There is a lack of specific health data on the active fluorinated substance, but the marketed formulation, which includes solvents and non-fluorinated copolymers, is often tested and results may be traced on the Internet.69 Polymers are generally of low availability/uptake and have low toxicity.
Environmental effects of fluorinated co-polymers
There is a lack of data. Probably only the solvent and degradation products of polymers are hazardous. The ultimate degradation products may be perfluoroalkanoic acids (PFAAs), including PFOA.
G. Fluorinated polyethers
OMNOVA Solutions Inc. produces under the trade name PolyFox a family of short-chain fluorosurfactants based on fluorinated polyethers with a molecular weight greater than 1,000 and with C2F5 or CF3 perfluoroalkyl side chain structures. The PolyFox product line includes anionic and non ionic surfactants, UV-radiation curable acrylic monomer derivatives and polyols.
The basic structure of PolyFox 656 compounds is illustrated in the following figures (x + y equals about 6):
It seems that these surfactants have a moderate surface tension that is not quite as low as that of conventional fluorinated surfactants. The new surfactants are claimed to have a broad processing window, with less interference with other compounds. Coating quality is improved as foaming is reduced. The latter is an important factor in producing and processing water-borne coatings.
PolyFox fluorosurfactants have been used in aqueous and solvent-borne semiconductor coating formulations. In a number of examples excellent wetting, flow and levelling properties have been achieved for semiconductor coatings.
In addition, the poly(alkylene oxide) chain of all PolyFox materials has an inherently low refractive index compared to other commercial polymers such as acrylics. The presence of even very short (-CF3, -C2F5) side chains further reduces the refractive index, and PolyFox materials have been used as antireflection layers in photo-resist and LCD screen applications. The PolyFox formulation is currently being used as a surfactant in floor polish products in the United States, Europe and Asia.
PolyFox products are priced competitively in comparison with any new C6-based materials but are more expensive than the C8-based materials, which is being phased out.70
Health effects of fluorinated polyethers
The acute toxicity of fluorinated polyethers is low (LD50 > 2 g/kg bw) but they may irritate skin and the respiratory system. Generally, data are lacking.
Environmental effects of fluorinated polyethers
Fluorinated polyethers have a high molecular weight that makes them less available for transport across biomembranes and therefore less biologically available. Furthermore, the polymer backbone linkage of the PolyFox molecules is an ether link, which is more environmentally stable than, for example, the ester/amide links of PFOS and telomer-based fluorosurfactants. This makes the PolyFox molecule more resistant to degradation to lower molecular weight carboxylic acids. PolyFox has low acute toxicity with regard to aquatic organisms and is not known to bioaccumulate.
PolyFox products seem to have reduced environmental impacts in comparison with all other fluorosurfactants on the market. This is because PolyFox materials use a C1- or C2 based platform rather than a C8- or C6-telomer-based platform. Since they are made with shorter fluorinated alkyl chain lengths (C2F5 or CF3 structures), they cannot produce the longer perfluorinated acids such as PFOA.
H. Siloxanes and silicone polymers
Siloxanes are chemical substances containing units with the general formula R2SiO, where “R” represents either hydrogen or a hydrocarbon group. They may be straight-chain or cyclic compounds and vary in molecular weight from a few hundred to several hundred thousand g/mol for the polymers. Siloxanes are building blocks for silicone products.
The principal siloxanes of interest from an environmental perspective are the volatile methyl siloxanes with short SiO backbones, in particular the cyclic siloxanes known as D4, D5 and D6 and the linear siloxanes MM (or HMDS), MDM, MD2M and MD3M. They are shown in table 6.
Table 6: Siloxanes of recent interest71
MM (or HMDS)
Out of these commercially used siloxanes, D4, D5, and MM are chemicals produced in high volumes in the European Union. The first two are the most commonly used siloxanes in the Nordic countries.72
Recent activities in the Nordic area have focused on investigating the environmental occurrence of the above-mentioned siloxanes, which are used in a large number of industrial and consumer products such as sealants, fuels, car polishes, cleaners, anti-foaming agents, car waxes and personal care and biomedical products.73 The widespread use of siloxanes and their broad application, high volatility and potential for toxic effects have raised concerns about these compounds within various disciplines of environmental science. Recent studies indicate that they are widespread in the environment.
Silicone polyethers are another class of silicone derivatives that have special surfactant properties. The leading manufacturers are Bluestar, Dow Corning, Evonik-Goldschmidt, Momentive and Wacker. Other companies sell specially formulated mixtures for specific applications.
Bluestar Silicones markets some PFOS alternatives based on silicone for textile applications under the trade name AdvantexTM.
