Chronic effects of PFOA and PFOS on sexual reproduction of freshwater rotifer Brachionus calyciflorus

Reproductive toxicity of PFOA, PFOS and their substitutes: A review based on epidemiological and toxicological evidence

Per- and polyfluoroalkyl substances (PFAS) have already drawn a lot of attention for their accumulation and reproductive toxicity in organisms. Perfluorooctanoic acid (PFOA) and perfluorooctanoic sulfonate (PFOS), two representative PFAS, are toxic to humans and animals. Due to their widespread use in environmental media with multiple toxicities, PFOA and PFOS have been banned in numerous countries, and many substitutes have been produced to meet market requirements. Unfortunately, most alternatives to PFOA and PFOS have proven to be cumulative and highly toxic. Of the reported multiple organ toxicities, reproductive toxicity deserves special attention. It has been confirmed through epidemiological studies that PFOS and PFOA are not only associated with reduced testosterone levels in humans, but also with an association with damage to the integrity of the blood testicular barrier. In addition, for women, PFOA and PFOS are correlated with abnormal sex hormone levels, and increase the risk of infertility and abnormal menstrual cycle. Nevertheless, there is controversial evidence on the epidemiological relationship that exists between PFOA and PFOS as well as sperm quality and reproductive hormones, while the evidence from animal studies is relatively consistent. Based on the published papers, the potential toxicity mechanisms for PFOA, PFOS and their substitutes were reviewed. For males, PFOA and PFOS may produce reproductive toxicity in the following five ways: (1) Apoptosis and autophagy in spermatogenic cells; (2) Apoptosis and differentiation disorders of Leydig cells; (3) Oxidative stress in sperm and disturbance of Ca2+ channels in sperm membrane; (4) Degradation of delicate intercellular junctions between Sertoli cells; (5) Activation of brain nuclei and shift of hypothalamic metabolome. For females, PFOA and PFOS may produce reproductive toxicity in the following five ways: (1) Damage to oocytes through oxidative stress; (2) Inhibition of corpus luteum function; (3) Inhibition of steroid hormone synthesis; (4) Damage to follicles by affecting gap junction intercellular communication (GJIC); (5) Inhibition of placental function. Besides, PFAS substitutes show similar reproductive toxicity with PFOA and PFOS, and are even more toxic to the placenta. Finally, based on the existing knowledge, future developments and direction of efforts in this field are suggested.

Poly- and Perfluoroalkyl Substances (PFAS): Do They Matter to Aquatic Ecosystems?

Poly- and perfluoroalkyl substances (PFASs) are a group of anthropogenic chemicals with an aliphatic fluorinated carbon chain. Due to their durability, bioaccumulation potential, and negative impacts on living organisms, these compounds have drawn lots of attention across the world. The negative impacts of PFASs on aquatic ecosystems are becoming a major concern due to their widespread use in increasing concentrations and constant leakage into the aquatic environment. Furthermore, by acting as agonists or antagonists, PFASs may alter the bioaccumulation and toxicity of certain substances. In many species, particularly aquatic organisms, PFASs can stay in the body and induce a variety of negative consequences, such as reproductive toxicity, oxidative stress, metabolic disruption, immunological toxicity, developmental toxicity, cellular damage and necrosis. PFAS bioaccumulation plays a significant role and has an impact on the composition of the intestinal microbiota, which is influenced by the kind of diet and is directly related to the host's well-being. PFASs also act as endocrine disruptor chemicals (EDCs) which can change the endocrine system and result in dysbiosis of gut microbes and other health repercussions. In silico investigation and analysis also shows that PFASs are incorporated into the maturing oocytes during vitellogenesis and are bound to vitellogenin and other yolk proteins. The present review reveals that aquatic species, especially fishes, are negatively affected by exposure to emerging PFASs. Additionally, the effects of PFAS pollution on aquatic ecosystems were investigated by evaluating a number of characteristics, including extracellular polymeric substances (EPSs) and chlorophyll content as well as the diversity of the microorganisms in the biofilms. Therefore, this review will provide crucial information on the possible adverse effects of PFASs on fish growth, reproduction, gut microbial dysbiosis, and its potential endocrine disruption. This information aims to help the researchers and academicians work and come up with possible remedial measures to protect aquatic ecosystems as future works need to be focus on techno-economic assessment, life cycle assessment, and multi criteria decision analysis systems that screen PFAS-containing samples. New innovative methods requires further development to reach detection at the permissible regulatory limits.

