A Comparison of Concrete Chemical Hardeners (Densifiers) By Roger Allbrandt, B.A. Environmental Biology   

“Retroplate” (Sodium Silicate) FGS “Permashine” (Lithium Silicate) “Green Umbrella” (Amorphous Silica) Background

The most common building material today is concrete. It is a used in building construction, consisting of a hard, chemically inert particulate substance, known as an aggregate (usually made from different types of sand and gravel), that is bonded together by cement and water. In 1756, British engineer, John Smeaton made the first modern concrete (hydraulic cement) by adding pebbles as a coarse aggregate and mixing powered brick into the cement. In 1824, English inventor, Joseph Aspdin invented Portland Cement, which has remained the dominant cement used in concrete production. Joseph Aspdin created the first true artificial cement by burning ground limestone and clay together. The burning process changed the chemical properties of the materials and Joseph Aspdin created stronger cement than what using plain crushed limestone would produce. Concrete that includes imbedded metal (usually steel) is called reinforced concrete or ferroconcrete. Reinforced concrete was invented (1849) by Joseph Monier, who received a patent in 1867. Joseph Monier was a Parisian gardener who made garden pots and tubs of concrete reinforced with an iron mesh. Reinforced concrete combines the tensile or bendable strength of metal and the compressional strength of concrete to withstand heavy loads. Joseph Monier exhibited his invention at the Paris Exposition of 1867. Besides his pots and tubs, Joseph Monier promoted reinforced concrete for use in railway ties, pipes, floors, arches, and bridges. Today we have removed the aggregate that was used 40 years ago, remove the metal that was used to reinforce concrete, we add fiber, water reducers, plasticizer, and hardeners. Today concrete is not the same as the product that was invented in 1756, or even the same product that was being used even ten years ago. Each step in the evolution of densifiers has been in direct response to the changes in concrete, and the perceived deficiency of the older products. Older densifiers were designed to work with the concrete that was being produced at the time. As concrete has changed the products that are being used in conjunction with concrete have changed. In the beginning it was okay to just harden concrete, then customers wanted the concrete to resist oils. Today the government, employees, and customers demand safer products that perform better than the products that have been available in the past.

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Comparison Chemical Hardeners (Densifiers) include three basic categories of chemicals: silicates, silicinates and silica:

Silicates - penetrate and harden. They are not good sealers. Disposal of the waste material is currently an issue. 1) The oldest is Magnesium Fluorosilicates, which have been around since 1905. This type of product requires multiple applications with varying rates of dilution. 2) Sodium Silicates developed initially in Germany in the 1930’s. Application of the product requires that it be applied at an average of 200 square feet per gallon, spread and worked until the surface tension is broken, mist with water, allowed to gel a second time and then rinsed and wet vacuumed to remove. 3) Potassium Silicates. The main difference between the sodium silicates and potassium silicates is sodium is more prevalent in the North American and potassium is predominate in Europe. 4) Lithium Silicates. Lithium silicates were developed to combat Alkali Silica Reaction (ASR). ASR is more prevalent in exterior applications where there is a constant source of water. Lithium silicates are less susceptible to solubilization than sodium or potassium. One of the by products of this particular silicate is its ability to reduce sweating on slabs. Chemistry: Lithium vs. Sodium and Potassium (Li vs. Na and K) 1) The smaller size of the Li ion of the SiO2/Li2O molecule vs. the Na or K ion is important. 2) The location of the Li ion in the SiO2/Li2O molecule is also important. The Li ion is “close”, actually touching the SiO2, while Na and K are “distant”. The inter-atomic distances of Na and K make them more available to react quickly with the available Ca or CaOH. The quicker the reaction, the less penetration is able to occur. 3) With silica to Li ratio of 20:1 vs. 3:1 for Na, the lithium silicate is more “potent,” relative to the silica content which is what reacts with the free Ca and CaOH to form C-S-H (calcium-silicate-hydrates). In addition, when LiSiO2 reacts, it does not produce free Na or NaOH, (sodium hydroxide) which can raise the pH of the concrete surface. 4) Na and K remain soluble in water. This solubility allows them to undergo expansion/contraction cycles with wet/dry cycles. Li becomes insoluble and remains stable throughout these environmental changes. In summary, lithium silicate has about 1/5 less “interfering” mass as a sodium silicate. This is the true beauty of the lithium and one in which size really matters. The smaller lithium ion stabilizes the silicate ions more efficiently with less mass and fewer molecules, resulting in improved performance while not contributing to higher pH levels. Naturally occurring sulfates of sodium, potassium, calcium, or magnesium are sometimes found in soil or in solution in ground water adjacent to concrete structures, or from sodium or potassium silicates added to concrete as hardeners. The sulfate ions in solution will attack the concrete. There are apparently 2