Worlée-Chemie produces silicone polymers, which in the paint and ink industry can in several cases be used as alternatives to fluorosurfactants as wetting agents. WorléeAdd® 340 is a low-viscous non ionic special modified silicone polyether (containing 3-(polyoxyethylene) propylheptamethyl trisiloxane, CAS no. 67674-67-3) that can improve surface wetting of aqueous systems on difficult substrates like polyethylene and polypropylene or contaminated substrates. It has a low surface tension and is claimed to be highly effective in improving wetting, spreading and levelling of water-borne coatings and eliminating surface defects without foam stabilizing. It is further claimed that the compound normally has no negative effect on recoating.
Another product, WorléeAdd® 345, is a mixture of a silicone polyether (10–15%) and a dioctyl sulfosuccinate (50–55%) in ethanol and water. This surfactant can be used to improve wetting properties of aqueous coatings for different substrates, where penetration into absorbing surfaces also is improved.
Perfluoroalkyl derivatives of siloxanes also exist; they include 1H,1H,2H,2H-perfluoroalkyl triethoxysilane, which is effective for glass and surface treatment.74 One compound, polyfluorooctyl triethoxysilane (1H,1H,2H,2H-perfluorooctyl triethoxysilane), has been banned in Denmark. The formula is:
Health effects of siloxanes and silicone polymers
A study carried out by the National Food Institute at the Technical University of Denmark investigated the toxic effects of siloxanes as a group in order to set a health-based quality criterion for ambient air. Toxic effects of D3, D4, D5, D6 and HMDS were studied using a “read-across” method, which is based on structural similarity and its relation to toxicity. The linear siloxane HMDS appeared to have lower potential for liver toxicity, but higher potential for lung toxicity, than the cyclic substances. Decreasing toxicity with increasing chain length was also observed. An ambient quality criterion of 0.01 mg/m3 was derived, based on lung toxicity, including a safety factor of 250.75 The silicone industry disagrees with the conclusions of this study.76
Some years ago polysiloxanes or silicone polymers were evaluated in a comprehensive monograph published by the European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC).77
Low-molecular-weight polydimethylsiloxanes have been studied extensively by industry to define their safety profile. These studies have demonstrated that the polydimethylsiloxanes studied all possess a very low potential for toxicity.
The Scientific Committee on Consumer Products in the European Union has published an Opinion on D4 in which the safety of D4’s use as a cosmetic ingredient has not been questioned.78 In the United States, the Cosmetic Ingredient Review panel is about to publish its final assessment of the safety of cyclomethicone, D3, D4, D5, D6 and D7.79 The panel has concluded that D4, D5, D6 and D7 are safe for use in cosmetics. D3 will be taken off the International Nomenclature of Cosmetic Ingredients (INCI) list because it is not a commercial product.
Other studies of siloxanes, however, indicate that they seem to be harmful when inhaled and that exposure may induce serious damage to eyes. Prolonged and frequent skin contact with WorléeAdd® 340 may cause skin irritation. In short, knowledge of the toxicity of siloxanes is still incomplete.
The polyfluoroalkyl siloxane discussed above was banned in Denmark because of lung damage in experimental mice.80
Environmental effects of siloxanes and silicone polymers
Siloxanes are widely distributed in the Nordic environment. In general, siloxanes are very stable and persistent compounds that do not degrade in the environment. The cyclic- and short-chain linear siloxanes bioconcentrate in aquatic organisms. These siloxanes may be toxic to aquatic organisms and are bioaccumulative; there are, however, still gaps in our knowledge.
According to the material safety datasheet for WorléeAdd 340, the silicone polymer in that product is classified as environmentally dangerous with the R phrases R51 (“Toxic to aquatic organisms”) and R53 (“May cause long-term adverse effects in the aquatic environment”). The R-phrase R53 indicates that the substance is bioaccumulative.
Canada has identified decamethyl cyclopentasiloxane (D5) and octamethylcyclotetrasiloxane (D4) as “inherently toxic to wildlife”.81
The cyclic siloxanes D4, D5 and D6 have been subjected to an environmental risk assessment by the United Kingdom Environment Agency applying European Union Technical Guidance. A review of the environmental properties of cyclic siloxanes is available on the Internet.82
I. Propylated aromatics
Rütgers Kureha Solvents produces various aromatic surfactants with the trade name Ruetasolv®; based on propylated naphthalenes and biphenyls, these products can be used as water-repelling agents for different applications such as corrosion protection systems, marine paints, resins, printing inks, coatings and electrical, electronic and mechanical applications.
