Short-chain Carboxylic Acids Research Articles

Caproic acid production from short-chained carboxylic acids produced by arrested anaerobic digestion of green waste: Development and optimization of a mixed caproic acid producing culture

Caproic acid is an important compound for producing a variety of chemicals and a potential precursor for Sustainable Aviation Fuels (SAF). This study aimed at developing a stable mixed culture producing caproic acid using short-chain carboxylic acids (SCCAs) derived from arrested anaerobic digestion (AAD) of green waste and optimizing chain elongation (CE) conditions. The results showed that the mixed culture was dominated by Clostridium sensu stricto 12 (53.09 %), optimally producing caproic acid at 37 °C, pH 7.20, with a 15 % inoculum concentration. Under these conditions, 75.59 % of the consumed electrons contributed to caproic acid formation. Gradual ethanol feeding in bioreactor experiments resulted in caproic acid titer of 13.36 g/L, with carbon conversion efficiency (CCE) of 81.91 % and electron transfer efficiency (ETE) of 76.39 %, surpassing batch experiments without gradual ethanol addition. These findings demonstrate that the effectiveness of a mixed culture can be improved, resulting in increased caproic acid production.

Blackcurrant Anthocyanins Attenuate Estrogen -Deficiency-Induced Bone Loss through Modulating Microbial-Derived Short-Chain Carboxylic Acids and Phytoestrogen Metabolites in Peri- and Early Postmenopausal Women.

The present study aimed to assess the effects of blackcurrant (BC) anthocyanins on concentrations of microbial-derived short-chain carboxylic acids (SCCAs) and metabolites of phytoestrogens. We then examined their associations with six-month changes in whole-body bone mineral density (BMD) and biomarkers of bone metabolism. Fecal and blood samples from a pilot randomized controlled trial were collected and analyzed from 37 eligible peri- and early postmenopausal women aged 45-60 years who were randomized into one of three treatment groups consuming one placebo capsule (control), 392 mg BC (low BC) or 784 mg BC (high BC) daily for six months. Significant differences were observed between groups at baseline in acetic, propionic, valeric, caproic and heptanoic acids (p < 0.05). Isobutyric acid significantly decreased from baseline (0 months) to six months in the control group (p < 0.05) and the high BC group had a significantly greater concentration than the control group at six months (p < 0.05). Butyric acid was significantly greater in the high BC group than low BC at six months (p < 0.05). Six-month changes in caproic and isobutyric acids showed weak correlations with changes in whole-body BMD (r = 0.3519, p < 0.05 and r = 0.3465, p < 0.05, respectively). Isovaleric and valeric acids displayed weak correlations with BALP (r = 0.3361, p < 0.05) and OPG (r = 0.3593, p < 0.05), respectively. Enterodiol was positively correlated with BALP (r = 0.6056, p < 0.01) while enterolactone was positively correlated with osteocalcin (r = 0.5902, p < 0.001) and negatively correlated with sclerostin (r = -0.3485, p < 0.05). The results suggest that BC may be a potential dietary agent to reduce postmenopausal bone loss through modulating microbially-derived SCCAs and phytoestrogen metabolites.

Carbon-negative bio-production of short-chain carboxylic acids (SCCAs) from syngas via the sequential two-stage bioprocess by Moorella thermoacetica and metabolically engineered Escherichia coli

Syngas can be efficiently converted to acetate and is environmentally friendly using Moorella thermoacetica under anaerobic conditions. Coupled with acetate production from syngas, using acetate to synthesize value-added compounds such as short-chain carboxylic acids (SCCAs) become a negative-carbon process. Escherichia coli is engineered to utilize acetate as the sole carbon source to produce SCCAs. By knocking out some acetyltransferase genes, combined with introducing exogenous pathway and additional cofactor engineering, the strains can synthesize 3.79 g/L of 3-hydroxypropionic acid (3-HP), 1.83 g/L of (R)-3-hydroxybutyric acid (R-3HB), and 2.31 g/L of butyrate. We used M. thermoacetica to produce acetate from syngas, subsequently, all engineered E. coli strains were able to produce SCCAs from syngas-derived acetate. The titer of 3-HP, R-3HB, and butyrate is 3.75, 1.68, and 2.04 g/L, with carbon sequestration rates of 51.1, 26.3, and 38.1 %, respectively. This coupled bioprocess has great potential for producing other value-added chemicals from syngas.

