Thyroid Endocrine Disruption and Mechanism of the Marine Antifouling Pollutant 4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one.

The antifoulant 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) is an emerging pollutant in the marine environment, which may disrupt the thyroid endocrine system. However, DCOIT toxicity in relation to thyroid endocrine disruption and the underlying mechanisms remains largely unclear. In this study, in vivo, in silico, in vitro, and ex vivo assays were performed to clarify DCOIT's thyroid toxicity. First, marine medaka (Oryzias melastigma) were exposed to environmentally realistic concentrations of DCOIT for an entire life cycle. The results demonstrated that DCOIT exposure potently stimulated the hypothalamic-pituitary-thyroid axis, characterized by hyperthyroidism symptom induction and prevalent key gene and protein upregulation in the brain. Moreover, the in silico and in vitro results evidenced that DCOIT could bind to thyroid hormone receptor ß (TRß) and interact synergistically with triiodothyronine, thus promoting GH3 cell proliferation. The CUT&Tag experiment found that DCOIT interfered with the affinity fingerprint of TRß to target genes implicated in thyroid hormone signaling cascade regulation. Furthermore, ex vivo, Chem-seq revealed that DCOIT directly bound to the genomic sequences of thyrotropin-releasing hormone receptor b and thyroid-stimulating hormone receptor in marine medaka brain tissues. In conclusion, the current multifaceted evidence confirmed that DCOIT has a strong potency for thyroid endocrine system disruption and provided comprehensive insights into its toxicity mechanisms.

Aggravating Pollution of Emerging Aryl Organophosphate Esters in Urban Estuarine Sediments of South China.

Emerging aryl organophosphate esters (aryl-OPEs) have been employed as substitutes for organohalogen flame retardants in recent years; however, their environmental occurrence and associated impacts in urban estuarine sediments have not been adequately investigated, impeding regulatory decision-making. Herein, field-based investigations and modeling based on surface sediment and sediment core analysis were employed to uncover the historical pollution and current environmental impacts of aryl-OPEs in the Pearl River Estuary, South China. Our results revealed a substantial increase in aryl-OPE emission, particularly emerging aryl-OPEs, through sediment transport to the estuary since the 2000s. The emerging aryl-OPEs comprised 83% of the total annual input in the past decade, with an average annual input of 155,000 g. Additionally, the emerging-to-traditional aryl-OPE concentration ratios increased with decreasing distance from the shore, peaking in the highly urbanized riverine outlets. These findings indicate that inventories of emerging aryl-OPEs are likely increasing in estuarine sediments and their emissions are surpassing those of traditional aryl-OPEs. Our risk-based priority screening approach indicates that some emerging aryl-OPEs, particularly bisphenol A bis(diphenyl phosphate), can pose a higher environmental risk than traditional aryl-OPEs in estuarine sediments. Overall, our study highlights the importance of recognizing the environmental impacts of emerging aryl-OPEs.

Stereoselective Bioconcentration and Neurotoxicity of Perfluoroethylcyclohexane Sulfonate in Marine Medaka.

Perfluoroethylcyclohexane sulfonate (PFECHS) is an emerging per- and polyfluoroalkyl substance used to replace perfluorooctane sulfonate (PFOS), mainly in aircraft hydraulic fluids. However, previous research indicates the potential neurotoxicity of this replacement chemical. In this study, marine medaka (Oryzias melastigma) was exposed to environmentally relevant concentrations of PFECHS (concentrations: 0, 0.08, 0.26, and 0.91 µg/L) from the embryonic stage for 90 days. After exposure, the brain and eyes of the medaka were collected to investigate the bioconcentration potential of PFECHS stereoisomers and their effects on the nervous systems. The determined bioconcentration factors (BCFs) of PFECHS ranged from 324 ± 97 to 435 ± 89 L/kg and from 454 ± 60 to 576 ± 86 L/kg in the brain and eyes of medaka, respectively. The BCFs of trans-PFECHS were higher than those of cis-PFECHS. PFECHS exposure significantly altered γ-aminobutyric acid (GABA) levels in the medaka brain and disrupted the GABAergic system, as revealed by proteomics, implying that PFECHS can disturb neural signal transduction like PFOS. PFECHS exposure resulted in significant alterations in multiple proteins associated with eye function in medaka. Abnormal locomotion was observed in PFECHS-exposed medaka larvae, which was rescued by adding exogenous GABA, suggesting the involvement of disrupted GABA signaling pathways in PFECHS neurotoxicity.

