Underground Pollution.
The concentration of many pollutants in groundwater is often higher than that in the most contaminated surface water supplies. Many of the chemicals are tasteless and odorless at concentrations believed to pose a threat to human health. The major groundwater pollutants are chlorides, nitrates, heavy metals, and toxic organics.
Since groundwater usually moves slowly through an aquifer, it may take years for pollution to show up in areas adjacent to sources of contamination. Once an aquifer is contaminated the pollutants may remain for centuries.
Ocean Pollution
The oceans receive pollutants from many sources. Oil pollutions is one of the more serious problems. About half of the oil that contaminates the ocean comes from human sources: oil well blowouts, tanker spills, and inland disposal of oil. Oil harms many organisms, especially if a spill occurs near an estuarine zone.
It may take two to ten years for aquatic life to recover from a spill. Thanks to public outcry and stricter controls, the number of oil spills has decreased substantially, although the problem is far from solved.
Plastic pollution has also become a major problem throughout the world. Plastic nets, plastic garbage, and plastic medical wastes are killing millions of marine mammals, turtles, and fish. Animals may become tangles in the plastic debris or may eat it and die. Because of public outcry, many governments have banned the dumping of plastics in oceans.
