Application of a multiple endpoint bacterial reporter assay to evaluate toxicological relevant endpoints of perfluorinated compounds with different functional groups and varying chain length

Insights into the enzymatic degradation of DNA expedited by typical perfluoroalkyl acids

Perfluoroalkyl acids (PFAAs) are considered forever chemicals, gaining increasing attention for their hazardous impacts. However, the ecological effects of PFAAs remain unclear. Environmental DNA (eDNA), as the environmental gene pool, is often collected for evaluating the ecotoxicological effects of pollutants. In this study, we found that all PFAAs investigated, including perfluorohexanoic acid, perfluorooctanoic acid, perfluorononanoic acid, and perfluorooctane sulfonate, even at low concentrations (0.02 and 0.05 mg/L), expedited the enzymatic degradation of DNA in a nonlinear dose-effect relationship, with DNA degradation fragment sizes being lower than 1,000 bp and 200 bp after 15 and 30 min of degradation, respectively. This phenomenon was attributed to the binding interaction between PFAAs and AT bases in DNA via groove binding. van der Waals force (especially dispersion force) and hydrogen bonding are the main binding forces. DNA binding with PFAAs led to decreased base stacking and right-handed helicity, resulting in loose DNA structure exposing more digestion sites for degrading enzymes, and accelerating the enzymatic degradation of DNA. The global ecological risk evaluation results indicated that PFAA contamination could cause medium and high molecular ecological risk in 497 samples from 11 contamination-hot countries (such as the USA, Canada, and China). The findings of this study show new insights into the influence of PFAAs on the environmental fates of biomacromolecules and reveal the hidden molecular ecological effects of PFAAs in the environment.

Associations between PFAS concentrations and the oxidative status in a free-living songbird (Parus major) near a fluorochemical facility

For the past 7 decades, PFAS have been used in many different products and applications, which has led to a widespread contamination of these compounds. Nevertheless at present, little is known about the effects of these compounds on avian wildlife. Therefore, this study investigated associations between PFAS concentrations in the plasma and the oxidative status (i.e. non-enzymatic antioxidants and biomarkers of oxidative stress) in great tits at two sites near a fluorochemical manufacturing facility. Different PFAS were detected in the blood plasma with a mean ΣPFAS of 16062 pg/μL at the site closest to the facility. The PFAS profile in the plasma consisted mainly of PFOS, PFOA, PFDA and PFDoDA, where concentrations were higher for these compounds at the site closest to the plant. Our results show a clear link between PFAS and the antioxidant status of the birds; total antioxidant capacity and peroxidase activity were higher near the plant site, while the glutaredoxin activity was higher further away. Additionally, positive associations were found between PFDoDA and glutathione-S-transferase activity, between PFOS and glutathione-S-transferase activity, between PFDA and peroxidase activity, and between PFOS and peroxidase activity. Lastly, a negative association was found between plasma PFDA concentrations and the total polyphenol content. Interestingly, malondialdehyde levels did not differ between sites, suggesting lipid peroxidation was not affected. Although our results suggest that great tits with elevated PFAS concentrations did not suffer oxidative damage, the antioxidant defence responses were significantly triggered by PFAS exposure. This implies that the great tits have managed to defend themselves against the possible oxidative damage coming from PFAS contamination, although the upregulated antioxidant defences may have fitness costs. Further, experiments are needed to investigate the specific mechanisms by which PFAS induce oxidative stress in avian species.

Microbial biotransformation mechanisms of PFPiAs in soil unveiled by metagenomic analysis

As alternatives of long-chain PFASs (Poly- and perfluoroalkyl substances), perfluoroalkyl phosphinic acids (PFPiAs) are increasingly observed in the environment, but their environmental behaviors have not been well understood. Here, the microbial biotransformation of C6/C6 and C8/C8 PFPiA in two soils (Soil N and Y) was investigated. After 252 d and 330 d of incubation with PFPiAs in Soil N and Y respectively, the levels of PFPiAs decreased distinctly, accompanied by the increasing perfluorohexaphosphonic acid (PFHxPA) or perfluorooctanophosphonic acid (PFOPA) formation, magnifying PFPiAs were susceptible to C-P cleavage, which was also confirmed by the density functional theory calculations. The half-lives of the PFPiAs were longer than one year, while generally shorter in Soil N than in Soil Y and that of C6/C6 was shorter than C8/C8 PFPiA (392 d and 746 d in Soil N, and 603 and 1155 d in Soil Y, respectively). Metagenomic sequencing analysis revealed that Proteobacteria as the primary host of the potential functional genes related to CP bond cleavage might be the crucial phyla contributing to the biotransformation of PFPiAs. Meanwhile, the more intensive interactions between the microbes in Soil N consistently contribute to its greater capacity for transforming PFPiAs.

Phytoremediation prospects of per- and polyfluoroalkyl substances: A review

Extensive use of per- and polyfluoroalkyl substances (PFASs) in various industrial activities and daily-life products has made them ubiquitous contaminants in soil and water. PFAS-contaminated soil acts as a long-term source of pollution to the adjacent surface water bodies, groundwater, soil microorganisms, and soil invertebrates. While several remediation strategies exist to eliminate PFASs from the soil, strong ionic interactions between charged groups on PFAS with soil constituents rendered these PFAS remediation technologies ineffective. Pilot and field-scale data from recent studies have shown a great potential of PFAS to bio-accumulate and distribute within plant compartments suggesting that phytoremediation could be a potential remediation technology to clean up PFAS contaminated soils. Even though several studies have been performed on the uptake and translocation of PFAS by different plant species, most of these studies are limited to agricultural crops and fruit species. In this review, the role of both aquatic and terrestrial plants in the phytoremediation of PFAS was discussed highlighting different mechanisms underlying the uptake of PFASs in the soil-plant and water-plant systems. This review further summarized a wide range of factors that influence the bioaccumulation and translocation of PFASs within plant compartments including both structural properties of PFASs and physiological properties of plant species. Even though phytoremediation appears to be a promising remediation technique, some limitations that reduced the feasibility of phytoremediation in the practical application have been emphasized in previous studies. Additional research directions are suggested, including advanced genetic engineering techniques and endophyte-assisted phytoremediation to upgrade the phytoremediation potential of plants for the successful removal of PFASs.

