Microbial Risks
Although
water treatment and sanitation methods continue to improve, the threat of
waterborne disease outbreaks persists. Animal
feeding lots, sewer overflows, and development can all put sources of pathogens
into close proximity to drinking water sources.
Drinking water comes from surface
sources (lakes, rivers, reservoirs), or groundwater (wells or springs).
Untreated surface water often contains waterborne pathogens; they can also be
found in groundwater sources. Transmission of pathogens can also occur because
of contaminated food and person-to-person or animal-to-person
contact.
In 1900, typhoid and other diarrheal
and enteric diseases were the third leading cause of death in the United
States. After drinking water filtration and chlorination were introduced in the
United States, the incidence of typhoid and other waterborne enteric diseases
declined dramatically.
More recently, two waterborne pathogens,
Cryptosporidium and Giardia intestinalis, have been associated with severe illness.
Neither Cryptosporidium nor Giardia intestinalis
multiplies in water, but chlorination is not effective against Cryptosporidium. However, modern methods of filtration such as
membrane filtration have been effective in removing the parasite.
Giardiasis, an infectious diarrheal
disease, has been linked to municipal drinking water contaminated with Giardia intestinalis, a microscopic
parasite trans-mitted by water contaminated with fecal matter from humans or
animals. Untreated mountain streams
and rivers contaminated by feces also carry the parasite.
Giardia
intestinalis
is now known as one of the most common causes of waterborne disease in the
United States. Giardiasis attacks three times as many children as adults. In
1989, the Environmental Protection Agency’s (EPA’s) Surface Water Treatment
Rule required filtration and/or strict protection of surface water sources to
protect consumers from Giardia intestinalis
in municipal water supplies.
Cryptosporidium, like Giardia intestinalis,
is a microscopic parasite that affects the gastrointestinal tracts of humans
and animals. It is introduced into the drinking water supply from fecal matter.
Before 1993, few people had heard of Cryptosporidium;
that year Milwaukee, Wisconsin, recorded the largest outbreak of
cryptosporidiosis in the history of the United States. Cryptosporidium caused more than 400,000
residents in and around Milwaukee to become ill, killed at least 50 people
whose immune systems were weakened by AIDS and cancer, and cost Milwaukee more
than $55 million.
Since 1998, EPA has issued or
proposed three new drinking water rules to protect against these and other
microbial contaminants.
Chemical Risks
Waterborne
pathogens, like Giardia intestinalis
and Cryptosporidium, are not the
only risks to drinking water. Industrial use of thousands of synthetic organic
chemicals like PCBs, increased rapidly during World War II. Chemicals such as
pesticides, plastics, and radioactive materials found their way into the
environment and drinking water sources from waste incinerators, landfills, and
even wastewater treatment facilities.
At the time, little thought was given
to the risk of contaminating the environment and drinking water sources.
Eventually, in 1962, the U.S. Public Health Service acknowledged the risk that
natural and synthetic organic compounds pose to the Nation’s water supply and
issued the first set of National Drinking Water Standards. EPA has since established
enforceable drinking water standards for dozens of chemicals.
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SPOTLIGHT
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Safe Groundwater:
Who’s Minding the Wells?
People who live in cities and towns rely on their
water system or local government to monitor their drinking water and ensure its
potability, or suitability for drinking, but people whose water comes from
private wells must monitor their own water for contaminants. About 23 million
people, mostly in rural areas of the United States, obtain their drinking water
from groundwater sources such as private wells.
One potential contaminant of
groundwater is the chemical methyl tertiary butyl ether (MTBE). MTBE is added to gasoline to boost octane and
reduce carbon dioxide emissions under the reformulated gasoline program of the
Clean Air Act Amendments. Sources of potential contamination include leaking
underground storage tanks, leaking pipelines, emissions from older marine
engines, and to a lesser degree, from storm water runoff and air deposition.
MTBE can travel rapidly through the
ground and into the groundwater, where it moves at nearly the same velocity as
groundwater itself. Therefore, when gasoline leaks from an underground tank or
is spilled, MTBE has a greater potential of contaminating drinking water.
Currently, there is limited
information about the health effects of ingesting MTBE in drinking water. Most
of the health-related research conducted to date has focused on adverse effects
associated with inhaling MTBE. In animal inhalation studies using high doses of
MTBE, results have been inconclusive: both
cancerous and noncancerous health effects have been observed. In 1997, EPA
issued a Drinking Water Advisory setting recommended limits on concentrations
of MTBE between 20 and 40 parts per billion (ppb) or lower to protect against
adverse taste and odor.
MTBE has been detected in an
increasing number of drinking water supplies throughout the Nation
(approximately 10% of wells tested). Studies have shown that MTBE is detected
in groundwater more often and at higher concentrations in areas where
reformulated gasoline is sold (i.e., where there is a fuel oxygenate mandate).
In Maryland, more than 200 well
owners have complained of MTBE problems with their well water. The affected
wells are generally on top of or near underground gasoline storage tanks.
Federal law set 1998 as the deadline for upgrading or removing any storage
tanks that leak, but there is evidence that newer tanks are also leaking.
The Maryland Department of the
Environment is hoping to receive financing from its State legislature to
conduct a study of the effects of MTBE on Maryland’s groundwater; a bill has
been introduced that would authorize the use of up to $300,000 per year for
such a study.
MTBE is detected by a turpentine-like
taste or smell in the water. If tests reveal
high levels of MTBE, the well water can be filtered through carbon as it
enters the home. Testing costs between $85 and $300 and is done by private
laboratories.