City-scale impacts of PFAS from normal and elevated temperature landfill leachates on wastewater treatment plant influent

The influence of elevated temperatures on PFAS leaching in municipal solid waste (MSW) landfills has not been well characterized in the published scientific literature. This study systematically examined the compositions and concentrations of per- and polyfluoroalkyl substances (PFAS) and precursors content in both normal temperature landfill and elevated temperature landfill (ETLF) leachates and compared to a municipal wastewater and to a WWTP influent with and without introduced leachates. The characterization of the samples involved the analysis of 71 PFAS target compounds before and after applying the total oxidizable precursor (TOP) assay, along with measuring fluorotelomer alcohols (FTOHs) and adsorbable organofluorine (AOF) levels. Summed PFAS concentrations in leachates were driven largely by fluorotelomer carboxylic acids (FTCAs), short-chain and ultrashort-chain perfluorinated carboxylic acids and sulfonic acids. Summed PFAS concentrations in ETLF leachate were significantly higher than in normal leachate for precursors and terminal PFAS products. TOP assay data demonstrated that ETLF leachate contained significantly higher concentrations of oxidizable PFAS precursors than normal leachate. PFAS profiles in leachates were distinct from municipal wastewater and from WWTP influent, suggesting diverse PFAS inputs to the WWTP. The presence of unknown precursors revealed by the TOP assay and AOF analyses highlights the complexity of PFAS sources impacting sewer networks, warranting further study to better characterize PFAS inputs to the WWTP on a city-wide scale.

Environmental pH and compound structure affect the activity of short-chain carboxylic acids against planktonic growth, biofilm formation, and eradication of the food pathogen Salmonella enterica.

Short-chain carboxylic acids (SCCAs) that are naturally produced by microbial fermentation play an essential role in delaying microbial spoilage. SCCAs are structurally diverse, but only a few of them are routinely used in food biopreservation. This study investigated the effects of environmental pH and intrinsic properties of 21 structurally different SCCAs on the antimicrobial and antibiofilm activity against Salmonella enterica. Inhibition of SCCA toward planktonic and biofilm growth of S. enterica was higher in an acidic environment (pH 4.5) that is common in fermented products, and for SCCA that possessed both a high acid dissociation strength (pKa) (>4.0) and a positive hydrophobicity [octanol/water partition coefficient (log Kow)]. Crotonic and caproic acids were identified as SCCAs with potential as biopreservatives even at near-neutral pH. SCCA with hydrophilic groups such as lactic acid did not inhibit S. enterica at concentrations up to 50 mM, while SCCA with benzene or methyl groups or a double bond prevented S. enterica growth and biofilm formation. Stimulation of biofilm formation was observed for formic, acetic, and propionic acid close to the minimum inhibitory concentration to reduce 50% of cell density (MIC50) of planktonic cells, and for citric and isocitric acid with an MIC50 of ≥50 mM. The presence of low concentrations of formic and propionic acids during biofilm formation conferred protection during eradication possibly due to a pre-adaptation effect, yet two consecutive acid treatments were successful in eradicating biofilms if the first acid treatment was two- to threefold of the MIC50.IMPORTANCEThis study provides a systematic comparison on the antimicrobial and antibiofilm activity of more than 20 structurally different SCCAs against a common food pathogen. We tested the antimicrobial activity at controlled pH and identified the structure-dependent antimicrobial effects of SCCA without the confounding influence of acidification. The combined effect of pKa and log Kow was identified as an important feature that should be considered when deciding for a specific SCCA in the application as antimicrobial. Our results imply that additional phenomena such as the use of SCCA as substrate and cellular pre-adaption effects have to be taken into consideration. We finally present a two-step treatment as an efficient approach to eradicate biofilms, which can be applied for the disinfection of contact surfaces and manufacturing equipment. Results obtained here can serve as guidelines for application of SCCA to avoid the growth of food pathogens and/or to develop biopreserved food systems.

