Summary and conclusions

Survey and environmental/health assessment of fluorinated substances in impregnated consumer products and impregnating agents

Background

During the past years increased awareness has arisen on a new type of persistent organic pollutants, which contains an alkyl chain typically between 4 and 12 carbon atoms, where all or most of the hydrogen atoms have been replaced by fluorine. This makes the chain very stable and practically non-degradable in the environment. The substances also contain a more reactive functional group, which may be an alcohol, a carboxylic acid, a sulfonic acid, a phosphoric acid or their derivatives.

Several hundreds of these per- or polyfluorinated^[1] compounds (PFCs) are known today. These substances are all surface active substances with an extreme low surface tension, and they repel water, grease and dirt, and are therefore used as detergents or impregnating agents in numerous industrial products and consumer products under trade names like Scotchgard^®, Baygard^®, Gore-Tex^®, Zonyl^® and Stainmaster^®.

A couple of years ago the main focus was on PFOS (perfluorooctane sulfonate) and PFOA (perfluorooctanoic acid) and related compounds, as these compounds have been found to be widespread in all environmental compartments in both industrial and remote sites such as the Arctic areas. Today this use has, however, shifted towards either perfluorinated substances with a shorter chain length (C₆ or shorter) or other classes of polyfluorinated substances such as fluorotelomer alcohols (FTOH).

The purpose of this project is to estimate the use of polyfluorinated compounds in impregnation and consumer products in Denmark, and to perform an update of the environmental and health assessment of polyfluorinated substances and their degradation products carried out previously for the Danish Environmental Protection Agency (Poulsen et al. 2005).

Estimation of consumption in Denmark

A search was carried out in the Danish Product Register to determine the registered use of fluorinated substances in consumer products in Denmark. The search was based on OECDs Preliminary 2006-list of about thousands PFCs. In total 92 fluorinated substances were identified, of which 48 substances were registered with a use of 0.00 tonnes meaning either a very low consumption or that a use amount had not been registered, as it should have been done. About 7.5 tonnes of the total 16.5 tonnes registered in the Danish Product Register count for substances that have a chain length lower than 8.

The most important use areas were: releasing agents, paint and lacquers, glue, surface active substances and galvano-technical products, which accounted for about 15 tonnes of the 16.5 tonnes in use in 2007. The consumption in the areas: polish and care products, impregnating agents, cleaning agents and surface active substances (non-metal, e.g. for paper and cardboard) accounted for about 0.5 tonnes (of the last 1.5 tonnes). These uses are, however, most likely much greater, because the Danish Product Register does not register all products containing fluorinated compounds on the Danish market but only chemical products for occupational use containing dangerous substances in a concentration of at least 0.1% or 1% (depending on the classification of the substances) . Therefore, the registered amounts will not give an adequate picture of the total sales in Denmark. In addition, contents of fluorinated compounds in imported finished consumer articles, such as all-weather clothes, are not registered at all. The products registered in the Danish Product Register may, however, afterwards be used for production of consumer articles.

Residues of PFOA in finished products, which are typically between 0.1 and 1% of the total content of fluorinated substances, are neither registered.

As a supplement to the search in the Danish Product Register, information was obtained on the content of fluorinated substances in various consumer products from Internet searches, the literature and from the official Danish statistics.

Several companies in Denmark as well as foreign producers/suppliers of fluorinated substances were also contacted in order to obtain information for developing an estimate of the consumption of fluorinated chemicals in consumer products in Denmark. This approach was, however, unsuccessful because most companies either could not provide any available information about these chemicals or would not participate with information to the project.

Based on all information the annual consumption of fluorinated substances in consumer products in Denmark was estimated to between 14 tonnes and more than 38 tonnes.

Environmental fate and levels

Concentrations of various PFCs have been extensively reported for all environmental compartments all over the world. Most studies have been performed on the North American continent, in Europe and in Japan. The number of compounds analyzed has been extended to a large series of perfluorinated carboxylates with carbon number from 7 to 16. Besides PFOS, the list of sulfonates has been extended to compounds with 7, 9 or 10 carbon atoms. The attention has also been focused on the precursor and intermediates of the more persistent PFOS and PFCAs (perfluorocarboxylic acids). The rest of the chemicals may, however, have a potential to degrade to PFOA or other PFCAs in the environment. The exact amount is not known, as this would require detailed knowledge of the fluorinated substances used, as only specific types of fluorinated substances can be degraded to PFOS, PFOA or other PFCAs in the environment.

