Water Pollution

views updated

Water pollution

Among the many environmental problems that offend and concern us, perhaps none is as powerful and dramatic as water pollution . Ugly, scummy water full of debris, sludge , and dark foam is surely one of the strongest and most easily recognized symbols of our misuse of the environment .

What is pollution? The verb "pollute" is derived from the Latin polluere : to foul or corrupt. Our most common meaning is to make something unfit or harmful to living things, especially by the addition of waste matter or sewage. A broader definition might include any physical, biological, or chemical change in water quality that adversely affects living organisms or makes water unsuitable for desired uses.

Paradoxically, however, a change that adversely affects one organism may be advantageous to another. Nutrients that stimulate oxygen consumption by bacteria and other decomposers in a river or lake, for instance, may be lethal to fish but will stimulate a flourishing community of decomposers. Whether the quality of the water has suffered depends on your perspective. There are natural sources of water contamination, such as poison springs, oil seeps, and sedimentation from erosion , but most discussions of water pollution focus on human-caused changes that affect water quality or usability.

The most serious water pollutants in terms of human health worldwide are pathogenic organisms. Altogether, at least 25 million deaths each year are blamed on these water-related diseases, including nearly two-thirds of the mortalities of children under five years old. The main source of these pathogens is from untreated or improperly treated human wastes. In the more developed countries, sewage treatment plants and other pollution control techniques have reduced or eliminated most of the worst sources of pathogens in inland surface waters. The United Nations estimates that 90% of the people in high-income countries have adequate sewage disposal, and 95% have clean drinking water.

For poor people, the situation is quite different. The United Nations estimates that three-quarters of the population in less-developed countries have inadequate sanitation , and that less than half have access to clean drinking water. Conditions are generally worse in remote, rural areas where sewage treatment is usually primitive or nonexistent, and purified water is either unavailable or too expensive to obtain. In the 33 poorest countries, 60% of the urban population have access to clean drinking water but only 20% of rural people do.

This lack of pollution control is reflected in surface and groundwater quality in countries that lack the resources or political will to enforce pollution control. In Poland, for example, 95% of all surface water is unfit to drink. The Vistula River, which winds through the country's most heavily industrialized region, is so badly polluted that more than half the river is utterly devoid of life and unsuited even for industrial use. In Russia, the lower Volga River is reported to be on the brink of disaster due to the 300 million tons (272.2 million metric tons) of solid waste and 20 trillion L (5 trillion gal) of liquid effluent dumped into it annually.

The less-developed countries of South America, Africa, and Asia have even worse water quality than do the poorer countries of Europe. Sewage treatment is usually either totally lacking or woefully inadequate. Low technological capabilities and little money for pollution control are made even worse by burgeoning populations, rapid urbanization, and the shift of heavy industry from developed countries where pollution laws are strict to less developed countries where regulations are more lenient.

In Malaysia, 42 of 50 major rivers are reported to be "ecological disasters." Residues from palm oil and rubber manufacturing, along with heavy erosion from logging of tropical rain forests, have destroyed all higher forms of life in most of these rivers. In the Philippines, domestic sewage makes up 60–70% of the total volume of Manila's Pasig River. Thousands of people use the river not only for bathing and washing clothes, but also as their source of drinking and cooking water. China treats only 2% of its sewage. Of 78 monitored rivers in China, 54 are reported to be seriously polluted. Of 44 major cities in China, 41 use "contaminated" water supplies, and few do more than rudimentary treatment before it is delivered to the public.

Pollution control standards and regulations usually distinguish between point and nonpoint pollution sources. Factories, power plants , sewage treatment plants, underground coal mines, and oil wells are classified as point sources because they discharge pollution from specific locations, such as drain pipes, ditches, or sewer outfalls. These sources are discrete and identifiable, so they are relatively easy to monitor and regulate. It is generally possible to divert effluent from the waste streams of these sources and treat it before it enters the environment.

