Toxic chemical pollution

Toxic pollution is contaminated water, soil, and air that is harmful or poisonous. It includes industrial wastes like toxic heavy metals from mining or chemicals from factories, and also sewage and particulates from power plants. ... In fact, toxic pollution is the largest cause of death in the world.

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Explanation:

in cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level. a contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness or gentleness of slopes.

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