Bioaugmentation of microalgae fermentation with yeast for enhancing microbial chain elongation: In-situ ethanol production and metabolic potential

Anaerobic microalgae fermentation, leveraging its cost-effectiveness and the adaptability of mixed cultures, holds promise for carboxylate biosynthesis. Microalgae, with their abundant carbohydrates and proteins, stand out as an optimal substrate for this process among various options. Furthermore, microalgae fermentation not only shows the potential to mitigate risks associated with algae blooms but also aligns with the need for sustainable practices. However, the limited utilization rate of microalgae in anaerobic fermentation poses challenges to achieving high production rates of desired products. In this study, we implemented a bioaugmentation process with yeast to enhance carboxylate production performance of microalgae fermentation. The results demonstrated a fourfold increase in carboxylate yield with the addition of yeast. In-situ ethanol production facilitated the conversion of short-chain carboxylic acids into medium-chain carboxylates, achieving a yield of 46.3 mM-C/g VS. The presence of yeast significantly enhanced substrate utilization from 20 % to 80 %, steering the metabolic pathway towards chain elongation. Metagenomic analysis further revealed metabolic shifts following yeast addition, particularly an increased abundance of genes involved in acetyl-CoA production. Notably, the aldehyde:ferredoxin oxidoreductase (AOR) pathway emerged as a key driver in butanol production. These findings highlight the improved performance of anaerobic microalgae fermentation with yeast, enabling efficient production of higher value bioproducts while eliminating the need for external electron donors.

Per- and polyfluoroalkyl substances in Chinese commercially available red swamp crayfish (Procambarus clarkii): Implications for human exposure and health risk assessment

The extensive utilization of per- and polyfluoroalkyl substances (PFASs) has led to their pervasive presence in the environment, resulting in contamination of aquatic products. Prolonged exposure to PFASs has been linked to direct hepatic and renal damage, along with the induction of oxidative stress, contributing to a spectrum of chronic ailments. Despite the recent surge in popularity of red swamp crayfish as a culinary delicacy in China, studies addressing PFASs' exposure and associated health risks from their consumption remain scarce. To address this gap, our study investigated the PFASs’ content in 85 paired edible tissue samples sourced from the five primary red swamp crayfish breeding provinces in China. The health risks associated with dietary exposure were also assessed. Our findings revealed widespread detection of PFASs in crayfish samples, with short-chain perfluoroalkyl carboxylic acids (PFCAs) exhibiting the highest concentrations. Notably, the total PFAS concentration in the hepatopancreas (median: 160 ng/g) significantly exceeded that in muscle tissue (5.95 ng/g), as did the concentration of every single substance. The hazard quotient of perfluorohexanesulfonic acid (PFHxS) via consuming crayfish during peak season exceeded 1. In this case, a potential total non-cancer health risk of PFASs, which is mainly from the hepatopancreas and associated with PFHxS, is also observed (hazard index>1). Thus, it is recommended to avoid consuming the hepatopancreas of red swamp crayfish. Greater attention should be paid to governance technology innovation and regulatory measure strengthening for short-chain PFASs.

Optimisation of the Production of Bio-Based Basic Chemicals from Biogenic Secondary Waste Through Dispersion

Biogenic waste from waste treatment plants, also known as secondary waste, can be used to produce bio-based carboxylic acids. Conventionally, these are produced by chemically synthesis of petroleum-based raw materials or synthesis of natural oils (e.g. coconut or palm kernel oil). Using organic residues and waste materials in a cascade to produce bio-based products can contribute to the circular bioeconomy. In the biological treatment process for production of bio-based carboxylic acids, microorganisms that are already present in the secondary waste use ethanol to convert short-chain carboxylic acids (with one to three carbon atoms) into medium-chain carboxylic acids (with four to ten carbon atoms). During the treatment process, medium-chain carboxylic acids are separated from the secondary waste by using in-situ extraction (liquid-liquid extraction). In previous studies, bioreactors without a dispersing function were used on a laboratory scale. In order to optimise the production and extraction of the formed medium-chain carboxylic acids, the bioreactors should be upgraded with a device for dispersing the extraction solvent in the secondary waste. Dispersing can increase the surface area between the extraction solvent and the secondary waste and therefore also the ability to extract the medium-chain carboxylic acids. To evaluate the effects of dispersing on the production of bio-based carboxylic acids, the production and extraction rates of static bioreactors without dispersing are compared with those of dynamic bioreactors with dispersing on a laboratory scale. Leachate from a composting plant was used as secondary waste. According to the results of the current study, it can be confirmed that dispersion has a positive effect on the biological treatment process. In addition to the increased degradation of the nutrient ethanol, the production of medium-chain carboxylic acids in the secondary waste as well as the extracted medium-chain carboxylic acids could be increased by dispersing.

