Comparing humic substance and protein compound effects on the bioaccumulation of perfluoroalkyl substances by Daphnia magna in water

The unique distribution pattern of PFAS in landfill organics

PFAS from degrading landfill waste partition into organic matter, leachate, and landfill gas. Driven by the limited understanding of PFAS distribution in landfill organics, we analyzed PFAS across various depths and seven spatially distinct locations within a municipal landfill. The measured PFAS concentrations in organics ranged from 6.71 to 73.06 µg kg-1, a sum of twenty-nine PFAS from six classes. Perfluorocarboxylic acids (PFCAs) and fluorotelomer carboxylic acids (FTCAs) were the dominant classes, constituting 25-82 % and 8-40 % of total PFAS at different depths. PFBA was the most dominant PFCA with a concentration range of 0.90-37.91 µg kg-1, while 5:3 FTCA was the most prevalent FTCA with a concentration of 0.26-17.99 µg kg-1. A clear vertical distribution of PFAS was observed, with significantly greater PFAS concentrations at the middle depths (20-35 ft), compared to the shallow (10-20 ft) and high depths (35-50 ft). A strong positive correlation (r > 0.50) was noted between total PFAS, total carbon, and dissolved organic matter in landfill organics. Multivariate statistical analysis inferred common sources and transformations of PFAS within the landfill. This study underscores the importance of a system-level analysis of PFAS fate in landfills, considering waste variability, chemical properties, release mechanisms, and PFAS transformations.

The combined effects of polystyrene nanoplastics and dissolved organic matter on the environmental bioavailability of carbamazepine

The bioavailability of active pharmaceutical ingredients (APIs) plays a crucial role in determining the toxicity and risk of contaminants in the environment. However, the bioavailability of APIs in complex environmental matrices is still unclear. In this study, the combined effects of polystyrene nanoplastics (PS NPs) with various particle sizes (50, 100, and 1000 nm) and fulvic acid (FA) on the bioavailability of carbamazepine (CBZ) were investigated via negligible depletion solid-phase microextraction (nd-SPME) and Daphnia magna (D. magna) accumulation. The uptake kinetic study revealed that both PS NPs and FA reduced the elimination rate (k2) in most cases. The availability of CBZ to nd-SPME was determined by the hydrodynamic particle size of PS NPs, whereas the bioavailability to D. magna depended on the intrinsic particle size. The CBZ bioavailability was greater in co-exposed matrices due to the attenuated sorption of PS NPs to CBZ by FA modification. Notably, co-exposure of PS NPs and FA resulted in a higher bioaccumulation factor (BAF) of CBZ, probably due to the desorption and reabsorption of particle-associated CBZ. This study demonstrated that both PS NP particle size and FA binding affect the bioavailability of CBZ, and nd-SPME can mimic only the bioaccumulation of CBZ via diffusion.

Nanoscale exopolymer reassembly-trap mechanism determines contrasting PFOS exposure patterns in aquatic animals with different feeding habitats: A nano-visualization study

The behavior and fate of PFOS (perfluorooctanesulfonate) in the aquatic environment have received great attention due to its high toxicity and persistence. The nanoscale supramolecular mechanisms of interaction between PFOS and ubiquitous EPS (exopolymers) remain unclear though EPS have been widely-known to influence the bioavailability of PFOS. Typically, the exposure patterns of PFOS in aquatic animals changed with the EPS-PFOS interaction are not fully understood. This study hypothesized that PFOS exposure and accumulation pathways depended on the PFOS-EPS interactive assembly behavior and animal species. Two model animals, zebrafish and chironomid larvae, with different feeding habitats were chosen for the exposure and accumulation tests at the environmental concentrations of PFOS in the absence and presence of EPS. It was found that PFOS triggered the self-assembly of EPS to form large aggregates which significantly trapped PFOS. PFOS accumulation was significantly promoted in zebrafish but drastically reduced in chironomid larvae because of the nanoscale interactive assembly between EPS and PFOS. The decreased dermal uptake but increased oral uptake of PFOS by zebrafish with large mouthpart size could be ascribed to the increased ingestion of PFOS-enriched EPS aggregates as food. For the chironomid larvae with small mouthpart size, the PFOS-EPS assemblies reduced the dermal, oral and intestinal uptake of PFOS. The nano-visualization evidences confirmed that the PFOS-enriched EPS-PFOS assemblies blocked PFOS penetration through skin of both animals. These findings provide novel knowledge about the ecological risk of PFOS in aquatic environments.

Effect of Co-exposure to Additional Substances on the Bioconcentration of Per(poly)fluoroalkyl Substances: A Meta-Analysis Based on Hydroponic Experimental Evidence

A consensus has yet to emerge regarding the bioconcentration responses of per(poly)fluoroalkyl substances under co-exposure with other additional substances in aqueous environments. This study employed a meta-analysis to systematically investigate the aforementioned issues on the basis of 1,085 published datasets of indoor hydroponic simulation experiments. A hierarchical meta-analysis model with an embedded variance covariance matrix was constructed to eliminate the non-independence and shared controls of the data. Overall, the co-exposure resulted in a notable reduction in PFAS bioaccumulation (cumulative effect size, CES =  - 0.4287, p < 0.05) and bioconcentration factor (R2 = 0.9507, k < 1, b < 0) in hydroponics. In particular, the inhibition of PFAS bioconcentration induced by dissolved organic matter (percentage form of the effect size, ESP =  - 48.98%) was more pronounced than that induced by metal ions (ESP =  - 35.54%), particulate matter (ESP =  - 24.70%) and persistent organic pollutants (ESP =  - 18.66%). A lower AS concentration and a lower concentration ratio of ASs to PFASs significantly promote PFAS bioaccumulation (p < 0.05). The bioaccumulation of PFASs with long chains or high fluoride contents tended to be exacerbated in the presence of ASs. Furthermore, the effect on PFAS bioaccumulation was also significantly dependent on the duration of co-exposure (p < 0.05). The findings of this study provide novel insights into the fate and bioconcentration of PFAS in aquatic environments under co-exposure conditions.

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.

