Per- and polyfluoroalkyl substances in the environment

In the paper

“Efficiency of these transformations decreases from aerobic to anoxic to anaerobic (60, 61) conditions, and PFCA yields and rates of formation depend on specific precursor and transformation conditions (9).”

What the sources say

• Disputed

  The Conclusions (p. 12) report PFCA transformation yields of 11.12%, 0.46%, and 3.39% under aerobic, anoxic, and anaerobic conditions, respectively. Transformation efficiency therefore does not decrease in the stated order: anaerobic yield exceeds anoxic yield. The paper does report decreasing 8:2 FTOH biodegradation rate constants, but those are distinct from PFCA transformation yields; the sentence’s separate claim about precursor-dependent yields and rates is cited to another source. (LLM, conf=0.88)

  Checked by a reasoning model — may be wrong.

  cites [60] sourceExperimental — accuracy not yet measured
• ?Not checked — no full text of the sourcecites [61] source
• Supported

  Citation (9) is attached to the claim about PFCA yields and formation rates, not the preceding aerobic-to-anaerobic comparison. The Nonpolymer perfluoroalkyl and polyfluoroalkyl substances section states that both vary with the precursor substance and degradation conditions; no page number is supplied for this passage. (LLM, conf=0.95)

  cites [9] source

In the paper

“With global production volumes of fluoropolymers surpassing 230,000 tonnes/year (2)”

What the sources say

• Partly supported

  The Discussion section (‘Scope of the present study and uncertainties’; page not provided) estimates fluoropolymer production at about 230,000 tonnes per year globally. That supports the scale and annual basis of the claim, but ‘about’ does not establish that production surpasses 230,000 tonnes. (LLM, conf=0.86)

  cites [2] sourceExperimental — accuracy not yet measured

In the paper

“PFAS have been incorporated in more than 200 use areas ranging from industrial-mining applications to food production and fire-fighting foams due to the innate chemical and thermal stability of the carbon-fluorine bond and ability to repel oil and water (2).”

What the sources say

• Supported

  The Results report more than 200 uses across 64 categories and give examples including drilling fluids and fire-fighting foams. The Introduction explains that C–F bonds make PFAS stable and that their perfluorocarbon portions are water- and oil-repellent. The Discussion also describes food packaging as a PFAS use. (LLM, conf=0.90)

  cites [2] source

In the paper

“This revised definition is more inclusive with unambiguous inclusion of PFAS such as side-chain fluorinated aromatics (Fig. 2) (11, 12).”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [10]
• ?Could not verify

  The Introduction’s “Environmental Risk of Fluoro-Agrochemicals” section discusses PFAS and perfluoroalkyl chains, but does not address an OECD definition or the classification of side-chain fluorinated aromatics. Searches for the 2021 OECD revision and side-chain fluorinated aromatics found no passage supporting the attributed claim; page numbers are unavailable in our copy. (LLM, conf=0.77)

  cites [11] sourceExperimental — accuracy not yet measured
• ?Could not verify

  The Chemotypes of the Fluoro-Pharmaceuticals on the Market section (page unavailable) classifies fluorinated drug structures, including aryl–CF3 compounds, but does not discuss PFAS definitions. Searches for the 2021 OECD revision and side-chain fluorinated aromatics found no passage addressing whether that definition includes them. (LLM, conf=0.78)

  cites [12] sourceExperimental — accuracy not yet measured

In the paper

“Major PFAS groups from direct fluorination include those hydrofluorocarbons, hydrofluoroethers, hydrochlorofluoroolefins and hydrofluoroolefins that contain a -CF3 moiety and have an overall global production of over one megatonne/year (24).”

What the sources say

• Partly supported

  Section 2.2 (page not available) says major commercial routes for HFCs and HFOs involve a reaction with hydrofluoric acid, and section 2.1.3.1 reports HFC production quantities. The cited paper does not identify the listed compounds as major PFAS groups from direct fluorination, address hydrofluoroethers or the -CF3 qualifier, or establish combined global production above one megatonne per year. (LLM, conf=0.82)

  cites [24] sourceExperimental — accuracy not yet measured

In the paper

“Within individual PFAS groups, the functional moieties of starting materials may further react following conventional reaction pathways to yield different PFAS (9); thus, depending on the complexity of synthetic routes, final products may contain a number of unreacted intermediates and degradation products (22, 23).”