Tissue Bioconcentration Pattern and Biotransformation of Per-Fluorooctanoic Acid (PFOA) in Cyprinus carpio (European Carp)—An Extensive In Vivo Study

The perfluoroalkyl substances (PFAS) represent a persistent class of synthetic chemicals that spread in the environment as a result of industrialization. Due to their bioaccumulative and endocrine disruption implications, these chemicals can affect food quality and human health, respectively. In the present study, the bioconcentration and biotransformation of perfluorooctanoic acid (PFOA) in common carp (Cyprinus carpio) were evaluated in a biphasic system (exposure and depuration). Carp were continuously exposed, under laboratory conditions, to 10 (Experiment 1) and 100 (Experiment 2) µg/L PFOA for 14 weeks, followed by a wash out period of 3 weeks. Fish organs and tissues were collected at 8, 12, 14 weeks of exposure and at week 17, after the depuration period. The results obtained from the LC-MS/MS analysis showed the presence of PFOA in all studied organs. The highest values of PFOA were identified in the gallbladder (up to 2572 ng/g d.w.) in Experiment 1 and in the gallbladder (up to 18,640 ng/g d.w.) and kidneys (up to 13,581 ng/g d.w.) in Experiment 2. The average BCF varied between 13.4 and 158 L/Kg in Experiment 1 and between 5.97 and 80.3 L/Kg in Experiment 2. Four biotransformation products were identified and quantified in all organs, namely: PFBA, PFPeA, PFHxA, and PFHpA. PFBA was proven to be the dominant biotransformation product, with the highest values being determined after 8 weeks of exposure in the kidney, gallbladder, brain, liver, and gonads in both experiments. Because freshwater fish are an important food resource for the human diet, the present study showed the fishes’ capacity to accumulate perfluoroalkyl substances and their metabolites. The study revealed the necessity of monitoring and risk studies of new and modern synthetic chemicals in aquatic resources.

Toxicity of Per- and Polyfluoroalkyl Substances to Aquatic Invertebrates, Planktons, and Microorganisms

Per- and polyfluoroalkyl substances (PFASs), recognized worldwide as emerging pollutants, may pose a substantial threat to human health and our environment due to their stability, high concentrations, wide distribution, and easy accumulation. Ever since perfluorooctane sulfonate and perfluorooctanoic acid were recognized by the Stockholm Convention on Persistent Organic Pollutants, the public has become increasingly concerned about potential contamination and the environmental risks associated with PFASs. Ubiquitous PFAS contamination of drinking water, groundwater, surface water, and sediment has been detected, especially in areas with rapid industrial and economic development. Its accumulation in living organisms and foods has accentuated the importance of investigations into aquatic organisms at the bottom of the food chain, as the stability and integrity of the food web as well as the population quantity and structure of the aquatic ecosystem may be affected. This review provides a comprehensive summary of the toxic and toxicity-related effects of PFASs on aquatic plankton, aquatic invertebrates and microorganisms, the characteristics of different target aquatic organisms in toxicity investigations, and a feasibility evaluation of PFAS substitutes to provide valuable suggestions for further utilization and regulation of PFASs and their substitutes.

Monitoring and ecological risk assessment of contaminants in freshwater bodies by bioindicators in China: a proposed framework

Bioindicators can provide pollution information with longer temporal duration and larger spatial scale. It is an ideal strategy for long-term monitoring of bioaccumulative contaminants. Bioindicator monitoring has been widely used; however, there were seldom detailed studies about bioindicator methodology in literature. The present study proposed a bioindicator framework suitable for the local conditions of China, including selection of bioindicator species, evaluation of impact factors, and derivation of threshold values using per- and polyfluoroalkyl substances (PFASs) as an example. The criteria that proper bioindicator species should meet and the procedure how the bioindicator species is selected were proposed, under which crucian carp (Carassius auratus) was selected as the local bioindicator for studied PFASs. Several factors which may affect accumulation of contaminants in bioindicators were suggested to produce reliable and comparable results. Derivation method of bioindicator thresholds for ecological risk assessment of aquatic ecosystems was firstly developed. The long-term and short-term ecological thresholds of perfluorooctanesulfonate using crucian carp as bioindicator are 3.329 and 1.402 μg/g wet weight respectively. Using the long-term thresholds derived from chronic toxicity data and the accumulative concentrations of contaminants obtained by bioindicator results, the bioindicator monitoring can be used for long-term ecological risk surveillance. The threshold derivation method can extend the application of bioindicator monitoring from the occurrence study to ecological risk surveillance, which is especially important for China who has made progresses on regular contaminant control and starts to be concerned about the ecological risks of the emerging contaminants. The framework can be used to create national and regional long-term freshwater bioindicator monitoring programs, with the purposes of ecological risk assessment, occurrence and temporal trend study, pollution source identification, international convention fulfillment, retrospective study, etc. The bioindicator framework will benefit the aquatic environmental safety and the hazardous chemical management in China.

