Legacy and Emerging Per- and Polyfluoroalkyl Substances Behave Distinctly in Spatial Distribution and Multimedia Partitioning: A Case Study in the Pearl River, China

Passive biomonitoring for per- and polyfluoroalkyl substances using invasive clams, C. fluminea

Per- and polyfluoroalkyl substances (PFAS) are a class of toxic manufactured chemicals in commercial and consumer products. They are resistant to environmental degradation and mobile in soil, air, and water. This study used the introduced bivalve Corbicula fluminea as a passive biomonitor at sampling locations in a primary drinking water source in Virginia, USA. Many potential PFAS sources were identified in the region. Perfluorohexane sulfonate (PFHxS) and 6:2 fluorotelomer sulfonic acid (6:2 FTS) levels were highest downstream of an airport. The highest levels of short-chain carboxylic acids were in locations downstream of a wastewater treatment plant. Measured PFAS concentrations varied by location in C. fluminea, sediment, and surface water samples. Two compounds were detected across all three mediums. Calculated partitioning coefficients confirm bioaccumulation of PFAS in C. fluminea and sorption to sediment. C. fluminea bioaccumulated two PFAS not found in the other mediums. Perfluoroalkyl carboxylic acids and short-chain compounds dominated in clam tissue, which contrasts with findings of accumulation of longer-chain and perfluorosulfonic acids in fish. These findings suggest the potential for using bivalves to complement other organisms to better understand the bioaccumulation of PFAS and their fate and transport in a freshwater ecosystem.

Multimedia distribution and release characteristics of emerging PFAS in wastewater treatment plants in Tianjin, China

Legacy and emerging PFAS in the air, wastewater, and sludge from two wastewater treatment plants (WWTPs) in Tianjin were investigated in this study. The semi-quantified nontarget PFAS accounted for up to 99 % of ƩPFAS in the gas phase, and aqueous film-forming foam (AFFF)-related PFAS were predominant in wastewater (up to 2250 ng/L, 79 % of ƩPFAS) and sludge (up to 4690 ng/g, 95 % of ƩPFAS). Furthermore, field-derived air particle-gas, air-wastewater, and wastewater particle-wastewater distribution coefficients of emerging PFAS are characterized, which have rarely been reported. The emerging substitute p-perfluorous nonenoxybenzenesulfonate (OBS) and AFFF-related cationic and zwitterionic PFAS show a stronger tendency to partition into particle phase in air and wastewater than perfluorooctane sulfonic acid (PFOS). The estimated total PFAS emissions from the effluent and sludge of WWTP A were 202 kg/y and 351 kg/y, respectively. While the target PFAS only accounted for 20-33 % of the total emissions, suggesting a significant underestimation of environmental releases of the nontarget PFAS and unknown perfluoroalkyl acid precursors through the wastewater and sludge disposal. Overall, this study highlights the importance of comprehensive monitoring and understanding the behavior of legacy and emerging PFAS in wastewater systems, and fills a critical gap in our understanding of PFAS exposure.

Deep Learning Bridged Bioactivity, Structure, and GC-HRMS-Readable Evidence to Decipher Nontarget Toxicants in Sediments

Identifying causative toxicants in mixtures is critical, but this task is challenging when mixtures contain multiple chemical classes. Effect-based methods are used to complement chemical analyses to identify toxicants, yet conventional bioassays typically rely on an apical and/or single endpoint, providing limited diagnostic potential to guide chemical prioritization. We proposed an event-driven taxonomy framework for mixture risk assessment that relied on high-throughput screening bioassays and toxicant identification integrated by deep learning. In this work, the framework was evaluated using chemical mixtures in sediments eliciting aryl-hydrocarbon receptor activation and oxidative stress response. Mixture prediction using target analysis explained <10% of observed sediment bioactivity. To identify additional contaminants, two deep learning models were developed to predict fingerprints of a pool of bioactive substances (event driver fingerprint, EDFP) and convert these candidates to MS-readable information (event driver ion, EDION) for nontarget analysis. Two libraries with 121 and 118 fingerprints were established, and 247 bioactive compounds were identified at confidence level 2 or 3 in sediment extract using GC-qToF-MS. Among them, 12 toxicants were analytically confirmed using reference standards. Collectively, we present a "bioactivity-signature-toxicant" strategy to deconvolute mixtures and to connect patchy data sets and guide nontarget analysis for diverse chemicals that elicit the same bioactivity.