Microplastics in Hong Kong's marine waters: Impact of rainfall and Pearl River discharge.

This study provided a systematic investigation of microplastics in Hong Kong's surface marine waters during the pandemic from 2019 to 2021. Microplastics (2.07 ± 4.00 particles/m3) exhibited significant temporal variations with higher abundance in the wet season, without a consistent trend after the mandatory mask-wearing requirement was announced. The impact of pandemic restrictions on microplastic distribution was found to be relatively minor. However, significant correlations between microplastic abundances and rainfall highlighted the substantial contribution of local emissions through surface runoff. Notably, sites in closer proximity to the Pearl River Delta exhibited higher microplastic abundances, indicating their association with emission sources. The influence of rainfall and adverse weather on marine microplastic loads demonstrated different sensitivities among various locations but can generally last for one month. These results revealed the impact of seasonal rainfall on coastal microplastics and emphasized the need for efforts to reduce microplastic discharge from land-based sources.

Medicating the coast in a metropolitan city: Enantiomeric profiles and joint probabilistic risk assessment of antidepressants and antihistamines.

Pharmaceuticals are receiving increasing attention as emerging contaminants in the aquatic environment. Herein, we investigated the occurrence of 11 antidepressants, 6 antihistamines and 4 metabolites in treated wastewater effluents, rivers, stormwater, and seawater in Hong Kong, with special focus on chirality. The average levels of ∑pharmaceuticals ranged from 0.525 to 1070 ng/L in all samples and the total annual mass load of target pharmaceuticals in the marine environment of Hong Kong was 756 kg/y. Antihistamines accounted for >80 % of ∑pharmaceuticals, with diphenhydramine and fexofenadine being predominant. The occurrence and enantiomeric profiles of brompheniramine and promethazine sulfoxide were reported in global natural waters for the first time. Among chiral pharmaceuticals, mirtazapine and fexofenadine exhibited R-preference, while others mostly exhibited S-preference, implying that the ecological risks derived from achiral data for chiral pharmaceuticals may be biased. The joint probabilistic risk assessment of fluoxetine revealed that R-fluoxetine and rac-fluoxetine presented different ecological risks from that of S-fluoxetine; Such assessment also revealed that target pharmaceuticals posed only minimal to low risks, except that diphenhydramine posed an intermediate risk. As estimated, 10 % aquatic species will be affected when the environmental level of diphenhydramine exceeds 7.40 ng/L, which was seen in 46.9 % samples. Collectively, this study highlights further investigations on the enantioselectivity of chiral pharmaceuticals, particularly on environmental behavior and ecotoxicity using local aquatic species as target organisms.

Isothiazolinone Disrupts Reproductive Endocrinology by Targeting the G-Protein-Coupled Receptor Signaling.

