Fluorinated Surfactants and Fluorinated Polymer Materials (IV):Strategy for Solving PFOS Problems

Xing Hang, Dou Zengpei, Xiao Zibing, Xiao Jinxin

Beijing FLUOBON Surfactant Institute, China

Abstract

Key words

fluorocarbon surfactant；POPs；PFOA；bioaccumulation；toxicity；sustainability；regulation

Since perfluorooctane sulfonyl fluoride/sulfonic acid/sulfonate and related derivatives (collectively known as PFOS) were listed as persistent organic pollutants (POPs) under the “Stockholm Convention on Persistent Organic Pollutants”, the production and application of PFOS have been regulated and restricted by the international community.Researchers have put forward a variety of countermeasures, but the researchers from different departments have different strategies because of different positions and different angles.Currently, the voices of environmental scientists and toxicologists dominate the research field of PFOS, and they try to emphasize the harm of PFOS.In contrast, the voices of production and application departments are drowned out, and they can only passively accept the regulation, or even take some disreputable means to avoid the supervision.Herein, the main strategies for solving the PFOS problems will be introduced, and as surfactant workers, our viewpoint will also be put forward.

The irreplaceable properties of fluorinated alkyl groups

Now fluorinated surfactants and fluoropolymers are faced with a dilemma caused by the problem of PFOS.On the one hand, the environmental problems of PFOS call for its abandonment, at least in the eyes of environmentalists and toxicologists.On the other hand, the unparalleled performance of PFOS endows it an extremely important application value in some key fields, especially high-tech fields.The fact is, in many applications, fluorinated alkyl substances cannot be replaced currently by non-fluoroalkyl compounds.Among the known chemicals, perfluoroalkanes have the lowest surface tension (even as low as 10 mN/m) under normal environmental conditions (normal pressure and temperature).In terms of reducing the surface tension of aqueous solutions, fluorinated surfactants are the most powerful.Therefore, when low surface tension is required, the unsubstitutability of fluorinated surfactants is more obvious.One example is aqueous film-forming foam (AFFF) which is a type of fire extinguishing agent.AFFF is one of the most widely used applications of PFOS.Early known as “l(fā)ight water” brand (it means using water to extinguish oil fires), the biggest advantage of AFFF is to quickly and effectively extinguish oil fires, especially largescale oil fires.Up to now, no other fire extinguishing agent can truly replace AFFF.Based on the current knowledge, only the fluorinated surfactant can spread its aqueous solution to form aqueous film on oil surface, and no other type of surfactants has such properties.Some companies have also claimed to have developed AFFF which is “fluorinefree”, however, it is totally commercial exploitation which is impracticable in scientific principle.Moreover, some companies have lauched products of fluorine-free firefighting foams which cover the oil surface with stable thick foams without forming aqueous film, however, the actual effectiveness and efficiency are unsatisfying and such “fluorinefree” product should be questioned espescially for large-scale oil fires.Furthermore, when a large-scale oil fire occurs, other fire extinguishing agents cannot put out the fire or can put out the fire slowly, but AFFF can put out the fire quickly—So, which is more important from the viewpoint of environmental protection, to put out the fire as soon as possible, or consider the biodegradability of the fluorinated surfactant? I believe it will be wise to choose the former, which is the fundamental reason why in the “Fourteenth meeting of the POPs Review Commtitee of the Stockholm Convention” (Reference No.:POPRC-14/3), the committeesuggestthat fire fighting foam to be changed from acceptable purposes to specific exemptions (P.S.the specific exemption of PFOS in fire-fighting foams is only allowed for Class B fire).But, it can be expected that the grace period can expire in the near future.Therefore, it is necessary to consider the countermeasures of the PFOS problem, unless new evidence that PFOS is harmless occurs (The probability is very small).

To explore the degradation methods of PFOS

The most active coping strategy is to study the degradation performance of PFOS and explore degradation methods so that PFOS can still be applied.Unfortunately, “fluorophage bacteria” have not been found in nature yet, but according to the natural law of biological evolution and the philosophical views of “mutually reinforce and neutralize each other” and “There is always one thing to overcome another”, since PFOS has been detected everywhere in nature now, it can not be ruled out that with the ubiquitous presence of PFOS in nature, fluorophage bacteria may exist.Waiting for natural evolution to produce fluorophage bacteria could be a long process.Before that, researchers should actively explore synthetic or cultured “fluorophage bacteria”.

