooms, and their releases from microalgae. A 21-day chronic exposure experiment showed that the widely distributed all-trans-RA (at-RA), at environmentally relevant concentrations (including worst-case scenarios, i.e., 10-2400 ng/L), delayed molting and development in both nauplius and copepodite stages of the copepod, with significant correlations between at-RA concentrations and developmental times. Transcriptomic analyses suggested that the toxic mechanisms may involve the down-regulation of calcium and nitric oxide synthase signaling in the cyclic guanosine monophosphate pathway by at-RA, leading to excessive formation of ecdysteroid binding to its receptor and thereby disrupting the normal ecdysis process. This was further supported by the over-expression of genes related to the ecdysteroid receptor and its heterodimer ultraspiracle, as well as by increased 20-hydroxyecdysone content in exposed copepods. Such new discoveries advance our understanding of the ecotoxicity of RAs, particularly in aquatic ecosystems that suffer from eutrophication and frequent algal blooms.

Microplastics (MPs) are widely distributed in aquatic environments, raising global concerns. However, determining their toxic effects on aquatic organisms and deriving water quality criteria (WQC) for hazardous substances remain challenging due to the heterogeneity of existing toxicity data. Additionally, acquiring sufficient data requires substantial resources. This study proposes a machine learning framework to predict the aquatic toxicity of five types of MPs. Three machine learning algorithms, k-nearest neighbors (kNN), support vector machine (SVM), and random forest (RF), were used to develop quantitative structure-toxicity relationships and derive site-specific WQC from predicted toxic end points. The RF model outperformed kNN and SVM in predictive accuracy after both internal and external validation. SHAP analysis revealed that particle size, density, and aquatic group accounted for 72% of the variability in the predictions. Polystyrene and polyethylene terephthalate exhibited significant toxicity in both freshwater and saltwater, with MPs being more toxic in freshwater. These findings highlight the need for site-specific WQC to protect aquatic ecosystems and improve ecological risk assessments of emerging contaminants.

Vertical seawalls are extensive and rapidly expanding in coastal cities and ports but provide inadequate habitat for intertidal fauna and flora as they lack necessary refugia from heat and desiccation stresses, lowering intertidal biodiversity. Ecological engineering through retrofitting suitable habitats aims to promote marine biodiversity through habitat provision. Two eco-engineered panel designs with augmented habitat complexity were tested on a seawall in a highly developed subtropical marina. One panel was commercially available, with a repetitive pattern of short extrusions - the Imported Commercially Available Design (ICAD). The other was a locally designed, double-sided panel with deep intrusions and shade behind the panel - the Hong Kong Design (HKD). Taxonomic richness of the intertidal fauna and flora on the panels were compared to flat, concrete panels (flat panel, representing a worst-case scenario) and scraped seawall plots (seawall control) for 18 months. Marine biodiversity on both eco-engineered panels was significantly higher than the flat concrete panels, and the HKD was colonised by the highest taxonomic richness (64 total taxa). The HKD had greater abundance of suspension feeders, higher richness within key functional groups, and enabled colonisation at higher tidal levels compared to the flat panel and seawall control. When compared to nearby vertical seawalls, the HKD and ICAD contributed to an increased within-site β diversity and functional diversity. These results imply that implementing similar eco-engineering of grey infrastructure while reducing other anthropogenic stressors can contribute to the aim of creating biodiverse intertidal ecosystems within coastal cities and ports.