Passive biomonitoring for per- and polyfluoroalkyl substances using invasive clams, C. fluminea

Per- and polyfluoroalkyl substances (PFAS) are a class of toxic manufactured chemicals in commercial and consumer products. They are resistant to environmental degradation and mobile in soil, air, and water. This study used the introduced bivalve Corbicula fluminea as a passive biomonitor at sampling locations in a primary drinking water source in Virginia, USA. Many potential PFAS sources were identified in the region. Perfluorohexane sulfonate (PFHxS) and 6:2 fluorotelomer sulfonic acid (6:2 FTS) levels were highest downstream of an airport. The highest levels of short-chain carboxylic acids were in locations downstream of a wastewater treatment plant. Measured PFAS concentrations varied by location in C. fluminea, sediment, and surface water samples. Two compounds were detected across all three mediums. Calculated partitioning coefficients confirm bioaccumulation of PFAS in C. fluminea and sorption to sediment. C. fluminea bioaccumulated two PFAS not found in the other mediums. Perfluoroalkyl carboxylic acids and short-chain compounds dominated in clam tissue, which contrasts with findings of accumulation of longer-chain and perfluorosulfonic acids in fish. These findings suggest the potential for using bivalves to complement other organisms to better understand the bioaccumulation of PFAS and their fate and transport in a freshwater ecosystem.

Determination of triazole fungicides in soybeans with cobalt-enhanced lanthanide metal chloride anion magnetic deep eutectic solvents in-situ dispersion extraction

In this work, we synthesized a series of magnetic deep eutectic solvents (MDESs) with lanthanide metal chlorides as paramagnetic metal centers and developed a reversed-phase dispersive liquid–liquid microextraction method (DLLME) based on the in-situ dispersion of MDESs for the extraction and preconcentration of triazole fungicides (TFs) from bean samples. Different MDESs were synthesized by combining quaternary ammonium salts, short-chain carboxylic acids, and lanthanide metal chlorides. The dissolution of short-chain carboxylic acids in n-hexane led to the in-situ dispersion of MDESs to replace the toxic dispersant of traditional DLLME species and shorten extraction time. Cobalt powder was added to encapsulate MDESs to enhance the magnetic properties after the extraction and achieve the purpose of easy phase separation. Notably, the highest extraction efficiency of TFs was observed in the MDES formed by tetrabutylammonium bromide, propionic acid, and gadolinium chloride in a ratio of 1:10:0.06. We optimized various parameters that affected the extraction efficiency of the method, including volume of MDES, extraction time, amount of cobalt powder, and volume of elution solvent. Under the optimal conditions, the detection limits (LODs) and quantification limits (LOQs) of the technique varied between 0.097–0.13 ng·g−1 and 0.32–0.43 ng·g−1, respectively. To assess the accuracy, the method was tested with samples spiking at three concentration levels, and the obtained results revealed that the recovery rates varied from 88.97–113.7%. To summarize, this study represents the initial application of in-situ dispersed lanthanide metal chloride anion-MDESs for analyzing bean samples and the proposed DLLME technique is rapid, straightforward, and efficient.

Paired electrocatalytic H2O2-persulfate activation for sulfamethoxazole mineralization in a filter-press cell using BDD and air diffusion electrodes

This paper deals with the paired electrocatalytic H2O2-persulfate (H2O2-PS) activation to yield SO4– and OH for the antibiotic sulfamethoxazole (SMX) mineralization. A filter-press cell with a boron-doped diamond (BDD) anode and a gas diffusion cathode (GDE) was used to form the PS (through the anodic oxidation (AO) of sulfate) and H2O2 (via oxygen reduction reaction, ORR). Bulk electrolysis in the flow cell reached accumulation values of 1.48 mM PS and 4.80 mM H2O2 in 100 mM Na2SO4 at pH 3, with current density and mean linear flow velocity of j = 10 mA cm−2, andu = 39.5 cm s−1. On the other hand, the influence of the initial sulfate concentration 50 ≤ CSO42-≤ 500 mM), applied current density (5 ≤ j ≤ 15 mA cm−2), initial PS and SMX concentrations (0 ≤ CPS ≤ 1 mM, 5 ≤ CSMX ≤ 20 mg L–1) was systematically addressed on the H2O2-PS process performance. The best trial achieved the total abatement of 20 mg L–1 of SMX in a 100 mM Na2SO4 + 0.5 mM PS at pH 3, u = 39.5 cm s−1, and j = 10 mA cm−2. Lastly, a degradation pathway of SMX was proposed in which most of the by-products consisted of short-chained carboxylic acids and ammonium. Scavenger tests revealed that the degradation of SMX is provoked by OH (68.3 %), SO4– (3.9 %), and other oxidants (27.8 %).