two chemical reactions involved in sulfate attack on concrete. First, the sulfate reacts with free calcium hydroxide which is liberated during the hydration of the cement to form calcium sulfate (gypsum). Next, the gypsum combines with hydrated calcium aluminate to form calcium sulfoaluminate (ettringite). Both of there reactions result in an increase in volume. The second reaction is mainly responsible for most of the disruption cause by volume increase of the concrete (ACI 201.2R): “(b) Symptoms. Visual examination will show map and pattern cracking as well as general disintegration of concrete.” EM 1110-2-2002 20 June 95 (http://140.194.76.129/publications/eng-manuals/em1110-2-2002/c-3.pdf) Leaching of sodium and potassium from concrete chemical densifiers into ground water is currently the issue of investigation by the Environmental Protection Agency (EPA).

Silicinates - excellent sealer, poor hardening characteristics. Real world typical life expectancy is 18 to 24 months, and then it should be reapplied. Disposal of the waste material is currently an issue. 1) Silicinates are applied the same way silicates, spray, scrub, mist, rinse, and vac. 2) Silicinates can offer increased abrasion resistance over silicates in the short term due to the coating effect of the silicinates. 3) Silicinates are either potassium or sodium. Silicates have been directly linked to silicosis. Silicates and silicinates have been tagged as carcinogens. Silicates and silicinates must be disposed of as hazardous material. There is significant research that documents the ill effects of sodium, potassium silicates and silicinates on reactive aggregate in concrete. Silicas – are the newest and most promising of the chemical hardeners: Silicas are applied simply by spraying them on the surface of the slab and allowing them to dry. The surface should be clean and void of any curing compound. Application rates are between 400 to 600 square feet per gallon. Unlike silicates or silicinates there is no scrubbing and rewetting of the product. Unlike silicates or silicinates there is no waste material to dispose of. Silicas increase abrasion resistance over silicates or silicinates by up to twice as much

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Silicas do not contribute to ASR Silicas do not raise the pH of the concrete since the product is neutral 6.5. Silicas have the highest increase in abrasion resistance Silicas have reduced application and labor costs Silicas have no hazardous waste to remove or dispose Silicas do not contribute to silicosis and are not carcinogenic unlike silicates which do contribute to silicosis and are carcinogenic Silicas will not contribute to sweating or efflorescence Silicas performance is not contingent on dwell time unlike silicates or silicinates In Summary, there are features and benefits to each of these types of chemical hardeners. The upside for the silicates is that they harden better than silicinates, Silicinates seal better than silicates. Silicates have been directly linked to silicosis. Silicates and silicinates have been tagged as carcinogens. Silicates and silicinates must be disposed of as hazardous material. There is significant research that documents the ill effects of sodium, potassium silicates and silicinates on reactive aggregate in concrete.

Currently the best technology for chemical densifiers is amorphous silica.

