Threats to Human Health: Use of Chlorine, an Obsolete Treatment Technology - Global Drinking Water Management and Conservation - page 194

Table 9.4 Odds Ratios estimated in Meta-Analysis (Villanueva et al. 2003 )
Combined unit increase Slope Standard error Odds ratio 95 percent C. I.

0.006 0.000128 1.006 1.004 - 1.009

20 years 1.13 1.08 1.20

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1.43
60 years 1.43 1.27 - 1.72
Dose-response regression slopes obtained from weighted least squares within study, and OR with
95 percent CI obtained from the meta-analysis of the five slopes and their standard errors. Both sexes

40 years 1.27 1.17

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Table 9.5 Pooled analysis of bladder cancer and THMs, by gender (Villanueva et al. 2004 )
Odds ratios (ORs) with 95 percent Confidence Intervals
Cumulative exposure to THMs (mg) Male Female

>0 1.30 (1.14 - 1.50) 1.06 (0.77 - 1.45)

0 - 15 1.00 1.00

>15 50 1.22 (1.01 1.48) 0.92 (0.65 1.32)

- - -

>50 400 1.28 (1.08 1.51) 0.94 (0.70 1.27)

- - -

>400 - 1000 1.31 (1.09 - 1.58) 1.02 (0.74 - 1.41)

>1000 1.50 (1.22 1.85) 0.92 (0.65 1.30)

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Another very important analysis was done by Villanueva et al. ( 2004 ), who
pooled the primary data from six case-control studies of bladder cancer in USA,
Canada, France, Italy, and Finland, respectively, by using THMs as indicator of
DBPs. They found that there was an odds ratio of 1.3 in men who were ever
exposed to THMs in drinking water compared with those who were never exposed
to THMs during the 40-year exposure window, while the odds ratio for women who
were ever exposed to THMs was 1.06. The results indicate that there was an
exposure-response relationship between DBPs intake and bladder cancer for men,
but no relationship was observed in women. Moreover, the risk of bladder cancer
for men can be increased by up to 50 percent when men are exposed to more than
1,000 mg THMs during the 40-year exposure window (Table 9.5 ).
Villanueva et al. ( 2004 ) further found that men exposed to chlorinated drinking
water for 35

45 years had an increased risk of bladder cancer compared with those
exposed for less than 5 years. That is, the probability of bladder cancer is 24 percent
higher after at least 35 years of exposure to THMs, while the probability is
15 percent higher due to chlorinated water after 5

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14 years. Similar results were
found when the odds ratios are adjusted for gender, age, center, smoking status,
education, ever worked in high-risk occupations, heavy coffee consumption (5
cups/day) and total

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fluid intake. Finally, Villanueva et al. ( 2004 ) stated that “ these

findings strengthen the hypothesis that the risk of bladder cancer is increased with
long-term exposure to disinfection byproducts at levels currently observed in many
industrialized countries

” (Table 9.6 ).