Bioaccumulation of perfluoroalkyl substances by Daphnia magna in water with different types and concentrations of protein

Species Difference? Bovine, Trout, and Human Plasma Protein Binding of Per- and Polyfluoroalkyl Substances

Per- and polyfluoroalkyl substances (PFAS) strongly bind to proteins and lipids in blood, which govern their accumulation and distribution in organisms. Understanding the plasma binding mechanism and species differences will facilitate the quantitative in vitro-to-in vivo extrapolation and improve risk assessment of PFAS. We studied the binding mechanism of 16 PFAS to bovine serum albumin (BSA), trout, and human plasma using solid-phase microextraction. Binding of anionic PFAS to BSA and human plasma was found to be highly concentration-dependent, while trout plasma binding was linear for the majority of the tested PFAS. At a molar ratio of PFAS to protein ν < 0.1 molPFAS/molprotein, the specific protein binding of anionic PFAS dominated their human plasma binding. This would be the scenario for physiological conditions (ν < 0.01), whereas in in vitro assays, PFAS are often dosed in excess (ν > 1) and nonspecific binding becomes dominant. BSA was shown to serve as a good surrogate for human plasma. As trout plasma contains more lipids, the nonspecific binding to lipids affected the affinities of PFAS for trout plasma. Mass balance models that are parameterized with the protein-water and lipid-water partitioning constants (chemical characteristics), as well as the protein and lipid contents of the plasma (species characteristics), were successfully used to predict the binding to human and trout plasma.

Influence of humic acid on the bioaccumulation, elimination, and toxicity of PFOS and TBBPA co-exposure in Mytilus unguiculatus Valenciennes

Tetrabromobisphenol A (TBBPA) and Perfluorooctane sulfonate (PFOS) are emerging contaminants which coexist in marine environments, posing significant risks to ecosystems and human health. The behavior of these contaminants in the presence of dissolved organic matter (DOM), specifically the co-contamination of TBBPA and PFOS, is not well understood. The bioaccumulation, distribution, elimination, and toxic effects of TBBPA and PFOS on thick-shell mussels (Mytilus unguiculatus V.), with the absence and presence of humic acid (HA), a typical DOM, were studied. The results showed that the uptake of TBBPA decreased and the uptake of PFOS increased when exposed to 1 mg/L HA. However, at higher concentrations of HA (5 and 25 mg/L), the opposite effect was observed. Combined exposure to HA, TBBPA, and PFOS resulted in oxidative stress in the digestive gland, with the severity of stress dependent on exposure time and HA dose. Histological analysis revealed a positive correlation between HA concentration and tissue damage caused by TBBPA and PFOS. This study provides insights into the influence of HA on the bioaccumulation-elimination patterns and toxicity of TBBPA and PFOS in marine bivalves, offering valuable data for ecological and health risk assessments of combined pollutants in aquatic environments rich in DOM.

The concentration of dissolved organic matter impacts the neurobehavior in female zebrafish exposed to cyclophosphamide

Cyclophosphamide (CP) is a broad-spectrum anticancer drug for various cancers and frequently detected in aquatic environments, reaching concentrations up to 22 μg/L. However, there is limited understanding of the toxicities of CP with the presence of dissolved organic matter, a ubiquitous component in aquatic environments, in fish. In this study, we investigated the behaviors, morphological alterations of retina, and related gene transcripts in zebrafish exposed to CP (0 and 50 μg/L) and Humic acid (HA, a main component of DOM) at concentrations of 0, 3, 10, and 30 mg-C/L for 30 days. The results showed that, relative to the zebrafish in CP treatment, HA at 30 mg-C/L increased the locomotion (12.1 % in the light and 7.2 % in the dark) and startle response (9.7 %), while inhibiting the anxiety (12.5 %) and cognition of female zebrafish (24.6 %). The levels of transcripts of neurotransmitter- (tph1b and ache), neuroinflammation-(il-6 and tnfα) and antioxidant-(gpx) related genes in the brain of female adult were also altered by CP with the presence of HA. In addition, HA promoted the transgenerational effects of CP on the neurobehaviors. Therefore, HA can enhance potential neurotoxicity of CP in female fish through alteration neurotransmission related genes. Our findings provide new insights into the toxicity and underlying mechanisms of CP with the presence of dissolved organic matter, thereby contribute to a deeper understanding of the risks posed by CP in aquatic ecosystems.

Assessment of Fetal Exposure and Elimination of Perfluoroalkyl and Polyfluoroalkyl Substances: New Evidence from Paired Serum, Placenta, and Meconium Samples

Multiple pieces of evidence have shown that prenatal exposure to perfluoroalkyl and polyfluoroalkyl substances (PFASs) is closely related to adverse birth outcomes for infants. However, difficult access to human samples limits our understanding of PFASs transport and metabolism across the human placental barrier, as well as the accurate assessment of fetal PFASs exposure. Herein, we assess fetal exposure to 28 PFASs based on paired serum, placenta, and meconium samples. Overall, 21 PFASs were identified first to be exposed to the fetus prenatally and to be metabolized and excreted by the fetus. In meconium samples, 25 PFASs were detected, with perfluorooctane sulfonate and perfluorohexane sulfonic acid being the dominant congeners, suggesting the metabolism and excretion of PFASs through meconium. Perfluoroalkyl sulfonic acids might be more easily eliminated through the meconium than perfluorinated carboxylic acids. Importantly, based on molecular docking, MRP1, OATP2B1, ASCT1, and P-gp were identified as crucial transporters in the dynamic placental transfer of PFASs between the mother and the fetus. ATSC5p and PubchemFP679 were recognized as critical structural features that affect the metabolism and secretion of PFASs through meconium. With increasing carbon chain length, both the transplacental transfer efficiency and meconium excretion efficiency of PFASs showed a structure-dependent manner. This study reports, for the first time, that meconium, which is a noninvasive and stable biological matrix, can be strong evidence of prenatal PFASs exposure.

Binding of Per- and Polyfluoroalkyl Substances (PFAS) to Serum Proteins: Implications for Toxicokinetics in Humans

Per- and polyfluoroalkyl substances (PFAS) are a diverse class of highly persistent anthropogenic chemicals that are detectable in the serum of most humans. PFAS exposure has been associated with many adverse effects on human health including immunotoxicity, increased risk of certain cancers, and metabolic disruption. PFAS binding to the most abundant blood serum proteins (human serum albumin [HSA] and globulins) is thought to affect transport to active sites, toxicity, and elimination half-lives. However, few studies have investigated the competitive binding of PFAS to these proteins in human serum. Here, we use C18 solid-phase microextraction fibers to measure HSA-water and globulin-water distribution coefficients (DHSA/w, Dglob/w) for PFAS with carbon chains containing 4 to 13 perfluorinated carbons (ηpfc = 4-13) and several functional head-groups. PFAS with ηpfc < 7 were highly bound to HSA relative to globulins, whereas PFAS with ηpfc ≥ 7 showed a greater propensity for binding to globulins. Experimentally measured DHSA/w and Dglob/w and concentrations of serum proteins successfully predicted the variability in PFAS binding in human serum. We estimated that the unbound fraction of serum PFAS varied by up to a factor of 2.5 among individuals participating in the 2017-2018 U.S. National Health and Nutrition Examination Survey. These results suggest that serum HSA and globulins are important covariates for epidemiological studies aimed at understanding the effects of PFAS exposure.

Development, Evaluation, and Application of Machine Learning Models for Accurate Prediction of Root Uptake of Per- and Polyfluoroalkyl Substances

Machine learning (ML) models were developed for understanding the root uptake of per- and polyfluoroalkyl substances (PFASs) under complex PFAS-crop-soil interactions. Three hundred root concentration factor (RCF) data points and 26 features associated with PFAS structures, crop properties, soil properties, and cultivation conditions were used for the model development. The optimal ML model, obtained by stratified sampling, Bayesian optimization, and 5-fold cross-validation, was explained by permutation feature importance, individual conditional expectation plot, and 3D interaction plot. The results showed that soil organic carbon contents, pH, chemical logP, soil PFAS concentration, root protein contents, and exposure time greatly affected the root uptake of PFASs with 0.43, 0.25, 0.10, 0.05, 0.05, and 0.05 of relative importance, respectively. Furthermore, these factors presented the key threshold ranges in favor of the PFAS uptake. Carbon-chain length was identified as the critical molecular structure affecting root uptake of PFASs with 0.12 of relative importance, based on the extended connectivity fingerprints. A user-friendly model was established with symbolic regression for accurately predicting RCF values of the PFASs (including branched PFAS isomerides). The present study provides a novel approach for profound insight into the uptake of PFASs by crops under complex PFAS-crop-soil interactions, aiming to ensure food safety and human health.

