Additional forms of water pollution

 Three last forms of water pollution exist in the forms of petroleum, radioactive substances, and heat.  Petroleum often pollutes waterbodies in the form of oil, resulting from oil spills.  The previously mentioned Exxon Valdez is an example of this type of water pollution.  These large-scale accidental discharges of petroleum are an important cause of pollution along shore lines.  Besides the supertankers, off-shore drilling operations contribute a large share of pollution.  One estimate is that one ton of oil is spilled for every million tons of oil transported. Radioactive substances are produced in the form of waste from nuclear power plants, and from the industrial, medical, and scientific use of radioactive materials.  Specific forms of waste are uranium and thorium mining and refining.  The last form of water pollution is heat.  Heat is a pollutant because increased temperatures result in the deaths of many aquatic organisms.  These decreases in temperatures are caused when a discharge of cooling water by factories and power plants occurs.