Effects of perfluorooctanoic acid (PFOA) on activated sludge microbial community under aerobic and anaerobic conditions

Per- and polyfluoroalkyl substances (PFASs) have received increasing attention due to their widespread presence in diverse environments including wastewater treatment plants (WWTPs) and their potential adverse health effects. Perfluorooctanoic acid (PFOA) is one of the most detected forms of PFASs in WWTPs. However, there is still a paucity of knowledge about the effect of PFASs on microorganisms of the key component of WWTP, activated sludge. In this study, lab-scale microcosm experiments were established to evaluate the influences of PFOA on activated sludge microbes under aerobic and anaerobic conditions. The diversity, structure, and microbe-microbe interaction of microbial community were determined by 16S rRNA gene amplicon sequencing and co-occurrence network analysis. After 90 days of exposure to PFOA, activated sludge microbial richness decreased under both aerobic and anaerobic conditions. Specifically, under aerobic condition, Rhodopseudomonas (mean relative abundance 3.6%), Flavobacterium (2.4%), and Ignavibacterium (6.6%) were enriched in PFOA-spiked activated sludge compared with that in the unspiked sludge (2.6%, 0.1%, and 1.9%, respectively). By contrast, after 90 days of exposure to PFOA, Eubacterium (2.1%), Hyphomicrobium (1.8%), and Methyloversatilis (1.2%) were enriched under anaerobic condition, and more abundant than that in the control sludge (0.4%, 1.5%, and 0.6%, respectively). These genera were the potential PFOA-resistant members. In addition, Azospirillum and Sporomusa were the most connected taxa in PFOA-aerobic and PFOA-anaerobic networks, respectively. Prediction of the functional gene showed that PFOA inhibited some gene expression of sludge microbes, such as transcription, amino acid transport and metabolism, and energy production and conversion. In summary, continued exposure to PFOA induced substantial shifts of the sludge bacterial diversity and composition under both aerobic and anaerobic conditions.

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.

Effects of Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonic Acid (PFOS) on Soil Microbial Community

The extensive application of perfluoroalkyl and polyfluoroalkyl substances (PFASs) causes their frequent detection in various environments. In this work, two typical PFASs, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), are selected to investigate their effects on soil microorganisms. Microbial community structure and microbe-microbe relationships were investigated by high-throughput sequencing and co-occurrence network analysis. Under 90 days of exposure, the alpha-diversity of soil microbial communities was increased with the PFOS treatment, followed by the PFOA treatment. The exposure of PFASs substantially changed the compositions of soil microbial communities, leading to the enrichment of more PFASs-tolerant bacteria, such as Proteobacteria, Burkholderiales, and Rhodocyclales. Comparative co-occurrence networks were constructed to investigate the microbe-microbe interactions under different PFASs treatments. The majority of nodes in the PFOA and PFOS networks were associated with the genus Azospirillum and Hydrogenophaga, respectively. The LEfSe analysis further identified a set of biomarkers in the soil microbial communities, such as Azospirillum, Methyloversatilis, Hydrogenophaga, Pseudoxanthomonas, and Fusibacter. The relative abundances of these biomarkers were also changed by different PFASs treatments. Functional gene prediction suggested that the microbial metabolism processes, such as nucleotide transport and metabolism, cell motility, carbohydrate transport and metabolism, energy production and conversion, and secondary metabolites biosynthesis transport and catabolism, might be inhibited under PFAS exposure, which may further affect soil ecological services.

In Vitro Antibacterial Mechanism of High-Voltage Electrostatic Field against Acinetobacter johnsonii

This study aimed to investigate the antibacterial properties and mechanisms of a high-voltage static electric field (HVEF) in Acinetobacter johnsonii, which were assessed from the perspective of biochemical properties and stress-related genes. The time/voltage-kill assays and growth curves showed that an HVEF decreased the number of bacteria and OD600 values. In addition, HVEF treatment caused the leakage of cell contents (nucleic acids and proteins), increased the electrical conductivity and amounts of reactive oxygen substances (ROS) (16.88 fold), and decreased the activity of Na+ K+-ATPase in A. johnsonii. Moreover, the changes in the expression levels of genes involved in oxidative stress and DNA damage in the treated A. johnsonii cells suggested that HVEF treatment could induce oxidative stress and DNA sub-damage. This study will provide useful information for the development and application of an HVEF in food safety.

Response of soil characteristics to biochar and Fe-Mn oxide-modified biochar application in phthalate-contaminated fluvo-aquic soils

Biochar (BC) derived from agricultural biomass is effective at immobilizing phthalate in the agricultural soil environment. In this study, we assessed the effects of 0.5%, 1%, and 2% BC and Fe-Mn oxide-modified biochar (FMBC) addition on dibutyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP) residues and biochemical characteristics in the rhizosphere soil of mature wheat polluted with DBP and DEHP using a pot experiment. Scanning electron microscopy showed that the surfaces and pores of BC and FMBC adhered soil mineral particles after remediation. Therefore, DBP and DEHP residues were increased in BC- and FMBC-treated soils. Illumina HiSeq sequencing showed that, compared with the control, BC and FMBC addition significantly enhanced the relative abundance of Firmicutes and reduced Proteobacteria. The abundance of Sphenodons and Pseudomonas, which degrade phthalates, tended to be higher in FMBC-amended soils than in BC-amended and control soils. This result may be related to an increase in available nutrients and organic matter following BC and FMBC application. Subsequently, the changes in soil bacterial abundance and community structure induced an increase in polyphenol oxidase, β-glucosidase, neutral phosphatase, and protease activity in BC and FMBC remediation. In comparison with the BC treatment, FMBC addition had a significantly positive effect on enzyme activity, and the microbial structure and was therefore more effective at immobilizing DBP and DEHP in the soil. Thus, our findings strongly suggest that FMBC is a reliable remediation material for phthalate-contaminated soil.