Estuaries, where upstream freshwater tributaries converge with marine systems, serve as accumulation hotspots for anthropogenic pollutants. With rising antibiotic usage, concerns over their hazardous impacts in estuaries are growing. Risk reduction and management strategies for pollutants rely on water quality benchmarks. However, saltwater benchmarks for antibiotics are lacking due to insufficient saltwater ecotoxicity data for constructing species sensitivity distribution (SSD) models. This study evaluated the ecotoxicity of four prevalent antibiotics (tetracycline, oxytetracycline, trimethoprim and norfloxacin) on eight saltwater species, generating new data to derive robust saltwater predicted no-effect concentrations (PNECs) using SSDs. Their ecological risks in global estuaries were also assessed. Results revealed that the four algal species were sensitive to tetracycline, oxytetracycline and trimethoprim (EC50: 8.34 - 30.13 mg/L), but showed low sensitivity to norfloxacin. The rotifer and copepod species showed varied sensitivities (LC50: 7.24 - 139.10 mg/L), while the fish species was tolerant to all four antibiotics. Hazard rankings based on derived chronic saltwater PNECs were: oxytetracycline (PNEC: 0.05 mg/L) > trimethoprim (0.07 mg/L) > tetracycline (0.08 mg/L) > norfloxacin (0.09 mg/L). Although ecological risk assessments indicated very low risk from these antibiotics in most global estuaries, a limited number of estuaries (n = 15) primarily in Asia and Africa showed risks ranging from low to medium. This study provides essential saltwater ecotoxicity data for establishing interim saltwater quality criteria for four broadly applied antibiotics and offers a timely overview of their ecological risks in estuaries worldwide, supporting the risk management of antibiotic contamination in global estuaries.

Marine protected areas (MPAs) have been established worldwide to protect biodiversity and enhance ecosystem services. Rare species play vital roles in marine conservation as they exhibit unique ecosystem functions and are vulnerable to extinction. However, determining their importance to conservation effects remains challenging due to the lack of feasible and standardized evaluation methods. The noninvasive environmental DNA (eDNA) method is increasingly used in marine biomonitoring because of its efficiency and sensitivity. Hill numbers provide a uniform evaluation scheme for assessing biodiversity. In this study, we calculated Hill numbers from eDNA data to determine marine fish diversity in MPAs. Traditional survey data and different bioinformatic clustering pipelines were also included to decide the impact of survey and analysis methods on ecological interpretation. The results showed that eDNA detected significantly more species than contemporaneous traditional survey data. We further found less significant inter-group differences for different seasons and pipelines when rare species diminished, indicating that excluding rare species in evaluations could affect the ecological interpretation of marine conservation effects. Protection time of MPAs demonstrated positive correlations with all diversity indices, albeit not statistically significant. In conclusion, we demonstrated the importance of rare species in marine biodiversity assessment and recommend appropriate usage of eDNA and downstream diversity indices to achieve a comprehensive evaluation of the marine conservation effect of MPAs.

Oyster reef restoration faces increasing demand for cost-effective and ecologically functional substrates, particularly in regions with abundant oyster shell waste. This study proposes a modular ecological concrete cube composed of recycled oyster shells (as coarse aggregate) and Portland cement, excluding fine aggregates, to evaluate whether this material can deliver sufficient mechanical strength and ecological performance for reef restoration, while reducing cost and promoting sustainability. We suspended ecological concrete cubes (100 × 100 × 100 mm) beneath oyster-culture rafts at 1.5 m depth in Maowei Bay, China, for one year, testing five oyster shell grain size groups (<1 cm to >4 cm) and a cement-only reference. Results showed that compressive strength declined with increasing shell grain size, ranging from 32.45 ± 3.17 MPa (<1 cm) to 0.58 ± 0.27 MPa (>4 cm), while porosity increased from 4.76 ± 0.73% to 54.99 ± 1.49%, indicating a strength-porosity trade-off. All cubes remained intact after one year of field deployment. Ecologically, pure cement cubes surpassed shell-containing concretes in oyster biomass (47.89 ± 5.43 g) and surface coverage (33.89 ± 8.08%) by the end of 12 months of deployment, likely due to surface roughening from biogenic deposition. In contrast, cubes with >2 cm shell aggregates showed the highest Shannon-Wiener biodiversity index (up to 0.55), attributed to enhanced microhabitat complexity and porosity. These findings suggest that crushed oyster shells are a feasible material for producing ecological concrete for oyster reef restoration and biodiversity enhancement. Smaller shell sizes (<2 cm) support rapid oyster colonization, while larger sizes (>2 cm) enhance biodiversity. This approach offers a scalable strategy for resource recycling and functional habitat creation in coastal environments.