The unintended exposure of humans and animals to isothiazolinones has led to an increasing concern regarding their health hazards. Isothiazolinones were previously found to disrupt reproductive endocrine homeostasis. However, the long-term reproductive toxicity and underlying mechanism remain unclear. In this study, life-cycle exposure of medaka to dichlorocthylisothiazolinone (DCOIT), a representative isothiazolinone, significantly stimulated the gonadotropin releasing hormone receptor (GnRHR)-mediated synthesis of follicle stimulating hormone and luteinizing hormone in the brain. Chem-Seq and proteome analyses revealed disturbances in the G-protein-coupled receptor, MAPK, and Ca2+ signaling cascades by DCOIT. The G protein αi subunit was identified as the binding target of DCOIT. Gαi bound by DCOIT had an enhanced affinity for the mitochondrial calcium uniporter, consequently changing Ca2+ subcellular compartmentalization. Stimulation of Ca2+ release from the endoplasmic reticulum and blockage of Ca2+ uptake into the mitochondria resulted in a considerably higher cytoplasmic Ca2+ concentration, which then activated the phosphorylation of MEK and ERK to dysregulate hormone synthesis. Overall, by comprehensively integrating in vivo, ex vivo, in silico, and in vitro evidence, this study proposes a new mode of endocrine disrupting toxicity based on isothiazolinones, which is expected to aid the risk assessment of the chemical library and favor the mechanism-driven design of safer alternatives.

Developmental cardiotoxicity of 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) in marine medaka (Oryzias melastigma).

The application of 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) as an antifouling biocide causes high toxicity to non-target marine organisms. To examine the developmental cardiotoxicity and mechanisms of DCOIT, we concurrently performed sub-chronic exposure and life-cycle exposure experiments using marine medaka embryos. After sub-chronic exposure to DCOIT at 1, 3, 10, and 33 µg/L, cardiac defects were caused by upregulation of cardiac gene transcriptions, decreasing heart size, and accelerating heartbeat. Hyperthyroidism in medaka larvae was identified as the cause of developmental cardiotoxicity of DCOIT sub-chronic exposure. In addition, parental life-cycle exposure to 1, 3, and 10 µg/L DCOIT led to transgenerational impairment of cardiogenesis in offspring medaka. A crossbreeding strategy discriminated a concentration-dependent mechanism of transgenerational cardiotoxicity. At 1 µg/L, the DCOIT-exposed female parent transferred a significantly higher amount of triiodothyronine (T3) hormone to offspring, corresponding to an accelerated heart rate. However, DCOIT at higher exposure concentrations modified the methylome imprinting in larval offspring, which was associated with cardiac dysfunction. Overall, the findings provide novel insights into the developmental cardiotoxicity of DCOIT. The high risks of DCOIT-even at environmentally realistic concentrations-raise concerns about its applicability as an antifoulant in a marine environment.

Isothiazolinone dysregulates the pattern of miRNA secretion: Endocrine implications for neurogenesis.

Isothiazolinones are extensively used as preservatives and disinfectants in personal care products and household items. The unintended exposure of humans and animals to isothiazolinones has led to increasing concerns about their health hazards. The compound 4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT), a representative isothiazolinone, can simultaneously induce endocrine disruption and neurotoxicity. However, the underlying mechanisms and linkages remain unclear. Our purpose was to elucidate the role of miRNAs as the signaling communicator during the crosstalk between endocrine and nervous systems in response to DCOIT stress. H295R cells were exposed to DCOIT, after which the alterations in intracellular miRNA composition, exosome secretory machinery, and extracellular miRNA composition were examined. Then, a PC12 cell line of neuronal differentiation potential was cultured with the extract of extracellular miRNAs from DCOIT-exposed H295R cell media to explore the functional implications in neurogenesis. The results showed that DCOIT exposure resulted in 349 differentially expressed miRNAs (DEMs) in H295R cells, which were closely related to the regulation of multiple endocrine pathways. In the media of H295R cells exposed to DCOIT, 66 DEMs were identified, showing distinct compositions compared to intracellular DEMs with only 2 common DEMs (e.g., novel-m0541-5p of inverse changes in the cell and medium). Functional annotation showed that extracellular DEMs were not only associated with sex endocrine synchronization, but were also implicated in nervous system development, morphogenesis, and tumor. Incubating PC12 cells with the extracellular exosomes (containing miRNAs) from DCOIT-exposed H295R cells significantly increased the neurite growth, promoted neuronal differentiation, and shaped the transcriptomic fingerprint, implying that miRNAs may communicate transduction of toxic information of DCOIT in endocrine system to neurons. Overall, the present findings provide novel insight into the endocrine disrupting and neural toxicity of DCOIT. The miRNAs have the potential to serve as the epigenetic mechanism of systems toxicology.

