Robert D. Morris, MD, Ph.D., MS, is the Director
of the Center for Environmental Epidemiology and an Assistant Professor at the
Medical College of Wisconsin. He is consultant to the California Department of
Health Services, US EPA, President's Cancer Panel and US Centers for Disease
Control. He also works with the National Academy of Sciences Committee on
Environmental Epidemiology and the National Cancer Institute. He is best known
for his research on chlorination, chlorination by-products, and cancer. His
well-known paper linking disinfection by-products to cancer was published in the
American Journal of Public Health in 1992. The following are excerpts from his
presentation at a 1995 Conference in Las Vegas.
Contaminants that are causing widespread concern
as of late are Disinfection By-Products (DBP's). Many believe that DBP's are the
single greatest health threat in water supplies. DBP's are contaminants, some of
them cancer causing, that are left behind by the very chemical (chlorine) that
utilities use to make their water potable.
Since the early 1900's chlorine has been added to
drinking water to control the spread of typhoid,
Cholera, and other diseases. About 15 years ago
scientific testing identified chlorine as a potential health hazard, but it is
not the chlorine in itself that is dangerous. Scientists discovered that
chlorine reacted with organic material in water, such as decaying leaves, to
produce hundreds of chemical by-products, several of which have been proven to
be carcinogenic (Trihalomethanes make up the bulk of the cancer-causing DBP's).
Other disinfection by-products may cause adverse effects on the liver, and
nervous and reproductive systems.
The use of chlorine for water treatment to reduce
the risk of infectious disease may account for a substantial portion of the
cancer risk associated with drinking water. Trihalomethanes are associated with
increased risk of bladder and rectal cancer, possibly accounting for 5,000 new
cases of bladder cancer and 8,000 new cases of rectal cancer per year in the
U.S.. Given the large number of people who consume chlorinated drinking water,
the number of cases of cancer potentially attributable to this exposure is
substantial. Obviously, something needs to be done.
To stop chlorination of drinking water to
eliminate the elevated cancer risks from disinfection by-products would be
foolhardy. Nonetheless, these findings support expanded efforts in research and
development of alternatives to chlorination for the disinfection of drinking
There are several alternatives in reducing DBP's
in our drinking water. The first is to keep the organic matter out of the source
water. We can also find different methods of disinfection (chloramination, for
example, produces fewer by-products). Since a large percentage of the DBP's are
developed after leaving the treatment plant, an alternative may be to protect
the water delivery system from organic matter.
In the meantime, our only viable course of action
is point-of-use filtration using an activated carbon filter. Currently carbon
filtration is the only known way to get cancer-causing Trihalomethanes and other
dangerous disinfection by-products out of our nation's drinking water.
The Risks of Disinfection By-Products in Drinking Water
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