Cellular Toxicity Associated with Exposure to Perfluorinated Carboxylates (PFCAs) and Their Metabolic Precursors

Unveiling per- and polyfluoroalkyl substance contamination in Chinese paper products and assessing their exposure risk

The contamination characteristics, migration patterns and health risks of per- and polyfluoroalkyl substances (PFAS) were investigated in 66 Chinese paper products by using target and non-target screening methods. Among 57 target PFASs, 5 and 6 PFASs were found in the hygiene paper products ( Collapse

Key Words

• Migration
• Non-target analysis
• Paper products
• Per- and polyfluoroalkyl substances
• Risk assessment

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MESH Headings

• Humans
• Fluorocarbons/analysis
• Ethanol
• Food
• Food Safety
• China
• Alkanesulfonic Acids/analysis

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Grants Collapse

Affiliation(s)

Yan-Fei Chen SCNU Environmental Research Institute, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety & MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China; School of Environment, South China Normal University, Guangzhou 510006, China
Ting Liu SCNU Environmental Research Institute, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety & MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China; School of Environment, South China Normal University, Guangzhou 510006, China
Li-Xin Hu SCNU Environmental Research Institute, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety & MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China; School of Environment, South China Normal University, Guangzhou 510006, China
Chang-Er Chen SCNU Environmental Research Institute, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety & MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China; School of Environment, South China Normal University, Guangzhou 510006, China
Bin Yang SCNU Environmental Research Institute, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety & MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China; School of Environment, South China Normal University, Guangzhou 510006, China.
Guang-Guo Ying SCNU Environmental Research Institute, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety & MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China; School of Environment, South China Normal University, Guangzhou 510006, China

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Polyfluoroalkyl phosphate esters (PAPs) as PFAS substitutes and precursors: An overview

Polyfluoroalkyl phosphate esters (PAPs) are emerging substitutes for legacy per- and polyfluoroalkyl substances (PFAS), which are widely applied in consumer products and closely related to people's daily lives. Increasing concern has been raised about the safety of PAPs due to their metabolism into perfluorooctanoic acid (PFOA) and other perfluorinated carboxylates (PFCAs) in vivo. This review summarizes the current knowledge on PAPs and highlights the knowledge gaps. PAPs dominated the PFAS profiles in wastewater, sludge, household dust, food-contact materials, paper products, paints, and cosmetics. They exhibit biomagnification due to their higher levels in top predators. PAPs have been detected in human blood worldwide, with the highest mean levels being found in the United States (1.9 ng/mL) and China (0.4 ng/mL). 6:2 diPAP is the predominant PAP among all identified matrices, followed by 8:2 diPAP. Toxicokinetic studies suggest that after entering the body, most PAPs undergo biotransformation, generating phase Ⅰ (i.e., PFCAs), phase II, and intermediate products with toxicity to be verified. Several epidemiological and toxicological studies have reported the antiandrogenic effect, estrogenic effect, thyroid disruption, oxidative damage, and reproductive toxicity of PAPs. More research is urgently needed on the source and fate of PAPs, human exposure pathways, toxicity other than reproductive and endocrine systems, toxic effects of metabolites, and mixed exposure effects.

A Review: Per- and Polyfluoroalkyl Substances-Biological Degradation

Per- and polyfluoroalkyl substances (PFASs), highly stable synthetic organic compounds with multiple carbon-fluorine bonds, are emerging as environmental contaminants, toxic, bioaccumulative, and environmentally persistent. PFASs are strongly resistant to biological and chemical degradation, and therefore PFASs present a challenge to researchers and scientists for a better understanding and application of remediation methods and biodegradation of PFASs and have become subject to strict government regulations. The review summarizes the recent knowledge of bacterial and fungal degradation of PFASs, as well as the enzymes involved in the processes of transformation/degradation of PFASs.

Per- and Polyfluoroalkyl Substances in Canadian Fast Food Packaging

A suite of analytical techniques was used to obtain a comprehensive picture of per- and polyfluoroalkyl substances (PFAS) in selected Canadian food packaging used for fast foods (n = 42). Particle-induced gamma ray emission spectroscopy revealed that 55% of the samples contained <3580, 19% contained 3580-10 800, and 26% > 10 800 μg F/m2. The highest total F (1 010 000-1 300 000 μg F/m2) was measured in molded "compostable" bowls. Targeted analysis of 8 samples with high total F revealed 4-15 individual PFAS in each sample, with 6:2 fluorotelomer methacrylate (FTMAc) and 6:2 fluorotelomer alcohol (FTOH) typically dominating. Up to 34% of the total fluorine was released from samples after hydrolysis, indicating the presence of unknown precursors. Nontargeted analysis detected 22 PFAS from 6 different groups, including degradation products of FTOH. Results indicate the use of side-chain fluorinated polymers and suggest that these products can release short-chain compounds that ultimately can be transformed to compounds of toxicological concern. Analysis after 2 years of storage showed overall decreases in PFAS consistent with the loss of volatile compounds such as 6:2 FTMAc and FTOH. The use of PFAS in food packaging such as "compostable" bowls represents a regrettable substitution of single-use plastic food packaging.

A review of omics-based PFAS exposure studies reveals common biochemical response pathways

Per and Polyfluoroalkyl Substances (PFAS) are a diverse group of man-made chemicals with a range of industrial applications and which are widespread in the environment. They are structurally diverse but comprise a common chemical feature of at least one (though usually more) perfluorocarbon moiety (-C_nF_2n-) attached to a functional group such as a carboxylic or sulphonic acid. The strength of the Carbon-Fluorine bond means the compounds do not break down easily and can thus bioaccumulate. PFAS are of high concern to regulators and the public due to their potential toxicity and high persistence. At high exposure levels, PFAS have been implicated in a range of harmful effects on human and environmental health, particularly problems in/with development, cholesterol and endocrine disruption, immune system function, and oncogenesis. However, most environmental toxicology studies use far higher levels of PFAS than are generally found in the environment. Additionally, since the type of exposure, the PFAS used, and the organisms tested all vary between studies, so do the results. Traditional ecotoxicology studies may thus not identify PFAS effects at environmentally relevant exposures. Here we conduct a review of omics-based PFAS exposure studies using laboratory ecotoxicological methodologies and environmentally relevant exposure levels and show that common biochemical response pathways are identified in multiple studies. A major pathway identified was the pentose phosphate shunt pathway. Such molecular markers of sublethal PFAS exposure will greatly benefit accurate and effective risk assessments to ensure that new PFAS regulations can consider the full effects of PFAS exposure on environmental and human health receptors.