Significant Variability in the Developmental Toxicity of Representative Perfluoroalkyl Acids as a Function of Chemical Speciation.

Current toxicological data of perfluoroalkyl acids (PFAAs) are disparate under similar exposure scenarios. To find the cause of the conflicting data, this study examined the influence of chemical speciation on the toxicity of representative PFAAs, including perfluorooctanoic acid (PFOA), perfluorobutane carboxylic acid (PFBA), and perfluorobutanesulfonic acid (PFBS). Zebrafish embryos were acutely exposed to PFAA, PFAA salt, and a pH-negative control, after which the developmental impairment and mechanisms were explored. The results showed that PFAAs were generally more toxic than the corresponding pH control, indicating that the embryonic toxicity of PFAAs was mainly caused by the pollutants themselves. In contrast to the high toxicity of PFAAs, PFAA salts only exhibited mild hazards to zebrafish embryos. Fingerprinting the changes along the thyroidal axis demonstrated distinct modes of endocrine disruption for PFAAs and PFAA salts. Furthermore, biolayer interferometry monitoring found that PFOA and PFBS acids bound more strongly with albumin proteins than did their salts. Accordingly, the acid of PFAAs accumulated significantly higher concentrations than their salt counterparts. The present findings highlight the importance of chemical forms to the outcome of developmental toxicity, calling for the discriminative risk assessment and management of PFAAs and salts.

Identification of key features relating to the coexistence mechanisms of trace elements and per- and polyfluoroalkyl substances (PFASs) in marine mammals.

Organic and inorganic substances coexist in the livers of marine mammals and may correlate with one another; however, their coexistence mechanisms and relevant key features remain largely unknown. In this study, temporal variations (2011-2021) in the concentrations of nine trace elements and 19 per- and polyfluoroalkyl substances (PFASs) in the livers of Indo-Pacific humpback dolphins (Sousa chinensis) and finless porpoises (Neophocaena phocaenoides) were investigated. Interannual Cd in dolphins increased significantly whereas Pb concentrations decreased over the past decade (p < 0.05). Interannual levels of seven and four PFASs in dolphins and porpoises decreased significantly with time (p < 0.05). By further extending the timescale to 1993-2021, the sensitivity of trace elements to annual change further increased, whereas the sensitivity of PFASs remained relatively stable. Cu levels, similar to the majority of PFASs, were negatively correlated with the body length of the studied cetaceans, which led to positive correlations of Cu with six long-chain perfluoroalkyl carboxylic acids, perfluorodecane sulfonic acid, and perfluoroethylcyclohexane sulfonic acid. The concentrations of trace elements in the cetacean liver were closely correlated with cetacean sex, species, and body length, whereas PFAS concentration was responsive to time-related features such as stranded season and year. By further employing a machine learning method, we demonstrated that body length and a time-related factor (year) played a crucial role in predicting the concentrations of certain trace elements and PFASs, respectively, particularly Cu and perfluoroheptanoic acid.

New Perspective to Understand and Prioritize the Ecological Impacts of Organophosphate Esters and Transformation Products in Urban Stormwater and Sewage Effluents.