Investigation on humic substance and tetracycline interaction mechanism: biophysical and theoretical studies and assessing their effect on biological activity

Tetracycline (TC) is a widely used antibiotic, and evaluating its interaction with humic substances (HS) that act as a complexing agent in the environment is essential to understanding the availability of this contaminant in the environment. This study evaluated the interaction between HS and TC using different spectroscopic techniques, theoretical studies, and biological assays simulating environmental conditions. TC interacts with HS, preferably by electrostatic forces, with a binding constant of 9.2 × 103 M-1 (30 °C). This process induces conformational changes in the superstructure, preferably in the HS, like protein fraction. Besides, studies using the 8-anilino-1-naphthalene sulfonate (ANS) probe indicated that the antibiotic alters the hydrophobicity degree on HS's surface. Synchronized fluorescence shows that the TC interaction occurs preferentially with the protein-like fraction of soil organic matter (KSV = 26.28 ± 1.03 M-1). The TC epitope was evaluated by 1H NMR and varied according to the pH (4.8 and 9.0) of the medium, as well as the main forces responsible for the stabilization of the HS-TC complex. The molecular docking studies showed that the formation of the HS-TC complex is carried out spontaneously (ΔG = -7.1 kcal mol-1) and is stabilized by hydrogen bonds and electrostatic interactions, as observed in the experimental spectroscopic results. Finally, biological assays indicated that HS influenced the antimicrobial activity of TC. Thus, this study contributed to understanding the dynamics and distribution of TC in the environment and HS's potential in the remediation of antibiotics of this class in natural systems, as these can have adverse effects on ecosystems and human health.

Binding interaction of environmental DNA with typical emerging perfluoroalkyl acids and its impact on bioavailability

As the replacement compounds of perfluoroalkyl acids (PFAAs), emerging PFAAs generally exhibit equal or more hazardous toxicity than legacy PFAAs. Numerous DNA as environmental organic matters coexists with emerging PFAAs, but their interactions and the resulting interaction impacts on the bioavailability of emerging PFAAs remain insufficiently understood. Here, we studied the binding strength and mechanism between DNA and emerging PFAAs (perfluorobutyric acid, perfluorobutylsulfonic acid, and hexafluoropropylene oxide dimer acid) using perfluorooctanoic acid as the control, and further investigated the impacts of DNA binding on the bioavailability of the emerging PFAAs. Isothermal titration calorimetry and quantum chemical calculation found that the emerging PFAAs could bind with DNA bases (main thymine) by van der Waals force and halogen-bond, showing the binding affinities in the range of 7.87 × 104 to L/mol to 6.54 × 106 L/mol. The PFAAs-DNA binding significantly decreased the bioavailability of the PFAAs in both seedlings and plants of pakchoi (Brassica chinensis L.), with little differences in bioavailability change extent among PFAAs. The findings highlight the universality and similarity of the DNA binding effects on PFAAs bioavailability, which can be the natural detoxification mechanism for response to the PFAAs pollution.

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.

Spatial and temporal variability of per- and polyfluoroalkyl substances (PFAS) in environmental media of a small pond: Toward an improved understanding of PFAS bioaccumulation in fish

Per- and polyfluoroalkyl substances (PFAS) are highly fluorinated compounds with many industrial applications, for instance as ingredients in fire-suppressing aqueous film-forming foams (AFFF). Several PFAS have been demonstrated to be persistent, bioaccumulative and toxic. This study better characterizes the bioaccumulation of PFAS in freshwater fish through a spatial and temporal analysis of surface water and sediment from a stormwater pond in a former Naval air station (NAS) with historic AFFF use. We sampled environmental media from four locations twice per week for five weeks and sampled fish at the end of the sampling effort. The primary PFAS identified in surface water, sediment, and biota were perfluorooctane sulfonate (PFOS) and perfluorohexane sulfonate (PFHxS) followed by perfluorooctanoic acid (PFOA) in environmental media and perfluoroheptane sulfonate (PFHpS) in biota. We observed significant temporal variability in surface water concentrations at the pond headwaters following stochastic events such as heavy rainfall for many compounds, particularly PFHxS. Sediment concentrations varied most across sampling locations. In fish, liver tissue presented the highest concentrations for all compounds except PFHxS, which was highest in muscle tissue, suggesting the influence of fine-scale aqueous PFAS fluctuations on tissue distribution. Calculated log bioaccumulation factors (BAFs) ranged from 0.13 to 2.30 for perfluoroalkyl carboxylates (PFCA) and 0.29-4.05 for perfluoroalkane sulfonates (PFSA) and fluctuated greatly with aqueous concentrations. The variability of PFAS concentrations in environmental media necessitates more frequent sampling efforts in field-based studies to better characterize PFAS contamination in aquatic ecosystems as well as exercising caution when considering single time-point BAFs due to uncertainty of system dynamics.

Comparisons in molecular weight distributions and size-dependent optical properties among model and reference natural dissolved organic matter

Humic acid (HA) and reference natural organic matter (NOM) have been widely used in environmental assessment, biogeochemistry, and ecotoxicity studies. Nevertheless, similarities and differences among the commonly used model/reference NOMs and bulk dissolved organic matter (DOM) have rarely been systematically evaluated. In this study, HA, SNOM (Suwannee River NOM) and MNOM (Mississippi River NOM), both from International Humic Substances Society, and freshly collected unfractionated NOM (FNOM) were concurrently characterized to evaluate their heterogeneous nature and size-dependent chemical properties. We found that molecular weight distributions, PARAFAC-derived fluorescent components, and size-dependent optical properties are NOM-specific and highly variable with pH. The < 1 kDa DOM abundance followed the order of HA < SNOM < MNOM < FNOM. In addition, FNOM was more hydrophilic and contained more protein-like and autochthonous components with a higher UV-absorbance ratio index (URI) and biological fluorescence index, whereas HA and SNOM contained more allochthonous, humic-like components with a higher aromaticity and lower URI. Significant differences in molecular composition and size spectra between FNOM and model/reference NOMs suggest that environmental role of NOMs should be evaluated at the levels of molecular weight and functionalities under the same experimental conditions and that HA and SNOM may not represent bulk NOM in the environment. This study provides new information about similarities and differences in DOM size-spectra and chemical properties between reference NOMs and in-situ NOM and highlights the need to better understand the heterogenous roles of NOMs in regulating the toxicity/bioavailability and environmental fate of pollutants 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.

Fractionation of perfluoroalkyl acids (PFAAs) along the aquatic food chain promoted by competitive effects between longer and shorter chain PFAAs

Perfluoroalkyl acids (PFAAs) are proteinophilic pollutants. We hypothesized that fractionation of PFAAs may occur along a food chain. To testify this hypothesis, we investigated the bioconcentration, bioaccumulation, and fractionation of 11 kinds of PFAAs (C-F = 3-11) along an aquatic food chain consisting of D. magna, zebrafish, and cichlid. The results showed that the proportions of PFNA, PFOA, and all shorter chain PFAAs in the D. magna and fish tissues were lower than the ones in exposure water, opposing to the other longer chain PFAAs. Predation promoted such fractionation differences, and the proportions of PFNA, PFOA, and all shorter chain PFAAs in organisms decreased while those of the other longer chain PFAAs increased along the food chain. The results of isothermal titration calorimetry and molecular docking experiments showed that binding affinities of PFAAs and fish proteins increased with the number of perfluorinated carbons, resulting in a substitution of shorter chain PFAAs by their longer chain analogues. It also triggered the differences in the uptake and elimination of PFFAs and competitive bioaccumulation between longer and shorter chain PFAAs. This study suggests that fractionation should be considered in studying environmental behaviors and evaluating ecological risks of multiple PFAAs.