First Evidence of In Vitro Effects of C6O4-A Substitute of PFOA-On Haemocytes of the Clam Ruditapes philippinarum

Alternative chemicals to per- and poly-fluoroalkyl substances have recently been introduced in various industrial processes. C6O4 (difluoro{[2,2,4,5-tetrafluoro-5-(trifluoromethoxy)-1,3-dioxolan-4-yl]oxy}acetic acid) is a new surfactant and emulsifier used as a replacement for perfluorooctanoic acid (PFOA). From an ecotoxicological point of view, in vitro assays are useful tools for assessing the negative effects and understanding the mechanisms of action of chemicals at the cellular level. Here, we present the results of an in vitro study in which the effects of C6O4 were evaluated-for the first time-on haemocytes of the clam Ruditapes philippinarum. Cells were exposed to three concentrations of C6O4 (0.05, 0.5, 5 μg/mL) and the effects on haemocyte viability, haemocyte morphology, differential haemocyte count, lysosomal membrane stability, superoxide anion production, acid phosphatase, and β-glucuronidase activities, as well as on the percentage of micronuclei and chromosomal aberrations were evaluated. The results demonstrated that C6O4 significantly affected haemocyte morphology, lysosomal membrane stability, hydrolytic enzyme activity, and superoxide anion production, and promoted chromosomal aberrations. To the best of our knowledge, this is the first study revealing the in vitro effects of C6O4, a substitute for PFOA, on haemocytes from a bivalve species.

Fate and transport of per- and polyfluoroalkyl substances (PFASs) in the vadose zone

Per- and polyfluoroalkyl substances (PFASs) are a heterogeneous group of persistent organic pollutants that have been detected in various environmental compartments around the globe. Emerging research has revealed the preferential accumulation of PFASs in shallow soil horizons, particularly at sites impacted by firefighting activities, agricultural applications, and atmospheric deposition. Once in the vadose zone, PFASs can sorb to soil, accumulate at interfaces, become volatilized, be taken up in biota, or leach to the underlying aquifer. At the same time, polyfluorinated precursor species may transform into highly recalcitrant perfluoroalkyl acids, changing their chemical identity and thus transport behavior along the way. In this review, we critically discuss the current state of the knowledge and aim to interconnect the complex processes that control the fate and transport of PFASs in the vadose zone. Furthermore, we identify key challenges and future research needs. Consequently, this review may serve as an interdisciplinary guide for the risk assessment and management of PFAS-contaminated sites.

Exposure to perfluorooctanesulfonate (PFOS) but not perflurorooctanoic acid (PFOA) at ppb concentration induces chronic toxicity in Daphnia carinata

Widespread environmental contamination of per- and polyfluoroalkyl substances (PFAS) is well established. Nevertheless, few studies have reported on the aquatic toxicity of PFAS, especially in indicator species such as Daphnia. In this study, the toxicity of two major PFAS, namely perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS), was investigated on water flea (Daphnia carinata) using a battery of comprehensive toxicity tests, including a 48 h acute and a 21-day chronic assays. The survival, growth, and reproduction of D. carinata were monitored over a 21-day life cycle. PFOS exhibited higher toxicity than PFOA. The 48 h LC₅₀ values (confidence interval) based on acute toxicity for PFOA and PFOS were 78.2 (54.9-105) mg L^-1 and 8.8 (6.4-11.6) mg L^-1, respectively. Chronic exposure to PFOS for 21 days displayed mortality and reproductive defects in D. carinata at a concentration as low as 0.001 mg L^-1. Genotoxicity assessment using comet assay revealed that exposure for 96 h to PFOS at 1 and 10.0 mg L^-1 significantly damaged the organism's genetic makeup. The results of this study have great implications for risk assessment of PFOS and PFOA in aquatic ecosystems, given the potential of PFOS to pose a risk to Daphnia even at lower concentrations (1 μg L^-1).

Influences of hexafluoropropylene oxide (HFPO) homologues on soil microbial communities

Hexafluoropropylene oxide (HFPO) homologues, as emerging perfluoroalkyl substances (PFASs) to replace legacy PFASs, have wide applications in the organofluorine industry and have been detected in the global environment. However, it is still unclear what effect HFPO homologues will exert on microbial abundance, community structure and function. The objective of this study was to assess potential impacts of HFPO homologue acids on archaea, bacteria, and ammonia-oxidizing archaea (AOA) and bacteria (AOB) in the soil environment. Grassland soil microcosms were supplemented with low (0.1 mg/kg) or high (10 mg/kg) dosages of dimer, trimer and tetramer acids of HFPO (HFPO-DA, HFPO-TA, and HFPO-TeA), respectively. The amendment of HFPO homologues acids initially decreased the abundance of archaea and bacteria but increased them in the later period. The addition of HFPO homologues acids raised AOA abundance but restrained AOB growth during the whole incubation. AOA and AOB community structures showed considerable variations. Potential nitrifying rate (PNR) showed an increase in the initial period followed by a decline in the later period. HFPO-DA had a lasting and suppressive effect on AOB and PNR even at a nearly environmental level. Overall, HFPO homologues with different carbon chain lengths had different impacts on soil microbial community and ammonia oxidation.

