10.3.2: Water Pollution
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Learning Objectives
After reading this module, students should be able to
- understand the major kinds of water pollutants and how they degrade water quality
- understand how and why the lack of safe drinking water in some parts of the world is a major problem
- know what sewage treatment does and why it is important
- know why it is more difficult to remediate groundwater pollution than surface water pollution
- understand how we can work toward solving the crisis involving water pollution
The Water Pollution Crisis
The Module 7.3 described one aspect of the global water crisis, the water shortages that afflict many arid and densely populated areas. The global water crisis also involves water pollution, because to be useful for drinking and irrigation, water must not be polluted beyond certain thresholds. According to the World Health Organization, in 2008 approximately 880 million people in the world (or 13% of world population) did not have access to improved (safe) drinking water (World Health Statistics, 2010) (See Figure \(\PageIndex{1}\)). At the same time, about 2.6 billion people (or 40% of world population) lived without improved sanitation (see Figure \(\PageIndex{2}\)), which is defined as having access to a public sewage system, septic tank, or even a simple pit latrine.  Almost all of these deaths are in developing countries, and around 90% of them occur among children under the age of 5 (see Figure \(\PageIndex{3}\)). Compounding the water crisis is the issue of social justice; poor people more commonly lack clean water and sanitation than wealthy people in similar areas. Globally, improving water, sanitation, and hygiene could prevent up to 9% of all disease and 6% of all deaths. In addition to the global waterborne disease crisis, chemical pollution from agriculture, industry, cities, and mining threatens global water quality. Some chemical pollutants have serious and well-known health effects; however, many others have poorly known long-term health effects. In the U.S. currently more than 40,000 water bodies fit the definition of “impaired” set by EPA (See Figure \(\PageIndex{4}\)), which means they could neither support a healthy ecosystem nor meet water quality standards. In Gallup public polls conducted over the past decade Americans consistently put water pollution and water supply as the top environmental concerns over issues such as air pollution, deforestation, species extinction, and global warming.
Figure \(\PageIndex{1}\) Proportion of Population by Country Using Improved Drinking Water Sources in 2008. Improved drinking water sources, e.g., household connections, public standpipes, boreholes, protected dug wells and springs, and rainwater collections, are defined as those more likely to provide safe water than unimproved water sources, e.g., unprotected wells and springs, vendor-provided water, bottled water (unless water for other uses is available from an improved source), and tanker truck-provided water. Source: World Health Organization Figure \(\PageIndex{2}\) Proportion of Population by Country Using Improved Sanitation Facilities in 2008. Improved sanitation facilities, e.g., connection to public sewers or septic systems, pour-flush latrines, pit latrines, and ventilated improved pit latrines, are defined as those more likely to be sanitary than unimproved facilities, e.g., bucket latrines, public latrines, and open pit latrines. Source: World Health Organization Figure \(\PageIndex{3}\) Deaths by Country from Diarrhea Caused by Unsafe Water, Unimproved Sanitation, and Poor Hygiene in Children Less than 5 Years Old, 2004. Source: World Health Organization Figure \(\PageIndex{4}\) Percentage of Impaired Water Bodies in a Watershed by State in USA Based on US EPA Data in 2000. Map of watersheds containing impaired water bodies from the U.S. Environmental Protection Agency's 1998 list of impaired waters Source: U.S. Geological SurveyWater Chemistry Overview
Compared to other molecules of similar molecular weight, water (H 2 O) has unique physical properties including high values for melting and boiling point, surface tension (water’s cohesion, or “stickiness”), and capacity to dissolve soluble minerals, i.e., act as a solvent. These properties are related to its asymmetrical structure and polar nature , which means it is electrically neutral overall but it has a net positive charge on the side with the two hydrogen atoms and a net negative charge on the oxygen side (see Figure \(\PageIndex{5}\)). This separation of the electrical charge within a water molecule results in hydrogen bonds with other water molecules, mineral surfaces (hydrogen bonding produces the water films on minerals in the unsaturated zone of the subsurface), and dissolved ions (atoms with a negative or positive charge). Many minerals and pollutants dissolve readily in water because water forms hydration shells (spheres of loosely coordinated, oriented water molecules) around ions.
Figure \(\PageIndex{5}\) Structure of Water, Polar Charge of Water, and Hydrogen Bonds between Water Molecules. Source : Michal Maňas at Wikimedia CommonsAny natural water contains dissolved chemicals; some of these are important human nutrients, while others can be harmful to human health. The abundance of a water pollutant is commonly given in very small concentration units such as parts per million (ppm) or even parts per billion (ppb). An arsenic concentration of 1 ppm means 1 part of arsenic per million parts of water. This is equivalent to one drop of arsenic in 50 liters of water. To give you a different perspective on appreciating small concentration units, converting 1 ppm to length units is 1 cm (0.4 in) in 10 km (6 miles) and converting 1 ppm to time units is 30 seconds in a year. Total dissolved solids (TDS) represent the total amount of dissolved material in water. Average TDS (salinity) values for rainwater, river water, and seawater are about 4 ppm, 120 ppm, and 35,000 ppm. As discussed in Module 5.2, the most important processes that affect the salinity of natural waters are evaporation, which distills nearly pure water and leaves the dissolved ions in the original water, and chemical weathering, which involves mineral dissolution that adds dissolved ions to water. Fresh water is commonly defined as containing less than either 1,000 or 500 ppm TDS, but the US Environmental Protection Agency (EPA) recommends that drinking water not exceed 500 ppm TDS or else it will have an unpleasant salty taste.
Water Pollution Overview
Water pollution is the contamination of water by an excess amount of a substance that can cause harm to human beings and the ecosystem. The level of water pollution depends on the abundance of the pollutant, the ecological impact of the pollutant, and the use of the water. Pollutants are derived from biological, chemical, or physical processes. Although natural processes such as volcanic eruptions or evaporation sometimes can cause water pollution, most pollution is derived from human, land-based activities (see Figure \(\PageIndex{6}\)). Water pollutants can move through different water reservoirs, as the water carrying them progresses through stages of the water cycle (see Figure \(\PageIndex{7}\)). Water residence time (the average time that a water molecule spends in a water reservoir) is very important to pollution problems because it affects pollution potential. Water in rivers has a relatively short residence time, so pollution usually is there only briefly. Of course, pollution in rivers may simply move to another reservoir, such as the ocean, where it can cause further problems. Groundwater is typically characterized by slow flow and longer residence time, which can make groundwater pollution particularly problematic. Finally, pollution residence time can be much greater than the water residence time because a pollutant may be taken up for a long time within the ecosystem or absorbed onto sediment.
Figure \(\PageIndex{6}\) Water Pollution. Obvious water pollution in the form of floating debris; invisible water pollutants sometimes can be much more harmful than visible ones. Source: Stephen Codrington at Wikimedia Commons Figure \(\PageIndex{7}\) Sources of Water Contamination. Sources of some water pollutants and movement of pollutants into different water reservoirs of the water cycle. Source: U.S. Geological SurveyPollutants enter water supplies from point sources, which are readily identifiable and relatively small locations, or nonpoint sources, which are large and more diffuse areas. Point sources of pollution include animal “factory” farms that raise a large number and high density of livestock such as cows, pigs, and chickens (see Figure \(\PageIndex{8}\)) and discharge pipes from a factories or sewage treatment plants. Combined sewer systems that have a single set of underground pipes to collect both sewage and storm water runoff from streets for wastewater treatment can be major point sources of pollutants. During heavy rain, storm water runoff may exceed sewer capacity, causing it to back up and spilling untreated sewage into surface waters (see Figure \(\PageIndex{9}\)). Nonpoint sources of pollution include agricultural fields, cities, and abandoned mines. Rainfall runs over the land and through the ground, picking up pollutants such as herbicides, pesticides, and fertilizer from agricultural fields and lawns; oil, antifreeze, car detergent, animal waste, and road salt from urban areas; and acid and toxic elements from abandoned mines. Then, this pollution is carried into surface water bodies and groundwater. Nonpoint source pollution, which is the leading cause of water pollution in the U.S., is usually much more difficult and expensive to control than point source pollution because of its low concentration, multiple sources, and much greater volume of water.