Due to their prevalence in urban contaminated water, the driving factors of organophosphate esters (OPEs) need to be well examined, and their related ecological impacts should include that of their transformation products (TPs). Additionally, a robust framework needs to be developed to integrate multiple variables related to ecological impacts for improving the ecological health assessment. Therefore, OPEs and TPs in urban stormwater and wastewater in Hong Kong were analyzed to fill these gaps. The results revealed that the total concentrations of OPEs in stormwater were positively correlated with the area of transportation land. Individual TP concentrations and the mass ratios of individual TPs/OPEs were somewhat higher in sewage effluents than that in stormwater. OPEs generally showed relatively higher risk quotients than TPs; however, the total risk quotients increased by approximately 38% when TPs were factored in. Moreover, the molecular docking results suggested that the investigated TPs might cause similar endocrine disruption in marine organisms as their parent OPEs. This study employed the Toxicological-Priority-Index scheme to successfully integrate the ecological risks and endocrine-disrupting effects to refine the ecological health assessment of the exposure to OPEs and their TPs, which can better inform the authority on the prioritization for regulating these contaminants of emerging concern in urban built environments.

Temporal Trends and Suspect Screening of Halogenated Flame Retardants and Their Metabolites in Blubbers of Cetaceans Stranded in Hong Kong Waters during 2013-2020.

Halogenated flame retardants (HFRs) are a large class of chemical additives intended to meet flammability safety requirements, and at present, they are ubiquitous in the environment. Herein, we conducted the target analysis and suspect screening of legacy and novel HFRs and their metabolites in the blubber of finless porpoises (Neophocaena phocaenoides; n = 70) and Indo-Pacific humpback dolphins (Sousa chinensis; n = 35) stranded in Hong Kong, a coastal city in the South China Sea, between 2013 and 2020. The average concentrations of total target HFRs (ΣHFRs) were 6.48 × 103 ± 1.01 × 104 and 1.40 × 104 ± 1.51 × 104 ng/g lipid weight in porpoises and dolphins, respectively. Significant decreasing temporal trends were observed in the concentrations of tetra-/penta-/hexa-bromodiphenyl ethers (tetra-/penta-/hexa-BDEs) in adult porpoises stranded from 2013-2015 to 2016-2020 (p < 0.05), probably because of their phasing out in China. No significant difference was found for the concentrations of decabromodiphenyl ether and hexabromocyclododecane, possibly due to their exemption from the ban in China until 2025 and 2021, respectively. Eight brominated compounds were additionally identified via suspect screening. A positive correlation was found between the concentrations of tetra-BDE and methyl-methoxy-tetra-BDE (Me-MeO-tetra-BDE) (p < 0.05), indicating that the metabolism of tetra-BDE may be a potential source of Me-MeO-tetra-BDE in marine mammals.

Nationwide distribution of per- and polyfluoroalkyl substances (PFAS) in road dust from India.

In India, information on the occurrence and distribution of legacy and emerging per- and polyfluoroalkyl substances (PFAS) is deficient. In the present study, nationwide 79 road dust samples were collected from 12 states and 1 union territory for the analysis of 34 PFAS. Overall, total concentrations of 21 quantified PFAS (∑21PFAS) ranged 23-861 pg/g (median: 116 pg/g), with perfluorooctane sulfonic acid (PFOS) being predominant (median: 19.9 pg/g). Short to long chain perfluoroalkyl carboxylic acids (PFCAs; C4 - C18) were detected, where the concentrations of PFAS decreased with the increase in PFAS carbon chain length. ∑21PFAS was highest in road dust from urban area (n = 27; median: 230 pg/g), followed by suburban (n = 21; median: 126 pg/g) and rural areas (n = 31; median: 76 pg/g), suggesting environmental impacts of industriallization and urbanization on PFAS distribution. PFAS composition in rural road dust was significantly different from those in suburban and urban samples (p < 0.01). Regarding 4 geographical regions of India, PFAS in road dust showed spatial difference where higher concentrations were found in South India compared to other regions. ∑21PFAS were positively associated with city-wise population of India (rs = 0.40, p < 0.01). Strong to moderate positive correlation was observed between ∑21PFAS, fluorotelomer sulfonic acids, and PFCAs (rs = 0.23, 0.30, and 0.28, respectively; p < 0.05) and the total state-wise vehicles in India, suggesting that vehicles exhaust or non-exhaust (e.g., vehicle tire debris and polishing material) might contribute to the PFAS occurrence in Indian road dust. Toddlers (2-5 years) had the highest estimated daily intake of ∑PFAS via road dust ingestion under average-case and worst-case scenarios (0.55 and 1.16 pg/kg bw/day, respectively). This is the first time to evaluate PFAS in Indian road dust nationwide, aiding to provide first-hand data for human exposure to PFAS in India.