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ORGANIC VS INORGANIC There are hundreds of products available to seal or stain wood, concrete and other masonry materials. These products are available through big box stores like Home Depot, Wal-Mart, Lowe’s and many other paint stores, contractor supply centers, lumber yards and websites. It is common knowledge that most of these products fail within 1-3 years. The big question is WHY? Why haven’t manufacturers like Dupont, GE, Sherman Williams, Olympic, Behr, Thompson’s, Dow Corning and hundreds of others been able to produce stains and sealers much better than they were over 20 years ago? The answer is complex, but here are a few of the more obvious reasons: 1. It is the American way to manufacturer products with built-in obsolescence 2. Flawed restoration and application procedures shorten the surface life of most products 3. Wood and concrete are difficult, unpredictable building materials to protect 4. Manufacturers are producing the best products they can given the raw materials and technology they are set up to utilize 5. Most manufacturers are striving to improve the performance of products whose base ingredients are produced from petroleum by-products, all of which are organic compounds. ORGANIC What does being Organic mean? Anything derived from a living or once-living organism is organic. All organic materials have a common trait that sets them apart from other materials; they naturally decompose. Decomposition is nature’s way of recycling organic matter. Decomposition of organic material is inevitable! Examples of Organic Materials are: The human body, all fruits and vegetables, fats and oils, gasoline, motor oil, paint, varnish, plastic, rubber, asphalt, epoxy, suntan lotion and even lipstick, etc. The decomposition of organic materials is sharply accelerated by being exposed to UV light, wind, atmospheric pollution, water, temperature changes and freeze/thaw cycles. Nearly all wood, concrete and masonry sealers, stains and finishes are organic, and will therefore decompose and fail when exposed to the harsh elements of nature. Additionally, most of these organic products contain Volatile Organic Compounds (VOC), which are hazardous to humans, animals and the environment. Many of these products are barely within Federal VOC Requirements. The Federal Government considers any amount of VOC to be dangerous to our health and environment.

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CHARACTERISTICS & PROPERTIES OF ORGANIC SEALERS Film Formers: Organic sealers form an “oil slick” type film when applied to wood, concrete and masonry materials. This film temporarily prevents moisture from penetrating the material but also prevents the material from breathing. Wood and concrete is hygroscopic. The moisture it attracts must escape through the surface in order to keep its interior from water damage. Wood swells and shrinks from trapped moisture, causing the film to pull apart or flake off and loose its ability to repel water. Decompose: All organic materials decompose and fail when exposed to UV, water, wind, atmospheric pollution and temperature changes. A good example is acrylic. When used on interior wood it will last for many years. When used on exterior materials such as wood, concrete and pavers it will begin to decompose quickly, becoming brittle and flake off. Mechanically Bonds: Organic paints, sealers, stains and finishes can only “stick” to materials. Mechanically bonding (sticking) to a material is a weak attachment and can be easily broken loose. It is often seen as peeling, chipping or flaking off the treated material. Hazardous: All organic sealers, stains, paints, and finishes have some degree of danger associated with them. Most are flammable, corrosive, carcinogenic, unsafe to breathe, ozone depleting, harmful to vegetation and animals as well as smell terrible. Destructive: Organic sealers, stains and water repellents are not compatible with standard building materials and actually cause deterioration of the materials they are stuck to. They remove small particles of the materials they are attached to when they begin to peel, chip or flake off. They also leave the material unprotected during their process of decomposition. Residue: Organic products decompose from the elements leaving behind chemical residue in and on the material they were attached to. A good example of this is that of a well known Water Sealer which leaves behind small particles of solvent and silicone after it appears to have worn off the treated material. This residue then prevents subsequent re-treatments from attaching solidly causing even faster product failure. Short Service Life: All organic materials have a short service life because of their built in ability to decompose when exposed to the harsh elements of nature. No manufacturer has ever, or will ever, be able to significantly alter the natural properties of organic materials given them by Mother Nature!

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INORGANIC What does being Inorganic mean? Inorganic describes materials made from natural compounds from the earth’s strata, such as titanium, lithium, potassium, quartz, zirconium, calcium, salt, sand, common rock, granite, marble, mica, ceramic, iron oxides, and water. Inorganic compounds are not derived from any living or once living organism. They are completely inert. Examples of Inorganic materials are: Cement, concrete, glass, steel, copper, iron, plaster, lime potash, diamonds, precious stones, and other minerals. Inorganic materials are extremely slow to deteriorate because they are not easily broken down by UV light, water, wind, oils, salts, extreme heat and cold or atmospheric pollutants. In the US, only about two percent of all wood, concrete and masonry sealers, stains, water repellents and other finishes are made from inorganic compounds. The basic technology to manufacture products made from inorganic compounds has been available for over 125 years in European countries. In America however, technology and manufacturing of these products is centered around organic chemistry because of its ties to the oil industry (petroleum byproducts). CHARACTERISTS & PROPERTIES OF INORGANIC SEALERS Non-Film Formers: Mineral based sealers are chemically incapable of forming an “oil slick” type film when applied to building materials. With inorganic mineral sealers, microscopic minerals penetrate deep into the pores of the treated material, forming a tight micro-crystalline structure that blocks the penetration of water and other contaminants. These mineral structures are just loose enough to allow vapor to escape upwards through the treated material, thus allowing the treated material to remain dry inside. This process is known as “breathing”. Decomposition: Inorganic materials do not decompose when exposed to the harsh elements of nature. Good examples of long lasting inorganic materials are concrete, glass and metal. Chemical Bond: Some minerals used in producing inorganic sealers are highly reactive and therefore able to chemically fuse within the treated material. Chemical fusion prevents the treatment from turning loose. It is not just stuck to the treated material; it becomes part of the material. Non-Hazardous: Most inorganic materials do not contain Volatile Organic Compounds (VOC). They are not flammable, and produce no dangerous fumes or ozone-depleting gasses. Most inorganic sealers do not harm vegetation and do not leach harmful particles from the treated material into surrounding soil. Non-Destructive: Inorganic sealers are compatible with all standard building materials, many of which are made of inorganic minerals. 3.