Effects of PFOS at ng/L levels on photostability of extracellular polymeric substances under solar irradiation by fluorescence and infrared spectroscopy

The ubiquitous EPS (extracellular polymeric substances), as a type of dissolved organic carbon, plays a key role in carbon cycling in water environment. When EPS meet the omnipresent PFOS (perfluorooctane sulfonate), they must interact with each other and exert profound effect on behavior and fate of both, which is still not well known. We hypothesized that the highly persistent PFOS at real environmental levels may significantly influence behavior of EPS under solar irradiation which may retard carbon turnover. In this study, 3D-EEM fluorescence spectroscopy and FTIR spectroscopy were used to probe responses of composition and structure of EPS under solar irradiation in the absence and presence of PFOS (5-500 ng/L). The experimental results showed that PFOS at ng/L levels significantly affected responses of EPS to sunlight irradiation and the effects were dependent on the components in EPS. Photostability of humic-like substances was significantly increased in the presence of PFOS; Degradation and unfolding of proteins induced by solar light were reduced by PFOS. In addition, degradation of both hydrophilic and hydrophobic functional groups by sunlight was inhibited by PFOS. The novel findings provide new insights for assessing the environmental behavior of EPS and PFOS and understanding the effect of PFOS on carbon cycling in water environments.

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.

Interactions between Extracellular DNA and Perfluoroalkyl Acids (PFAAs) Decrease the Bioavailability of PFAAs in Pakchoi (Brassica chinensis L.)

Perfluoroalkyl acids (PFAAs) are emerging ionic organic pollutants worldwide. Great amounts of extracellular DNA (∼mg/kg) coexist with PFAAs in the environment. However, PFAA-DNA interactions and effects of such interactions have not been well studied. Herein, we used isothermal titration calorimetry (ITC), spectroscopy, and computational simulations to investigate the PFAA-DNA interactions. ITC assays showed that specific binding affinities of PFHxA-DNA, PFOA-DNA, PFNA-DNA, and PFOS-DNA were 5.14 × 10⁵, 3.29 × 10⁵, 1.99 × 10⁵, and 2.18 × 10⁴ L/mol, respectively, which were about 1-2 orders of magnitude stronger than those of PFAAs with human serum albumin. Spectral analysis suggested interactions of PFAAs with adenine (A), cytosine (C), guanine (G), and thymine (T), among which grooves associated with thymine were the major binding sites. Molecular dynamics simulations and quantum chemical calculations suggested that hydrogen bonds and van der Waals forces were the main interaction forces. Such a PFAA-DNA binding decreased the bioavailability of PFAAs in plant seedlings. The findings will help to improve the current understanding of the interaction between PFAAs and biomacromolecules, as well as how such interactions affect the bioavailability of PFAAs.

Underlying Mechanisms for Low-Molecular-Weight Dissolved Organic Matter to Promote Translocation and Transformation of Chlorinated Polyfluoroalkyl Ether Sulfonate in Wheat

Dissolved organic matter (DOM) such as fulvic acid (FA) and humic acid (HA) in soil considerably affects the fate of per- and polyfluoroalkyl substances (PFASs). However, the effect of DOM on their behavior in plants remains unclear. Herein, hydroponic experiments indicate that FA and HA reduce the accumulation of an emerging PFAS of high concern, 6:2 chlorinated polyfluoroalkyl ether sulfonate (6:2 Cl-PFESA), in wheat roots by reducing its bioavailability in the solution. Nevertheless, FA with low molecular weight (MW) promotes its absorption and translocation from the roots to the shoots by stimulating the activity and the related genes of the plasma membrane H⁺-ATPase, whereas high-MW HA shows the opposite effect. Moreover, in vivo and in vitro experiments indicate that 6:2 Cl-PFESA undergoes reductive dechlorination, which is regulated mainly using nitrate reductase and glutathione transferase. HA and FA, particularly the latter, promote the dechlorination of 6:2 Cl-PFESA in wheat by enhancing electron transfer efficiency and superoxide production. Transcriptomic analysis indicates that FA also stimulates catalytic activity, cation binding, and oxidoreductase activity, facilitating 6:2 Cl-PFESA transformation in wheat.

The role of dissolved organic matter during Per- and Polyfluorinated Substance (PFAS) adsorption, degradation, and plant uptake: A review

The negative effects of polyfluoroalkyl substances (PFAS) on the environment and health have recently attracted much attention. This article reviews the influence of soil- and water-derived dissolved organic matter (DOM) on the environmental fate of PFAS. In addition to being co-adsorped with PFAS to increase the adsorption capacity, DOM competes with PFAS for adsorption sites on the surface of the material, thereby reducing the removal rate of PFAS or increasing water solubility, which facilitates desorption of PFAS in the soil. It can quench some active species and inhibit the degradation of PFAS. In contrast, before DOM in water self-degrades, DOM has a greater promoting effect on the degradation of PFAS because DOM can complex with iron, iodine, among others, and act as an electron shuttle to enhance electron transfer. In soil aggregates, DOM can prevent microorganisms from being poisoned by direct exposure to PFAS. In addition, DOM increases the desorption of PFAS in plant root soil, affecting its bioavailability. In general, DOM plays a bidirectional role in adsorption, degradation, and plant uptake of PFAS, which depends on the types and functional groups of DOM. It is necessary to enhance the positive role of DOM in reducing the environmental risks posed by PFAS. In future, attention should be paid to the DOM-induced reduction of PFAS and development of a green and efficient continuous defluorination technology.

Graphene oxide chronic exposure enhanced perfluorooctane sulfonate mediated toxicity through oxidative stress generation in freshwater clam Corbicula fluminea

Graphene oxide (GO), a frequently utilized graphene family nanomaterial, is inevitably released into the aquatic environment and interacts with organic pollutants, including perfluorooctane sulfonate (PFOS), a well-known persistent organic pollutant. To determine the adverse effects of GO chronic exposure on PFOS bioaccumulation and toxicity, adult freshwater bivalves, namely Asian clams (Corbicula fluminea) were treated for 28 days with PFOS (500 ng/L) and different concentrations of GO (0.2, 1, 5 mg/L) as PFOS single and GO single exposure groups, as well as PFOS-GO mixture exposure groups. Our results demonstrated that the bioaccumulation of PFOS was significantly enhanced by co-exposure in gills and visceral masses, which was 1.64-2.91 times higher in gills than in visceral masses. Both single, as well as co-exposure, caused a significant reduction in clams' siphoning behavior, compared to the controls. Further, the co-exposure significantly increased the production of reactive oxygen species (ROS), exacerbating malondialdehyde (MDA) content, enhancing superoxide dismutase (SOD) and catalase (CAT), while decreasing glutathione reductase (GR) and glutathione S-transferase (GST) enzymatic activities in clam tissues. And co-exposure significantly altered the expressions of se-gpx, sod, cyp30, hsp40, and hsp22 genes (associated with oxidative stress and xenobiotic metabolism) both in gills and visceral masses. Moreover, co-exposure caused significant histopathological changes such as cilia degradation in the gills, expansion of tubule lumens in digestive glands, and oocyte shrinkage in gonads. Finally, the enhanced integrated biomarker response (EIBR) index revealed that co-exposure to 500 ng/L PFOS + 1 mg/L/5 mg/L GO was the most stressful circumstance. Overall, our findings suggested that the presence of GO increased PFOS bioaccumulation in tissues, inducing multifaceted negative implications at molecular and behavioral levels through oxidative stress generation in Asian clams.