They may also be used as plasticizers and film-forming aids in emulsion paints and adhesives. The various isopropyl naphthalenes and isopropyl biphenyls are very hydrophobic substances that are compatible with almost all raw materials such as epoxy resins, polyurethane resins, resin esters, hydrocarbon resins, polystyrene, elastomers, dispersions, emulsions, styrene acrylate-copolymers, vinyl acetate and ethylene vinyl acetate co-polymers, mineral oils and bitumen.
Propylated aromatic products are all colourless liquids with a boiling point of about 300C and have very low solubility in water.
Ruetasolv DI Ruetasolv TTPN Ruetasolv BP 4201 Ruetasolv BP 4103
CAS no. 38640-62-9 CAS no. 35860-37-8 CAS no. 69009-90-1 CAS no. 25640-78-2
Health effects of propylated aromatics
The substances p-isopropyl-1,1’-biphenyl (Ruetasolv BP 4103) and p,p’-diisopropyl-1,1’-biphenyl (Ruetasolv BP 4201) can cause skin sensitization or dermatitis upon repeated contact with skin, and long-term exposure causes irritation of the eyes, nose, throat, mucous membranes and respiratory tract. p-Isopropyl-1,1’-biphenyl has a very low acute toxicity with oral LD50 values for rats of > 4 g/kg. Central nervous system, liver and kidney damage have, however, been reported as chronic effects of that chemical in animals.
Isopropylated naphthalenes are also irritating substances. The acute toxicity of diisopropylnaphthalene (Ruetasolv DI) is very low, with an oral LD50 value for rats of 3,900 mg/kg.
Environmental effects of propylated aromatics
The biphenyls and the naphthalenes have high octanol/water partition coefficients (log KOW), and the bioconcentration factor (BCF) for the substances is greater than 100. These chemicals are therefore potentially bioaccumulative. The biphenyl moiety seems to be easily biodegradable, whereas the naphthalene moiety biodegrades slowly. The sparse available information suggests that the biphenyls are acutely toxic to aquatic organisms, whereas naphthalene appears to have no acute toxic effects on the investigated fish species.
Several companies produce surfactants based on 50–75% of the sodium salt of di(2 ethylhexyl) sulfosuccinate, which can be used as a wetting agent for aqueous systems of detergents, cleaners, paints and coatings. It is also used in pesticides.
Following is the chemical structure of the sodium salt of di(2-ethylhexyl) sulfosuccinate (CAS no. 577-11-7):
In a product from BASF (Lutensit A-BO) the sulfosuccinate is mixed with water and ethanol, and in a product from Cognis (Hydropalat® 875) the sulfosuccinate is mixed with water and 2,2 dimethylpropane-1,3-diol.
The product from Cognis can be used as a wetting agent in aqueous coating systems and is particularly suitable for difficult-to-wet substrates like plastics, metal, cellulose film, silicone-treated papers and glass. This surfactant may also be used as an emulsifier for emulsion polymerization. Another area where it can be used as an alternative to fluorinated surfactants is in optimizing the colour acceptance of aqueous pigment concentrates in different coatings. The product has medium foam formation.
Münzing Chemie also produces a surfactant (Edaplan® LA 451) based on a sulfosuccinate derivative in ethanol and water, which also can be used as a wetting agent for aqueous paints and coatings. The identity of the sulfosuccinate has not been disclosed. The product is claimed to have good wetting properties, no increase in foam and good recoatability. The surface tension is moderate. Application areas are decorative paints, wood and furniture coatings, automotive and repair coatings, industrial coatings, printing inks and overprint varnishes.
Health effects of sulfosuccinates
Toxicological information is scarce. Sulfosuccinates are irritants to eyes, skin and the respiratory system, especially upon prolonged or repeated contact. Dermatitis has been observed as a long-term effect, as have central nervous system depression and injury to the heart, the liver and blood-forming organs. The substance di(2-ethylhexyl) sulfosuccinate has low acute toxicity if swallowed (LD50 (oral, rat) = 1.9 g/kg). Information found in the United States Government’s Hazardous Substances Data Bank suggests that di(2-ethylhexyl) sulfosuccinate is mildly toxic (upon ingestion) to humans, with a probable oral lethal dose (in humans) of 0.5–5 g/kg. A possible metabolite is the branched 2-ethylhexanol, which may have reproductive effects.
Environmental effects of sulfosuccinates
Di(2-ethylhexyl) sulfosuccinate is easily biodegradable and not likely to bioaccumulate; however, a 96hLC50 value of 10–100 mg/l for Leuciscus idus (a small fresh-water cyprinoid fish) shows that the sulfosuccinate is harmful to aquatic organisms. More information is needed in order to make an accurate assessment.
