CFCs toxicity

Air Paiticuiate, odors, SO2. HC Major polluter SO2, HC, CO, hydrogen sulfide, acid mist Major polluter organic chemicals (benzene, toluene), odors, CFCs Toxic gases Biochemical pollution... 

One of the chief uses of chloromethane is as a starting material from which sili cone polymers are made Dichloromethane is widely used as a paint stripper Trichloromethane was once used as an inhalation anesthetic but its toxicity caused it to be replaced by safer materials many years ago Tetrachloromethane is the starting mate rial for the preparation of several chlorofluorocarbons (CFCs) at one time widely used as refrigerant gases Most of the world s industrialized nations have agreed to phase out all uses of CFCs because these compounds have been implicated m atmospheric processes that degrade the Earth s ozone layer... 

Health and Safety Factors. The toxicity of aHphatic CFCs and HCFCs generally decreases as the number of fluorine atoms increases (16), as shown in Table 7, but there are exceptions as in the case of 141b vs 142b. Also, some derivatives like HCFC-132b can have low acute but high chronic toxicides (29). 

The use of CFCs such as fluorotrichloromethane became quite widespread, particularly as for many years the material was believed to cause few toxic and environmental problems. However, evidence that such materials were damaging the ozone layer became substantial and the use of such materials is to be discouraged and is illegal in many countries. To some extent CFCs have been substituted by methylene chloride (also illegal in some countries) and other fluoro compounds, but these too may prove to be environmentally unacceptable. For this reason there has been increased dependence on the use of the isocyanate-water reaction to generate sufficient carbon dioxide to give products of the required density. 

CFCs have been widely used as cleaning solvents, as they are nonflammable and their toxicity is low. Now, flammable solvents are coming back into favor. A news item from a manufacturer described "a new ozone-friendly cleaning process for the electronics industry, which "uses a unique hydrocarbon-alcohol formulation. It did not remind readers that the mixture is flammable and that they should check that their equipment and procedures are suitable. 

The haloalkanes (also called alkyl halides) are alkanes in which at least one hydrogen atom has been replaced by a halogen atom. Although they have important uses, many haloalkanes are highly toxic and a threat to the environment. The haloalkane 1,2-dichlorofluoroethane, CHC1FCH2C1, is an example of a chlorofluorocarbon (CFC), one of the compounds held responsible for the depletion of the ozone layer (see Box 13.3). Many pesticides are aromatic compounds with several halogen atoms. 

The term CFCs is a general abbreviation for ChloroFluoroCarbons. They have been extensively used since their discovery in the thirties, mainly as refrigerant, foam blowing agent, or solvent because of their unique properties (non toxic, non flammable, cheap). However, after the first warning of Rowland and Molina [1] in 1974 that CFCs could destroy the protective ozone layer, the world has moved rapidly towards a phase-out of CFCs. Because the destruction of stratospheric ozone would lead to an increase of harmful UV-B radiation reaching the earth s surface, the production and use of CFCs is prohibited (since January 1, 1995 in the European Union and since January 1, 1996 worldwide). 

Measurement or estimation of health impacts under TSCA would be premature, since relatively little has been done to regulate new or existing chemicals that could result in health benefits. The principal exception to this generalization is the ban on aerosol uses of CFCs, whose chronic effects on human health derive from their environmental impact rather than direct biological toxicity. Compared with other environmental laws, such as the Clean Air Act, the regulatory accomplishments of TSCA are somewhat insubstantial. 

Uranium production does have a notable impact on ozone depletion. The Environmental Protection Agency s (EPA) Toxic Release Inventory showed that in 1999, the nation s two commercial nuclear fuel-manufacturing plants released 88% of the ozone-depleting chemical CFC-11 by industrial sources in the U.S. and 14% of the discharges in the whole world. 

Ozone depleters (e.g. CFCs, 1,1,1-trichloroethane) Least acceptable Toxic and carcinogenic solvents (CCI4, benzene)... 

Many of the fluorine compounds, such as CFCs, are inert and nontoxic to humans. But many other types of compounds, particularly the salts and acids of fluorine, are very toxic when either inhaled or ingested. They are also strong irritants to the skin. 

Chlorinated derivatives of methane include methyl chloride, methylene chloride, chloroform, carbon tetrachloride, and several chlorofluorohydrocarbons (CFCs). We discuss carbon tetrachloride (CT) as a representative example of this group. CT was originally prepared in 1839 and was one of the first organic chemicals to be produced on a large scale by the end of the nineteenth century and beginning of the twentieth century. CT is the most toxic of the chloromethanes and the most unstable on thermal oxidation (Holbrook 2000). 

In actual fact a great deal has also been undertaken in this area in the past. Many of the hazardous substances mentioned above have now more or less disappeared from the market. Some were banned (e.g. DDT, CFCs, PCBs), their functions now being performed by less hazardous substances. Other hazardous substances have at least been considerably curtailed in their use with safety requirements being imposed (e.g. chlorinated solvents, highly toxic heavy metals). This has also led to the reduction of risks emanating from hazardous substances in many areas. 

Volatile organic compounds (VOC) contribute to the formation of tropospheric ozone (summer smog). Certain halogenated hydrocarbons (e.g. CFCs) also destroy the stratospheric ozone layer. Chlorinated solvents are hazardous to water and, if disposed of incorrectly (e.g. burning), may emit highly toxic substances (e.g. dioxins). 

Polychlorinated biphenyls (PCBs), CFCs, petroleum products, and dioxin are major toxic contaminants in air (Section 3.3.2), soil (Section 3.5.3), and also in water. The readers are referred to Sections 3.3.2 and 3.5.3 for details about PCB characteristics, health effects, treatment technologies, and so on. For water quality management, they have been included in the list of the USEPA priority pollutants [86]. 

Figure 1.5 Triangular diagram of CFCs based on methane, showing toxic and flammable regions, as well as their commercial names and their normal boiling points in...

CC12FCC1F2. These compounds are non-toxic and non-flammable, and their thermodynamic properties are ideally suited for the compression/ expansion cycle in cooling and heat pump appliances. However, CFCs are chemically very inert, so when they are vented into the atmosphere, they do not react with atmospheric constituents. They diffuse unscathed first into the troposphere, then penetrate slowly into the stratosphere. There, the solar UV radiation photodissociates these compounds, liberating free chlorine atoms (the C-Cl bond is weaker than the C-F bond). The chlorine atoms react with atmospheric O3 to form chlorine oxide, which in turn reacts with atmospheric atomic oxygen regenerating chlorine atoms ... 

Testing of a number of the chlorofluorocarbon (CFC) alternatives indicates that most of these chemicals have low acute toxicity, and low to moderate chronic toxicity. Some chemicals, originally proposed as alternatives, have been dropped from consid-... 

United States Environmental Protection Agency, Information on air pollutants such as nitrogen oxides, greenhouse gases, CFC s, and toxic chemicals. 

Third, even where it is clear that a particular type of chemical has caused a particular incident of damage, and we can identify who was causally responsible for the existence of that chemical (if not necessarily its presence in a particular location), the first condition, that the conduct transgressed a norm, is often not met. This is because those norms require only that foreseeable consequences are taken into account one is not responsible for consequences that could not have been foreseen. Thus Du Pont, the main manufacturer of chlorofluorocarbons (CFCs) — non-toxic and non-flammable chemicals that were used as a refrigerant and aerosol propellant for many decades — have not been held to account for the hole in the ozone layer caused by those chemicals because at the time the key decisions to manufacture them were made, in the 1930s, these effects could not have been predicted (Colborn et al, 1996, pp243-245). 

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