Research Priorities for the Environmental Risk Assessment of Per- and Polyfluorinated Substances

Per- and polyfluorinated substances (PFAS) are a group of thousands of ubiquitously applied persistent industrial chemicals. The field of PFAS environmental research is developing rapidly, but suffers from substantial biases toward specific compounds, environmental compartments, and organisms. The aim of our study was therefore to highlight current developments and to identify knowledge gaps and subsequent research needs that would contribute to a comprehensive environmental risk assessment for PFAS. To this end, we consulted the open literature and databases and found that knowledge of the environmental fate of PFAS is based on the analysis of <1% of the compounds categorized as PFAS. Moreover, soils and suspended particulate matter remain largely understudied. The bioavailability, bioaccumulation, and food web transfer studies of PFAS also focus on a very limited number of compounds and are biased toward aquatic biota, predominantly fish, and less frequently aquatic invertebrates and macrophytes. The available ecotoxicity data revealed that only a few PFAS have been well studied for their environmental hazards, and that PFAS ecotoxicity data are also strongly biased toward aquatic organisms. Ecotoxicity studies in the terrestrial environment are needed, as well as chronic, multigenerational, and community ecotoxicity research, in light of the persistency and bioaccumulation of PFAS. Finally, we identified an urgent need to unravel the relationships among sorption, bioaccumulation, and ecotoxicity on the one hand and molecular descriptors of PFAS chemical structures and physicochemical properties on the other, to allow predictions of exposure, bioaccumulation, and toxicity. Environ Toxicol Chem 2023;42:2302-2316. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Efflux transport proteins of Tetrahymena thermophila play important roles in resistance to perfluorooctane sulfonate exposure

The biotoxicity of perfluorooctane sulfonate (PFOS) has been a concern. However, the effects of PFOS on Tetrahymena thermophila, a unicellular model organism, remain unclear. This study aimed to investigate the toxicity and detoxification mechanism of PFOS in this protozoan. PFOS did not show prominent toxic effects on T. thermophila. Cell viability of T. thermophila can be concentration-dependently increased by PFOS. PFOS also increased the stability of cell membranes and the activity of lysosomes. However, PFOS inhibited efflux transporter activities. Most of the PFOS amount remained in the culture medium during the culture periods. Only a low amount of PFOS was absorbed by cells, where PFOS molecules were mainly combined with membrane proteins. The expressions of four membrane protein genes involved in transporting xenobiotics were analyzed by real time-PCR. The gene abcg25 was significantly up-regulated. The growth of abcg25 gene knockout protozoans under PFOS treatment was slightly inhibited. However, the amount of PFOS adsorbed by the knockout protozoans showed no significant difference from the Wild-type protozoans. We concluded that the ABCG25 protein might play a key role in preventing PFOS from entering the cell or being exported from the cells to protect T. thermophila against PFOS. However, ABCG25 was not the only membrane protein able to bind with PFOS.

Exploring the Accumulation Behavior and Heterogeneity of Perfluorooctanesulfonic Acid in Zebrafish Primary Organ Cells by Single-Cell Mass Cytometry

Perfluorooctanesulfonic acid (PFOS) is a commonly found environmental pollutant with potential toxicity and health risks to biosystems and ecosystems. Study of the accumulation behavior and heterogeneity of PFOS in biological primary organ cells provides us significant insights to explore its cytotoxicity, carcinogenicity, and mutagenicity. Here a single-cell mass cytometry system was established for the high-throughput analysis of trace PFOS and the exploration of its accumulation behavior and heterogeneity in zebrafish primary organ cells. The single-cell mass cytometry system applied a ∼25 μm constant-inner-diameter capillary as the single-cell generation and transportation channel with an etched tip-end of 40 μm as the nanoelectrospray emitter for mass spectrometric analysis. The single-cell mass cytometry system showed satisfactory semiquantitative performance and sensitivity for analysis of PFOS in single cells, with a high detection throughput of ∼35 cells/min. Subsequently, the liver, intestine, heart, and brain from PFOS-exposed zebrafish (100 pg/μL, 28 days) were dissociated and prepared as cell suspensions, and the cell suspensions were introduced into the single-cell mass cytometry system for high-throughput analysis of PFOS in individual primary organ cells. Significant cellular accumulation heterogeneities were observed, with the highest content in liver cells, followed by intestine cells, then heart cells, and the lowest in brain cells. In addition, the dynamics of PFOS in the zebrafish liver, intestine, heart, and brain cells showed typical violin plot distributions and were well-described using a gamma (γ) function.

Per/polyfluoroalkyl substances modulate plasmid transfer of antibiotic resistance genes: A balance between oxidative stress and energy support

Emerging contaminants can accelerate the transmission of antibiotic resistance genes (ARGs) from environmental bacteria to human pathogens via plasmid conjugation, posing a great challenge to the public health. Although the toxic effects of per/polyfluoroalkyl substances (PFAS) as persistent organic pollutants have been understood, it is still unclear whether and how PFAS modulate the transmission of ARGs. In this study, we for the first time reported that perfluorooctanoic acid (PFOA), perfluorododecanoic acid (PFDoA) and ammonium perfluoro (2-methyl-3-oxahexanoate) (GenX) at relatively low concentrations (0.01, 0.1 mg/L) promoted the conjugative transfer of plasmid RP4 within Escherichia coli, while the plasmid conjugation was inhibited by PFOA, PFDoA and GenX at relatively high concentrations (1, 10 mg/L). The non-unidirectional conjugation result was ascribed to the co-regulation of ROS overproduction, enhanced cell membrane permeability, shortage of energy support as well as l-arginine pool depletion. Taking the well-known PFOA as an example, it significantly enhanced the conjugation frequency by 1.4 and 3.4 times at relatively low concentrations (0.01, 0.1 mg/L), respectively. Exposure to PFOA resulted in enhanced cell membrane permeability and ROS overproduction in donor cells. At high concentrations of PFOA (1, 10 mg/L), although enhanced oxidative stress and cell membrane permeability still occurred, the ATP contents in E. coli decreased, which contributed to the inhibited conjugation. Transcriptome analysis further showed that the expression levels of genes related to arginine biosynthesis (argA, argC, argF, argG, argI) and transport (artJ, artM, artQ) pathways were significantly increased. Intracellular l-arginine concentration deficiency were observed at high concentrations of PFOA. With the supplementary exogenous arginine, it was demonstrated that arginine upregulated conjugation transfer- related genes (trfAp, trbBp) and restores the cell number of transconjugants in PFOA-treated group. Therefore, the inhibited conjugation at high concentrations PFOA were attributed to the shortage of ATP and the depletion of L-arginine pool. These findings provide important insights into the effect environmental concentrations of PFAS on the conjugative transfer of ARGs, and update the regulation mechanism of plasmid conjugation, which is critical for the management of antibiotic resistance in aquatic environments.

Bioaccumulation of per- and polyfluoroalkyl substances by freshwater benthic macroinvertebrates: Impact of species and sediment organic carbon content

Per- and polyfluoroalkyl substances (PFAS) in aquatic environments have caused global concern due to their persistence, toxicity, and potential bioaccumulation of some compounds. As an important compartment of the aquatic ecosystem, sediment properties impact PFAS partitioning between aqueous and solid phases, but little is known about the influence of sediment organic carbon content on PFAS bioaccumulation in benthic organisms. In this study, three freshwater benthic macroinvertebrates - worms (Lumbriculus variegatus), mussels (Elliptio complanata) and snails (Physella acuta) - were exposed for 28 days to PFAS spiked synthetic sediment equilibrated with a synthetic surface water. Using microcosms, sediment organic carbon content - 2%, 5% and 8% - was manipulated to assess its impact on PFAS bioaccumulation. Worms were found to have substantially greater PFAS bioaccumulation compared to mussels and snails. The bioaccumulation factors (BAFs) and biota sediment accumulation factors (BSAFs) in worms were both one to two magnitudes higher than in mussels and snails, likely due to different habitat-specific uptake pathways and elimination capacities among species. In these experiments, increasing sediment organic carbon content decreased the bioaccumulation of PFAS to benthic macroinvertebrates. In worms, sediment organic carbon content was hypothesized to impact PFAS bioaccumulation by affecting PFAS partitioning and sediment ingestion rate. Notably, the BSAF values of 8:2 fluorotelomer sulfonic acid (FTS) were the largest among 14 PFAS for all species, suggesting that the benthic macroinvertebrates probably have different metabolic mechanisms for fluorotelomer sulfonic acids compared to fish evaluated in published literature. Understanding the impact of species and sediment organic carbon on PFAS bioaccumulation is key to developing environmental quality guidelines and evaluating potential ecological risks to higher trophic level species.

Warming Affects Bioconcentration and Bioaccumulation of Per- and Polyfluoroalkyl Substances by Pelagic and Benthic Organisms in a Water-Sediment System

Warming and exposure to emerging global pollutants, such as per- and polyfluoroalkyl substances (PFAS), are significant stressors in the aquatic ecosystem. However, little is known about the warming effect on the bioaccumulation of PFAS in aquatic organisms. In this study, the pelagic organisms Daphnia magna and zebrafish, and the benthic organism Chironomus plumosus were exposed to 13 PFAS in a sediment-water system with a known amount of each PFAS at different temperatures (16, 20, and 24 °C). The results showed that the steady-state body burden (C_b-ss) of PFAS in pelagic organisms increased with increasing temperatures, mainly attributed to increased water concentrations. The uptake rate constant (k_u) and elimination rate constant (k_e) in pelagic organisms increased with increasing temperature. In contrast, warming did not significantly change or even mitigate C_b-ss of PFAS in the benthic organism Chironomus plumosus, except for PFPeA and PFHpA, which was consistent with declined sediment concentrations. The mitigation could be explained by the decreased bioaccumulation factor due to a more significant percent increase in k_e than k_u, especially for long-chain PFAS. This study suggests that the warming effect on the PFAS concentration varies among different media, which should be considered for their ecological risk assessment under climate change.