Combined adsorption and electrochemical oxidation of perfluorooctanoic acid (PFOA) using graphite intercalated compound

Perfluorooctanoic acid (PFOA) is a bioaccumulative synthetic chemical containing strong C–F bonds and is one of the most common per- and polyfluoroalkyl substances (PFAS) detected in the environment. Graphite intercalated compound (GIC) flakes were used to adsorb and degrade PFOA through electrochemical oxidation. The adsorption followed the Langmuir model with a loading capacity of 2.6 µg PFOA g−1 GIC and a second-order kinetics (3.354 g µg−1 min−1). 99.4% of PFOA was removed by the process with a half-life of 15 min. When PFOA molecules broke down, they released various by-products, such as short-chain perfluoro carboxylic acids like PFHpA, PFHxA, and PFBA. This breakdown indicates the cleavage of the perfluorocarbon chain and the release of CF2 units, suggesting a transformation or degradation of the original compound into these smaller acids. Shorter-chain perfluorinated compounds had slower degradation rates compared to longer-chain ones. Combining these two methods (adsorption and in situ electrochemical oxidation) was found to be advantageous because adsorption can initially concentrate the PFOA molecules, making it easier for the electrochemical process to target and degrade them. The electrochemical process can potentially break down or transform the PFAS compounds into less harmful substances through oxidation or other reactions.

The effects of two short-chain perfluoroalkyl carboxylic acids (PFCAs) on northern leopard frog (Rana pipiens) tadpole development

Short-chain perfluoroalkyl carboxylic acids (PFCAs) have been detected in the environment globally. The presence and persistence of these compounds in the environment may lead to chronic wildlife exposure. We used northern leopard frog (Rana pipiens) tadpoles to investigate the chronic toxicity and the bioconcentration of two short-chain PFCAs, perfluorobutanoic acid (PFBA) and perfluorohexanoic acid (PFHxA). We exposed Gosner stage 25 tadpoles to PFBA and PFHxA (as individual chemicals) at nominal concentrations of 0.1, 1, 10, 100, and 1000 µg/L for 43–46 days. Tadpoles exposed to 0.1 to 100 µg/L of PFBA and PFHxA had significantly higher mean snout-to-vent lengths, mean masses, and scaled mass indexes than control tadpoles. These results indicate that exposure to short-chain PFCAs influences tadpole growth. Further investigation into the mechanism(s) causing the observed changes in tadpole growth is warranted. We observed a significantly higher proportion of males in the PFBA 1 µg/L treatment group, however further histological analyses are required to confirm visual sex identification before making concrete conclusions on the effects of PFCAs on amphibian sex ratios. PFBA concentrations in tissues were higher than PFHxA concentrations; a pattern that contrasts with previously published studies using fish, suggesting potential differences between taxa in PFBA and PFHxA bioconcentration. Bioconcentration factors were <10 L/kg wet weight, indicating low bioconcentration potential in tadpoles. Our results suggest that PFBA and PFHxA may have effects at environmentally-relevant concentrations (0.1–10 µg/L) and further investigation is required before these compounds can be deemed a “safe” alternative to their long-chain counterparts.

Novel Lactobacillaceae strains and consortia to produce propionate-containing fermentates as biopreservatives.