Emerging and legacy per- and polyfluoroalkyl substances (PFAS) in fluorochemical wastewater along full-scale treatment processes: Source, fate, and ecological risk

The increasing applications of emerging per- and polyfluoroalkyl substances (PFAS) have raised global concern. However, the release of emerging PFAS from the fluorochemical industry remains unclear. Herein, the occurrence of 48 emerging and legacy PFAS in wastewater from 10 fluorochemical manufacturers and mass flows of PFAS in a centralized wastewater treatment plant were investigated. Their distribution and ecological risk in neighboring riverine water were also evaluated. In wastewater from fluorochemical manufacturers, PFAS concentrations were in the range of 14,700-5200,000 ng/L and 2 H,2 H-perfluorooctanoic acid (6:2 FTCA), perfluorooctanoic acid (PFOA), N-ethyl perfluorooctane sulfonamide (N-EtFOSA), and 1 H,1 H,2 H,2 H-perfluorodecanesulfonate (8:2 FTS) were the major PFAS detected. Several PFAS displayed increased mass flows after wastewater treatment, especially PFOA and 6:2 FTCA. The mass flows of PFAS increased from - 20% to 233% after the activated sludge system but decreased by only 0-13% after the activated carbon filtration. In riverine water, PFAS concentrations were in the range of 5900-39,100 ng/L and 6:2 FTCA, 1 H,1 H,2 H,2 H-perfluorodecyl phosphate monoester (8:2 monoPAP), 1 H,1 H,2 H,2 H-perfluorooctyl phosphate monoester (6:2 monoPAP), PFOA, and perfluorohexanoic acid (PFHxA) were the major PFAS detected. PFOA and 6:2 FTCA exhibited comparable hazard quotients for ecological risk. Current wastewater treatment processes cannot fully remove various PFAS discharged by fluorochemical manufacturers, and further investigations on their risk are needed for better chemical management.

Legacy and alternative per-and polyfluoroalkyl substances (PFASs) in the Bohai Bay Rim: Occurrence, partitioning behavior, risk assessment, and emission scenario analysis

The use of alternative per- and polyfluoroalkyl substances (PFASs) has been practiced because of the restrictions on legacy PFASs. However, knowledge gaps exist on the ecological risks of alternatives and relationships between restrictions and emissions. This study systematically analyzed the occurrence characteristics, water-sediment partitioning behaviors, ecological risks, and emissions of legacy and alternative PFASs in the Bohai Bay Rim (BBR). The mean concentration of total PFASs was 46.105 ng/L in surface water and 6.125 ng/g dry weight (dw) in sediments. As an alternative for perfluorooctanoic acid (PFOA), hexafluoropropylene oxide dimer acid (GenX) had a concentration second only to PFOA in surface water. In sediments, perfluorobutyric acid (PFBA) and GenX were the two predominant contaminants. In the water-sediment partitioning system, GenX, 9-chlorohexadecafluoro-3-oxanone-1-sulfonic acid (F-53B), and 11-chloroeicosafluoro-3-oxaundecane-1-sulfonic acid (8:2 Cl-PFESA) tended to be enriched towards sediments. The species sensitivity distribution (SSD) models revealed the low ecological risks of PFASs and their alternatives in the BBR. Moreover, predicted no-effected concentrations (PNECs) indicated that short-chain alternatives like PFBA and perfluorobutane sulfonate (PFBS) were safer for aquatic ecosystems, while caution should be exercised when using GenX and F-53B. Due to the incremental replacement of PFOA by GenX, cumulative emissions of 1317.96 kg PFOA and 667.22 kg GenX were estimated during 2004-2022, in which PFOA emissions were reduced by 59.2 % due to restrictions implemented since 2016. If more stringent restrictions are implemented from 2023 to 2030, PFOA emissions will further decrease by 85.0 %, but GenX emissions will increase by an additional 21.3 %. Simultaneously, GenX concentrations in surface water are forecasted to surge by 2.02 to 2.45 times in 2023. This study deepens the understanding of PFAS alternatives and assists authorities in developing policies to administer PFAS alternatives.

