Chapter 21: Water Pollution: Sustainably Managing a
Renewable Resource
21.1 Surface Water Pollution
Nations produce many different types of water pollutants. The water in all countries is
plagued with pollutants from human and animal wastes, but in the industrial nations toxic
chemicals also contribute to water pollution.
Sources of Water Pollution
Water pollutants arise from natural and anthropogenic sources. They travel freely from
one location to another through rivers, streams, and groundwater. They are also
transported from one medium (land or air) to another (water).
Point and Nonpoint Sources
Water pollution arises from identifiable point sources, such as factories, and from diffuse
nonpoint sources, such as farm fields and streets. Point sources are much easier to
control.
Organic Nutrients
Organic nutrients come from a variety of sources, primarily treated and untreated waste
(human and other animals) accidentally and intentionally released into waterways.
Organic compounds stimulate bacterial growth, which depletes oxygen levels in water
bodies, killing off oxygen-dependent species. Oxygen levels can return to normal levels,
but only if the influx of organic materials ceases.
Inorganic Nutrients—Nitrates and Phosphates
Inorganic nutrients stimulate excess plant growth, which impairs navigation and
swimming and disrupts the aquatic environment. When the plants die, they decompose,
causing oxygen levels to decline precipitously—an effect that can be harmful to a host of
organisms.
Eutrophication and Natural Succession
The accumulation of nutrients in lakes, from both natural and human sources, is called
natural and cultural eutrophication, respectively. Combined with the deposition of
sediment from human activities, cultural eutrophication causes lakes to age prematurely.
Infectious Agents
Numerous infectious agents are found in surface waters, especially in the less developed
nations where they cause considerable amounts of suffering and death. Sewage treatment
facilities and drinking water purification have greatly reduced the incidence of disease in
more developed countries, although outbreaks do occur. To monitor infectious agents,
officials generally measure fecal coliform levels, a harmless bacterium itself, but an
indicator of the presence of fecal contamination.
Toxic Organic Water Pollutants
Numerous toxic chemicals enter the waterways from factories, homes, farms, lawns, and
gardens. They may have many different effects on people and the environment. As a rule,
concentrations in surface waters are low.
Toxic Inorganic Water Pollutants
Numerous inorganic pollutants such as acids and heavy metals make their way into the
surface and groundwater of industrial nations, usually from industrial sources. Some,
such as lead and mercury, are of major concern.
Mercury is emitted from many sources, among them vinyl factories and coal-fired power
plants, and is one of the most common and most toxic inorganic pollutants, primarily
exerting its effect through the nervous system.
Nitrates can be converted to nitrites, which bind to hemoglobin and reduce the oxygencarrying capacity of the blood.
Road salts used to remove ice and make driving safe can profoundly affect aquatic
ecosystems, forests, and orchards.
Chlorine is routinely added to water to kill harmful organisms. Unfortunately, it also
reacts with organic compounds to form substances toxic to humans and other organisms.
Sediment
Sediment washed from the land because of many poorly planned and executed human
activities such as mining and farming has profound effects on the chemical and physical
nature of ecosystems. Such changes have profound impacts on aquatic organisms and
humans who depend on them.
Thermal Pollution
Water from rivers and lakes is used to cool many industrial processes, electric power
production being one of the major ones. Heat generated by these processes is often
discharged directly into surface waters, where it kills organisms outright or shifts the
composition of the aquatic system.
21.2 Groundwater Pollution
Groundwater is an important source of drinking water in many nations and may be
heavily contaminated in numerous industrialized nations by industrial waste pits, septic
tanks, oil wells, and landfills. Groundwater in some rural areas may also be contaminated
by agricultural chemicals, notably pesticides and fertilizer.
Effects of Groundwater Pollution
Thousands of chemicals may be found in a nation’s groundwater. Many of them are
potentially harmful to human health, causing problems for unborn children (miscarriage,
birth defects, and premature infant death) and adults (rashes and neurological problems).
Cleaning Up Groundwater
Groundwater moves slowly and takes many years to cleanse itself. Preventing
groundwater pollution is essential to creating a sustainable water supply. Equally
important are efforts to clean up groundwater supplies already contaminated by
potentially toxic chemicals.
21.3 Ocean Pollution
The oceans are polluted by chemicals spilled into them directly and by pollutants washed
from the lands and transported to them by rivers.
Oil in the Seas
Half of the oil polluting the oceans comes from natural seepage; the rest comes from
human sources, including tanker accidents and inland disposal. The largest natural source
is inland disposal.
Oil spilled from human sources evaporates, is broken down by naturally occurring
bacteria, or sinks to the bottom. Before it is eliminated, however, it can cause serious
environmental damage. The extent of the damage depends on the amount spilled, the
location of the spill, the prevailing weather conditions, and the season.
Many efforts are under way in the United States and other countries to reduce oil spills,
including new standards for the construction of oil tankers.
Conservation, recycling, and renewable resource use can all reduce our dependence on oil
and reduce oil pollution in the seas.
Plastic Pollution
Millions of tons of plastic are dumped into the ocean each year, killing hundreds of
thousands of marine mammals, fish, and birds.
Many steps have been taken to reduce the disposal of plastic into the ocean, but huge
amounts are still being disposed of each year, posing a serious threat to sea life.
Medical Wastes and Sewage Sludge
Medical wastes and sewage have long been dumped into the ocean, but steps have been
taken to eliminate both practices. The direct dumping of sewage has stopped entirely, but
millions of gallons of sewage enter the sea each year from sewage treatment plants
located near the coast.
Red Tide
Outbreaks of microscopic and often highly toxic algae appear to be on the rise worldwide
and may be caused by an increase in inorganic nutrient pollution from agriculture,
industry, and the human population.
The Case of the Dying Seals
A massive seal die-off in the late 1980s, caused by a virus, may ultimately have resulted
from immune system suppression caused by a common pollutant, PCBs.
21.4 Water Pollution Control
Reducing water pollution requires efforts on two levels – those that capture wastes
emitted from various sources (the so-called end-of-pipe solutions) and those that prevent
waste production and pollution.
Legislative Controls
Legislation to address water pollution has historically focused on point sources –
primarily factories and sewage treatment plants. Gains made in controlling such sources,
however, have often been offset by increasing levels of pollution from nonpoint sources
such as city streets, lawns, and farm fields.
Controlling Nonpoint Pollution
In the United States, efforts to control nonpoint water pollution are still in their infancy
but are gaining in popularity because they are often economical solutions that offer other
benefits as well. Especially important are efforts to control agricultural runoff.
The U.S. government and many states have done a better job of addressing groundwater
pollution than nonpoint water pollution because groundwater is an important source of
drinking water for many communities.
Water Pollution Control Technologies: End-of-Pipe Approaches
Sewage treatment plants receive waste from may sources within cities, including homes,
office buildings, factories, hospitals, and, in some cases, stormwater drainage systems.
Primary treatment is a means of filtering out large objects and solid organic matter.
Secondary treatment further destroys organic matter and removes much of the nitrogen
and phosphorus in sewage by employing bacteria and other decomposers.
Tertiary treatment brings sewage wastewater near to drinking water quality but is rarely
used because it is so costly.
Sustainable Solutions for Water Pollution
Preventing pollution is a key to creating clean, healthy ground and surface waters, which
are a prerequisite to living sustainably on the Earth. Efforts to reduce consumption;
recycling materials, industrial waste, and municipal sewage; using renewable resources;
and stabilizing population growth – all of these will collectively serve to reduce our
production of water pollutants.