Two long, straight wires separated by 0.1 m carry currents o…
Questions
Twо lоng, strаight wires sepаrаted by 0.1 m carry currents оf 18 A and 6 A in the same direction as shown. Determine the magnitude of the magnetic field at the point P.
Phytоremediаtiоn: Mоther Nаture's Solution to Toxic Pollution By the end of the 1990s, the U.S. Environmentаl Protection Agency (E.P.A.) had a daunting task ahead with over 20,000 contaminated sites on its cleanup list. The removal of toxic pollutants from these sites was estimated to cost billions, if not trillions of dollars, due to the high-tech and expensive solutions that were previously recommended. However, in recent years, scientists have been looking towards nature itself for a solution to eliminate toxic contaminants from the ground. This promising new pollution cleanup method is known as phytoremediation, a natural process that can work on a variety of pollutants. Phytoremediation is the use of plants that have the ability to take in, break down, or transform pollutants such as lead and uranium, thereby reducing soil pollution. These plants possess genetic makeup that allows them to absorb, degrade or transform substances that may be harmful to other plants and animals. According to Louis Licht, a graduate student at the University of Iowa, "It’s an elegantly simple solution." While scientists have long recognized the abilities of certain plants to absorb and tolerate toxic substances, the idea of using these plants on contaminated sites has gained support in the last decade. Phytoremediation promises great results from basic biological principles. The plants clean up sites in two fundamental ways, depending on the type of contaminant involved. For organic contaminants like spilled oil, the plants or microbes around their roots break down the substance. The remainder can either be absorbed by the plant or left in the soil or water. For an inorganic contaminant such as cadmium or zinc, the plants absorb the substance and trap it. The plants must then be harvested and safely disposed. However, many companies don’t throw away the plants, but process them to reclaim the trapped contaminant. Different plants are effective for different types of contaminants. The mulberry bush, for instance, is useful for industrial sludge; some grasses attack petroleum wastes, while sunflowers (along with soil additives) remove lead. Canola plants are grown in California’s San Joaquin Valley to absorb excess selenium in the soil to help prevent an environmental catastrophe like the one that occurred there in the 1980s. Irrigated farming caused naturally occurring selenium to rise to the soil surface, and excess water was pumped onto the fields, causing selenium to flow off into drainage ditches, eventually ending up in Kesterson National Wildlife Refuge. The selenium in ponds at the refuge accumulated in plants and fish and subsequently deformed and killed water birds. Gary Banuelos, a plant scientist with the U.S. Department of Agriculture (U.S.D.A.), helped remedy the problem by recommending that farmers add selenium-accumulating canola plants to their crop rotations. As a result, selenium levels in runoff have been reduced and are being managed. Although the underlying problem of too much selenium in the soil has not been solved, phytoremediation has reduced the deposits that may lead to another selenium-induced disaster. Phytoremediation has the potential to clean up many of the E.P.A.’s 20,000 contaminated sites using natural methods rather than high-tech solutions.