The human fecal microbiome contributes to the biotransformation of the PFAS surfactant 8:2 monosubstituted polyfluoroalkyl phosphate ester

Polyfluoroalkyl phosphate esters (PAPs) can be found throughout society due to their numerous commercial applications. However, they also pose an environmental and health concern given their ability to undergo hydrolysis and oxidation to several bioactive and persistent products, including the perfluorocarboxylic acids (PFCAs). The metabolism of PAPs has been shown to occur in mammalian liver and intestine, however metabolism by the gut microbiome has not yet been investigated. In this study, human fecal samples were used to model the microbial population of the colon, to test whether these anaerobic microbes could facilitate 8:2 monosubstituted PAP (monoPAP) transformation. In vitro testing was completed by incubating the fecal samples with 8:2 monoPAP (400-10,000 nM) up to 120 minutes in an anaerobic chamber. Reactions were then terminated and the samples prepared for GC- and LC-MS/MS analysis. Metabolites of interest were the immediate hydrolysis product, the 8:2 fluorotelomer alcohol (FTOH), and 11 additional metabolites previously shown to form from 8:2 FTOH in both oxic and anoxic environments. The kinetics of 8:2 monoPAP transformation by gut microbiota were compared to those in human S9 liver and intestine fractions, both of which have active levels of hydrolyzing and oxidative enzymes that transform 8:2 monoPAP. Transformation rates from 8:2 monoPAP to 8:2 FTOH were highest in liver S9 > intestine S9 > fecal suspensions. The gut microbiome also produced a unique composition of oxidative metabolites, where the following intermediate metabolites were more abundant than terminal PFCAs: 8:2 fluorotelomer unsaturated carboxylic acid (FTUCA) > 8:2 fluorotelomer carboxylic acid (FTCA) > 7:2 Ketone ≈ perfluorohexanoic acid (PFHxA). Hydrolytic and oxidative metabolites contributed up to 30% of the molar balance after microbial 8:2 monoPAP transformation. Together, the results suggest that the gut microbiome can play a notable role in PAP biotransformation.

A Bad Start in Life? Maternal Transfer of Legacy and Emerging Poly- and Perfluoroalkyl Substances to Eggs in an Arctic Seabird

In birds, maternal transfer is a major exposure route for several contaminants, including poly- and perfluoroalkyl substances (PFAS). Little is known, however, about the extent of the transfer of the different PFAS compounds to the eggs, especially for alternative fluorinated compounds. In the present study, we measured legacy and emerging PFAS, including Gen-X, ADONA, and F-53B, in the plasma of prelaying black-legged kittiwake females breeding in Svalbard and the yolk of their eggs. We aimed to (1) describe the contaminant levels and patterns in both females and eggs, and (2) investigate the maternal transfer, that is, biological variables and the relationship between the females and their eggs for each compound. Contamination of both females and eggs were dominated by linPFOS then PFUnA or PFTriA. We notably found 7:3 fluorotelomer carboxylic acid─a precursor of long-chain carboxylates─in 84% of the egg yolks, and provide the first documented finding of ADONA in wildlife. Emerging compounds were all below the detection limit in female plasma. There was a linear association between females and eggs for most of the PFAS. Analyses of maternal transfer ratios in females and eggs suggest that the transfer is increasing with PFAS carbon chain length, therefore the longest chain perfluoroalkyl carboxylic acids (PFCAs) were preferentially transferred to the eggs. The mean ∑_PFAS in the second-laid eggs was 73% of that in the first-laid eggs. Additional effort on assessing the outcome of maternal transfers on avian development physiology is essential, especially for PFCAs and emerging fluorinated compounds which are under-represented in experimental studies.

Widening the Lens on PFASs: Direct Human Exposure to Perfluoroalkyl Acid Precursors (pre-PFAAs)

Determining health risks associated with per-/polyfluoroalkyl substances (PFASs) is a highly complex problem requiring massive efforts for scientists, risk assessors, and regulators. Among the most poorly understood pressing questions is the relative importance of pre-PFAAs, which are PFASs that degrade to highly persistent perfluoroalkyl acids. How many of the vast number of existing pre-PFAAs are relevant for direct human exposure, and what are the predominant exposure pathways? What evidence of direct exposure to pre-PFAAs is provided by human biomonitoring studies? How important are pre-PFAAs and their biotransformation products for human health risk assessment? This article outlines recent progress and recommendations toward widening the lens on human PFAS exposure to include the pre-PFAA subclass.

Emerging investigator series: human CYP2A6 catalyzes the oxidation of 6:2 fluorotelomer alcohol

The biotransformation of 6:2 fluorotelomer alcohol (6:2 FTOH) results in the production of bioactive and persistent metabolites, including perfluorinated carboxylic acids (PFCAs). While the products of 6:2 FTOH metabolism have been elucidated in several animal models, the responsible cytochrome P450 (CYP) isoform(s) have not been reported. Here, we characterized the in vitro oxidation of 6:2 FTOH using human liver microsomes and recombinant human CYPs. Six major xenobiotic metabolizing CYPs were screened for their capacity to catalyze 6:2 FTOH oxidation using chemical inhibitors selective towards CYP isoforms. Of the CYP isoforms investigated, CYP2A6 was the only enzyme capable of catalyzing 6:2 FTOH in human liver microsomes, with K_M and V_max values of 4076 ng mL^-1 and 69 ng mL^-1 min^-1, respectively. We further probed the metabolic mechanism by plotting the 6:2 FTOH kinetic profile and extrapolating data to several possible kinetic models. 6:2 FTOH oxidation followed the typical one-site Michaelis-Menten kinetic model. This study also reports that 6:2 FTOH loss is associated with active CYP2A6 by incubating microsomes with the selective CYP2A6 inhibitor tranylcypromine, which bound competitively to the enzyme as determined by an increased K_M (8796 ng mL^-1) but unchanged V_max value. Collectively, these findings provide a mechanistic perspective on the potential importance of CYP2A6 in the metabolic activation and phase I elimination of 6:2 FTOH and indirect human exposure to PFCAs.

Detection and removal of poly and perfluoroalkyl polluting substances for sustainable environment

PFAs (poly and perfluoroalkyl compounds) are hazardous and bioaccumulative chemicals that do not readily biodegrade or neutralize under normal environmental conditions. They have various industrial, commercial, domestic and defence applications. According to the Organization for Economic Co-operation and Development, there are around 4700 PFAs registered to date. They are present in every stream of life, and they are often emerging and are even difficult to be detected by the standard chemical methods. This review aims to focus on the sources of various PFAs and the toxicities they impose on the environment and especially on humankind. Drinking water, food packaging, industrial areas and commercial household products are the primary PFAs sources. Some of the well-known treatment methods for remediation of PFAs presented in the literature are activated carbon, filtration, reverse osmosis, nano filtration, oxidation processes etc. The crucial stage of handling the PFAs occurs in determining and analysing the type of PFA and its remedy. This paper provides a state-of-the-art review of determination & tools, and techniques for remediation of PFAs in the environment. Improving new treatment methodologies that are economical and sustainable are essential for excluding the PFAs from the environment.

