As PFCs are moderately soluble and have little or no vapour pressure, their volatility is regarded to be negligible. These two latter properties determine the equilibrium distribution between water and air (Henry’s Law Constant) which suggests that PFCs are unlikely to partition into the gas-phase (3M 2000).
Furthermore, fluorotelomers (F(CF2)nCH2CH2OH) and sulfonamides have been cited as possible candidates for carboxylated and sulfonated PFC biospheric contamination. FTOHs are polyfluorinated compounds typically characterized by even numbered perfluorinated carbons and two non-fluorinated carbons adjacent to a hydroxyl group. Measured vapor pressures of FTOHs range from 140 to 990 Pa (Stock et al. 2004). Calculated Henry Law Constants for this class of compounds using available solubility and vapour pressure data reveal the propensity for FTOHs to partition into air. This is supported by air sampling studies which have detected FTOHs at tropospheric concentrations (Stock et al. 2004). The sulfonamides are known to be volatile (Simik 2005).
Production of PFCs in Industry
PFOS (C8F17SO3–) and PFOA (C7F15COO–) are two of the perfluorinated surfactants that have received the greatest attention due to their ubiquitous presence in the environment and persistent, bioaccumulative and toxic properties. This class of compounds has been utilised in a variety of industrial and consumer applications. PFOS and PFOA can be produced synthetically or through the degradation or metabolism of other perfluorochemical products (Giesy & Kannan 2002). Although fluorinated organic compounds (FOCs) are naturally occurring, perfluorochemicals are entirely anthropogenic in origin.
The main mechanisms used to produce PFCs have been the Simons Electro-Chemical Fluorination (ECF) process and the telomerisation process. The electrochemical fluorination process was developed by 3M and used to synthesise PFOS, PFOA and sulfonamides (Table 1). In this process, organic feedstocks are dispersed in liquid anhydrous fluoride and an electric current is passed through the solution perfluorinating the molecule replacing the hydrogen atoms (3M 2000). The process is inexpensive and generates PFCs with straight and branched chained, even and odd-numbered perfluorocarbons. It should be noted that commercialised POSF derived products contain ~70% linear POSF derivatives and ~30% branched POSF-derived impurities. Impurities present in the manufactured product are of shorter chain length and may be released into the environment (Giesy & Kannan 2002). According to 3M, these residues are present at ~1% in the final commercialised product (Giesy & Kannan 2002). Other major manufacturers of the PFCs use the telomerisation process to derive its products. This process is used by DuPont to produce poly(tetrafluorethylene) or PTFE also know as Teflon and FTOHs. This method gives a well-defined product with fewer isomers (Simik 2005).
Table 1. Environmentally relevant fluorochemical structures.
Uses
The 3M Corporation (the principle global producer of PFCs) in May 2000 voluntarily discontinued the production of materials based on perfluorooctanesulfonyl fluoride (POSF) (3M 2000). Using POSF as a basic building block, unique chemicals were created by further reactions with functionalized hydrocarbon molecules. Depending on the specific functional derivatisation or the
degree of polymerization, such POSF-based products may degrade or metabolize, to an undetermined degree, to PFOS. PFOS related polymers have been used on a wide range of fabrics to provide soil, water and oil resistance. They have generally been applied to the textile surface to create a protective barrier. These products are known to contain ~ 1% of low molecular weight residual from the manufacturing process, as previously mentioned (Giesy & Kannan 2002). Use of these products is becoming much less, however there will remain treated fabrics in use. In addition, PFOS-related substances have been used to treat a range of paper types and products. As for fabrics, the main function is to impart grease, oil and water resistance. Such products have been used in food contact applications. These uses are no longer considered to be significant due to 3M’s phase-out. In 2000 PFOS production equated to ~ 3700 metric tonnes and in 2003 production ceased completely (DEFRA 2004). Additional PFOS based applications include metal plating, semi-conductors, photographic, aviation, and fire fighting foams in which PFOS itself was used as a component in aqueous film forming foam (AFFF) (OECD 2002).
PFOA is primarily a reactive intermediate used in the manufacture of fluoropolymers and fluoroelastomers. The major fluoropolymers manufactured using PFOA salts are PTFE and polyvinylidine fluoride (PVDF). PTFE is widely used in many industrial and consumer products including surface coatings on textiles and carpets, as well as in personal care products, and non-stick coatings on cookware. Ninety-seven percent of PFOA that was produced by 3M was used by its industrial customers and in its own processes as a fluoropolymer processing aid (US EPA 2002).