Biopreservation refers to the use of natural or controlled microbial single strains or consortia, and/or their metabolites such as short-chain carboxylic acids (SCCA), to improve the shelf-life of foods. This study aimed at establishing a novel Lactobacillaceae-driven bioprocess that led to the production of the SCCA propionate through the cross-feeding on 1,2-propanediol (1,2-PD) derived from the deoxyhexoses rhamnose or fucose. When grown as single cultures in Hungate tubes, strains of Lacticaseibacillus rhamnosus preferred fucose over rhamnose and produced 1,2-PD in addition to lactate, acetate, and formate, while Limosilactobacillus reuteri metabolized 1,2-PD into propionate, propanol and propanal. Loigolactobacillus coryniformis used fucose to produce 1,2-PD and only formed propionate when supplied with 1,2-PD. Fermentates collected from batch fermentations in bioreactor using two-strain consortia (L. rhamnosus and L. reuteri) or fed-batch fermentations of single strain cultures of L. coryniformis with rhamnose contained mixtures of SCCA consisting of mainly lactate and acetate and also propionate. Synthetic mixtures that contained SCCA at concentrations present in the fermentates were more antimicrobial against Salmonella enterica if propionate was present. Together, this study (i) demonstrates the potential of single strains and two-strain consortia to produce propionate in the presence of deoxyhexoses extending the fermentation metabolite profile of Lactobacillaceae, and (ii) emphasizes the potential of applying propionate-containing fermentates as biopreservatives.

Dietary supplementation with probiotics promotes weight loss by reshaping the gut microbiome and energy metabolism in obese dogs.

Obesity and overweight among companion animals are significant concerns, paralleling the issues observed in human populations. Recent research has highlighted the potential benefits of various probiotics in addressing weight-related changes, obesity, and associated pathologies. In this study, we delved into the beneficial probiotic mechanisms in high-fat-induced obese canines, revealing that Enterococcus faecium IDCC 2102 (IDCC 2102) and Bifidobacterium lactis IDCC 4301 (IDCC 4301) have the capacity to mitigate the increase in body weight and lipid accumulation in obese canines subjected to a high-fat diet and hyperlipidemic Caenorhabditis elegans (C. elegans) strain VS29. Both IDCC 2102 and IDCC 4301 demonstrated the ability to reduce systemic inflammation and hormonal disruptions induced by obesity. Notably, these probiotics induced modifications in the microbiota by promoting lactic acid bacteria, including Lactobacillaceae, Ruminococcaceae, and S24-7, with concomitant activation of pyruvate metabolism. IDCC 4301, through the generation of bacterial short-chain fatty acids and carboxylic acids, facilitated glycolysis and contributed to ATP synthesis. Meanwhile, IDCC 2102 produced bacterial metabolites such as acetic acid and butyric acid, exhibiting a particular ability to stimulate dopamine synthesis in a canine model. This stimulation led to the restoration of eating behavior and improvements in glucose and insulin tolerance. In summary, we propose novel probiotics for the treatment of obese animals based on the modifications induced by IDCC 2102 and IDCC 4301. These probiotics enhanced systemic energy utilization in response to high caloric intake, thereby preventing lipid accumulation and restoring stability to the fecal microbiota. Consequently, this intervention resulted in a reduction in systemic inflammation caused by the high-fat diet.IMPORTANCEProbiotic supplementation affected commensal bacterial proliferation, and administering probiotics increased glycolysis and activated pyruvate metabolism in the body, which is related to propanate metabolism as a result of pyruvate metabolism activation boosting bacterial fatty acid production via dopamine and carboxylic acid specialized pathways, hence contributing to increased ATP synthesis and energy metabolism activity.

Interspecies comparison of metabolism of two novel prototype PFAS

As a result of proposed global restrictions and regulations on current-use per-and polyfluoroalkyl substances (PFAS), research on possible alternatives is highly required. In this study, phase I in vitro metabolism of two novel prototype PFAS in human and rat was investigated. These prototype chemicals are intended to be safer-by-design and expected to mineralize completely, and thus be less persistent in the environment compared to the PFAS available on the market. Following incubation with rat liver S9 (RL-S9) fractions, two main metabolites per initial substance were produced, namely an alcohol and a short-chain carboxylic acid. While with human liver S9 (HL-S9) fractions, only the short-chain carboxylic acid was detected. Beyond these major metabolites, two and five additional metabolites were identified at very low levels by non-targeted screening for the ether- and thioether-linked prototype chemicals, respectively. Overall, complete mineralization during the in vitro hepatic metabolism of these novel PFAS by HL-S9 and RL-S9 fractions was not observed. The reaction kinetics of the surfactants was determined by using the metabolite formation, rather than the substrate depletion approach. With rat liver enzymes, the formation rates of primary metabolite alcohols were at least two orders of magnitude higher than those of secondary metabolite carboxylic acids. When incubating with human liver enzymes, the formation rates of single metabolite carboxylic acids, were similar or smaller than those experienced in rat. It also indicates that the overall metabolic rate and clearance of surfactants are significantly higher in rat liver than in human liver. The maximum formation rate of the thioether congener exceeded 10-fold that of the ether in humans but were similar in rats. Overall, the results suggest that metabolism of the prototype chemicals followed a similar trend to those reported in studies of fluorotelomer alcohols.

