Major Pollutants and Their Sources.

⇐ ПредыдущаяСтр 8 из 14Следующая ⇒

Soil pollution is defined as the build-up in soils of persistent toxic compounds, chemicals, salts, radioactive materials, or disease causing agents, which have adverse effects on plant growth and animal health.

Until the 1970s, there was little talk of soil pollution and its devastating effects. In the 1980s, the U.S. Superfund was created to set guidelines for the handling of hazardous material and soil contamination cleanup. Today there are more than 200, 000 sites awaiting EPA (Environmental Protection Agency) soil cleanup, which is very expensive and labor-intensive work. Even a small cleanup project can cost $10, 000, while larger areas require millions of dollars to clean it up for future use.

Soil pollution is caused by the presence of man-made chemicals or other alteration in the natural soil environment. This type of contamination typically arises from the rupture of underground storage tanks, application of pesticides, percolation of contaminated surface water to subsurface strata, oil and fuel dumping, leaching of wastes from landfills or direct discharge of industrial wastes to the soil. The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other heavy metals. This occurrence of this phenomenon is correlated with the degree of industrializations and intensities of chemical usage.

Past and present economic activities have often resulted in the pollution of the underlying soil where these activities take place. Industry is to blame for some of the biggest soil-pollution disasters. Heavy metals come from iron, steel, power and chemical manufacturing plants that recklessly use the Earth as a dumping ground for their refuse. Plants that burn their waste on-site are guilty of releasing heavy metals into the atmosphere, which come to settle in the soil, thus leaving behind lasting effects for years to come. Even companies that try to dispose of their waste properly contribute to the problem when faulty landfills and bursting underground bins leach undesirable toxins into the soil.

Mining leaves a tremendous impact on the surrounding communities. The 2001 West Virginia Geological and Economic Survey found that people living near mines have a 70 percent higher risk of kidney disease, 64 percent higher risk for chronic obstructive pulmonary disease and a 30 percent higher risk of high blood pressure.

The most common toxic soil pollutants include metals and their compounds, organic chemicals, oils and tars, pesticides, explosive and toxic gases, radioactive materials, biologically active materials, combustible materials, asbestos and other hazardous materials. These substances commonly arise from the disposal of industrial and domestic waste products in designated landfills or uncontrolled dumps.

Heavy metals. Soil contamination by heavy metals, such as cadmium, lead, chromium, copper, zinc, mercury and arsenic, is a matter of great concern. Heavy metals are present naturally in the soil, but their levels are increased by:

• industry (non-ferrous industries, power plants, iron, steel and chemical industries);

• agriculture (irrigation with polluted water, use of mineral fertilisers)

• waste incineration;

• combustion of fossil fuels;

• road traffic.

Pollution of agricultural soils by heavy metals may lead to reduced yields and elevated levels of these elements in agricultural products, and thus to their introduction into the food chain. Heavy metal deposits on grassland soils remain predominantly in the top few centimetres and are directly ingested with soil by grazing animals. Heavy metals are toxic and inhibit the soil's microorganic activity. Their concentration in the soil can remain for decades or even centuries.

Reduction of heavy metal emissions is the most direct way to decrease the atmospheric deposition of these elements and their build-up in the soil. Despite the great increase in traffic, for example, a reduction in lead emissions has been achieved through incentives to use unleaded petrol.

Implementing complex measures that reduce soil acidification could more efficiently reduce heavy metals. On agricultural land, heavy metal quantities can be decreased by using low-metal content resources for fertilisers, replacing inorganic pesticides with organic products, and other similar methods.

Organic pollutants. Pesticides pollute the soil directly by affecting the organisms that reside in it. Soil, however, can act as a vector for the pollution of surface water and groundwater. Organic pollutants enter the soil via atmospheric deposition, direct spreading onto land, contamination by wastewater and waste disposal.

In addition to pesticides, organic contaminants include many other components, such as oils, tars, chlorinated hydrocarbons, PCBs and dioxins. There is such a wide variety of organic substances that their detection and monitoring in the soil is practically impossible. Pesticides (mainly fungicides, herbicides and insecticides) are used in agriculture to protect crops and to ensure a quality harvest. Persistent or mobile pesticides are especially dangerous, as are those that affect non-targeted organisms.

The use of pesticides may lead to:

• destruction of the soil's micro-flora and fauna, leading to both physical and chemical deterioration;

• severe yield reduction in crops;

• leaching of toxic chemicals into groundwater and potentially threatening drinking water resources.

Some improvements in application and legislation may reduce the side effects of pesticides, such as:

• banning broad-spectrum and highly mobile pesticides;

• employing integrated pest-management;

• enforcing biological control; and

• developing biotechnologies.

Nitrates and phosphorus. Nitrogen and phosphorus are elements essential to all forms of life and are therefore relevant to soil systems and food crops. Although they are important plant nutrients, excessive application may lead to nitrogen or phosphate saturation in the soil, and eventual contamination of the groundwater. The amount of leaching depends on the soil, the local climate and the style of crop management.

Phosphorus accumulates in the upper layer of soil in regions with high livestock densities. In soils saturated with phosphorus, especially those with shallow groundwater, high phosphorus concentration occurs in the upper groundwater layer and in surface water, resulting in eutrophication.

The problem of nitrate pollution is recognised internationally and is usually associated with intensive agriculture practices. Good agricultural practices that alleviate the problem are:

• the selection of crops that require fewer nutrients;

• a timely application of fertiliser (in the growing season);

• improved methods of manure application;

• shortening the length of the grazing season; and

• reducing the intensity of grassland use (by lowering cattle density).

Artificial radionuclides. Contamination of soil with artificial radionuclides (cesium-137, strontium-90 and some plutonium isotopes) has given rise to increased public concern since the Chernobyl accident.

Radionuclides in the upper layers of soil may expose plants and animals to radiation and, in extreme cases, present a threat to humans in the form of direct ionising radiation. Radionuclides can enter the food chain through the soil, leading to intake by humans and animals through ingestion, while wind-blown contaminated soil particles could lead to exposure through inhalation.

The existence of unauthorised dumps is one of the environmental problems in Europe that deserves utmost attention. The remediation costs of polluted areas in Europe are roughly estimated at more than EUR 100 billion.

After you read Text 1. Look at the texts and try to find:

1. The definition of soil pollution.

2. The main causes of soil pollution.

3. The main types of pollutants and their sources.

4. Some effects of organic pollutants use.

5. Artificial radio-nuclides and their affects.

6. Heavy metals contamination affects.

As you read Texts 2

· Which paragraphs contain the following information? Prove the statements with the text.

A The effects of soil pollution which potentially can happen.

B Encouraging recycling programs and educating consumers about the dangers of littering.

C Soil chemistry changes can manifest in the alteration of metabolism of endemic microorganisms.

D Somestrategies for treatment.

E The traditional methods of soil pollution treatment.

Text 2. Ecosystem effects.

⇐ Предыдущая 3 4 5 6 789 10 11 12 Следующая ⇒