What the sources say

• Supported

  The citation to Buck et al. (9) is attached to the first clause. In “Manufacturing Processes > Telomerization” (page unavailable), the paper describes raw-material intermediates being reacted further to produce a range of fluorotelomer-based products. The statement about what final products may contain has separate citations (22, 23) and is not attributed to this source. (LLM, conf=0.91)

  cites [9] source
• ?Not checked — no full text of the sourcecites [22] source
• ?Not checked — no full text of the sourcecites [23] source

In the paper

“Addition of the -CF3 moiety can reduce biological degradation, increase biological activity, and assist with membrane transport, making the parent compound longer lasting or more effective”

What the sources say

• Partly supported

  The Chemotype section says fluorinated groups can improve binding to biological targets, and the Agrochemical Type section says increased fluorine content can improve uptake across surface barriers and movement within membranes. The Environmental Risk section describes resistance to enzymatic degradation for fluoro-agrochemicals generally. These passages support the proposed effects at a broader level, but do not establish that adding a -CF3 moiety specifically produces all three effects in a parent compound; page numbers are unavailable in our copy. (LLM, conf=0.83)

  cites [11] sourceExperimental — accuracy not yet measured
• Partly supported

  “Fluoro-Pharmaceuticals in the Past Three Decades” (page not supplied) says C–F bonds often increase metabolic stability, supporting the reduced-degradation part in general. It describes effects on absorption as complex and does not establish that adding a –CF3 group assists membrane transport or increases biological activity relative to the parent compound. The potency example in “Chiral Fluoro-Pharmaceuticals” compares two fluorinated enantiomers, not a –CF3-modified compound with its parent. (LLM, conf=0.85)

  cites [12] sourceExperimental — accuracy not yet measured

In the paper

“Historically, hundreds of PACF/PASF-based derivatives with a wide range of perfluorocarbon-chain lengths were produced, on the order of kilotonnes/year (15, 29), and used for industrial and consumer applications (2).”

What the sources say

• ?Not checked — no full text of the sourcecites [15] source
• ?Not checked — no full text of the sourcecites [29] source
• Supported

  The citation to this paper is attached to the industrial and consumer applications, not the kilotonnes-per-year figure. The Results identify PACF- and PASF-based substances among the PFAS whose uses were surveyed, and the Conclusions state that PFAS are used across industry branches and in many consumer products. No page numbers were provided in our copy. (LLM, conf=0.85)

  cites [2] source

In the paper

“with unknown, but likely considerable amounts being produced and used annually (e.g., prozac).”

What the sources say

• ?Could not verify

  The chemotype-classification section describes fluorinated aromatic agrochemicals, but gives no annual production or use amounts. The Introduction discusses fluorinated pharmaceuticals, while the passages found for production volume do not mention Prozac or estimate quantities for side-chain fluorinated aromatics. Searches for Prozac, annual amounts, production volume, and fluoxetine did not verify the attributed claim. (LLM, conf=0.76)

  cites [11] sourceExperimental — accuracy not yet measured
• Partly supported

  The Chemotypes of the Fluoro-Pharmaceuticals on the Market section identifies 54 aryl–CF3 pharmaceuticals, supporting the presence of side-chain-fluorinated aromatics among marketed drugs. But the paper counts registered drugs, not amounts produced or used annually; searches for production quantities and Prozac did not establish that part of the claim. (LLM, conf=0.78)

  cites [12] sourceExperimental — accuracy not yet measured

In the paper

“Oligomerization is less aggressive and mainly results in homologous series of target compounds (9), as have been observed near fluoropolymer (20) and perfluoropolyether (21) manufacturing and processing sites.”

What the sources say

• Partly supported

  The Manufacturing Processes > Telomerization section (page unavailable) describes a reaction that yields a mixture of related perfluoroalkyl iodides with progressively longer chains, supporting the homologous-series part of the citation. It does not describe oligomerization as “less aggressive” or compare its aggressiveness with another process. The observations near manufacturing sites are attached to other citations in the citing sentence, so they are not assessed against this source. (LLM, conf=0.76)

  cites [9] sourceExperimental — accuracy not yet measured
• ?Not checked — no full text of the sourcecites [20] source
• Supported

  The paper reports multiple chloroperfluoropolyether carboxylate congeners in New Jersey soils sampled around Solvay and identifies five consistent congeners in water downstream of a Solvay facility in Italy (Abstract; page not specified). This supports the observation attributed to citation (21). The separate claim that oligomerization is less aggressive is attached to citation (9), not this source. (LLM, conf=0.90)

  cites [21] sourceExperimental — accuracy not yet measured

In the paper

“High concentrations of organic solvents have been shown to inhibit PFOA degradation under in-situ remedial chemical-oxidation studies, suggesting that interactions of PFAS with other non-PFAS co-contaminants can alter PFAS transformation (40).”