Uptake, Tissue Distribution, and Elimination of 8:2 Polyfluoroalkyl Phosphate Diesters in Mytilus galloprovincialis

Although the distribution of 8:2 polyfluoroalkyl phosphate diester (8:2 diPAP) in aquatic environments has been reported, details on its uptake, tissue specificity, and elimination in bivalve mollusks remain to be clarified. The present study is the first report on the accumulation and elimination of 8:2 diPAP in mussels (Mytilus galloprovincialis). The tissue-specific accumulation and depuration of 8:2 diPAP and its metabolites were investigated via semistatic seawater exposure (8:2 diPAP at a nominal concentration of 10 μg/L), through water-borne exposure with static daily renewal over a 72-h exposure period and a 360-h depuration period. The digestive gland was found to be the target organ where accumulation and biotransformation primarily occur. The bioaccumulation factor values (mL/g dry wt) in different organs were in the following order: digestive gland (1249) > adductor muscle (315) > gills (289) > gonad (82.9) > mantle (33.0). Moreover, the distribution of 8:2 diPAP among tissues may be related to the total protein content. The 8:2 diPAP tended to be excreted in feces. The compounds 8:2 fluorotelomer carboxylic acid, 8:2 fluorotelomer unsaturated carboxylic acid, 7:3 fluorotelomer carboxylic acid, perfluorooctanoic acid, and perfluoroheptanoic acid were detected and quantified as phase I metabolites, and the concentration of all phase I metabolites relative to the 8:2 diPAP concentration (72 h) was 0.304 mol%. A phase II metabolite, 8:2 fluorotelomer alcohol conjugated with sulfate, was detected but not quantitated in the digestive gland. A biotransformation pathway of 8:2 diPAP in M. galloprovincialis was proposed on the basis of the results obtained in the present study and previous studies. These findings improve our understanding of the accumulation of perfluorocarboxylic acids in bivalve mollusks. Environ Toxicol Chem 2021;40:1992-2004. © 2021 SETAC.

Biotransformation of perfluoroalkyl acid precursors from various environmental systems: advances and perspectives

Perfluoroalkyl acids (PFAAs) are widely used in industrial production and daily life because of their unique physicochemical properties, such as their hydrophobicity, oleophobicity, surface activity, and thermal stability. Perfluorosulfonic acids (PFSAs) and perfluorocarboxylic acids (PFCAs) are the most studied PFAAs due to their global occurrence. PFAAs are environmentally persistent, toxic, and the long-chain homologs are also bioaccumulative. Exposure to PFAAs may arise directly from emission or indirectly via the environmental release and degradation of PFAA precursors. Precursors themselves or their conversion intermediates can present deleterious effects, including hepatotoxicity, reproductive toxicity, developmental toxicity, and genetic toxicity. Therefore, exposure to PFAA precursors constitutes a potential hazard for environmental contamination. In order to comprehensively evaluate the environmental fate and effects of PFAA precursors and their connection with PFSAs and PFCAs, we review environmental biodegradability studies carried out with microbial strains, activated sludge, plants, and earthworms over the past decade. In particular, we review perfluorooctyl-sulfonamide-based precursors, including perfluroooctane sulfonamide (FOSA) and its N-ethyl derivative (EtFOSA), N-ethyl perfluorooctane sulfonamido ethanol (EtFOSE), and EtFOSE-based phosphate diester (DiSAmPAP). Fluorotelomerization-based precursors are also reviewed, including fluorotelomer alcohols (FTOH), fluorotelomer sulfonates (FTSA), and a suite of their transformation products. Though limited information is currently available on zwitterionic PFAS precursors, a preliminary review of data available for 6:2 fluorotelomer sulfonamide betaine (FTAB) was also conducted. Furthermore, we update and refine the recent knowledge on biotransformation strategies with a focus on metabolic pathways and mechanisms involved in the biotransformation of PFAA precursors. The biotransformation of PFAA precursors mainly involves the cleavage of carbon-fluorine (C-F) bonds and the degradation of non-fluorinated functional groups via oxidation, dealkylation, and defluorination to form shorter-chained PFAAs. Based on the existing research, the current problems and future research directions on the biotransformation of PFAA precursors are proposed.

Regulating PFAS as a Chemical Class under the California Safer Consumer Products Program

BACKGROUND

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a group of manmade chemicals containing at least one fully fluorinated carbon atom. The widespread use, large number, and diverse chemical structures of PFAS pose challenges to any sufficiently protective regulation, emissions reduction, and remediation at contaminated sites. Regulating only a subset of PFAS has led to their replacement with other members of the class with similar hazards, that is, regrettable substitutions. Regulations that focus solely on perfluoroalkyl acids (PFAAs) are ineffective, given that nearly all other PFAS can generate PFAAs in the environment.

OBJECTIVES

In this commentary, we present the rationale adopted by the State of California's Department of Toxic Substances Control (DTSC) for regulating PFAS as a class in certain consumer products.

DISCUSSION

We at the California DTSC propose regulating certain consumer products if they contain any member of the class of PFAS because: a) all PFAS, or their degradation, reaction, or metabolism products, display at least one common hazard trait according to the California Code of Regulations, namely environmental persistence; and b) certain key PFAS that are the degradation, reaction or metabolism products, or impurities of nearly all other PFAS display additional hazard traits, including toxicity; are widespread in the environment, humans, and biota; and will continue to cause adverse impacts for as long as any PFAS continue to be used. Regulating PFAS as a class is thus logical, necessary, and forward-thinking. This technical position may be helpful to other regulatory agencies in comprehensively addressing this large class of chemicals with common hazard traits. https://doi.org/10.1289/EHP7431.