Figure \(\PageIndex{8}\) A Commercial Meat Chicken Production House. This chicken factory farm is a possible major point source of water pollution. Source: Larry Rana at Wikimedia Commons Figure \(\PageIndex{9}\) Combined Sewer System. A combined sewer system is a possible major point source of water pollution during heavy rain due to overflow of untreated sewage. During dry weather (and small storms), all flows are handled by the publicly owned treatment works (POTW). During large storms, the relief structure allows some of the combined stormwater and sewage to be discharged untreated to an adjacent water body. Source: U.S. Environmental Protection Agency at Wikimedia CommonsTypes of Water Pollutants
Oxyden-demanding waste is an extremely important pollutant to ecosystems. Most surface water in contact with the atmosphere has a small amount of dissolved oxygen, which is needed by aquatic organisms for cellular respiration. Bacteria decompose dead organic matter (chemically represented in a simplified way as CH 2 O) and remove dissolved oxygen (O 2 ) according to the following reaction:
\[ CH2O+O2→CO2+H2O \nonumber\]
Too much decaying organic matter in water is a pollutant because it removes oxygen from water, which can kill fish, shellfish, and aquatic insects. The amount of oxygen used by aerobic (in the presence of oxygen) bacterial decomposition of organic matter is called biochemical oxygen demand (BOD). The major source of dead organic matter in most natural waters is sewage; grass and leaves are smaller sources. An unpolluted water body with respect to oxygen is a turbulent river that flows through a natural forest. Turbulence continually brings water in contact with the atmosphere where the O 2 content is restored. The dissolved oxygen content in such a river ranges from 10 to 14 ppm O 2 , BOD is low, and clean-water fish, e.g., bass, trout, and perch dominate. A polluted water body with respect to oxygen is a stagnant deep lake in an urban setting with a combined sewer system. This system favors a high input of dead organic carbon from sewage overflows and limited chance for water circulation and contact with the atmosphere. In such a lake, the dissolved O 2 content is ≤5 ppm O 2 , BOD is high, and low O 2 -tolerant fish, e.g., carp and catfish dominate.
Excessive plant nutrients, particularly nitrogen (N) and phosphorous (P), are pollutants closely related to oxygen-demanding waste. Aquatic plants require about 15 nutrients for growth, most of which are plentiful in water. N and P are called limiting nutrients , because they usually are present in water at low concentrations and therefore restrict the total amount of plant growth. This explains why N and P are major ingredients in most fertilizer. High concentrations of N and P from human sources (mostly agricultural and urban runoff including fertilizer, sewage, and P-based detergent) can cause cultural eutrophication, which involves the rapid growth of aquatic plants, particularly algae, called an algal bloom . Thick mats of floating and rooted green or sometimes red algae (see Figure \(\PageIndex{10}\)) create water pollution, damage the ecosystem by clogging fish gills and blocking sunlight, and damage lake aesthetics by making recreation difficult and creating an eyesore. A small percentage of algal species produce toxins that can kill fish, mammals, and birds, and may cause human illness; explosive growths of these algae are called harmful algal blooms (see Figure \(\PageIndex{11}\)). When the prolific algal layer dies, it becomes oxygen-demanding waste, which can create very low O 2 water (<~2 ppm O 2 ), called hypoxia or dead zone because it causes death to organisms that are unable to leave that environment. An estimated 50% of lakes in North America, Europe, and Asia are negatively impacted by cultural eutrophication. In addition, the size and number of marine hypoxic zones have grown dramatically over the past 50 years (see Figure \(\PageIndex{12}\)), including a very large dead zone located offshore Louisiana in the Gulf of Mexico. Cultural eutrophication and hypoxia are difficult to combat, because they are caused primarily by nonpoint source pollution, which is difficult to regulate, and N and P, which are difficult to remove from wastewater.
Figure \(\PageIndex{10}\) Algal Bloom in River in Sichuan, China. Algal blooms can present problems for ecosystems and human society. Source: Felix Andrews via Wikimedia Commons Figure \(\PageIndex{11}\) Harmful Algal Bloom. Harmful algal bloom with deep red color. Source: Kai Schumann via National Oceanic and Atmospheric Administration Figure \(\PageIndex{12}\) Aquatic Dead Zones. Zones of hypoxia shown as red circles. Black dots show hypoxia zones of unknown size, brown shading shows population density, and blue shading shows density of particulate organic carbon, an indicator of organic productivity. Source: Robert Simmon & Jesse Allen at NASA Earth Observatory via Wikimedia CommonsPathogens are disease-causing microorganisms, e.g., viruses, bacteria, parasitic worms, and protozoa, which cause a variety of intestinal diseases such as dysentery, typhoid fever, hepatitis, and cholera. Pathogens are the major cause of the water pollution crisis discussed at the beginning of this section.  Pathogens enter water primarily from human and animal fecal waste due to inadequate sewage treatment. In many underdeveloped countries, sewage is discharged into local waters either untreated or after only rudimentary treatment. In developed countries untreated sewage discharge can occur from overflows of combined sewer systems, poorly managed livestock factory farms, and leaky or broken sewage collection systems (see Figure \(\PageIndex{14}\)). Water with pathogens can be remediated by adding chlorine or ozone, by boiling, or by treating the sewage in the first place.
Figure \(\PageIndex{13}\) Overflowing Sanitary Sewer. A manhole cover blown off by a June 2006 sanitary sewer overflow in Rhode Island. Source: U.S. Environmental Protection Agency via Wikimedia CommonsOil spills are another kind of organic pollution. Oil spills can result from supertanker accidents such as the Exxon Valdez in 1989, which spilled 10 million gallons of oil into the rich ecosystem of offshore south Alaska and killed massive numbers of animals. The largest marine oil spill was the Deepwater Horizon disaster, which began with a natural gas explosion (see Figure \(\PageIndex{14}\) ) at an oil well 65 km offshore of Louisiana and flowed for 3 months in 2010, releasing an estimated 200 million gallons of oil. The worst oil spill ever occurred during the Persian Gulf war of 1991, when Iraq deliberately dumped approximately 200 million gallons of oil in offshore Kuwait and set more than 700 oil well fires that released enormous clouds of smoke and acid rain for over nine months. During an oil spill on water, oil floats to the surface because it is less dense than water, and the lightest hydrocarbons evaporate, decreasing the size of the spill but polluting the air. Then, bacteria begin to decompose the remaining oil, in a process that can take many years. After several months only about 15% of the original volume may remain, but it is in thick asphalt lumps, a form that is particularly harmful to birds, fish, and shellfish. Cleanup operations can include skimmer ships that vacuum oil from the water surface (effective only for small spills), controlled burning (works only in early stages before the light, ignitable part evaporates but also pollutes the air), dispersants (detergents that break up oil to accelerate its decomposition, but some dispersants may be toxic to the ecosystem), and bioremediation (adding microorganisms that specialize in quickly decomposing oil, but this can disrupt the natural ecosystem).
Figure \(\PageIndex{14}\) Deepwater Horizon Explosion. Boats fighting the fire from an explosion at the Deepwater Horizon drilling rig in Gulf of Mexico offshore Louisiana on April 20, 2010. Source: United States Coast Guard via Wikimedia CommonsToxic chemicals involve many different kinds and sources, primarily from industry and mining. General kinds of toxic chemicals include hazardous chemicals , which are a wide variety of synthetic organic and inorganic chemicals such as acids, bases, cyanide, and a class of compounds called persistent organic pollutants that includes DDT (pesticide), dioxin (herbicide by-product), and PCBs (polychlorinated biphenyls, which were used as a liquid insulator in electric transformers). Persistent organic pollutants are long-lived in the environment, accumulate through the food chain (bioaccumulation), and can be toxic. Another category of toxic chemicals includes radioactive materials such as cesium, iodine, uranium, and radon gas, which can result in long-term exposure to radioactivity if it gets into the body. A final group of toxic chemicals is heavy metals such as lead, mercury, arsenic, cadmium, and chromium, which can accumulate through the food chain. Heavy metals are commonly produced by industry and at metallic ore mines. Arsenic and mercury are discussed in more detail below. The US EPA regulates 83 contaminants in drinking water to ensure a safe public water supply. Similarly, at the international level the World Health Organization has drinking water standards for a variety of contaminants.
Arsenic (As) has been famous as an agent of death for many centuries. In large doses arsenic causes cancer and can be fatal. Only recently have scientists recognized that health problems can be caused by drinking small arsenic concentrations in water over a long time. It attacks the central nervous system and can damage the respiratory system, bladder, lungs, liver, and kidneys. It enters the water supply naturally from weathering of As-rich minerals and from human activities such as coal burning and smelting of metallic ores. The worst case of arsenic poisoning occurred in the densely populated impoverished country of Bangladesh, which had experienced 100,000s of deaths from diarrhea and cholera each year from drinking surface water contaminated with pathogens due to improper sewage treatment. In the 1970s the United Nations provided aid for millions of shallow water wells, which resulted in a dramatic drop in pathogenic diseases. Unfortunately, many of the wells produced water naturally rich in arsenic. Tragically, there are an estimated 77 million people (about half of the population) who inadvertently may have been exposed to toxic levels of arsenic in Bangladesh as a result. The World Health Organization has called it the largest mass poisoning of a population in history.