What the sources say

• Supported

  The Results and Discussion section, under “Implications for Groundwater Remediation,” states that high solvent concentrations prevented PFOA transformation because the solvents scavenged sulfate radicals. This supports the claim that non-PFAS co-contaminants can alter PFAS transformation under conditions representative of in situ chemical oxidation. No page number is supplied in our copy. (LLM, conf=0.93)

  cites [40] source

In the paper

“These soil concentrations have been used to define global-background PFAS ranges in surface soils (means ~10-60 pg/g), such that surface soils rarely contain lower PFAS and higher concentrations suggest local/regional sources (88).”

What the sources say

• Partly supported

  Table 1 (Results and discussion; page unavailable) gives global-background means of about 11–58 pg/g for the reported compounds, and Methods treats high concentrations as potentially reflecting local or regional sources. The paper does not establish that surface soils rarely have concentrations below those means; Table 1 also reports some Southern Hemisphere means below 10 pg/g. (LLM, conf=0.86)

  cites [88] sourceExperimental — accuracy not yet measured

In the paper

“Atmospheric residence time governs transport distance (83) and depends on a variety of PFAS properties including volatility, reactivity, molecular weight, and vapor-particulate partitioning (82, 84, 85).”

What the sources say

• ?Not checked — no full text of the sourcecites [83] source
• ?Not checked — no full text of the sourcecites [82] source
• Supported

  Citation 83 is attached to the claim that atmospheric residence time governs transport distance, not to the subsequent list of PFAS properties. In §3.4 (page unavailable), the paper links predicted atmospheric lifetime to the spatial distribution of deposition and reports that most emitted PFAS travels beyond approximately 150 km. (LLM, conf=0.84)

  cites [84] source

In the paper

“In terrestrial settings, PFAS transport usually is via aqueous advection, with migration retarded by sorption on NOM, minerals and at fluid-fluid interfaces (particularly air-water) (91).”

What the sources say

• Partly supported

  The Introduction (page not available) identifies sorption to solids and adsorption at fluid-fluid interfaces as processes affecting PFAS transport; it also reports significant air-water interfacial retention in unsaturated porous media. It does not specify NOM or minerals as the sorbing solids, or state that terrestrial transport usually occurs via aqueous advection. (LLM, conf=0.86)

  cites [91] sourceExperimental — accuracy not yet measured

In the paper

“PFAS precursors are susceptible to in-vivo metabolic conversion to terminal acids or sulfonamides post-exposure as well as transformation during (or subsequent to) atmospheric or oceanic transport (see previous sections).”

What the sources say

• Partly supported

  The Introduction says PFAA precursors transform both in the environment and in vivo to acids such as PFOS. Model Development describes an in-vivo pathway through sulfonamide intermediates to PFOS. The paper does not establish transformation during or after atmospheric or oceanic transport, or identify sulfonamides as terminal products. Page numbers were not available in our copy. (LLM, conf=0.87)

  cites [119] sourceExperimental — accuracy not yet measured
• Partly supported

  The Biomonitoring section (page unavailable) says PFAS precursors can biotransform in humans and wildlife into terminal products such as PFOS and PFOA. The Overview of PFAS Sources and Environmental Pathways (page unavailable) describes atmospheric transport with precursor degradation, but contrasts this with oceanic transport of terminal products. It identifies sulfonamides as precursors, not terminal products, and does not establish transformation during or after oceanic transport. (LLM, conf=0.86)

  cites [120] sourceExperimental — accuracy not yet measured

In the paper

“Solubilized (i.e., waterborne) rather than dietary exposure was linked to reduced amphipod survival and reproduction (133) while higher trophic-level organisms are exposed primarily through ingestion (109).”

What the sources say

• ?Not checked — no full text of the sourcecites [133] source
• Partly supported

  Citation (109) is attached to the claim about higher trophic-level organisms, not the amphipod finding. In “Approaches for quantifying exposure sources” (page unavailable), the review says dietary intake is generally the largest PFAS exposure source for human adults. It does not establish that ingestion is the primary exposure route for higher trophic-level organisms generally. (LLM, conf=0.83)

  cites [109] sourceExperimental — accuracy not yet measured

In the paper

“Widespread global persistence of PFAS has resulted in detectable concentrations of the compounds in the blood of almost the entire human population (6).”

