Halogen disinfectants

US Environmental Protection Agency (US EPA) has surveyed 10 operating water utilities for the presence of 22 halogenated disinfection by-products in chlorine-treated water (31). Table 4 presents the frequency and range of concentrations of those by-products of greatest concern. Table 5 summarizes the current knowledge of health effects of selected chlorination by-products. Researchers are continuously studying the by-products associated with ozonation. To date, however, extensive studies of by-products of treatment with ozone, chloramination, and chlorine dioxide have not been conducted. 

J. Glater, M.R. Zachariah, S.B. McCray, J.W. McCutchen, Reverse osmosis membrane sensitivity to ozone and halogen disinfectants. Desalination 48 (1983) 1. 

The equihbrium constant of this reaction is 5.4 x 10 at 25°C, ie, iodine hydrolyzes to a much smaller extent than do the other halogens (49). The species concentrations are highly pH dependent at pH = 5, about 99% is present as elemental at pH = 7, the and HIO species are present in almost equal concentrations and at pH = 8, only 12% is present as and 88% as HIO. The dissociation constant for HIO is ca 2.3 x 10 and the pH has tittle effect on the lO ion formation. At higher pH values, the HIO converts to iodate ion. This latter species has been shown to possess no disinfection activity. An aqueous solution containing iodate, iodide, and a free iodine or triodide ion has a pH of about 7. A thorough discussion of the kinetics of iodine hydrolysis is available (49). 

Propylene oxide is a useful chemical intermediate. Additionally, it has found use for etherification of wood (qv) to provide dimensional stabiUty (255,256), for purification of mixtures of organosiUcon compounds (257), for disinfection of cmde oil and petroleum products (258), for steriliza tion of medical equipment and disinfection of foods (259,260), and for stabilization of halogenated organics (261—263). 

Potable Water Treatment. Treatment of drinking water accounts for about 24% of the total activated carbon used in Hquid-phase apphcations (74). Rivers, lakes, and groundwater from weUs, the most common drinking water sources, are often contaminated with bacteria, vimses, natural vegetation decay products, halogenated materials, and volatile organic compounds. Normal water disinfection and filtration treatment steps remove or destroy the bulk of these materials (75). However, treatment by activated carbon is an important additional step in many plants to remove toxic and other organic materials (76—78) for safety and palatability. 

Although pH determines the ratio of hypohalous acid to hypohaUte ion, the fraction of the total available halogen present as HOX is dependent on of the halamine as well as the concentration of excess amine. In the case of chloroisocyanurates, which are the most widely used /V-ch1oramine disinfectants in swimming pools and spas, the extent of hydrolysis at 1 ppm av CI2 (as monochloroisocyanurate) is - 34% but only - 1% when 25 ppm cyanuric acid is added (4). Nevertheless, effective disinfection can stiU occur with chloroisocyanurates if a sufficient FAC is maintained, eg, 1—3 ppm. The observed reduction in disinfection rate because of cyanuric acid (6) has been shown to be direcdy related to the concentration of HOCl formed by hydrolysis of chloroisocyanurates (10). 

The interhalogen compounds are the bromine- and iodine-base materials. It is the larger, more positive halogen that is the reactive portion of the interhalogen molecule during the disinfection process. Although only used on a limited basis at present, there are members of this class that show great promise as environmentally safe disinfectants. 

Two approaches that have been investigated recently for disinfection are mixtures of bromine and chlorine, and mixtures containing bromide or iodide salts. Some evidence exists that mixtures of bromine and chlorine have superior germicidal properties than either halogen alone. It is believed that the increased bacterial activity of these mixtures can be attributed to the attacks by bromine on sites other than those affected by chlorine. The oxidation of bromide or iodide salts can be used to prepare interhalogen compounds or the hypollalous acid in accordance with the following reaction ... 

Of the four halogens, iodine is the weakest oxidizing agent. Tincture of iodine, a 10% solution of I2 in alcohol, is sometimes used as an antiseptic. Hospitals most often use a product called povidone-iodine, a quite powerful iodine-containing antiseptic and disinfectant, which can be diluted with water to the desired strength. These applications of molecular iodine should not delude you into thinking that the solid is harmless. On the contrary, if I2(s) is allowed to remain in contact with your skin, it can cause painful bums that are slow to heal. 

Chlorine and iodine have been used extensively since their introduction as disinfecting agents in the early 19th century. Preparations containing these halogens such as Dakin s solution and tincture of iodine were early inclusions in many pharmacopoeiae and national formularies. More recent formulations of these elemens have improved activity, stability and ease of use. 

Many derivatives of phenol are now made by a synthetic process. Homologous series of substituted derivatives have been prepared and tested for antimicrobial activity. A combination of alkyl substitution and halogenation has produced useful derivatives including clorinated phenols which are constituents of a number of proprietary disinfectants. Two ofthe most widely used derivatives are/ -chloro-m-cresol (4-chloro-3-methylphenol, chlorocresol, Fig. 10.7C) which is mostly employed as a preservative at a concentration of 0.1%, and / -chloro-m-xylenol (4-chloro-3,5-dimethylphenol, chloroxylenol. Fig. 10.7C) which is used for skin disinfection, although less than formerly. Chloroxylenol is sparingly soluble in water and must be solubihzed, for example in a suitable soap solution in conjunction with terpineol or pine oil. Its antimicrobial capacity is weak and is reduced by the presence of organic matter. 

Mar f chemical disinfectants (see also Chapter 10), in particular the halogens, some phenohcs and QACs, are inactivated in the presence of organic matter and it is essential that all cleaning materials such as buckets and fogging sprays are kept cleaa Halogens rapidly deteriorate at their use-dilution levels and QACs are liable to become contaminated with P5. aeruginosa if stored diluted. For such reasons it is preferable to store the bulk of the disinfectant in a concentrated form and to dilute it to the use concentration only as required. 

Halogenation is important for disinfecting drinking water supplies, generally nsing molecular chlorine. Most attention has been directed to the adverse production of haloforms and haloacetates from reactions of chlorine with natural substrates, although in water containing bromide/iodide, a nnmber of other reactions may occur. 

Fujita et al. [18] studied formation of halogenated (chlorinated and brominated) NPEOs and NPECs during wastewater treatment. Halogenated derivatives were found to be produced during the disinfection processes by chlorination accounting for up to 10% of total nonylphenolic compounds. They were found in 25 of 40 WWTPs with concentrations up to 6.5 xgL 1 in secondary effluent and 52.4 jig L-1 in final effluent. Of all halogenated compounds, BrNPECs (nEo = 1-2) were found to be the most abundant. 

PEI resists mineral acids, dilute bases (pH less than 9), freons, oils, greases, gasoline, most fuels, certain hydrocarbons and fully halogenated hydrocarbons, most cooking oils and greases, most detergents and disinfectants... 

Determination of Chlorinated Disinfection Byproducts and Chlorinated Solvents, and Halogenated... 

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