RE: WATER POLLUTION
water_pollution_full_chpater.ppt (Size: 1.11 MB / Downloads: 94)
Types and Sources of Water Pollution
Water pollution is any chemical, biological, or physical change in water quality that has a harmful effect on living organisms or makes water unsuitable for desired uses.
disease–causing agents: bacteria, viruses, protozoa, and parasites;
oxygen demanding wastes: organic wastes that can be decomposed by aerobic bacteria;
water–soluble inorganic chemicals: acids, salts, and compounds with heavy metals;
inorganic chemicals: oil, gasoline, plastics, pesticides, cleaning solvents, detergents, etc.
sediment: suspended matter, insoluble particles of soil and other solids; biggest class of pollution by weight;
water–soluble radioactive isotopes: ionizing radiation sources;
genetic pollution: introduction of non–native species;
thermal pollution: heat added to water.
Point and Nonpoint Sources
It is easier to control pollution that comes from a specific source.
point sources discharge pollutants at specific locations through pipes, ditches, or sewers (e.g., factories, sewage treatment plants, mines, oil wells, oil tankers);
nonpoint sources can not be traced to a single site of discharge (e.g., acid deposition, substances picked up in runoff, seepage into groundwater);
nonpoint source water pollution from agriculture is largest source of water pollution in the U.S. (64% of pollutants into streams and 57% of pollutants entering lakes).
Pollution of Streams and Lakes
Water pollution control laws enacted in the 1970s have greatly increased the number and quality of wastewater treatment plants in the U.S.
also improvements in Canada, Japan, and most western European countries;
large fish kill and contamination of drinking water still occur, especially in developing countries;
lakes, reservoirs and ponds are more vulnerable to contamination than streams because of less mixing and aeration.
Coastal areas – especially wetlands and estuaries, coral reefs, and mangrove swamps – bear the brunt of enormous inputs of wastes into the ocean.
half of the world's population lives within 100 km (60 miles) of the ocean and 14 of the 15 largest metropolitan areas are near coastal waters;
in the U.S. about 35% of municipal sewage ends up virtually untreated in marine waters;
the ocean is the ultimate repository of waste, since surface waters flow into the ocean;
dumping of industrial waste directly into the ocean off U.S. coasts has stopped, but many countries still dump large quantities of toxic substances.
Crude and refined petroleum are accidentally and deliberately released into the environment fromvarious sources.
most oil is released in normal operation of offshore wells, from washing tankers, and pipeline and storage tank leaks;
tanker and offshore drilling rig accidents can release large amounts of oil in a short period of time;
Drinking Water Quality
Much of the world's drinking water is contaminated and poses serious health threats.
currently most drinking water is purified by storage in a reservoir, where suspended matter settles out, and then treated by sand filters, activated charcoal, and addition of chlorine;
U.S. Safe Drinking Water Act of 1974 requires EPA to establish national drinking water standards; currently efforts by industry to weaken the standards;
many individuals turning to bottled water and home filters; bottled water is often more contaminated than tap water.