Emerging perfluoroalkyl substance impacts soil microbial community and ammonia oxidation

Legacy perfluoroalkyl and poly-fluoroalkyl substances (PFASs) are gradually phased out because of their persistence, bioaccumulation, toxicity, long-distance transport and ubiquity in the environment. Alternatively, emerging PFASs are manufactured and released into the environment. It is accepted that PFASs can impact microbiota, although it is still unclear whether emerging PFASs are toxic towards soil microbiota. However, it could be assumed that OBS could impact soil microorganisms because it had similar chemical properties (toxicity and persistence) as legacy PFASs. The present study aimed to explore the influences of an emerging PFAS, namely sodium p-perfluorous nonenoxybenzene sulfonate (OBS), on archaeal, bacterial, and ammonia-oxidizing archaea (AOA) and bacteria (AOB) communities and ammonia oxidation. Grassland soil was amended with OBS at different dosages (0, 1, 10 and 100 mg/kg). After OBS amendment, tolerant microorganisms (e.g., archaea and AOA) were promoted, while susceptive microorganisms (e.g., bacteria and AOB) were inhibited. OBS amendment greatly changed microbial structure. Potential nitrifying activity was inhibited by OBS in a dose-dependent manner during the whole incubation. Furthermore, AOB might play a more important role in ammonia oxidation than AOA. Overall, OBS influenced ammonia oxidation by regulating the activity, abundance and structure of ammonia-oxidizing microorganisms, and could also exert influences on total bacterial and archaeal populations.

Toxicity of perfluorinated compounds to soil microbial activity: Effect of carbon chain length, functional group and soil properties

Perfluorinated compounds (PFCs) have been detected at various concentrations in different environment compartments due to their widespread usage. Nowadays, soil environment has become a prominent sink of PFCs from surface runoff and penetration, but few researches have been conducted in the toxicity of PFCs to soil microorganisms. To address the issue, microcalorimetry was applied to investigate the toxicity of six PFCs with different carbon chain length (4, 8, and 10) and functional group (carboxylic and sulfonic) to microbial activities in three Chinese soils varying widely in soil properties. Adsorption of PFCs by soil matrix was a key factor in controlling the toxicity of PFCs to soil microorganisms. The differences of carbon chain length and functional groups of PFCs have different impacts on soil microbial activity while affecting adsorption progress. Particularly, the sulfonic PFCs expressed higher toxicity than the carboxylic. It is also identified that the longer the chain length, the greater the toxicity of PFCs. Soil pH was another relevant factor of soil adsorption, and with the increase of pH, adsorption capability increased. Soil available P, N and K were essential nutrients in soil, and suggested to improve microbial activity under PFCs stress.

Toxicity of perfluorooctane sulfonate on Phanerochaete chrysosporium: Growth, pollutant degradation and transcriptomics

As a persistent organic pollutant listed in the Stockholm Convention, perfluorooctane sulfonate (PFOS) is extremely refractory to degradation under ambient conditions. Its potential ecotoxicity has aroused great concerns and research interests. However, little is known about the toxicity of PFOS on fungus. In this study, the white rot fungus Phanerochaete chrysosporium (P. chrysosporium) was adopted to assess the toxicity of PFOS in liquid culture. The addition of 100 mg/L PFOS potassium salt significantly decreased the fungal biomass by up to 76.4% comparing with un-amended control during the incubation period. The hyphostroma of P. chrysosporium was wizened and its cell membrane was thickened, while its vesicle structure was increased, based on the observation with scanning electron microscope (SEM) and transmission electron microscope (TEM). Nevertheless, the PFOS dosage of below 100 mg/L did not show a considerable damage to the growth of P. chrysosporium. The degradation of malachite green (MG) and 2,4-dichlorophenol (2,4-DCP) by P. chrysosporium was negatively affected by PFOS. At the initial dosage of 100 mg/L PFOS, the decolorization efficiency of MG and the degradation efficiency of 2,4-DCP decreased by 37% and 20%, respectively. This might be attributed to the inhibition of PFOS on MnP and LiP activities. The activities of MnP and LiP decreased by 20.6% and 43.4%, respectively. At a high dosage PFOS (100 mg/L), P. chrysosporium could show a high adsorption of MG but lose its pollutant degradation ability. Transcriptome analysis indicated that PFOS contamination could lead to the change of gene expression in the studied white rot fungus, and the genes regulating membrane structure, cell redox process, and cell transport, synthesis and metabolism were impacted. Membrane damage and oxidative damage were the two main mechanisms of PFOS' toxicity to P. chrysosporium.

Evaluation of Single and Joint Toxicity of Perfluorinated Carboxylic Acids and Copper to Metal-Resistant Arthrobacter Strains

Perfluorocarboxylic acid compounds (PFCAs) and copper have been regarded as ubiquitous environmental contaminants in aquatic ecosystems worldwide. However, data on their possible joint toxic effects on microorganisms are still lacking. To study the combined effects of four PFCAs with different carbon chain lengths and copper, a series of experiments were conducted to explore the acute toxicity of these PFCAs in the absence and presence of copper on a metal-resistant Arthrobacter strain GQ-9 by microcalorimetry. The thermokinetic parameters, including growth rate constant (k), inhibitory ratio (I), and half inhibitory concentration (IC₅₀), were calculated and compared using the data obtained from the power-time curves. Our work revealed that GQ-9 is more resistant to perfluorooctanoic acid (PFOA) than Escherichia coli. The single and joint toxicity of PFCAs with copper are dose- and carbon chain length-dependent. The longer the carbon chain length of PFCAs, the higher the toxicity. In addition, PFCAs interacted synergistically with copper. This work could provide useful information for the risk assessment of co-exposure to perfluorinated compounds and heavy metals in natural environments.

Higher plasma oxidative damage and lower plasma antioxidant defences in an Arctic seabird exposed to longer perfluoroalkyl acids

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) may cause detrimental effects on physiological function and reproduction of Arctic animals. However, there is a paucity of information on the link between PFASs and oxidative stress, which can have potential detrimental effects on key fitness traits, such as cellular homeostasis or reproduction. We have examined the correlations between multiple blood-based markers of oxidative status and several perfluoroalkyl acids (i.e., with 8 or more carbons) in male Arctic black-legged kittiwakes (Rissa tridactyla) during the pre-laying period. Higher protein oxidative damage was found in those birds having higher concentrations of perfluorododecanoic acid (PFDoA), perfluorotridecanoic acid (PFTriA) and perfluorotetradecanoic acid (PFTeA). Lower plasmatic non-enzymatic micro-molecular antioxidants were found in those birds having higher concentrations of perfluoroundecanoic acid (PFUnA), PFDoA and PFTeA. Effect size estimates showed that the significant correlations between PFASs and oxidative status markers were intermediate to strong. The non-enzymatic antioxidant capacity (including antioxidants of protein origin) was significantly lower in those birds having higher plasma concentration of linear perfluorooctanesulfonic acid (PFOSlin). In contrast, the activity of the antioxidant enzyme glutathione peroxidase in erythrocytes was not associated with any PFAS compounds. Our results suggest that increased oxidative stress might be one consequence of long-chain PFAS exposure. Experimental work will be needed to demonstrate whether PFASs cause toxic effects on free-living vertebrates through increased oxidative stress.