Role of bioavailability and protein binding of four anionic perfluoroalkyl substances in cell-based bioassays for quantitative in vitro to in vivo extrapolations

Perfluoroalkyl substances (PFAS) are persistent and pose a risk to human health. High throughput screening (HTS) cell-based bioassays may inform risk assessment of PFAS provided that quantitative in vitro to in vivo extrapolation (QIVIVE) can be developed. The QIVIVE ratio is the ratio of nominal (C_nom) or freely dissolved concentration (C_free) in human blood to C_nom or C_free in the bioassays. Considering that the concentrations of PFAS in human plasma and in vitro bioassays may vary by orders of magnitude, we tested the hypothesis that anionic PFAS bind to proteins concentration-dependently and therefore the binding differs substantially between human plasma and bioassays, which has an impact on QIVIVE. Solid phase microextraction (SPME) with C18-coated fibers served to quantify the C_free of four anionic PFAS (perfluorobutanoate (PFBA), perfluorooctanoate (PFOA), perfluorohexane sulfonate (PFHxS) and perfluorooctane sulfonate (PFOS)) in the presence of proteins and lipid, medium components, cells and human plasma over five orders of magnitude in concentrations. The C18-SPME method was used to quantify the non-linear binding to proteins, human plasma and medium, and the partition constants to cells. These binding parameters were used to predict C_free of PFAS in cell bioassays and human plasma by a concentration-dependent mass balance model (MBM). The approach was illustrated with a reporter gene assay indicating activation of the peroxisome proliferator-activated receptor gamma (PPARγ-GeneBLAzer). Blood plasma levels were collected from literature for occupational exposure and the general population. The QIVIVE_nom ratios were higher than the QIVIVE_free ratios due to the strong affinity to proteins and large differences in protein contents between human blood and bioassays. For human health risk assessment, the QIVIVE_free ratios of many in vitro assays need to be combined to cover all health relevant endpoints. If C_free cannot be measured, they can be estimated with the MBM and concentration-dependent distribution ratios.

Tissue-specific accumulation, depuration, and effects of perfluorooctanoic acid on fish: Influences of aqueous pH and sex

Perfluorooctanoic acid (PFOA) is widely distributed in nature, particularly in aquatic environments. Its bioaccumulation and toxicity in aquatic organisms can be affected by both the chemical status of PFOA in water and the physiology of the organism. However, research on the patterns of these effects is scarce. In this study, we investigated the influence of aqueous pH (pH 6, acidic; pH 7.5, neutral; pH 9, basic) and fish sex on PFOA uptake, clearance, and biochemical effects in crucian carp (C. auratus) using flow-through exposure. In the 17-d kinetic experiment, PFOA bioaccumulation adhered to a uniform first-order model in which PFOA uptake rates from water to blood and liver in acidic conditions were faster than those in other conditions, indicating possible acidic pH influence on PFOA uptake. PFOA clearance rates in these compartments of males were slower than in females, which was attributed to the notably stronger expression of Oat2 (organic anion transporter 2, responsible for reabsorption) in the kidneys of males. Similar responses were observed for peroxisome proliferation-related biomarkers at different pH levels and in different sexes. These biochemical responses were driven by the internal concentrations of PFOA. The inhibition acetylcholinesterase activity in the fish brain was closely linked to changes in P-glycoprotein content, demonstrating a protective relationship. Collectively, an aqueous pH lower than 7.5 might affect the uptake of PFOA by fish. The clearance discrepancies between the sexes highlight the importance of anion carriers for ionizable organic compounds in aquatic organisms.

Molecular interactions between bovine serum albumin (BSA) and trihalophenol: Insights from spectroscopic, calorimetric and molecular modeling studies

The issue of disinfection byproducts (DBPs) in the water has received critical attention due to the health effects on humans. In the water environment, interactions between bovine serum albumins (BSA), the most abundant water-soluble protein, and DBPs unavoidably occur. In this study, comparative binding interactions of two aromatic DBPs - 2,4,6-trichlorophenol (TCP) and 2,4,6-tribromophenol (TBP) with BSA were investigated systematically utilizing fluorescence spectrometry, UV absorption spectrometry, isothermal titration calorimetry and molecular docking approach. The fluorescence quenching results indicated that TCP/TBP could quench the endogenous fluorescence of BSA through static quenching mechanisms, and TBP showed a more substantial quenching effect. The binding constants were determined for TCP-BSA (3.638 × 10⁵ L/mol, 303 K) and TBP-BSA (6.394 × 10⁵ L/mol, 303 K) complexes, with TBP showing higher binding affinity than TCP. The thermodynamic study and docking analysis suggested that hydrogen bonding and van der Waals forces were the primary interaction forces. Both of TCP and TBP were located in the subdomain IIIA of BSA, and TBP could form more stable complex than TCP. The results of the present study contributed valuable information on the environmental behaviors of halophenols in water environment from perspectives of binding with BSA.

An unexpected synergistic toxicity caused by competitive bioconcentration of perfluoroalkyl acid mixtures to Daphnia magna: Further promoted by elevated temperature

The mixed pollution of the global water environment by perfluoroalkyl acids (PFAAs) and their ecological risks have aroused widespread concern. However, the relationship between the combined toxicity of PFAA mixtures and their accumulation in aquatic organisms is not well understood in the context of global warming. Here, we study the bioconcentration and combined toxicity of three PFAA mixtures (PFOA, PFDA, PFDoA) to Daphnia magna (D. magna) under different exposure concentrations and temperatures. The results show that although competitive bioconcentration exists, the combined toxicity of the PFAA mixtures to D. magna is synergistic. These contradictory phenomena occur because although the longer-chain PFDoA inhibits the bioconcentration of the shorter-chain PFOA and PFDA, the bioconcentration of PFDoA itself is promoted, and PFDoA is more toxic to D. magna than PFOA and PFDA. The toxic equivalent concentration for the PFAA mixture is 1.38-1.67 times higher than that obtained from simple addition for the three PFAAs when exposed separately. Moreover, elevated temperature promotes not only the bioconcentration of each PFAA and the competition of bioconcentration between shorter-chain and longer-chain PAFF, but also the synergistic toxicity of PFAA mixtures to D. magna. This study suggests that the effect of the interactions among different PFAAs on their bioconcentration and toxicity under different water environmental conditions, such as temperature, should be considered for ecological risk assessment of PFAA mixtures.

Occurrence and Risks of Per- and Polyfluoroalkyl Substances in Shellfish

PURPOSE OF REVIEW

Per- and polyfluoroalkyl substances (PFAS) are a diverse class of persistent, fluorinated surfactants used widely in industrial and commercial applications with known adverse health effects. Seafood consumption is thought to be an underappreciated source of PFAS exposure in the general population. This review synthesizes the current understanding of PFAS occurrence in shellfish, a term used to describe animals such as mollusk bivalves, certain gastropods (snails), cephalopods (e.g., octopuses and squid), and crustaceans, and highlights scientific gaps relative to bioaccumulation and the protection of shellfish consumers.

RECENT FINDINGS

A range of sampling methodologies are used across studies, and the suite of PFAS surveyed across studies is highly variable. Concentrations of PFAS observed in shellfish vary by geographic location, shellfish species, habitat, and across PFAS compounds, and studies informing estimates of bioaccumulation of PFAS in shellfish are extremely limited at this time. This review identifies several important opportunities for researchers to standardize PFAS sampling techniques, sample preparation, and analytical methodologies to allow for better comparison of PFAS analytes both within and across future studies. Increasing the range of geographic locations where samples are collected is also a critical priority to support a greater knowledge of worldwide PFAS contamination. When put into the context of risk to consumer, concentrations of PFAS, especially PFOS, found in shellfish collected from sites containing aqueous film-forming foam (AFFF) and industrial contamination may present risks to frequent consumers. Further research is needed to protect shellfish consumers and to inform shellfish advisories and health protective policies.

Natural colloids at environmentally relevant concentrations affect the absorption and removal of benzophenone-3 in zebrafish

Aquatic natural colloids are closely related to the environmental behavior of pollutants, which may affect their bioavailability in aquatic organisms. This study explored the potential mechanisms of the natural colloids at environmentally relevant concentrations affecting the bioaccumulation process of benzophenone-3 (BP3) in zebrafish (Danio rerio). The results of kinetic model fitting showed that the natural colloids decreased the uptake and loss rate of BP3 by zebrafish but prolonged the time to reach the cumulative equilibrium, eventually resulting in a higher cumulative concentration in zebrafish. According to the tissue concentration at equilibrium and the results of toxicokinetic analysis, the presence of high molecular colloids could enhance the bioaccumulation of freely dissolved BP3 due to its high desorption rate with BP3 in the intestines of fish, increasing the freely dissolved BP3 concentrations to which zebrafish were exposed. Both natural colloids and BP3 could enhance the cell permeability of zebrafish, which allowed colloid-bound BP3 to directly enter the fish and accumulate in its muscle. Besides, although both natural colloids and BP3 could cause the metabolic disorders in adult zebrafish, they affected the physiological and biochemical activities of zebrafish through different pathways. The disturbance of glutathione metabolism in zebrafish induced by natural colloids may be the reason for the diminished ability of zebrafish to clear and transform BP3 in the mixture system. The carrier effect of natural colloids and reduced clearance ability of zebrafish eventually increased the bioaccumulation of BP3 in zebrafish. This study highlights the significance of natural colloids at environmentally relevant concentrations on the biological effects of emerging contaminants in actual waters, however, natural colloids are always ignored in most field investigation of pollutants, which would ultimately lead to an underestimation of the true ecological risk of pollutants.

