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| Soil pollution Soil pollution is the destruction of Earth's thin layer of healthy, productive soil, where much of our food is grown. Without fertile soil, farmers could not grow enough food to support the world's people. Healthy soil depends on bacteria, fungi, and small animals to break down wastes in the soil and release nutrients. These nutrients help plants grow. Fertilizers and pesticides can limit the ability of soil organisms to process wastes. As a result, farmers who overuse fertilizers and pesticides can destroy the soil's productivity. A number of other human activities can also damage soil. The irrigation of soil in dry areas with poor drainage can leave water standing in fields. When this standing water evaporates, it leaves salt deposits behind, making the soil too salty for growing crops. Mining operations and smelters contaminate soil with toxic heavy metals. Many scientists believe acid rain can also reduce soil fertility. Solid waste Solid waste is probably the most visible form of pollution. Every year, people dispose of billions of tons of solid garbage. Industrial wastes account for the majority of the discarded material. Solid waste from homes, offices, and stores is called municipal solid waste. It includes paper, plastic, glass, metal cans, food scraps, and yard trimmings. Other waste consists of junked automobiles, scrap metal, leftover materials from agricultural processes, and mining wastes known as spoil. The handling of solid waste is a problem because most disposal methods damage the environment. Open dumps ruin the natural beauty of the land and provide a home for rats and other disease-carrying animals. Both open dumps and landfills (areas of buried wastes) may contain toxins that seep into ground water or flow into streams and lakes. The uncontrolled burning of solid waste creates smoke and other air pollution. Even burning waste in incinerators can release toxic chemicals, ash, and harmful metals into the air. Hazardous waste Hazardous waste is composed of discarded substances that can threaten human health and the environment. A waste is hazardous if it corrodes (wears away) other materials; explodes; ignites easily; reacts strongly with water; or is poisonous. Sources of hazardous waste include industries, hospitals, and laboratories. Such waste can cause immediate injury when people breathe, swallow, or touch it. When buried in the ground or left in open dumps, some hazardous waste can contaminate air, ground water, and food crops. The mishandling or accidental release of hazardous waste has caused a number of disasters around the world. For example, in 1978, hazardous chemicals leaking from a waste disposal site in the Love Canal area of western New York threatened the health of nearby residents. Hundreds of people were forced to abandon their homes. In 1984, a leak of poisonous gas from a pesticide plant in Bhopal, India, killed more than 2,800 people and caused eye and respiratory damage to more than 20,000. Some hazardous waste can seriously harm the health of people, wildlife, and plants. These pollutants include radiation, pesticides, and heavy metals. Radiation is an invisible pollutant that can contaminate any part of the environment. Most radiation comes from natural sources, such as minerals and the sun's rays. Scientists can also produce radioactive elements in their laboratories. Exposure to large amounts of radiation can harm cells and result in cancer. Radioactive waste produced by nuclear reactors and weapons factories pose a potentially serious environmental problem. Some of this waste will remain radioactive for thousands of years. The safe storage of radioactive waste is both difficult and expensive. Pesticides can travel great distances through the environment. When sprayed on crops or in gardens, pesticides can be blown by the wind to other areas. They can also flow with rain water into nearby streams or can seep through the soil into ground water. Some pesticides can remain in the environment for many years and pass from one organism to another. For example, when pesticides are present in a stream, small fish and other organisms can absorb them. Larger fish who eat these contaminated organisms build up even larger amounts of pesticides in their flesh. This process is called bioaccumulation. | ||