Perfluoroalkyl substances (PFASs) influence the structure and function of soil bacterial community: Greenhouse experiment

Environmental threats posed by perfluoroalkyl substances (PFASs) have received a great deal of attention in recent years. However, little is known about the influences of PFASs on microorganisms in the environment. In this study, several typical PFASs were selected, and their effects on bacterial communities were measured by Illumina MiSeq sequencing. The richness (Chao1 estimator), diversity (Shannon index) and community structure of the bacterial community changed after the exposure to PFASs (1 μg PFOS/g soil). The amendment of PFASs increased bacterial richness but decreased bacterial diversity, because PFASs stimulated the growth of some bacteria (e.g., Firmicutes, Acidobacteria and Actinobacteria) but inhibited other bacteria such as Latescibacteria and Chloroflexi. When low concentrations (0.01 μg/g and 0.1 μg/g) of perfluorooctane sulphonate (PFOS) were added, the promotion action was stronger than the toxic effect on soil bacteria. Conversely, the toxicity was stronger than the promotion action under high concentrations of PFOS (10 μg PFOS/g soil). PFASs pollution obviously disrupted the normal function of soil microorganisms. PFBS and PFHxS could activate sucrase and urease, while PFOS and 6:2FTS could inhibit these enzymes' activities. The reduction of soil functional genes also confirmed that PFOS, 6:2FTS and 6:2F53B inhibited soil enzyme activity and further destroyed the cellular structure, immune system and gene expression of soil bacteria. The effects of PFASs with long carbon chains on soil bacterial community and function was more obvious than that of short-chain PFASs.

Immunotoxicity in green mussels under perfluoroalkyl substance (PFAS) exposure: Reversible response and response model development

The immunotoxicity of 4 commonly detected perfluoroalkyl substances (PFASs), namely, perfluorooctanesulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorodecanoic acid (PFDA) was investigated by measuring biomarkers of the immune profile of green mussels, Perna viridis. The biomarkers included neutral red retention, phagocytosis, and spontaneous cytotoxicity, all of which were tested on mussel hemocytes. Hemocytes are an important component of the invertebrate immune system. We found that exposure to PFASs could lead to reduced hemocyte cell viability and suppress immune function by up to 50% of normal performance within the experimental exposure range. The results indicate that PFASs have an immunotoxic potential and thus could pose severe health risks to aquatic organisms. The reported immunotoxicity is likely to result from the compounds' direct and indirect interactions with the hemocyte membrane, and therefore likely to affect the functionality of these cells. The immunotoxic response was found to be related to the organism's burden of PFASs, and was reversible when the compounds were removed from the test organisms. Based on this relationship, models using an organism's PFAS concentration and bioaccumulation factor (BAF) as the independent variables were established to quantify PFAS-induced immunotoxicity. The models help us to gain a better understanding of the toxic mechanism of PFASs, and provide a tool to evaluate adverse effects for the whole group of compounds with one mathematical equation. Environ Toxicol Chem 2018;37:1138-1145. © 2018 SETAC.

Toxicity of perfluorooctane sulfonate and perfluorooctanoic acid to Escherichia coli: Membrane disruption, oxidative stress, and DNA damage induced cell inactivation and/or death

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are two widely used polyfluorinated compounds (PFCs) and are persistent in the environment. This study for the first time systematically investigated their toxicities and the underlying mechanisms to Escherichia coli. Much higher toxicity was observed for PFOA than PFOS, with the 3 h half growth inhibition concentrations (IC50) determined to be 10.6 ± 1.0 and 374 ± 3 mg L(-1), respectively, while the bacterial accumulation of PFOS was much greater than that of PFOA. The PFC exposures disrupted cell membranes as evidenced by the dose-dependent variations of cell structures (by transmission electron microscopy observations), surface properties (electronegativity, hydrophobicity, and membrane fluidity), and membrane compositions (by gas chromatogram and Fourier transform infrared spectroscopy analyses). The increases in the contents of intracellular reactive oxygen species (ROS) and malondialdehyde and the activity of superoxide dismutase indicated the increment of oxidative stress induced by the PFCs in the bacterial cells. The fact that the cell growth inhibition was mitigated by the addition of ROS scavenger (N-acetyl cysteine) further evidenced the important role of oxidative damage in the toxicities of PFOS and PFOA. Eighteen genes involved in cell division, membrane instability, oxidative stress, and DNA damage of the exposed cells were up or down expressed, indicating the DNA damage by the PFCs. The toxicities of PFOS and PFOA to E. coli were therefore ascribed to the membrane disruption, oxidative stress, and DNA damage induced cell inactivation and/or death. The difference in the bactericidal effect between PFOS and PFOA was supposed to be related to their different dominating toxicity mechanisms, i.e., membrane disruption and oxidative damage, respectively. The outcomes will shed new light on the assessment of ecological effects of PFCs.