Halogenated organic compounds (HOCs) are ubiquitous in marine environments, while photochemical halogenation of autochthonous dissolved organic matter (DOM) is considered the principal source of natural HOCs in surface seawater. Microplastics (MPs), as carbon-rich polymers, can release abundant DOM that may serve as exogenous precursors for photohalogenation, yet the formation mechanisms, molecular traits, and implications of MP derived-HOCs (MP-HOCs) in marine systems remain unclear. Herein, we conducted 180-day artificial weathering experiments in sunlit seawater using polyethylene, polypropylene, and polystyrene as models, investigating the molecular signatures of MP-HOCs. Ultrahigh-resolution mass spectrum yielded a total of 2768 unique HOC formulas in various MP leachates. Electron paramagnetic resonance and molecular network analyses indicated recombination with carbon-centered radicals (e.g., •CH3) induced by halogen radicals (e.g., •X) as the potential mechanism for MP-HOC formation. Comparison between MP-HOCs and naturally occurring aquatic HOCs in the Yangtze River Estuary (YRE-HOCs) revealed an overlap of 296 formulas, accounting for 59% of YRE-HOCs. Notably, there was still ~90% of HOC formulas that were unique to MP leachates, showing higher aliphatic/proteins-like composition (40% vs 15%) but lower oxygen-to‑carbon ratio (0.38 vs 0.42) and molecular weight (399 vs 462 Da) than YRE-HOCs. Furthermore, MP-HOCs exhibited longer potential biochemical transformation times and greater hydrophobicity and biotoxicity compared with non-HOCs based on the molecular-predicted results, which might affect marine ecosystem functions. This work provides the first systematic molecular fingerprints of MP-HOCs in sunlit seawater, demonstrates their significant contribution to the oceanic HOC pool, and offers a new perspective on the marine ecological effects of global plastic pollution.

Initial success has been achieved in Hong Kong in controlling primary air pollutants, but ambient ozone levels kept increasing during the past three decades. Volatile organic compounds (VOCs) are important for mitigating ozone pollution as its major precursors. This study analyzed VOC characteristics of roadside, suburban, and rural sites in Hong Kong to investigate their compositions, concentrations, and source contributions. Here we show that the TVOC concentrations were 23.05 ± 13.24, 12.68 ± 15.36, and 5.16 ± 5.48 ppbv for roadside, suburban, and rural sites between May 2015 to June 2019, respectively. By using Positive Matrix Factorization (PMF) model, six sources were identified at the roadside site over five years: Liquefied petroleum gas (LPG) usage (33–46%), gasoline evaporation (8–31%), aged air mass (11–28%), gasoline exhaust (5–16%), diesel exhaust (2–16%) and fuel filling (7–9%). Similarly, six sources were distinguished at the suburban site, including LPG usage (30–33%), solvent usage (20–26%), diesel exhaust (14–26%), gasoline evaporation (8–16%), aged air mass (4–11%), and biogenic emissions (2–5%). At the rural site, four sources were identified, including aged air mass (33–51%), solvent usage (25–30%), vehicular emissions (11–28%), and biogenic emissions (6–12%). The analysis further revealed that fuel filling and LPG usage were the primary contributors to OFP and OH reactivity at the roadside site, while solvent usage and biogenic emissions accounted for almost half of OFP and OH reactivity at the suburban and rural sites, respectively. These findings highlight the importance of identifying and characterizing VOC sources at different sites to help policymakers develop targeted measures for pollution mitigation in specific areas.

The rising concentrations of xenobiotic aromatic compounds in the environment pose significant risks to human and ecosystem health. Developing a universal, environmentally benign, and scalable platform for mineralizing organic pollutants before their release into the environment is therefore crucial. Electrocatalysis can be highly advantageous for wastewater treatment because it is immediately responsive upon applying potential, requires no additional chemicals, and typically uses heterogeneous catalysts. However, achieving efficient electrochemical mineralization of wastewater pollutants at parts-per-million (ppm) levels remains a challenge. Here, we report the use of manganese dioxide (MnO2), an Earth-abundant, chemically benign, and cost-effective electrocatalyst, to achieve over 99 % mineralization of triclosan (TCS) and other halogenated phenols at ppm levels. Two highly active MnO2 phases-α-MnO2-CC and δ-MnO2-CC-were fabricated on inexpensive carbon cloth (CC) support and evaluated for their ability to oxidatively degrade TCS in pH-neutral conditions, including simulated chlorinated wastewater, real wastewater, and both synthetic and real landfill leachates. Total organic carbon analysis confirmed the effective degradation of TCS. Electron paramagnetic resonance and ultraviolet-visible spectroscopy identified reactive oxygen species, enabling the construction of a detailed TCS degradation pathway. Upon optimization, the TCS removal rate reached 38.38 nmol min-1, surpassing previously reported rates achieved with precious and toxic metal co-catalysts. These findings highlight MnO2-CC as a promising, eco-friendly electrocatalyst with strong potential for upscaled remediation of organic pollutants in wastewater treatment.