Mercury (Hg) is used in a variety of electrical products, such as dry cell batteries, fluorescent light bulbs, and switches, as well as in the manufacture of paint, paper, vinyl chloride, and fungicides. In the methylmercury form (CH 3 Hg + ) it is highly toxic; ≥ 1 ppb of methylmercury represents water contaminated with mercury. Mercury concentrates in the food chain, especially in fish, in a process caused biomagnification (see Sidebar Biomagnification ). It acts on the central nervous system and can cause loss of sight, feeling, and hearing as well as nervousness, shakiness, and death. Like arsenic, mercury enters the water supply naturally from weathering of Hg-rich minerals and from human activities such as coal burning and metal processing. A famous mercury poisoning case in Minamata, Japan involved methylmercury-rich industrial discharge that caused high Hg levels in fish. People in the local fishing villages ate fish up to three times per day for over 30 years, which resulted in over 2,000 deaths. During that time the responsible company and national government did little to mitigate, help alleviate, or even acknowledge the problem.
Biomagnification
Biomagnification represents the processes in an ecosystem that cause greater concentrations of a chemical, such as methylmercury, in organisms higher up the food chain. Mercury and methylmercury are present in only very small concentrations in seawater; however, at the base of the food chain algae absorb methylmercury. Then, small fish eat the algae, large fish and other organisms higher in the food chain eat the small fish, and so on. Fish and other aquatic organisms absorb methylmercury rapidly but eliminate it slowly from the body. Therefore, each step up the food chain increases the concentration from the step below (see Figure \(\PageIndex{15}\)). Largemouth bass can concentrate methylmercury up to 10 million times over the water concentration and fish-eating birds can concentrate it even higher. Other chemicals that exhibit biomagnification are DDT, PCBs, and arsenic.
Figure \(\PageIndex{15}\) An illustrative example of biomagnification of mercury from water through the food chain and into a bird's egg. Source: U.S. Geological SurveyOther water pollutants include sediment and heat. Muddy water is bad for drinking but even worse for underwater plants that need sunlight for photosynthesis. Much of the sediment in water bodies is derived from the erosion of soil, so it also represents a loss of agricultural productivity. Thermal pollution involves the release of heated waters from power plants and industry to surface water, causing a drop in the dissolved O 2 content, which can stress fish.
Hard water contains abundant calcium and magnesium, which reduces its ability to develop soapsuds and enhances scale (calcium and magnesium carbonate minerals) formation on hot water equipment. Water softeners remove calcium and magnesium, which allows the water to lather easily and resist scale formation. Hard water develops naturally from the dissolution of calcium and magnesium carbonate minerals in soil; it does not have negative health effects in people.
Groundwater pollution can occur from underground sources and all of the pollution sources that contaminate surface waters. Common sources of groundwater pollution are leaking underground storage tanks for fuel, septic tanks, agricultural activity, and landfills. Common groundwater pollutants include nitrate, pesticides, volatile organic compounds, and petroleum products. Polluted groundwater can be a more serious problem than polluted surface water because the pollution in groundwater may go undetected for a long time because usually it moves very slowly. As a result, the pollution in groundwater may create a contaminant plume, a large body of flowing polluted groundwater (see Figure \(\PageIndex{15}\)), making cleanup very costly. By the time groundwater contamination is detected, the entity responsible for the pollution may be bankrupt or nonexistent. Another troublesome feature of groundwater pollution is that small amounts of certain pollutants, e.g., petroleum products and organic solvents, can contaminate large areas. In Denver, Colorado 80 liters of several organic solvents contaminated 4.5 trillion liters of groundwater and produced a 5 km long contaminant plume. Most groundwater contamination occurs in shallow, unconfined aquifers located near the contamination source. Confined aquifers are less susceptible to pollution from the surface because of protection by the confining layer. A major threat to groundwater quality is from underground fuel storage tanks. Fuel tanks commonly are stored underground at gas stations to reduce explosion hazards. Before 1988 in the U.S. these storage tanks could be made of metal, which can corrode, leak, and quickly contaminate local groundwater. Now, leak detectors are required and the metal storage tanks are supposed to be protected from corrosion or replaced with fiberglass tanks. Currently there are around 600,000 underground fuel storage tanks in the U.S. and over 30% still do not comply with EPA regulations regarding either release prevention or leak detection.
Figure \(\PageIndex{16}\) Contaminant Plume in Groundwater. Mapping how a contaminant plume will migrate once it reaches groundwater requires understanding of the pollutant's chemical properties, local soil characteristics, and how permeable the aquifer is. Source: United States Geological SurveySustainable Solutions to the Water Pollution Crisis?
Resolution of the global water pollution crisis described at the beginning of this section requires multiple approaches to improve the quality of our fresh water and move towards sustainability. The most deadly form of water pollution, pathogenic microorganisms that cause waterborne diseases, kills almost 2 million people in underdeveloped countries every year. The best strategy for addressing this problem is proper sewage (wastewater) treatment. Untreated sewage is not only a major cause of pathogenic diseases, but also a major source of other pollutants, including oxygen-demanding waste, plant nutrients (N and P), and toxic heavy metals. Wastewater treatment is done at a sewage treatment plant in urban areas and through a septic tank system in rural areas.
The main purpose of a sewage treatment plant is to remove organic matter (oxygen-demanding waste) and kill bacteria; special methods also can be used to remove plant nutrients and other pollutants. The numerous processing steps at a conventional sewage treatment plant (see Figure \(\PageIndex{17}\)) include pretreatment (screening and removal of sand and gravel), primary treatment (settling or floatation to remove organic solids, fat, and grease), secondary treatment (aerobic bacterial decomposition of organic solids), tertiary treatment (bacterial decomposition of nutrients and filtration), disinfection (treatment with chlorine, ozone, ultraviolet light, or bleach), and either discharge to surface waters (usually a local river) or reuse for some other purpose, such as irrigation, habitat preservation, and artificial groundwater recharge. The concentrated organic solid produced during primary and secondarytreatment is called sludge, which is treated in a variety of ways including landfill disposal, incineration, use as fertilizer, and anaerobic bacterial decomposition, which is done in the absence of oxygen. Anaerobic decomposition of sludge produces methane gas, which can be used as an energy source. To reduce water pollution problems, separate sewer systems (where street runoff goes to rivers and only wastewater goes to a wastewater treatment plant) are much better than combined sewer systems, which can overflow and release untreated sewage into surface waters during heavy rain. Some cities such as Chicago, Illinois have constructed large underground caverns and also use abandoned rock quarries to hold storm sewer overflow. After the rain stops, the stored water goes to the sewage treatment plant for processing.
Figure \(\PageIndex{17}\) Steps at a Sewage Treatment Plant. The numerous processing steps at a conventional sewage treatment plant include pretreatment (screening and removal of sand and gravel), primary treatment (settling or floatation to remove organic solids, fat, and grease), secondary treatment (aerobic bacterial decomposition of organic solids), tertiary treatment (bacterial decomposition of nutrients and filtration), disinfection (treatment with chlorine, ozone, ultraviolet light, or bleach), and either discharge to surface waters (usually a local river) or reuse for some other purpose, such as irrigation, habitat preservation, and artificial groundwater recharge. Source: Leonard G. via WikipediaA septic tank system is an individual sewage treatment system for homes in rural and even some urban settings. The basic components of a septic tank system (see Figure \(\PageIndex{18}\)) include a sewer line from the house, a septic tank (a large container where sludge settles to the bottom and microorganisms decompose the organic solids anaerobically), and the drain field (network of perforated pipes where the clarified water seeps into the soil and is further purified by bacteria). Water pollution problems occur if the septic tank malfunctions, which usually occurs when a system is established in the wrong type of soil or maintained poorly.
Figure \(\PageIndex{18}\) Septic System. Septic tank system for sewage treatment. Source: United States Geological SurveyFor many developing countries, financial aid is necessary to build adequate sewage treatment facilities; however, the World Health Organization estimates an estimated cost savings of between $3 and $34 for every $1 invested in clean water delivery and sanitation ( Water for Life, 2005 ). The cost savings are from health care savings, gains in work and school productivity, and deaths prevented. Simple and inexpensive techniques for treating water at home include chlorination, filters, and solar disinfection. Another alternative is to use constructed wetlands technology (marshes built to treat contaminated water), which is simpler and cheaper than a conventional sewage treatment plant.
Bottled water is not a sustainable solution to the water crisis, despite exponential growth in popularity in the U.S. and the world. Bottled water is not necessarily any safer than the U.S. public water supply, it costs on average about 700 times more than U.S. tap water, and every year it uses approximately 200 billion plastic and glass bottles that have a relatively low rate of recycling. Compared to tap water, it uses much more energy, mainly in bottle manufacturing and long-distance transportation. If you don’t like the taste of your tap water, then please use a water filter instead of bottled water!