A classic cationic textile surfactant is 1-(stearamidomethyl) pyridinium chloride, which was previously marketed by ICI as Velan PF:
The substance reacted with cellulose at elevated temperatures to form a durable water-repellent finish on cotton. It was later found that the reaction was restricted to the surface of the fibres and that the high cure temperature weakened the fabric. Sodium acetate had to be added to prevent the decomposition of the cellulose by the hydrogen chloride formed. Also, the pyridine liberated during the reaction had an unpleasant odour and the fabric had to be scoured after the cure. The toxicological properties of pyridine ended its use in the 1970s, when government regulation of such substances increased. Pyridine might be evaluated differently now. Further information about its properties is lacking.
Health effects of stearamidomethyl pyridine chloride
Published data on this chemical are lacking.
Environmental effects of stearamidomethyl pyridine chloride
Possible replacements for fluorosurfactants in some applications are anionic surfactants based on aliphatic alcohols. The BASF product Emulphor® FAS 30 is the sodium salt of fatty alcohol polyglycol ether sulfates, which are preferentially used in the emulsion polymerization of acrylate and methacrylate esters, styrene and vinyl esters. These anionic emulsifiers are also combined with non ionic Emulan® grades in order to achieve desired properties such as a particular particle size or emulsion stability. Because of their “foaming” properties, fatty alcohol polyglycol ether sulfates are also used in cosmetics and fire-fighting foams.
A fatty alcohol polyglycol ether sulfate has the following general formula:
in which R1 represents a linear or branched alkyl and/or alkenyl group having, for example, 12 to 16 carbon atoms, n represents a number mainly from 2 to 4 and X represents a cation selected from the group consisting of sodium, ammonium or substituted ammonium.
A related non-fluorosurfactant is Enthone® (ethoxylated oleyl amine, CAS no. 26635-93-8), used in decorative chrome plating and in many other applications.83 Its general formula is as follows:
R-N(CH2CH2O) mH(CH2CH2O) nH
Health effects of polypropylene glycol ether, amines and sulfates
Emulphor FAS 30 has low acute toxicity by ingestion (oral LD50 > 2 g/kg b.w.) and is not considered to be irritating. There is a lack of data on this chemical. Enthone and other polyethylene glycol amines are non-toxic and non-irritating non-ionic emulsifiers.
Environmental effects of polypropylene glycol ether, amines and sulfates
Emulphor FAS 30 is readily biodegradable (> 70% elimination according to the OECD biodegradation screening test (301E)) and does not seem to be acutely toxic to aquatic organisms, as the reported 96hLC50 value for fish (Leuciscus idus) is > 100 mg/L. Enthone is readily degradable, with low toxicity. There is, however, a lack of data on these chemicals.
V. Comparative assessment of PFOS and possible alternatives
Comparative assessment of PFOS and its possible alternatives with regard to technical, socioeconomic, environmental, health and safety considerations is a very complex task requiring much more data and other information than are normally available. Often much more information is available about PFOS than about possible alternatives, which may be newly developed substances covered by patents and trade secrets. For this reason rigid selection criteria are not useful; information on the alternatives will be scarcer, and it will be of lower scientific quality because much of it will be non-peer-reviewed.
In addition, if sufficient information is available then one may have to subjectively weigh price and fitness for use against hazard. None of the alternatives will be perfect and without hazards, but at least they should be less hazardous than PFOS. That is the case, for example, with fluorinated alternatives with fluorinated alkyl chains shorter than C8. They are less toxic and bioaccumulative but still persistent indefinitely in the environment.
It might be that the C6-chemistry is not sufficiently safe. This is illustrated by the similar half life of perfluorohexane sulfonate compared to PFOS in human blood. Furthermore, chemicals with fluorinated chains longer than C8 seem to be more toxic and bioaccumulative than PFOS.
Further, in evaluating the technical properties, fitness for use and durability of the alternatives for each separate application, it is necessary to evaluate socio-economic considerations; differences between branches, enterprises (including size), countries and regions; product importance; economic constraints; and social costs. The availability of alternatives seems to be the same worldwide, because the providers are mainly large international companies.
Economically useful data will probably also be scarce. In general, very little information about the prices of alternatives was found in the Danish survey 84 even though the producers of alternative products were asked specifically about such information. The information received, however, suggests that the alternatives are in general priced comparably to the PFOS-related compounds. One company mentioned that the price of alternatives was intentionally kept at the same level as that of PFOS related compounds. While it was impossible to obtain exact prices, in the coatings and paints area the non-fluorinated alternatives were found to be cheaper.
More recent information indicates that some alternatives may be priced comparably to one other but be more expensive than PFOS derivatives. For instance, PFOS seems to be less expensive than PFBS. Some price examples for laboratory chemicals are shown in table 7. The purity and prices of bulk materials may be lower.