What the sources say

• Partly supported

  The Introduction says that widespread exposure, together with the environmental persistence and biological half-lives of some PFAS, has led to measurable PFAS in the blood of nearly the entire population in developed countries. The citing sentence extends that finding to almost the entire global population and attributes it to persistence alone; the passage does not support those extensions. No page number was supplied for the passage. (LLM, conf=0.90)

  cites [6] sourceExperimental — accuracy not yet measured

In the paper

“Seabirds, marine mammals, and terrestrial species show the greatest magnification factors compared with exclusively aquatic food webs in which organisms with gills eliminate perfluoroalkyl acids more efficiently (120).”

What the sources say

• Supported

  The PFAS bioaccumulation metrics section reports the highest PFAA trophic magnification factors in avian and marine mammal food webs, with lower factors in aquatic food webs. The bioaccumulation modeling section also includes terrestrial wildlife among air-breathing animals with greater biomagnification. The paper presents efficient elimination through gills as the proposed explanation for the aquatic contrast. (LLM, conf=0.90)

  cites [120] source

In the paper

“Given the strength of the C-F bond, complete mineralization is difficult, with fluorinated products of incomplete destruction remaining a concern (142, 143).”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [142]
• Supported

  In “Theoretical combustion requirements” (page not provided), the review says C–F bond cleavage requires substantial energy and may produce stable fluorinated intermediates. It describes complete mineralization as dependent on combustion conditions and identifies thermal degradation by-products as a primary concern. (LLM, conf=0.92)

  cites [143] source

In the paper

“Conversely, potential perfluoroalkyl-acid bioaccumulation in other fauna is greatest in long-chain compounds (120), with clear trends of bioaccumulation increasing with chain length (Figs. 4C, 4F, 5) (121).”

What the sources say

• Supported

  The ‘PFAS bioaccumulation metrics’ section reports that long-chain PFCAs with 12–14 carbons generally have the highest bioaccumulation potential. It also reports increasing bioaccumulation with chain length in several aquatic animal groups, while noting exceptions; the cited source supports the first, general claim rather than an exception-free rule. (LLM, conf=0.90)

  cites [120] source
• ?Not checked — no full text of the sourcecites [121] source

In the paper

“PFAS-impacted drinking water often is the primary route of human exposure (146), and treatment techniques for aqueous media are the most well-established—although performance and cost for removal of some short-chain PFAS can be particularly challenging.”

What the sources say

• Partly supported

  In “Why are PFAAs in drinking water a current concern?” (page unavailable), the paper says that even low drinking-water concentrations substantially increase PFAA blood levels in exposed communities. It does not establish that drinking water is often the primary human exposure route; it also identifies diet and consumer products as exposure sources. Citation (146) is attached to the exposure-route clause, not the subsequent treatment-techniques clause. (LLM, conf=0.83)

  cites [146] sourceExperimental — accuracy not yet measured

In the paper

“At higher trophic levels, PFSAs (e.g., PFOS) bioaccumulate at greater rates than PFCAs (e.g., PFOA) of the same chain length (Fig. 5) (114, 129) and tend to be more toxic (4).”

What the sources say

• ?Not checked — no full text of the sourcecites [114] source
• ?Not checked — no full text of the sourcecites [129] source
• Supported

  Citation (4) is attached to the toxicity comparison, not the bioaccumulation comparison, which has separate citations. The paper’s Toxicity overview states that sulfonates were more toxic than carboxylates of similar chain length in birds and rodents, and reports the same pattern for C8 PFOS and PFOA in fish. Page numbers were not provided in the supplied passages. (LLM, conf=0.93)

  cites [4] source

In the paper

“Using these approaches, a number of moderate- and long-chain PFAS have been shown to 1) elicit varying degrees of oxidative stress and modify the antioxidant defense systems of invertebrates, 2) induce neurotoxic and reprotoxic effects across species, and 3) reside in organisms longer than or comparable to any known class of anthropogenic contaminants (120).”