Several studies performed with the volatile precursor compounds in smog chambers have found that FTOHs and perfluorosulfonamides react in the atmosphere with OH-radicals to yield the acidic compounds. The reaction time is long enough (about 20 days) for these compounds to be transported to remote regions, where deposition and further bioaccumulation in the food chain occurs. The “precursor” theory for explaining the presence of PFCs in remote regions (e.g. the Arctic) has been supported by atmospheric measurements of FTOHs and perfluoroalkylsulfonamides in both industrial and remote regions. Atmospheric concentrations were higher close to sources, but these compounds were also detected in the Tactic atmosphere. Oceanic transport of ionic PFCs has also been proposed as alternative or supplemental transport path to remote regions, with the compounds directly dissolved in water or present as a film on the surface foam. Another theory hypothesizes transport of PFOS and PFCAs directly from the sources bound on atmospheric particulate phase.

Indoor measurements of PFCs concentrations have been performed in both the gaseous and particulate phases and in house dust. Indoor concentrations were up to 100 times higher than outdoor concentrations, and carpets were identified as a major source of PFCs.

Lowering of analytical detection limits has made it possible to measure PFCs in environmental waters, included rainwater and oceanic waters at very low concentrations.

Several studies have been published dealing with concentrations and fate of PFCs in waste water treatment plants (WWTPs), as these systems have been identified as important sources for PFCs to the aquatic and terrestrial environments, as PFOS and PFCAs were not degradable in WWTPs. Both PFOS, PFCAs and their precursors have been found in waste water and sewage sludge from WWTPs.

High PFC concentrations in wildlife have been reported for a wide range of animals globally, including in the Arctic and the Antarctic. Especially PFOS have been more or less found in all samples with concentrations varying from sub-ng/g levels to several µg/g, with birds living close to a fluorochemical plant as the worst case. The bioaccumulation potential of some PFCs has been confirmed by several bioaccumulation studies in different food webs.

Temporal trends studies have been performed on archived biologic materials, in general covering time spans from the 1970s-1980s to the present. The PFCs concentrations, especially those of PFOS, have been found to gradually increase up to the present years. Only in a study from the Canadian Arctic it has been observed a decrease in PFOS concentration after 2000, which was explained as a rapid response after the stop of PFOS production in USA. Such a decline has not been found in Greenland.

Ecotoxicity

The toxicity of PFOS and PFOA has been studied in different aquatic organisms (algae, invertebrates and fish). Generally, PFOA and PFOS are not toxic at the normal environmental concentrations in water. However, effects have been observed for specific cellular functions, such as mechanisms involving the uptake of xenobiotics. Other biological endpoints affected by PFOA and PFOS are survival, growth, and emergence. Some intermediate degradation products of fluorotelomer acids have been found to be more toxic by a factor 10,000 than their end products (PFCAs).

Human exposure

The main exposures to perfluorinated substances seem to be by direct product exposure, through food intake or by inhalation/ingestion of indoor dusts, but exact information is lacking.

Human levels

Polyfluorinated chemicals (PFCs) have in contrary to most other persistent organic pollutants (POPs) a low affinity to lipids in adipose tissues but bind to proteins in cell membranes and accumulate in various body tissues of exposed organisms, including in liver, kidneys, testes and brain. The accumulation in fats and muscles is minimal.

In the blood perfluorinated chemicals are mainly bound to serum proteins, especially albumin. The mean half-lives in human blood were 5.4 years for PFOS, 8.5 years for PFHxS (perfluorohexane sulfonate), and 3.8 years for PFOA in retired fluorochemical workers but the whole body half-life may be even longer, since the elimination of these chemicals from the human body seems to be insignificant.

Blood levels of perfluorinated chemicals have been monitored in many countries but most data has been published from USA. In all countries, besides Korea, PFOS has been determined in far higher concentrations than the other PFCs. Typical average serum levels of PFOS in industrialized countries are 20-30 ng/mL with maximum levels less than 100 ng/mL. The second most abundant PFC is normally PFOA with typical average serum levels of 3-5 ng/mL. Some of the highest PFOS blood levels (2-3 times the typical levels) in the general population were determined in industrial areas of USA and China. Such levels may be 10 times higher than in rural and remote areas.

Recently, some preliminary data from Denmark was published. The average PFOS level in blood serum was 35 ng PFOS/mL with a maximum concentration of 107 ng/mL. That is somewhat higher concentration than in our neighbour countries.