Effect of PFOA/PFOS pre-exposure on the toxicity of the herbicides 2,4-D, Atrazine, Diuron and Paraquat to a model aquatic photosynthetic microorganism

Pre-exposure to the perfluorinated compounds (PFCs) perfluorooctano sulphonate (PFOS) or perfluorooctanoic acid (PFOA) on the toxicity of four herbicides of different types and modes of action towards the self-luminescent recombinant cyanobacterium Anabaena CPB4337 was evaluated. The rationale of the approach is that both PFOS and PFOA as surfactants are known to modify cell membrane properties and pre-exposure to them might alter herbicide toxicity towards the cyanobacterium. Anabaena CPB4337 was pre-exposed during 72h to PFOS or PFOA at a concentration below their no observed effect concentration (NOEC). After pre-exposure, cells were exposed to increasing concentrations of 2,4-D Atrazine, Diuron and Paraquat and the toxicity was compared to that of non-pre-exposed ones. The data clearly showed that PFCs pre-treatment significantly altered the toxicity of the tested herbicides. However the effects resulting from PFOA and PFOS pre-exposure were not homogeneous for all the herbicides. In general PFOA pre-exposure resulted in increased herbicide toxicity except for atrazine, while PFOS pre-exposure resulted in increased toxicity for paraquat and diuron, and reduced toxicity for atrazine with no significant effect on 2,4-D toxicity. The strongest modifying effect was found for paraquat whose toxicity doubled with PFOA pre-exposure. Further analysis of membrane properties by flow cytometry revealed that both PFOA and PFOS were able to modify membrane integrity and membrane potential of Anabaena CPB4337 at the concentrations used in the pre-exposure experiments. These results reveal relevant indirect effects of PFCs pollution with eco-toxicological implications.

Identification of Novel Polyfluorinated Ether Sulfonates as PFOS Alternatives in Municipal Sewage Sludge in China

A 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFAES) with the trade name F-53B, is an alternative to perfluorooctanesulfonate (PFOS) in electroplating industry that is uniquely used in China. It was developed as a mist suppressant initially in the 1970s, but the environmental behaviors and potential adverse effects of the 6:2 Cl-PFAES have only recently been investigated. In this work, the occurrence and distribution of perfluoroalkyl sulfonate (PFSA), fluorotelomer sulfonate (FTSA), and PFAES analogues were investigated in municipal sewage sludge samples collected around China. Perfluorobutane, perfluorohexane, perfluorooctane, and perfluorodecanesulfonates, 6:2 and 8:2 FTSAs, and the emerging 6:2 Cl-PFAES were detected. Moreover, 8:2 and 10:2 Cl-PFAESs were identified for the first time as new polyfluorinated contaminants using high resolution mass spectrometry. These fluorinated analytes were further quantified with the aid of commercial and laboratory-purified standards. PFOS was the predominant contaminant with a geometric mean (GM) value of 3.19 ng/g dry weight (d.w.), which was subsequently followed by 6:2 Cl-PFAES and 8:2 Cl-PFAES (GM: 2.15 and 0.50 ng/g d.w., respectively). Both 6:2 and 8:2 Cl-PFAES were positively detected as the major components in the F-53B commercial product, and discrete 6:2 Cl-PFAES/8:2 Cl-PFAES ratios in the product and sludge samples might suggest 8:2 Cl-PFAES had enhanced sorption behavior in the sludge due to the increase in hydrophobicity.

Evolutionary ecotoxicology of perfluoralkyl substances (PFASs) inferred from multigenerational exposure: a case study with Chironomus riparius (Diptera, Chironomidae)

A multigeneration toxicity test on Chironomus riparius was performed with the aim of investigating the evolutionary consequences of exposure to perfluoralkyl substances (perfluorooctane sulfonic acid, PFOS; perfluorooctanoic acid, PFOA; perfluorobutane sulfonate, PFBS). Six-hundred larvae were bred per treatment and per generation until emergence and egg deposition under a nominal concentration of 10μg/L of contaminants. Newborn larvae were used to start the next generation. Evolution of genetic variability was evaluated along a total of 10 consecutive generations based on 5 microsatellite loci. Analysis of life-history traits (survival, sex ratio and reproduction) was also carried out. Rapid genetic variability reduction was observed in all treatments, including controls, across generations due to the test conditions. Nevertheless, an increased mutation rate determined a stronger conservation of genetic variability in PFOS and, at minor extent, in PFBS exposed populations compared to controls. No significant effects were induced by exposure to PFOA. Direct mutagenicity or induced stress conditions may be at the base of increased mutation rate, indicating the potential risk of mutational load caused by exposure to PFOS and PFBS. The test provided the opportunity to evaluate the use of approximate Bayesian computation (ABC) and coalescent approaches in evolutionary ecotoxicology. A weak performance was evidenced for ABC, either in terms of bias or dispersion of effective population sizes and of estimates of mutation rate. On the contrary, coalescent simulations proved the sensitivity of traditional genetic endpoints (i.e. heterozygosity and number of alleles) to the alteration of mutation rate, but not to erosion of genetic effective size.

Oxidative toxicity of perfluorinated chemicals in green mussel and bioaccumulation factor dependent quantitative structure-activity relationship

Concerns regarding perfluorinated chemicals (PFCs) have risen in recent years because of their ubiquitous presence and high persistency. However, data on the environmental impacts of PFCs on marine organisms are very limited. Oxidative toxicity has been suggested to be one of the major toxic pathways for PFCs to induce adverse effects on organisms. To investigate PFC-induced oxidative stress and oxidative toxicity, a series of antioxidant enzyme activities and oxidative damage biomarkers were examined to assess the adverse effects of the following 4 commonly detected compounds: perfluoro-octanesulfonate, perfluoro-ocanoic acid, perfluorononanoic acid, and perfluorodecanoic acid, on green mussel (Perna viridis). Quantitative structure-activity relationship (QSAR) models were also established. The results showed that all the tested PFCs are able to induce antioxidant response and oxidative damage on green mussels in a dose-dependent manner. At low exposure levels (0 µg/L-100 µg/L), activation of antioxidant enzymes (catalase [CAT] and superoxide dismutase [SOD]) was observed, which is an adaptive response to the excessive reactive oxygen species induced by PFCs, while at high exposure levels (100 µg/L-10 000 µg/L), PFCs were found to inhibit some enzyme activity (glutathione S-transferase and SOD) where the organism's ability to respond in an adaptive manner was compromised. The oxidative stress under high PFC exposure concentration also led to lipid and DNA damage. PFC-induced oxidative toxicity was found to be correlated with the bioaccumulation potential of PFCs. Based on this relationship, QSAR models were established using the bioaccumulation factor (BAF) as the molecular descriptor for the first time. Compared with previous octanol-water partition coefficient-dependent QSAR models, the BAF-dependent QSAR model is more suitable for the impact assessment of PFCs and thus provides a more accurate description of the toxic behavior of these compounds.