What the sources say

• Partly supported

  Split into 2 atoms — 0 confirmed, 1 partially supported, 0 disputed, 0 misattributed, 1 unverifiable. Expand the claim to see per-atom verdicts.

  cites [120] sourceExperimental — accuracy not yet measured

In the paper

“While this can be an effective short-term site-management technique, it is not a permanent solution, and likely will not retain all PFAS species effectively (148, 150, 151).”

What the sources say

• ?Not checked — no full text of the sourcecites [148] source
• Supported

  The stabilization discussion (p. 32) reports reduced leaching but identifies PFBA as an exception and says effectiveness varies by PFAS characteristics. The conclusion (p. 46) says immobilization reduces leaching without removing PFAS mass and that immobilized compounds may become bioavailable again over time. Together, these support the claim that stabilization can be useful for site management but is neither permanent nor equally effective for all PFAS. (LLM, conf=0.90)

  cites [150] source
• Partly supported

  The Abstract says stabilization can inhibit PFAS migration but does not destroy or remove PFAS. The results section (labeled “118 D” in our copy) reports substantial, but incomplete, reductions in leaching for the compounds tested. The study was limited to laboratory testing; it does not establish short-term in-situ performance, long-term permanence, or retention across all PFAS species. (LLM, conf=0.86)

  cites [151] sourceExperimental — accuracy not yet measured

In the paper

“Another approach to site management is in-situ modification to enhance mobility of PFAS for pump-and-treat application or to stabilize PFAS migration using GAC or other sorbents (e.g., clays) to limit impacts (150).”

What the sources say

• Partly supported

  Section 4.1.1 (p. 26) describes in-situ soil flushing to mobilize and extract contaminants, but does not identify pump-and-treat as the application. Section 4.2.1 describes activated carbon, including GAC, and clay-based sorbents for PFAS removal; the stabilization discussion (p. 32) reports reduced PFAS leaching with some additives. (LLM, conf=0.85)

  cites [150] sourceExperimental — accuracy not yet measured

In the paper

“Although many of these technologies have shown the ability to destroy select PFAS, none have demonstrated long-term performance approaching mineralization at full scale with natural- and industrial-water matrices for a wide assortment of PFAS.”

What the sources say

• Partly supported

  The Summary and Conclusion (section 5; page not provided) says some technologies achieve high destruction of parent PFAS, but none has shown complete mineralization at full scale under membrane-concentrate water qualities and treatment conditions. It does not establish the broader claim about long-term performance across natural- and industrial-water matrices and a wide assortment of PFAS. (LLM, conf=0.87)

  cites [149] sourceExperimental — accuracy not yet measured
• ?Not checked — no full text of the sourcecites [156] source

In the paper

“Incineration by itself has been shown to at least partially destroy even highly fluorinated wastes (143), and advanced thermal oxidation can be used on solid, liquid, and gas samples to convert PFAS to constituent gases with an acid-scrubber cleanup (152).”

What the sources say

• Partly supported

  The cited review’s “Full-scale incineration studies” section reports PFAS destruction in waste gas streams using a thermal oxidizer and four-stage scrubbing system. It does not establish that the system treats solid and liquid samples, converts PFAS specifically into constituent gases, or uses an acid scrubber. The separate incineration claim is attached to citation (143), not this source (152); page numbers are unavailable in our copy. (LLM, conf=0.85)

  cites [143] sourceExperimental — accuracy not yet measured
• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [152]

In the paper

“More than a megatonne is produced yearly and thousands of PFAS wind up in end-use products.”

In the paper

“Efforts to remediate PFAS-contaminated matrices still are in their infancy with much current research targeting drinking water.”

In the paper

“estimated cumulative global emissions of perfluoroalkyl acids summing to ≥46,000 tonnes (7)”

What the sources say

• ?Not checked — no full text of the sourcecites [7] source

In the paper

“PFAS are a class of substances within a wide universe of organofluorine compounds (8)”

What the sources say

• ?Not checked — no full text of the sourcecites [8] source

In the paper

“PFAS also have a wide range of bioaccumulation and adverse-effect concerns, governed by their varied physiochemical properties.”

In the paper

“As PFAS flow through commerce from primary manufacturer to commercial user to final disposal, environmental release occurs via both controlled and fugitive waste streams”

In the paper

“with an ever-expanding inventory of >1400 individual chemicals in the Toxic Substances Control Act Inventory and >8000 unique known structures (1)”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [1]

In the paper

“PFAS are synthesized by two processes, direct fluorination (e.g., electrochemical) and oligomerization (e.g., fluorotelomerization).”