Emerging and legacy per- and polyfluoroalkyl substances in house dust from South China: Contamination status and human exposure assessment

Our study investigated a large variety of per- and polyfluoroalkyl substances (PFASs) in house dust collected from Guangzhou, South China during 2015-2018. The perfluorobutane sulfonic acid (PFBS) exhibited the highest median concentration (17.6 ng/g), followed by linear perfluorooctanoic acid (L-PFOA; 4.8 ng/g), linear perfluorooctane sulfonic acid (L-PFOS; 4.2 ng/g), 6:2 fluorotelomer phosphate diester (6:2 diPAP; 3.4 ng/g), perfluorodecanoic acid (PFDA; 1.2 ng/g) and perfluoroundecanoic acid (PFUdA; 1.2 ng/g), and 6:2 chlorinated perfluoroalkyl ether sulfonic acid (6:2 Cl-PFESA; 1.1 ng/g). Total concentrations of PFASs (median: 53 ng/g) were generally within the 25-50 percentile of the concentration range reported in global studies. However, our samples exhibited composition profiles different from those reported in many other regions. Analysis based on this and previous studies revealed that the compositions in house dust from East Asia, North America, and Europe exhibit a region-specific pattern. This may indicate region-specific market demands, application patterns, as well as associated human exposure risks. Exploration of dwelling characterizations suggested that renovation history appeared to be a significant factor influencing PFAS concentrations in house dust, although other factors may exist and play a role. Estimation of daily intakes via dust ingestion and dermal contact indicates low exposure risks from these two pathways. However, the PFAS chemical-specific biological effects, possible mixture effects, as well as additional exposure pathways, imply that the risk from indoor PFAS exposure should not be overlooked.

Risk to human health related to the presence of perfluoroalkyl substances in food

The European Commission asked EFSA for a scientific evaluation on the risks to human health related to the presence of perfluoroalkyl substances (PFASs) in food. Based on several similar effects in animals, toxicokinetics and observed concentrations in human blood, the CONTAM Panel decided to perform the assessment for the sum of four PFASs: PFOA, PFNA, PFHxS and PFOS. These made up half of the lower bound (LB) exposure to those PFASs with available occurrence data, the remaining contribution being primarily from PFASs with short half-lives. Equal potencies were assumed for the four PFASs included in the assessment. The mean LB exposure in adolescents and adult age groups ranged from 3 to 22, the 95th percentile from 9 to 70 ng/kg body weight (bw) per week. Toddlers and 'other children' showed a twofold higher exposure. Upper bound exposure was 4- to 49-fold higher than LB levels, but the latter were considered more reliable. 'Fish meat', 'Fruit and fruit products' and 'Eggs and egg products' contributed most to the exposure. Based on available studies in animals and humans, effects on the immune system were considered the most critical for the risk assessment. From a human study, a lowest BMDL 10 of 17.5 ng/mL for the sum of the four PFASs in serum was identified for 1-year-old children. Using PBPK modelling, this serum level of 17.5 ng/mL in children was estimated to correspond to long-term maternal exposure of 0.63 ng/kg bw per day. Since accumulation over time is important, a tolerable weekly intake (TWI) of 4.4 ng/kg bw per week was established. This TWI also protects against other potential adverse effects observed in humans. Based on the estimated LB exposure, but also reported serum levels, the CONTAM Panel concluded that parts of the European population exceed this TWI, which is of concern.

Role of non-coding-RNAs in response to environmental stressors and consequences on human health

Environmental risk factors, including physicochemical agents, noise and mental stress, have a considerable impact on human health. This environmental exposure may lead to epigenetic reprogramming, including changes in non-coding RNAs (ncRNAs) signatures, which can contribute to the pathophysiology state. Oxidative stress is one of the results of this environmental disturbance by modifying cellular processes such as apoptosis, signal transduction cascades, and DNA repair mechanisms. In this review, we delineate environmental risk factors and their influence on (ncRNAs) in connection to disease. We focus on well-studied miRNAs and analyze the novel roles of long-non-coding-RNAs (lncRNAs). We discuss commonly regulated lncRNAs after exposure to different stressors, such as UV, heavy metals and pesticides among others, and the potential role of these lncRNA as exposure biomarkers, epigenetic regulators and potential therapeutic targets to diminish the deleterious secondary response to environmental agents.

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Environmental stressors induce epigenetic changes that lead to long-lasting gene expression changes and pathology development.

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NcRNAs, miRNAs and lncRNAs, are epigenetic modifiers susceptible to changes in expression after environmental insults .

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LncRNAs influence cell function partnering with other biomolecules such as proteins, DNA, RNA or other ncRNAs.

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LncRNA dysregulation affects cell development, carcinogenesis, vascular disease and neurodegenerative disorders.

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ncRNA signatures can be potentially used as biomarkers to identify exposure to specific environmental stressors.

Strategies for grouping per- and polyfluoroalkyl substances (PFAS) to protect human and environmental health

Grouping strategies are needed for per- and polyfluoroalkyl substances (PFAS), in part, because it would be time and resource intensive to test and evaluate the more than 4700 PFAS on the global market on a chemical-by-chemical basis. In this paper we review various grouping strategies that could be used to inform actions on these chemicals and outline the motivations, advantages and disadvantages for each. Grouping strategies are subdivided into (1) those based on the intrinsic properties of the PFAS (e.g. persistence, bioaccumulation potential, toxicity, mobility, molecular size) and (2) those that inform risk assessment through estimation of cumulative exposure and/or effects. The most precautionary grouping approach of those reviewed within this article suggests phasing out PFAS based on their high persistence alone (the so-called "P-sufficient" approach). The least precautionary grouping approach reviewed advocates only grouping PFAS for risk assessment that have the same toxicological effects, modes and mechanisms of action, and elimination kinetics, which would need to be well documented across different PFAS. It is recognised that, given jurisdictional differences in chemical assessment philosophies and methodologies, no one strategy will be generally acceptable. The guiding question we apply to the reviewed grouping strategies is: grouping for what purpose? The motivation behind the grouping (e.g. determining use in products vs. setting guideline levels for contaminated environments) may lead to different grouping decisions. This assessment provides the necessary context for grouping strategies such that they can be adopted as they are, or built on further, to protect human and environmental health from potential PFAS-related effects.

Chemical food contaminants during food processing: sources and control

With the development in international food trade, there has been emerging risks in the food chain. Food contamination can be caused by several factors in a complex food chain. This articles provides a comprehensive review of known chemical contaminants from the production of raw materials to the consumption of food products as well as prevention and control measures. Specifically, this review discusses the following topics, raw material contamination caused by environmental pollution, endogenous food contamination caused by processing methods, and cold chain system challenges in food e-commerce.

