R. J. FRIESEN, editor I
university of Woterloo Waterloo, Ontario. Conodo
. /'
Chlorine in Your Water J G. Smith University of Waterloo Waterloo, Ontario N2L 3Gl In North America, the use of chlorine or hypochlorites to disinfect water supplies is very common. Historically, the first use of chlorine as a germicide was in 1846 when the practice of a physician scrubbing and cleansing his hands in chlorine water was introduced at the Vienna General Hospital. With the recognition that some diseases (e.g., cholera) were transmitted through the water supply, chlorination became common, as did legislation requiring chlorination of both water supplies and waste waters. In the United States alone, about 200,000 tons of chlorine are used yearly for this purpose. A solution of chlorine in water is not a simple system. Three species are present: chlorine (Cld, hypochlorous acid (HOC1) and hypochlorite ion (OCI-)
+
CC
H?O
t
HOCl
+
H+
+
OH
OH
OH
I
CI msnor.hlorupl~molr
dichlorophenalr
Humans are especially sensitive to 2,6-dichlorophenol-a 656 / Journal of Chemical Education
d~chlorophenolr
-
Cl-
HOCl F= H+ + OC1and the relative amounts depend upon the pH. If the solution is strongly acidic, free chlorine predominates; if strongly basic, the hypochlorite ion predominates. Water usually falls into the 6 to 8 p H range and here the active agent is hypochlorous acid. Its germicidal activity, which is 150-300 times greater than hypochlorite ion, has been attributed to its unique ability to penetrate bacterial cell walls. Concentrations of less than 10 ppm are normally used to disinfect water. The reactivity of hypochlorous acid has disadvantages when organic impurities are present in the treated water. Reactions can occur between the organic compounds to form chlorine-containing products. The effect of these new products on aquatic life and on humans has recently become a matter of concern. A frequent complaint of people consuming chlorinated water is connected with unpleasant odors and tastes. While improper chlorination of water does introduce an "off' taste, the usual cause is the presence of a chlorination product from an organic contaminant. The most carefullystudied problem involves phenol, a commonly used chemical intermediate which frequently contaminates industrial waste waters. Chlorination leads to substitution of the aromatic ring hydrogens by chlorine to give monochloro- and dichloro- phenols. ?H
detectable "off" flavor is reported a t one part in 10,000 million. The usual solution to tastelodor problems is superchlorination-a process pioneered in the twenties with the Toronto water supply. Briefly, this process uses more chlorine than needed to disinfect the water, and the chlorination continues to produce compounds (e.g., trichlorophenol) which do not have ohjectionahle odors and tastes. At the University of Waterloo, we have been investigating how far this chlorination can go and have detected products such as the "other products" shown in the equation below.
other praduers
The question of toxicity of chlorinated industrial wastes towards aquatic life has been investigated recently. Many pulp and paper mills bleach pulp with chlorine and the effluents from this process are toxic to fish. Several toxic compounds have been identified, some of which are wood extractives formed in the living tree (e.g., resin acids and unsaturated fatty acids). However, others are chlorinated derivatives of the phenolic constituents of wood such as
CI
4 OH
OH
or oxidation products such as
: *CI c
CI
Increasing concern has been shown over the effect of toxic compounds on humans, even though present in very low concentrations, in water supplies. Late in 1974, the results were released of an analytical study of the New Orleans' drinking water. Some 66 compounds were identified, most being present in concentrations of one part per billion. However, chloroform (CHC13)-a suspected carcinogen-was present a t 100 times this level. A second study, released a t ahout the same time, dealt with a statistical analysis of the cancer mortality rate among white males. Those who drank water from the Mis-
sissippi river had a 15 per cent higher cancer mortality rate than those who obtained their water from wells. Well water, in contrast to river water, is not likely to be contaminated with chemicals. This is the first time that two such studies appear to link a human health ~ r o b l e mto chlorination. It is premature to conclude that chlorination does increase the-incidence of cancer since factors such as smoking, diet, alcohol consumption and air pollution were not included in the statistical study. However, there is cause for concern. A marked expansion in the analytical survey of municipal water supplies has been scheduled by the US. Environmental Protection Agency. No doubt, additional statistical analyses of health problems will be included. There is the additional chemical problem of the source of the chloroform detected in water supplies. Chloroform is a common industrial solvent, and i t is quite possible that i t is simply another pollutant. As such, proper treatment of industrial wastes will remove it. However, hypochlorous acid is known to react with methyl ketones to produce chloroform. The reaction, shown below, is a general one, .
II
RCCH:,
+ 3HOCI
I
+
RCOH
+ CHCb + 2 H P
and, a t one time was adapted to a chemical test for the structural unit
One of the most common organic solvents in use is acetone 0
and the chlorination of water containing acetone might well be the source of the chloroform detected in New Orleans. What alternatives are there to chlorination? T o eliminate treatment of water supplies would be foolish. Studies oerformed on communities before and after the introduction of adequate water treatment showed that the general overall health of the community greatly improved. For every person saved from death by typhoid, three other persons were saved from death by other causes-many of
which were not thought to he connected with the quality of the water supply. The elimination of all organic impurities from water supplies is one solution, but a very difficult one to achieve and certainly very expensive. The most likely solution is finding an alternative to chlorine as a disinfectant. While several methods have been suggested, the use of ozone appears to be the most promising. Communities in Europe have used ozone for a number of years, and both our provincial and federal environmental agencies are now interested in the process. Ozone has been shown to be effective against bacteria and viruses, but it does not react with ammonia (a common impurity in water) to form less reactive compounds. I t is a strong oxidant. and ozonated organics are biodemaded moreeasily th& chlorinated comp&nds. Its disadvantages are two: (1) its instabilitv in water means that no residuum exists to maintain wate; protection should water hecome contaminated during distribution, and (2) the cost of generating ozone is substantially high& than using chlorine. Other methods such as ultra-sonics or lasers are being investigated, but must be viewed as possible long-range s&tions. New Journal The magazine, Canadian Chemical Education, seeks to stimulate an exchange of ideas between teachers of the first three or four years-of chemistry learning, be i t a t high school, junior college or introductory university level. For a sample copy of the magazine, write to the Editor, Reg Friesen, Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1. Canadian Chemical Education appears six times per year. The subscription rate is $5.00 per year in Canada, $6.00 elsewhere. CHEM ED 75 Report and Vldeotapes
An extensive report of CHEM ED 75-a conference of North American classroom chemistry teachers-will be published during the fall. Copies will be available a t a cost of $1.75 each from Mr. L. H. Sihley, CHEM ED 75, Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1. (Conference registrants will automatically receive a copy.) Videotapes of many of the sessions are available for purchase. For information, write to Mr. Hector LeBlanc, Lincoln County Board of Education, 112 Oakdale Avenue, St. Catharines, Ontario L2P 359.
Volume 52, Number 10, October 1975 / 657