In contrast, nonpoint sources of water pollution are scattered or diffused, having no specific location where they discharge into a particular body of water. Nonpoint sources include runoff from farm fields, golf courses , lawns and gardens, construction sites, logging areas, roads, streets, and parking lots. Multiple origins and scattered locations make this pollution more difficult to monitor, regulate, and treat than point sources.

Desert soils often contain high salt concentrations that can be mobilized by irrigation and concentrated by evaporation, reaching levels that are toxic for plants and animals. Salt levels in the San Joaquin River in central California rose about 50% between 1930 to 1970 as a result of agricultural runoff. Salinity levels in the Colorado River and surrounding farm fields have become so high in recent years that millions of acres of valuable croplands have had to be abandoned. The United States is building a huge desalination plant at Yuma, Arizona, to reduce salinity in the river. In northern states, millions of tons of sodium chloride and calcium chloride are used to melt road ice in the winter. The corrosive damage to highways and automobiles and the toxic effects on vegetation are enormous. Leaching of road salts into surface waters has a similarly devastating effect on aquatic ecosystems.

Acids are released by mining and as by-products of industrial processes, such as leather tanning, metal smelting and plating, petroleum distillation, and organic chemical synthesis. Coal mining is an especially important source of acid water pollution. Sulfides in coal are solubilized to make sulfuric acid. Thousands of miles of streams in the United States have been poisoned by acids and metals, some so severely that they are essentially lifeless.

Thousands of different natural and synthetic organic chemicals are used in the chemical industry to make pesticides, plastics , pharmaceuticals, pigments, and other products that we use in everyday life. Many of these chemicals are highly toxic. Exposure to very low concentrations can cause birth defects , genetic disorders, and cancer . Some synthetic chemicals are resistant to degradation, allowing them to persist in the environment for many years. Contamination of surface waters and groundwater by these chemicals is a serious threat to human health.

Hundreds of millions of tons of hazardous organic wastes are thought to be stored in dumps, landfills, lagoons, and underground tanks in the United States. Many, perhaps most, of these sites are leaking toxic chemicals into surface waters or groundwater or both. The Environmental Protection Agency (EPA) estimates that about 26,000 hazardous waste sites will require cleanup because they pose an imminent threat to public health, mostly through water pollution.

Although the oceans are vast, unmistakable signs of human abuse can be seen even in the most remote places. Garbage and human wastes from coastal cities are dumped into the ocean. Silt , fertilizers, and pesticides from farm fields smothered coral reefs, coastal spawning beds, and over-fertilize estuaries. Every year millions of tons of plastic litter and discarded fishing nets entangle aquatic organisms, dooming them to a slow death. Generally coastal areas, where the highest concentrations of sea life are found and human activities take place, are most critically affected.

The amount of oxygen dissolved in water is a good indicator of water quality and of the kinds of life it will support. Water with an oxygen content above 8 parts per million (ppm) will support game fish and other desirable forms of aquatic life. Water with less than 2 ppm oxygen will support only worms, bacteria, fungi , and other decomposers. Oxygen is added to water by diffusion from the air, especially when turbulence and mixing rates are high, and by photosynthesis of green plants, algae, and cyanobacteria. Oxygen is removed from water by respiration and chemical processes that consume oxygen.

In spite of the multitude of bad news about water quality, some encouraging pollution control stories are emerging. One of the most outstanding examples is the Thames River in London. Since the beginning of the Industrial Revolution, the Thames had been little more than an open sewer, full of vile and toxic waste products from domestic and industrial sewers. In the l950s, however, England undertook a massive cleanup of the Thames. More than $250 million in public funds plus millions more from industry were spent to curb pollution. By the early l980s, the river was showing remarkable signs of rejuvenation. Oxygen levels had rebounded and some 95 species of fish had returned, including the pollution-sensitive salmon , which had not been seen in London for 300 years. With a little effort, care, and concern for the environment, similar improvements can develop elsewhere.

[William P. Cunningham ]