INORGANIC MINERAL SEALER TECHNOLOGY There are basically three types of inorganic mineral water sealer technologies: Sodium Silicates, Potassium Silicates and Lithium Silicates. Each of these mineral families contains different properties and therefore produces strikingly different results when used in the production of water repellents and sealers. Sodium Silicates: Sodium silicate formulas make up 94% of all mineral based water sealers available on the market in the US. Their performance characteristics are: 1. Least expensive silicate to manufacture into a finished sealer 2. An antiquated technology developed by the Army in the 1940’s 3. Is known to contribute to Alkali-Silica Reaction (ASR) in concrete 4. Typical formulation is only 3-7% silicate and the rest is water 5. Large particle size prevents deep penetration in most materials 6. Cannot be used to treat wood. It will not adhere to wood fibers 7. Forms an aero gel when dry, which can be re-emulsified and floated to the surface causing a white residue on the wood called efflorescence 8. Badly effloresces on most masonry and brick surfaces 9. Will not bead water so proving it has been applies is nearly impossible 10. Short service life 11. Hundreds of companies sell various formulas without stating the main ingredient is sodium silicate, which makes purchasing confusing 12. Sold mainly over the internet to end users & contractors interested more in profit than performance 13. Sodium silicates may absorb water, rather than repel it, on some masonry materials Potassium Silicates: Potassium silicate formulas make up less than 3% of the mineral based water sealers available in the US. Their performance characteristics are: 1. Highly reactive, harder to formulate and more costly than sodium 2. Multiple particle sizes make penetration controllable and more complete 3. Extremely hard mineral used in match heads and atomic triggers 4. Certain hybrid blends are self-reactive allowing them to be effective in low or no alkaline materials, such as old worn concrete 5. Will not cause efflorescence, but can leave a stubborn white residue if over applied 6. Will not deeply penetrate dense substrates 7. Some potassium formulations will actually absorb water rather than repel it 8. Can expand inside the treated material causing internal pressure which contributes to crazing and map cracking on the surface of concrete 9. Potassium and sodium silicates both have a tendency to react violently and unevenly sometimes leaving clumps of reacted and un-reacted calcium scattered throughout the wear surface

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Lithium Silicates: Lithium silicate formulas make up less than 1% of the mineral based water sealers available in the US. The latest state-of-the-art lithium technology is the most significant advancement in concrete sealers and hardeners in over fifty years. Their performance characteristics are: 1. Non-expansive and cannot contribute to Alkali-Silica Reaction (ASR) 2. Non-soluble and will not absorb water or cause sweating 3. Ions are smaller than sodium and potassium ions so deeper penetration into dense substrates is possible 4. Lithium is widely recognized as “Green Chemistry” 5. Prevents efflorescence and leaching of lime 6. Once applied, Lithium silicate protection improves with age 7. Can be burnished to create a glass like finish on concrete 8. Seals, hardens and densifies concrete and other masonry materials 9. Unaffected by salt spray and chemical attack 10. US DOT tests have demonstrated that treating ASR-affected concrete with lithium compounds can reduce or eliminate expansion due to ASR 11. Less sensitive to application procedures than potassium sealers 12. Higher reactivity than potassium for a more complete crystalline structure 13. Zerovoc LithiSeal is self-reactive and therefore highly effective in old or worn concrete and masonry structures 14. Concrete and masonry materials treated with Lithium Silicate sealers are considered permanently water repellant