Well owners can protect their
groundwater supply by keeping contaminants such as gasoline and used motor oil
away from the well area and out of septic systems and never mixing or using
pesticides, fertilizers, degreasers, or other pollutants near the well.
To guard against MTBE and other
contaminants, well owners also should periodically inspect the well for cracks
or damage, disinfect the well once a year, have the well tested yearly for
bacteria and nitrates, and have pumps and septic systems inspected
periodically. Testing for nitrate and bacteria typically costs $10 to $20.
EPA’s Safe Drinking Water Hot-line (800-426-4791) can provide more information
and access to its publications.
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Examples Of FEDERAL SAFE WATER
PROJECTS
h
The
Centers for Disease Control and Prevention (CDC), in collaboration with the
U.S. Environmental Protection Agency (EPA), conducts surveillance for
waterborne disease outbreaks. When outbreaks occur, CDC often joins with State
health departments and other Federal agencies to conduct investigations.
h
CDC’s
National Center for Infectious Diseases and EPA are conducting studies to
determine the incidence of illnesses from drinking water. Laboratory tools
being developed at CDC are being used to better understand sources of water
contamination and causes of waterborne outbreaks.
h CDC’s National Center for
Environmental Health (NCEH) is conducting a multiphase project to assess the
extent of human exposure to naturally occurring toxins (e.g., neuro- and hepato-toxins produced by blue-green algae) in drinking water and to identify
potential human health outcomes associated with these exposures.
h NCEH is conducting studies that focus on the public
health impact of disinfection by-products. Disinfection by-products are
produced when disinfectants are used to reduce microbial contamination in
drinking water (e.g., chlorine). Epidemiologic studies have found associations
between exposure to high levels of disinfection by-products and subsequent
bladder cancer, spontaneous abortion, and birth defects.
h The National Institute of
Environmental Health Sciences (NIEHS) National Toxicology Program (NTP), in collaboration with EPA, is
also conducting toxicity and carcinogenicity studies of the potential public
health impact of disinfection by-products. NTP studies also study disinfection
by-products for their reproductive effects, birth defects, immunotoxicity, and
neurotoxicity.
h NTP is collaborating with
the Chemical Industry Institute of Toxicology (CIIT) to evaluate disinfection
by-products by inhalation since some of these chemicals are volatile and
exposure may occur during showers or during cooking.
h NTP is collaborating with
EPA to evaluate chemical contaminants and naturally occurring toxins found in
drinking water sources, which are not removed by standard drinking water
treatment processes.
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Regulatory Response
In
response to the growing environmental movement, the National Environmental
Policy Act became law in January 1970. Forty-four organizations from nine
Federal agencies were
combined to form EPA in December of that year.
These and similar congressional
actions in the 1970s provided many of the basic laws needed to protect the
water quality and the environment. The Safe Drinking Water Act (SDWA), for
example,
authorizes EPA to protect drinking water in the United States by establishing
safety standards for drinking water and requiring all public water utilities to
comply with these standards. (A public water supply is defined as one that
serves more than 25 persons or has more than 15 service connections.)
Currently, EPA regulates 90 drinking water contaminants and has established
practices to ensure that public water systems have the capacity and training
necessary to ensure delivery of safe water.
The latest amendments (1996) to SDWA
contains a new focus on source water protection and the consumer’s right to
know. Source water protection means preventing initial contamination (thereby
reducing the reliance on treatment of drinking water supplies) by managing potential
sources of contamination.
Between now and 2003, States will
examine the sources of the Nation’s 170,000 public water supply systems to
determine how susceptible they are to contamination. The results of these
source water assessments must be made available to the public. Through these
assessments, communities can learn about potential threats to their water
supply and develop protection measures
to lessen those threats.
Under SDWA’s new right-to-know rules,
water systems must send annual water quality
reports (known as consumer confidence reports) to their customers,
describing, among other things, levels of contaminants in their drinking water
and the likely sources of those contaminants. These reports must be delivered
by July 1, each year. EPA has established a Local Drinking Water Information
Web site, at http://www.epa.gov/safewater/dwinfo.htm, that allows individuals
to get water quality information about their local water supply, including
their state source water assessments.
Interagency Effort
Although
EPA has primary regulatory responsibility in the Federal effort to protect the
Nation’s drinking water, many agencies under the U.S. Department of Health and
Human Services, such as the Centers for Disease Control and Prevention (CDC)
and the National Institute of Environmental Health Sciences (NIEHS), are
involved in providing safe drinking water.
CDC works with EPA in coordinating
surveillance and recording incidents and characteristics of waterborne disease
outbreaks. CDC also joins with State health departments and other Federal
agencies to examine unusual occurrences of death and illness, conducts
epidemiological studies, and develops tests of human exposure to toxic and
infectious agents.
NIEHS oversees multi-disciplinary
biomedical research programs like the National Toxicology Program (NTP)
established in 1978 by the Secretary of Health and Human Services. NTP
activities include coordinating toxicology research and testing activities, and
informing regulatory and research agencies and the public about potentially
toxic chemicals. NIEHS also is involved in prevention and intervention efforts, and community outreach.
Healthy People 2010, officially
launched in January, contains several national health objectives that identify
threats to a community’s supply of safe drinking water and establish goals to
prevent these threats. These objectives can serve as a guide for community
action and education, and congressional research, program planning, and goal
setting.
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