Perfluoroalkylated substances

Abstract

GENERAL Perfluoroalkylated substances (PFAS) is the collective name for a group of fluorinated chemicals, including oligomers and polymers. There are two major production routes for PFAS: Electrochemical fluorination and telomerisation. The products from the first process contain a sulfonyl group (the so-called ECFproducts). The products from the second production process contain an ethylene group (telomers). POSF (C8F17SO2F) is the most important production intermediate for electrochemical fluorination. 8:2 FTOH (C8F17C2H4OH) is the pivotal substance for telomer production. The most important difference between the two production processes is that ECF yields even and odd numbered, branched and straight perfluoroalkyl chains, whereas telomerisation only yields even, linear chains. Both ECF-products and telomers have four major forms of appearance, namely monomeric, homo-polymeric, co-polymeric, and phosphate esters. Co-polymers, based on acrylates or methacrylates, are the most common form of appearance. Until the 3M company decided to phase out their PFAS production line, they were the major producer of PFAS. Other important suppliers of PFAS chemistry are DuPont, Asahiglass, Clariant, Daikin and Ciba. For the present study 15 perfluoroalkylated substances have been selected. These substances are used in commercial products, monomers for polymers, important production intermediates or important degradation products. PFAS have special physical and chemical properties, including chemical inertness, high thermal stability, low surface energy, hydrophobicity and oleophobicity. These properties make PFAS valuable compounds for a wide variety of applications, including carpet, textile, leather and paper and board protection, fire-fighting foams, and specialty surfactants. SOURCES AND EMISSIONS Several applications may lead to emissions of PFAS. The most important is the emission due to wear of PFAS treated tissue (carpet, textile, leather). These emissions are polymeric substances; whether this may lead to monomeric PFAS is not known. The use of fire-fighting foams for calamities or training leads to emissions of monomeric PFAS to the environment. Furthermore, emissions from fluorochemical production sites may be a route of introduction of PFAS into the environment. The use and associated emissions from these applications were assessed in the current report. The most important application of PFAS in the Netherlands is in paper and paper board treatment, but all this paper is imported. The carpet, leather and presumably the textile industry are the biggest users of PFAS based products in the Netherlands. BEHAVIOUR IN THE AQUATIC ENVIRONMENT For a proper assessment of the behaviour of PFAS in the environment many data are lacking. The available data show that the standard concepts of environmental modelling are not applicable. PFAS distribution is not solely based on hydrophobic and hydrophilic interactions, but most likely also on electrostatic interactions. The most important accumulation positions in (aqiatic) biota are expected to be blood and liver. n-EtFOSE, n-MeFOSE and n-EtFOSA (ECF-products) and 6:2 FTOH, 8:2 FTOH and 10:2 FTOH can readily escape from the water phase to air, considering their relatively high Henry’s Law constants (HLC). Some of these chemicals have been detected in air recently. This may be an important factor in the global distribution of the PFAS. Other fluorinated chemicals have lower HLC and are expected to remain in the water phase. PFOS and 8:2 FTOH exhibit a high sorption potential and desorption is difficult. Test results show that the perfluoroalkyl chain of ECF-products is not affected by biodegradation, hydrolysis or photolysis. The non-fluorinated part of ECF-products is expected to degrade to sulfonate or carboxylate. The degradation products of telomers are not known, but it is expected that the perfluorinated chain is not affected by degradation, hydrolysis or direct photolysis. Indirect photolysis by OH radicals in air may lead to the decomposition of fluorinated chemicals. 8:2 FTOH was shown to be transformed to some extent in rats to PFOA. For fluorinated organic polymers no degradation data are available. PFOS is highly bioaccumulative, considering its bioaccumulation factor of 6300-125000. PFOA hardly bioconcentrates (BCF = 1.8) and 8:2 FTOH has a bioconcentration factor of 87-1100. OCCURENCE PFOS and to a much lesser extent PFOA have been detected in the environment on a global scale. No validated sampling or analytical method for PFAS exist as yet. Point sources may lead to elevated levels of PFAS in biota and the abiotic environment. Concentrations of PFAS are higher in more urbanised or industrialised areas, in biota and in the abiotic environment. Concentrations in biota from North America were highest, followed by biota from Europe. Concentrations in biota from remote locations such as the Arctic were much lower. All PFAS that have been detected in biota were present in blood, liver, kidney, muscle or brain. PFOS concentrations ranged from below limited of quantification to 907 ng/g wet weight. No data are available for the occurrence of telomers in the environment. In humans, PFOS and PFOA has been detected in occupationally exposed workers and in the general public. Levels in fluorochemical production workers were 0.135-2.44 mg/L (PFOS) and 0.106-6.8 mg/L (PFOA); concentrations in the general public were 17-53 ?g/L (PFOS) and 3-17 ?g/L (PFOA). TOXICITY Toxicity tests for PFOS and PFOA have been performed, although many of them with limited reliability. Therefore the assessment of toxicity of PFAS should be considered as a first estimation. The results show that PFOS has moderate acute toxicity to freshwater fish and slight acute toxicicity to invertebrates. Toxicity to algae is practically nihil. The chronic toxicity of PFOS to freshwater fish is low and practically nihil to invertebrates. PFOS has moderate acute and slight chronic toxicity to marine invertebrates. Due to the relative data richness an assessment factor of 50 can be applied to the lowest chronic toxicity data to derive the proposed value for the Dutch quality objectives (iMPC) for PFOS of 5 ?g/L. PFOS concentrations in fresh water were shown to exceed the iMPC, in case of point sources. In other freshwaters, the iMPC was approached. PFOA has slight acute toxicity to freshwater invertebrates and algae, while being practically non-toxic to freshwater fish. Due to the limited number of studies currently available, an assessment factor of 1000 has to be applied to the lowest acute toxicity data to derive the iMPC for PFOA of 3.8 ?g/L. This iMPC may be approached close to point sources. For telomers no conclusions regarding their toxicity can be drawn. Both PFOS and PFOA have long half-lives (8.67 and 1-3.5 years, respectively) in the human body. Both chemicals are distributed to liver, plasma and kidney. To rodents PFOS and PFOA exhibit low acute toxicity, but they are eye irritating. In chronic feeding tests with rodents and primates the primary target was the liver for PFOS and PFOA. PFOA was found to be weakly carcinogenic. Mutagenicity testing of PFOS did not show any mutagenic effects. PFOA did induce chromosomal aberrations and polyploidy in Chinese hamster ovary cells, but did not show mutagenic effects in most mutagenicity test, including an in vivo micronucleus test. In a developmental effect study with PFOS the no observed adverse effect level (NOAEL) and the lowest observed adverse effect level (LOAEL) for the second generation of rodents were determined to be 0.1 mg/kg/day and 0.4 mg/kg/day, respectively. POLICY In the Netherlands, no specific policy concerning PFAS exists. In the USA the production and import of some ECF-products is regulated and a hazard assessment on PFOA has been performed. The governments from Canada, the United Kingdom and Denmark have programmed studies on the potential risks of PFAS. Furthermore, the OECD has performed a hazard assessment on PFOS. The 3M corporation has performed various studies on the toxicology, pharmacokinetics and environmental fate and effects of ECF-products, notably PFOS. The Association of Plastic Manufacturers in Europe, APME, has set up a research program on the toxicology, pharmaco-kinetics and environmental fate and effects of PFOA. The manufacturers of telomers, gathered in the Telomer Research Program (TRP), have set up a research program on the toxicology, pharmacokinetics and environmental fate and effects of 8:2 FTOH.