A review of recent studies on toxicity, sequestration, and degradation of per- and polyfluoroalkyl substances (PFAS)

The fate, effects, and treatment of per- and polyfluoroalkyl substances (PFAS), an anthropogenic class of chemicals used in industrial and commercial production, are topics of great interest in recent research and news cycles. This interest stems from the ubiquity of PFAS in the global environment as well as their significant toxicological effects in humans and wildlife. Research on toxicity, sequestration, removal, and degradation of PFAS has grown rapidly, leading to a flood of valuable knowledge that can get swamped out in the perpetual rise in the number of publications. Selected papers from the Journal of Hazardous Materials between January 2018 and May 2022 on the toxicity, sequestration, and degradation of PFAS are reviewed in this article and made available as open-access publications for one year, in order to facilitate the distribution of critical knowledge surrounding PFAS. This review discusses routes of toxicity as observed in mammalian and cellular models, and the observed human health effects in exposed communities. Studies that evaluate of toxicity through in-silico approaches are highlighted in this paper. Removal of PFAS through modified carbon sorbents, nanoparticles, and anion exchange materials are discussed while comparing treatment efficiencies for different classes of PFAS. Finally, various biotic and abiotic degradation techniques, and the pathways and mechanisms involved are reviewed to provide a better understanding on the removal efficiencies and cost effectiveness of existing treatment strategies.

Assessment of Bioactive Surfactant Levels in Selected Cereal Products

Per- and polyfluoroalkyl substances (PFASs) are bioactive surfactants that are widespread in the environment and living organisms. This study presents measurements of PFAS in selected food of plant origin that are part of the healthy eating pyramid, including bread, rolls, flour, bran, buckwheat, millet, rice, and noodles. A simple and reliable analytical method was developed for the simultaneous determination of seven perfluorocarboxylic acids (PFCAs) and three perfluoroalkane sulfonates (PFSAs) in cereal-based products. Out of the 10 PFASs, 5 PFASs were detected at levels above LOQ. The most frequently detected compound was perfluorooctanoic acid (PFOA), which was quantified in 65.2% of samples, while none of the others were present in more than 40.0% of tested products. Perfluorobutanoic acid (PFBA) was the predominant PFAS in cereal-based products, and its maximum measured concentration was 202.85 ng/g for wheat bran. The soil–root–shoot interactions in relation to PFAS transfer to the above-ground parts of plants and PFAS’s ability to interfere with proteins are most likely the sources of these compounds in commonly consumed cereal products. As PFBA contributes greatly to total PFAS concentration, this food group should be included in future dietary exposure assessments.

Exposure pathways and bioaccumulation of per- and polyfluoroalkyl substances in freshwater aquatic ecosystems: Key considerations

Due to the bioaccumulative behavior, toxicity, and recalcitrance to degradation, per- and polyfluoroalkyl substances (PFAS) are a focus for many researchers investigating freshwater aquatic ecosystems. PFAS are a diverse set of chemicals that accumulate and transport quite differently in the environment depending on the length of their fluoroalkyl chains and their functional groups. This diversity in PFAS chemical characteristics combined with varying environmental factors also impact the bioaccumulation of these compounds in different organisms. In this review, we evaluate environmental factors (such as organic carbon, proteins, lipids, and dissolved cations) as well as PFAS characteristics (head group, chain-length, and concentration) that contribute to the significant variation seen in the literature of bioaccumulation metrics reported for organisms in aquatic ecosystems. Of the factors evaluated, it was found that PFAS concentration, dissolved organic matter, sediment organic matter, and biotransformation of precursor PFAS tended to significantly impact reported bioaccumulation metrics the most. Based on this review, it is highly suggested that future studies provide sufficient details of important environmental factors, specific organism traits/ behavior, and PFAS concentrations/compounds when reporting on bioaccumulation metrics to further fill data gaps and improve our understanding of PFAS in aquatic ecosystems.

Distribution of perfluoroalkyl substances (PFASs) in water, sediment, and fish tissue, and the potential human health risks due to fish consumption in Lake Hawassa, Ethiopia

Due to their global distribution, persistence, bioaccumulative potential and toxicity, perfluoroalkyl substances (PFASs) are considered as hazardous chemicals. Although many studies on PFASs pollution in aquatic environments have been done in the Northern hemisphere, less is known on PFASs pollution in African aquatic ecosystems and the risks they pose to humans through consumption of contaminated biota. The objective of this study was to determine the spatial distribution of PFASs in water, sediment, and fish tissue in Lake Hawassa, Ethiopia, and to investigate possible human health risks due to fish consumption. Among the PFASs detected in water and sediment, perfluorooctanoic acid (PFOA) was the most abundant with mean concentrations of 6.93 ng/L and 0.23 ng/g dw respectively. Long-chained PFASs dominated the PFAS accumulation profiles in fish tissues, with higher concentrations measured in liver compared to muscle tissue. The detected concentrations of PFASs were, however, often similar to those reported in other African aquatic ecosystems. This study showed no potential health risk due to consumption of contaminated fish based on mean concentrations and fish consumption. However, it is expected that peoples who consume more fish (fishermen and local peoples living close to Lake Hawassa) may suffer health risks due to PFASs contamination.

Insights into the impacts of dissolved organic matter of different origins on bioaccumulation and translocation of per- and polyfluoroalkyl substances (PFASs) in wheat

Per- and polyfluoroalkyl substances (PFASs) have been found to be widely present in soil. Dissolved organic matter (DOM) in soil are supposed to greatly affect the bioavailability of PFASs in soil. Herein, hydroponic experiments were conducted to understand the impacts of two kinds of typical DOM, bovine serum albumin (BSA) and humic acid (HA), on the uptake and translocation of legacy PFASs and their emerging alternatives, perfluorooctane sulfonic acid (PFOS), perfluorooctane acid (PFOA), perfluorohexane sulfonic (PFHxS) and 6:2 chlorinated polyfluoroalkyl ether sulfonate (6:2 Cl-PFESA) in wheat (Triticum aestivum L.). The results indicated that both HA and BSA significantly inhibited the bioaccumulation and translocation of PFASs in the roots and shoots of wheat, and the impacts of BSA were greater than HA. This difference was explained by the greater binding affinities of the four PFASs with BSA than with HA, as evidenced by the equilibrium dialysis and isothermal titration calorimetry (ITC) analyses. It was noting that inhibition impacts of the BSA-HA mixture (1:1) were lower than BSA alone. The results of Fourier transform infrared (FT-IR) spectroscopy and excitation-emission matrix (EEM) fluorescence spectroscopy suggested that HA could bind with the fluorescent tryptophan residues in BSA greatly, competing the binding sites with PFASs and forming a cover on the surface of BSA. As a result, the binding of PFASs with BSA-HA complex was much lower than that with BSA, but close to HA. The results of this study shed light on the impacts of DOM in soil on the bioaccumulation and translocation of PFASs in plants.

Role of extracellular polymeric substances in leaching and bioconcentration of benzophenone-3 from microplastic fragments

Adverse effects of microplastics (MPs) are exacerbated by plastic additives such as benzophenone-3 (BP-3). The aim of the present study was to evaluate the role of extracellular polymeric substances (EPS) of Chlorella vulgaris in leaching BP-3 additive (3.0 ± 0.2% wt/wt) from polyethylene MP fragments (99.8 ± 4.1 µm) and subsequent bioconcentration in Daphnia magna. BP-3 leaching in M4 medium was higher at pH 8 than at pH 6, because of the higher solubility of BP-3 (pK_a=7.07) at pH 8. However, EPS reduced BP-3 leaching in M4 medium, possibly because of repulsive interactions between the negatively charged EPS and anionic BP-3. Thus, BP-3 leaching was greater at lower pH (6 >8) and EPS concentration (20 >50 mg L^-1 as total organic carbon), which was well related to BP-3 sorption capacity of EPS. Although BP-3 uptake in D. magna was decreased at pH 8 by increasing EPS concentration, the bioconcentration of BP-3 in D. magna was increased, possibly because of reduced BP-3 elimination. These findings suggest the important role of EPS in the bioconcentration of anionic plastic additives, which should be further evaluated to understand the underlying toxicokinetic mechanisms.

New insights into the colloidal stability of graphene oxide in aquatic environment: Interplays of photoaging and proteins

Wide application leads to release of graphene oxide (GO) in aquatic environment, where it is subjected to photoaging and changes in physicochemical properties. As important component of natural organic matters, proteins may greatly affect the aggregation behaviors of photoaged GO. The effects of a typical model protein (bovine serum albumin, BSA) on the colloidal stability of photoaged GO were firstly investigated. Photoaging reduced the lateral size and oxygen-containing groups of GO, while the graphene domains and hydrophobicity increased as a function of irradiation time (0-24 h). Consequently, the photoaged GO became less stable than the pristine one in electrolyte solutions. Adsorption of BSA on the surface of the photoaged GO decreased as well, leading to thinner BSA coating on the photoaged GO. In the solutions with low concentrations of electrolytes, the aggregation rate constants (k) of all the photoaged GO firstly increased to the maximum agglomeration rate constants (k_fast, regime I), maintained at k_fast (regime Ⅱ) and then decreased to zero (regime Ⅲ) as the BSA concentration increased. In both regime I and III, the photoaged GO were less stable at the same BSA concentrations, and the impacts of BSA on the colloidal stability of the photoaged GO were less than the pristine one, which was attributed to the weaker interactions between the photoaged GO and BSA. This study provided new insights into the colloidal stability and fate of GO nanomaterials, which are subjected to extensive light irradiation, in wastewater and protein-rich aquatic environment.

