Also chlorinated solvents toxicity

Uses. Tetrahydrofurfuryl alcohol is of interest in chemical and related industries where low toxicity and minimal environmental impact are important (134). For many years tetrahydrofurfuryl alcohol has been used as a specialty organic solvent. The fastest growing appHcations are in formulations for cleaners (135) and paint strippers (136), often as a replacement for chlorinated solvents (137). Other major appHcations include formulations for crop sprays, water-based paints, and the dyeing and finishing of textiles and leathers. Tetrahydrofurfuryl alcohol also finds appHcation as an intermediate in pharmaceutical appHcations. 

On high toxicity sites even with a very small amount of material escaping from the site, may have extreme consequences. Military Agents are high toxicity compounds which are designed to be lethal in very very small quantities. They are also extremely stable and hard to destroy. A number of industrial chemicals, particularly pesticides also fall into this category. Chlorinated solvents, PCB s and some pesticides, herbicides, and biocides fall into this category. 

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). 

The photo-Fenton processes are explored as photochemical pretreatment of nonbiodegradable and ubiquitous environmental pollutants and/or extremely toxic compoimds in wastewaters, such as persistent organic dyes under visible light irradiation (151,154,180,181) and under UV irradiation (139,182), azo dye factory wastewaters (140,162,183-185), herbicides (186-188), pesticides (152,153,189,190), insecticides (191), pharmaceuticals and wastewaters from medical laboratories (192-197), smdactants (198), industrial effluents with persistent toxic pollutants (199), industrial solvents and wastewaters (167,200), chlorinated solvents (201), and municipal wastewater (202). The photo-Fenton process was proposed to improve the biodegradability of especially biorecalcitrant wastewater, coming from textile industry, and the method was also suggested for water disinfection (203-205). 

Chlorinated hydrocarbons have a better solvency than the corresponding nonchlorinated compounds for most resins, polymers, rubber, waxes, asphalt, and bitumen. Chlorinated hydrocarbons are miscible with other organic solvents, but are insoluble in water. They have a sweetish odor. Increasing the number of chlorine substituents reduces the combustibility and improves the solvency, but also increases the toxicity. 

Chlorinated solvents are advected, dispersed, and sorbed in ground water systems. They also volatilize although their different components have varying degrees of volatility. Chlorinated solvents additionally hydrolyze and undergo other chemical reactions such as dehydrohalogenation or elimination and oxidation and reduction. These abiotic reactions, as will be seen later in the chapter, are typically not complete and often result in the formation of an intermediate that may be at least as toxic as the original contaminant. 

Sohd-state sensors SoHd-state sensors, also referred to as metal oxide sensors, are best used as general survey instruments because of their lack of selectivity/specificity. This type of sensor has a rather narrow working range of 1-50 ppm. A variety of MOS sensors are available for the detection of combustible gases, chlorinated solvents, and some toxic gases, such as carbon monoxide and hydrogen sulfide. 

One of the best-known classes of groundwater contaminants includes chemicals known as chlorinated solvents one example of this class of compounds is dry cleaning fluid, also known as perchloroethylene (PCE). As a general mle, the chlorine present in chlorinated solvents makes them more toxic than the respective non-chlorinated organic molecules. Unlike petroleum-based fuels, solvents are usually heavier than water and thus tend to sink to the bottoms of aquifers, forming the so-called dense non-aqueous phase liquid (DNAPL) DNAPLs usually represent a long-term secondary source of pollution. This makes solvent-contaminated aquifers much more difficult to clean up. 

Many solvents have been suggested for use in these decaffeination processes. Initially benzene was used but it is never used today because of its toxicity and flammability. When chlorinated solvents first became available at low prices, trichlorethylene was sometimes used but this solvent also has now been superseded. Methylene chloride is the only chlorinated hydrocarbon currently used as a decaffeination solvent. Other commercially used solvents are ethyl acetate, coffee oil and other triglycerides [12]. In addition to the decaffeination processes outlined above, which are based on conventional solvent extraction with organic solvents, water decaffeination and supercritical carbon dioxide extraction have now become well-established processes. It is still necessary in these processes to humidify the beans before extraction (step 1) and to return them to their initial humidity afterwards (step 4), but the remaining steps in the extraction process differ substantially from those in the conventional solvent extraction processes. Steam stripping (step 3), for example, is only necessary in processes using organic solvents. 

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