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AMORPHOUS SILICA IN WORKING ENVIRONMENTS A Toxicological Overview Lecture given at the “ Silica 2001“ in Mulhouse, France Sept. 2001 by

Dr. Monika Maier Product Safety, Aerosil & Silanes, Degussa AG, P.O.B. 1345, 63403 Hanau, Germany [email protected]

INTRODUCTION Synthetic amorphous silica (silicon dioxide, SiO2) is used in a wide range of industrial products. Amorphous silica may be produced by different types of processes: thermal, pyrogenic, or fumed silica is produced using a vapor-phase process; wet processes lead to precipitated silica or silica gel. In addition, silicas may be surface-modified to gain special properties. Due to their physicochemical properties silicas are widely used in synthetic resins, plastics, cosmetics, nutritional products, and drugs, e.g. as free flow or anticaking agent. Therefore, with respect to consumer safety as well as potential hazards to workers during silica processing or consumer product formulation, the toxicological profile of synthetic amorphous silica is of great interest. This overview mainly addresses the situation in the working environment. Toxicological evidence is presented concerning acute toxicity, repeated dose toxicity,

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skin and eye irritation, skin sensitisation, genetic toxicity, and reproductive toxicity. Human epidemiological data will be given where available. As dermal toxicity and effects due to inhaled material are most important for workers, they are the main topics of this overview.

ACUTE TOXICITY Numerous studies were performed following oral administration of synthetic amorphous silicas to rats. During the observation periods, no death occurred and no signs of toxicity were observed. In addition, there were no macroscopical findings at necropsy of the animals. According to this data, synthetic amorphous silica may be judged to be not toxic up to 5000 mg/kg/bw. For testing acute dermal toxicity, intact and damaged skin of rabbits was treated with different types of synthetic amorphous silica for 24 hours. There were no signs of systemic toxicity. After application to intact skin, only slight redness was observed. In damaged skin, redness and swelling occured. Therefore, it can be concluded that synthetic amorphous silica is not toxic by the dermal route.

For inhalation toxicity, the following results from studies according to the OECD guideline are available (due to technical limitations, the maximum attainable concentration in the air was below 5 mg/l): after the 4 hours exposure, no clinical signswere observed. No mortality occurred during the exposure period or during the subsequent observation period of 14 days. At autopsy, no abnormalities were found in gross pathology.

SKIN AND EYE IRRITATION A great number of animal studies was carried out with regard to skin and eye irritation. According to the resulting data, the topical application of synthetic amorphous silica does not lead to irritation. Instillation of silica to the eyes also did not cause irritation. From occupational physicians, there are case reports for the working environment describing dryness or degenerative eczema of the skin in workers with chronic contact to synthetic amorphous silica. These reactions may be avoided by the employment of an intensive skin care program.

creating essentials SKIN SENSITISATION Animal data on skin sensitisation are not available. For humans, data collected from industrial hygiene surveillance do not indicate any potential for skin sensitisation. As mentioned above, there are reports describing degenerative eczema resulting from dryness of the skin that may be misinterpreted as a sign of sensitisation or allergy.

GENETIC TOXICITY Several common in vitro assays with synthetic amorphous silica (Salmonella typhimurium, Escherichia coli, Saccharomyces cerevisiae) demonstrated the absence of mutagenicity. In addition, there were also negative results with the toluene extract. In cultured mammalian cells, neither point mutations nor chromosomal aberrations were induced. No genotoxicity was detected using in vivo assays. According to the available data, there is no evidence for a genotoxic potential of synthetic amorphous silica.

REPRODUCTIVE TOXICITY Several studies have been carried out in rats, mice, hamsters, and rabbits to investigate toxic effects on fertility as well as maternal and embryonic development. Synthetic amorphous silica given by gavage did not affect parent fertility. No teratogenic effects or Feb05

abnormalities in the development of the progeny could be detected.