Occurrence and toxicity of perfluoroalkyl acids along the estuarine and coastal regions under varied environmental factors

Due to the significant economic and ecological value, the increasing pollution threat to estuarine and coastal regions is of great concern. Perfluoroalkyl acids (PFAAs) are emerging pollutants which possess adverse ecological risk. In this review, we have compiled the data on the levels of PFAAs in environmental samples, mainly in estuarine and coastal zones. A worldwide map was generated to show the distribution of PFAAs. The experimental results have also been considered, which, together with those of environmental samples, has allowed us to infer about the factors that intervene in the behavior of PFAAs. The presence of PFAAs is determined primarily by the source of pollution. Salinity is as well shown as a significant condition, dependent too on the sampling environment. The analysis of PFAAs from environmental samples constitutes a fundamental tool for the surveillance of these pollutants, but the lack of homogeneity of protocols for sampling, as well as for the results presentation, limits the comparative capacity. Laboratory studies are also an essential tool in the analysis of particular aspects related to PFAAs, but many times the conditions tested are not environmentally significant. In this way, it would not be prudent to establish "paradigms" about the behavior of the PFAAs in certain areas or organisms, instead to suggest the points that can be considered fundamental for each issue addressed. The main variables that appear to intervene in estuarine and coastal regions are mainly the proximity to the source of pollution, salinity, pH, precipitation (rain) as well as types of PFAAs. All these can synergistically lead to different impacts on the ecosystem. Therefore, the particular risks of PFAAs in estuarine and coastal regions is a set of multiple variables, dependent on each sampling condition and according to the previously named parameters.

A critical review of modeling Poly- and Perfluoroalkyl Substances (PFAS) in the soil-water environment

Due to their health effects and the recalcitrant nature of their CF bonds, Poly- and Perfluoroalkyl Substances (PFAS) are widely investigated for their distribution, remediation, and toxicology in ecosystems. However, very few studies have focused on modeling PFAS in the soil-water environment. In this review, we summarized the recent development in PFAS modeling for various chemical, physical, and biological processes, including sorption, volatilization, degradation, bioaccumulation, and transport. PFAS sorption is kinetic in nature with sorption equilibrium commonly quantified by either a linear, the Freundlich, or the Langmuir isotherms. Volatilization of PFAS depends on carbon chain length and ionization status and has been simulated by a two-layer diffusion process across the air water interface. First-order kinetics is commonly used for physical, chemical, and biological degradation processes. Uptake by plants and other biota can be passive and/or active. As surfactants, PFAS have a tendency to be sorbed or concentrated on air-water or non-aqueous phase liquid (NAPL)-water interfaces, where the same three isotherms for soil sorption are adopted. PFAS transport in the soil-water environment is simulated by solving the convection-dispersion equation (CDE) that is coupled to PFAS sorption, phase transfer, as well as physical, chemical, and biological transformations. As the physicochemical properties and concentration vary greatly among the potentially thousands of PFAS species in the environment, systematic efforts are needed to identify models and model parameters to simulate their fate, transport, and response to remediation techniques. Since many process formulations are empirical in nature, mechanistic approaches are needed to further the understanding of PFAS-soil-water-plant interactions so that the model parameters are less site dependent and more predictive in simulating PFAS remediation efficiency.

Improvement of α-amylase to the metabolism adaptions of soil bacteria against PFOS exposure

Toxicity of perfluoroalkyl substances (PFASs) in soils towards bacteria shows an impact on its ecosystem function. This study aims to obtain insight into the effect of hydrolase (e.g. α-amylase) in soil on metabolism adaptions of bacteria (e.g. Bacillus substilis) against PFOS exposure. Results show that exogenous α-amylase alleviates PFOS toxicity to bacteria growth, disturbance to membrane permeability and stimulation to reactive oxygen species (ROS) production. The mechanisms were owing to that α-amylase strongly influences the strategies of metabolism adaptions of bacteria against PFOS stress. In details, α-amylase prompts bacteria to regulate the secretion of extracellular polymeric substances (EPSs) and the production of metabolic signal (acetic acid), which leads to changes in the physicochemical properties (hydrophilicity, surface charge) of the bacterial surface and the inactivation of the interaction with PFOS, thereby reducing the PFOS toxicity. Molecular simulations show that PFOS combines with Srt A at Gly 53 and Trp 171, which may induce the increase of permeability and changes of surface characteristics. Meanwhile, α-amylase competes with Srt A to bind PFOS at Arg 125 and Lys 176. This competition changes the physicochemical characteristics of PFOS and its bioavailability, further improving the metabolism adaptions of bacteria against PFOS. Altogether, this work provides direct evidences about α-amylase buffering effect of PFOS and demonstrates that the presence of α-amylase affects the essential but complex metabolic response in bacteria triggered by PFOS.

Dynamics, thermodynamics, and mechanism of perfluorooctane sulfonate (PFOS) sorption to various soil particle-size fractions of paddy soil

Soil is an important sink for perfluorooctane sulfonate (PFOS) that is a typical persistent organic pollutant with high toxicity. Understanding of PFOS sorption to various particle-size fractions of soil provides an insight into the mobility and bioavailability of PFOS in soil. This study evaluated kinetics, isotherms, and mechanisms of PFOS sorption to six soil particle-size fractions of paddy soil at environmentally relevant concentrations (0.01-1 μg/mL). The used soil particle-size fractions included coarse sand (120.4-724.4 mm), fine sand (45.7-316.2 mm), coarse silt (17.3-79.4 mm), fine silt (1.9-39.8 mm), clay (0.5-4.4 mm), and humic acid fractions (8.2-83.7 mm) labeled as F1~F6, respectively. PFOS sorption followed pseudo-second-order kinetics related to film diffusion and intraparticle diffusion, with speed-limiting phase acted by the latter. PFOS sorption isotherm data followed Freundlich model, with generally convex isotherms in larger size fractions (F1~F3) but concave isotherms in smaller size fractions (F4 and F5) and humic acid fraction (F6). Increasing organic matter content, Brunner-Emmet-Teller surface area, and smaller size fractions were conducive to PFOS sorption. Hydrophobic force, divalent metal ion-bridging effect, ligand exchange, hydrogen bonding, and protein-like interaction played roles in PFOS sorption. But hydrophobic force controlled the PFOS sorption, because its relevant organic matter governed the contribution of the soil fractions to the overall PFOS sorption. The larger size fractions dominated the PFOS sorption to the original soil because of their high mass percentages (~80%). This likely caused greater potential risks of PFOS migration into groundwater and bioaccumulation in crops at higher temperatures and c_e values, based on their convex isotherms with an exothermic physical process.

Elevated temperature enhances the bioavailability of pyrene to Daphnia magna in the presence of dissolved organic matter: Implications for the effect of climate warming

Dissolved organic matter (DOM) is an essential factor in natural waters to affect the bioavailability of hydrophobic organic compounds (HOCs). Climate warming may influence the partition of HOCs between DOM and water as well as the physiology of organisms. Thus, we hypothesized that elevated temperature might affect the bioavailability of HOCs in the presence of DOM. To test this hypothesis, the effect of temperature on the bioavailability of pyrene to Daphnia magna (D. magna) in water-DOM (fulvic acid) system was investigated. The results showed that, although the concentration of freely dissolved pyrene increased slightly with temperature in the presence of DOM when the level of total dissolved pyrene was kept constant, D. magna immobilization (increased by 50.0-167%) and internal body burden of pyrene (increased by 18.4-41.5%) increased significantly with every 4 °C increase in temperature (16, 20, 24 °C). The main reasonable explanation for this result is that elevated temperature promoted pyrene uptake by D. magna. It was found that the increase percentage of 1-hydroxypyrene (main metabolite of pyrene) concentrations with temperature was higher than that of pyrene concentrations in the body except gut of D. magna. This result indicated that increased temperature might enhance the metabolic rates of D. magna, thus leading to increased uptake rate of freely dissolved and DOM-associated pyrene. This study suggests that elevated temperature might enhance the bioavailability of HOCs in natural waters through influencing both the bioavailable fraction of HOCs and their uptake rates in aquatic organisms, and this should be considered for evaluating their eco-environmental risks under the context of climate warming.

Perfluorinated alkyl substances impede growth, reproduction, lipid metabolism and lifespan in Daphnia magna

Per- and polyfluorinated alkyl substances (PFASs) are synthetic organofluorine compounds with unique stability accompanied with hydrophobic and lipophobic properties. Perfluorooctane sulfonate (PFOS) and Perfluorooctanoic acid (PFOA) are of high concern due to their wide application in consumer and industrial products, extreme persistence, abundant occurrence in the environment and their toxic effect to humans and animals. However, knowledge on the molecular mechanisms of toxicity and the effects on reproduction output remain scarce. In this study, we analyzed the effects of PFOS and PFOA on Daphnia magna. Acute toxicity, development, reproduction, lipid metabolism (lipid-accumulation) and lifespan was investigated, as well as the expression of genes related to these endpoints. Exposure of PFOS and PFOA at 1, 10 and 25 μM did not cause acute lethality. Hatching was reduced following exposure to both compounds, and lifespan was decreased following exposure to 25 μM PFOS. Body length of Daphnia magna was reduced significantly by 25 μM PFOS following 7 days exposure. Lipid staining revealed that all PFAS exposures increased lipid accumulation. qRT-PCR analysis of genes involved in lipid metabolism suggests that the increase in lipid content could be due to inhibition of genes involved on absorption and catabolism of fatty acids. Exposure to both PFOA and PFOS reduced the fecundity significantly. Downregulation of genes involved in development and reproductive process, including vtg2, vasa, EcRA, EcRB, usp, jhe, HR3, ftz-F1, E74 and E75 were observed. The alterations in developmental and reproductive genes as well as the disturbed lipid metabolism provides mechanistic insight into the possible causes for decreased fecundity and lifespan observed following exposure to both PFOS and PFOA.