In the paper

“Whereas some PFAS transformation pathways have been well-characterized, others degrade through yet unknown pathways”

In the paper

“In contrast, most historical work within the research community has focused on a small set of perfluoroalkyl(ether) acids and their precursors, with an emphasis on environmental and biological occurrence investigations.”

In the paper

“In both studies, enhanced degradation was attributed to the organic carbon content of the soil, as addition of carbon sources can increase microbial degradation rates through co-metabolic processes (52).”

What the sources say

• ?Not checked — no full text of the sourcecites [52] source

In the paper

“Direct fluorination is aggressive and often results in uncontrolled chemical reactions such as carbon-chain shortening and re-arrangement (17-19), leading to a wide range of byproducts including cyclic and branched isomers.”

What the sources say

• ?Not checked — no full text of the sourcecites [17] source
• ?Not checked — no full text of the sourcecites [18] source
• ?Not checked — no full text of the sourcecites [19] source

In the paper

“some conditions (e.g., within industrial stacks) can promote partitioning to air via particulate sorption, and volatile PFAS such as FTOHs can exist in the gas phase (42), making atmospheric/photochemical transformation possible.”

What the sources say

• ?Not checked — no full text of the sourcecites [42] source

In the paper

“These are high-production polymers possessing fluorinated backbones, with fluoropolymers being produced on the scale of 100s kilotonnes/year and unknown, but likely considerable, amounts for perfluoropolyethers.”

In the paper

“On average perfluorooctanoic acid (PFOA) yields from 8:2 FTOH were reported to be 25% in aerobic soils compared to <1% in anaerobic sludge (62).”

What the sources say

• ?Not checked — no full text of the sourcecites [62] source

In the paper

“Critical data gaps include PFAS identities, locations/quantities of production and processing, and final uses of products, limiting the capability to identify where environmental and human exposure occur.”

In the paper

“this complexity has not been clearly communicated with a comprehensive overview of different fluoropolymers and perfluoropolyethers on the market.”

In the paper

“Given their variety and complexity, their subsequent bioavailability and degradability are highly variable and complex, which is generally overlooked, understudied and/or unknown.”

In the paper

“While having low global-warming potentials, hydrofluoroethers and hydrofluoroolefins can ultimately degrade to highly persistent perfluorocarboxylic acids (PFCAs) such as trifluoroacetate”

What the sources say

• ?Not checked — no full text of the sourcecites [27] source

In the paper

“The fluorine in PFAS is mined from fluorite (CaF2) mineral deposits, which is digested to form hydrofluoric acid (HF) (Fig. 1).”

In the paper

“Fluorotelomers were historically produced on the order of 9 kilotonnes/year (33), with current amounts being unknown.”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [33]

In the paper

“Perfluoroalkene derivatives such as p-perfluorous nonenoxybenzene sulfonate have been produced since the 1980s; large-scale production (on the scale of kilotonnes/year) recently was initiated in China as an alternative to perfluorooctane sulfonate (PFOS) in firefighting and oil production (35).”

What the sources say

• ?Not checked — no full text of the sourcecites [35] source

In the paper

“Since the early 2000s, numerous long-chain (fluoroalkyl carbon number ≥6) PACF/PASF-based derivatives have been - and are being - phased out due to widespread concern, whereas shorter-chain PACF/PASF-based derivatives still are being produced and widely used, although in unknown amounts (15, 29).”

What the sources say

• ?Not checked — no full text of the sourcecites [15] source
• ?Not checked — no full text of the sourcecites [29] source

In the paper

“these unintentional PFAS can constitute an important part of human and environmental exposure, and merit scrutiny.”

In the paper

“In the soil-water environment, microbe-facilitated functional group biotransformation can occur aerobically (43, 44) or anaerobically (45-47), and some microbes that carry out these reactions have been identified (46, 48, 49).”

What the sources say

• ?Not checked — no full text of the sourcecites [43] source
• ?Not checked — no full text of the sourcecites [44] source
• ?Not checked — no full text of the sourcecites [45] source
• ?Not checked — no full text of the sourcecites [46] source
• ?Not checked — no full text of the sourcecites [47] source

In the paper

“degradation studies conducted under controlled conditions result in considerable variation in biotransformation potential and possibly different major stable perfluorinated degradation products when extrapolating half-lives and major products from laboratory to environmental conditions.”

