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More environmentally friendly alternatives to PFOS-compounds and PFOA

8 Discussion and conclusions

• 8.1 Discussion of the different use areas for PFOS-related compounds
• 8.2 Discussion of the use of PFOA and salts
• 8.3 Release to the Environment
• 8.4 Health and environmental aspects of PFOS, PFOA and other polyfluorinated substances
• 8.5 Health and environmental aspects of the identified non-polyfluorinated alternatives
  • 8.5.1 Environmental effects
  • 8.5.2 Health effects
• 8.6 Conclusions

Different reports have recently mapped the use of PFOS-related compounds in Europe and in the particular countries. These are:

• Risk reduction strategy for PFOS, prepared for DEFRA, UK by RPA (RPA 2004).
• Strategy for reduction for PFOS-related compounds, Kemikalieinspektionen, Sweden (Kemikalieinspektionen 2004).
• Mass flow analyses of use of PFAS substances in products in Norway, Norwegian Pollution Control Authority (Statens Forureningstilsyn 2004).
• Survey of PFOS and similar substances in consumer products in Denmark, prepared for Danish EPA, Denmark (Havelund 2002).
• Perfluoroalkylated substances, RIKZ, Holland (Hekster et al. 2002).

Our survey of the use of PFOS- and PFOA-related substances and its alternatives is based on information in the reports mentioned above and on additional information mainly gathered during the project period by searching databases, contacting individuals and companies, mainly Danish. Our survey is described in Chapter 4 and summarised in Table 8.1:

Table 8.1: Summary of the use areas of PFOS and related substances and their alternatives.

The overall picture is that the formerly most used PFOS-related substances in general have been phased out and substituted with other fluorinated surfactants, such as C₆-fluorotelomer-based products or short-chained perfluorinated compounds like PFBS (perfluorobutane sulfonate).

The reason for this continuous use of fluorinated compounds is that polyfluorinated surfactants have superior properties compared to other and less expensive surfactants.

8.1 Discussion of the different use areas for PFOS-related compounds

Today, the former major use areas for PFOS-related compounds like impregnation of textiles, leather and carpets as well as impregnation of paper and cardboard seem to be more or less historical as other alternatives are in use today. The Danish survey from 2002 does, however, register use of PFOS-related substances for the impregnation area. This may be explained by the fact that the Danish survey is older than the Swedish and UK surveys. Therefore, the use of PFOS-related compounds in impregnating agents in Denmark may already be historical or the use can be assumed to disappear in the near future. The substances used instead of the PFOS-related compounds for impregnation products seem to be other highly fluorinated compounds like PFBS or telomer-based polymers. Silicone based products have also been mentioned as alternatives to PFOS-related compounds. For impregnation of paper and cardboard the Norwegian survey claims that other highly fluorinated compounds are not used instead, as all PFAS-based products seem to have gone out of use. However, telomer-based substances are used as alternatives, as stated by DuPont.

Cleaning agents have been one of the larger use areas for PFOS-related compounds, but this is an area, where the use of PFOS-related substances seems to be more or less historical. The Norwegian survey states that in some specific cleaning products for cleaning of glass PFAS-substances are still used. The Danish survey has registered a use of PFOS-related substances for cleaning agents, but also states that substitution has taken place within cleaning products for industrial use. As the Danish survey is older than the other surveys, the use of PFOS-related compounds in cleaning agents in Denmark may also already be historical or the use can be assumed to disappear in the near future. None of the surveys have identified, which alternative compounds that are used instead of PFOS or PFAS-based compounds, but the alternatives may be non-PFAS-based products as the Norwegian survey has examined the use of all PFAS-based products.

Waxes and floor polishes have been and still are one of the larger use areas for PFOS-related compounds. Some substitution has been carried out, where fluorinated compounds of lower chain length have been used, e.g. C₄-perfluorinated compounds, fluorotelomer-based substances or fluorinated polyethers have been used. In some waxes and floor polishes PFAS compounds are still used. In fact, PFOS-related surfactants are still today allowed in small concentrations in the Swan eco-labelled film-forming floor care products. The argument is that these surfactants are difficult to replace.

The paint and varnish area has formerly been one of the major use areas for PFOS-related compounds. Even though the Danish survey has identified a large use of PFOS-related compounds in paint, ink and varnish products, the survey also states that the substitution of PFOS-compounds by and large has been carried out in Denmark. This is in line with the other surveys that also claim that the paint and varnish industry no longer uses PFOS-related compounds. The substances used instead are other highly fluorinated compounds with shorter chain length (like PFBS), telomer-based substances or non-fluorinated compounds such as propylated aromatics, aliphatic alcohols, silicones or sulfosuccinates. According to the information received it may be difficult in short term to avoid fluorinated surfactants for very special purposes, where an extreme low surface tension is needed. In other cases other non-fluorinated surfactants may do the job, but reformulation of the products may be necessary.