Figure \(\PageIndex{19}\) Storm Drain. Curbside storm drain receiving urban runoff. Source: By Robert Lawton via Wikimedia CommonsAdditional sustainable solutions to the water pollution crisis include legislation to eliminate or greatly reduce point sources of water pollution. In the U.S., the Clean Water Act of 1972 and later amendments led to major improvements in water quality (see Sidebar Clean Water Act). Nonpoint sources of water pollution, e.g., agricultural runoff and urban runoff (see Figure \(\PageIndex{19}\)), are much harder to regulate because of their widespread, diffuse nature. There are many construction and agricultural practices that reduce polluted runoff including no-till farming and sediment traps. Artificial aeration or mechanical mixing can remediate lakes with oxygen depletion. Specific things that we can do to reduce urban runoff include the following: keep soil, leaves, and grass clippings off driveways, sidewalks, and streets; don't pour used motor oil, antifreeze, paints, pesticides, or any household hazardous chemical down the storm sewer or drain; recycle used motor oil; use hazardous waste disposal programs offered by the community; compost your organic waste; don't use fertilizers and herbicides on your lawn; and flush pet waste down the toilet.
Clean Water Act
During the early 1900s rapid industrialization in the U.S. resulted in widespread water pollution due to free discharge of waste into surface waters. The Cuyahoga River in northeast Ohio caught fire numerous times (see Figure \(\PageIndex{20}\)), including a famous fire in 1969 that caught the nation’s attention. In 1972 Congress passed one of the most important environmental laws in U.S. history, the Federal Water Pollution Control Act, which is more commonly called the Clean Water Act. The purpose of the Clean Water Act and later amendments is to maintain and restore water quality, or in simpler terms to make our water swimmable and fishable. It became illegal to dump pollution into surface water unless there was formal permission and U.S. water quality improved significantly as a result. More progress is needed because currently the EPA considers over 40,000 U.S. water bodies as impaired, most commonly due to pathogens, metals, plant nutrients, and oxygen depletion. Another concern is protecting groundwater quality, which is not yet addressed sufficiently by federal law.
Figure \(\PageIndex{20}\) Cuyahoga River on Fire. Source: National Oceanic and AtmosphericSometimes slow flow through a soil can naturally purify groundwater because some pollutants, such as P, pesticides, and heavy metals, chemically bind with surfaces of soil clays and iron oxides. Other pollutants are not retained by soil particles: These include N, road salt, gasoline fuel, the herbicide atrazine, tetrachloroethylene (a carcinogenic cleaning solvent used in dry cleaning), and vinyl chloride. In other cases, slow groundwater flow can allow bacteria to decompose dead organic matter and certain pesticides. There are many other ways to remediate polluted groundwater. Sometimes the best solution is to stop the pollution source and allow natural cleanup. Specific treatment methods depend on the geology, hydrology, and pollutant because some light contaminants flow on top of groundwater, others dissolve and flow with groundwater, and dense contaminants can sink below groundwater. A common cleanup method called pump and treat involves pumping out the contaminated groundwater and treating it by oxidation, filtration, or biological methods. Sometimes soil must be excavated and sent to a landfill. In-situ treatment methods include adding chemicals to immobilize heavy metals, creating a permeable reaction zone with metallic iron that can destroy organic solvents, or using bioremediation by adding oxygen or nutrients to stimulate growth of microorganisms.
Review Questions
- What are the major kinds of water pollutants and how do they degrade water quality?
- How would you rank the water pollution problems described in this chapter? Why?
- Why is untreated sewage such an important water pollutant to remediate?
- What should society learn from the case history of Love Canal?
- Why are people facing a crisis involving water pollution and how can we solve it?
References
Water for Life: Making it Happen (2005) World Health Organization and UNICEF. Retrieved from http://www.who.int/water_sanitation_health/waterforlife.pdf
World Health Statistics (2010) World Health Organization. Retrieved from http://www.who.int/whosis/whostat/EN_WHS10_Full.pdf
Glossary
- arsenic
- A type of water pollutant that can be fatal in large doses and can cause health problems in small doses over a long time.
- biochemical oxygen demand
- The amount of oxygen used by aerobic (in presence of oxygen) bacterial decomposition of organic matter.
- bioremediation
- Method of groundwater remediation involving the addition oxygen or nutrients. to stimulate growth of microorganisms, which decompose an organic pollutant.
- bottled water
- Drinking water packaged in plastic bottles or glass bottles, bottled water is not a sustainable solution to the water crisis because of the nonrenewable energy and material resources involved in manufacturing and transporting it.
- combined sewer systems
- A single set of underground pipes used to collect both sewage and. storm water runoff from streets for wastewater treatment.
- constructed wetland
- Marsh built to treat contaminated water.
- contaminant plume
- A large body of flowing polluted groundwater.
- cultural eutrophication
- Rapid aquatic plant growth, particularly algae, in a surface water body.
- excessive plant nutrient
- A type of water pollutant involving a limiting plant nutrient that usually is present in water at low concentrations and therefore restricts the total amount of plant growth, examples include nitrogen and phosphorous.
- hard water
- Water with abundant calcium and magnesium, which reduces its ability to develop soapsuds and enhances scale; hard water does not have negative health effects in people.
- heat
- A type of water pollutant that causes a drop in the dissolved oxygen content, which can stress fish.
- heavy metal
- A type of water pollutant involving elements such as lead, mercury, arsenic, cadmium, and chromium, which can accumulate through the food chain.
- hypoxia
- Very low oxygen water due to prolific growth of algae, algal death, and then decomposition, also called dead zone.
- mercury
- A type of water pollutant that acts on the central nervous system and can cause loss of sight, feeling, and hearing as well as nervousness, shakiness, and death.
- nonpoint source (of water pollution)
- Large and diffuse location where a pollution source occurs.
- oil spill
- A type of organic water pollutant involving the release of liquid petroleum into the environment due to human activity.
- oxygen-demanding waste
- A type of water pollutant involving abundant dead organic matter.
- pathogens
- Disease-causing microorganisms, e.g., viruses, bacteria, parasitic worms, and protozoa, which cause a variety of intestinal diseases such as dysentery, typhoid fever, hepatitis, and cholera.
- persistent organic pollutant
- A group of organic water pollutants that are long-lived in the environment, accumulate through the food chain, and can be toxic.
- point source (of water pollution)
- Readily identifiable and relatively small location where a pollution source occurs.
- sediment
- A type of water pollutant that degrades drinking water and can kill underwater plants that need sunlight for photosynthesis.
- septic tank system
- An individual sewage treatment system for homes in rural and even some urban settings.
- sewage treatment plant
- A facility that processes wastewater with the main goal of removing organic matter (oxygen-demanding waste) and killing bacteria.
- sludge
- Concentrated organic solid produced during primary and secondarytreatment of sewage treatment.
- solvent
- Capacity of a liquid such as water to dissolve soluble minerals.
- total dissolved solids
- Total amount of dissolved material in water, typically reported in parts per million (ppm) units.
- toxic chemical
- A type of organic water pollutant involving chemicals with a severe human health risk.
- underground fuel storage tank
- A type of water pollutant if it leaks.
- water pollution
- Contamination of water by an excess amount of a substance that can cause harm to human beings and the ecosystem.


6.4: Dual basis
The dual basis is a basis associated to the basis of a vector space. In three-dimensional space, it is isomorphous to the basis of the reciprocal lattice. It is mathematically defined as follows:
Given a basis of n vectors e i spanning the direct space E n , and a vector x = x i e i , let us consider the n quantities defined by the scalar products of x with the basis vectors, e i :
x i = x . e i = x j e j . e i = x j g ji ,
where the g ji 's are the doubly covariant components of the metric tensor.
By solving these equations in terms of x j , one gets:
x j = x i g ij
where the matrix of the g ij 's is inverse of that of the g ij 's ( g ik g jk = δ i j ). The development of vector x with respect to basis vectors e i can now also be written:
x = x i e i = x i g ij e j
The set of n vectors e i = g ij e j that span the space E n forms a basis since vector x can be written:
x = x i e i
This basis is the dual basis and the n quantities x i defined above are the coordinates of x with respect to the dual basis. In a similar way one can express the direct basis vectors in terms of the dual basis vectors:
e i = g ij e j
The scalar products of the basis vectors of the dual and direct bases are:
g i j = e i . e j = g ik e k . e j = g ik g jk = δ i j .
One has therefore, since the matrices g ik and g ij are inverse:
g i j = e i . e j = δ i j .
These relations show that the dual basis vectors satisfy the definition conditions of the reciprocal vectors. In a three-dimensional space the dual basis and the basis of reciprocal space are identical.


6.1: Uniform Distribution
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If you have a situation where the probability is always the same, then this is known as a uniform distribution. An example would be waiting for a commuter train. The commuter trains on the Blue and Green Lines for the Regional Transit Authority (RTA) in Cleveland, OH, have a waiting time during peak hours of ten minutes ("2012 annual report," 2012). If you are waiting for a train, you have anywhere from zero minutes to ten minutes to wait. Your probability of having to wait any number of minutes in that interval is the same. This is a uniform distribution. The graph of this distribution is in Figure \(\PageIndex{1}\) .