Interactions between dissolved organic matter and perfluoroalkyl acids in natural rivers and lakes: A case study of the northwest of Taihu Lake Basin, China

Understanding the interactions between dissolved organic matter (DOM) and perfluoroalkyl acids (PFAAs) is essential for predicting the distribution, transport, and fate of PFAAs in aquatic environments. Based on field investigations in the northwest of Taihu Lake Basin combined with laboratory experiments, we obtained DOM and PFAA concentrations as well as compositions and investigated key factors of DOM affecting PFAA variability and capture of PFAAs by DOM. Results indicated that the total concentrations of PFAAs were 73.4-689 ng/L in surface water and that PFAAs were dominated by C3-7 perfluoroalkyl carboxylic acids and perfluorooctane sulfonic acid. The main components of DOM included tyrosine-, fulvic-, and tryptophan-like substances. The Mantel test revealed a significant positive correlation between DOM and PFAAs (P = 0.0001). Fulvic-like substances were identified as the most crucial factors affecting PFAA variability. The laboratory experiments revealed that DOM can spontaneously aggregate into a microgel. Furthermore, 19.1-50.9% of PFAAs, DOM characteristic peaks, and several metals (Ca, Mg, Cu, and Fe) can be removed during aggregation, indicating the capacity of DOM binding organic/inorganic substances. The fulvic-like substances were more effectively removed than the protein-like substances. The distribution coefficients of all PFAAs except perfluorohexanoic acid significantly correlated with their perfluorinated carbon numbers (r = 0.975, p<0.001). Our results provided insights into the interactions between DOM and PFAAs, improving the understanding of the distribution, transport, and fate of PFAAs in aquatic environments.

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.

Evaluation of single and joint toxicity of perfluorooctanoic acid and arsenite to earthworm (Eisenia fetida): A multi-biomarker approach

Perfluorooctanoic acid (PFOA) and arsenic are ubiquitous environmental contaminants and could co-exist in soil. However, data on their possible combined toxic effects on terrestrial organisms are still lacking. In this study, we exposed earthworm Eisenia fetida to artificial soil spiked with different sub-lethal levels of PFOA, arsenite (As(III)) or their mixture for 28 days. The bioaccumulation and multi-biomarker responses in the earthworms were measured. Results showed that the co-existence of PFOA and As(III) in soil enhanced the bioaccumulation of arsenic while reduced the bioaccumulation of PFOA. Most selected biomarkers exhibited significant responses at higher exposure levels and indicated oxidative damages. Biomarker Response Index (BRI) was used to integrate the multi-biomarker responses and the results showed significant dose-effect relationships between biological health status and exposure levels. Moreover, variation analysis of multi-biomarkers and BRI proved that As(III) exhibited more toxicity than PFOA to the earthworms. Based on BRI results, Effect Addition Index (EAI) was calculated to evaluate the joint effects of the two toxicants. According to EAI, the joint toxicity of PFOA and As(III) was related to exposure concentration, changing from synergism to slight antagonism with the increase of exposure level. These results provide valuable toxicological information for the risk assessment of co-exposure to PFOA and arsenic in the soil environment. Moreover, this study proved that BRI is an effective tool to integrate multi-biomarker responses, and its combination with EAI provides a useful combined approach to evaluate the joint effects of mixed contamination systems.

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.

Perfluorinated compounds in a river basin from QingHai-Tibet Plateau: Occurrence, sources and key factors

The occurrence of perfluorinated compounds (PFCs) in different environmental media in the QingHai-Tibet Plateau has been limitedly investigated. In this study, the water, sediments, soils and agricultural product samples were collected in the Huangshui River basin, and contents of the PFCs and values of water parameters were determined. This study investigated dominantly regulating factors of the distribution of PFCs in the water emphatically, explored the sources and assessed potential risks of the PFCs integrally. The results showed that perfluorohexanesulfonic acid, perfluorooctanesulfonic acid, perfluorobutanoic acid (PFBA) and perfluorooctanoic acid presented high maximum concentrations of 3207.42, 3015.96, 1941.89 and 826.4 ng L-1 in the water, respectively. There were 12 PFCs detected in crops, with the maximum concentration of 5206.86 ng g-1 for PFBA. The significantly positive correlation (p < 0.05) was observed between the concentrations of PFBA in crops and that in adjacent rivers, indicating that the irrigation most likely contributed to the accumulation of PFBA in the studied crops. The occurrence of the PFCs in the water during the dry season was dominantly regulated by fluorescent dissolved organic matters via the hydrophobic interaction, while it was primarily regulated by the total nitrogen and electrical conductivity via electrostatic interaction during the wet season. The PFCs in the water were mainly from the wastewater discharged from wastewater treatment plants and carpet factories, while the resuspension of the PFCs in sediments was also an important contribution especially in wet season. The PFCs in the river has posed sustained risk to the public health, especially children.

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.

Influence of suspended sediment on the bioavailability of benzophenone-3: Focus on accumulation and multi-biological effects in Daphnia magna

The UV-filter benzophenone-3 (BP3) tends to associate with suspended sediment (SPS) due to hydrophobicity, which could alter its toxicological effects on non-target aquatic organisms. In this study, the freshwater cladoceran Daphnia magna (D. magna) was selected as a model organism to investigate the impacts of the source and composition of SPS on the accumulation and multiple toxicological effects (from the molecular level to individual level) of BP3. Among the three components of SPS, amorphous organic carbon (AOC) and minerals promoted the body burden of BP3, while black carbon (BC) inhibited the bioaccumulation. The inhibition effects of BP3 on swimming and feeding behaviors of D. magna were also enhanced due to the presence of AOC and BC. Compared with BP3 exposure alone, higher oxidative stress and neurotoxicity were observed in the presence of SPS containing AOC, BC and minerals, corresponding to that superoxide dismutase, catalase and glutathione-S-transferase activities were further induced, and acetylcholinesterase activity was inhibited. Furthermore, BP3 induced mRNA expression levels of the endocrine system (ecdysone receptor, cytochrome P450 CYP314) and metabolic system (toxicant nuclear receptor HR96, P-glycoprotein), and the presence of SPS containing AOC, BC and minerals exhibited an enhanced effect. Combined with all endpoints, evident relationship was observed between the bioaccumulation level and the response of individual behavior and molecular biomarkers. The results demonstrated that the effects of SPS compositions on bioaccumulation and toxicological effects of organic UV-filters should be considered in aquatic environments.