FTOHs are widely used as precursor compounds in the production of fluorinated polymers used
in paper and carpet treatments and have similar applications as those of PFOS-based products. They are also used in the manufacture of paints, adhesives, waxes, polishes, metals, electronics, and caulks (Simik 2005). The worldwide production of FTOHs for the period of 2000-2002 was estimated to be between 5 and 6.5 × 106 kg year-1, of which 40% is produced in North America (Ellis et al. 2004).
As a result of 3M’s cessation of PFOS related chemistries, the level of product use in many areas has decreased significantly over the last two or three years, in some cases to zero. Users have moved to alternative fluorine-based products (telomer based) in some areas, and to other technologies in other areas. In the E.U there currently is no legislative force to regulate PFC emissions. However, there have been a number of international initiatives to address PFC emissions including the U.S.A’ s Significant New Use Rule, OECD international collaborative risk assessment and the Government of Canada’s addition of PFCs to their List Of Toxic Substances (DEFRA 2004).
Emmsions and Pathways To the Environment
There are no known natural sources of PFCs. As yet the mechanisms and pathways leading to accumulation of PFCs in wildlife and the environment has not been well characterised. Releases of fluorochemicals into the environment can occur at each stage of the fluorochemical products life-cycle. They can be released when the fluorochemical is synthesised, continue during incorporation of the fluoro-chemical into a product, during the distribution of the product to users, during the use of the product by consumers, as well as from landfills after the use of the products (3M 2000).
It has been well documented that the manufacturing processes constitutes a major source for PFOS to the local environment. PFC concentrations have been found to be greater in biota situated closer to industrialised areas. During the ECF process, various waste products containing PFOS based substances are released into the atmosphere or into wastewater treatment systems, as well as by products. These by products can be recycled in the product manufacturing process or discharged into controlled, in-house waste water treatment systems. The resulting treatment sludge is landfilled (3M 2000). High local emissions are supported by one study that has showed extremely high concentrations of PFOS in wood mice collected in the immediate vicinity to 3M’s fluorochemical plant in Antwerpen, Belgium (Hoff et al., 2004). Another study reported that concentrations of the measured fluorochemicals increased downstream of a fluorochemical manufacturing facility, indicating that effluent from manufacturing is one likely source of organic fluorochemicals into the aquatic systems (Hansen et al. 2002). It is also possible that volatile precursors that can degrade to PFOS and PFOA such as sulfonamides and FTOHs, could escape from the production facilities during the manufacture of PFC products.
Given the wide range of products containing PFOS and PFOA, sources other than manufacture could result in emissions to the environment. These include leachates from landfills, atmospheric losses for combustion and commercial uses, wash-offs from fire fighting foams, and wash-offs from PFC treated products such as textiles (DEFRA 2004). Furthermore, PFOS itself has been measured in the original formulation of the commonly used textile stain protectant ScotchGardTM. Presumably, PFCs applied to textiles that are washed can be incorporated into residential wastewater streams. In addition, PFOS an PFOA containing fire fighting foams can be used in significant quantities in airports and training facilities and has been known to contaminate nearby surface and groundwaters. PFOA was found to be at a concentration 120 µg/L in groundwater in the vicinity of a fire-training area, ten years after contamination (Moody et al. 2003). It is likely that all these PFOA and PFOS sources direct to surface and groundwaters.
A principle route for PFCs into the environment is through sewage treatment plants that collect residential and industrial wastewater. Elevated concentrations have been observed such
treatment facilities. Fluoropolymers are known to biodegrade into PFOS and PFOA. Presumably, biodegradation of polymeric material that incorporate PFOS and PFOA can occur in the sewage treatment plant, leading to its release in aquatic systems. The solubility of PFCs may also confer ability for them to contaminate mains water supplies, thereby constituting a potential source of human exposure to these substances. The sludge produced by a waste water treatment plant may contain high PFC concentrations and constitute the dominant mass flow through the plant. Sewage sludge is often land applied constituting potential human and ecological risks, especially if it ends up in agricultural soil. Studies in the US have identified the presence of PFOS in surface water and sediment downstream of a production facility, as well as in wastewater treatment plant effluent, sewage sludge and landfill leachate at a number of urban centres in the US (OECD 2002; 3M 2003).