Influence of dissolved organic matter on the accumulation, metabolite production and multi-biological effects of environmentally relevant fluoxetine in crucian carp (Carassius auratus)

Fluoxetine is a widely prescribed antidepressant that has been frequently detected in aquatic environments and is associated with a series of neurological, behavioural and neuroendocrine disruptions in nontarget organisms. However, studies on its effects in fish under realistic environmental conditions are still limited. In this study, we determined the influences of an environmentally relevant concentration of fluoxetine (100 ng/L) on crucian carp (Carassius auratus) in the presence of dissolved organic matter (DOM). Endpoints that were assessed included accumulation of fluoxetine and metabolite formation as well as related biological responses involving neurotransmission and metabolic processes. Fluoxetine was significantly bioconcentrated in the fish brain and liver and largely transformed to the active metabolite norfluoxetine. Brain neurotransmission processes related to serotonin and choline and liver metabolic status were simultaneously altered. DOM added at 1 mg/L had no effect on the accumulation of fluoxetine or its metabolites in different tissues of the fish. However, at 10 mg/L DOM facilitated fluoxetine and norfluoxetine accumulation in the liver, brain, kidney, gill and bile tissues of the fish. The neuroendocrine-disrupting effects on fish caused by fluoxetine were also enhanced by the co-addition of DOM at 10 mg/L. Binding with fluoxetine and the inhibition of metabolic functions caused by DOM may be responsible for this increase in effects. These findings imply that at high concentrations DOM can increase the toxicity of environmentally relevant concentrations of fluoxetine to fish.

Multicompartment occurrence and partitioning of alternative and legacy per- and polyfluoroalkyl substances in an impacted river in China

Per- and polyfluoroalkyl substances (PFASs) are emerging global environmental contaminants. Exploring the occurrence and environmental behavior of PFASs in the aquatic environment is a key step in solving global fluorine chemical pollution problems. In this study, surface water, pore water, and sediment were collected from the main tributary and the middle and lower reaches of the Daling River, adjacent to the Fuxin fluorochemical manufacturing facilities in Liaoning Province in China, to elucidate the occurrence and partition behavior of PFASs. The total concentrations of PFASs ranged from 48.4 to 4578 ng/L in the overlying water, from 173 to 9952 ng/L in the pore water, and from 2.16 to 40.3 ng/g dw in the sediment fraction. Generally, perfluorobutanoic acid (PFBA) and perfluorobutane sulfonate (PFBS) were the predominant congeners in the samples, with the mean relative content fractions being almost consistently >40% in the dissolved phase and >25% in the sediment. Hexafluoropropylene oxide dimer acid (HFPO-DA) and chlorinated polyfluorinated ether sulfonic acid (6:2 Cl-PFESA) were detected, albeit at low levels. In addition, the detection frequency and the contribution of legacy long-chain PFASs in sediment were higher than those in the overlying water and pore water. Except for perfluorohexane sulfonate (PFHxS), the concentrations of the alternative PFASs in the pore water were higher than in the overlying water. The organic carbon fraction was a more important controlling factor for PFAS sediment levels than cations content. As with legacy long-chain PFASs, HFPO-DA and 6:2 Cl-PFESA tended to partition into the solid phase, whereas short-chain PFASs were readily distributed in the aqueous phase. Such research results will be helpful in modeling the transport and fate of PFASs released by point sources into coastal waters through rivers and in developing effective risk assessment and management strategies for the control of PFAS pollution.

Influence of aquatic colloids on the bioaccumulation and biological effects of diclofenac in zebrafish (Danio rerio)

Natural aquatic colloids play an important role in the migration, transformation of pollutants in the environment, but their potential effects are often ignored in ecotoxicology research. In this study, diclofenac (DCF) was selected as a typical drug to study the effects of natural colloids on the bioaccumulation and biotoxicity in juvenile zebrafish (Danio rerio) exposed to an environmentally relevant concentration (1 μg/L) and a high concentration (100 μg/L) of DCF. The results showed that the presence of colloids accelerated and enhanced the accumulation of DCF in zebrafish muscle and viscera, and the effects are greater at the environmentally relevant concentration of DCF. However, the colloids enhanced the burden in the head in the environmentally relevant concentration group, but reduced it in the high concentration group. This observation may be related to the occurrence of variations in the contribution of the adsorption forms of DCF and the colloids depending on different DCF concentrations. At the same time, the presence of colloids can significantly induce AChE activity of DCF in the brain and alter swimming activity and shoaling behaviour of the individuals, however no significant effects on the attack and shock behaviour were observed. These findings indicate that the combination of natural colloids and pollutants may change with pollutant concentrations, thereby altering the bioaccumulation and biological effects in aquatic organisms.

Bioavailability and Bioaccumulation of 6:2 Fluorotelomer Sulfonate, 6:2 Chlorinated Polyfluoroalkyl Ether Sulfonates, and Perfluorophosphinates in a Soil-Plant System

As emerging alternatives of legacy perfluoroalkyl substances, 6:2 fluorotelomer sulfonate (6:2 FTS), 6:2 chlorinated polyfluoroalkyl ether sulfonates (6:2 Cl-PFESA), and perfluorophosphinates (C6/C6 and C8/C8 PFPiAs) are supposed to be partitioned to soil and highly persistent in the environment. The uptake of novel per- and polyfluoroalkyl substances (PFASs) by plants represents a potential pathway for their transfer in the food chain. In this study, the bioavailability of these four novel PFASs in soil and the bioaccumulation characteristics in greenhouse-grown wheat (Triticum aestivum L.), maize (Zea mays L.), soybean (Glycine max L. Merrill), and pumpkin (Cucurbita maxima L.) were investigated. The results indicated that these novel PFASs with higher hydrophobicity were more easily sequestrated in soil, and the fractions extracted by methanol could well describe their bioavailability, which could be stimulated by low-molecular-weight organic acids at rhizospheric concentrations. A negative relationship was found between root soil concentration factors (RSCFs) and hydrophobicity (log Kow) of the target PFASs. This correlation was also found in the translocation factors (TF) from roots to shoots. Furthermore, the uptake and transfer of the target PFASs were regulated by the protein contents in plant roots and shoots.

Negligible effects of TiO2 nanoparticles at environmentally relevant concentrations on the translocation and accumulation of perfluorooctanoic acid and perfluorooctanesulfonate in hydroponically grown pumpkin seedlings (Cucurbita maxima × C. moschata)

Titanium dioxide nanoparticles (TiO₂-NPs) are widely distributed in the environment. It has been demonstrated that TiO₂-NPs could modify the environmental fate and bioavailability of organic pollutants, which affects ecological risks of TiO₂-NPs and organic pollutants. In this study, the uptake, translocation and accumulation of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) in pumpkin plants was investigated in the presence of TiO₂-NPs. We reported for the first time the negligible effects of TiO₂-NPs at environmentally relevant concentrations (0.05-5 mg/L) on the uptake and accumulation of PFOA and PFOS in hydroponically grown pumpkin seedlings regardless of root, stem and leaf. This phenomenon was independent of the initial concentrations of PFOA/PFOS and TiO₂-NPs in the exposure solution. Also, seedling mass and contents of chlorophyll and anthocyanin were not affected by the co-exposure. Adsorption tests demonstrated the negligible adsorption of PFOA/PFOS on TiO₂-NPs in the exposure solution. Moreover, uptake of PFOA/PFOS was insensitive to aquaporin inhibitor AgNO₃ but significantly inhibited by niflumic acid (anion channel blocker) and 2,4-dinitrophenol (metabolic inhibitor) whereas Ti concentration in root was not affected by niflumic acid and 2,4-dinitrophenol but significantly decreased by AgNO₃, indicating that transport of PFOA/PFOS and TiO₂-NPs were via different routes into the pumpkin seedling. It was proposed that different pathways by which TiO₂-NPs and PFOA/PFOS transported into the pumpkin seedling and negligible adsorption of PFOA/PFOS on TiO₂-NPs contributed to the negligible effects of TiO₂-NPs on the uptake, translocation and accumulation of PFOA/PFOS in pumpkin seedlings. In total, this work would improve our understanding of the ecological risks of TiO₂-NPs in the environment.

Occurrence of perfluorinated compounds in agricultural environment, vegetables, and fruits in regions influenced by a fluorine-chemical industrial park in China

The occurrence of perfluorinated compounds (PFCs) in vegetables and fruits, as well as agricultural environment, was investigated in the downstream regions of Changshu fluorine-chemical industrial park (CFCIP) in China. Twenty-one PFCs were analyzed in irrigation water, agricultural soil, typical vegetables, and fruits, with the maximum total PFC concentrations of 369.9 ng/L, 64.7 ng/g dw, 11.5 ng/g ww, and 10.5 ng/g ww, respectively. Short-chained perfluoroalkyl carboxylic acids (PFCAs) such as perfluorooctanoic acid (PFOA), perfluorobutanoic acid (PFBA), and perfluorohexanoic acid were the dominant PFCs in terms of their concentrations and detection frequency. PFCs in irrigation water and agricultural soils showed a decreasing trend with increasing distance from CFCIP, while this pattern was not observed in agricultural products. The predominant compounds varied in different vegetables and fruits. Simultaneous bioaccumulation of PFBA and PFOA was found in melons and solanaceous species and pears. Leafy vegetables and grapes exhibited high bioaccumulation of PFOA and PFBA, respectively. Health risk assessment by calculating estimated daily intake showed that no direct risk was caused by the consumption of vegetables and fruits for the residents in the investigated regions. However, the tolerable weekly intake of PFOA exceeded the established thresholds for the adult residents. A comprehensive health assessment of the dietary exposure of PFCs, including all exposure pathways, in fluorine-chemical industrial park-impacted regions is needed.