Microplastics are well-known emerging pollutants in aquatic environments, increasingly shown to release significant amounts of non-natural dissolved organic matter (DOM) into water systems. However, the molecular composition of DOM leached from different types of microplastics after long-term photochemical aging, and their impact on the aquatic carbon cycle, remain poorly understood. The potential presence and contribution of microplastic-derived DOM to the river-to-ocean continuum on a large scale have yet to be well-established. Using ultra-high-resolution Fourier-transform ion cyclotron resonance mass spectrometry, this study identified 155, 152, and 465 DOM molecules released from microplastics of polypropylene, polyethylene, and polystyrene, respectively, showing high potential for accumulation after 180 days of ultraviolet exposure. These molecules were subsequently detected in an extensive DOM dataset comprising 947 natural water samples, with an average detection frequency of 64.6 %. Polystyrene-derived DOM molecules exhibit a strong resemblance to natural refractory DOM at the molecular level, suggesting its potential contribution to the long-term carbon pool. In contrast, polypropylene- and polyethylene-derived DOM molecules indicate more biologically labile structures that favor short-term carbon cycling. These findings emphasize the varying impacts of different microplastic types on carbon cycling, with polystyrene-derived DOM potentially contributing to refractory carbon pools and broader climate implications.

Bisphenol A (BPA) is a commonly used endocrine-disrupting chemical found in high levels in wastewater worldwide. Aerobic denitrification is a promising alternative to conventional nitrogen removal processes. However, the effects of BPA on this novel nitrogen removal process have rarely been reported. Herein, we investigated the removal and interaction effects of BPA (0, 0.1, 1, and 10 mg/L) in aerobic denitrifying cultures. Our experimental results demonstrated that the aerobic denitrification system could remove 66%-86% of BPA from wastewater. Fourier transform infrared spectroscopy revealed that polysaccharides and amides were the primary sites for adsorption. An increase in the type and number of intermolecular hydrogen bonds might enhance the ability of aerobic denitrifying cultures to adsorb BPA. Adsorption kinetics analysis demonstrated that inhomogeneous multilayer adsorption was the leading cause of BPA removal. Adsorbed BPA decreased the sedimentation, flocculation, and hydrophobicity of aerobic denitrifying cultures, triggering changes in the levels of proteins and polysaccharides in extracellular polymeric substances. As the influent BPA increased from 0 to 10 mg/L, the nitrate-nitrogen and total organic carbon in the reactor effluent increased from 0.4 f 0.2 and 26 f 7.9 mg/L to 18.8 f 9.3 and 116.2 f 55.6 mg/L, respectively. BPA (initial concentration range: 1-10 mg/L) significantly influenced the abundance of genes involved in the nitrogen transformation pathway, contributing to the increase in the abundance of gaseous NOx-transformed genes and altering the relative abundance of denitrifying bacteria, particularly Thauera. Correlation analyses revealed that Pseudomonas, Thauera, and AKYH767 are important for maintaining systemic nitrogen transformations and BPA adsorption.

Rubber-derived chemicals (RDCs), which include rubber additives (RAs) and their transformation products (TPs), can be released into aquatic environments when rubber products, such as vehicle tires, are in use or discarded. However, RDCs and associated ecological risks have not been thoroughly investigated inside urban sewer networks and their receiving water bodies. To address these issues, we investigated the RDCs in Hong Kong's municipal sewer networks, including sewage and stormwater, as well as their receiving waters, such as rivers and coastal water. Among 45 target RDCs, the vulcanizing agents and corrosion inhibitors were found to be predominant in the water samples, accounting for 26-66 % and 29-72 % of total concentrations of 45 RDCs (∑45RDC), respectively, while antioxidants and their TPs presented in smaller quantities, accounting for 0.21-26 % and 0-15 % of ∑45RDC, respectively. Ten RAs from five classes were additionally identified by suspect screening. An estimated mass load of ∑45RDC amounting to 1690 kg/month is discharged into the coastal marine environment of Hong Kong, with sewage effluent being the primary source. Population density and vehicle-related factors (e.g., traffic load) were the major drivers shaping the spatial distribution of RDCs in surface water. Based on the ecological risk assessment outcomes, 16 out of 45 RDCs exhibited medium to high risks, and lists of candidate contaminants for various water bodies were proposed to support future risk management in water quality. These findings suggest that RDCs in stormwater and rivers should be carefully monitored, and management strategies should be developed to mitigate their risks.