Formation of perfluorocarboxylic acids from 6:2 fluorotelomer sulfonate (6:2 FTS) in landfill leachate: Role of microbial communities

Fluorotelomer compounds in landfill leachate can undergo biotransformation under aerobic conditions and act as a secondary source of perfluorocarboxylic acids (PFCAs) to the environment. Very little is known about the role of various microbial communities towards fluorotelomer compounds biotransformation. Using an inoculum prepared from the sediment of a leachate collection ditch, 6:2 fluorotelomer sulfonate (6:2 FTS) biotransformation experiments were carried out. Specific substrates (i.e., glucose, ammonia) and ammonia-oxidizing inhibitor (allylthiourea) were used to produce two experimental runs with heterotrophic (HET) growth only and heterotrophic with ammonia-oxidizing and nitrite- oxidizing bacteria (HET + AOB + NOB). After 10 days, ∼20% of the spiked 6:2 FTS removal was observed in HET + AOB + NOB, compared to ∼7% under HET condition. Higher 6:2 FTS removal in HET + AOB + NOB likely resulted from ammonia monooxygenase enzyme that catalyzes the first step of ammonia oxidation. The HET + AOB + NOB condition also showed higher PFCA (C4-C6) formation (∼2% of initially spiked 6:2 FTS), possibly due to higher overall bioactivity. Microbial community analysis through 16s rRNA sequencing confirmed that Proteobacteria and Bacteroidetes were the most abundant phyla (>75% relative abundance) under all experimental conditions. High abundance of Actinobacteria (>17%) was observed under the HET + AOB + NOB condition on day 7. Since Actinobacteria can synthesize a wide range of enzymes including monooxygenases, they likely play an important role in 6:2 FTS biotransformation and PFCA production.

Biotransformation of 6:2 fluorotelomer alcohol by the whole soybean (Glycine max L. Merrill) seedlings

Fluorotelomer alcohols (FTOHs) are important precursors of perfluorocarboxylic acids (PFCAs) in the environment and biota. With the growing application of 6:2 FTOH [F(CF2)6CH2CH2OH] in product formulation, it is becoming increasingly urgent to investigate its biological fates in different species. In this study, biotransformation of 6:2 FTOH by young soybean plants (Glycine max L. Merrill) were investigated using hydroponic experiments. During the 144 h-exposure, 6:2 FTCA [F(CF2)6CH2COOH], 6:2 FTUCA [F(CF2)5CFCHCOOH], 5:3 FTUCA [F(CF2)5CHCHCOOH], 5:3 FTCA [F(CF2)5CH2CH2COOH], PFHxA [F(CF2)5COOH] and PFPeA [F(CF2)4COOH] were phase I metabolites in soybean. At the end of exposure, 5:3 FTCA (5.08 mol%), PFHxA (2.34 mol%) and PFPeA (0.58 mol%) were three main metabolites in soybean-solution system. 5:3 FTCA was predominant in soybean roots and stems, while PFHxA was the most abundant product in leaves. PFBA [F(CF2)3COOH] and 4:3 FTCA [F(CF2)4CH2CH2COOH] detected in the hydroponic solution most-likely came from the transformation of 5:3 FTCA by root-associated microbes. Moreover, phase II metabolites of 6:2 FTOH were identified and monitored in soybean tissues. Alcohol dehydrogenase, aldehyde dehydrogenase and glutathione S-transferase were found to participate in 6:2 FTOH metabolism. Based on the phase I and phase II metabolism of 6:2 FTOH in soybean, this study for the first time provides evidences for the transformation pathways of 6:2 FTOH in plants.

Cost-Effective Detection of Perfluoroalkyl Carboxylic Acids with Gas Chromatography: Optimization of Derivatization Approaches and Method Validation

The reliable quantification of perfluoroalkyl carboxylic acids (PFCAs) in environmental samples like surface water by using gas chromatography (GC) remains challenging because the polar PFCAs call for derivatization before injection and problems involving the integration of sample pretreatment and derivatization procedures. Here we proposed a cost-effective method for the GC based determination of C4–C12 PFCAs in surface water samples by integrating solid phase extraction and PFCAs anilide derivatization. First, we assessed the performance of different PFCAs derivatization methods, namely esterification and amidation. Esterification was unable to derivatize C4–C6 PFCAs. On the contrary, amidation procedures by using 2,4-difluoroaniline (DFA) and N,N′-dicyclohexylcarbodiimide (DCC) could successfully transform all the PFCA analogs to produce anilide derivatives, which could be easily detected by GC. Then the reaction conditions in the amidation approach were further optimized by using orthogonal design experiments. After optimizing the instrumental parameters of GC, the limits of detection (LOD) of this derivatization method were determined to be 1.14–6.32 μg L⁻¹. Finally, in order to establish an intact method for the quantification of PFCAs in surface water samples, solid phase extraction (SPE) was used for extraction and cleanup, which was further integrated with the subsequent amidation process. The SPE-amidation-GC method was validated for application, with good accuracy and precision reflected by the PFCAs recoveries and derivatization of triplicates. The method reported here could provide a promising and cost-effective alternative for the simultaneous determination of C4–C12 PFCAs in environmental water samples.

Toxicokinetics of 8:2 fluorotelomer alcohol (8:2-FTOH) in male and female Hsd:Sprague Dawley SD rats after intravenous and gavage administration

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8:2 fluorotelomer is rapidly distributed and eliminated in rats.

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Perfluorooctanoic acid and 7:3-fluorotelomer acid are detectable metabolites.

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Sex differences in kinetics were seen only in perfluorooctanoic acid.

Fluorotelomer alcohols (FTOHs) are used in the production of persistent per- and polyfluorinated alkyl substances (PFAS). Rodents and humans metabolize FTOHs to perfluoralkyl carboxylic acids which have several associated toxicities. Thus, understanding the toxicokinetics of these FTOHs and their metabolites will be useful for interpreting their toxicity for humans. Here, male and female Hsd:Sprague-Dawley SD rats were administered a single dose of 8:2-FTOH via gavage (males: 12, 24, 48 mg/kg; females: 40, 80, 160 mg/kg) or IV (males: 12 mg/kg; females: 40 mg/kg). Toxicokinetics of 8:2-FTOH and two primary metabolites, perfluorooctanoic acid (PFOA) and 7:3-fluorotelomer acid (7:3-FTA) were determined in plasma. Concentrations (total) of these chemicals were determined in the liver, kidney, and brain. There was rapid absorption and distribution of 8:2-FTOH after gavage administration in male rats. The plasma elimination half-life ranged from 1.1 to 1.7 hours. Kinetic parameters of 8:2-FTOH in females were similar to that in males. Bioavailability of 8:2-FTOH ranged from 22 to 41% for both sexes with no dose-dependent trends. 8:2-FTOH metabolites, PFOA and 7:3-FTA were detected in plasma following administration of the parent FTOH. Consistent with existing literature, the plasma half-life of PFOA was longer in males than in females (198–353 hours and 4.47–6.9 hours, respectively). The plasma half-life of 7:3-FTA was around 2–3 days in both sexes. 8:2-FTOH and 7:3-FTA were detected in all tissues; PFOA was found in the liver and kidney but not the brain. Detectable concentrations of metabolites persisted longer than the parent FTOH. These data demonstrate that in rats given a single gavage dose, 8:2-FTOH is rapidly absorbed, metabolized to form PFOA and 7:3-FTA, distributed to tissues, and eliminated faster than its metabolites. Sex differences were observed in the tissue distribution and elimination of PFOA, but not 8:2-FTOH and 7:3-FTA.