In some studies blood plasma or whole blood were analysed instead of blood serum. Analysis of plasma will give the same results as serum but whole blood levels will be 2-3 times lower than serum levels, because PFCs are attached to the serum proteins. Levels of PFCs in cord blood are about the half of levels in maternal blood, thus some transfer to placenta occurs. Levels of PFCs in human semen were ten times lower than in blood serum, and levels in human milk are 100 times lower than in blood, so these fluids are not quite suitable for biological monitoring of PFCs.

Toxicokinetics

In animal experiments the studied PFCs are readily absorbed in the gastro-intestinal tract, and some compounds penetrate the intact skin. The peak blood levels are seen 1-2 hours after exposure, and the substances clear rapidly from the blood.

PFOA and PFOS are both considered being metabolically inert, and other perfluoroalkyl acids both with shorter and longer alkyl chain do have similar properties. Their precursors and functional derivatives will ultimately be transformed to the basic acids. For example, the fluorotelomer alcohol 8:2 FTOH is rapidly transformed to PFOA, PFNA (perfluorononanoic acid) and other metabolites in mice and rats. In the same way N-Ethyl perfluorooctane sulfonamidoethanol (EtFOSE) is metabolised to perfluorooctane sulfonamidoethanol (PFOSE), perfluorooctane sulfonamide (PFOSA) and finally to perfluorooctane sulfonate (PFOS).

Once absorbed in the body PFOA is eliminated unchanged as the free carboxylic acid and mainly with urine and to a less extent in faeces. Thus the renal elimination is critical for detoxification, and the elimination decreases with increasing chain length among the perfluorocarboxylic acids (PFCAs). The biological half-life of PFOA in male rats is 70 times longer than that in female rats for which it was only 2 hrs. The sex-related clearance of PFOA differs between animal species. In hamsters it is opposite rats. In mice and rabbits there are no sex difference; and mice had a slow excretion as male rats; and rabbits had a fast excretion as female rats. In dogs the plasma half-life of PFOA was about 20 days in males and the half in females. In monkeys the biological half-life was several months. As mentioned above the excretion of PFCs in humans is insignificant, thus animal bioassays may not be a good model for effects in human. The reasons for these large species differences are not known.

Toxicology

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

Although the perfluoroalkyl sulfonic acids and -carboxylic acids are closely related structurally, these chemicals elicit different biological responses in vitro and in vivo. The acute lethal toxicity is moderate corresponding to a classification as harmful. PFOS is more toxic than PFOA, and the toxicity of perfluorinated chemicals increases generally with the length of the alkyl chain. PFCAs with a branched alkyl chain seem to be less toxic than linear isomers.

The liver is the primary target organ for PFCs. PFOS and PFCAs cause peroxisome proliferation in the rodent liver as well as induction of various enzymes involved in lipid and steroid metabolism. Levels of serum cholesterol, thyroid hormones, and testosterone are reduced, and levels of estradiol are increased. PFDA (perfluorodecanoic acid) with a longer alkyl chain seems even accumulative and more active than PFOA. Toxic effects, such as induction of fatty liver and uncoupling of the mitochondrial respiratory chain, have been reported.

PFOS, PFOSA, PFHxS and perfluorinated carboxylic acids with carbon chain length of 7-10 can rapidly and reversibly inhibit gap junction intercellular communication in a dose-dependent manner, and with PFDA inhibiting more than PFOA. Gap junction intercellular communication (GJIC) is the major pathway of intracellular signal transduction, and it is thus important for normal cell growth and function. Defects in this communication may lead to teratogenesis, neuropathy, infertility, diabetes, autoimmune disorders, cancer, and other diseases.

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

In experimental animals PFOS causes developmental effects including reduction of foetal weight, cleft palate, oedema, delayed ossification of bones, and cardiac abnormalities. However, the structural abnormalities were found in the highest PFOS dose groups, where significant reductions of weight gain and food consumption were also observed in the pregnant dams.

Risk assessment

The U.K. Committee on Toxicity (2006) has recommended a provisionally Tolerable Daily Intake (TDI) for PFOA and PFOS of 3 mg/kg bw/d and 0.3 mg/kg bw/d, respectively, using an uncertainty factor of 100. They conclude that for some small children the TDI may already be exceeded.

This assessment was based on results from animal experiments, which may be very arbitrary and unreliable, because the renal clearances of PFOA and PFOS are almost insignificant in humans, contrary to a large active excretion in experimental animals. This means that these chemicals in humans leave the blood mainly by redistribution to internal organs and not by elimination from the body. This may increase the internal exposure time in critical organs considerable.

Fodnoter

[1] ”Poly” means that many of the hydrogen atoms have been replaced with fluor; ”per” means that all hydrogen in the alkyl chain have been replaced with fluor.