Maternal and Neonatal Effects of Maternal Oral Exposure to Perfluoro-2-methoxyacetic Acid (PFMOAA) during Pregnancy and Early Lactation in the Sprague-Dawley Rat.

Perfluoro-2-methoxyacetic acid (PFMOAA) is a short-chain perfluoroalkyl ether carboxylic acid that has been detected at high concentrations (∼10 μg/L) in drinking water in eastern North Carolina, USA, and in human serum and breastmilk in China. Despite documented human exposure there are almost no toxicity data available to inform risk assessment of PFMOAA. Here we exposed pregnant Sprague-Dawley rats to a range of PFMOAA doses (10-450 mg/kg/d) via oral gavage from gestation day (GD) 8 to postnatal day (PND) 2 and compared results to those we previously reported for perfluorooctanoic acid (PFOA) and hexafluoropropylene oxide-dimer acid (HFPO-DA or GenX). Newborn pups displayed reduced birthweight (≥30 mg/kg), depleted liver glycogen concentrations (all doses), hypoglycemia (≥125 mg/kg), and numerous significantly altered genes in the liver associated with fatty acid and glucose metabolism similar to gene changes produced by HFPO-DA. Pup survival was significantly reduced at ≥125 mg/kg, and at necropsy on PND2 both maternal and neonatal animals displayed increased liver weights, increased serum aspartate aminotransferase (AST), and reduced serum thyroid hormones at all doses (≥10 mg/kg). Pups also displayed highly elevated serum cholesterol at all doses. PFMOAA concentrations in serum and liver increased with maternal oral dose in both maternal and F1 animals and were similar to those we reported for PFOA but considerably higher than HFPO-DA. We calculated 10% effect levels (ED10 or EC10) and relative potency factors (RPF; PFOA = index chemical) among the three compounds based on maternal oral dose and maternal serum concentration (μM). Reduced pup liver glycogen, increased liver weights and reduced thyroid hormone levels (maternal and pup) were the most sensitive end points modeled. PFMOAA was ∼3-7-fold less potent than PFOA for most end points based on maternal serum RPFs, but slightly more potent for increased maternal and pup liver weights. PFMOAA is a maternal and developmental toxicant in the rat producing a constellation of adverse effects similar to PFOA and HFPO-DA.

Novel PFAS-specific monitoring approach for highly impacted surface waters

In regulatory environmental monitoring programs, only a very small fraction of the vast number of per- and polyfluoroalkyl substances (PFAS) are investigated by target analysis. Therefore, non-target analysis (NTA) studies are increasingly conducted to detect unknown or unnoticed PFAS. These studies are often based on a few grab samples. Thus, discontinuously emitted PFAS from industrial batch processes might be easily overlooked. To address this deficiency and obtain in-depth information on the occurrence and temporal trend of PFAS in surface water impacted by treated industrial waste water, a comprehensive target and NTA study was implemented for 29 months.Elevated PFAS concentrations with up to 10.8 μg L−1 were detected in the river water by target analysis. In addition to PFAS target analysis, the water samples were analyzed by liquid chromatography-high-resolution tandem mass spectrometry (LC-HRMS/MS). Data processing strategies and various filtering steps were applied to prioritize PFAS. Substances were identified by comparing data to available internal and external PFAS suspect lists, a fragment ion and neutral loss list, and spectral libraries. Several compounds were unequivocally identified based on reference standards.Fifty-five PFAS were (tentatively) identified using NTA. Of those, 43 could be assigned to 13 different homologous series. Partly fluorinated short-chain carboxylic acids (H-PFCA) and sulfonic acids (H-PFSA) were predominantly found in addition to perfluoroalkyl carboxylic acids (PFCA) and the alkyl ether carboxylic acid DONA. To the best of our knowledge, 12 PFAS were reported in surface water for the first time. Signal intensities of individual PFAS and signal ratios varied widely over time, which may indicate batch operations leading to discontinuous emission. Results and insights from this screening approach on PFAS can be used to optimize forthcoming surface water monitoring programs by including newly identified PFAS and selecting appropriate sampling intervals.