Plant uptake and translocation of perfluoroalkyl acids in a wheat-soil system

Application of per- and polyfluoroalkyl substances (PFASs) is shifting to short-chain analogs (C ≤ 6) that raises concerns for their potential ecotoxicological risks. In the present study, pot experiments were carried out to study the effects of perfluoroalkyl acids (PFAAs), including perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs), with different carbon chain lengths (C4, C6, and C8) on the growth of wheat seedlings and their plant uptake and transfer at two spiking levels (200 and 2000 μg/kg soil). Exposure to C4 PFAAs slightly inhibited chlorophyll activity, whereas exposure to C8 PFAAs showed enhancement. The bioaccumulation factors (BAFs) for C4 PFAAs in wheat were over 10, while BAFs for C8 PFAAs were all below 1. Rhizospheric and root to shoot transfer factors for PFAAs were both negatively correlated with their log K_ow (p < 0.05). PFCAs exhibited both higher rhizospheric mobility and accumulation potentials than PFSAs of the same chain lengths. Hence, perfluoroalkyl chain governs the mobility of PFAAs in a soil-plant system besides interactions of their head groups, and the substitution with shorter chain PFASs raises concerns for their higher plant accumulation potential that brings higher ecotoxicological and human exposure risks via food chains.

Perfluoroalkyl acid exposure induces protective mitochondrial and endoplasmic reticulum autophagy in lung cells

Wide application of perfluoroalkyl acids (PFAAs) has raised great concerns on their side-effects on human health. PFAAs have been shown to accumulate mainly in the liver and cause hepatotoxicity. However, PFAAs can also deposit in lung tissues through air-borne particles and cause serious pulmonary toxicity. But the underlying mechanisms are still largely unknown. Autophagy is a type of programmed cell death parallel to necrosis and apoptosis, and may be involved in the lung toxicity of PFAAs. In this study, lung cancer cells, A549, were employed as the model to investigate the effects of three PFAAs with different carbon chain lengths on cell autophagy. Through Western blot analysis on LC3-I/II ratio of cells exposed to non-cytotoxic concentration (200 µM) and cytotoxic concentration (350 µM), we found concentration-dependent increase of autophagosomes in cells, which was further confirmed by TEM examination on ultra-thin section of cells and fluorescence imaging on autophagosomes in live cells. The abundance of p62 increased with the PFAAs concentration indicating the blockage of autophagy flux. Furthermore, we identified the mitochondrial autophagy (mitophagy) and endoplasmic reticulum autophagy (ER-phagy) morphologically as the major types of autophagy, suggesting the disruption on mitochondria and ERs. These organelle damages were confirmed by the overgeneration of ROS, hyperpolarization of mitochondrial membrane potential, as well as the up-regulation of ER-stress-related proteins, ATF4 and p-IRE1. Further analysis on the signaling pathways showed that PFAAs activated the MAPK pathways and inhibited the PI3K/Akt pathway, with potencies following the order of PFDA > PFNA > PFOA. Anti-oxidant (NAC) treatment did not rescue cells from death, indicating that oxidative stress is not the reason of cytotoxicity. Inhibition of autophagy by Atg5 siRNA and chloroquine even increased the toxicity of PFAAs, suggesting that PFAAs-autophagy was induced as the secondary effects of organelle damages and played a protective role during cell death.

The Role of MicroRNAs in Environmental Risk Factors, Noise-Induced Hearing Loss, and Mental Stress

SIGNIFICANCE

MicroRNAs (miRNAs) are important regulators of gene expression and define part of the epigenetic signature. Their influence on every realm of biomedicine is established and progressively increasing. The impact of environment on human health is enormous. Among environmental risk factors impinging on quality of life are those of chemical nature (toxic chemicals, heavy metals, pollutants, and pesticides) as well as those related to everyday life such as exposure to noise or mental and psychosocial stress. Recent Advances: This review elaborates on the relationship between miRNAs and these environmental risk factors.

CRITICAL ISSUES

The most relevant facts underlying the role of miRNAs in the response to these environmental stressors, including redox regulatory changes and oxidative stress, are highlighted and discussed. In the cases wherein miRNA mutations are relevant for this response, the pertinent literature is also reviewed.

FUTURE DIRECTIONS

We conclude that, even though in some cases important advances have been made regarding close correlations between specific miRNAs and biological responses to environmental risk factors, a need for prospective large-cohort studies is likely necessary to establish causative roles. Antioxid. Redox Signal. 28, 773-796.

Effects of microbial activity on perfluorinated carboxylic acids (PFCAs) generation during aerobic biotransformation of fluorotelomer alcohols in activated sludge

Biotransformation of fluorotelomer alcohols (FTOHs) in wastewater treatment plants (WWTPs) can release toxic intermediates and perfluorinated carboxylic acids (PFCAs) to the aqueous environment. However, little information is known about the role of relevant microbial activity (i.e., autotrophs and/or heterotrophs) in biotransformation of FTOHs. Additionally, the dynamics of microbial community in sludge after exposure to FTOHs remain unclear. In the present research, using domestic and industrial WWTP sludge, we performed lab-scale batch experiments to characterize the FTOHs biodegradation property under aerobic condition. Both heterotrophs and the autotrophs were associated with FTOHs biotransformation. However, the microbial activity influenced PFCAs generation efficiency. Autotrophs based on ammonia oxidation (50mgN/L) resulted in more effective generation of PFCAs than heterotrophs based on glucose (200mgC/L) metabolism. Moreover, autotrophs generated more amounts of short-chain PFCAs (carbon number ≤7) than the heterotrophs. The ammonia monooxygenase (AMO) in ammonia oxidizing microorganisms (AOMs) are suggested as responsible for the enhanced generation of PFCAs during FTOHs biotransformation. In the sludge that had been exposed to poly- and perfluorinated alkyl substances in an industrial WWTP, Chlorobi was the predominant microorganisms (36.9%), followed by Proteobacteria (20.2%), Bacteroidetes (11.1%), Chloroflexi (6.2%), Crenarchaeota (5.6%), Planctomycetes (4.2%), and Acidobacteria (3.5%). In the present research, the dosed 8:2 FTOH (12.1mg/L) and its biotransformation products (intermediates and PFCAs) could force a shift in microbial community composition in the sludge. After 192h, Proteobacteria significantly increased and dominated. These results provide knowledge for comprehending the effects of microbial activity on FTOHs biodegradation and the information about interaction between microbial community and the exposure to FTOHs in activated sludge.