Suppose you want to know the probability that you will have to wait between five and ten minutes for the next train. You can look at the probability graphically such as in Figure \(\PageIndex{2}\) .
How would you find this probability? Calculus says that the probability is the area under the curve. Notice that the shape of the shaded area is a rectangle, and the area of a rectangle is length times width. The length is \(10-5=5\) and the width is 0.1. The probability is \(P(5<x<10)=0.1 * 5=0.5\), where and x is the waiting time during peak hours.
Example \(\PageIndex{1}\) finding probabilities in a uniform distribution
The commuter trains on the Blue and Green Lines for the Regional Transit Authority (RTA) in Cleveland, OH, have a waiting time during peak rush hour periods of ten minutes ("2012 annual report," 2012).
- State the random variable.
- Find the probability that you have to wait between four and six minutes for a train.
- Find the probability that you have to wait between three and seven minutes for a train.
- Find the probability that you have to wait between zero and ten minutes for a train.
- Find the probability of waiting exactly five minutes.
Solution
a. x = waiting time during peak hours
b. \(P(4<x<6)=(6-4)^{*} 0.1=0.2\)
c. \(P(3<x<7)=(7-3) * 0.1=0.4\)
d. \(P(0<x<10)=(10-0) * 0.1=1.0\)
e. Since this would be just one line, and the width of the line is 0, then the \(P(x=5)=0 * 0.1=0\).
Notice that in Example \(\PageIndex{1}\)d, the probability is equal to one. This is because the probability that was computed is the area under the entire curve. Just like in discrete probability distributions, where the total probability was one, the probability of the entire curve is one. This is the reason that the height of the curve is 0.1. In general, the height of a uniform distribution that ranges between a and b , is \(\dfrac{1}{b-a}\).
Homework
Exercise \(\PageIndex{1}\)
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The commuter trains on the Blue and Green Lines for the Regional Transit Authority (RTA) in Cleveland, OH, have a waiting time during peak rush hour periods of ten minutes ("2012 annual report," 2012).
- State the random variable.
- Find the probability of waiting between two and five minutes.
- Find the probability of waiting between seven and ten minutes.
- Find the probability of waiting eight minutes exactly.
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The commuter trains on the Red Line for the Regional Transit Authority (RTA) in Cleveland, OH, have a waiting time during peak rush hour periods of eight minutes ("2012 annual report," 2012).
- State the random variable.
- Find the height of this uniform distribution.
- Find the probability of waiting between four and five minutes.
- Find the probability of waiting between three and eight minutes.
- Find the probability of waiting five minutes exactly.
- Answer
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1. a. See solutions, b. \(P(2<x<5)=0.3\), c. \(P(7<x<10)=0.3\), d. \(P(x=8)=0\)


4: Understanding Financial Management
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Education is one of the few things you can buy that will last a lifetime. It can’t rust, corrode, break down, or wear out. It can’t be stolen, repossessed, or destroyed. Once you have a degree, no one can take it away. That makes your education a safer investment than real estate, gold, oil, diamonds, or stocks.
Higher levels of education are associated with the following (Alzheimer’s Association 2012):
In short, education is a good deal for you and for society. It’s worth investing in it periodically to update your skills, reach your goals, and get more of what you want in life. In this module, you will learn about the guidelines important to creating your own financial plan so that you are able to confidently invest in your future.
Thumbnail: www.pexels.com/photo/silver-...-coins-128867/ (CC0 1.0; Pixabay).


1.2.9: Trends in Entrepreneurship and Small-Business Ownership
What Trends are Shaping Entrepreneurship and Small-business Ownership?
Entrepreneurship has changed since the heady days of the late 1990s, when starting a dot-com while still in college seemed a quick route to riches and stock options. Much entrepreneurial opportunity comes from major changes in demographics, society, and technology, and at present there is a confluence of all three. A major demographic group is moving into a significantly different stage in life, and minorities are increasing their business ownership in remarkable numbers. We have created a society in which we expect to have our problems taken care of, and the technological revolution stands ready with already-developed solutions. Evolving social and demographic trends, combined with the challenge of operating in a fast-paced technology-dominated business climate, are changing the face of entrepreneurship and small-business ownership.
Into the Future: Start-ups Drive the Economy
Did new business ventures drive the economic recovery from the 2001–2002 and 2007–2009 to recessions, and are they continuing to make significant contributions to the U.S. economy? The economists who review Department of Labor employment surveys and SBA statistics think so. “Small business drives the American economy,” says Dr. Chad Moutray, former chief economist for the SBA’s Office of Advocacy. “Main Street provides the jobs and spurs our economic growth. American entrepreneurs are creative and productive.” Numbers alone do not tell the whole story, however. Are these newly self-employed workers profiting from their ventures, or are they just biding their time during a period of unemployment?
U.S. small businesses employed 57.9 million people in 2016, representing nearly 48 percent of the workforce. The number of net new jobs added to the economy was 1.4 million.
The highest rate of growth is coming from women-owned firms, which continues to rise at rates higher than the national average—and with even stronger growth rates since the recession. There were an estimated 11.6 million women-owned businesses employing nearly 9 million people in 2016, generating more than $1.7 trillion in revenue.
Between 2007 and 2017, women-owned firms increased by 114 percent, compared to a 44 percent increase among all businesses. This means that growth rates for women-owned businesses are 2.5 times faster than the national average. Employment growth was also stronger than national rates. Women-owned businesses increased 27 percent over the past 20 years, while overall business employment has increased by 13 percent since 2007.
These trends show that more workers are striking out on their own and earning money doing it. It has become very clear that encouraging small-business activity leads to continued strong overall economic growth.
Changing Demographics Create Entrepreneurial Diversity
The mantra, “60 is the new 40,” describes today’s Baby Boomers who indulge in much less knitting and golf in their retirement years. The AARP predicts that silver-haired entrepreneurs will continue to rise in the coming years. According to a recent study by the Kauffman Foundation, Baby Boomers are twice as likely as Millennials to start a new business. In fact, close to 25 percent of all new entrepreneurs fall between the ages of 55 and 64. This has created a ripple effect in the way we work. Boomers have accelerated the growing acceptance of working from home, adding to the millions of U.S. workers already showing up to work in their slippers. In addition, the ongoing corporate brain drain could mean that small businesses will be able to tap into the expertise of seasoned free agents at less-than-corporate prices—and that seniors themselves will become independent consultants to businesses of all sizes.
The growing numbers of Baby Boomer entrepreneurs has prompted some forward-thinking companies to recognize business opportunities in technology. At one time there was a concern that the aging of the population would create a drag on the economy. Conventional wisdom says that the early parenthood years are the big spending years. As we age, we spend less and, because Boomers are such a big demographic group, this was going to create a long-term economic decline. Not true, it now appears. The Boomer generation has built sizable wealth, and they are not afraid to spend it to make their lives more comfortable.
Minorities are also adding to the entrepreneurial mix. As we saw in Table <IP_ADDRESS>, minority groups and women are increasing business ownership at a much faster rate than the national average, reflecting their confidence in the U.S. economy. These overwhelming increases in minority business ownership paralleled the demand for U.S. Small Business Administration loan products. Loans to minority business owners in fiscal year 2017 set a record—more than $9.5 billion, or 31 percent, of SBA’s total loan portfolio.
The latest Kauffman Foundation Index of Startup Activity found that immigrants and Latinos have swelled the growing numbers of self-employed Americans in recent years, increasing the diversity of the country’s entrepreneurial class. Overall, minority-owned businesses increased 38 percent. The SBA notes that the number of Hispanic-owned businesses has increased more than 46 percent between 2007 and 2012.

 Whether you own chains of dry cleaners in Queens, car dealerships in Chicago, or oil wells in West Texas, fortunes have been made in every state in the Union. There are some places, however, where the chances of creating wealth are much greater than others. That is the reason why people who hope to strike it rich move to places such as Manhattan or Palo Alto. It’s not because the cost of living is low or the quality of life as a struggling entrepreneur is fun. Whether starting a software or soft-drink company, entrepreneurs tend to follow the money
But not all companies follow the herd. Guild Education, founded in 2015 by Rachel Carlson and Brittany Stich at Stanford University, left San Francisco due to the high cost of living that could slow down the company’s growth. “We have a lot of women who are executives and department heads here, starting with myself and my co-founder,” CEO Rachel Carlson said. “So when we left, we deliberately chose a place where you can have a family.” Guild Education’s mission is to help large employers offer college education and tuition reimbursement as a benefit to the 64 million working-age adults who lack a college degree.