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.

Organic ultraviolet filter mixture promotes bleaching of reef corals upon the threat of elevated seawater temperature.

Global reef degradation is a critical environmental health issue that has triggered intensive research on ocean warming, but the implications of emerging contaminants in coral habitats are largely overlooked. Laboratory experiments assessing organic ultraviolet (UV) filter exposure have shown that these chemicals negatively affect coral health; their ubiquitous occurrence in association with ocean warming may pose great challenges to coral health. We investigated both short- (10-day) and long-term (60-day) single and co-exposures of coral nubbins to environmentally relevant organic UV filter mixtures (200 ng/L of 12 compounds) and elevated water temperatures (30 °C) to investigate their effects and potential mechanisms of action. The initial 10-day exposure of Seriatopora caliendrum resulted in bleaching only under co-exposure conditions (compounds + temperature). The 60-day mesocosm study entailed the same exposure settings with nubbins of three species (S. caliendrum, Pocillopora acuta and Montipora aequituberculata). Bleaching (37.5 %) and mortality (12.5 %) of S. caliendrum were observed under UV filter mixture exposure. In the co-exposure treatment, 100 % S. caliendrum and P. acuta bleached associating with 100 % and 50 % mortality, respectively, and significant increase of catalase activities in P. acuta and M. aequituberculata nubbins were found. Biochemical and molecular analyses indicated significant alteration of oxidative stress and metabolic enzymes. The results suggest that upon the adverse effects of thermal stress, organic UV filter mixture at environmental concentrations can cause bleaching in corals by inducing a significant oxidative stress and detoxification burden, suggesting that emerging contaminants may play a unique role in global reef degradation.

Enantiospecific Uptake and Depuration Kinetics of Chiral Metoprolol and Venlafaxine in Marine Medaka (Oryzias melastigma): Tissue Distribution and Metabolite Formation.

The increasing use of chiral pharmaceuticals has led to their widespread presence in the environment. However, their toxicokinetics have rarely been reported. Therefore, the tissue-specific uptake and depuration kinetics of two pairs of pharmaceutical enantiomers, S-(-)-metoprolol versus R-(+)-metoprolol and S-(+)-venlafaxine versus R-(-)-venlafaxine, were studied in marine medaka (Oryzias melastigma) during a 28-day exposure and 14-day clearance period. The toxicokinetics of the studied pharmaceuticals, including uptake and depuration rate constants, depuration half-life (t1/2), and bioconcentration factor (BCF), were reported for the first time. The whole-fish results demonstrated a higher S- than R-venlafaxine bioaccumulation potential, whereas no significant difference was observed between S- and R-metoprolol. O-desmethyl-metoprolol (ODM) and α-hydroxy-metoprolol (AHM) were the main metoprolol metabolites identified by suspect screening, and the ratios of ODM to AHM were 3.08 and 1.35 for S- and R-metoprolol, respectively. N,O-Didesmethyl-venlafaxine (NODDV) and N-desmethyl-venlafaxine (NDV) were the main venlafaxine metabolites, and the ratios of NODDV to NDV were 1.55 and 0.73 for S- and R-venlafaxine, respectively. The highest tissue-specific BCFs of the four enantiomers were all found in the eyes, meriting in-depth investigation.

Dysfunction of liver-gut axis in marine medaka exposed to hypoxia and perfluorobutanesulfonate.