Microplastics (MPs) widely pollute marine environments, where the release of MPs-derived dissolved organic matter (MPs-DOM) induced by UV irradiation has been widely documented. However, the effect of MPs' inherent properties on photochemical transformation of MPs-DOM and its implication for oceanic carbon cycles remain poorly understood. Herein, we conducted 180 day artificial weathering experiments under sunlit seawater using polyethylene (PE) and polypropylene (PP) with different sizes as models, investigating the temporally dynamic features of MPs-DOM. Results showed that PP can release more MPs-DOM than PE, and concentrations of MPs-DOM derived from small-sized MPs (∼250 μm) were 2-6 times higher than those of large-sized MPs (∼5 mm). Spectroscopy and ultrahigh-resolution mass spectrum further revealed that protein-like substances can be persistently produced from MPs with lower photochemical activity (i.e., PE and large-size PP), while DOM derived from MPs with higher photochemical activity (i.e., small-size PP) could be gradually transformed from biolabile components to biorecalcitrant molecules. Furthermore, the persistently accumulated molecules were matched and projected onto an aquatic DOM database, and their relative intensity exhibited a gradually increasing trend across the river-to-ocean continuum at the molecular level. This work reveals the structure-reactivity relationships for MPs-DOM transformation and highlights MPs' potential impact in marine organic carbon cycles.

Chlorinated paraffins (CPs) readily deposit in sediments upon entering estuaries and adjacent seas. Time-series investigations are indispensable for the long-term monitoring of historical releases and identifying CPs of emerging concerns in the marine environment. In this study, short-, medium-, and long-chain CPs (SCCPs, MCCPs, and LCCPs) were investigated using time-of-flight high-resolution mass spectrometry (ToF-HRMS) in sediment cores, dated between the 1920s and the 2010s sampled from Hong Kong waters and Lingdingyang of the Pearl River Estuary (PRE), South China. Levels of SCCPs remained steady since the 1980s, while increasing trends of MCCPs and LCCPs were observed, indicating a market supply shift from SCCPs to MCCPs and LCCPs, potentially influenced by global restrictions. This is the first study to report C18-31 CPs in Chinese marine sediments. C>20 very long-chain CPs (C>20 vLCCPs) subcategorized from LCCPs were semi-quantified via ToF-HRMS and positively correlated with those of other CP categories, implying their synchronized release in the investigated regions. C>20 vLCCPs, contributing an average of 27% of total CP concentrations in two cores, were found at higher levels than LCCPs (7%). Hence, the risk of C>20 vLCCP contamination should not be ignored. By highlighting the temporal variations in the world's largest producer and consumer of CPs, the present study augments the database of the continuous deposition of SCCPs and MCCPs in marine sediments in the PRE and highlights the unrecognized risks of LCCP contaminations.

Environmental communication effectively influences environmental intentions, yet its ability to translate these intentions into actual behavior changes remains understudied, especially in coastal ecological engineering contexts. This study investigates this potential inconsistency by employing the intention-behavior gap concept and examining the impact of four distinct informational interventions: social pressure, negative framing, positive framing, and emotion. Based on a between-subject experiment and the data from 5258 participants, our findings revealed that information conveying social pressure, positive framing, and emotional appeals significantly increased participants' intentions in comparison to the control group. However, none of the information interventions significantly affected actual behavior in support of ecological engineering. Consequently, social pressure, positive framing, and emotion information slightly yet significantly enlarge the intention-behavior gap. Additionally, our results suggest that positive framing surpasses negative framing in eliciting supportive intentions for ecological engineering. Finally, different types of past behaviors appear to influence subsequent actions through different mechanisms.

