Carcinogenic chlorinated organic compounds

Ozone can be used to replace chlorine for the sterilization of water. Replacement of chlorine is desirable because chlorination increases the salinity of water. The more salt in the water the less value it has for later use in, for example, irrigation of cropland. When used to sterilize water, chlorine reacts with trace organic compounds to form carcinogenic chlorine compounds such as chloroform. The use of ozone to replace chlorine in water treatment will eliminate chlorination-induced salinity and carcinogenic chlorinated organic compounds. Because of its instability, any residual ozone not consumed in purifying the water rapidly decomposes to ordinary oxygen. 

Based on animal studies and mutagenicity studies, trace amounts of organic polymers do not appear to present a toxicity problem in drinking water. The reaction products with both chlorine and ozone also appear to have low toxicity. The principal concern is the presence of unreuctcd monomer and other toxic and potentially carcinogenic nonpolymeric organic compounds in commercial polymeric flocculants. The principal contpuimds are acrylamide in acrylamide based polymers, dimethyldiallyammonium chloride in allylie polymers, and epichlorohydrin and chlorinated propanols in polyamines, as well as the rcaclion products of these compounds with ozone and chlorine. 

Chlorinated organic compounds present in water, due to their carcinogenic nature, have become a great concern with respect to human health. Such substances are formed when humic acids react with chlorine in disinfection processes. Ozonation alone is generally not suited for the complete oxidation of chlorinated compounds because scavenger compounds such as acetic acid, formic acid, and oxalic acid can form and accumulate as by-products in the... 

The conversion of wood to fiber produces hundreds of chemical compounds that are discharged as effluents into surface water. Processes that use chlorine to bleach pulp produce substantial quantities of toxic chlorinated organic compounds, including dioxins and furans, compounds that attack the respiratory, musculoskeletal, reproductive, and CNS, skin, liver, and kidneys. These compounds are considered human carcinogens. 

Chlorinated organic compounds (COCs) refer to the substitution of one or more hydrogen in aliphatic and aromatic hydrocarbons and their derivatives by chlorine. COCs are widely used in the fields of chemistry, medicine, electronics, pesticides, etc. Many COCs are endocrine disturbance substances, show carcinogenic effects, and have been listed as priority pollutants by the US Environmental Protection Agency (USEPA). When released into the environment, COCs are transported in both air and water. However, COCs are chemically stable and difficult to destroy, and they are eventually deposited in soils and sediments due to their hydrophobic-ity. Soils and sediments contaminated with COCs are long-term sources of pollutants and pose great threats to human health and ecosystems. Therefore, remediation of these contaminated soils and sediments is of great importance. 

Direct thermal combustion represents the conventional technology for the destruction of chlorinated organic compounds. However, besides the very high temperatures (>1000 °C), this route has the typical disadvantage of generating more toxic by-products, such as the polychlorinated carcinogenic and environmentally persistent dibenzodioxins and polychlorinated dibenzofiirans [57]. 

The toxicity of chlorine residuals to aquatic life has been well documented. Studies indicate that at chlorine concentrations in excess of 0.01 mg/1, serious hazard to marine and estuarine life exists. This has led to the dechlorination of wastewaters before they are discharged into surface water bodies. In addition to being toxic to aquatic life, residuals of chlorine can produce halogenated organic compounds that are potentially toxic to man. Trihalomelhanes (chloroform and bromoform), which are carcinogens, are produced by chlorination. 

Chlorine dioxide has been used widely in Europe since the early 1940 s as a drinking water disinfectant. More recently the USA has suggested the use of chlorine dioxide to reduce the formation of chloro-organic compounds particularly chloroform and other trihalomethanes (THM s) which are known carcinogens(7). 

Potential hazards to humans may be connected with the use of chlorine-based washing systems. Apart from the direct occupational hazard, there are increasing concerns about the formation of potentially harmful by-products. Chlorine may react with organic compounds on the products and form hazardous organochlorines that are considered to be potential carcinogens (Beuchat, 1998 Betts and Everis, 2005). Betts and Everis (2005) suggest that a ban on the use of hypochlorite systems is likely in the future. 

This includes bioremediation cases of contaminated sites with several toxic and carcinogenic pollutants, such as petroleum hydrocarbons, PAHs, dichlorobenzene, chlorinated hydrocarbons, carbon tetrachloride, Dicamba, methyl bromide, trinitrotoluene, silicon-based organic compounds, dioxins, alkyl-phenol polyethoxylates, nonylphenol ethoxylates, and polychlorinated biphenyls. The following is a brief summary of each case. 

Formation of trihalomethanes. Reactions of chlorine with organic compounds such as fulvic and humic acids and humin produce undesirable by-products. These by-products are known as disinfection by-products, DBFs. Examples of DBFs are chloroform and bromochloromethane these DBFs are suspected carcinogens. Snoeyink and Jenkins (1980) wrote a series of reactions that demonstrate the basic steps by which chloroform may be formed from an acetyl-group containing organic compounds. These reactions are shown in Figure 17.4. 

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