Here's the part on Chlorination from the paper... 
The Risks of Chlorination
Chlorine is an element widely used in modern chemistry be cause it
readily reacts with so many substances. The vast majority of public
water systems in this country use chlorine to disinfect their
drinking water. But the widespread application of chlorine as a
drinking water disinfecting agent has raised concerns about the
risk of human exposure to chlorine and its by-products. Past
experience with chlorine based compounds such as DDT, PCBs, and
CFCs, which were later found to pose risks to health and the
environment, have encouraged some environmental groups to call for
a total ban on all uses of chlorine, rather than waiting to study
each use of chlorine and its potential alternatives (Amato
1993).
Chlorine is toxic not just to microbes but to humans as well.
Chlorine gas escaping at the treatment plant can cause acute health
effects in workers, since the chemical is highly irritant to the
eyes, nasal passages, and respiratory system. Inhalation of the gas
can prove fatal at concentrations as low as 0.1% by volume (1,000
ppm) (AWWA 1984). At the minute amounts used in drinking water,
however, the acute toxicity of chlorine is quite low. It is rather
the potential long term risk of cancer from chronic exposure to
moderate amounts of chlorine that is the major concern with the
chemical in the drinking water supply. Much of the cancer risk from
chlorine stems from the class of complex chloroorganic compounds,
known as trihalomethanes (THMs), that are formed as one of the
major by products of the chlorination process. Trihalomethanes are
formed when chlorine is added to water containing organic
materials, such as the humic and fulvic acids emitted from
decomposing plant and animal materials in the water supply (Rook
1974; Bellar et al. 1974). Although THMs occur with chlorination of
both surface and ground waters, their concentration is much greater
with surface water because of its higher levels of naturally
occurring organic materials.
Of particular concern among the THMs is chloroform, the most
prevalent and thoroughly studied member of the THM group. Ingestion
of chloroform has been associated with an increased incidence of
cancerous tumors in multiple laboratory animal bioassays. These
tumors occurred at several sites, most notably in the kidney and
liver, as well as across several different species and strains of
animals (National Cancer Institute 1976; Roe et al. 1979) (see
Table 7.1). Although many of the animal studies focused on
chloroform administered in corn oil or toothpaste, others also
found increased evidence of tumors when the chloroform was
administered in drinking water (Jorgenson et al. 1985).
Using the mouse liver tumor data (NCI 1976), the EPA originally
estimated an upper-bound cancer risk--that is, a worst-case
analysis--that indicated that the lifetime risk from exposure to
chloroform could reach as high as one cancer per 2,500 members of
the population exposed (EPA 1977). On the basis of this analysis,
the agency began to regulate chloroform and other THMs in 1979,
setting a "maximum contaminant level" of 0.10 milligrams per liter
(or 100 parts per billion) for total trihalomethanes in the
drinking water supply. The incremental lifetime cancer risk from
ingesting chloroform in household water at this level has been
estimated to be about two in 100,000 (Maxwell et al. 1991). In
other words, if 200 million people drank household water at EPA's
maximum chloroform level for their entire lives, about 4,000 would
die of chloroform induced cancer.
Chloroform is not the only by-product formed in the chlorination
process that has been subjected to animal toxicity testing. Other
major trihalomethanes, as well as trichloroacetic acid,
dichloroacetic acid, various haloacetonitriles, and chlorophenols
have been reported to show carcinogenicity, mutagenicity, or other
toxic properties (Cotruvo and Regelski 1989; Simmon and Tardiff
1978; Herren-Freund et al. 1987; Bull 1982). For other by-products,
however, such as various chlorinated acids, alcohols, aldehydes,
and ketones, there is limited information on their potential toxic
effects (Cotruvo and Regelski 1989). There is also a plethora of
nonvolatile byproducts formed in the chlorination process for which
there are limited data on toxicity and other effects (NAS 1987).
Identifying and testing these substances has been a relatively slow
process, and much work is continuing in this area (Bull
1982).
In humans, chlorinated water has been associated with an increased
risk of bladder, colon, and rectal cancer in multiple
epidemiological studies (Crump and Guess 1982; Williamson 1981).
These studies, in general, have found the risks of bladder, colon,
and rectal cancer associated with drinking chlorinated water to be
about 1.1 to 2.0 times higher than the risk for drinking the same
quantity of unchlorinated water (Crump and Guess 1982). The
aggregate cancer risk from drinking chlorinated water over a
lifetime, however, remains modest.
One of the studies finding a significant positive association, the
large case control work by Cantor and colleagues (1987), suggests
that lifetime consumption of chlorinated water in creases the risk
of bladder cancer by a factor of about two. The study compared
those residing for more than forty years in communities where
drinking water was chlorinated with those who drink unchlorinated
water. This association may result in about 1,000 to 3,000 excess
bladder cancers per year in the United States and could explain as
much as 25 to 30 percent of the occurrence of bladder cancer in
adults residing in chlorinated communities (Cantor et al.
1987).
As with many epidemiological studies, however, there are numerous
problems with the studies of chlorinated water. Multiple
uncontrolled confounding factors (for example, smoking, diet,
occupation, lifestyle) could also explain part or all of the
observed cancer rates. Inexactness in measuring the chlorine level,
water consumption, population migration, and other variables
detracts from the definitiveness of the estimated association.
Also, because much of the nation's water is chlorinated, the number
of individuals who can serve as study controls those who drink
unchlorinated water-is limited. Taken together, however, these
studies have been interpreted as suggesting a significant
association of bladder, colon, and rectal cancer with chlorinated
drinking water (EPA 1985). This risk is highest in drinking water
contaminated with organic material, but, given the myriad
by-products formed in the chlorination process, any of a number of
substances or combination of substances could be involved.
Additional health effects from chlorine have also been revealed in
human studies. Of particular interest is a suggested relationship
between consumption of chlorinated water and an increase in the
total serum cholesterol levels of populations suffering from a diet
deficient in calcium. While the increase in cholesterol levels was
found to be small, it suggests that consumption of chlorinated
water could be a possible risk factor for cardiovascular disease as
well as for cancer (Wones et al. 1989; Zeighami et al. 1990).
Ingestion is not the only route of exposure to these substances in
drinking water. There may also be adverse effects from inhalation
or dermal exposure during showering, bathing, or swimming. It has
been postulated, for example, that exposure to volatile chemicals
in drinking water through inhalation may be as large or even larger
than exposure from ingestion alone (Maxwell et al. 1991; McKone
1987).
As with most suspected carcinogens, the adverse health effects
associated with chlorine by-products are largely chronic,
cumulative, and may involve a long latency period before they
appear. The health risks are estimated assuming a constant exposure
of many years or often many decades. It may also be several decades
before any adverse effects, such as excess cases of cancer, become
apparent.