It is worth mentioning that in the literature there are examples of microbiologically catalyzed defluorination reactions[1]indeed, and there is also some evidence (though rarely) that naturally occurring defluorinating enzymes do exist.[2]These scattered research results also give us confidence.

In our previous paper[3]the biodegradation pathways of various fluoroalkyl substances have been introduced in detail.In addition to biological degradation, chemical degradation, photodegradation[4]and sonochemical degradation[5]are also important research directions.Some examples of degradation of fluoroalkyl substances are shown as follows:PFOA was degraded (98% in 28 days) in the presence of Fe (III) under sunlight；a paper suggests that photolysis of longfluorocarbon-chain perfluorinated-alkane sulfonates (PFSA) and perfluorinated-alkylcarboxylic acids (PFCA) was possible in environmental conditions；[6]in addition, PFOA has been successfully degraded to shorter PFCA and F- using a horseradish peroxidase (an iron(III) heme-centered enzyme)-catalyzed reaction with hydrogen peroxide and a co-substrate, 4-methoxyphenol；Atmospheric degradation of CnF2n+1C2H4OH (n∶2 FTOH)-derived surfactants and polymers in atmosphere-mimicking conditions has been intensely studied；[7]an “unzipping” cycle that involves fluoro-alkoxy, perfluorinated-alkyl and perfluorinated-alkyl peroxy radicals, and splitting off of COF2yields shorter fluorocarbon-chain PFCA homologues.[6]

To seek the separation and recycling method of PFOS

Recycling of chemicals is our ideal goal, but the vast majority of chemicals have not achieved this, the key of which is the cost-benefit ratio.If the cost of recycling is high, users will more choose to discard them into the environment.The synthesis of PFOS is not easy and relatively high-cost.If it can be recycled, the cost-benefit ratio can be guaranteed.Take AFFF as an example.In fact, the pollution of AFFF to the environment can be controlled to a small extent.Actual emission of PFOS from AFFF should be very small because fires are occasional, and the fire is sprayed with premix solution in which the content of PFOS is generally low (often a few tens to a few hundreds ppm).More importantly, if the fire zone is relatively small, the spray of extinguishing agent can be controlled so that it does not or less enter the biosphere.Most AFFF products are expected to be stored for a long time and need to be renewed after a certain period of time (In fact, the emission of AFFF to the environment mainly occurs in this process).What we should do is just to renew the extinguishing agent by recycling rather than emissions.For AFFF, it is possible.The key point is that it is not the fluorinated surfactants in AFFF that have changed but it is the non-fluorine components in the formulation that have become invalid.Fluorinated surfactants have high stability which, of course, causes their difficulty in biodegradation.If the fluorinated surfactant becomes invalid, the main reason is that it reacts with some components in the formula to form precipitates.For example, when anionic fluorinated surfactant is used, if there were polycations or multivalent metal ions in the formula, the formula would have a shortterm stability due to the high viscosity, but after a long time it wouldl generate insoluble precipitates, making the fluorinated surfactant ineffective.This problem is easier to be solved by adjusting the formula.Even if precipitates are formed, other components can be added to convert the precipitates into non-precipitates so that the fluorinated surfactant can be used again.The primary cause of invalidation of AFFF is that other components (foaming agents, foam stabilizers, thickeners, etc.) degrade or react during long-term storage, rather than fluorinated surfactants.Therefore, after the invalidation of AFFF, there is no need to discharge it as waste, and it may be possible to be reused by adding some components.Of course, this requires new technologies, which compels the relevant enterprises to increase technical input.Therefore, it is difficult to enforce the emission ban in reality, which leads to various problems of government regulation.

In order to enable PFOS in cycle use, the key is the separation methods.Fortunately, PFOS is relatively less water-soluble than other chemicals, e.g., potassium perfluorooctane sulfonate has a water solubility of approximately 600 mg/L (1.1 mmol/L) at room temperature, so that it can be isolated from other water-soluble chemicals in the formula, which may be useful for periodic renewal of AFFF concentrates.In fact, if we could recycle AFFF by regularly renewing it, we could solve a large part of the environmental emissions of PFOS, since AFFF is one of the major sources of PFOS emissions.

What is difficult is the separation of PFOS from wastewater.Once PFOS is emitted in the environment, the concentration of PFOS in wastewater is very low, and thus it is difficult to separate PFOS with the solubility method mentioned above.Therefore, it requires the development of better separation method at very low concentration or finding effective gathering method.With good and feasible methods, technologies for removal of per- and polyfluorinated substances (PFAS) from drinking waters can also be developed.Moreover, effective wastewater cleaning procedures can be established and PFOS can be separated in wastewater treatment plants and even recycled.