Since moving to Denver, Guild Education has raised another $21 million in venture capital, bringing the total funding to $31.5 million with a company valuation of $125 million. The company headquarters in Denver is next door to a Montessori school and employs 58 employees. “We were joking that we’re the polar opposite of Apple,” said Carlson. “Remember when the new ‘mothership’ came out? Every single parent noticed that it had a huge gym but not a daycare.”
According to PwC’s quarterly venture capital study, “MoneyTree Report,” the top regions in the United States for venture-backed deals in the third quarter of 2017 were San Francisco ($4.1 billion), New York Metro ($4.2 billion), Silicon Valley (Bay Area $2.2 billion), and New England ($1.8 billion).
In 2017, equity financing in U.S. start-ups rose for the third straight quarter, reaching $19 billion, according to the PwC/CB Insights “MoneyTree Report Q3 2017.” “Financing was boosted by a large number of mega-rounds,” says Tom Ciccolella, Partner, U.S. Ventures Leader at PwC. Twenty-six mega-rounds of $100 million in companies such as WeWork, 23andMe, Fanatics, and NAUTO contributed to the strong activity levels in the first three quarters of 2017. The top five U.S. industry sectors with the most deals and funding were Internet, Healthcare, Mobile and Telecommunications, Software (Non-Internet/Mobile), and Consumer Products.
CONCEPT CHECK
- What significant trends are occurring in the small-business arena?
- How is entrepreneurial diversity impacting small business and the economy?
- How do ethics impact decision-making with small-business owners?


4.4: Planetary Evolution
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Learning Objectives
By the end of this section, you will be able to:
- Describe the geological activity during the evolution of the planets, particularly on the terrestrial planets
- Describe the factors that affect differences in elevation on the terrestrial planets
- Explain how the differences in atmosphere on Venus, Earth, and Mars evolved from similar starting points in the early history of the solar system
While we await more discoveries and better understanding of other planetary systems, let us look again at the early history of our own solar system, after the dissipation of our dust disk. The era of giant impacts was probably confined to the first 100 million years of solar system history, ending by about 4.4 billion years ago. Shortly thereafter, the planets cooled and began to assume their present aspects. Up until about 4 billion years ago, they continued to acquire volatile materials, and their surfaces were heavily cratered from the remaining debris that hit them. However, as external influences declined, all the terrestrial planets as well as the moons of the outer planets began to follow their own evolutionary courses. The nature of this evolution depended on each object’s composition, mass, and distance from the Sun.
Geological Activity
We have seen a wide range in the level of geological activity on the terrestrial planets and icy moons. Internal sources of such activity (as opposed to pummeling from above) require energy, either in the form of primordial heat left over from the formation of a planet or from the decay of radioactive elements in the interior. The larger the planet or moon, the more likely it is to retain its internal heat and the more slowly it cools—this is the “baked potato effect” mentioned in Other Worlds: An Introduction to the Solar System. Therefore, we are more likely to see evidence of continuing geological activity on the surface of larger (solid) worlds (Figure \(\PageIndex{1}\)). Jupiter’s moon Io is an interesting exception to this rule; we saw that it has an unusual source of heat from the gravitational flexing of its interior by the tidal pull of Jupiter. Europa is probably also heated by jovian tides. Saturn may be having a similar effect on its moon Enceladus.
The Moon, the smallest of the terrestrial worlds, was internally active until about 3.3 billion years ago, when its major volcanism ceased. Since that time, its mantle has cooled and become solid, and today even internal seismic activity has declined to almost zero. The Moon is a geologically dead world. Although we know much less about Mercury, it seems likely that this planet, too, ceased most volcanic activity about the same time the Moon did.
Mars represents an intermediate case, and it has been much more active than the Moon. The southern hemisphere crust had formed by 4 billion years ago, and the northern hemisphere volcanic plains seem to be contemporary with the lunar maria. However, the Tharsis bulge formed somewhat later, and activity in the large Tharsis volcanoes has apparently continued on and off to the present era.
Earth and Venus are the largest and most active terrestrial planets. Our planet experiences global plate tectonics driven by convection in its mantle. As a result, our surface is continually reworked, and most of Earth’s surface material is less than 200 million years old. Venus has generally similar levels of volcanic activity, but unlike Earth, it has not experienced plate tectonics. Most of its surface appears to be no more than 500 million years old. We did see that the surface of our sister planet is being modified by a kind of “blob tectonics”—where hot material from below puckers and bursts through the surface, leading to coronae, pancake volcanoes, and other such features. A better understanding of the geological differences between Venus and Earth is a high priority for planetary geologists.
The geological evolution of the icy moons and Pluto has been somewhat different from that of the terrestrial planets. Tidal energy sources have been active, and the materials nature has to work with are not the same. On these outer worlds, we see evidence of low-temperature volcanism, with the silicate lava of the inner planets being supplemented by sulfur compounds on Io, and replaced by water and other ices on Pluto and other outer-planet moons.
Elevation Differences
Let’s look at some specific examples of how planets differ. The mountains on the terrestrial planets owe their origins to different processes. On the Moon and Mercury, the major mountains are ejecta thrown up by the large basin-forming impacts that took place billions of years ago. Most large mountains on Mars are volcanoes, produced by repeated eruptions of lava from the same vents. There are similar (but smaller) volcanoes on Earth and Venus. However, the highest mountains on Earth and Venus are the result of compression and uplift of the surface. On Earth, this crustal compression results from collisions of one continental plate with another.
It is interesting to compare the maximum heights of the volcanoes on Earth, Venus, and Mars (Figure \(\PageIndex{2}\)). On Venus and Earth, the maximum elevation differences between these mountains and their surroundings are about 10 kilometers. Olympus Mons, in contrast, towers more than 20 kilometers above its surroundings and nearly 30 kilometers above the lowest elevation areas on Mars.
One reason Olympus Mons (Figure \(\PageIndex{3}\)) is so much higher than its terrestrial counterparts is that the crustal plates on Earth never stop moving long enough to let a really large volcano grow. Instead, the moving plate creates a long row of volcanoes like the Hawaiian Islands. On Mars (and perhaps Venus) the crust remains stationary with respect to the underlying hot spot, and so a single volcano can continue to grow for hundreds of millions of years.
A second difference relates to the strength of gravity on the three planets. The surface gravity on Venus is nearly the same as that on Earth, but on Mars it is only about one third as great. In order for a mountain to survive, its internal strength must be great enough to support its weight against the force of gravity. Volcanic rocks have known strengths, and we can calculate that on Earth, 10 kilometers is about the limit. For instance, when new lava is added to the top of Mauna Loa in Hawaii, the mountain slumps downward under its own weight. The same height limit applies on Venus, where the force of gravity is the same as Earth’s. On Mars, however, with its lesser surface gravity, much greater elevation differences can be supported, which helps explain why Olympus Mons is more than twice as high as the tallest mountains of Venus or Earth.
By the way, the same kind of calculation that determines the limiting height of a mountain can be used to ascertain the largest body that can have an irregular shape. Gravity, if it can, pulls all objects into the most “efficient” shape (where all the outside points are equally distant from the center). All the planets and larger moons are nearly spherical, due to the force of their own gravity pulling them into a sphere. But the smaller the object, the greater the departure from spherical shape that the strength of its rocks can support. For silicate bodies, the limiting diameter is about 400 kilometers; larger objects will always be approximately spherical, while smaller ones can have almost any shape (as we see in photographs of asteroids, such as Figure \(\PageIndex{4}\)).
Atmospheres
The atmospheres of the planets were formed by a combination of gas escaping from their interiors and the impacts of volatile-rich debris from the outer solar system. Each of the terrestrial planets must have originally had similar atmospheres, but Mercury was too small and too hot to retain its gas. The Moon probably never had an atmosphere since the material composing it was depleted in volatile materials.
The predominant volatile gas on the terrestrial planets is now carbon dioxide (\(\ce{CO2}\)), but initially there were probably also hydrogen-containing gases. In this more chemically reduced (hydrogen-dominated) environment, there should have been large amounts of carbon monoxide (\(\ce{CO}\)) and traces of ammonia (\(\ce{NH3}\)) and methane (\(\ce{CH4}\)). Ultraviolet light from the Sun split apart the molecules of reducing gases in the inner solar system, however. Most of the light hydrogen atoms escaped, leaving behind the oxidized (oxygen-dominated) atmospheres we see today on Earth, Venus, and Mars.
The fate of water was different on each of these three planets, depending on its size and distance from the Sun. Early in its history, Mars apparently had a thick atmosphere with abundant liquid water, but it could not retain those conditions. The \(\ce{CO2}\) necessary for a substantial greenhouse effect was lost, the temperature dropped, and eventually the remaining water froze. On Venus the reverse process took place, with a runaway greenhouse effect leading to the permanent loss of water. Only Earth managed to maintain the delicate balance that permits liquid water to persist on its surface.
