Environmental Chapter 3.doc

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Environmental Science
Zachariah Campbell

Environmental Chapter 3: Water Quality and Water Resources • Sustainability of human society depends on the availability of plentiful and potable water • Our water supply faces a combination of old threats from human and industrial wastes and new threats from demand overload and climate change Introduction • Most of the world still ensures the scourge of waterborne diseases that were familiar to the cities of the Western world during the nineteenth century • Diarrheal deaths, most due to waterborne infectious agents, kill over 2 million children annually • Use of oral rehydration therapy has substantially reduced mortality associated with water-borne diseases, but intensive efforts to provide improved water and sanitary infrastructure in developing nations have been less successful • Growing evidence indicates that updating the means of disposal of human wastes improves human health to a greater extent that purveying clean water supplies Sources of Water • Drinking water is obtained primarily from surface water, such as streams, rivers, lakes, or from groundwater through artesian or other types of wells • Other means of obtaining drinking water include collecting rainwater and desalinating seawater • Surface water is more prone to contamination by microbial pathogens and chemicals, since it directly receives industrial and municipal wastewater and runoff from the land • Ground water is usually less contaminated than surface water because the soil through which is percolates serves as a filter -exceptions occur when there is a direct or short path form the surface to the groundwater, when concentrated wastes deep in the soil leach into groundwater, as beneath a landfill, or when wastes are injected directly into the ground Uses of Water • Water is used for a variety of purposes by developed societies; human consumption is actually one of the smallest uses • Worldwide, 70% of the total withdrawal of water is used for irrigating agricultural land • Industrial uses are substantial in the developing world -most is used for cooling or flushing equipment -it is thus returned to streams, rivers, or coastal waters, often either warmed or contaminated by chemicals • Within the home, more tap water is used for flushing toilets, showering, washing clothes, and in many places watering lawns and washing cars than for drinking and cooking Sources of Contamination • Many chemicals, such as pesticides and fertilizers, enter drinking-water sources after being deliberately applied to the land and washing into surface or ground waters • Animals wastes from farms and wilderness areas enter water in a similar fashion • Industrial waste chemicals and municipal wastes containing human fecal material and whatever chemicals have entered the system may be directly disposed of into surface water • Other chemicals reach drinking water after moving through soils • Some toxicants such as arsenic and radon occur naturally in the earth’s crust and contaminate groundwater that is in contact with deposits of these substances • Lastly, our methods of treating and distributing drinking water lead to some chemicals being present within our drinking-water supplies • Point sources; sources of contaminants that discharge into receiving waters from a pipe or other identifiable -include industrial wastes and sewage treatment plants • Nonpoint sources; sources of contaminants that cannot be defined by discrete pipes or other devices -agricultural runoff, the runoff of oils and other chemicals from streets and highways, the multitude of leaking septic systems and gasoline storage tanks, and airborne emissions of mercury and other substances that may settle on and dissolve in source waters for drinking purposes • Many countries, particularly those in the developing world, continue to have serious problems with point-source contamination of water due to poor enforcement of existing laws • Despite the success of regulations in reducing point-source contamination, however, drinking water remains vulnerable to contamination from non-point sources Water Treatment Process • The developed world reduced the burden of waterborne diseases outbreaks by implementing a process to treat drinking water in the late nineteenth and early twentieth century • Water treatment process -first water is pumped from its source -next step involves adding a chemical coagulant -sedimentation -prior to distribution, water is disinfected, usually with some form of chlorine • These steps are meant to remove tiny particles, including microbes, from the water, but they do not remove chemicals to a significant degree • Water with chemical contamination may need to undergo additional treatment, such as activated charcoal or special ion exchange resins • Chlorine or chloramines is the only way to maintain a level of disinfecting agent in the water as it is distributed through pipes and reservoirs to consumers • Treatment techniques in the developing world often rely on point-of-use methods performed in individual homes • Boiling water is the traditional method of water purification; since it requires substantial energy production, its usefulness is limited -involves risk of scalding and lung injury • Iodine tablets have been used for many years • Newer techniques include the use of dark plastic bottles that collect solar energy to disinfect water and combination of chemical disinfectants and special narrow-necked storage bottles that prevent recontamination of water -both techniques are only effective against microbial pathogens and do not reduce the concentrations of chemical contaminants in the water Biological Threats to Water Quality • WHO described five ways water may be associated with human diseases -waterborne diseases; transmitted by microorganisms that survive within water and are directly ingested -water-washed diseases; those exacerbated by inadequate washing of hands or food, such as trachoma, other skin and eye infections, and many of the fecal-oral pathogens that cause water-borne diseases -water-based diseases; caused by organisms that spend part of their life cycle as larval forms within freshwater and come in contact with humans through bathing or ingesting of infested water -water-related diseases; such as dengue fever and malaria, are caused by organisms that breed or otherwise spend part of their life cycle in water but do not come in contact with human hosts via water exposure -water-dispersed infections; caused by microorganisms, such as Legionella, that proliferate within water supplies and are transmitted to humans by dispersal of air and inhalation • The majority of waterborne pathogens infect the gastrointestinal tract -enter water through human or animal fecal material -a few microbial pathogens have the capacity to grow within the pipes of water distribution systems -most contaminate source water from which drinking water is obtained • To monitor quality of source and drinking water, measures of coliform bacteria and or water turbidity are commonly used -quick but unreliable; can miss contamination by viruses and protozoa • When contamination is relatively continuous and treatment processes not effective, endemic disease rates are high • Worldwide, the main bacterial pathogens spread by water are Salmonella species, Shigella species, pathogenic E.coli, and Vibrio cholerae • In general, bacterial pathogens are more effectively controlled than viral or protozoal pathogens by existing water treatment processes -most bacteria are susceptible to inactivation by chlorine • Outbreaks that have been characterized as ‘acute gastroenteritis of unknown etiology’ are felt to be mostly due to viruses • Main waterborne viral pathogens are Norwalk and Norwalk-like viruses • Due to small size, viruses pass through both soil and water treatment
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