Fire-fighting foams have been one of the quantitatively smaller use areas of PFOS-related compounds but a use area with a high risk for environmental exposure. Today, the fire-fighting foams on the market are PFOS-free, and have been replaced by fluorotelomers, predominantly C₆-telomers. However, information received indicates that fluoroalkyl compounds of higher chain length also occur as impurities in the fire-fighting foams. As fire-fighting foams have a long shelf life, there may still be foams in stock, which are based on PFOS-compounds. However, an important factor within this area is that many fire-fighting foam users are using fluorine-free synthetic foams or protein foams for training exercises.

The photographic industry is one of the smaller use areas of PFOS-related compounds. A shift to digital techniques has reduced the use of PFOS-related compounds drastically (with about 80%), but for the remaining uses no alternatives have been identified so far. The alternatives that have replaced the PFOS-related compounds are fluorotelomers based products (C₃ or C₄) and non-fluorinated compounds like hydrocarbon surfactants and silicone products.

Manufacturing of semiconductors is also one of the smaller use areas of PFOS-related compounds. PFOS-related compounds are still being used, but new techniques are being developed within this field that do not require PFOS-related compounds. However, it may take up to 5 years before these PFOS-free techniques are ready for commercial use.

Hydraulic oils for the airplane industry are also one of the smaller areas, where PFAS-related compounds are still being used, as fluorotelomers have been tested as alternatives, but cannot be used. PFAS-free alternatives are not yet available and it may take up to ten years before a PFAS-free solution has been found.

Metal surface treatment – especially chromium plating and chromating – covers some of the larger use areas of PFOS-related compounds. For some purposes – decorative chromium plating – solutions that do not require PFOS-compounds have been identified, but for chromating and hard chromium plating the industry is still working on alternatives.

Plumbing is one of the minor use areas of PFOS-related compounds. PFOS-related compounds are being used in fluxing agents in the process of plumbing with leaded soldering tin. However, as lead is being phased-out in electrical and electronic equipment from 2006, this will automatically end the use of PFOS-related compounds.

Today the largest use areas of PFOS-based compounds therefore seem to be:

• Cleaning agents for glass cleaning
• Waxes and floor polishes
• Photographic industry
• Manufacturing of semiconductors
• Metal surface treatment

For manufacturing of semiconductors no PFOS-free techniques are available yet and PFOS-free solutions do not seem to be found in the near future. The PFOS-related compounds are not found in the semiconductor products, but are only used as processing chemicals, which means that the spreading of PFOS-based chemicals within this area is more controllable. The same can be concluded for the use of PFOS-related chemicals within metal surface treatment and the photographic industry. The PFOS-related compounds will not be a part of the end product, for which reason the emission of PFOS-related chemicals to the environment to some extent can be controlled.

In contrast, the PFOS-related chemicals are ingredients of the cleaning agents, the waxes and the floor polishes. In these specific use areas the emission of PFOS-related chemicals to the environment is much more diffuse and much more difficult to control.

As most of the cleaning agent area today are PFOS-free, the most important area with respect to emission of PFOS-related compounds today seems to be the use area of waxes and floor polishes.

8.2 Discussion of the use of PFOA and salts

PFOA and its salts are used as a processing aid in the manufacture of fluoropolymers such as polytetrafluoroethylene, a process not occurring in Denmark.

DuPont has for the last 30 years investigated possible alternatives to PFOA as processing aid in the production of fluoropolymers. Several fluorohydrocarbons have been tested, but the results showed that the presence of hydrogen in the surfactant resulted in problems with the polymerisation. Supercritical carbon dioxide as reaction medium has also been tested in a pilot-scale facility. However, DuPont does not expect that this process will ever evolve into a technology that would have the capability to totally replace the current water-based polymerisation process. The conclusion so far from testing over the last 30 years is that there are no viable alternatives to PFOA.

In Denmark only the ammonium salt of PFOA is found in very small quantities in a few products. Other PFOA-related substances were not found via a search in the Danish Product Register.

The PFOA ammonium salt was registered for fluxing agents (used in plumbing) and in a primer and topcoat used for fluoroplastic coating. The use in fluxing agents is very limited and will cease, when leaded plumbing are banned from the year 2006, as lead-free plumbing does not require the use of these fluxing agents.