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.

Multimedia distribution and trophic transfer of PPCPs in the middle and lower reaches of the Yarlung Zangbo River

The increasing human presence is having an impact on plateau ecosystems, but the special environment and lack of data make it difficult to assess the real ecological risks of pharmaceutical and personal care products (PPCPs) in the river of plateau. The occurrence, distribution and trophic transfer of nineteen PPCPs were investigated in the middle and lower reaches of the Yarlung Zangbo River on the Tibetan Plateau. All the targeted PPCPs were detected in filtrated water, and seventeen PPCPs were detected in the colloid, sediment and suspended particulate matter (SPM). The distribution coefficients of colloid-infiltration water (IFW) were 1-2 orders of magnitude larger than those in the SPM-IFW, which were 1-2 orders of magnitude greater than those in the sediment-IFW. Colloids are sinks for PPCPs with up to 78.55% of the water being in the colloidal phase, in which important factors such as protein and protein-like substances are found. PPCPs in the rivers of the plateau showed high bioaccumulation ability. The fugacity-based bioaccumulation model was established and revealed that the fish in the Tibetan Plateau ingested PPCPs mainly through water instead of food and excreted them mainly through metabolism. In addition, the trophic dilution effect in the food web was observed with trophic magnification factors ranging from 0.06 to 0.22. The positive correlation between the K_d in the colloid-IFW and the bioaccumulation factors implied that natural colloids can not only regulate the behaviour of PPCPs in the environment, but also play an important role in bioaccumulation, which may affect the scientific nature of biological risk assessment.

Lethal and sublethal toxicity of perfluorooctanoic acid (PFOA) in chronic tests with Hyalella azteca (amphipod) and early-life stage tests with Pimephales promelas (fathead minnow)

Perfluoroalkyl substances (PFAS), including perfluorooctanoic acid (PFOA), are industrial chemicals that are of concern due to their environmental presence, persistence, bioaccumulative potential, toxicity, and capacity for long-range transport. Despite a large body of research on environmental exposure, insufficient chronic aquatic toxicity data exist to develop water quality targets for clean-up of federal contaminated sites in Canada. Thus, our objective was to assess the aqueous toxicity of PFOA in chronic tests with Hyalella azteca (amphipod) and early-life stage tests with Pimephales promelas (fathead minnow). Toxicity data were analyzed based on measured PFOA concentrations. Amphipod exposures were 42 d (0.84-97 mg/L) and examined survival, growth, and reproduction. Fathead minnow exposures were 21 d (0.010-76 mg/L), which encompassed hatching (5 d) and larval stages until 16 d post-hatch; endpoints included hatching success, deformities at hatch, and larval survival and growth. Amphipod survival was significantly reduced at 97 mg/L (42-d LC50 = 51 mg/L), but growth and reproduction were more sensitive endpoints (42-d EC50 for both endpoints = 2.3 mg/L). Fathead minnows were less sensitive than amphipods, exhibiting no significant effects in all endpoints with the exception of uninflated swim bladder, which was significantly higher at 76 mg/L (15%) than controls (0%). Maximum concentrations of PFOA are generally in the ng/L range in global surface waters, but can reach the μg/L range in close proximity to major source inputs; therefore, environmental concentrations are well below those that caused toxicity in the current study. Our data will provide valuable information with which to assess the risk of PFOA at contaminated sites, and to set a target for site remediation.

Suspended sediment exacerbates perfluorooctane sulfonate mediated toxicity through reactive oxygen species generation in freshwater clam Corbicula fluminea

Perfluorooctane sulfonate (PFOS) potentially adsorbs on the surface of suspended sediment (SPS), which can develop a toxic "pool" bioavailable to benthic organisms. In this study, the freshwater clam Corbicula fluminea was employed as a zoobenthos model to study the effects of SPS (collected from the Yellow River) on the bioaccumulation and toxicity (from the molecular level to cellular and physiological levels) caused by PFOS exposure. Besides, the enhanced integrated biomarker response (EIBR) system was applied as an index to evaluate the in-depth toxic effects of PFOS and SPS single and co-exposure at various treatment levels. Our results demonstrated that PFOS-SPS co-exposure (at sub-lethal doses of PFOS) significantly increased the bioaccumulation of PFOS, and induced the elevated levels of reactive oxygen species (ROS), the significantly increased activities of superoxide dismutase (SOD) and catalase (CAT) enzymes, the significantly increased content of malondialdehyde (MDA), and the significantly upregulated expression levels of sod, selenium-dependent glutathione peroxidase (se-gpx), heat shock protein 22 (hsp22), heat shock protein 40 (hsp40) and cytochrome P450 30 (cyp30) genes. Further, the co-exposure induced the significantly higher histopathological alterations in the gonads and digestive glands, and even elevated the inhibition of siphoning behavior in clams. In addition, the EIBR index also revealed the highest values for PFOS and SPS co-exposure, compared to the individual SPS or PFOS exposure. The results indicated that at high levels of PFOS exposure (especially at 1000 μg/L), the presence of SPS might increase the generation of ROS by influencing the bioaccumulation of PFOS, which enhanced the toxicity of PFOS to C. fluminea. These results potentially provide basic information for the comprehensive evaluation of the toxic effects of PFOS on benthos in a multi-sediment river ecosystem.

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.

Joint effect of nanoplastics and humic acid on the uptake of PAHs for Daphnia magna: A model study

Nanoplastics (NPs) are emerging pollutants which can adsorb large amounts of hydrophobic organic compounds (HOCs) and be ingested by aquatic organisms. NPs interact with dissolved organic matter (DOM) and result in significant impacts on the bioaccumulation of HOCs in the actual environment. For the first time, the joint effects of two complex matrices on the bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) to Daphnia magna (D. magna) were studied by modeling calculation. The complex matrices, nano-sized polystyrene (PS) and/or humic acid (HA), were under environmentally realistic concentrations. A biodynamic model was modified and the uptake fluxes from all exposure pathways were quantified using the experimental data. A flux estimation showed that the bioaccumulation amounts at equilibrium were mostly dependent on dermal uptake (≥99.3 % of the total). The PS matrix would retard the intestinal uptake process in D. magna, especially for the less hydrophobic PAHs; while the HA or the HA-PS matrix would facilitate the mass transfer of PAHs from the matrix to lipids in the gut. Moreover, the biota matrix accumulation factor (BMAF) were calculated to verify the biodynamic model. This work is helpful to clarify the bioaccumulation effects of PAHs in complex environmental systems.