Critical features identification for chemical chronic toxicity based on mechanistic forecast models

Facing billions of tons of pollutants entering the ocean each year, aquatic toxicity is becoming a crucial endpoint for evaluating chemical adverse effects on ecosystems. Notably, huge amount of toxic chemicals at environmental relevant doses can cause potential adverse effects. However, chronic aquatic toxicity effects of chemicals are much scarcer, especially at population level. Rotifers are highly sensitive to toxicants even at chronic low-doses and their communities are usually considered as effective indicators for assessing the status of aquatic ecosystems. Therefore, the no observed effect concentration (NOEC) for population abundance of rotifers were selected as endpoints to develop machine learning models for the prediction of chemical aquatic chronic toxicity. In this study, forty-eight binary models were built by eight types of chemical descriptors combined with six machine learning algorithms. The best binary model was 1D & 2D molecular descriptors - random trees model (RT) with high balanced accuracy (BA) (0.83 for training and 0.83 for validation set), and Matthews correlation coefficient (MCC) (0.72 for training set and 0.67 for validation set). Moreover, the optimal model identified the primary factors (SpMAD_Dzp, AMW, MATS2v) and filtered out three high alerting substructures [c1cc(Cl)cc1, CNCO, CCOP(=S)(OCC)O] influencing the chronic aquatic toxicity. These results showed that the compounds with low molecular volume, high polarity and molecular weight could contribute to adverse effects on rotifers, facilitating the deeper understanding of chronic toxicity mechanisms. In addition, forecast models had better performances than the common models embedded into ECOSAR software. This study provided insights into structural features responsible for the toxicity of different groups of chemicals and thereby allowed for the rational design of green and safer alternatives.

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

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

Bioaccumulation, Biodistribution, Toxicology and Biomonitoring of Organofluorine Compounds in Aquatic Organisms

This review is a survey of recent advances in studies concerning the impact of poly- and perfluorinated organic compounds in aquatic organisms. After a brief introduction on poly- and perfluorinated compounds (PFCs) features, an overview of recent monitoring studies is reported illustrating ranges of recorded concentrations in water, sediments, and species. Besides presenting general concepts defining bioaccumulative potential and its indicators, the biodistribution of PFCs is described taking in consideration different tissues/organs of the investigated species as well as differences between studies in the wild or under controlled laboratory conditions. The potential use of species as bioindicators for biomonitoring studies are discussed and data are summarized in a table reporting the number of monitored PFCs and their total concentration as a function of investigated species. Moreover, biomolecular effects on taxonomically different species are illustrated. In the final paragraph, main findings have been summarized and possible solutions to environmental threats posed by PFCs in the aquatic environment are discussed.

Assessing the human health risks of per- and polyfluoroalkyl substances: A need for greater focus on their interactions as mixtures