REPEATED DOSE TOXICITY To address oral repeated dose toxicity of synthetic amorphous silica, studies in rats and dogs have been carried out. Silica was administered with the diet or given by gavage for up to 6 months. The results confirm the absence of significant toxicity. No substance related abnormalities could be detected at autopsy. Different types of synthetic amorphous silica have been tested in rats at various concentrations for subacute or subchronic inhalation toxicity. Transient increases in markers of inflammation and cell injury have been reported. In some studies, an increase in lung collagen, focal fibrosis, and nodule formation were observed. As shown in studies with a post-exposure recovery period the observed effects were clearly temporary. Marked differences between synthetic amorphous silica and crystalline silica have been described. In contrast to crystalline silica, amorphous silica did not produce persistent changes or progressive lesions resembling silicosis. During recovery, inflammation markers rapidly decrease for amorphous silica, whereas the markers remain elevated after crystalline silica.

Several animal species, including mice, rats, guinea pigs, rabbits, and monkeys have been tested for chronic effects of the inhalation of synthetic amorphous silicas. The results of long-term inhalation studies (up to 18 months) differ markedly with respect to species, airborne concentration, and type of silica. Inflammatory responses, granulomatous nodule formation, and emphysema were observed. But studies with a recovery period showed that pulmonary effects diminished with time. Unlike exposure to crystalline silica, synthetic amorphous silica does not induce irreversible or progressive lung injury. Chronic inhalation of crystalline silica can produce lung tumors in rats, whereas this has not been shown for amorphous silica. The mechanisms underlying this difference are unknown. A significant role has been postulated for chronic inflammation and cell proliferation. Both amorphous and crystalline silica show a high degree of inflammatory cell response after subchronic exposure, but genotoxic effects in alveolar epithelial cells occured only after crystalline silica. Besides the inflammatory response, particle biopersistence, solubility, and direct or indirect epithelial cell cytotoxicity may be responsible for the induction of either mutagenic events or target cell death.

creating essentials HUMAN EPIDEMIOLOGICAL DATA In many epidemiological studies on workers with longterm exposure to synthetic amorphous silica no silicosis was found. There is only sparse information about the exposure to non-crystalline silica and the development of chronic obstructive pulmonary disease (COPD). In most cases, a correlation of respiratory symptoms with smoking or other confounding factors was described, but not with the exposure to synthetic amorphous silica. With regard to carcinogenicity, there is no evidence in the literature for an association between the exposure of workers to synthetic amorphous silica and lung cancer development or mortality. As to synthetic amorphous silica and airway function, valuable epidemiological data are currently collected by manufacturers in Germany. This study is carried out to gain further information about the association between chronic exposure to synthetic amorphous silica in the working environment and lung function or respiratory morbidity. The current workforce exposed to amorphous silica at several production plants represents the study population. Current workers without exposure Feb05

to amorphous silica serve as controls. Recently, an interim analysis has become available. The data show: 1. There is a clear doserelationship between smoking behaviour and symptoms of chronic bronchitis as well as reduced lung function. 2. There is no clear connection between the exposure to synthetic amorphous silica and the presence of chronic respiratory morbidity.

CONCLUSION It is generally believed, that the toxicological profile of synthetic amorphous silica is dominantly determinded by its nonabsorbability. Synthetic amorphous silica is practically insoluble in water and chemically inert. It is therefore unlikely to be absorbed from the gastrointestinal tract in significant amounts. Taken together with the available data from toxicological assays, synthetic amorphous silica may be judged as obviously nontoxic when used at currently applied levels. According to current epidemiological data, there is no evidence of lung cancer or other long-term respiratory health defects in workers employed in the production

of synthetic amorphous silica. In her monograph on Silica, the International Agency for Research on Cancer (IARC) concluded that “there is inadequate evidence for the carcinogenicity of amorphous silica to humans” (Group 3).

LITERATURE FDA Research Laboratories, 1973 IUCLID Data Set of the EUROPEAN Commission, February 2000 Wahrheit DB et al.; Fund Appl Toxicol 16, 590-601, 1991 Reuzel PGJ et al.; Fund Chem Toxicol 29, 341-354,1991 Johnston CJ, Driscoll KE, Finkelstein JN et al.; Toxicol Sci 56,405-413, 2000 Straif K et al.; presentation at the meeting of the German Association of Epidemiology, Garmisch-Partenkirchen, September 6-7, 2001

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