Those PFAS with poor water solubility usually have strong adsorbability.[6]PFAS, especially the long-fluorocarbon-chain (C12～15) PFCA, adsorb strongly onto suspended solid particulates and sediments.PFOA was shown to interact with soilbound proteins.PFAS adsorb to soil, sediments and sewage sludge, and subsequently release to surface and ground waters and into crops.PFCA and C8F17SO2N(CH3)CH2CH2OH (N-MeFOSE), and PFSA adsorb differentially on smaller and larger particles, respectively.PFOS may form complexes with clay through hydrogen bonds at the mineral's surface,while perfluorohexane sulfonates (PFHxS) would bind with the inner OHs.[6]Using such adsorption behavior of PFAS, it is possible to collect them by selecting appropriate adsorbents and thus recycle PFAS.At present, there is some progress in this aspect,[8-13]such as reverse osmosis and the adsorption by activated carbon, but it has not reached the level of industrial application yet.

To seek substitutes for PFOS

Seeking substitutes is the fundamental solution to the problems of PFOS.The so-called alternatives currently are merely variants of the existing commercial products, most of which are still not environmentally friendly (we hope such situation is temporary).More creative methods and technological changes are necessary.It needs to conceive, synthesize, and evaluate conceptually novel, costeffective compounds or systems with performance similar to long-fluorocarbon-chain PFAS but with shorter fluorocarbon chains (possibly multiple fluorocarbon chains) and lesser amounts of fluorine.Some commercial substitutes and corresponding enterprises are listed in Table 1.[1]

The following is a list of the main current substitutes for PFOS.

Table 1.Non-exhaustive tradenames and companies for nowadays produced replacement products of PFOS[1]

Short-fluorocarbon-chain PFAS

Current regulation considers that PFCA with fluorocarbon-chains of less than 7 carbons and PFSA of less than 6 are not bioaccumulative and have little biomagnification potential.[6]Shorter PFCA and PFSA also appear much less toxic, although the consequences of higher vapor pressure, water solubility, mobility, different partition behavior, etc.are not yet fully evaluated.Therefore, the R&D departments in the chemical processing industry for fluorinated monomers are trying to focus on the research of shorter fluoroalkyl side chains with 4 or 6 fluorocarbon atoms.The notion that the shortfluorocarbon-chain PFAS are generally effectual in spite of lesser physical performance logically raises the question whether decades of use and release to the environment of long-fluorocarbon-chain PFAS were befitting.In other words, it means that technically, at least to some extent, the use of long-chain PFAS is untenable and causes pollution.

Here are three problems:

1) The performance of short-fluorocarbon-chain PFAS.Almost all of the literature believes that the performance of C8PFAS cannot be achieved by shortfluorocarbon-chain PFAS, and the performance of short-fluorocarbon-chain PFAS products launched by some large companies are indeed inferior to those of C8products.In fact, though popular, such opinion is wrong.According to the relationship between structure and performance of surfactants, we believe that if the structures of fluorocarbon chain, linker, hydrophilic group and counterions are carefully adjusted, the PFAS with good performance can still be obtained.In this regard, the authors already have some theoretical research results[14,15]and corresponding products.[16]

2) How short the fluorocarbon chain will be suitable? A number of experiments have shown that when the fluorocarbon chain is as short as C4, basically there is no need to worry about its bioaccumulation.Therefore, C4or shorter is appropriate.As for C6, some large companies are also trying to publicize their characteristics of non-POPs.However, many studies have pointed out the POPs nature of C6products.Therefore, we believe that C6PFAS can only be used as an emergency option, and in the long run, C6is still POPs, although its POPs properties are weaker than PFOS.

3) It should be realized that short-fluorobonchain PFAS are still difficult to degrade.However, PFAS with short fluorocarbon chains (≤C4) are not POPs because they are basically nonbioaccumulative.