Multiple crop bioaccumulation and human exposure of perfluoroalkyl substances around a mega fluorochemical industrial park, China: Implication for planting optimization and food safety

Perfluoroalkyl substances (PFASs) have become a recognized concern due to their mobility, persistence, ubiquity and health hazards in the environment. In this study, ten types of vegetables and three types of grain crops were collected in two open-air fields with different distances (0.3 km, 10 km) from a mega fluorochemical industrial park (FIP), China. Bioaccumulation characteristics of PFASs in light of crop types and organs were explored, followed by analyzing human exposure and risks to local residents with different age groups and dietary habits. Elevated levels of ∑PFASs were found nearby the FIP ranging from 79.9 ng/g to 200 ng/g in soils and from 58.8 ng/g to 8085 ng/g in crops. Perfluorooctanoic acid (PFOA) was the predominant PFAS component in soil; while shorter-chain perfluoroalkyl carboxylic acids (PFCAs), especially perfluorobutanoic acid (PFBA), were the major PFAS contaminants in multiple crops, resulting from their bioaccumulation preference. Depending on the crop types, the bioaccumulation factors (BAFs) of ∑PFASs for edible parts varied from 0.36 to 48.0, and the highest values were found in shoot vegetables compared with those in fruit vegetables, flower vegetables, root vegetables and grain crops. For typical grains, the BAFs of ∑PFASs decreased in the order of soybean (Glycine max (Linn.) Merr.), wheat (Triticum aestivum L.) and corn (Zea mays L.), possibly related to their protein and lipid content. Among specific organs in the whole plants, leaves exhibited the highest BAFs of ∑PFASs compared with corresponding roots, stems, husks or grains. With increasing carbon chain lengths of individual PFCAs (C4-C8), the logarithm of their BAFs for edible parts of various crops showed a linear decrease (0.1-1.16 log decrease per CF₂ unit), and the largest decrease was observed in grains. Human exposure to PFOA via the consumption of contaminated crops represents a health risk for local residents, especially for low-age consumers or urban consumers with higher vegetable diet. Implications for planting optimization and food safety were provided aiming to reduce health hazards of PFASs.

Antioxidant defence system is responsible for the toxicological interactions of mixtures: A case study on PFOS and PFOA in Daphnia magna

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are two types of perfluorinated compounds (PFCs) frequently studied in recent years due to their potential for bioaccumulation and toxicity to humans. Usually, PFCs can co-exist in various environment. Therefore, over- or under-estimated risk assessments would result if antagonism or synergism occurred in mixture toxicity. In the present study, the acute and chronic toxicities of single and mixtures of PFOA and PFOS to Daphnia magna were investigated. PFOS was more toxic than PFOA, both in 48-h acute toxicity and 21-d chronic toxicity. In acute toxicity tests, mixture toxicities showed strong synergistic effects on mortality. The experimental EC₅₀ of the mixture is 4.44 × 10^-5 mol/L, whereas the predicted EC₅₀ is 8.19 × 10^-5 mol/L by Concentration Addition Model and 9.73 × 10^-5 mol/L by Independent Action Model. In chronic toxicity tests, synergistic effects were also found in the aspects of offspring. The offspring rate is reduced significantly to 39.8% at the 9.61 × 10^-7 mol/L of mixture, while, PFOS and PFOA do not have effects when they are tested individually at corresponding concentrations. To explore the potential mechanism of the synergistic effect, the interactions between PFCs and proteins, including acetylcholinesterase, superoxide dismutase, catalase, ecdysone receptor and glutathione-S-transferase, were investigated by the Molecular Docking. The docking results revealed that the driving forces for the binding of PFCs with proteins were predominantly hydrophobic and hydrogen-bonding interactions. Based on the binding models, we deduced that the potential mechanism of synergism is that PFOS and PFOA have similar binding modes with catalase and have different binding modes with superoxide dismutase. Overall, these data provide experimental evidence that there is strong synergism in acute and chronic toxicity of mixtures to D. magna and demonstrate that molecular structure of some components of the antioxidant defence system contributes to the synergistic interaction.

Effects of fluorescent dissolved organic matters (FDOMs) on perfluoroalkyl acids (PFAAs) in lake and river water

This study presents the effects of fluorescent dissolved organic matters (FDOM) on perfluoroalkyl acids (PFAAs) in western Lake Chaohu and its inflow rivers. The surface water samples from the 27 sites in western Lake Chaohu and its inflow rivers were collected in March and September 2013. The contents of PFAAs and the FDOM in the water samples were measured by a high-performance liquid chromatograph - mass spectrometer (HPLC-MS) and by a fluorescence spectrophotometer, respectively. The temporal-spatial distributions of PFAAs and FDOM, as well as their interrelationships, were investigated. Eleven PFAA components were detected, and the mean concentration of total PFAAs (TPFAAs) in western Lake Chaohu and its inflow rivers were 12.93 ± 5.19 ng/L and 11.84 ± 9.50 ng/L, respectively. PFOA was the predominant contaminant in two regions (7.13 ± 3.07 ng/L and 4.30 ± 2.14 ng/L) followed by PFHxA (1.72 ± 0.80 ng/L and 1.42 ± 1.41 ng/L) and PFBA (1.44 ± 0.78 ng/L and 1.37 ± 0.78 ng/L). The mean concentration of total FDOM in western Lake Chaohu and its inflow rivers were 220.0 ± 40.30 μg quinine sulfate units (Q.S.)/L and 406.3 ± 213.1 μg Q.S./L, respectively. The significant, positive correlations were observed between the PFAAs and FDOMs in both the lake area and the inflow rivers. However, no significant correlation was observed between PFAAs and the dissolved organic carbon (DOC) in the lake area. This finding indicated that the residues and distributions of PFAAs were significantly dependent on the compositions of dissolved organic matters (DOM) and not on the total content of DOM.

Comparison of the accumulation and metabolite of fluoxetine in zebrafish larva under different environmental conditions with or without carbon nanotubes

Few studies have focused on the influence of environmental conditions on the bioavailability of pollutants interacted with nanomaterials in organisms. In this study, we primarily compared the influence of multiwalled carbon nanotubes (MWCNTs) on the bioavailability of fluoxetine in zebrafish (Danio rerio) larva under different environmental conditions: natural organic matter (NOM) and salinity. The results showed that fluoxetine accumulated in the larvae and then transformed into the metabolite norfluoxetine, with the metabolic rates from 2.8 to 3.5. Following co-exposure to MWCNTs, the accumulation of fluoxetine and norfluoxetine were further enhanced, suggesting a superior carrier of MWCNTs for fluoxetine, especially the functional MWCNTs. The consistent increase in the fluoxetine and norfluoxetine accumulation highlights the bioavailability of absorbed fluoxetine on MWCNTs in zebrafish larvae. The presence of NOM promoted the accumulation of fluoxetine and norfluoxetine in zebrafish, but alleviated the carrier effects of MWCNTs, acting as a natural antidote. Salinity negatively influenced the bioavailability of fluoxetine in the larvae, and further reversed the enhancements caused by MWCNTs. These findings provide a new insight into the influence of environmental conditions on the interactions between nanomaterials and pollutants in organisms.

Effects of natural dissolved organic matter on the complexation and biodegradation of 17α-ethinylestradiol in freshwater lakes

Natural dissolved organic matter (DOM) produced in algal blooms and overgrowths of macrophyte changes the elimination and ecotoxicity of estrogens in freshwater lakes. The complexation of 17α-ethinylestradiol (EE2) and various DOMs, including the water- and sediment-derived DOMs from the algal-dominant zone in Lake Taihu (TW and TS, respectively) and the macrophyte-dominant zone in Poyang Lake (PW and PS, respectively), and the humic acid (HA), was investigated along with the subsequent effects on EE2 biodegradation. Dialysis equilibrium experiments showed that binding to DOM significantly decreased the freely soluble concentrations of EE2. The binding capacity of the five DOMs followed the order of PW < TW < PS ≈ TS < HA. A negative correlation was found between the organic-carbon-normalized sorption coefficient (logK_DOC) and the absorption ratio (E₂/E₃) of DOM, indicating that the large sized, aromatic molecules were involved in the complexation. The reduced freely soluble concentrations of EE2 did not inhibit its biodegradation by an EE2-degrading strain, Rhodobacter blasticus. Conversely, the autochthonous-dominated water-derived DOMs stimulated a more extensive biodegradation of EE2 than the sediment-derived DOMs, and the existence of HA resulted in the smallest increase in EE2 biodegradation. The promoting effect was associated with the increased concentration, activity, and transforming rate of R. blasticus by the bioavailable components in DOM. The present study suggests that the significant impact of natural DOM should be fully considered when assessing the fate and ecological risks of estrogens in eutrophic waters.

A microscale solid-phase microextraction probe for the in situ analysis of perfluoroalkyl substances and lipids in biological tissues using mass spectrometry

An ambient mass spectrometry method for rapid, in situ, and microscale analysis of PFASs and lipids simultaneously in biological tissues for investigation of their biological correlation.