Biotransformation of 8:2 polyfluoroalkyl phosphate diester in gilthead bream (Sparus aurata)

Polyfluoroalkyl phosphate esters (PAPs) are high production volume surfactants used in the food contact paper and packaging industry. PAPs may transform to persistent perfluoroalkyl carboxylic acids (PFCAs) under biotic conditions, but little is known about their fate and behavior in aquatic organisms. Here we report for the first time on the uptake, tissue distribution, and biotransformation of 8:2 polyfluoroalkyl phosphate diester (8:2 diPAP) in fish. Gilt-head bream (Sparus aurata) were dosed via the diet (8:2 diPAP at 29μg/g) for 7days, during which time 8:2 diPAP and its transformation products were monitored in plasma, liver, muscle, gills, bile and brain. 8:2 diPAP tended to accumulate in liver, plasma and gills, and to a lesser extent in muscle, bile and brain. Several transformation products (observed previously in other organisms) were also observed in most tissues and biofluids, including both saturated and unsaturated fluorotelomer acids (8:2 FTCA, 8:2 FTUCA, 7:3 FTCA), and perfluorooctanoic acid (PFOA). 8:2 FTCA was the major metabolite in all tissues/biofluids, except for bile, where PFOA occurred at the highest concentrations. Unexpectedly high PFOA levels (up to 3.7ng/g) were also detected in brain. Phase 2 metabolites, which have been reported in fish following exposure to fluorotelomer alcohols, were not observed in these experiments, probably due to their low abundance. Nevertheless, the detection of PFOA indicates that exposure to PAPs may be an indirect route of exposure to PFCAs in fish.

Biotransformation of 6:2 polyfluoroalkyl phosphates (6:2 PAPs): Effects of degradative bacteria and co-substrates

Polyfluoroalkyl phosphates (PAPs), a group of fluorotelomer alcohol (FTOH)-based surfactants commonly used in water- and grease-proof food contact paper, have been suggested as a direct source of human exposure to health-concerned perfluoroalkyl carboxylic acids (PFCAs). This study investigated factors affecting biotranformation of 6:2 polyfluoroalkyl phosphates (6:2 PAPs) by three known FTOH-degrading Pseudomonas strains (Pseudomonas butanovora, P. oleovorans, and P. fluorescens DSM 8341) under different co-substrate conditions and compared to that by activated sludge samples. The three pure strains transformed 6:2 PAPs into eight different per- and poly-fluoroalkyl carboxylic acids (PFCAs) and/or PFCA precursors. P. fluorescens DSM 8341 produced 5:2 sFTOH [CF₃(CF₂)₄CH(OH)CH₃] and P. oleovorans produced 5:2 ketone [CF₃(CF₂)₄C(O)CH₃] as the primary transformation product, respectively, with citrate having a minimal impact on the transformation. P. butanovora with lactate produced more diverse transformation products than those by any two strains. Activated sludge was more efficient at transforming 6:2 PAPs and produced more transformation products including PFHpA [CF₃(CF₂)₅COOH] and PFPeA [CF₃(CF₂)₃COOH], with 5:2 sFTOH as the most abundant product on day 30. The abundance of the alkane hydroxylase (alkB) gene related to alkane oxidation, the changes of total microbial population as well as their community structure in activated sludge during 6:2 PAPs biotransformation were also investigated.

Biotransformation of 8:2 fluorotelomer alcohol by recombinant human cytochrome P450s, human liver microsomes and human liver cytosol

Biotransformation of 8:2 fluorotelomer alcohol (8:2 FTOH) can form potentially more toxic metabolites. However, the responsible cytochrome P450 (CYP) isoform(s) and phase II metabolism have not been studied in humans. Here, we characterized the in vitro metabolism of 8:2 FTOH by recombinant human CYPs, human liver microsomes, and human liver cytosol. The results showed that among the 11 isoforms investigated, CYP2C19 was the only enzyme capable of catalyzing 8:2 FTOH with Km and Vmax values of 18.8 μM and 8.52 pmol min(-1) pmol(-1) P450, respectively. The phase I metabolite was identified as 8:2 fluorotelomer aldehyde (8:2 FTAL). HLMs also catalyzed 8:2 FTOH transformation, with the Vmax and intrinsic clearance (CLint) values similar to those of CYP2C19 after the protein content is taken into account. Molecular docking showed that the hydroxyl group of 8:2 FTOH accesses the heme iron-oxo of CYP2C19 in an energetically favored orientation. 8:2 FTOH was also transformed by phase II enzymes to form O-glucuronide and O-sulfate conjugates. The CLint values follow the order of sulfation > oxidation > glucuronidation, suggesting that conjugation is the major metabolic pathway, which explains the low yield of perfluoroalkyl acids (PFCAs). These results provide new insight into fluorotelomer alcohol biotransformation and indirect human exposure to PFCAs.

Fast and simple determination of perfluorinated compounds and their potential precursors in different packaging materials

A simple and fast analytical method for the determination of fourteen perfluorinated compounds (PFCs), including three perfluoroalkylsulfonates (PFSAs), seven perfluorocarboxylic acids (PFCAs), three perfluorophosphonic acids (PFPAs) and perfluorooctanesulfonamide (PFOSA) and ten potential precursors, including four polyfluoroalkyl phosphates (PAPs), four fluorotelomer saturated acids (FTCAs) and two fluorotelomer unsaturated acids (FTUCAs) in different packaging materials was developed in the present work. In order to achieve this objective the optimization of an ultrasonic probe-assisted extraction (UPAE) method was carried out before the analysis of the target compounds by liquid-chromatography-triple quadrupole-tandem mass spectrometry (LC-QqQ-MS/MS). 7 mL of 1 % acetic acid in methanol and a 2.5-min single extraction cycle were sufficient for the extraction of all the target analytes. The optimized analytical method was validated in terms of recovery, precision and method detection limits (MDLs). Apparent recovery values after correction with the corresponding labeled standard were in the 69-103 % and 62-98 % range for samples fortified at 25 ng/g and 50 ng/g concentration levels, respectively and MDL values in the 0.6-2.2 ng/g range were obtained. The developed method was applied to the analysis of plastic (milk bottle, muffin cup, pre-cooked food wrapper and cup of coffee) and cardboard materials (microwave popcorn bag, greaseproof paper for French fries, cardboard box for pizza and cinema cardboard box for popcorn). To the best of our knowledge, this is the first method that describes the determination of fourteen PFCs and ten potential precursors in packaging materials. Moreover, 6:2 FTCA, 6:2 FTUCA and 5:3 FTCA analytes were detected for the first time in microwave popcorn bags.