Summary recommendations on "Analytical methods for substances in the Watch List under the Water Framework Directive"

The Watch List (WL) is a monitoring program under the European Water Framework Directive (WFD) to obtain high-quality Union-wide monitoring data on potential water pollutants for which scarce monitoring data or data of insufficient quality are available. The main purpose of the WL data collection is to determine if the substances pose a risk to the aquatic environment at EU level and subsequently to decide whether a threshold, the Environmental Quality Standards (EQS) should be set for them and, potentially to be listed as priority substance in the WFD. The first WL was established in 2015 and contained 10 individual or groups of substances while the 4th WL was launched in 2022. The results of monitoring the substances of the first WL showed that some countries had difficulties to reach an analytical Limit of Quantification (LOQ) below or equal to the Predicted No-Effect Concentrations (PNEC) or EQS. The Joint Research Centre (JRC) of the European Commission (EC) organised a series of workshops to support the EU Member States (MS) and their activities under the WFD. Sharing the knowledge among the Member States on the analytical methods is important to deliver good data quality. The outcome and the discussion engaged with the experts are described in this paper, and in addition a literature review of the most important publications on the analysis of 17-alpha-ethinylestradiol (EE2), amoxicillin, ciprofloxacin, metaflumizone, fipronil, metformin, and guanylurea from the last years is presented.

Emerging and legacy per- and polyfluoroalkyl substances in Daling River and its estuary, Northern China

Strict restriction on legacy per- and polyfluoroalkyl substances (PFASs) has caused a dramatic increase in production and usage of emerging PFASs over the last decades. However, the environmental behaviors of emerging PFASs is largely unknown in Daling River, Northern China. In this study, the potential sources, sediment-water partitioning and substitution trends of PFASs were investigated in overlying water and sediments from Daling River and its estuary. Perfluorooctane sulfonate and 6:2 fluorotelomer sulfonic acid were major compounds, and sodium p-perfluorous nonenoxybenzene sulfonate was first detected. Firefighting foam manufacturing and fluoropolymer production were the main sources of PFASs. Compared to legacy PFASs (C8), the emerging PFASs (C6 - C9) were more incline to distribute into overlying water. Substitution trends indicated 6:2 fluorotelomer sulfonic acid and hexafluoropropylene oxide trimer acid as the important alternatives of perfluorooctane sulfonate and perfluorooctanoic acid, respectively. The results were meaningful for understanding the environmental behaviors of emerging PFASs.

Legacy and emerging per- and polyfluoroalkyl substances in the Shuidong bay of South China: Occurrence, partitioning behavior, and ecological risks

With the phase-out of legacy per- and polyfluoroalkyl substances (PFASs), PFAS alternatives have been increasingly used in industrial production and daily life. However, available information on the occurrence of PFASs and PFAS alternatives in semi-enclosed bays remains limited. As a representative semi-enclosed bay in Guangdong Province, China, Shuidong Bay has experienced severe anthropogenic pollution (industrial, shipping, cultural, and domestic) in recent decades. Water pollution in Shuidong Bay has worsened, and PFASs have been identified as ubiquitous environmental pollutants in this bay. In this study, 23 PFASs, including 5 emerging PFASs, were analyzed in water, suspended particulate matter (SPM), and sediment samples collected from Shuidong Bay. We determined that perfluorobutanoic acid (PFBA) was the predominant PFAS compound in seawater, whereas 6:2 fluorotelomer sulfonic acid (FTS) and perfluorooctane sulfonamide acetate (FOSAA) were dominant in SPM and sediment, respectively. The sediment-water partitioning coefficients were greatly dependent on the perfluorinated carbon chain length. Chlorophyll a concentration had a significant effect on the dissolved concentrations of PFASs in seawater. The ecological risk assessment indicated that the PFASs detected in the seawater and sediment samples posed no considerable risks to aquatic organisms. This study provides a valuable reference for evaluating PFAS contamination in Shuidong Bay and conducting ecological risk assessments for aquatic organisms.