In the paper

“data suggest that the presence of complex mixtures could indirectly alter biodegradation and that the presence of one PFAS may affect the transformation rate of another, although transformation kinetics of PFAS mixtures has not been reported.”

In the paper

“With long-chain PFAS preferentially adsorbing to soil phases, molecular weight can be used as an approximate indicator of relative stability amongst PFAS sharing common reaction centers (43).”

What the sources say

• ?Not checked — no full text of the sourcecites [43] source

In the paper

“in a study of soils collected from remote sites globally, all samples contained PFAS, with homologue ratios (e.g., PFOA/perfluorononanoic acid, PFOA/PFNA) consistent with atmospheric transport (79).”

What the sources say

• ?Not checked — no full text of the sourcecites [79] source

In the paper

“biodegradation studies of N-ethyl-perfluorooctanesulfonamido-ethanol in sludge reported a half-life of 0.7-4.2 days, yet the biodegradation in marine sediments was found to proceed at much slower rates (t1/2, 4 °C = 160 days and t1/2, 25 °C = 44 days)”

What the sources say

• ?Not checked — no full text of the sourcecites [66] source

In the paper

“Ferric and aluminum (oxy)hydroxides bear pH-dependent, positive surface charges below their zero-point of charge at pH~8, so these minerals can electrostatically sorb anionic PFAS.”

In the paper

“Comparing the sorption of cationic, zwitterionic and anionic PFAS showed i) concentration-dependent sorption for cationic and zwitterionic PFAS, ii) pronounced sorption hysteresis for zwitterions, and iii) major electrostatic and NOM sorption for cationic and zwitterionic PFAS (94).”

What the sources say

• ?Not checked — no full text of the sourcecites [94] source

In the paper

“Early precursor PFAS include volatile species (FTOHs and sulfonamido ethanols, Fig. 3), the presence of which has been established globally (80-82).”

What the sources say

• ?Not checked — no full text of the sourcecites [80] source
• ?Not checked — no full text of the sourcecites [81] source
• ?Not checked — no full text of the sourcecites [82] source

In the paper

“Transport of PFAS into terrestrial plants occurs via a variety of pathways, with the most studied being uptake through roots.”

In the paper

“Exploring surface-soil sorption mechanisms of two PFAS having sulfonate termini revealed an easily extractable fraction, as well as less reversibly sorbed fractions composed of i) perfluoroalkyl groups hydrophobically associating with NOM, ii) sulfonate moieties covalently binding to NOM–OH groups forming ester linkages, and iii) physical entrapment in NOM or minerals (93).”

What the sources say

• ?Not checked — no full text of the sourcecites [93] source

In the paper

“ii) shorter chains vary little amongst each other, and iii) shorter chains exceeds that of longer.”

What the sources say

• ?Not checked — no full text of the sourcecites [97] source

In the paper

“Authigenic minerals typically are abundant in the subsurface and these minerals possess surface charges for electrostatic sorption.”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [92]

In the paper

“The high NOM concentrations of surface soils typically diminish precipitously in the first several centimeters below ground surface where mineral surfaces come to dominate the vertically more-expansive subsurface realm (Fig. 4) (92).”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [92]

In the paper

“transformation rate is dependent on a number of other environmental factors including pH, temperature and microbial population (70), and these factors contribute to a wide variation of reported precursor half-lives.”

What the sources say

• ?Not checked — no full text of the sourcecites [70] source

In the paper

“It also was observed that log Kd for anionic PFAS increased with decreasing pH, a pattern consistent with increasing positive electrostatic charge on pH-dependent surfaces of (oxy)hydroxide minerals.”

What the sources say

• ?Not checked — no full text of the sourcecites [95] source

In the paper

“Bioaccumulation factors for terrestrial vegetation are greater for PFCAs than PFSAs, with shorter-chain perfluoroalkyl acids bioaccumulating to a greater degree than longer, largely driven by variation in PFAS solubility (126), followed by uptake and translocation into tissues (e.g., Fig. 4C) (100, 101).”

What the sources say

• ?Not checked — no full text of the sourcecites [126] source
• ?Not checked — no full text of the sourcecites [100] source
• ?Not checked — no full text of the sourcecites [101] source

In the paper

“Estimation of environmental exposure is hindered by the sheer number of functionally diverse PFAS and is further complicated by their presence as complex mixtures.”