8.3 Release to the Environment

Emissions to the environment (air, soil and water) of PFOS-related and other perfluorinated substances may happen directly from the production and processing plants. However, most important is releases during use (indoor or outdoor) and disposal of products containing these substances. Environmental sources of fluorinated telomers are currently unknown but these substances may be released at manufacturing of perfluorinated compounds and at the decomposition of polymeric materials and consumer products that incorporate telomers.

PFOS-related chemicals are not the only environmental problem. Other PFAS-based chemicals such as PFHxS and PFBS with shorter chain length and perfluorinated carboxylic acids (PFCA) including PFOA are also found in the environment. Furthermore, the fluorotelomers, which in some cases are used as alternatives to PFOS-based compounds are also found in the environment and they seem to be long-range transported and degraded to PFOA and other PFCAs in the environment

Impregnation products, fire-fighting foams, the photographic industry and hydraulic oils within the airplane industry are still use areas that contribute to the total PFOS/PFOA concentration in the environment as these uses predominantly seem to use fluorotelomers or PFAS compounds with shorter chain length (like PFBS) as alternatives to the former PFOS-compounds. However, the photographic industry does not seem to be the biggest problem, as this industry represents a smaller use area, and as the PFAS compounds are not a part of the final products. No information has been found on the size of the hydraulic oil use area. However, this area is not expected to be that large.

The PFAS emissions from the photographic industry are more controllable compared to the diffuse emissions that the fire-fighting foams, the impregnating products and the hydraulic oils represent. The fire-fighting foams represent a huge leak to the environment during use. With regard to the hydraulic oils, most of the oils can be assumed to be collected at regular check-ups and repairs, but some of the oil may also be leaked to the environment by accident.

The use of impregnation agents to protect domestic products such as clothes and carpets may also be one of the most important exposure ways for the human population. Measurements have confirmed that PFOA and PFOS can be found in vacuum cleaner dust in private households. The most important human exposure may be through inhalation of air and the dust in private homes and offices.

On the other hand, fire-fighting foams represent the area where there is the largest risk of a huge leak directly to the environment. Studies have shown that the fluorinated surfactants used in fire-fighting foams and their degradation products may occur in ground water and surface waters five or more years after its last known use. It is important to notice that fire-fighting foams made from fluorinated surfactants is the only technology, which can quickly and effectively extinguish fires from highly combustible and flammable materials like oils and gasoline. Therefore, the only real alternative to the PFOS-based fire-fighting foams is the other fluorosurfactants. However, a shift to the non-fluorinated training foams is a way forward to avoid unnecessary emissions to the environment of the fluorinated compounds.

8.4 Health and environmental aspects of PFOS, PFOA and other polyfluorinated substances

Perfluoroalkylated substances are present in the environment primarily in the form of the most stable PFOS and PFOA, which are the final degradation products of various perfluorooctyl compounds. Recently, when the many PFOS uses have been phased out, the environmental concentrations of other related substances such as PFBS, PFHxS and PFNA have been increasing. PFOS, PFOA and other polyfluorinated compounds are now considered as global environmental contaminants. They have been found in indoor air, outdoor air, soil, ground water, surface waters and even at 1000 m depth in the Pacific Ocean. Perfluorinated compounds are widely distributed in wildlife. PFOS has been detected in blood and liver samples from various species of aquatic animals (seal, otter, sea lion, dolphin, polar bear, mink), birds, fish and amphibians. Some samples also contained other related substances such as PFOSA, PFHxS, PFNA and PFOA.

Some perfluorinated substances have even been found in blood and liver samples from the general human population. Whereas PFOS and PFOA and perfluorinated acids with longer alkyl chain are considered to be bioaccumulative in wildlife and human tissues, perfluorinated acids with fully fluorinated chain lengths of C₅ and below do not seem to accumulate significantly.

The occurrence of PFOS and PFOA in the wildlife in remote areas such as the Arctic is puzzling. The binding to water and the low volatility make it less likely that PFOS and PFOA will be spread long-range with the air by the "grass-hopping" and cold condensation mechanisms as persistent organic pollutants (POPs). However, the prevailing hypothesis is that long-range transport to the arctic occurs via volatile precursors of both PFOS and PFOA, with subsequent degradation to these stable products. Volatile PFOS-precursors are a.o. MeFOSE and EtFOSE. It has been hypothesized that fluorotelomer alcohols (FTOH) may be long-range transported and hereby reach remote arctic areas, where they can degrade to the more stable PFOA. Atmospheric lifetime of short chain FTOHs, as determined with its reaction with OH-radicals, is approximately 20 days making the molecule able to travel about 7000 km. Therefore, they may be long-range transported and hereby reach remote areas, where they can degrade to PFOA.