Genotoxicity of perfluorinated chemicals (PFCs) to the green mussel (Perna viridis)

Concerns regarding perfluorinated chemicals (PFCs) have grown significantly in recent years. However, regulations and guidelines regarding the emission and treatment of PFCs are still missing in most parts of the world, mostly due to the lack of PFC toxicity data. In the current study, the genotoxic effects of four common PFCs, named perfluorooctanesulfonate (PFOS), perfluoroocanoic acid (PFOA), perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA) were investigated on marine mussels. The effects of exposure time and concentration on the toxic behavior of the compounds were also examined. Genotoxicity of PFCs was assessed in biomarker assays, showing that exposure to the target compounds could damage the organism's genetic material to varying extents, including DNA strand breaks and fragmentation, chromosomal breaks and apoptosis. The adverse effects increased with both exposure concentration and time and were related with the organism burden of PFCs. The integrated biomarker response analysis demonstrated that PFOS exhibited a higher genotoxicity than the other tested compounds. The EC50 values and confidence intervals based on integrative genotoxicity were 33 (29-37), 594 (341-1036), 195 (144-265) and 78 (73-84) μg/L for PFOS, PFOA, PFNA and PFDA respectively, classifying PFOS as a highly genotoxic compound. Although primary DNA damage was shown to be recoverable after exposure ceased, permanent genetic damage caused by elevated PFC concentrations was not restored. This is the first ecotoxicity study of PFCs that focuses on the genotoxic effects of the compounds, clearly indicating the genotoxicity of the tested PFCs and demonstrating that functional groups have a major impact on the compounds' genotoxic behavior.

Multi-biomarker responses in green mussels exposed to PFCs: effects at molecular, cellular, and physiological levels

Perfluorinated chemicals (PFCs) are extremely persistent and have been found extensively in the environment and wildlife. Oceans are the final sink for many persistent organic pollutants (POPs) including PFCs. However, to date, there has been a lack of studies that investigated the environmental consequences of PFCs on marine organisms. To fill in this gap, environmental toxicity of two dominant PFCs, perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA), was examined in a sentinel species, green mussel Perna viridis, using a series of biomarkers corresponding to different biological levels (molecular, cellular, and physiological). Correlations among these biomarkers were also investigated. The results showed that the tested compounds can induce a series adverse effect at different biological levels, including oxidative stress, DNA damage, membrane instability, suppressed filtration rate, and reduced body weight. Correlation analysis revealed that excess production of reactive oxygen species could be the major toxic pathway. An indirect mode of toxic action was also explored where adverse impacts could be secondary effects of PFC exposure. The joint analysis of biomarkers from multiple biological levels resulted in a comprehensive understanding of how PFC exposure can influence the health of organisms. The correlations of these biomarkers also provided a new perspective of the ecological consequences of PFCs.

Environmental toxicity of PFCs: an enhanced integrated biomarker assessment and structure-activity analysis

Perfluorinated chemicals (PFCs) are a group of compounds with varying carbon chains and functional groups. Currently, available toxicity studies of PFCs are limited mainly to dominant species. While many other PFCs are detected in the environment and biota, it is important to extend toxicity studies to different types of PFCs to better assess their environmental and ecological impacts. In the present study, the environmental toxicity of perfluorooctanesulfonate, perfluoroocanoic acid, perfluorononanoic acid, and perfluorodecanoic acid were evaluated in green mussel, Perna viridis, using a new and improved integrated biomarker approach, the enhanced integrated biomarker response (EIBR) system, with biomarkers from multiple biological levels. Structure-activity relationships were also examined based on the biomarker results. The results show that the 4 PFCs have distinct toxicity patterns and the integrative toxicity, in terms of the EIBR value, is governed by the fluorinated chain length. In addition to commonly recognized chain length and functional group effects, several structural factors are also involved in the toxic actions of PFCs, including hydrophobicity and molecular size, and so on. By integrating biomarkers from multiple biological levels with weight-of-evidence, the proposed EIBR provides a new perspective and an ecologically relevant assessment of the environmental toxicity of the pollutants. The results of EIBR and structure-activity analysis are also useful to predict toxic behaviors of other PFCs in the group and facilitate the decision-making process.

Perfluorinated sulfonate and carboxylate compounds in eggs of seabirds breeding in the Canadian Arctic: temporal trends (1975-2011) and interspecies comparison

Perfluorinated sulfonates (PFSAs) and perfluorinated carboxylates (PFCAs), as well as selected precursor compounds, were measured in eggs of thick-billed murres (Uria lomvia) and northern fulmars (Fulmarus glacialis) from Prince Leopold Island in the Canadian Arctic between 1975 and 2011 as well as in eggs of three additional species (black guillemot Cepphus grylle, black-legged kittiwake Rissa tridactyla, glaucous gull Larus hyperboreus) sampled in 2008. ΣPFCA concentrations increased significantly from 1975 to 2011 in the murre and fulmar eggs at an average annual rate of 0.56 and 0.91 ng g(-1) ww, respectively, whereas perfluorooctane sulfonate (PFOS) concentrations did not change significantly. The interspecies comparison of eggs sampled in 2008 found that black guillemots had the highest PFOS and lowest ΣPFCA levels, and northern fulmars had the highest ΣPFCA levels. PFUnA (C(11)) and PFTrA (C(13)) were the predominant PFCAs measured in eggs of all five species except for the black guillemot where PFDA (C(10)) contributed almost equally with PFTrA (C(13)) to the PFCA profile. Based on published toxicity thresholds, levels of neither perfluorooctanoate (PFOA) nor PFOS in seabird eggs from the Canadian Arctic are of toxicological concern. These are the first interspecies comparisons for PFASs in seabirds from the Canadian Arctic.