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.

Interaction and coexistence characteristics of dissolved organic matter with toxic metals and pesticides in shallow groundwater

The long-term and large-scale utilization of fertilizers and pesticides in facility agriculture leads to groundwater pollution. However, the coexistence and interactions between organic fertilizers (i.e., organic matter), toxic metals, and pesticides in shallow groundwater have seldom been studied. Thus, the study sought to characterize said interactions via fluorescence, ultraviolet-visible spectroscopy (UV-Vis), and Fourier-transform infrared spectroscopy coupled with two-dimensional correlation spectroscopy and chemometric techniques. The results indicated that groundwater DOM was comprised of protein-, polysaccharide-, and lignin-like substances derived from organic fertilizers. Protein-like substances accounted for the binding of Co, Ni, and Fe, while polysaccharide- and lignin-like substances were mainly responsible for Cr and Mo complexation. Moreover, lignin- and polysaccharide-like substances played a key role in the binding of pesticides (i.e., dichlorodiphenyltrichloroethane [DDT], endosulfan, γ-hexachlorocyclohexane [γ-HCH], monocrotophos, chlorpyrifos, and chlorfenvinphos), rendering the conversion of γ-HCH to β-hexachlorocyclohexane (β-HCH) and the degradation of DDT to dichlorobenzene dichloroethylene (DDE) ineffective. However, the presence of protein-like substances in groundwater benefited the degradation and conversion of γ-HCH and α-endosulfan. Redundancy analyses showed that lignin- and polysaccharide-like matter had the most impacts on the coexistence of DOM with toxic metals and pesticides.

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.

Occurrence, toxicity and transformation of six typical benzotriazoles in the environment: A review

Benzotriazoles (BTs) are a group of heterocyclic compounds which have been widely applied in industrial activities and domestic life mainly as corrosive inhibitors. BTs have been ubiquitously detected in receiving environments and cause potential toxicity to non-target organisms. This paper reviews the occurrence and fate of six selected benzotriazole compounds in different environmental and biological matrices, as well as the transformation and toxicity. Due to their high hydrophilicity and insufficient removal in wastewater treatment plants (WWTPs), these compounds were widely detected in aquatic environments with concentrations mainly from tens ng/L to tens μg/L. Considerable residual levels of BTs in plant, fish, air, tap water and human urine have implied the potential risks to various organsims. The reported acute toxicity of BTs are generally low (EC₅₀ in mg/L level). Some observed sublethal effects including endocrine disrupting effects, hepatotoxicity and neurotoxicity, as well as the ability to promote the development of endometrial carcinoma still raise a concern. BTs are found often more recalcitrant to biodegradation compared to photolysis and ozonation. Environmental factors including pH, temperature, irradiation wavelength, redox condition as well as components of matrix are proved crucial to the removal of BTs. Further studies are needed to explore the precise environment fate and toxicity mechanism of BTs, and develop advanced treatment technologies to reduce the potential ecological risks of BTs.

The concentration of dissolved organic matter impacts the metabolic response in Daphnia magna exposed to 17α-ethynylestradiol and perfluorooctane sulfonate

The pharmaceutical 17α-ethynylestradiol (EE2) and the industrial chemical perfluorooctane sulfonate (PFOS) are organic contaminants frequently detected in freshwater environments. It is hypothesized that hydrophobic organic contaminants can sorb to dissolved organic matter (DOM) and this may reduce the toxicity of these contaminants by reducing the contaminants' bioavailability. To investigate this hypothesis, ¹H nuclear magnetic resonance (NMR)-based metabolomics was used to determine how the metabolome of Daphnia magna changes when a range of DOM concentrations are added during EE2 and PFOS exposure experiments. D. magna were exposed for 48 h to sub-lethal concentrations of 1 mg/L EE2 or 30 mg/L PFOS in the presence of 0, 1, 2, 3 and 4 mg dissolved organic carbon (DOC)/L. EE2 exposure resulted in increased amino acids and decreased glucose in D. magna. All DOM concentrations were able to lessen these metabolite disturbances from EE2 exposure, likely due to reductions in the bioavailability of EE2 through interactions with DOM. Exposure to PFOS resulted in decreased amino acids, and the presence of 1 mg DOC/L did not alter this metabolic response. However, PFOS exposure with the higher DOM concentrations resulted in a different pattern of metabolite changes which may be due to combined impacts of PFOS and DOM on the metabolome or due to an increase in PFOS bioavailability and uptake in D. magna. These results suggest that the concentration of DOM influences the sensitive biochemical changes in organisms that occur during acute sub-lethal exposure to organic contaminants.

Metabolomic responses to pre-chlorinated and final effluent wastewater with the addition of a sub-lethal persistent contaminant in Daphnia magna

Consumer products such as perfluorooctanesulfonic acid (PFOS) and pharmaceuticals (PCPPs) enter aquatic ecosystems through inefficient removal during wastewater treatment. Often, the sterilization process of wastewater includes the addition of sodium hypochlorite that can react with PCPPs and other organic matter (i.e., dissolve organic matter) to generate disinfection by-products and can cause the final effluent to be more harmful to aquatic organisms. Here, we exposed Daphnia magna to two stages of wastewater, the pre-chlorinated wastewater (PreCl) and the final effluent. In addition, we exposed D. magna, to the final effluent with a concentration gradient of added PFOS, to investigate if this persistent contaminant altered the toxicity of the final effluent. After 48 h of contaminant exposure, we measured the daphnids metabolic responses to the different stages of wastewater treatment, and with the addition of PFOS, utilizing proton nuclear magnetic resonance spectroscopy and liquid chromatography tandem mass spectrometry. We found few significant changes to the metabolic profile of animals exposed to the PreCl wastewater; however, animals exposed to the final effluent displayed increases in many amino acids and decreases in some sugar metabolites. With the addition of PFOS to the final effluent, the metabolic profile shifted from increased amino acids and decreased sugar metabolites and energy molecules especially at the low and high concentrations of PFOS. Overall, our results demonstrate the metabolome is sensitive to changes in the final effluent that are caused by sterilization, and with the addition of a persistent contaminant, the metabolic profile is further altered.

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.