Cultivar-Dependent Accumulation and Translocation of Perfluorooctanesulfonate among Lettuce ( Lactuca sativa L.) Cultivars Grown on Perfluorooctanesulfonate-Contaminated Soil

Perfluorooctanesulfonate (PFOS) is a toxic and persistent organic pollutant that can be widely detected in agricultural soils. In this study, two lettuce cultivars with low PFOS accumulation were screened out to reduce the exposure of PFOS to the human body via vegetable consumption. The screened low-PFOS cultivars may help to ensure food safety, despite planting in highly PFOS-polluted soils (1.0 mg/kg), due to their high tolerance to PFOS and 4.4-5.7 times lower shoot PFOS concentration than the high-PFOS cultivars. Protein content and protein-mediated transpiration played key roles in regulating PFOS accumulation in the lettuce cultivars tested. Lower protein content, lower stomatal conductance, and lower transpiration rate resulted in low PFOS accumulation. This study reveals the mechanism of forming low-PFOS accumulation of lettuce cultivars at physiological and biochemical levels and lays a foundation for developing a cost-effective and safe approach to grow vegetables in PFOS-polluted soils.

Distribution, partitioning and inhalation exposure of perfluoroalkyl acids (PFAAs) in urban and rural air near Lake Chaohu, China

To investigate the distribution, partitioning, and inhalation exposure risks of perfluoroalkyl acids (PFAAs), gaseous and particulate samples were collected monthly between September 2013 and September 2015 in urban and rural areas near Lake Chaohu. Twelve PFAAs were determined by liquid chromatography-mass spectrometry. The mean concentrations of PFAAs in the gaseous phase and the particulate phase were 40.31 ± 31.47 pg/m³ and 63.26 ± 41.87 pg/m³, respectively. Perfluorobutanoic acid (PFBA) was the predominant contaminant in the gaseous phase (32.56% ± 9.28%), while perfluorooctanoic acid (PFOA) was the main contaminant in the particulate phase (33.21% ± 18.69%). The ratios of gaseous to particulate distribution ranged from 0.01 to 16.75. The gaseous-particulate partitioning coefficients, ranging from 0.01 to 23.41 ± 10^-2 m³/μg, were significantly correlated with PM₁₀ concentrations and meteorological conditions, such as temperature and air pressure. The inhalation exposures of PFOA and PFOS were 1.94-60.2 pg/(kg·d) and 0.30-4.22 pg/(kg·d), respectively. The carcinogenic risk of PFOA for urban males was the highest and that for rural females was the lowest; the risks were lower than the acceptable level (10^-6) defined by the US Environmental Protection Agency (USEPA). The non-carcinogenic risks of PFOA and PFOS were far below one.

Competitive sorption of lead and methylene blue onto black soil and their interaction with dissolved organic matter using two-dimensional correlation analyses

This study investigated the competitive sorption of black soil to adsorb Pb(II) and methylene blue (MB) from multi-contaminated soils. According to the experimental data, the process of adsorption can be clearly explained by pseudo-second-order kinetic equation. Both single and binary systems of the adsorption isotherms had a good fit with Langmuir models. The maximal adsorption abilities of Pb(II) and MB acquired from binary systems sorption were attenuated compared to those from the single system (Pb(II): 77.70 > 65.96 mg g^-1; MB: 242.31 > 222.36 mg g^-1). Pb(II) and MB can inhibit each other's sorption ability. A combination of three-dimensional excitation-emission matrix (3D-EEM), synchronous fluorescence spectra as well as two-dimensional correlation spectroscopy (2D-COS) were employed to determine the binding of dissolved organic matter (DOM) for Pb(II) and MB during soil sorption process. As a result, 3D-EEM implicated that the two main composes of DOM were humic acid-like substances and the fluorescence of DOM specimens were gradually diminished with increasing concentrations of Pb(II) and MB. According to synchronous fluorescence spectra, static quenching of Pb(II) and MB mainly led to fluorescence quenching. Specifically, fluorescence-2D-COS implicated that Pb(II) and MB bound to fluorescence in the following sequence: the earlier occurrence of the humic-like fraction compared to that of protein-like fraction. FTIR-2D-COS results concluded that the structural change sequence of DOM by Pb(II) binding followed the order: 1700＞863＞1332＞1529＞1200＞1086 cm^-1 and the sequence of the MB binding affinities followed the order: 1520＞1399＞1345＞1152＞1602＞993＞881 cm^-1. These findings would be beneficial to understand the mechanism of adsorb multi-component systems and have the potential to contribute significance to the interaction mechanism of multi-component with soil DOM at the molecular level.

Evaluation of Daphnia magna metabolic responses to organic contaminant exposure with and without dissolved organic matter using 1H nuclear magnetic resonance (NMR)-based metabolomics

Previous studies have shown that contaminant toxicity to target organisms is altered by the presence of dissolved organic matter (DOM). Contaminants can bind to DOM and this may alter the bioavailability and subsequent toxicity of the contaminants. However, molecular-level techniques are needed to more closely evaluate the impact of DOM on the sub-lethal biochemical responses to emerging contaminants. To investigate how DOM may alter the metabolic response to organic contaminant exposure, ¹H nuclear magnetic resonance (NMR)-based metabolomics was used to investigate how the metabolome of Daphnia magna changes when Suwannee River DOM (5 mg organic carbon/L) is included in the acute exposure of four contaminants with varying hydrophobicity. Sub-lethal concentrations of the hydrophobic contaminant 17α-ethynylestradiol (EE2), the relatively more polar compounds carbamazepine and imidacloprid, or the anionic contaminant perfluorooctane sulfonate (PFOS) were used. A 48-h exposure to DOM alone had a minor impact on the metabolome of D. magna. There were significant increases in amino acids from EE2 exposure which were reduced in the presence of DOM, suggesting that DOM may alleviate the sub-lethal metabolic response from EE2 exposure through sorption and a reduction in freely dissolved EE2. The metabolome was relatively unaltered with exposure to carbamazepine and imidacloprid in the presence of DOM which is likely because these contaminants are water soluble and did not strongly interact with DOM. PFOS exposure resulted in a more significant metabolic response with DOM suggesting that DOM enhanced the uptake and bioavailability of PFOS in D. magna. As such, the presence of DOM should be considered when determining sensitive molecular-level changes in organisms to sub-lethal organic contaminant exposure.

Structural characteristics, analytical techniques and interactions with organic contaminants of dissolved organic matter derived from crop straw: a critical review

Dissolved organic matter (DOM) represents one of the most mobile and reactive organic compounds in an ecosystem and plays an important role in the fate and transport of soil organic pollutants, nutrient cycling and more importantly global climate change. Advances in environment geochemistry in the past two decades have improved our knowledge about the genesis, composition, and structure of DOM, and its effect on the environment. Application of analytical technology, for example UV-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), Nuclear magnetic resonance (NMR) spectroscopy, and three-dimensional fluorescence spectroscopy (3D-EEM) have resulted in these advances. At present, crop straw, as a part of energy development strategy, is mainly used for soil amendment, fodder, fertilizer and industrial materials. Moreover, the fermentation and decomposition of straw should be also promoted for ecological agriculture. However, few studies have focused on the structural properties of DOM derived from crop straw in farmland soil. In this article, DOM derived from crop straw, which is abbreviated to "CDOM", presents active physicochemical properties that can affect the migration and bioavailability of organic contaminants (OCs) in terrestrial ecosystems. The objectives of this review paper are: (i) to discuss the structural characteristics, analytical techniques and interactions between CDOM and OCs in farmland soil; (ii) to present a critical analysis of the impact of CDOM on the physicochemical transformation and transport of OCs in farmland soils; (iii) to provide the perspectives in future research. Therefore, the findings obtained from this study can be utilized to evaluate the relations of interactions between CDOM and OCs in agricultural soils, in order to support some suggestions for future development in agricultural waste recycling, buffering of organic pollution, and the effect on the global carbon cycle.

Dissolved organic matter affects both bioconcentration kinetics and steady-state concentrations of polycyclic aromatic hydrocarbons in zebrafish (Danio rerio)

Dissolved organic matter (DOM) is ubiquitous in natural aquatic ecosystems. The association of hydrophobic organic compounds (HOCs), such as polycyclic aromatic hydrocarbons (PAHs), with DOM may have a large impact on HOC fractions in water and their bioconcentration in fish. However, the effects of DOM on HOC bioconcentration in fish are not well understood, especially whether DOM will affect the bioconcentration steady-state concentrations of HOCs in fish is still confusing. Thus, this study investigated the effects of three DOM including gallic acid (GA), tannic acid (TA), and humic acid (HA) with molecular weights ranging from 170 Da to about 10 kDa at different concentrations (1, 5, and 15 mgOC L^-1) on the bioconcentration of PAHs including phenanthrene, anthracene, fluoranthene, and pyrene in zebrafish (Danio rerio), with the PAH freely dissolved concentrations maintained constant by passive dosing systems. The results revealed that the presence of DOM generally increased the bioconcentration steady-state concentrations of the PAHs in zebrafish (C_b-ss), with the increase ranging from 28.1% to 204.0%, and the increase of C_b-ss promoted by TA with middle molecular weight (1700 Da) was the highest among the studied DOM. Moreover, the C_b-ss increased with the concentrations of GA with low molecular weight and TA with middle molecular weight in water, whereas decreased with increasing concentrations of HA with high molecular weight. The uptake rate constants of the PAHs in zebrafish with DOM were higher than that without DOM. Ingestion of DOM and direct accumulation of PAHs associated with DOM might be primary influencing mechanisms of DOM on the C_b-ss, and whether the facilitated diffusive mass transfer by DOM will affect the C_b-ss needs to be further studied. This study suggested that DOM-associated HOCs should be considered in future HOC risk assessment in addition to the freely dissolved HOCs.