Chlorinated Water link to Cancer, and by-products (trihalomethanes) of Chlorination causes lymphoma, leukemia, and cancers of the liver, kidney, and/or intestine of rats and mice.

This following study shows that rats who drank chlorine (in the form of sodium hypochlorite and chloramine) developed more lymphoma and leukemia cancers.

Soffritti M, Belpoggi F, Lenzi A, Maltoni C (1997) Results of long-term
carcinogenicity studies of chlorine in rats. Ann NY Acad Sci, 837:
189-208.

Four groups, each of 50 male and 50 female Sprague-Dawley rats, of the
colony used in the Cancer Research Center of Bentivoglio of the Ramazzini
Foundation, 12 weeks old at the start of the study, received drinking
water containing sodium hypochlorite, resulting in concentrations of
active chlorine of 750, 500, and 100 mg/l (treated groups), and tap water
(active chlorine < 0.2 mg/l) (control group), respectively, for 104 weeks.
Among the female rats of the treated groups, an increased incidence of
lymphomas and leukemias has been observed, although this is not clearly
dose related. Moreover, sporadic cases of some tumors, the occurrence of
which is extremely unusual among the untreated rats of the colony used
(historical controls), were detected in chlorine-exposed animals. The
results of this study confirm the results of the experiment of the United
States National Toxicology Program (1991), which showed an increase of
leukemia among female Fischer 344/N rats following the administration of
chlorine (in the form of sodium hypochlorite and chloramine) in their
drinking water. The data here presented call for further research aimed at
quantifying the oncogenic risks related to the chlorination of drinking
water, to be used as a basis for consequent public health measures.

The following study was done to clear up confusion on whether chlorine and chloramine in drinking water causes cancer. They also studied the trihaomethanes by-products. The trihalomethanes caused cancer in the liver, kidney, and/or intestine of rats and mice. Future Research in the cancer-drinking water link should be directed to these chemical by-products of chlorination.

Dunnick JK, Melnick RL (1993) Assessment of the carcinogenic potential of
chlorinated water: experimental studies of chlorine, chloramine, and
trihalomethanes. J Natl Cancer Inst, 85: 817-822.

BACKGROUND: Water chlorination has been one of the major disease
prevention treatments of this century. While epidemiologic studies suggest
an association between cancer in humans and consumption of chlorination
byproducts in drinking water, these studies have not been adequate to draw
definite conclusions about the carcinogenic potential of the individual
byproducts.

PURPOSE: The purpose of this study was to investigate the carcinogenic
potential of chlorinated or chloraminated drinking water and of four
organic trihalomethane byproducts of chlorination (chloroform,
bromodichloromethane, chlorodibromomethane, and bromoform) in rats and
mice.

METHODS: Bromodichloromethane, chlorodibromomethane, bromoform, chlorine,
or chloramine was administered to both sexes of F344/N rats and (C57BL/6 x
C3H)F1 mice (hereafter called B6C3F1 mice). Chloroform was given to both
sexes of Osborne-Mendel rats and B6C3F1 mice. Chlorine or chloramine was
administered daily in the drinking water for 2 years at doses ranging from
0.05 to 0.3 mmol/kg per day. The trihalomethanes were administered by
gavage in corn oil at doses ranging from 0.15 to 4.0 mmol/kg per day for 2
years, with the exception of chloroform, which was given for 78 weeks.

RESULTS: The trihalomethanes were carcinogenic in the liver, kidney,
and/or intestine of rodents. There was equivocal evidence for
carcinogenicity in female rats that received chlorinated or chloraminated
drinking water; this evidence was based on a marginal increase in the
incidence of mononuclear cell leukemia. Rodents were generally exposed to
lower doses of chlorine and chloramine than to the trihalomethanes, but
the doses in these studies were the maximum that the animals would consume
in the drinking water. The highest doses used in the chlorine and
chloramine studies were equivalent to a daily gavage dose of
bromodichloromethane that induced neoplasms of the large intestine in
rats. In contrast to the results with the trihalomethanes, administration
of chlorine or chloramine did not cause a clear carcinogenic response in
rats or mice after long-term exposure.

CONCLUSION: These results suggest that organic byproducts of chlorination
are the chemicals of greatest concern in assessment of the carcinogenic
potential of chlorinated drinking water.