Steroid metabolites as overlooked emerging contaminants: Insights from multimedia partitioning and source-sink simulation in an estuarine environment

Steroids have been attracting global attention given potential carcinogenic and endocrine-disrupting effects, yet the environmental status of steroids, especially their metabolites, in estuarine environment remain largely unexplored. This study investigated 31 steroids and metabolites in suspended particulate matter (SPM), water phase and sediments of the Pearl River Estuary (PRE) during the dry and wet seasons to elucidate their spatiotemporal patterning, partitioning behavior, and environmental fate. The results showed that natural steroids predominated in SPM and sediments while the metabolites predominated in water. The spatial distribution of steroids and metabolites varied seasonally, with hydrophobicity and environmental factors influencing phase partitioning in the estuary. Furthermore, a natural steroid, progesterone (P) could serve as a trustworthy chemical indicator to estimate the concentrations of steroids and metabolites in the PRE. Importantly, the mass budget of P was estimated using an improved multi-box mass balance model, revealing that outflow to the South China Sea was the primary sink of P in water (∼87%) and degradation was the primary sink of P in sediments (∼68%) of the PRE. Overall, this study offers insightful information about the distribution and environmental fate of steroids and metabolites in estuarine environment, with implications for future management strategies.

Trophodynamics of halogenated organic pollutants (HOPs) in aquatic food webs

Halogenated organic pollutants (HOPs) represent hazardous and persistent compounds characterized by their capacity to accumulate within organisms and endure in the environment. These substances are frequently transmitted through aquatic food webs, engendering potential hazards to ecosystems and human well-being. The trophodynamics of HOPs in aquatic food webs has garnered worldwide attention within the scientific community. Despite comprehensive research endeavors, the prevailing trajectory of HOPs, whether inclined toward biomagnification or biodilution within global aquatic food webs, remains unresolved. Furthermore, while numerous studies have probed the variables influencing the trophic magnification factor (TMF), the paramount determinant remains elusive. Collating a compendium of pertinent literature encompassing TMFs from the Web of Science between 1994 and 2023, our analysis underscores the disparities in attention accorded to legacy HOPs compared to emerging counterparts. A discernible pattern of biomagnification characterizes the behavior of HOPs within aquatic food webs. Geographically, the northern hemisphere, including Asia, Europe, and North America, has demonstrated greater biomagnification than its southern hemisphere counterparts. Utilizing a boosted regression tree (BRT) approach, we reveal that the food web length and type emerge as pivotal determinants influencing TMFs. This review provides a valuable basis for gauging ecological and health risks, thereby facilitating the formulation of robust standards for managing aquatic environments.

Source, transport, and fate of perfluoroalkyl acids (PFAAs) in turbid bay environments: Significant roles of suspended sediment and water column stratification

The coastal area was the major region receiving pollution from land-based sources into the sea. Perfluoroalkyl acids (PFAAs) in famous bays had aroused wide concern, but the importance of underdeveloped or small bays with notable levels of PFAAs were often neglected. Moreover, the roles of suspended sediment (SPS) and water column stratification on PFAA behaviors were unclear. In this study, PFAAs distribution in multiphase-multilayer in four underdeveloped bays (two urban bays and two island bays) were investigated. The urban bays not only had higher PFAA contamination but also posed a greater threat of short-chain PFAAs in water-SPS-sediment system than the island bays. The major source of PFAAs in water and SPS was domestic sewage in urban bays and was rainfall-runoff in island bays. Water column stratification with higher PFAA partition in water-SPS system in the surface layer than in the bottom layer was only found in the urban bays due to the higher human activity intensity. These provided new perspectives for managing emerging contaminants and establishing water quality criteria in the turbid coastal environment. The key role of SPS as a carrier offered possibilities to accurately differentiate the effects of dissolved and particulate PFAAs on bioavailability.