Humans are exposed to complex mixtures of per- and polyfluoroalkyl substances (PFAS). However, human health risk assessment of PFAS currently relies on animal toxicity data derived from individual substance exposure, which may not adequately predict the risk from combined exposure due to possible interactions that can influence the overall risk. Long-chain perfluoroalkyl acids (PFAAs), particularly perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are recognised as global emerging contaminants of concern due to their ubiquitous distribution in all environmental media, wildlife, and humans, persistency, bioaccumulative-, toxic-, and human health-risk potentials. This article reviews the current understanding of the human health risks associated with PFAS exposure focusing on more recent toxicological and epidemiological studies from 2010 to 2020. The existing information on PFAA mixtures was also reviewed in an attempt to highlight the need for greater focus on their potential interactions as mixtures within the class of these chemicals. A growing number of toxicological studies have indicated several adverse health outcomes of PFAA exposure, including developmental and reproductive toxicity, neurotoxicity, hepatotoxicity, genotoxicity, immunotoxicity, thyroid disruption, and carcinogenicity. Epidemiological findings further support some of these adverse human health outcomes. However, the mechanisms underlying these adverse effects are not well defined. A few in vitro studies focusing on PFAA mixtures revealed that these compounds may act additively or interact synergistically/antagonistically depending on the species, dose level, dose ratio, and mixture components. Hence, the combined effects or potential interactions of PFAS mixtures should be considered and integrated into toxicity assessment to obtain a realistic and more refined human health risk assessment.

Chronic Effects of Bromate on Sexual Reproduction of Freshwater Rotifer Brachionus calyciflorus

The effects of potassium bromate (KBrO₃), sodium bromate (NaBrO₃), and potassium bromide (KBr) on the sexual reproduction of the rotifer Brachionus calyciflorus were studied by 2-d population growth, 4-d sexual reproduction, and 7-d resting egg production tests. The results showed that low concentrations of bromate promote 2-d and 4-d rotifer population growth, while high concentrations limit it. Bromate stress significantly affected parameters of rotifer sexual reproduction, including the ratio of mictic to amictic females, the mictic rate of rotifers, and the fertilization rate of mictic females. KBrO₃ at 0.001, 0.01, 1, and 10 mg/L, NaBrO₃ at 1 and 10 mg/L, and KBr at 100 and 200 mg/L significantly increased resting egg production, while KBrO₃ at 100 and 200 mg/L, and NaBrO₃ at 200 mg/L significantly decreased it. Resting egg production appears to provide a sensitive endpoint in evaluating the effect of bromate on rotifer sexual reproduction.

Perfluorooctane sulfonate exerts inflammatory bowel disease-like intestinal injury in rats

Background

Perfluorooctane sulfonate (PFOS), a type of perfluorinated compounds (PFCs), can induce various organ toxicity, including hepatomegaly, immunotoxicity, and gut microbiota disorder. PFCs have been associated with inflammatory bowel disease (IBD). Yet, whether PFOS exposure causes IBD-like disorder and the underlying mechanism remains undefined. Here, we investigated the influence of PFOS exposure on the development of IBD-like disorder in rats.

Methods

Sprague-Dawley rats were intraperitoneally injected with PFOS (1 or 10 mg/kg) or normal saline (NS) every other day for 15 days. Body weight, serum concentrations of serum amyloid A (SAA) and high sensitivity C reactive protein (hsCRP) were measured. Pathological assessments of villi height and crypt depth in the proximal duodenum and jejunum were performed using H&E staining. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was used to assay cell apoptosis in the jejunum. The infiltration of inflammatory cells and cytokines in the jejunum were detected by immunohistochemistry analysis.

Results

PFOS (10 mg/kg) significantly increased the body weight, SAA and hsCRP, whereas no significant differences were observed in PFOS 1 mg/kg group of rats. The villi height and crypt depth in the proximal duodenum and jejunum were significantly reduced upon PFOS exposure. PFOS induced higher histopathological score in intestinal tissues compared to NS. Notably, TUNEL-positive cells were significantly higher in the jejunum upon PFOS exposure. Further, neutrophil and macrophage accumulated, and inflammatory cytokines infiltration were also remarkably increased in rats exposed to PFOS.

Conclusion

PFOS induces IBD-like phenotypes in rats, with associated inflammatory infiltration to intestinal.

Adverse effects of perfluoroalkyl acids on fish and other aquatic organisms: A review

