Environmental Problems, Their Causes, and Sustainability 1

Today everybody is downwind or downstream from somebodyelse.WILLIAM RUCKELSHAUSThis chapter addresses the following questions:■■■■■■What pollutes water, where do the pollutants comefrom, and what effects do they have?What are the major water pollution problems ofstreams and lakes?What causes groundwater pollution, and how canit be prevented?What are the major water pollution problems ofoceans?How can we prevent and reduce surface waterpollution?How safe is drinking water, and how can it bemade safer?22-1 TYPES, EFFECTS, AND SOURCESOF WATER POLLUTIONWhat Are the Major Types and Effects ofWater Pollutants? Unseen ThreatsInfectious bacteria, inorganic and organic chemicals,and excess heat pollute water.Water pollution is any chemical, biological, or physicalchange in water quality that has a harmful effect onliving organisms or that makes water unsuitable fordesired uses. Table 22-1 lists the major classes of waterpollutants along with their major human sources andharmful effects. Study this table carefully. Note that excessiveheat is considered a water pollutant.Table 22-2 lists some common diseases that can betransmitted to humans through drinking water contaminatedwith infectious agents. The World HealthOrganization (WHO) estimates that 3.4 million peopleTable 22-1Major Categories of Water PollutantsINFECTIOUS AGENTSExamples: Bacteria, viruses,protozoa, and parasiticwormsMajor Human Sources:Human and animal wastesHarmful Effects: DiseaseOXYGEN-DEMANDINGWASTESExamples: Organicwaste such as animalmanure and plant debris thatcan be decomposed byaerobic (oxygen-requiring)bacteriaMajor Human Sources:Sewage, animal feedlots, papermills, and food processingfacilitiesHarmful Effects: Large populationsof bacteria decomposingthese wastes can degradewater quality by depleting waterof dissolved oxygen. Thiscauses fish and other forms ofoxygen-consuming aquatic lifeto die.INORGANIC CHEMICALSExamples: Water-soluble(1) acids, (2) compounds oftoxic metals such as lead (Pb),arsenic (As), and selenium(Se), and (3) salts such assodium chloride (NaCl) inocean water and fluorides (F – )found in some soilsMajor Human Sources:Surface runoff, industrialeffluents, and householdcleansersHarmful Effects: Can(1) make fresh water unusablefor drinking or irrigation,(2) cause skin cancers andcrippling spinal and neckdamage (F – ), (3) damage thenervous system, liver, and kidneys(Pb and As), (4) harm fishand other aquatic life, (5) lowercrop yields, and (6) acceleratecorrosion of metals exposed tosuch water.ORGANIC CHEMICALSExamples: Oil, gasoline, plastics,pesticides, cleaning solvents,detergentsMajor Human Sources: Industrialeffluents, householdcleansers, surface runoff fromfarms and yardsHarmful Effects: Can(1) threaten human health bycausing nervous systemdamage (some pesticides),reproductive disorders (somesolvents), and some cancers(gasoline, oil, and some solvents)and (2) harm fish andwildlife.PLANT NUTRIENTSExamples: Water-solublecompounds containing nitrate(NO 3– ), phosphate (PO 43–),and ammonium (NH 4+ )ionsMajor Human Sources:Sewage, manure, and runoffof agricultural and urbanfertilizersHarmful Effects: Can causeexcessive growth of algae andother aquatic plants, whichdie, decay, deplete water ofdissolved oxygen, and kill fish.Drinking water with excessivelevels of nitrates lowers theoxygen-carrying capacity ofthe blood and can kill unbornchildren and infants (“bluebabysyndrome”).SEDIMENTExamples: Soil, siltMajor Human Sources: LanderosionHarmful Effects: Can(1) cloud water and reducephotosynthesis, (2) disruptaquatic food webs, (3) carrypesticides, bacteria, and otherharmful substances, (4) settleout and destroy feeding andspawning grounds of fish, and(5) clog and fill lakes, artificialreservoirs, stream channels,and harbors.RADIOACTIVE MATERIALSExamples: Radioactiveisotopes of iodine, radon,uranium, cesium, andthoriumMajor Human Sources:Nuclear and coal-burningpower plants, mining andprocessing of uranium andother ores, nuclear weaponsproduction, natural sourcesHarmful Effects: Geneticmutations, miscarriages,birth defects, and certaincancersHEAT (THERMALPOLLUTION)Examples: Excessive heatMajor Human Sources:Water cooling of electricpower plants and some typesof industrial plants. Almosthalf of all water withdrawn inthe United States each year isfor cooling electric powerplants.Harmful Effects: Lowersdissolved oxygen levels andmakes aquatic organismsmore vulnerable to disease,parasites, and toxic chemicals.When a power plantfirst opens or shuts downfor repair, fish and otherorganisms adapted to aparticular temperature rangecan be killed by the abruptchange in water temperature—knownas thermalshock.492 CHAPTER 22 Water Pollution