Bioavailability of Pyrene Associated with Different Types of Protein Compounds: Direct Evidence for Its Uptake by Daphnia magna

The protein-like dissolved organic matter (DOM) is ubiquitous in aquatic environments. However, the bioavailability of protein-like DOM-associated hydrophobic organic compounds (HOCs) is not well-understood, and in particular, the direct evidence of their uptake by organisms is scarce. In the present work, tryptone (2000 Da), bovine serum albumin (BSA; 66 000 Da), and phycocyanin (120 000 Da) were chosen as model protein-like DOM, which were labeled by commercial fluorescein (cy5) to investigate the uptake mechanisms of protein compound-associated pyrene (a typical HOC) by Daphnia magna. The pyrene concentration in the tissues except the gut and immobilization of D. magna were detected to calculate the bioavailable fraction of protein compound-associated pyrene when the freely dissolved pyrene concentration was controlled through passive dosing devices. The results demonstrated that the tryptone could permeate cellular membrane and directly enter the tissues of  D. magna from the exposure solutions, whereas BSA and phycocyanin might indirectly enter the tissues from the gut. A part of pyrene associated with protein compounds was bioavailable to D. magna; the order of their bioavailable fractions was trypone (54.6-58.1%) > phycocyanin (21.6-32.8%) > BSA (17.7-26.8%). The difference was principally related to the uptake mechanisms of pyrene associated with different types of protein. This work suggests that the protein compound-associated HOCs should be considered to evaluate the bioavailability and eco-environmental hazard of HOCs in natural waters.

Investigation of Daphnia magna Sub-Lethal Exposure to Organophosphate Esters in the Presence of Dissolved Organic Matter Using ¹H NMR-Based Metabolomics

Organophosphate esters (OPEs) are frequently detected in aquatic environments. Hydrophobic OPEs with high octanol-water partition coefficients (Log K_OW) will likely sorb to dissolved organic matter (DOM) and consequently alter OPE bioavailability and sub-lethal toxicity. ¹H nuclear magnetic resonance (NMR)-based metabolomics was used to evaluate how DOM (5 mg organic carbon/L) alters the metabolic response of Daphnia magna exposed to sub-lethal concentrations of three individual OPEs with varying hydrophobicity. D. magna exposed to the hydrophilic contaminant (Log K_OW = 1.43) tris(2-chloroethyl) phosphate (TCEP) did not have substantial metabolic changes and DOM did not alter the metabolic response. There were significant increases in amino acids and a decrease in glucose from exposure to the hydrophobic contaminant (Log K_OW = 3.65) tris(2-butoxyethyl) phosphate (TBOEP) which DOM did not mitigate, likely due to the high sub-lethal toxicity of TBOEP. Exposure to DOM and the hydrophobic contaminant (Log K_OW = 4.76) triphenyl phosphate (TPhP) resulted in a unique metabolic response which was unlike TPhP only exposure, perhaps because DOM may be an additional stressor with TPhP exposure. Therefore, Log K_OW values may not always predict how sub-lethal contaminant toxicity will change with DOM and there should be more consideration to incorporate DOM in sub-lethal ecotoxicology testing.

Effects of dissolved organic matter, feeding, and water flow on the bioconcentration of diclofenac in crucian carp (Carassius auratus)

Diclofenac (DCF), a prevalent anti-inflammatory drug, is frequently detected in aquatic organisms. However, little is known about the environmental factors that affect the bioconcentration of DCF in aquatic environments. Here, we firstly investigated the bioconcentration of DCF by crucian carp (Carassius auratus) following aqueous exposure (3.57, 14.5, and 71.8 μg L^-1) for 21 days. DCF can accumulate in crucian carp, and the maximum bioconcentration factors (BCFs) of 121 L kg^-1 in the liver, 52.3 L kg^-1 in the gills, and 46.8 L kg^-1 in the muscle were always found at 3.57 μg L^-1 after 14 days of exposure. Secondly, the influences of dissolved organic matter (DOM), feeding, and water flow on the bioconcentration of DCF were determined at the nominal concentration of 4 μg L^-1 for 14 days. The BCFs of DCF in various fish tissues decreased by 0.5-85% with the increasing DOM concentrations. Feeding also led to lower body burden of DCF in fish tissues (6-55%) with the increasing food amount. In hydrodynamic experiment, the BCFs of DCF decreased by15-57% at most in various fish tissues. Collectively, our results demonstrated the bioconcentration of DCF in fish can be influenced by various environmental factors, which should be considered in the risk assessment of pharmaceuticals.

The effects of dissolved organic matter and feeding on bioconcentration and oxidative stress of ethylhexyl dimethyl p-aminobenzoate (OD-PABA) to crucian carp (Carassius auratus)

Bioconcentration of UV filters in organisms is an important indicator for the assessment of environmental hazards. However, bioconcentration testing rarely accounts for the influence of natural aquatic environmental factors. In order to better assess the ecological risk of organic UV filters (OUV-Fs) in an actual water environment, this study determined the influences of dissolved organic matter (DOM) (0, 1, 10, and 20 mg/L) and feeding (0, 0.5, 1, and 2% body weight/d) on bioconcentration of ethylhexyl dimethyl p-aminobenzoate (OD-PABA) in various tissues of crucian carp (Carassius auratus). Moreover, oxidative stress in the fish liver caused by the OD-PABA was also investigated by measuring activities of superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST), and levels of glutathione (GSH) and malondialdehyde (MDA). The bioconcentration of OD-PABA in the fish tissues was significantly decreased with the presence of DOM indicating a reduction of OD-PABA bioavailability caused by DOM. The bioconcentration factors (BCFs) decreased by 28.00~50.93% in the muscle, 72.67~96.74% in the gill, 37.84~87.72% in the liver, and 10.32~79.38% in the kidney at different DOM concentrations compared to those of the non-DOM treatments. Significant changes in SOD, CAT, GST, GSH, and MDA levels were found in the DOM- and OD-PABA-alone treatments. However, there were no significant differences in the SOD, CAT, GST, and MDA levels found when co-exposure to OD-PABA and DOM. Feeding led to lower OD-PABA concentrations in the fish tissues, and the concentrations were decreased with increasing feeding ratios. BCFs in various tissues reduced by 39.75~72.52% in the muscle, 56.86~79.73% in the gill, 66.41~87.50% in the liver, and 75.88~89.10% in the kidney, respectively. In the unfed treatments, the levels of SOD and MDA were significantly higher than those of the fed ones while GST and GSH levels were remarkably inhibited indicating the enhanced effect of starvation to oxidative stress. There was no markedly alternation of the biomarker levels observed between different fed treatments. In conclusion, our study indicated that both DOM and feeding reduced bioconcentration of OD-PABA and alleviated oxidative stress to some extent in the crucian carp.

