Civil Engineering Reference
In-Depth Information
acid is the predominant species between pH 2 and pH 7, and hypochlorite ion is the
predominant at high pH values. In aqueous systems, chlorine reacts with ammonia to
form chloramines. See Chapters 14 and 19 for more extensive discussions of chlorine
chemistry.
Chlorine remains the most widely used disinfectant and oxidant in U.S. drinking
water systems.
Health Effects
The primary health concerns for chlorine are associated with the
formation of halogenated organics, such as trihalomethanes and haloacetic acids. These
are discussed in Chapter 3. For chlorine itself, no evidence has been reported of re-
productive or developmental effects. No systematic effects were observed in rodents
following oral exposure to chlorine in distilled water at levels up to 275 mg / L over a
two-year period. Chlorinated water has been shown to be mutagenic to bacterial strains
and mammalian cells; however, investigations with rodents to determine the potential
carcinogenicity of chlorine have been negative.
3
Chlorine Dioxide, Chlorite, and Chlorate
Formation and Occurrence
Chlorine dioxide has been used on a limited basis in
U.S. drinking water systems as either a disinfectant or as a preoxidant for taste and
odor control or color removal. It is an explosive gas, but it is stable in water in the
absence of light and elevated temperature. Because of its instability, it is normally
generated at the point of use.
In drinking water, the predominant reaction products are chlorite, chlorate, and
chloride. Approximately 50 to 70 percent of the chlorine dioxide will initially react to
form chlorite. A fraction of the chlorite will, in turn, be reduced to chloride.
Pure chlorine dioxide per se does not react to form THMs, although some chlorine
may be present as an impurity, leading to low levels of THM formation. Also, chlo-
rine dioxide does not react with ammonia, but it will react with other amines. Since
chlorine dioxide does not react with water as chlorine does, residual chlorine dioxide
may be easily separable from water with mild aeration.
Health Effects
The health effects of chlorine dioxide, chlorite, and chlorate have been evaluated sep-
arately, as discussed below.
Chlorine Dioxide.
Generally, health concerns for chlorine dioxide are the same as those
described for chlorite (see below), because chlorine dioxide converts to chlorite in
vivo. No studies of the carcinogenic effects of ingested chlorine dioxide are available,
but concentrates of ClO
2
-treated water did not increase the incidence of lung tumors
in mice.
3
Chlorite.
Adverse effects of chlorite on the hematological systems of laboratory ani-
mals is well documented. In a variety of reproductive effect tests, chlorite was asso-
ciated with a decrease in growth rate of rat pups, and delayed neurodevelopment was
reported in rat pups exposed perinatally to chlorite. A two-generation reproductive and
developmental study by the Chemical Manufacturers Association found neurodevel-
opmental effects at 6 mg / kg-day
1
.
18
Mutagenicity testing of chlorite with mice has
been negative, and no tumorigenic activity has been observed in animals given an oral