Temporal variation of per- and polyfluoroalkyl substances (PFASs) abundances in Shenzhen Bay sediments over past 65 years

We examined the vertical distribution of per- and polyfluoroalkyl substances (PFASs) and total organic carbon in sediment cores located in Shenzhen Bay area. We investigated the 210Pbex specific activity of the sediments and calculated the flux of PFASs to understand the temporal variation of PFASs in the past 65 years. The results showed that the concentrations of PFASs generally decreased with depth, ranging from 13 to 251 pg/g dw. The highest PFASs detected were perfluorobutanesulfonic acid, perfluorooctanoic acid, and perfluorohexanoic acid, which correspond to raw materials used in fire-fighting foam and food packaging industries. The flux of PFASs in Shenzhen Bay showed varying growth after 1978 when China's GDP entered a rapid growth stage. Our findings suggest that the vertical distribution of PFASs in Shenzhen Bay is fluctuating with the changes in industrial types and economic development, with implications for studying the fate of other persistent pollutants in the oceans.

Distribution and potential health risks of perfluoroalkyl substances (PFASs) in water, sediment, and fish in Dongjiang River Basin, Southern China

Per- and polyfluoroalkyl substances (PFASs) have attracted worldwide attention due to their high stability, refractory degradation, and bioaccumulation. The Dongjiang River is one of the most important water sources in the Pearl River Delta region. It flows from Jiangxi Province to Guangdong Province and finally into the Pearl River, providing domestic water for cities such as Guangzhou, Shenzhen, and Hong Kong. In this study, 17 PFASs in water, sediment, and fish in the Dongjiang River Basin in southern China were investigated using high-performance liquid chromatography-mass spectrometry. Total PFAS concentrations ranged from 20.83 to 372.8 ng/L in water, from 1.050 to 3.050 ng/g in sediments, and from 12.28 to 117.4 ng/g in fish. Among six species of fish, Oreochromis mossambicus (mean: 68.55 ng/g) had the highest concentration of PFASs, while Tilapia zillii (36.90 ng/g) had the lowest concentration. Perfluorooctanoic acid (PFOA) predominates in water and sediments, while perfluorooctanesulfonic acid (PFOS) predominates in fish. Long-chain perfluorocarboxylates (PFCAs) and perfluorosulfonates (PFSAs) showed higher bioaccumulation, and the field-sourced sediment-water partition coefficients (Kd) and bioaccumulation factors (BAFs) of PFASs increased with the length of perfluorocarbon chains. PFAS concentration in the lower reaches (urban area) of the Dongjiang River is higher than that in the upper and middle reaches (rural area). The calculated hazard ratio (HR) of PFOS and PFOA levels in fish in the Dongjiang River Basin was far less than 1; hence, the potential risk to human health was limited.

Ecological risk of galaxolide and its transformation product galaxolidone: evidence from the literature and a case study in Guangzhou waterways

Galaxolidone (HHCB-lac) is a major transformation product of the commonly used synthetic musk galaxolide (HHCB) and is ubiquitous in the environment along with the parent compound. Although many studies have shown the harmful effects of HHCB, little attention has been paid to the potential ecological risk of HHCB-lac. Herein, we reviewed the concentrations and ratios of HHCB and HHCB-lac (HHCB-lac : HHCB) in different media reported in the literature, derived the predicted no-effect concentrations (PNECs) for the two compounds using ECOSAR predictions and species sensitivity distribution (SSD) estimates, and assessed their ecological risks in the aquatic environment. The literature data indicated that HHCB-lac and HHCB were generally present in the environment at ratios of 0.01-10. Using the derived PNECs (2.14 and 18.4 μg L-1 for HHCB and HHCB-lac, respectively), HHCB in the aquatic environment was assessed to have medium to high risks, while HHCB-lac was assessed to have low risks. Furthermore, we carried out a case study on the occurrence and ecological risks of HHCB and HHCB-lac in Guangzhou waterways. The concentrations of the two compounds in Guangzhou waterways ranged from 20 to 2620 ng L-1 and 3 to 740 ng L-1, respectively, and the ratios were in the range of 0.15 to 0.64. The field study data also showed medium to high risks of HHCB and low risks of HHCB-lac. Additionally, the endocrine effects of HHCB and HHCB-lac were confirmed by Endocrine Disruptome, which calls for greater scrutiny of the potential effects of HHCB and HHCB-lac on human health.