With the water gone, Venus and Mars each ended up with an atmosphere of about 96 percent carbon dioxide and a few percent nitrogen. On Earth, the presence first of water and then of life led to a very different kind of atmosphere. The \(\ce{CO2}\) was removed and deposited in marine sediment. The proliferation of life forms that could photosynthesize eventually led to the release of more oxygen than natural chemical reactions can remove from the atmosphere. As a result, thanks to the life on its surface, Earth finds itself with a great deficiency of \(\ce{CO2}\), with nitrogen as the most abundant gas, and the only planetary atmosphere that contains free oxygen.
 This object must have contained sufficient volatiles—such as ammonia, methane, and nitrogen—to form an atmosphere. Thus, today Titan’s atmosphere consists primarily of nitrogen. Compared with those on the inner planets, temperatures on Titan are too low for either carbon dioxide or water to be in vapor form. With these two common volatiles frozen solid, it is perhaps not too surprising that nitrogen has ended up as the primary atmospheric constituent.
We see that nature, starting with one set of chemical constituents, can fashion a wide range of final atmospheres appropriate to the conditions and history of each world. The atmosphere we have on Earth is the result of many eons of evolution and adaptation. And, as we saw, it can be changed by the actions of the life forms that inhabit the planet.
One of the motivations for exploration of our planetary system is the search for life, beginning with a survey for potentially habitable environments. Mercury, Venus, and the Moon are not suitable; neither are most of the moons in the outer solar system. The giant planets, which do not have solid surfaces, also fail the test for habitability.
So far, the search for habitable environments has focused on the presence of liquid water. Earth and Europa both have large oceans, although Europa’s ocean is covered with a thick crust of ice. Mars has a long history of liquid water on its surface, although the surface today is mostly dry and cold. However, there is strong evidence for subsurface water on Mars, and even today water flows briefly on the surface under the right conditions. Enceladus may have the most accessible liquid water, which is squirting into space by means of the geysers observed with our Cassini spacecraft. Titan is in many ways the most interesting world we have explored. It is far too cold for liquid water, but with its thick atmosphere and hydrocarbon lakes, it may be the best place to search for “life as we don’t know it.”
We now come to the end of our study of the planetary system. Although we have learned a great deal about the other planets during the past few decades of spacecraft exploration, much remains unknown. Discoveries in recent years of geological activity on Titan and Enceladus were unexpected, as was the complex surface of Pluto revealed by New Horizons. The study of exoplanetary systems provides a new perspective, teaching us that there is much more variety among planetary systems than scientists had imagined a few decades ago. The exploration of the solar system is one of the greatest human adventures, and, in many ways, it has just begun.
Key Concepts and Summary
After their common beginning, each of the planets evolved on its own path. Different possible outcomes are illustrated by comparison of the terrestrial planets (Earth, Venus, Mars, Mercury, and the Moon). All are rocky, differentiated objects. The level of geological activity is proportional to mass: greatest for Earth and Venus, less for Mars, and absent for the Moon and Mercury. However, tides from another nearby world can also generate heat to drive geological activity, as shown by Io, Europa, and Enceladus. Pluto is also active, to the surprise of planetary scientists. On the surfaces of solid worlds, mountains can result from impacts, volcanism, or uplift. Whatever their origin, higher mountains can be supported on smaller planets that have less surface gravity. The atmospheres of the terrestrial planets may have acquired volatile materials from comet impacts. The Moon and Mercury lost their atmospheres; most volatiles on Mars are frozen due to its greater distance from the Sun and its thinner atmosphere; and Venus retained \(\ce{CO2}\) but lost \(\ce{H2O}\) when it developed a massive greenhouse effect. Only Earth still has liquid water on its surface and hence can support life.


14.1: Understanding Environmental Health
By the end of this section, you should be able to:
- Discuss how the environment and human health are linked.
- Describe the principles and frameworks used in environmental health.
- Explain Nightingale’s environmental theory and its ongoing impact on nursing.
Nearly one-fourth of the worldwide burden of disease could be avoided by creating healthier environments (World Health Organization [WHO], 2023a). The conditions for a healthy environment include clean air, a stable climate, sufficient water, sanitation , safe chemical usage , radiation protection , healthy and safe workplaces, sound agricultural practices, healthy communities and built environment s, and preserved nature (WHO, 2023a). Healthy People 2030 includes environmental health, considered a social determinant , as an objective. However, environmental hazards and their impact are not equally distributed, with some communities, such as those with lower-income residents or BIPOC populations, shouldering a disproportionate burden. As discussed in Structural Racism and Systemic Inequities, such communities are more likely to be located in areas with high levels of pollution and hazards, often resulting from discriminatory practices in land use, zoning , and the siting of industrial facilities and waste. Furthermore, these communities may lack or have limited access to resources and political influence to advocate for a healthier environment or mitigate the impact of hazards, leading to an increased risk for numerous adverse health outcomes , including respiratory illnesses, cancer, neurological disorders, and developmental delays.
Nurses are critical for promoting and protecting public health, and knowledge about environmental health is essential to provide optimal, targeted care to populations and individuals. Nurses can identify, prevent, and address environmental health issues, which is particularly important given the increasing impact of environmental hazards on human health.
Linking the Environment and Human Health
Environmental health profoundly influences human health through an intricate relationship and various pathways that shape the well-being of individuals and communities. Industrialized society irresponsibly releases vast amounts of pollutants and toxic waste into the biosphere , alters landscapes, and disrupts global climate, resulting in serious degradation of the Earth’s ecosystems . The consequences of such actions eventually impact human populations’ health and well-being. Air quality, for example, directly affects respiratory health, with exposure to pollutants such as ozone aggravating respiratory illnesses like asthma and COPD. Similarly, water quality is of paramount importance; contaminated water elevates the risk of ingesting harmful chemicals such as lead or the transmission of waterborne diseases. Food production and nutrition depend on the health of soil, water, and air. Food safety is also dependent on environmental health, as contamination during production, processing, and distribution can lead to outbreaks of foodborne illnesses such as salmonellosis. Waste management and sanitation systems are critical to protecting the environment and our health from contamination and diseases such as cholera (CDC, 2022d). Inequities compound the issue, with vulnerable populations disproportionately bearing the burden of environmental hazards due to factors such as proximity to industrial sites.
Climate change, discussed in detail in Environmental Exposure and Health Outcomes, introduces another layer of complexity into the relationship between the environment and human health. More frequent extreme weather events amplify risks to both the environment and human health. For instance, extreme heat events exacerbate respiratory and cardiovascular disorders and can lead to wildfires, which further degrade air quality. Warmer temperatures expand the range of disease-carrying vectors , thereby increasing the prevalence of vector-borne diseases such as Lyme disease, caused by Lyme borreliosis carried by ticks and transmitted directly to humans. Environmental disasters can impact our mental health, leading to disorders such as anxiety , PTSD , and depression .
Addressing environmental health requires collaboration among health providers, scientists, engineers, urban planners, public health professionals, organizations and businesses, and agencies across all levels of government. Improving air quality and air quality standards, ensuring the safety and quality of water sources, providing sufficient waste management and sanitation, promoting green spaces , and adopting sustainable practices are required to safeguard both the environment and the health of populations.
This video from the Centers for Disease Control and Prevention (CDC) discusses the role the environment plays in maintaining an individual's overall health and well-being.
Watch the video, and then respond to the following questions.
- What are some of the ways that the National Center for Environmental Health is working to improve public health safety?
- What are some of the potential health risks associated with environmental exposures?
- How can nurses address population health challenges associated with environmental factors such as monitoring chemical exposures and preventing childhood lead poisoning?
Frameworks and Principles of Environmental Health
Environmental health aims to prevent illness, death, and disability by reducing exposure to harmful environmental conditions and promoting behavior change. Human behaviors and interactions with the environment have a significant impact on health, including air and water quality, food safety, management of hazardous waste, and efforts to address climate change. Nurses must be equipped to recognize and manage environmental risks that impact their clients and communities, as these risks can significantly affect health outcomes. The section below discusses frameworks and principles to provide guidelines and strategies for addressing environmental health in clients and populations.
In this video, Mighty Fine of the American Public Health Association explores how the environment affects our health.
Watch the video, and then respond to the following questions.
- How did environmental health initiatives in the early 20th century contribute to reducing infectious diseases in the United States? What were some of the key strategies used?
- The video highlights the concept of environmental justice. How do environmental hazards disproportionately affect BIPOC populations, low-income areas, and underserved groups?
- How does the involvement of local governments differ from national efforts in promoting environmental health? What challenges might local governments face when implementing initiatives to improve environmental health within their communities?