Quantifying Bioavailability of Pyrene Associated with Dissolved Organic Matter of Various Molecular Weights to Daphnia magna

Dissolved organic matter (DOM) is a key environmental factor for the bioavailability of hydrophobic organic compounds (HOCs) in natural waters. However, the bioavailability of DOM-associated HOCs is not clear. In this research, pyrene was selected as a model HOC, and its freely dissolved concentration (C_free) was maintained by passive dosing systems. The immobilization and pyrene content in the tissues excluding gut of Daphnia magna were examined to quantify the bioavailability of DOM-associated pyrene. The results indicated that DOM promoted the bioavailability of pyrene when the C_free of pyrene was kept constant, and the bioavailability of pyrene associated with DOM of various molecular weights was ordered as middle molecular weight (5 000-10 000 Da) DOM > lower molecular weight (<1 000, 1 000-3 000, and 3 000-5 000 Da) DOM > higher molecular weight (>10 000 Da) DOM. The influencing mechanisms of DOM molecular weight were related with the partition of pyrene between DOM and water, the uptake routes of DOM by D. magna, and the desorption or release of pyrene from DOM in the gut of D. magna. The findings obtained in this research suggest that the bioavailability of DOM-associated HOCs should be taken into account for the eco-environmental risk assessment of HOCs in water systems.

Characterization of atrazine binding to dissolved organic matter of soil under different types of land use

Atrazine is widely used in agriculture. In this study, dissolved organic matter (DOM) from soils under four types of land use (forest (F), meadow (M), cropland (C) and wetland (W)) was used to investigate the binding characteristics of atrazine. Fluorescence excitation-emission matrix-parallel factor (EEM-PARAFAC) analysis, two-dimensional correlation spectroscopy (2D-COS) and Stern-Volmer model were combined to explore the complexation between DOM and atrazine. The EEM-PARAFAC indicated that DOM from different sources had different structures, and humic-like components had more obvious quenching effects than protein-like components. The Stern-Volmer model combined with correlation analysis showed that log K values of PARAFAC components had a significant correlation with the humification of DOM, especially for C3 component, and they were all in the same order as follows: meadow soil (5.68)>wetland soil (5.44)>cropland soil (5.35)>forest soil (5.04). The 2D-COS further confirmed that humic-like components firstly combined with atrazine followed by protein-like components. These findings suggest that DOM components can significantly influence the bioavailability, mobility and migration of atrazine in different land uses.

Impact of humic acid on the photoreductive degradation of perfluorooctane sulfonate (PFOS) by UV/Iodide process

Iodide photolysis under UV illumination affords an effective method to produce hydrated electrons (e_aq^-) in aqueous solution. Therefore, UV/Iodide photolysis can be utilized for the reductive degradation of many recalcitrant pollutants. However, the effect of naturally occurring organic matter (NOM) such as humic and fulvic acids (HA/FA), which may impact the efficiency of UV/Iodide photoreduction, is poorly understood. In this study, the UV photoreductive degradation of perfluorooctane sulfonate (PFOS) in the presence of I^- and HA is studied. PFOS undergoes a relatively slow direct photoreduction in pure water, a moderate level of degradation via UV/Iodide, but a rapid degradation via UV/Iodide/HA photolysis. After 1.5 h of photolysis, 86.0% of the initial [PFOS] was degraded in the presence of both I^- and HA with a corresponding defluorination ratio of 55.6%, whereas only 51.7% of PFOS was degraded with a defluorination ratio of 4.4% via UV/Iodide illumination in the absence of HA. The relative enhancement in the presence of HA in the photodegradation of PFOS can be attributed to several factors: a) HA enhances the effective generation of e_aq^- due to the reduction of I₂, HOI, IO₃^- and I₃^- back to I^-; b) certain functional groups of HA (i.e., quinones) enhance the electron transfer efficiency as electron shuttles; c) a weakly-bonded association of I^- and PFOS with HA increases the reaction probability; and d) absorption of UV photons by HA itself produces e_aq^-. The degradation and defluorination efficiency of PFOS by UV/Iodide/HA process is dependent on pH and HA concentration. As pH increases from 7.0 to 10.0, the enhancement effect of HA improves significantly. The optimal HA concentration for the degradation of 0.03 mM PFOS is 1.0 mg L^-1.

Long-Chain Perfluoroalkyl acids (PFAAs) Affect the Bioconcentration and Tissue Distribution of Short-Chain PFAAs in Zebrafish (Danio rerio)

Short- and long-chain perfluoroalkyl acids (PFAAs), ubiquitously coexisting in the environment, can be accumulated in organisms by binding with proteins and their binding affinities generally increase with their chain length. Therefore, we hypothesized that long-chain PFAAs will affect the bioconcentration of short-chain PFAAs in organisms. To testify this hypothesis, the bioconcentration and tissue distribution of five short-chain PFAAs (linear C-F = 3-6) were investigated in zebrafish in the absence and presence of six long-chain PFAAs (linear C-F = 7-11). The results showed that the concentrations of the short-chain PFAAs in zebrafish tissues increased with exposure time until steady states reached in the absence of long-chain PFAAs. However, in the presence of long-chain PFAAs, these short-chain PFAAs in tissues increased until peak values reached and then decreased until steady states, and the uptake and elimination rate constants of short-chain PFAAs declined in all tissues and their BCF_ss decreased by 24-89%. The inhibitive effect of long-chain PFAAs may be attributed to their competition for transporters and binding sites of proteins in zebrafish with short-chain PFAAs. These results suggest that the effect of long-chain PFAAs on the bioconcentration of short-chain PFAAs should be taken into account in assessing the ecological and environmental effects of short-chain PFAAs.

Ecological effect and risk towards aquatic plants induced by perfluoroalkyl substances: Bridging natural to culturing flora

In the present study, the concentrations and proportions of perfluoroalkyl substances (PFASs) in water and sediments (in different seasons) from the Qing River were investigated. The highest concentration of PFASs in water (207.59 ng L^-1) was found in summer. The composition of PFASs in water changed with time, perfluorobutane sulfonate (PFBS) was the predominant compound in spring and summer, while long-chain PFASs, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), started to increase in autumn and winter. The PFASs concentration in sediments ranged from 0.96 to 4.05 ng g^-1 dw. The proportion of long-chain PFASs was higher than that of short-chain PFASs in sediments, the dominant component in sediments was PFOA with a contribution of 24.6-75.4% to total PFASs in sediments, followed by PFOS. The concentrations of PFASs in roots of emergent plants were relatively higher than those in submerged plants. However, the translocation effect of PFASs was not remarkable. Bioaccumulation factors (BAFs) of the aquatic plants indicated the absorption of PFASs were effective. BAFs in submerged plants basically increased with increasing chain length accordingly. In general, aquatic plants had the absorption preference for long-chain PFASs, especially PFOS, which was the predominant compounds in both submerged and emergent plants. Based on the results above, hornworts were selected to be cultivated indoor in the nutrient solution spiked gradient concentrations of PFOS to assess the general ecological risk. The results revealed that hornworts were resistant to PFOS and might be used as remediation flora to eliminate PFOS contamination.