Influence of dissolved organic carbon on multimedia distribution and toxicity of fipronil and its transformation products in lotic waterways

Environmental fate and ecological impacts of fipronil and its transformation products (FIPs) in aquatic environment have caused worldwide attention, however, the influence of dissolved organic carbon (DOC) on multimedia distribution, bioavailability, and toxicity of FIPs in field waterways was largely unknown. Here, we collected 11 companion water and sediment samples along a lotic stream in Guangzhou, South China. FIPs were ubiquitous with total water concentrations ranging from 1.22 to 43.2 ng/L (14.8 ± 12.9 ng/L) and fipronil sulfone was predominant in both water and sediment. More than 70% of FIPs in aqueous phase were bound to DOC and the K_DOC values of FIPs were approximately 1-2 orders of magnitude higher than K_d-s/K_OC, emphasizing the significance of DOC in phase partitioning and transport of FIPs in aquatic environment. Water and sediment samples were more toxic to Chironomus dilutus than Hyallela azteca, and FIPs (especially fipronil sulfone) pronouncedly contributed toxicity to C. dilutus. Toxic units (TU) based on freely dissolved concentrations in water determined by solid phase microextraction significantly improved toxicity estimation of FIPs to the invertebrates compared to TUs based on aqueous concentrations. The present study highlights the significance of DOC association on fate and ecological risk of hydrophobic insecticides in lotic ecosystem.

Legacy and novel perfluoroalkyl substances in major economic species of invertebrates in South China Sea: Health implication from consumption

Continuously release of perfluoroalkyl substances (PFASs) would pose non-negligible impacts on environment, organisms, and human health. In present study, 18 PFASs in 7 typical economic invertebrates and their habitats were investigated from the South China Sea. The higher concentrations of PFASs in the nearshore water (6.61-15.54 ng/L) and sediment (0.82-8.84 ng/g) obviously due to frequent human activities. Long-chain PFASs have tendency to accumulate in sediment, however, short-chain PFASs dominated in biota. The acute reference dose (%ARfD) and hazard ratios (HR) of major PFASs in biota were all <100 %, and also below 1, respectively, which means that consumption of PFASs from seafood does not pose risk and threat to human health. However, it should be taken into account that the HR of PFHxA in Mimachlamys nobilis reached 0.82. Potential adverse effects toward human health induced by short-chain PFASs (such as <6 C) via invertebrate seafood consumption should be concerned.

Distribution characteristics of photoinitiators and their flux estimation from the Pearl River Delta to the coastal waters of the South China Sea

