The
following article is reprinted from the US Environment Protection
Agency's web site.
Drinking
Water Priority Rulemaking: Microbial and Disinfection Byproduct
Rules
Disinfection
of drinking water is one of the major public health advances in
the 20th century. One hundred years ago, typhoid and cholera epidemics
were common throughout American cities. Disinfection was a major
factor in reducing these epidemics, and it is an essential part
of drinking water treatment today. However, the disinfectants
themselves can react with naturally-occurring materials in the
water to form unintended organic and inorganic byproducts which
may pose health risks.
Over
the past ten years, we have also learned that there are specific
microbial pathogens, such as Cryptosporidium, that are highly
resistant to traditional disinfection practices. In 1993, Cryptosporidium
caused 400,000 people in Milwaukee to experience intestinal illness.
More than 4,000 were hospitalized, and at least 50 deaths have
been attributed to the disease. There have also been cryptosporidiosis
outbreaks in Nevada, Oregon, and Georgia over the past several
years.
A
major challenge for water suppliers is how to balance the risks
from microbial pathogens and disinfection byproducts. It is important
to provide protection from these microbial pathogens while simultaneously
ensuring decreasing health risks to the population from disinfection
byproducts (DBPs). The 1996 Safe Drinking Water Act (SDWA) Amendments
require EPA to develop rules to achieve these goals.
Public
Health Concerns
Most
Americans drink tap water that meets all existing health standards
all the time. These new rules will further strengthen existing
drinking water standards and thus increase protection for many
water systems.
EPA's
Science Advisory Board concluded in 1990 that exposure to microbial
contaminants such as bacteria, viruses, and protozoa (e.g., Giardia
lamblia and Cryptosporidium) was likely the greatest remaining
health risk management challenge for drinking water suppliers.
Acute health effects from exposure to microbial pathogens are
documented and associated illness can range from mild to moderate
cases lasting only a few days to more severe infections that can
last several weeks and may result in death for those with weakened
immune systems.
In
addition, while disinfectants are effective in controlling many
microorganisms, they react with natural organic and inorganic
matter in source water and distribution systems to form potentially
harmful DBPs. Many of these DBPs have been shown to cause
cancer and reproductive and developmental effects in laboratory
animals. More than 200 million people consume water that has been
disinfected. Because of the large population exposed,
health risks associated with DBPs, even if small, need to be taken
seriously.