With objectives to explore the interactive mode on the function of liver-gut axis, adult marine medaka were exposed for 7 days to environmentally realistic concentrations of perfluorobutanesulfonate (PFBS) (0 and 10 µg/L) under normoxia or hypoxia condition. Furthermore, PFBS exposure was extended to 21 days to reveal the temporal progression in toxicity. The results showed that hypoxia exposure significantly disturbed lipid metabolism, caused oxidative damage, and induced inflammation in the livers of medaka. The composition of gut microbiota was also drastically shifted by hypoxia acute exposure. In contrast, the effect of PFBS was much milder. Hypoxia was thus the determinant of the combined toxicity. Depending on the exposure duration, a time-course recovery from PFBS innate toxicity was generally noted. Overall, the present study underlines the hypoxic and temporal variation in the dysregulation of liver-gut axis by PFBS, which is expected to support a comprehensive ecological risk assessment.

Toxicity of perfluorobutanesulfonate on gill functions of marine medaka (Oryzias melastigma): A time course and hypoxia co-exposure study.

Perfluorobutanesulfonate (PFBS) is found in hypoxia regions. Results of previous studies have shown that hypoxia was capable of altering the inherent toxicity of PFBS. However, regarding gill functions, hypoxic influences and time course progression of toxic effects of PFBS remain unclear. In this study, with the aim to reveal the interaction behavior between PFBS and hypoxia, adult marine medaka Oryzias melastigma were exposed for 7 days to 0 or 10 µg PFBS/L under normoxic or hypoxic conditions. Subsequently, to explore the time-course transition in gill toxicity, medaka were exposed to PFBS for 21 days. The results showed that hypoxia dramatically increased the respiratory rate of medaka gill, which was further enhanced by exposure to PFBS; although exposure to PFBS under normoxic conditions for 7 days did not alter respiration, exposure to PFBS for 21 days significantly accelerated the respiration rate of female medaka. Concurrently, both hypoxia and PFBS were potent to interrupt the gene transcriptions and Na+, K+-ATPase enzymatic activity that play pivotal roles in the osmoregulation in gills of marine medaka, consequently disrupting homeostasis of major ions in blood, such as Na+, Cl-, and Ca2+. In addition, composition and diversity of the microbiome residing on surfaces of the gill were profiled by using amplicon sequencing. Acute exposure to hypoxia for only 7 days caused a significant decrease in diversity of the bacterial community of gill whatever the presence of PFBS, while PFBS exposure for 21 days increased the diversity of gill microbial community. Principal component analysis revealed that, compared with PFBS, hypoxia was the predominant driver of gill microbiome dysbiosis. Depending on duration of exposure, a divergence was caused in the microbial community of gill. Overall, the current findings underline the interaction between hypoxia and PFBS on gill function and demonstrate the temporal variation in PFBS toxicity.

Microplastic occurrence and ecological risk assessment in the eight outlets of the Pearl River Estuary, a new insight into the riverine microplastic input to the northern South China Sea.

Estuaries are unique transition zones connecting terrestrial and coastal environments and are recognized as primary conveyors for land-derived plastics to open oceans. Riverine microplastics (MPs) have been commonly investigated using sequential sampling which might not effectively reflect the actual load. In this study, sampling at eight outlets was performed during a complete tidal cycle to estimate the MP flux to the Pearl River Estuarine (PRE) using a concurrent sampling strategy. The MP abundances ranged from 2.90 ± 0.57-5.9 ± 2.27 particles/L. A remarkable difference between tides in MP abundances suggests tidal effect should not be overlooked in assessment. The MP load through the eight outlets was estimated at 304 trillion particles or 1102 tons into the PRE annually. Additionally, similar potential ecological risk assessment among eight rivers implied that environmental threats posed by less urbanized and populated rural areas on the western side have been under-evaluating for decades.