Photoinitiators (PIs) are widely used in industrial polymerization processes. It has been reported that PIs are ubiquitous in indoor environments and that humans are exposed to PIs, but the occurrence of PIs in natural environments are rarely known. In the present study, 25 PIs, including 9 benzophenones (BZPs), 8 amine co-initiators (ACIs), 4 thioxanthones (TXs) and 4 phosphine oxides (POs), were analyzed in water and sediment samples collected from eight riverine outlets of the Pearl River Delta (PRD). Eighteen, 14, and 14 of the 25 target PIs were detected in water, suspended particulate matter (SPM) and sediment samples, respectively. The total concentrations of PIs in water, SPM, and sediment were in the ranges of 2.88‒96.1 ng/L, 9.25‒923 ng/g dry weight (dw), and 3.79‒56.9 ng/g dw, with geometric mean concentration (GM) of 10.8 ng/L, 48.6 ng/g dw, and 17.1 ng/g dw, respectively. A significant linear regression was observed between the log partitioning coefficients (K_d) values of PIs and their log octanol water partition coefficient (K_ow) values (R² = 0.535, p < 0.05). The annual riverine input of PIs to the coastal waters of the South China Sea via eight main outlets of the PRD was estimated to be 4.12 × 10³ kg/year, and the ∑BZPs, ∑ACIs, ∑TXs and ∑POs contributed to 1.96 × 10³, 1.24 × 10³, 89.6 and 830 kg/year, respectively. This is the first report of a systematic description of the occurrence characteristics of PIs exposure in water, SPM, and sediment. The environmental fate and risks of PIs in aquatic environments need further investigations.

Legacy and Emerging Per- and Polyfluoroalkyl Substances in a Subtropical Marine Food Web: Suspect Screening, Isomer Profile, and Identification of Analytical Interference

The ban/elimination of legacy per- and polyfluoroalkyl substances (PFASs) has led to a dramatic increase in the production and use of various emerging PFASs over the past decade. However, trophodynamics of many emerging PFASs in aquatic food webs remain poorly understood. In this study, samples of seawaters and marine organisms including 15 fish species, 21 crustacean species, and two cetacean species were collected from the northern South China Sea (SCS) to investigate the trophic biomagnification potential of legacy and emerging PFASs. Bis(trifluoromethylsulfonyl)imide was found in seawater via suspect screening (concentration up to 1.50 ng/L) but not in the biota, indicating its negligible bioaccumulation potential. A chlorinated perfluorooctane sulfonate (PFOS) analytical interfering compound was identified with a predicted formula of C₁₄H₂₃O₅SCl₆^- (most abundant at m/z = 514.9373). Significant trophic magnification was observed for 22 PFASs, and the trophic magnification factors of cis- and trans-perfluoroethylcyclohexane sulfonate isomers (1.92 and 2.25, respectively) were reported for the first time. Perfluorohexanoic acid was trophic-magnified, possibly attributed to the PFAS precursor degradation. The hazard index of PFOS was close to 1, implying a potential human health risk via dietary exposure to PFASs in seafood on the premise of continuous PFAS discharge to the SCS.

Widespread Occurrence and Transport of p-Phenylenediamines and Their Quinones in Sediments across Urban Rivers, Estuaries, Coasts, and Deep-Sea Regions

p-Phenylenediamines (PPDs) are widely used as antioxidants in tire rubber, and their derived quinone transformation products (PPD-Qs) may pose a threat to marine ecosystems. A compelling example is N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD)-derived quinone, called 6PPD-Q, as the causal toxicant for stormwater-linked acute mortality toward coho salmon. However, the knowledge of the co-occurrences of PPDs and PPD-Qs and their transport from freshwater to oceanic waterbodies on a large geographical scale remains unknown. Herein, we performed the first large-scale survey of these chemicals in sediments across urban rivers, estuaries, coasts, and deep-sea regions. Our results demonstrated that seven PPDs and four PPD-Qs are ubiquitously present in riverine, estuarine, and coastal sediments, and most of them also occur in deep-sea sediments. The most dominant chemicals of concern were identified as 6PPD and 6PPD-Q. Total sedimentary concentrations of PPDs and PPD-Qs presented a clear spatial trend with decreasing levels from urban rivers (medians: 39.7 and 15.2 ng/g) to estuaries (14.0 and 5.85 ng/g) and then toward coasts (9.47 and 2.97 ng/g) and deep-sea regions (5.24 and 3.96 ng/g). Interestingly, spatial variation in the ratios of 6PPD to 6PPD-Q (R_6PPD/6PPD-Q) also presented a clear decreasing trend. Our field measurements implied that riverine outflows of PPDs and PPD-Qs may be an important route to transport these tire rubber-derived chemicals to coastal and open oceans.