Perfluoroalkyl acids (PFAAs) have been widely used in many industrial and consumer products. They have been detected ubiquitously in ambient water along with other environmental matrices, and their adverse effects on aquatic organisms have been a subject of active investigation. Here, we intended to summarize and synthesize the existing body of knowledge on PFAA toxicity through an extensive literature review, and shed light on areas where further research is warranted. PFAA toxicity appears to be influenced by the sex and developmental stages of aquatic organisms, but not significantly by exposure route. PFAA-induced aquatic toxicity could be classified as metabolism disturbance, reproduction disruption, oxidative stress, developmental toxicity, thyroid disruption, etc. At the molecular level, these responses can be initiated by key events, such as nuclear receptor activation, reactive oxygen species induction, or interaction with a membrane, followed by a cascade of downstream responses. PFAA-induced toxicity involves diverse metabolic processes, and therefore elucidating crosstalk or interactions among diverse metabolic pathways is a challenging task. In the presence of other chemicals, PFAAs can function as agonists or antagonists, resulting in different directions of combined toxicity. Therefore, mixture toxicity with other groups of chemicals is another research opportunity. Experimental evidence supports the trans-generational toxicity of PFAAs, suggesting that their long-term consequences for aquatic ecosystems should become of concern. A recent global ban of several PFAAs resulted in an increasing dependence on PFAA alternatives. The lack of sufficient toxicological information on this emerging group of chemicals warrant caution and rigorous toxicological assessments.

PFOA and PFOS interact with superoxide dismutase and induce cytotoxicity in mouse primary hepatocytes: A combined cellular and molecular methods

This study investigated the adverse effects of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) on mouse primary hepatocytes by conducting cell viability, apoptosis, intracellular oxidative stress level, superoxide dismutase (SOD), catalase (CAT) activity and glutathione level assays. It was shown that PFOA and PFOS altered antioxidant enzymes activities and triggered oxidative stress, and thus exhibited cytotoxicity to the hepatocytes. Molecular mechanisms of SOD activities were measured and structural changes were explored by isothermal titration calorimetry and multiple spectroscopy. PFOA and PFOS bind to SOD via electrostatic forces with 7.634 ± 0.06 and 9.7 ± 0.4 sites, respectively, leading to structural and conformational changes. The overall results demonstrated that PFOS and PFOA are able to interact with SOD directly, resulting in producing oxidative stress and induce apoptosis.

Assessing the human health risks of perfluorooctane sulfonate by in vivo and in vitro studies

The wide use of perfluorooctane sulfonate (PFOS) has led to increasing concern about its human health risks over the past decade. In vivo and in vitro studies are important and effective means to ascertain the toxic effects of PFOS on humans and its toxic mechanisms. This article systematically reviews the human health risks of PFOS based on the currently known facts found by in vivo and in vitro studies from 2008 to 2018. Exposure to PFOS has caused hepatotoxicity, neurotoxicity, reproductive toxicity, immunotoxicity, thyroid disruption, cardiovascular toxicity, pulmonary toxicity, and renal toxicity in laboratory animals and many in vitro human systems. These results and related epidemiological studies confirmed the human health risks of PFOS, especially for exposure via food and drinking water. Oxidative stress and physiological process disruption based on fatty acid similarity were widely studied mechanisms of PFOS toxicity. Future research for assessing the human health risks of PFOS is recommended in the chronic toxicity and molecular mechanisms, the application of various omics, and the integration of toxicological and epidemiological data.

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.

Effect of single-wall carbon nanotubes on bioconcentration and toxicity of perfluorooctane sulfonate in zebrafish (Danio rerio)

The wide application of nanoparticles will lead its release into the aquatic environment, which may alter the bioavailability and toxicity of other contaminants to aquatic organisms. This work aimed to study the effects of perfluorooctane sulfonate (PFOS), single-wall carbon nanotubes (SWCNT), and their mixture on PFOS accumulation, antioxidant defenses and acetylcholinesterase (AChE) activity in zebrafish. The fish was dissected after being exposed (24, 48, 72 and 96h) separately to PFOS, SWCNT and PFOS+SWCNT co-exposure. The bioaccumulation of PFOS in fish tissues (liver, intestines, gills and brain) decreased with increasing dosage of SWCNT, however, the opposite trend was observed in fish skin, which indicated that the bioavailability of PFOS changed by adsorption on SWCNT. Meanwhile, co-exposure induced more reactive oxygen species (ROS) than PFOS alone and enhanced the effect of PFOS on the superoxide dismutase (SOD), and catalase (CAT) and AChE activities. Furthermore, the integrated biomarker response (IBR) showed that co-exposure was the most stressful circumstance.

