Trihalomethanes in drinking water and human colorectal cancer

The relation of trihalomethanes (THM) to colorectal cancer was evaluated. A total of 395 colorectal cancer deaths among white women teachers in New York State was compared to an equal number of deaths of teachers from noncancerous causes. Cumulative chloroform (CHCI₃) exposure was estimated by the application of a statistical model to operational records from the individual water treatment facilities that served the home and work addresses of each study subject during the 20 years prior to death. The odds of exposure to a surface source containing little or no THM was no greater for cases than for controls. The odds ratio=1.07; the 90% confidence interval=0.79–1.43; and the P=.68. The distribution of CHCI₃ exposure was not significantly different between cases and controls (rated by Wilcoxon signed rank statistic=-0.52; P=.60). No effect of cumulative CHCI₃ exposure on outcome was seen in a logistic analysis controlling for average source type, population density, marital status, age, and year of death (likelihood ratio test statistic=0.047; P=.83).