On the other hand products containing perfluorinated substances may also be used for example in fire-fighting foam at bases in remote areas. Recently a hypothesis has also been brought forward that ocean current transport may in part explain the presence of PFOS and PFOA in the arctic.

Studies show that PFOS and other perfluorinated chemicals are readily absorbed in the body. Both PFOA and PFOS are considered to be metabolically inert, and other perfluorocarboxylic acids and perfluorosulfonic acids do have similar properties, which means that their functional derivatives may be transformed to the parent compound. For example, the fluorotelomer alcohol 8:2 FTOH is transformed to PFOA in rats.

Once absorbed in the body, PFOA and PFOS may bind to proteins and may accumulate in various body tissues, including blood and liver; for PFOS also in testis and brain. The half-life of PFOA is about 2-4 years in humans and 1 month in monkeys. The half-life of PFOS is longer than for PFOA – about 200 days in monkeys. The half-life in humans was not found.

The acute lethal toxicities of PFOS and PFOA are moderate corresponding to a classification as harmful, if swallowed. PFOS is more toxic than PFOA, and the toxicity of related substances increases with the length of the alkyl chain.

The liver is the primary target organ for perfluorinated compounds, and these chemicals cause peroxisome proliferation in the rodent liver as well as induction of various enzymes involved in lipid metabolism. PFOS seems to be more active than PFOA concerning this effect but again PFDA with a longer alkyl chain is even more active. Toxic effects have been reported, such as induction of fatty liver and uncoupling of the mitochondrial respiratory chain. PFOA also affects the serum levels of various hormones, i.e. reducing testosterone and increasing estradiol in rats. Thus, it is considered an endocrine disruptor.

Although the fluorinated chemicals do not seem to be mutagenic, PFOA has induced testis cancer, and PFOS and EtFOSE have induced liver cancer in experimental animals. USEPA classifies PFOA as a carcinogen in animals.

PFOS and PFOA cause developmental effects, including reduction of foetal weight, cleft palate, oedema, delayed ossification of bones, and cardiac abnormalities. However, the structural abnormalities were only found in the highest PFOS dose groups, where significant reductions of weight gain and food consumption were also observed in the pregnant dams. Thus the relevance may be questioned. Other tested PFAS (PFBS and PFHxS) had no significant effect on reproduction even at high doses.

In general, the information in open literature about the toxicology of the perfluorinated compounds is rather sparse, and it will take some time and efforts, before sufficient information for evaluation of the full impact of the present levels in humans is available. The experience from the work environment has not indicated any important adverse health effects among exposed workers, besides a retrospective cohort mortality study of a perfluorooctanesulfonyl fluoride (PFOSF) production workforce, which reported an excess of bladder cancer at high-exposure jobs.

With respect to aquatic toxicity PFOS is considered to be moderately acute toxic and slightly chronically toxic to aquatic organisms. PFOA is practically non-toxic. EtFOSA is slightly acute toxic to daphnids. There seems to be large species difference in the biological response, because PFOS was three orders of magnitude more toxic to the aquatic midge Chironomus tentans than to most other aquatic organisms. The scarce database indicates a need for further studies.

8.5 Health and environmental aspects of the identified non-polyfluorinated alternatives

Not many alternatives to perfluorinated compounds have been identified during this project. The same was the case in the different surveys from Holland, the UK, Norway and Sweden, which also have investigated this subject. The mentioned alternatives were primarily silicone-based products or hydrocarbon based surfactants.

The area, where most non-fluorinated alternatives were identified within this project, was the paint and varnish area. In this area silicone-based products and hydrocarbon surfactants (such as aliphatic alcohols, sulfosuccinates, and propylated aromatics) are also used as alternatives, but in general it seems that these alternatives cannot be used, where extreme demands regarding low surface tension are needed. In these cases fluorinated surfactants seem to be the only substances that can reach the very low surface tension levels.

These specific alternatives have been investigated closer for their environmental and health effects, but in general very little information about the specific products was available. Most information was found in the material safety data sheets for the specific substances, supplemented with very few data from different search databases as Toxnet, HSDB, ECOTOX and Chemfate.

As no alternative for PFOA is found, it is impossible to review the health and environmental aspects of these substances. However, PFOA use is mainly limited to be a polymerisation aid for fluoropolymers.