Background concentrations and spatial distribution of PFAS in surface waters and sediments of the greater Melbourne area, Australia

A survey of per- and polyfluoroalkyl substances (PFAS) was conducted in Melbourne, Australia to determine background concentrations in residential, industrial, municipal wastewater treatment plants, and rural land uses. Surface water and sediment samples collected from 65 sites with different catchment land uses were analysed for thirty-three PFAS. Twenty-two out of thirty-three targeted PFAS were detected, with at least one PFAS species was detected in 98% water samples and 8% sediment samples. One site was determined to have point-source pollution from an airport (surface water Σ33PFAS = 4261 ng/L) and was excluded from statistical analyses. The median Σ33PFAS concentration in surface water was 63.5 ng/L and the average was 78.6 ng/L (range < DL-526 ng/L). PFAS species with the highest median concentrations were PFBA (11.3 ng/L), PFHxA (9.2 ng/L), PFOA (8.3 ng/L), PFOS (8.0 ng/L), PFPeA (7.5 ng/L), PFHpA (3.2 ng/L), and PFHxS (2.9 ng/L).The average Σ4PFAS in sediments was 0.35 ng/g d.w. (range = <DL-6.7 ng/g) and the congeners detected were PFOS, N-MeFOSAA, N-EtFOSAA, and N-EtFOSE. Significantly higher concentrations of all PFAS were found in urban areas than rural, except for PFBA which was evenly dispersed throughout all areas. Short-chain perfluoroalkyl carboxylic acids (PFCAs), PFBA, PFPeA, PFHxA, PFHpA, and the PFSA, PFBS were evenly dispersed throughout urban and industrial areas. PFOA, PFNA, and PFDA were higher, but not significantly, in residential catchments than industrial catchments. Industrial areas had significantly higher concentrations of perfluoroalkyl sulfonic acids (PFSAs), PFPeS, PFHxS, and PFOS, and 6:2 FTS than other urbanised areas. The distribution of PFAS throughout catchment types in this study displayed similar trends to other studies including findings of PFBA in background areas. Ongoing monitoring of defined catchments is recommended to improve understanding of PFAS sources and changes in environmental profiles, and to assess the implications of its occurrence throughout the environment.

Reductive degradation mechanism of perfluorooctanoic acid (PFOA) during vacuum ultraviolet (VUV) reactions combining with sulfite and iodide

In this study, PFOA removal and defluorination were examined during vacuum ultraviolet (VUV) photolysis in the presence of sulfite and sulfite/iodide conditions. PFOA (24 μM) degradation rate constant (kobs) and defluorination amount in VUV photolysis, and VUV/sulfite, and VUV/sulfite/iodide reactions under nitrogen-purging condition were 5.50 × 10−3, 7.26 × 10−2, 1.60 × 10−1 min−1, and 34.6, 72.7, 73.9% in 6 h, respectively. When tert-butanol (t-BuOH), NO2−, and NO3− ions were added as radical scavengers, hydrated electrons (eaq−) was confirmed as the main species responsible for degrading PFOA and mediating defluorination in VUV-based reactions. While, during VUV photolysis, short-chain perfluoroalkyl carboxylic acids (PFCAs), such as PFHpA, PFHxA, PFPeA, and PFBA, were mainly produced as transformation products (TPs) by the chain-shortening mechanism, additional 14 and 15 TPs were identified in the VUV/sulfite and VUV/sulfite/iodide reactions by LC-QTOF/MS, respectively. The main degradation mechanisms in these reactions are H–F exchange (e.g., TP395 (m/z = 394.9739) and TP377 (m/z = 376.9838)), •SO3−–F exchange (TP474, m/z = 474.9323), carbon double bond formation by defluorination (e.g., TP392 (m/z = 392.9455), TP410 (m/z = 410.9355), and TP436 (m/z = 436.9347)), and H–F exchange followed by hydration reaction (TP393, m/z = 392.9773), respectively. PFOA degradation pathways were proposed for these VUV-based reactions based on the identified TPs, their time profiles, and the density functional theory (DFT). Finally, the toxicity of PFOA and its TPs produced during three reactions were assessed using ECOSAR simulation.