Acute exposure studies have reported that chemical speciation significantly affects the developmental toxicity of perfluoroalkyl acids (PFAAs). However, the mechanisms underlying the chronic toxicity of PFAAs as a function of chemical speciation remain unknown. With an aim to gain more insights into the PFAA structure-toxicity relationship, this study exposed adult zebrafish to the acids and salts of perfluorooctanoate (PFOA), perfluorobutanoate (PFBA), and perfluorobutanesulfonate (PFBS) at environmentally realistic concentrations for 5 months. In the F0 generation, PFAA acids induced hypothyroidism symptoms more potently than their salt counterparts. After parental exposure, a chemical speciation-dependent transfer behavior was noted, with a greater burden of PFAA acids in the offspring. Similarly, PFAA acids were associated with higher risks of transgenerational defects and thyroid dysfunction during offspring embryogenesis. PFAA acids bound to thyroid receptor beta (TRβ) more strongly than their salts. An antagonistic interaction of PFOA and PFBS with TR activity was observed in vitro via the reduction of TRβ accessibility to target genes. CUT&Tag sequencing revealed disturbances due to PFAAs on the genomic target profile of TRβ, indicating that PFOA and PFBS interfere with multiple thyroidal and nervous processes. In conclusion, current findings provided evidence regarding the critical effects of chemical speciation on PFAA toxicity, highlighting the need to perform discriminative risk assessment and chemical management.

National Aquatic Germplasm Resources Reserves (NAGRRs) are pivotal protected areas in delivering ecological and socio-economic advantages. This study focuses on three NAGRRs in the South China Sea, meticulously examining the pollution levels of 31 common endocrine-disrupting chemicals (EDCs) within these protected areas and their surrounding coastal areas. The highest cumulative concentrations in the dissolved phase, suspended particulate matter (SPM) phase, and surface sediment were recorded at 280.59 ng/L in the dry season, 192.89 ng/L in the wet season, and 411.89 ng/g dry weight in the dry season, respectively. The log KD-SED (2.17-5.49 in the wet season and 2.51-5.50 in the dry season) were relatively lower than log KD-SPM (3.21-6.09 during the wet season and 3.79-5.75 during the dry season), suggesting a higher likelihood of EDC distribution to the SPM than surface sediment. The sum of five estradiol equivalent concentrations in the waters of the coastal and protected areas significantly surpassed the threshold for endocrine-disrupting activity, suggesting that the targeted estrogens in these regions may potentially disrupt the endocrine systems of aquatic organisms. Norgestrel, 17 alpha-ethinylestradiol, 4-tert-octylphenol, bisphenol A, bisphenol B, and bisphenol F were pinpointed as pollutants necessitating urgent concern due to their ecological risks and detection frequencies. These research findings provided valuable insights into the effective management and remediation of emerging pollutants within NAGRRs, thereby contributing to strengthening their protection and biodiversity conservation.

Per- and polyfluoroalkyl substances (PFAS) are synthetic long-lasting chemicals. Marine sediment is a major repository for PFAS in the environment; accordingly, this work investigated 45 legacy and emerging PFAS in samples of surface sediments and sediment cores (1940s-2020s) collected in the Pearl River outlets, its estuary, and the adjacent northern South China Sea (NSCS), one of the global pollution hotspots. The range of total PFAS concentrations in surface sediments from the river outlets and the NSCS was 244-14400 pg/g dry weight (dw) and 31.6-363 pg/g dw, respectively. In sediment cores, perfluorooctanesulfonate (PFOS) concentrations initially increased and then declined around ten years ago. Levels of long-chain perfluorinated carboxylates have been increasing since the 1980s and experienced an accelerated rise in the 2000s. Hydrogen-substituted polyfluoroalkyl ether sulfonate (H-PFESA) was widely found in sediment samples for the first time. The ratios of 6:2 H-PFESA to 6:2 chlorinated (Cl-) PFESA in sediment cores exceeded those in surface sediment and exhibited an increasing trend with the sediment age, implying the gradual transformation of 6:2 Cl-PFESA to its hydrogen-substituted analog in sediments. A preliminary risk assessment indicated that ∑6:2 PFESAs and PFOS posed medium to high risks over recent decades.