Pollutants in Groundwater:
Table of Contents
Public concern about groundwater degradation
from point-and nonpoint-source contaminants continues to increase. If
such concern is to generate responsible action, it must be informed by
facts. Media coverage has not been particularly helpful in this regard:
too often, the public is presented with fragmented or sensationalized
information. As a result, misconceptions abound about why particular problems
occur, what health risks those problems impose, and how those risks might
best be reduced. This fact sheet discusses some of the more common groundwater
contaminants and clarifies the potential health risks associated
Groundwater pollutants can be either organic
or inorganic. Organic materials are composed primarily of carbon and hydrogen;
they may also contain smaller amounts of chlorine, nitrogen, sulfur, and
phosphorus. Of the
Inorganic pollutants include materials such
as nitrate, which can come from fertilizers or decayed organic materials;
chlorides; and heavy metals, such as copper
Organic pollutants in drinking water seldom
exceed trace concentrations: a few parts per
Toxicity is the inherent ability
to impair health. Toxic substances can cause cancer, birth defects, and
other illnesses. The severity of the effect usually depends on the dose,
defined as the weight of the contaminant consumed per day divided by body
weight. Dosages are usually measured in milligrams per kilogram of body
weight per day. Acute toxicity refers to a contaminant's ability to cause
immediately detectable health problems. Chronic toxicity refers
to a contaminant's ability to cause health problems years after a long-term
exposure. Keep in mind that some contaminants that cause no detectable
health problems at low doses can cause death at
Nonlethal acute toxicity is easier to diagnose and treat than chronic toxicity since the ensuing health problems are generally brief and reversible. When the exposure to the chemical ceases, so do the effects, provided that the dosage has not been too high. Examples of organic chemicals that can be acutely toxic are the polychlorinated and polybrominated biphenyls (PCBs and PBBs)a group of chemicals used in paints, electrical transformers, insulators, and the pesticides aldicarb, paraquat, and DDT. Symptoms of acute toxicity can include diarrhea, nausea, convulsions, blurred vision, and difficulty in breathing.
Health problems from chronic toxicity are more difficult to diagnose because they often remain latent for years. Once such problems become manifest, they may be difficult or impossible to treat. These complications make chronic toxicity from organic pollutants the major concern of those investigating water quality. Depending on the chronic health problems they cause, pollutants are typically grouped in the following three classes: carcinogens, mutagens, and teratogens.
Any chemical that causes cancer, either directly
or indirectly, is a carcinogen. Although carcinogenesis receives
more research attention than any other chronic effect, scientists have
not determined the precise relationship between carcinogens and cancer.
They do know, however, that carcinogens stimulate various forms of
Among the chemicals designated as causing cancer are vinyl chloride, a component of some resins; benzene, a solvent produced in petroleum refining; and benzo(a)pyrene, which results from the incomplete combustion of coal, kerosene, and shale. Benzo(a)pyrene also results from grilling foods. Numerous other chemicals are known to produce cancer in animals; they include the pesticides ethylene dibromide (EDB), kepone, heptachlor, and dieldrin.
A chemical capable of producing an inheritable
change in the genetic material is called a mutagen. We know little
about the mutagenic effects of organic chemicals because most suspected
mutagens have been tested only on microorganisms and animals. Chemicals
found to be mutagenic on the basis of such tests include vinyl chloride,
benzo(a) pyrene, bromoform, chlorodibromomethane, and the fungicides Folpet
Any chemical that produces a birth defect
is called a teratogen. True understanding of teratogens is very
limited. Some of the chemicals shown to have teratogenic effects in animals
are nicotine and the pesticides
Besides the health problems discussed above,
organic pollutants may also cause arteriosclerosis, heart diseases, hypertension,
emphysema, bronchitis, and kidney and liver dysfunction. Some evidence
also links certain organic chemicals to metabolic disorders that stimulate
Humans ingest nitrates from food and water.
Once nitrate enters the body of humans older than
Infants under six months, however, are susceptible to nitrate poisoning because their undeveloped digestive tracts possess bacteria that convert nitrate into nitrite, which is toxic. When nitrite enters the bloodstream, it reacts with oxygen-carrying hemoglobin and forms a compound called methemoglobin. This compound reduces the blood's ability to carry oxygen. As oxygen levels decrease, infants may show signs of suffocation, a condition called methemoglobinetnia.
The most conspicuous symptom of methemoglobinemia
is bluish skin, most noticeably around the eyes and mouth. If detected
rapidly, methemoglobinemia can be successfully treated with an injection
of methylene blue, which changes methemoglobin back to hemoglobin. Untreated,
the condition is extremely serious: death occurs when
While rare, infant deaths from methemoglobinemia
(or blue baby syndrome) have been linked to high levels of nitrate in
well water. Doctors recommend using bottled water to make formula when
nitrate levels exceed the drinking water standard set by the Public Health
Because bacteria in the rumen convert nitrate to oxygen-seeking nitrite, nitrate poisoning occurs most often in ruminant animals such as cattle and sheep. Monogastric animals such as swine and chickens have no rumen; thus they rapidly eliminate nitrate in their urine. Young monogastric animals, however, are similar to human infants in that they are highly susceptible to nitrate poisoning until their digestive systems develop. Although horses are monogastric, their large cecum acts as a rumen, converting nitrate to nitrite. Consequently, horses are more susceptible to nitrate poisoning than are other monogastric animals.
Through overfertilization or stress, many
plants accumulate nitrate levels that can harm livestock. In water, however,
nitrate rarely proves harmful. High nitrate water generally threatens
animals only when it is added to high nitrate concentrations already present
Symptoms of methemoglobinemia in animals include lack of coordination, labored breathing, blue coloring of mucous membranes, vomiting, and abortions. Dairy cows, however, can have reduced milk production without showing any symptoms. If you suspect that your animals may have nitrate poisoning, your veterinarian can conduct a test and, if necessary, administer an injection of methylene blue, the antidote.
Recently, a number of other health problems have been linked to high concentrations of nitrate. Some studies suggest that an increase in esophageal and stomach cancers may be related to N-nitrosamines, organic compounds formed in the mouth or digestive system by the interaction of nitrite (formed from nitrate) with compounds containing organic nitrogen (secondary amines). N-nitrosamines are potent animal carcinogens.
Most laboratories report the nitrate content
as parts per million or milligrams per liter (mg/L) of either nitrate
(NO3) or nitrate-nitrogen (NO3-N). To compare different
results, you must know if they are reported as NO3 or NO3-N.
To convert NO3-N to NO3, multiply by 4.4. For example,
Water contaminated with nitrate can be treated
so that it meets drinking standards. Treatments are expensive, however,
and include processes such as reverse osmosis, deionization, and distillation.
Boiling, softening, or disinfection will not reduce the water's
Wells with elevated nitrate levels should be inspected for well head protection and possible on-site sources of contamination. Common sources of nitrate include septic systems, animal manure, decaying organic matter, and commercial nitrogen fertilizers.
For more information on nitrate, refer to
Nitrogen Management and Water Quality
Special appreciation is given to the
Cooperative Extension Service of Kansas State University (