Products based on non-perfluorinated segments

It is also a strategy to avoid using PFOA or PFOS by replacing the perfluorinated segments with non-perfluorinated segments.Such non-perfluorinated segments mean introducing one or more heteroatoms (such as O, N, S), fluorine-free groups (such as CH2) and non-perfluorocarbon atoms (such as CFH) to the perfluorinated chains.These groups are considered as “weak points” or “biodegradable sites” which allow the fluorocarbon chain to degrade from these sites.One industrialized example is the emulsifier for emulsion polymerization of fluoroolefins such as tetrafluoroethylene, which is used to produce polymers with polyfluorinated backbone, and it requires the high level of performance that are currently only available among long-fluorocarbonchain PFAS.Historically, perfluorooctanoates (PFOA) such as ammonium perfluorooctanoate had been used.In order to circumvent the environmental issues of the historic PFOA/PFNA (perfluorononanoate)-type processing aids, ether oxygens or other “weak points” were introduced in the fluorocarbon-chain that would ensure degradability while the acid function and total number of fluorinated carbons remained essentially the same.There are mainly five types of such fluorinated surfactants reported:[1]

1) Fluorinated surfactants with terminal groups of CF3O or (CF3)2N, e.g., CF3-X-(CH2)n-SO3Na (X=O, C6H4O or N (CF3),n=8～12).

2) Fluorinated polyethers (achieved either by oligomerization of hexafluoropropylene oxide (F[CF(CF3)CF2O]nCF(CF3)CFO) or by ring opening cationic oligomerization of fluorinated oxetanes.

3) The telomers prepared from vinylidene fluoride (VDF) with 1-iodoperfluoralkanes:Rf-(CH2CF2)2-Y.

4) The radical telomers prepared from 3, 3, 3-trifluoropropene (TFP) with perfluoroalkyliodide：CnF2n+1-[CH2CH(CF3)]2-Y.

5) The radical cotelomers prepared from VDF and TFP, e.g., CnF2n+1-{(CH2CF2)n-[CH2CH(CF3)]p}x-Y.

Where Rfis CnF2n+1— (n=1～4) or (CF3)2CF—, and Y is “l(fā)inker + hydrophilic group”.

At present, there is still a lot of controversy about such substitutes,[6]especially To What Extent they can degrade.

PFAS with extra long fluorocarbon chain

Some manufacturers prefer to study PFAS with longer fluorocarbon chains, such as PFCA with fluorocarbon number greater than 7, PFSA with fluorocarbon number greater than 8, and their salts and other derivatives, especially PFAS with C10F21— and C12F25— groups.In many literatures, both extra long PFAS and short PFAS have been used as substitutes for PFOS.Short PFAS have been proved to be non-POPs, but the use of longer PFAS as substitutes for PFOS is puzzling and unreasonable.Since the performance of surfactants usually increase with the hydrophobic chain length (unless the hydrophobic chain length is too long to be dissolved, which makes the surfactant unusable), the same is true for longer PFAS.In our previous studies[17]on the interactions between surfactants and proteins, it has also been proved for many times that the interactions between surfactants and proteins are enhanced with the increase of carbon chain length.As mentioned previously,[3]the bioaccumulation and toxicity of PFAS increase with the increase of fluorocarbon chain length.Therefore, the current use of longer fluorocarbon chain PFAS is suspected of evading supervision.

For some of the PFAS with longer fluorocarbon chains, the application problems may be more complex.In the initial state they may be water soluble due to the relatively large proportion of hydrophilic part (such as increasing the number of hydrophilic group, or increase the length of EO chains), but during the degradation process their characteristics of POPs may be reduced if their hydrophilic part are biodegraded first and thus poor water soluble compounds, such as long perfluorinated alkylsulfonate/carboxylate, are produced.These insoluble long perfluorinated compounds, although are difficult to degrade, but may be difficult to enter the living body, too.After all, when it comes to the term of toxicity, it will be meaningful only when it is linked to the concentration.Therefore, it is possible that the characteristics of POPs for extra long PFAS after degradation may be reduced (of course, in most cases, living body probably ingest them before degradation).This can be understood from the example of perfluoroalkanes used as blood substitutes.Considered from this view, there is possibility for extra long fluorocarbon chain PFAS to serve as a kind of substitutes for PFOS.If the above conjecture is applied to the modification of solid surface, such as fabric finishing agent, the feasibility may be more obvious.However, the above conjecture remains to be proved.Unfortunately, the fluorocarbon chain in commercial products is usually merely one or two carbon longer than PFOS or PFOA.