Human placental transfer of perfluoroalkyl acid precursors: Levels and profiles in paired maternal and cord serum

Perfluoroalkyl acids (PFAAs) precursors, the indirect source of PFAA exposure, have been observed in environmental and human samples. However, the maternal-fetal transfer of these chemicals has not been well examined. In this study, 50 paired maternal and cord serum samples collected in Jiangsu province of China were analyzed for fifteen PFAA precursors. Among the detected PFAAs, 6:2 fluorotelomer sulfonate (6:2 FTS), N-methyl- and N-ethyl-perfluorooctanesulfonamidoacetates had comparable detection rate in both maternal and cord sera, while the mean concentrations and detection rates of 8:2 FTS and perfluorooctane sulfonamide (PFOSA) were higher in maternal sera compared to cord sera (Mann-Whitney U test, P < 0.05). Analysis of variance and least significant difference tests showed that the youngest maternal age group (21-24 years old) had the highest concentration of 6:2 FTS in cord sera. Maternal serum PFOSA was found significantly correlated with the cord serum perfluorooctanesulfonate (PFOS) (Spearman test, r = 0.361, P = 0.010), indicating that maternal serum PFOSA might be an indirect source of PFOS in fetuses. The obtained results suggested the potential prenatal exposure and human placental transfer of perfluoroalkyl acid precursors.

World-Wide Indoor Exposure to Polyfluoroalkyl Phosphate Esters (PAPs) and other PFASs in Household Dust

Human exposure to perfluorooctanoic acid (PFOA) and other per- and polyfluoroalkyl substances (PFASs) is ongoing and in some cases increasing, despite efforts made to reduce emissions. The role of precursor compounds such as polyfluorinated phosphate esters (PAPs) has received increasing attention, but there are knowledge gaps regarding their occurrence and impact on human exposure. In this study, mono-, di-, and triPAPs, perfluorinated alkyl acids (PFAAs), saturated, and unsaturated fluorotelomer carboxylic acids (FTCA/FTUCAs), perfluoroalkane sulfonamides, and sulfonamidethanols (FOSA/FOSEs), and one fluorotelomer sulfonic acid (FTSA)) were compared in household dust samples from Canada, the Faroe Islands, Sweden, Greece, Spain, Nepal, Japan, and Australia. Mono-, di-, and triPAPs, including several diPAP homologues, were frequently detected in dust from all countries, revealing an ubiquitous spread in private households from diverse geographic areas, with significant differences between countries. The median levels of monoPAPs and diPAPs ranged from 3.7 ng/g to 1 023 ng/g and 3.6 ng/g to 692 ng/g, respectively, with the lowest levels found in Nepal and the highest in Japan. The levels of PAPs exceeded those of the other PFAS classes. These findings reveal the importance of PAPs as a source of PFAS exposure worldwide.

Immortalized Human Hepatic Cell Lines for In Vitro Testing and Research Purposes

The ubiquitous shortage of primary human hepatocytes has urged the scientific community to search for alternative cell sources, such as immortalized hepatic cell lines. Over the years, several human hepatic cell lines have been produced, whether or not using a combination of viral oncogenes and human telomerase reverse transcriptase protein. Conditional approaches for hepatocyte immortalization have also been established and allow generation of growth-controlled cell lines. A variety of immortalized human hepatocytes have already proven useful as tools for liver-based in vitro testing and fundamental research purposes. The present chapter describes currently applied immortalization strategies and provides an overview of the actually available immortalized human hepatic cell lines and their in vitro applications.

Controlling electrodeposited conducting polymer nanostructures with the number and the length of fluorinated chains for adjusting superhydrophobic properties and adhesion

Controlling the formation of surface nanostructures is highly important for various applications, and in particular for superhydrophobic properties.

Strategies for immortalization of primary hepatocytes

The liver has the unique capacity to regenerate in response to a damaging event. Liver regeneration is hereby largely driven by hepatocyte proliferation, which in turn relies on cell cycling. The hepatocyte cell cycle is a complex process that is tightly regulated by several well-established mechanisms. In vitro, isolated hepatocytes do not longer retain this proliferative capacity. However, in vitro cell growth can be boosted by immortalization of hepatocytes. Well-defined immortalization genes can be artificially overexpressed in hepatocytes or the cells can be conditionally immortalized leading to controlled cell proliferation. This paper discusses the current immortalization techniques and provides a state-of-the-art overview of the actually available immortalized hepatocyte-derived cell lines and their applications.

Fate and effects of poly- and perfluoroalkyl substances in the aquatic environment: a review

Polyfluoroalkyl and perfluoroalkyl substances (PFASs) are distributed ubiquitously in the aquatic environment, which raises concern for the flora and fauna in hydrosystems. The present critical review focuses on the fate and adverse effects of PFASs in the aquatic environment. The PFASs are continuously emitted into the environment from point and nonpoint sources such as sewage treatment plants and atmospheric deposition, respectively. Although concentrations of single substances may be too low to cause adverse effects, their mixtures can be of significant environmental concern. The production of C8 -based PFASs (i.e., perfluorooctane sulfonate [PFOS] and perfluorooctanoate [PFOA]) is largely phased out; however, the emissions of other PFASs, in particular short-chain PFASs and PFAS precursors, are increasing. The PFAS precursors can finally degrade to persistent degradation products, which are, in particular, perfluoroalkane sulfonates (PFSAs) and perfluoroalkyl carboxylates (PFCAs). In the environment, PFSAs and PFCAs are subject to partitioning processes, whereby short-chain PFSAs and PFCAs are mainly distributed in the water phase, whereas long-chain PFSAs and PFCAs tend to bind to particles and have a substantial bioaccumulation potential. However, there are fundamental knowledge gaps about the interactive toxicity of PFAS precursors and their persistent degradation products but also interactions with other natural and anthropogenic stressors. Moreover, because of the continuous emission of PFASs, further information about their ecotoxicological potential among multiple generations, species interactions, and mixture toxicity seems fundamental to reliably assess the risks for PFASs to affect ecosystem structure and function in the aquatic environment.