Trihalomethanes, THMs

Trihalomethanes. Wherever chlorine is used as a disinfectant in drinking-water treatment, trihalomethanes (THMs) generaUy are present in the finished water. The THMs usuaUy formed are trichloromethane (chloroform), bromodichloromethane, dibromochloromethane, and tribromomethane (bromoform). There are four main techniques for the analysis of THMs headspace, Hquid— Hquid extraction (Ue), adsorption—elution (purge—trap), and direct aqueous injection. The final step in each technique involves separation by gas—Hquid chromatography with a 2 mm ID coUed glass column containing 10 wt % squalene on chromosorb-W-AW (149—177 p.m (80—100 mesh)) with detection generaUy by electron capture. 

AC filtration does remove some organic chemicals that can be harmful if present in quantities above the EPA Health Advisory Level (HAL). Included in this category are trihalomethanes (THM), pesticides, industrial solvents (halogenated... 

Brewing Potable water treatment Removal of trihalomethanes (THM) and phenolics... 

Activated carbon filters are employed primarily as RW contaminant removal systems for chlorine (by chemisorption) and various organics such as trihalomethanes (THMs), petroleum products, and pesticides (by adsorption). In addition, they act as physical filters and therefore incorporate sufficient freeboard in their designs to permit periodic backwashing. 

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). 

We mentioned in Chapter 2 (Section 2.6.1) that a purge-and-trap procedure sometimes precedes an analysis by gas chromatography. An example of this procedure is found in the City of Lincoln, Nebraska, Water Treatment Plant Laboratory. Water treatment includes chlorination. When water is chlorinated, chlorine reacts with organic matter to form trihalomethanes (THMs), such as chloroform, bromoform, bromodichloromethane, and chlorod-ibromomethane. THMs in water are regulated by the Safe Drinking Water Act, and so the laboratory must analyze the treated water to determine their concentration. 

Kroll RB, Robinson GD, Chung JH. 1994a. Characterization of trihalomethane (THM)-induced renal dysfunction in the rat. II Relative potency of THMs in promoting renal dysfunction. Arch Environ Contam Toxicol 27(l) 5-7. 

This problem can be solved knowing that for certain sets of compounds such as the trihalomethanes (THMs), B is approximately independent of the compound s particular structure that is, plots of In Kaw versus T-1 show a set of parallel lines. Given that B is nearly constant within in the temperature range, and substituting B in eq. 12.5.3 by C and BT ] by Co leads to... 

NOTE Chlorine is widely used in the protection of drinking water, the manufacture of pharmaceuticals, crop pesticides, paper, rubbers, resins and plastics, and thousands of other products. Nevertheless, since the early 1990s, there has been a groundswell of opinion to either ban or severely limit the use of chlorine in all manners of processes. This is based on observations associated with the probable adverse effect to the environment from certain chlorinated organic chemicals, such as polychlorinated biphenyl (PCB) and the insecticide DDT. There is also concern in a number of other areas, for example, that free chlorine may contribute to effluent toxicity due to the formation of chloramines and trihalomethanes (THMs). In the United States in 1993 to 1994, this opinion was fueled by the possibility that the Environmental Protection Agency (EPA) would... 

Trihalomethanes (THMs) are priority pollutants listed by the U.S. Environmental Protection Agency (EPA). They are recalcitrant in nature, thus their destruction is difficult. The most commonly encountered THMs in drinking water threatening human health are chloroform, bromodichloromethane, dibromochloromethane, and bromoform. Tang and Tassos (1997) studied the oxidation kinetics and mechanisms of these four THMs. 

The absence of chromatographic separation makes MIMS a fast technique. It is advantageous in some applications where only select compounds are to be detected or the total concentration of a mixture is to be determined. For instance, the total concentration of trihalomethanes (THMs, including chloroform, bromoform, bromodichloromethane, and dibromo-chloromethane) in drinking water can be determined by MIMS in less than... 

Finally, Sotelo et al. [179], while studying the ozonation of resorcinol and phloroglucinol, two precursors of trihalomethanes (THM) during water chlorination, found some polar intermediates that confirmed the proposed phenol mechanism reported elsewhere [42]. From the identified intermediates it was deduced that ozonation of phenols yields more oxygenated compounds that eventually could be removed in biological steps. 

A significant advantage of UV over use of chemical oxidizers for microbial control is that no trihalomethane (THM) compounds are generated (see Chapter 8.2.1). Additionally, the need to store and feed a hazardous chemical oxidizer is avoided. 

The trihalomethanes (THM) standard is a measurement of total trihalomethanes for a 4-quarter running annual average, based on average values throughout the distribution system. 

Chlorine reacts with naturally occurring organic matter in raw water to form a range of unwanted by-products. Guideline values have been established for a number of these byproducts. The compounds most widely considered as representatives of chlorination by-products for the purposes of setting standards and monitoring are the trihalomethanes (THMs) which include chloroform, bromodichloromethane, chlorodibromomethane and bromoform. 

Disinfectants are usually only monitored to ensure that disinfection has taken place. Certain disinfectants, such as chlorine, are sometimes monitored at the tap or in the distribution system, as a measure of the quality in distribution. A wide range of potential by-products of disinfection may be formed in treatment, particularly if natural organic matter is present at high concentrations. The most commonly monitored by-products are the trihalomethanes (THMs) formed through chlorination THMs are normally considered to be an adequate marker of the total disinfection by-products from chlorination. Some countries also monitor haloacetic acids, but these are difficult and expensive to analyse because of their high polarity. Bromate is sometimes measured when ozone is used, but its formation relates to bromide concentrations in the raw water and the conditions of ozonation. Analysis can be extremely difficult and monitoring is not usually considered except where standards have been set or on an infrequent basis. 

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