In recent years, the application of longfluorocarbon-chain PFAS has increased rapidly, resulting in a significant increase in environmental emissions.The very persistent higher PFCA are also commonly found in human sera.C7～11and C13PFCA and (CnF2n+1C2H4O)2P (O) OH (n=4～8) were found in most inhabitants of two German cities, as well as C4～10PFAS and a wide range of their precursors.Increasing concentrations of PFNA likely indicates indirect exposure via biotransformation of FTOHbased substances.[6]

Products of telomerization

Products of telomerization mainly refer to PFAS prepared with CnF2n+1(CH2CH2)mI or CnF2n+1(CH2CH2)mOH as raw materials.The most common ones aren=8 andm=1.Since the degradation products of such PFAS are carboxylates, they do not belong to PFOS according to the definition of PFOS, so many people regard them as substitutes for PFOS, which has caused great controversy in recent years.

At present, “Stockholm Convention” mainly limits and prohibits PFOS which are mainly produced by electrochemical fluorination, and it has not yet made clear provisions on the products of telomerization.Many manufacturers regard their products of telomerization prepared from CnF2n+1(CH2CH2)mI and CnF2n+1(CH2CH2)mOH as substitutes for PFOS because the degradation products of such PFAS are carboxylates while perfluorinated carboxylates exhibit weaker characteristics of POPs than perfluorinated alkane sulfonates.At present, the fluorinated surfactants synthesized from CnF2n+1(CH2)mI withn≥8 definitely have the characteristics of POPs (In the case ofn=8, they belong to C8).Therefore, at least such products ofn=8 should not be used as substitutes for PFOS.

As a strategy to cope with the PFOS problem, the manufacturers of telomers have launched several series ofn=6 PFAS (C6).C6still has the characteristics of POPs though weaker than C8.Therefore, the promotion of C6as an environmentally friendly alternative to PFOS is not tenable.The fluorinated surfactants with long fluorocarbon chains available on the market, either produced by oligomerization or telomerization, can only be considered as a loophole of the “Stockholm Convention”, which is not in line with the environmental protection spirit of the convention.It can be expected that after the complete ban of PFOS, it is probable to turn to the fluorinated surfactants with fluorocarbon chain length of C6.So this is only temporary.The ultimate strategy is to develop fluorinated surfactants based on C4or even less.As mentioned above, when the number of fluorocarbons is equal to 4, the harm is basically negligible.

As mentioned above, it can be seen that some of these substitutes are correct, while others play edge ball by using the loophole in the PFOS definition.

Products with branched fluorocarbon chain

This plan is just an idea.Biomonitoring of PFCA and PFSA in human urine indicated that major branched PFOA and PFOS isomers may be excreted faster than the linear one (although one PFOS isomer had an estimated 90-year half-life).[6]This may provide enlightenment for the selection of PFOS substitutes.However, branched isomers appear to cross the placenta more efficiently than linear ones；in addition, fluorocarbon-chain branching tends also to decrease fluorinated surfactant efficiency and aptitude to organize in compact films on surfaces.[6]Even if the gains in terms of bioaccumulation, excretion rate and toxicity were significant, and functional efficacy comparable, cost-effective largescale separation of specific PFAS isomers does not seem realistic.

Reducing the concentration of PFOS

Currently, the “Stockholm Convention” is not a complete ban on PFOS, and instead, it merely limits the usage amount in most areas.In the “European Parliament Moves to Restrict Perfluorooctane Sulfonates (PFOS)” on October 25, 2006, the limit for PFOS is as follows:Placing on the market and use is allowed in concentrations of PFOS equal to or below 0.005% when it occurs in substances or in preparations；concentrations of PFOS in semi-finished products or articles, or parts thereof is allowed, if the concentration of PFOS is lower than 0.1% by weight calculated with reference to the mass of structurally or micro-structurally distinct parts that contain PFOS or, for textiles or other coated materials, if the amount of PFOS is lower than 1 μg/m2of the coated material.[9]In summary, if the concentration of PFOS can be reduced below the prescribed limit, PFOS can still be used.On the premise of maintaining the product performance, to reduce the amount of PFOS, one can improve the performance of the surfactant itself, mix with other surfactants, and improve the formula by adding other additives.The specific methods to reduce the concentration of PFOS are discussed below.