Toxicological interactions of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) with selected pollutants

The combined toxicity of the perfluorinated surfactants perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and several pollutants (Hg(2+), Cd(2+), 2,4-D, propylparaben, mitomycin C and furazolidone) has been examined with a bioluminescent cyanobacterial toxicity test. Hg(2+), Cd(2+), mitomycin C and furazolidone could be included in the "Acute aquatic hazard" category established in the Regulation (EC) No 1272/2008 being "very toxic to aquatic life". Toxicological interactions of PFOA, PFOS with these pollutants in binary, ternary and multicomponent mixtures were studied using the combination-index method. PFOA and PFOS showed an antagonistic interaction at the whole range of effect levels, this may explain in part the finding that PFOA and PFOS interacted in an inverse way with the organic pollutants; the relative hydrophobicity of the tested compounds would also explain this interaction pattern. The interaction of both PFOS and PFOA with heavy metals was mostly antagonistic, decreasing metal toxicity. With increasing complexity of the mixtures, the CI method predicted synergism at low to very low levels of effect; pollutant combinations at their mixture NOECs were tested and confirmed the predicted synergism.

Toxicity ranking and toxic mode of action evaluation of commonly used agricultural adjuvants on the basis of bacterial gene expression profiles

The omnipresent group of pesticide adjuvants are often referred to as “inert” ingredients, a rather misleading term since consumers associate this term with “safe”. The upcoming new EU regulation concerning the introduction of plant protection products on the market (EC1107/2009) includes for the first time the demand for information on the possible negative effects of not only the active ingredients but also the used adjuvants. This new regulation requires basic toxicological information that allows decisions on the use/ban or preference of use of available adjuvants. In this study we obtained toxicological relevant information through a multiple endpoint reporter assay for a broad selection of commonly used adjuvants including several solvents (e.g. isophorone) and non-ionic surfactants (e.g. ethoxylated alcohols). The used assay allows the toxicity screening in a mechanistic way, with direct measurement of specific toxicological responses (e.g. oxidative stress, DNA damage, membrane damage and general cell lesions). The results show that the selected solvents are less toxic than the surfactants, suggesting that solvents may have a preference of use, but further research on more compounds is needed to confirm this observation. The gene expression profiles of the selected surfactants reveal that a phenol (ethoxylated tristyrylphenol) and an organosilicone surfactant (ethoxylated trisiloxane) show little or no inductions at EC₂₀ concentrations, making them preferred surfactants for use in different applications. The organosilicone surfactant shows little or no toxicity and good adjuvant properties. However, this study also illustrates possible genotoxicity (induction of the bacterial SOS response) for several surfactants (POEA, AE, tri-EO, EO FA and EO NP) and one solvent (gamma-butyrolactone). Although the number of compounds that were evaluated is rather limited (13), the results show that the used reporter assay is a promising tool to rank commonly used agricultural adjuvants based on toxicity and toxic mode of action data.

Bacterial gene profiling assay applied as an alternative method for mode of action classification: pilot study using chlorinated anilines

Polar narcotic structural analogues (e.g., chlorinated anilines with a differing degree of chlorosubstitution, such as aniline, 4-chloroaniline, 3,5-dichloroaniline, and 2,3,4-trichloroaniline) are assumed to induce their toxic effects via the same predominant mode of action (MOA; membrane damage) at equitoxic exposure concentrations. In this study, a bacterial gene profiling assay consisting of 14 general stress genes was used to test this hypothesis for these four compounds. Although we found a consistent induction of membrane damage, the response cascade and the extent of the response differed among the different chemical treatments. The higher chlorosubstituted anilines also triggered significantly more genes involved in other general stress MOA classes (oxidative stress and protein perturbation). These findings illustrate that, along with the commonly used physicochemistry-based MOA categorization methods, alternative tests such as the bacterial gene profiling assay can yield valuable biological information on the MOA of a certain chemical or group of chemicals that is crucial in high-quality environmental risk assessment. In a second phase, the experimental gene profiling data sets of the chlorinated anilines were analyzed and weighed against existing data on other polar and non polar narcotic compounds to obtain a broader comparison in which the predefined chemical MOAs (narcosis and polar narcosis) were contrasted with the biological MOAs (gene expression profiles). Although additional optimization of the assay is needed, our results show that the bacterial gene profiling assay opens new perspectives for biology-based chemical grouping, thereby further enabling targeted MOA-based risk assessment.

Selection of scFv phages specific for chloramphenicol acetyl transferase (CAT), as alternatives for antibodies in CAT detection assays

Reporter gene assays are commonly used in applied toxicology to measure the transcription of genes involved in toxic responses. In these reporter gene assays, transgenic cells are used, which contain a promoter-operator region of a gene of interest fused to a reporter gene. The transcription of the gene of interest can be measured by the detection of the reporter protein. Chloramphenicol acetyl transferase (CAT) is frequently used as a reporter protein in mammalian reporter gene assays. Although CAT can be measured by different detection systems, like enzymatic and immune assays, most of these tests are expensive, time-consuming and labor-intensive. The excellent characteristics of phages, like their high affinity and specificity, their fast, cheap and animal-friendly manufacturing process with low batch-to-batch variations and their stability, make them appropriate as alternatives for antibodies in detection assays. Therefore, in this study single-chain variable fragment (scFv) phages were selected with affinity for CAT. Several scFv phages were selected that showed affinity towards CAT in a screening ELISA. Surface plasmon resonance analyses showed that the tested scFv phages have an affinity for CAT with a dissociation constant (K(d)) around 1 µM. The selected scFv phages in this study could be used as capture elements in a highly sensitive sandwich ELISA to detect CAT concentration as low as 0.1 ng ml⁻¹ or 4 pM. This low detection limit demonstrates the potential of the scFv phages as an alternative for capturing antibodies in a highly sensitive detection test to measure CAT concentrations in reporter gene assays.