While PFOS and PFOA can certainly enter local aquatic systems hydrologically, it does not explain how they can appear in remote ecosystems with no direct source of contaminant. The presence of PFOS and PFOA in a wide variety of Arctic biota, far from anthropogenic sources, demonstrates the capacity of the PFCs to undergo long-range transport. As previously mentioned, PFOS and PFOA will tend not to partition into the gas-phase rendering them unamenable to atmospheric, long-range tgransport (Simik 2005). A greater understanding of the mechanisms behind the global distribution of PFCs is beginning to emerge. A plausible hypothesis is that these chemicals are atmospherically transported to remote areas as volatile precursors with subsequent oxidation in the atmosphere or biodegradation or metabolism within organisms to form PFOS and PFOA. A probable volatile precursor to pefluorinated carboxylates is FTOH. Seemingly, volatilisation of FTOHs occur during the manufacturing process and from the products in which they are incorporated and from biodegradation of fluoropolymers (Simik 2005; Ellis et al. 2004). The volatilisation hypothesis is a plausible one given their detection in the gas phase of the atmosphere from a range of sampled environments including; indoor environments, urban areas, in locale of carpet treatment facilities and in the North American troposphere. The relatively high vapour pressure and low water solubility of FTOHs are likely to deter wet or dry atmospheric deposition and prolong the gas phase. Reports indicate that half-life in the gas phase is sufficiently long enough to allow for widespread hemispheric distribution and that atmospheric reactivity occurs to yield non-volatile perfluorocarboxylates such as PFOA and perfluorononanoic acid (PFNA). If oxidative degradation of FTOHs occurs in the atmosphere, the resulting perfluorocarboxylates would most certainly deposit to aquatic and terrestrial surfaces as they are water soluble with a lower vapour pressure(Simik 2005; Ellis et al. 2004). In addition, biodegradation of FTOH has been shown to be a source of pefluorocarboxylates. If deposition to of FTOH to surfaces should occur, metabolic biotransformation may yield perfluorocarboxylates. FTOH has been shown to be metabolised to PFOA in adult male rats. Furthermore, microbial biodegradation of FTOH to yield perfluorocarboxylates has been shown. The presence of straight chained odd-chain length perfluorcarboxylates in remote environmental media such as Arctic polar bear serum and surface waters, indicates that PFC contamination is derived from straight chained FTOHs (Simik 2005; Ellis et al. 2004).
While it the fate of fluorotelomers has been established less is known about the contribution of sulfonamides to PFOS in remote environments. Known PFOS precursors such as sulfonamides are somewhat less volatile than FTOH and maybe subject to wet deposition. Alternative, hypothesis include long-range waterborne transport and particle transport. Referring to the latter possibility, PFOS has been measured on particles over the Great Lakes and particles are known to travel large distances (Simik 2005; Stock 2004; Giesy & Kannan 2002).
Environmental Levels in Biota
Numerous global biomonitoring efforts have elucidated the environmental distribution of sulfonated and carboxylated perfluorochemicals in the tissues of many animals around the globe. Furthermore, these studies have revealed the potential for PFCs to bioaccumulate and biomagnify in food chains (3M 2000; Hansen et al. 2001; Giesy & Kannan 2001; Kannan et al. 2002; Martin et al. 2004). As part of this global biomonitoring program over 1200 samples of blood, liver and other tissues were collected from specimens from a variety of species around the world. Analysed biota included fish, birds, freshwater mammals, marine mammals, and oysters. Areas of focus included North America (the Great Lakes and marine coast), the Arctic, Asia, and Europe. Analyses of these samples indicated that PFOS is present in the livers, blood, and other tissues of animals, especially in piscivorous animals (OECD 2002). Table 2 summarizes the data acquired for the highest concentrations of PFOS found in species.
Table 2. Selected data of the highest PFOS concentrations found in biota (OECD 2002).
This work demonstrated that principally PFOS and PFOA and sulfonamides are distributed on a global scale, including remote environments and can be bioaccumulative in blood and organs and biomagnify in various food chains. PFOS was detectable in most of the samples at concentrations >1 ng/g (Renner 2004). Generally the highest concentrations were found in top predators in food chains containing fish. For example, mink from the midwestern U.S. contained significant concentrations of PFOS in their livers (970-3680 ng/g, wet wt). Mink are opportunistic predators but do eat fish as part of their diet. When mink were fed carp from Saginaw Bay, Michigan, containing an average concentration of 120 ng PFOS/g (wet wt), under laboratory conditions, the estimated biomagnification factor based on the concentrations of PFOS in livers of mink was approximately 22. The authors compared the results from remote areas with those from more industrial locations. Martin et al. (2004) comments that PFOS is widely distributed in remote regions, including the Polar Regions, but that the levels found in more urban and industrial areas (e.g. the Baltic, Great Lakes) are several times higher, indicating industrialised area as the principle source.