The expression of several reproductive hormone receptors can be modified by perfluorooctane sulfonate (PFOS) in adult male rats

This study was undertaken to evaluate the possible role of several reproductive hormone receptors on the disruption of the hypothalamic-pituitary-testis (HPT) axis activity induced by perfluorooctane sulfonate (PFOS). The studied receptors are the gonadotropin-releasing hormone receptor (GnRHr), luteinizing hormone receptor (LHr), follicle-stimulating hormone receptor (FSHr), and the androgen receptor (Ar). Adult male rats were orally treated with 1.0; 3.0 and 6.0 mg of PFOS kg(-1) d(-1) for 28 days. In general terms, PFOS can modify the relative gene and protein expressions of these receptors in several tissues of the reproductive axis. At the testicular level, apart from the expected inhibition of both gene and protein expressions of FSHr and Ar, PFOS also stimulates the GnRHr protein and the LHr gene expression. The receptors of the main hormones involved in the HPT axis may have an important role in the disruption exerted by PFOS on this axis.

Photoinduced Hydrodefluorination Mechanisms of Perfluorooctanoic Acid by the SiC/Graphene Catalyst

Cleavage of the strong carbon-fluorine bonds is critical for elimination of perfluorooctanoic acid (PFOA) from the environment. In this work, we investigated the decomposition of PFOA with the SiC/graphene catalyst under UV light irradiation. The decomposition rate constant (k) with SiC/graphene was 0.096 h(-1), 2.2 times higher than that with commercial nano-TiO2. Surface fluorination on SiC/graphene was analyzed by X-ray photoelectron spectroscopy (XPS), revealing the conversions of Si-H bonds into Si-F bonds. A different route was found to generate the reactive Si-H bonds on SiC/graphene, substituting for silylium (R3Si(+)) to activate C-F bonds. During the activation process, photogenerated electrons on SiC transfer rapidly to perfluoroalkyl groups by the medium of graphene, further reducing the electron cloud density of C-F bonds to promote the activation. The hydrogen-containing hydrodefluorination intermediates including (CF3(CF2)2CFH, CF3(CF2)3CH2, CF3(CF2)4CH2, and CF3(CF2)4CFHCOOH) were detected to verify the hydrodefluorination process. The photoinduced hydrodefluorination mechanisms of PFOA can be consequently inferred as follows: (1) fluorine atoms in perfluoroalkyl groups were replaced by hydrogen atoms due to the nucleophilic substitution reaction via the Si-H/C-F redistribution, and (2) generation of CH2 carbene from the hydrogen-containing perfluoroalkyl groups and the C-C bonds scission by the Photo-Kolbe decarboxylation reaction under UV light excitation. This photoinduced hydrodefluorination provides insight into the photocatalytic decomposition of perfluorocarboxylic acids (PFCAs) in an aqueous environment.

Full life-cycle toxicity assessment on triclosan using rotifer Brachionus calyciflorus

Triclosan (TCS) is an antimicrobial and is an aquatic contaminant. Little is known on aquatic toxicity of TCS. Rotifers are common members of freshwater zooplankton. In this study, Brachionus calyciflorus was chosen as a test organism to assess the acute and complete life cycle toxicity of TCS in this study. The acute toxicity results showed that the 24-h median lethal concentration (LC50) of TCS was 345±0.11μg/L (95% confidence limits of 212-564µg/L). Reproductive bioassays demonstrated that TCS could inhibit the population growth rate at the concentration higher than 1.0μg/L. Resting egg production encompasses the full life-cycle of rotifer, and thus its hatching rate were explored to assess the toxicity of TCS towards rotifer population at TCS concentrations ranging from 0.1 to 200µg/L at two different growth periods. When resting eggs were exposed to TCS during the formation period, 0.1 and 1.0µg/L of TCS increased the hatching rate from 0.402 to 0.502, and 0.475, respectively. Exposure to 100 and 200µg/L of TCS reduced the hatching rate to 0.309 and 0.275, respectively. When the resting eggs were formed in the control medium and hatched in medium with TCS, their hatching rates were not significantly influenced by TCS, except that 200µg/L of TCS decreased the hatching rate from 0.402 to 0.34 significantly. The effects of TCS exposure on the hatching rate during the formation period were greater than those during the resting egg hatching period.

