Threats to Human Health: Use of Chlorine, an Obsolete Treatment Technology - Global Drinking Water Management and Conservation - page 195

Table 9.6 Association of Average Exposure to THMs Higher than 1 μ g/L with Bladder Cancer,
Within Speci c Time Windows of Exposures for Men (Villanueva et al. 2004 )
Time window before the interview OR (95 percent CI) a Adjusting for

All Other Time Periods

OR (95 percent CI)

5 - 14 years 1.15 (1.00 - 1.32) 1.05 (0.84 - 1.31)

15 24 years 1.19 (1.04 1.36) 0.92 (0.70 1.21)

- - -

1.58)
35 - 45 years 1.24 (1.07 - 1.44) 1.13 (0.93 - 1.37)
a Odds Ratios are adjusted for sex, age, center, smoking status, education, ever worked in high-risk
occupations, heavy coffee consumption (5 cups/day) and total fluid intake. The analysis was
conducted only among subjects with 70 percent exposure information

25 34 years 1.29 (1.12 1.48) 1.22 (0.95

- - -

9.2.1.2 Colon and Rectal Cancer

A study conducted in Iowa, USA from 1986 to 1987 by Doyle et al. ( 1997 ).
assessed the relationship between chlorination DBPs in drinking water and colon
cancer in women. They found that the exposure to chlorination DBPs in drinking
water was associated with increased risk of colon cancer for women. These

findings
are consistent with some, but not all previous epidemiological and animal studies,
and suggest that long-term exposure to chlorination DBPs in drinking water may be
associated with an increased risk of cancer in humans (Doyle et al. 1997 ).
King et al. ( 2000 ) undertook a population-based case-control study in southern
Ontario, Canada from 1992 to 1994 to assess the relationship between chlorinated
byproducts in public water supplies and cancers of the colon and rectum by using
the THMs as an indicator of DBPs. The analyses included 767 colon cases, 661
rectal cases, and 1,545 controls. For men, colon cancer risk was increased and
associated with cumulative exposure to THMs in drinking water, and men exposed
to chlorinated drinking water for 35 years had an increased risk of colon cancer
compared with those who were exposed to THMs for less than 10 years. The
probability of colon cancer reached 53 percent higher after at least 35 years of
exposure to THMs (see Table 9.7 ). The cumulative THM exposure was associated
with a 17 percent increase in risk for each 1,000 g/L per year. Moreover, the long-

term (at least 35 years) exposure to a THM level of 75

μ

g/L was associated with a
doubled colon cancer risk in men, while these relationships were not observed
among women. Furthermore, in the analysis of rectal cancer, no relationship was
observed between rectal cancer risk and any of the measures of exposure to
chlorination DBPs for either gender (see Table 9.7 ).
In contrast, Bove et al. ( 2007 ) conducted a case control study of 128 cases and
253 controls in Monroe County, Western New York State, USA from 1998 to 2003
to assess the effects of exposure to four primary THMs in drinking water on rectal
cancer among white males by using a logistic regression, and found that increasing
levels of three of the four primary THMs did correspond with an increase in risk for
rectal cancer, although risk of rectal cancer did not increase with total level of

μ