Since PFOS is believed to be released to the environment mainly through water from sewage treatment plants one major route for PFOS into food chains could be through fish. PFOS have shown a high oral uptake (95%) within 24 hours in the gastrointestinal tract in studies on rats (OECD 2002). Taken together, this could constitute the basis of the highly elevated levels that have been observed in top predators in food chains containing fish.
Presence in Humans
In 1974, Guy et al. reported results for the determination of organic fluorine levels in plasma from 106 individuals from five cities in the U.S. By concentrating the organic fluorine from 20 L of plasma and performing nuclear magnetic resonance (NMR) analysis, Guy et al. postulated that the PFOA or a structurally related compound maybe the source of the organic fluorine. Subsequently, further studies have revealed wide spread part per billion presence of PFOS in non-occupationally exposed humans (OECD 2002; Olsen et al. 2003a; Olsen et al. 2003b). PFOS levels in general public have also been measured in samples from Germany, Belgium and Netherlands. The highest PFOS levels were found in samples from the Netherlands (mean value 53 ppb) and the lowest from samples in Belgium (mean value 17 ppb) (OECD 2002). Blood samples have also been taken from the general public in various locations and from different age groups within the U.S.A. Mean concentration level were found to be 43 ppb (OECD 2002).
PFOS serum levels have been measured in workers involved in both the manufacturing of
perfluorochemicals and the processing of these compounds into products, such as fire protection and surface protection products. Serum PFOS concentrations among production employees working in POSF-related processes have averaged between 0.5 and 2 ppm depending on work activity (range < 0.1–12 ppm) (OECD 2002; Olsen et al. 1999).
Toxic Action
Toxicokinetic studies with radiolabeled PFOS in male rats indicated that PFOS is well-absorbed orally (>95%), distributes primarily in the serum and liver, and undergoes extensive enterohepatic circulation (3M 2000). Scientists speculate that the body recognizes PFOS as a bile acid and continues to recycle it as it does with authentic bile acids (Renner 2004). Laboratory animal studies have shown varying liver to serum to PFOS concentration ratios, which might suggest different pharmacokinetics between species. In cynomolgus monkeys the 1:1 to 2:1 liver to serum ratio is present which is comparable to that found in human samples (Olsen et al. 2003b).
No clear association between human exposure to PFCs and adverse health effects has been established. Olsen et al. (1999) found no association with occupational exposure to PFOS and toxicological effects. However, on the basis of the following results from animal studies a potential risk could exist for developmental and other adverse effects associated with exposures to PFCs in humans. Evidence of the toxicity of PFOS and PFOA is available from chronic to acute exposures to rats and monkeys. The most relevant studies are outlined.
Subchronic exposure to PFOS in rodents and primates results in adverse health effects, including reduction of body weight, liver hypertrophy, and decreased serum cholesterol. Furthermore, exposure to PFOS during pregnancy in rats results in maternal and developmental toxicity. Specifically, significant reductions of maternal weight gains and a marked decrease in circulating thyroid hormones in a dose-dependent manner were observed in pregnant rats exposed to PFOS. The altered thyroid hormone metabolism, also detected in cynomolgus adult monkeys exposed to PFOS, is of potential concern because thyroid hormones regulate growth, metabolic rate, cardiac performance, and body temperature, and play a critical role in the normal development of the lung, inner ears, and nervous system. PFOS exposure may impair functionality in target organs such as the liver. The PFOS-exposed rat and mouse fetuses displayed a variety of birth defects. Furthermore, in utero exposure to PFOS in rats increased post-natal mortality (OECD 2002).
Significantly, Ten years of employment in PFOA production jobs was associated with a 3.3-fold increase in prostate cancer mortality, compared with no employment in PFOA production
jobs, although only six prostate cancer deaths occurred overall and four among the exposed workers (US EPA 2002). In a two-year cancer study conducted by 3M, PFOA doubled the incidence of mammary tumours in exposed laboratory animals (Hogue 2005).
Summary
Sulfonated and carboxylated perlfuorinated compounds fulfil the persistant organic pollutant (POP) criteria specified by the Stockholm Convention. Since 3Ms discontinuation of pefluorinated chemistries, these compounds have been given worldwide concern. The scenario of the perfluorochemicals, brings to light how imprudent industrial and commercial imperatives can override environmental and health considerations.