Synthesis of fluorinated surfactants with high performance

The performance of fluorinated surfactants are usually a result of the balance between fluorocarbon chains, linkers, and hydrophilic groups (and sometimes counterions).Even with the same fluorocarbon chain of the same carbon number, the difference in the linker or hydrophilic group can make big difference in performance.Therefore, through indepth study of the relationship between structure and performance of fluorinated surfactants, high-performance fluorinated surfactants can be obtained by changing the structure of linking group, hydrophilic group and even counterion, so as to achieve the ideal performance at a lower concentration.Here are two examples.Ammonium perfluorooctanoate has higher surface activity than sodium perfluorooctanoate, while C4F9SO2NH(CH2)3N+H(CH3)2Cl-has higher surface activity than sodium perfluorobutane sulfonate.Another example is fluorine-containing fabric finishing agents (water- and oil-repellents).[18]Changing the structure of the linking groups, hydrocarbon alkyl groups and other groups in the molecules while maintaining the fluoroalkyl groups (such as C8F17—) unchanged can also lead to significant differences in performance.There have been a lot of mature experience on the relationship between structure and performance for common surfactants.[19]However, the literature works on fluorinated surfactants in this area are few, and more research is needed.On the other hand, it also provides big research space for workers and reseachers of fluorinated surfactants.

It should be pointed out that the improvement of the performance of fluorinated surfactants is also a double-edged sword, and the damage to the environment and animals caused by the structural changes of the compounds needs to be further evaluated.

Formulating the mixtures of fluorinated surfactants and hydrocarbon surfactants

According to the principles of formulating surfactant mixtures, PFOS can be mixed with other surfactants, which can greatly reduce the amount of fluorinated surfactants and reduce the cost.If the concentration is lower than the required limit, the restriction from “Stockholm Convention” can be avoided.In addition, the combination of hydrocarbon surfactants in the formula may bring other benefits in many cases, e.g., the addition of hydrocarbon surfactants can reduce the oil-water interfacial tension.

Among all the mixed systems, the mixture of cationic-anionic surfactants has the strongest synergistic effect.Some of the mixtures of cationicanionic hydrogenated-fluorinated surfactants can not only significantly reduce the amount of fluorinated surfactant, but also significantly improve the performance of the fluorinated surfactant.There have been a lot of fundamental research and practical applications in this field.One example is the mixture of F[CF(CF3)CF2O]2CF(CF3)COONa and CnH2n+1N (CH3)3Br (n=8,10,12).[20]

Optimization of the formulas

Fluorinated surfactants are rarely used alone.A terminal product formulation often contains hydrocarbon surfactants that are compatible with fluorinated surfactants, as well as a variety of additives, the selection of which has a significant impact on the performance of the product.Take AFFF as example,[21]in addition to the key components such as fluorinated surfactants and hydrocarbon surfactants, the formula also contains foaming agent, foam stabilizer, burnback resistant, thickening agent, chelating agent, metal corrosion inhibitor and organic solvents and other additives, which greatly influence the performance of AFFF.By choosing suitable additives, the purpose of reducing the dosage of fluorinated surfactants can be achieved.

The wrong coping strategies

Avoidance of supervision is the wrong strategy to solve the problem of PFOS.In the situation of the limitation of PFOS under the “Stockholm Convention”, many manufacturers and users take a variety of legal but unreasonable means to elude regulation, for example, the fractionation of use among many, often undisclosed PFAS or mixtures thereof；reducing tonnages used in a given location below analytical “visibility” or below certain regulatory thresholds (e.g.the 100 tons limit that requires data on bioaccumulation for REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) authorization)；multiplication of components in a technical product；formally changing categories (e.g.from polyether to polymer) for certain compounds.All these countermeasures can be used to elude regulation.

For lack of information, some PFAS have remained unnoticed while already in use for 30 years.Some rules do not apply to imported finished goods.While direct emissions of regulated substances decrease, emissions of these substances through production and degradation of precursors continue.

Summary

While waiting for (exclusively) biodegradation to cleanup the mess, more responsible use of PFAS would appear wise.Responsible conduct commands that long-fluorocarbon-chain compounds use be restricted to applications for which societal benefit/risk ratio is clearly proven, such as those related to safety, health, energy and high technology devices and recycled uses.All uses do obviously not simultaneously require the full set of extreme properties only provided by long-fluorocarbonchain compounds.Optimization of fluorine content/performance/need for performance has to be considered systematically.Of course, liberal use of high tonnages of the shorter-fluorocarbon-chain compounds should not be granted.High tonnage convenience applications should preferably be left to non-fluorinated products (provided they are less persistent and safe).Risk versus benefit to society (e.g.safety, energy and raw material savings) needs to be evaluated for each high tonnage application.The risk associated with any countermeasure needs also to be taken into consideration.These are hard works but must be done.