Development of a total dissolved solids (TDS) chronic effects benchmark for a northern Canadian lake

Laboratory chronic toxicity tests with plankton, benthos, and fish early life stages were conducted with total dissolved solids (TDS) at an ionic composition specific to Snap Lake (Northwest Territories, Canada), which receives treated effluent from the Snap Lake Diamond Mine. Snap Lake TDS composition has remained consistent from 2007 to 2014 and is expected to remain unchanged through the life of the mine: Cl (45%-47%), Ca (20%-21%), Na (10%-11%), sulfate (9%); carbonate (5%-7%), nitrate (4%), Mg (2%-3%), and minor contributions from K and fluoride. The TDS concentrations that resulted in negligible effects (i.e., 10% or 20% effect concentrations) to taxa representative of resident biota ranged from greater than 1100 to greater than 2200 mg/L, with the exception of a 21% effect concentration of 990 mg/L for 1 of 2 early life stage fish dry fertilization tests (wet fertilization results were >1480 mg/L). A conservative, site-specific, chronic effects benchmark for Snap Lake TDS of 1000 mg/L was derived, below the lowest negligible effect concentration for the most sensitive resident taxon tested, the cladoceran, Daphnia magna (>1100 mg/L). Cladocerans typically only constitute a few percent of the zooplankton community and biomass in Snap Lake; other plankton effect concentrations ranged from greater than 1330 to greater than 1510 mg/L. Chironomids, representative of the lake benthos, were not affected by greater than 1380 mg/L TDS. Early life stage tests with 3 fish species resulted in 10% to 20% effect concentrations ranging from greater than 1410 to greater than 2200 mg/L. The testing undertaken is generally applicable to northern freshwaters, and the concept can readily be adapted to other freshwaters either for TDS where ionic composition does not change or for major ionic components, where TDS composition does change.

Electrochemical oxidation of perfluorinated compounds in water

Perfluorinated compounds (PFCs) are persistent and refractory organic pollutants that have been detected in various environmental matrices and municipal wastewater. Electrochemical oxidation (EO) is a promising remediation technique for wastewater contaminated with PFCs. A number of recent studies have demonstrated that the "non-active" anodes, including boron-doped diamond, tin oxide, and lead dioxide, are effective in PFCs elimination in wastewater due to their high oxygen evolution potential. Many researchers have conducted experiments to investigate the optimal conditions (i.e., potential, current density, pH value, plate distance, initial PFCs concentration, electrolyte, and other factors) for PFCs elimination to obtain the maximal elimination efficiency and current efficiency. The EO mechanism and pathways of PFCs have been clearly elucidated, which undergo electron transfer, Kolbe decarboxylation or desulfonation, hydrolysis, and radical reaction. In addition, the safety evaluation and energy consumption evaluation of the EO technology have also been summarized to decrease toxic ion release from electrode and reduce the cost of this technique. Although the ultrasonication and hydrothermal techniques combined with the EO process can improve the removal efficiency and current efficiency significantly, these coupled techniques have not been commercialized and applied in industrial wastewater treatment. Finally, key challenges facing EO technology are listed and the directions for further research are pointed out (such as combination with other techniques, treatment for natural waters contaminated by low levels of PFCs, and reactor design).

Evaluation of single and joint toxicity of perfluorooctane sulfonate and zinc to Limnodrilus hoffmeisteri: Acute toxicity, bioaccumulation and oxidative stress

Perfluorooctane sulfonate (PFOS) and zinc have been detected in aquatic environment widely. In order to study the combined effects of PFOS and Zn, a series of experiments was conducted to explore the acute mortality, bioaccumulation and antioxidant status of Limnodrilus hoffmeisteri. The acute toxicity was evaluated by calculating 24h-EC50 values, and it was observed that 24h-EC50 values in single and joint treatments decreased with decreasing pH value or increasing exposure concentration. Toxic unit analysis suggested that the combined effects of the PFOS+Zn binary mixture were mostly simple addition, with 8 groups showing synergism and only one group showing antagonism. The analysis of internal Zn and PFOS concentration showed that the possible interaction between Zn and PFOS can affect the bioaccumulation of the two chemicals in L. hoffmeisteri. In addition, oxidative stress status was assessed by measuring oxidation-related biochemical parameters such as superoxide dismutase, glutathione peroxidase and malondialdehyde, and the integrated biomarker response index was estimated to rank the toxicity order. Exposures to Zn and PFOS were found to evoke some changes in the antioxidant defense system, and a strong self-adaptive ability was noticed for L. hoffmeisteri after 10 d exposure.