8.5.1 Environmental effects

In general the alternative hydrocarbon surfactants seem to be readily biodegradable. The fatty alcohol polyglycolether sulfate is readily biodegradable and does not seem to be toxic to aquatic organisms. The sulfosuccinates are likewise easily biodegradable, do not seem to bioconcentrate, but are harmful to aquatic organisms. The biphenyls and the naphthalene derivatives are potentially bioaccumulative. The biphenyl moiety seems to be easily biodegradable, whereas the naphthalene moiety only slowly biodegrades. The sparse information suggests that the biphenyls are acutely toxic to aquatic organisms, whereas the naphthalene has no acute toxic effects in the investigated fish species.

Of the investigated alternatives, the silicone polymers seem to have the most adverse environmental effects. The specific compound investigated is classified as environmentally dangerous (R51/53 "Toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment"), as the substance is toxic to aquatic organisms and is bioaccumulative.

8.5.2 Health effects

In general very sparse information about the health effects of the alternative substances is found. Therefore, most of the information is based on the material safety data sheets.

The fatty alcohol polyglycolether sulfate is acutely toxic by ingestion but is not considered to be irritating.

The sulfosuccinates are irritants to eyes, skin and the respiratory system. Dermatitis has been observed as a long-term effect as well as CNS depression. The substance is mildly harmful to toxic, if swallowed.

The naphthalene- and biphenyl compounds are irritating substances, and the biphenyl compounds may produce skin sensitisation or dermatitis. Furthermore, one of the biphenyl compounds is known to cause CNS damage as well as liver and kidney damage. The parent compound naphthalene is classified as possible carcinogenic in humans (IARC Group 2B). However, no carcinogenicity has been identified for the specific naphthalene derivatives used as alternatives to perfluorinated compounds.

The silicone polymers are irritating substances and are harmful by inhalation.

8.6 Conclusions

The results of the different surveys of PFOS and other perfluoroalkylated compounds indicate that the former, and for some areas present, use of these substances has generated a global environmental contamination problem. A recent Nordic screening investigation has shown that the pollution in Denmark with these chemicals seems to be comparable with other industrialised countries but more studies are needed to really describe the situation and trends.

In most of these areas the industry is trying to find suitable alternatives. For some major use areas PFOS-related substances have already been substituted and diminished the problems. Today, PFOS-related substances are primarily used in areas, where it has not been possible yet, clearly to identify alternatives to the PFOS-related substances.

The environmental assessments of the non-fluorinated alternatives show that in most cases these alternatives are not of a similar environmental concern as they are easily biodegradable. However, the silicone polymers may be more problematic as they are persistent, bioaccumulative and at the same time are toxic to aquatic organisms.

The survey of the use of PFAS-related substances shows that it is possible to reduce the use by simple means. The use of non-fluorinated fire-fighting foams for training purposes is a good example of, how it is easily possible to eliminate unnecessary use of fluorinated surfactants. However, some fire-fighting facilities are still using fluorinated fire-fighting foams for both training exercises and "real fire" situations. Furthermore, it is likely that many of the facilities using fire-fighting foams may have stocks of earlier generation of fire-fighting foams still being used.

Although the use of PFOS-related substances has been reduced, the use of other perfluorinated substances is still considerable, as the PFOS-related chemicals in many cases have been replaced with other perfluorinated compounds with shorter chain length like PFBS or telomer-based substances with an alkyl chain length of C₆ or below. Furthermore, the used telomers are not limited to C₆-compounds, as the telomerisation process yields a mixture of fluorotelomers with different chain length. Therefore products based on fluorotelomer compounds also contain some compounds with longer chains, even though the telomer mixture predominantly is based on C₆. The large use of C₆-telomers in products like fire-fighting foams and impregnating agents may still be an environmental problem.

A shift to telomer compounds instead of perfluoroalkylated substances (PFAS) does not eliminate the problems with PFAS, but only reduces the problem, as PFAS may still be formed in the environment due to the part of the telomers containing the longer than C₆-chain lengths.

Even though the short-chained fluorinated compounds (of an alkyl chain length of C₅ or less) have been identified as less bioaccumulative and toxic, they are still substances that will persist in the environment for decades. The toxicity and ecotoxicity of the shorter chained fluorinated compounds are yet to be examined, and many studies are underway. Nevertheless, the implications for human health and the environment are unclear, and if adverse effects are discovered in the future, it will not be possible to "call back" the already emitted substances.

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Version 1.0 June 2005, © Danish Environmental Protection Agency