In the paper

“Given travel times exceeding 24 years for flow from the landfill to the water-supply well, several PFCA homologues fell to non-detect levels, but perfluorobutanoic acid, perfluorohexanoic acid and PFOA exhibited a pattern of lower downgradient/upgradient ratios (specifically, downgradient Well 1/upgradient Well OW1f03) with increasing PFCA chain length (Fig. 4D).”

What the sources say

• ?Not checked — no full text of the sourcecites [105] source

In the paper

“Biomagnification in predators is related to trophic level, food-chain length, and capacity to metabolize PFAS precursors (125).”

What the sources say

• ?Not checked — no full text of the sourcecites [125] source

In the paper

“Long-chain PFAS concentrations tend to increase with trophic level in aquatic food webs, consistent with biomagnification processes (127).”

What the sources say

• ?Not checked — no full text of the sourcecites [127] source

In the paper

“Many existing treatment technologies are only capable of concentrating PFAS (144), and concentrated treatment residuals can result in reintroduction of PFAS into the environment (Fig 6);”

What the sources say

• ?Not checked — no full text of the sourcecites [144] source

In the paper

“For instance, unexposed progeny of fish exposed to PFOA and PFOS had lower survival rates, reduced growth, and thyroid-related effects as revealed by histology (138).”

What the sources say

• ?Not checked — no full text of the sourcecites [138] source

In the paper

“for example, treatment of drinking water can reduce human exposure at the site of treatment while also acting as a PFAS source where residuals are generated, reinforcing the need for a preventative and holistic approach (145).”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites [145]

In the paper

“For example, while PFSAs were the most abundant PFAS in both sediment and water at sites contaminated with AFFF (114), aquatic invertebrates exposed to AFFF displayed elevated concentrations of PFCAs as well as the 6:2 fluorotelomer sulfonate (114, 115).”

What the sources say

• ?Not checked — no full text of the sourcecites [114] source
• ?Not checked — no full text of the sourcecites [115] source

In the paper

“PFAS do not behave like neutral, hydrophobic organic contaminants and instead are hypothesized to involve both phospholipids and proteinaceous tissues due in part to their anionic nature (123).”

What the sources say

• ?Not checked — no full text of the sourcecites [123] source

In the paper

“Discrepancies in the relative concentrations of PFAS in fish compared to benthic invertebrates appear largely dependent on the compounds’ functional group and exposure routes, with elevated PFAS concentrations often linked to site-specific sources and/or benthic prey (131-133).”

What the sources say

• ?Not checked — no full text of the sourcecites [131] source
• ?Not checked — no full text of the sourcecites [132] source
• ?Not checked — no full text of the sourcecites [133] source

In the paper

“Current international reporting practices used to document PFAS synthesis, production volumes, and potential releases vary among countries and are not always tailored to provide the knowledge necessary to adequately track and understand the movement of these compounds in the environment.”

In the paper

“Such sequestration is a temporary solution. Since most PFAS do not naturally degrade to non-fluorinated chemical species, these long-term sinks are time-delayed sources.”

In the paper

“However, under regulatory frameworks around the world, information on many PFAS is protected as confidential-business information and will not be included in this inventory (16), thereby necessitating substantial continued discovery and forensic-identification efforts around the world.”

What the sources say

• ?Not checked — no full text of the sourcecites [16] source

In the paper

“Also, the energy costs of many of these technologies limit their sustainability and desirability, and the formation of harmful byproducts (e.g. bromate, perchlorate) remain a concern (144).”

What the sources say

• ?Not checked — no full text of the sourcecites [144] source

In the paper

“Other PFAS, such as those classified as chemical substances of unknown or variable composition, byproducts and biological materials and polymers, may be too complex to fully characterize and can challenge scientific investigation.”

In the paper

“Environmental media such as soils that can be diffusely contaminated via i) wet/dry deposition, ii) land application of PFAS-enriched materials such as biosolids, wastewater or leachate, and iii) usage of PFAS-containing products such as AFFFs and pesticides, or uncontrolled release via unlined landfills or spills (Print Fig.).”

In the paper

“However, thermal treatment requires substantial temperatures (>700 °C) for a sufficient period to convert PFAS into HF and non-fluorinated products, with more highly fluorinated species requiring more time and higher temperature (153, 154).”

What the sources say

• ?Not checked — no full text of the sourcecites [153] source
• ?Not checked — no full text of the sourcecites [154] source

In the paper

“GAC typically is reactivated and single-use resins typically are incinerated where little is known regarding PFAS fate in full-scale facilities.”