Nightingale’s Environmental Theory
Florence Nightingale was an early advocate for public health and hygiene, her environmental strategy aimed to improve living conditions and prevent the spread of diseases. Nightingale’s Environmental Theory viewed nursing as the process of using the client’s environment to assist them in their recovery (Gilbert, 2020). Observing that many wounded soldiers were dying from preventable diseases during the Crimean War (1853–1856), Nightingale realized that the unsanitary conditions in military hospitals contributed to the high mortality rate. To address this issue, she developed an environmental strategy that focused on fresh air, clean water, sanitation, hygiene, and light (Gilbert, 2020).
Although less well known as a statistician today, Nightingale was the first woman inducted into the renowned Royal Statistical Society. During the Crimean War, she painstakingly collected and analyzed data on the causes of death and mortality rates of soldiers. To effectively communicate her findings, Nightingale developed innovative visualization methods, including the coxcomb , a graphic representation similar to a pie chart, to demonstrate that a substantial proportion of soldier deaths were due to disease, exposure, and infection rather than injuries from battle and were therefore preventable (Figure 14.2).
This animation discusses the significance of Nightingale’s work on statistics and its lasting impact.
Watch the video, and then respond to the following questions.
- How did Nightingale’s background in statistics and her meticulous, data-driven approach impact health care during the Crimean War and after?
- Nightingale’s work laid the foundation for modern practices like maintaining cleanliness in health care facilities. In what other ways do you think her principles and methodologies continue to influence modern health care?
- Nightingale’s ability to transform data into easily understandable infographics played a significant role in conveying her message to policymakers and the public. How important do you think data visualization is in communicating complex health care information today? How might effective data visualization lead to better health care outcomes?
One Health
The One Health approach (CDC, 2022f) emphasizes the interconnectedness of human health, animal health, and the environment. With growing populations and expanded habitats, closer contact between humans and animals increases disease transmission, while environmental changes and global movements amplify disease spread. These shifts have led to the rise of both known and emerging zoonotic diseases, impacting millions of humans and animals each year. Common One Health issues include emerging zoonotic diseases , antimicrobial resistance , vector-borne diseases, food safety, environmental contamination, and the impacts of climate change . For example, vector-borne diseases such as Lyme, transmitted from ticks to humans, now occur in a wider area as ticks adapt to environmental change. As a result, populations that were previously not at risk of Lyme disease now face increased likelihood of exposure. The CDC uses One Health to monitor and manage public health threats and plan effective public health interventions in collaboration with partners. Ultimately, One Health aims to prevent zoonotic outbreaks, enhance food and water safety and security, mitigate antimicrobial resistance, safeguard global health, and promote biodiversity and conservation. Learn more about One Health in action here.
Upstream vs. Downstream
As introduced in What Is Population Health?, upstream and downstream approaches to health and health care represent different points in the chain of events leading to particular positive or negative health outcomes. Upstream approaches focus on the beginning of the causal pathway by addressing underlying factors, such as the social, economic, and environmental determinants that contribute to health outcomes. Upstream factors are often difficult to see or measure, but they can have a profound impact on human health. For example, programs to reduce poverty or promote sustainable agriculture, campaigns to raise awareness or educate the public on a particular topic, and environmental regulations to reduce pollution are upstream interventions aimed at improving overall health outcomes.
Conversely, downstream factors occur later in the chain of events. These factors are more specific and often relate to individual behaviors and health care delivery systems. Downstream factors are more visible and easier to measure, but they are often the result of upstream factors. Examples of downstream factors in environmental health include individual lifestyle choices and access to medical and preventive care. Interventions using a downstream approach focus on mitigating the immediate effects of health problems, such as screenings, medications, procedures, and individual behavior change programs. While downstream interventions are necessary for treating existing health problems, they often fail to address their root causes and may not lead to long-term improvements in population health. For example, one upstream factor that contributes to air pollution is the burning of fossil fuels , which releases harmful pollutants into the air that cause respiratory problems, heart disease, and cancer. A recent study found that nitrogen oxide, particulate matter, and ozone from U.S. oil and gas production alone resulted in 7,500 additional deaths, 410,000 incidents of asthma attacks, and 2,200 fresh cases of childhood asthma throughout the United States in the year 2016 (Buonocore et al., 2023). An upstream approach would be to control air pollution and reduce exposure. On the other hand, downstream consequences of air pollution include asthma attacks, heart attacks, and premature deaths. Downstream interventions would focus on mitigating the impact of the air pollution by providing treatment for respiratory issues or distributing masks for outdoor use during times when air quality is poor. Addressing upstream factors helps to prevent environmental problems from occurring; addressing downstream factors mitigates the impact of environmental problems.
Environmental Justice
Environmental justice refers to the fair and equitable treatment and meaningful engagement of every individual, irrespective of race, color, national origin, or socioeconomic status , in the development, execution, and enforcement of environmental laws and policies (U.S. Department of Energy, 2023). The goals of environmental justice are to offer equal protection from hazards and to ensure equal involvement of communities in making decisions about policies and regulations that impact them. Advocates of environmental justice aim to ameliorate the disproportionate burden of environmental hazards encountered by certain marginalized and vulnerable populations (Environmental Protection Agency [EPA], 2023j). Environmental justice connects environmental issues with broader social justice concerns, recognizing that environmental degradation often intersects with issues related to health inequities, housing, education, and economic opportunity. As such, advocates seek to foster sustainable and inclusive communities that prioritize the well-being and health of all residents. They work to raise awareness about these issues, mobilize affected communities, and promote policies and practices that prioritize environmental equity and fairness.
The concept of environmental justice emerged in the 1970s in response to environmental issues often faced by low-income communities, BIPOC communities, and other marginalized groups (Lynch et al., 2021). These communities carry a greater burden, with increased exposure to pollution, toxic substances, hazardous waste, and other environmental hazards due to structural factors such as discriminatory land-use policies , socioeconomic disparities , and lack of political power. Examples of environmental justice issues include siting of polluting industries in low-income neighborhoods, lack of access to clean and safe drinking water in certain communities, and unequal enforcement of environmental regulations. For more on these issues, see Structural Racism and Systemic Inequities.
The movement gained momentum in the 1990s, with the term officially recognized in the Presidential Executive Order 12898 in 1994, directing federal agencies to address environmental justice issues in their programs and policies (EPA, 2023a). In 2021, President Biden issued an executive order to initiate Justice40 , an environmental justice initiative aiming to address environmental and climate issues while prioritizing equity and justice for disadvantaged communities. The initiative, based on the principle that communities that have been disproportionately harmed by pollution and climate change should be first in line to benefit from the transition to a clean energy economy, commits to investing 40 percent of the overall benefits from federal climate and clean energy programs into these communities (EPA, 2023m). Justice40 represents a significant step toward integrating environmental justice principles into federal climate and environmental policies, with a focus on rectifying historical and systemic disparities in environmental protection and climate action (Exec. Order No. 14008, 2021).
Environmental Health Sciences
Exposure assessment, toxicology, epidemiology, and risk assessment are interconnected approaches that play a vital role in the field of public health and environmental health:
Exposure assessment is a subfield that measures, characterizes, and models the frequency, magnitude, and contact duration of agents with an exposed population. Exposure assessments also evaluate the effectiveness of interventions and provide health professionals with information about the source, routes, and areas of uncertainty to help determine a course of action (CDC, 2022b).
Toxicology examines how harmful natural substances (toxins) or harmful artificial substances (toxicants) affect living organisms. The primary goal of toxicology is to assess the potential risks associated with exposure to various chemicals, including drugs, industrial products and by-products, environmental pollutants, pesticides, minerals, and metals. Toxicologists examine how these substances enter the body; how they are distributed, metabolized, and eliminated; and how they affect both organs and systems. The Agency for Toxic Substances and Disease Registry (ATSDR) develops toxicological profiles for hazardous materials, ranked by frequency, toxicity, and likelihood of human exposure. These “ Tox Profiles ” are extensively researched and peer reviewed. Nurses can access the current list of 275 substances at the ATSDR’s Substance Priority List.
Environmental epidemiology focuses on the links between environmental exposures and human health outcomes. Environmental epidemiologists identify potential environmental health hazards, quantify risk, and explore how different environmental factors, such as air and water pollution, chemicals, radiation, and climate change, impact health. The findings are used to inform public health policy, protect communities from risk, and develop interventions aimed at reducing exposures and improving population health.
Biomonitoring is a scientific methodology used to assess the presence and concentration of specific substances, such as chemicals and pollutants, in living organisms. Samples of blood, urine, saliva, hair, nails, and more may be utilized. Biomonitoring examines the extent of an individual’s or population’s exposure to environmental agents and uses this data to monitor the accumulation and impact of substances over time, identify potential health risks, inform regulations, and develop targeted interventions. The CDC runs a national biomonitoring program that measures the presence of over 400 chemicals at over 500 laboratories, and the agency has made numerous significant advances in improving population health, including the reduction of exposure to secondhand smoke and lead (CDC, 2022a).
Environmental burden is how public health professionals quantify and compare the impact of environmental risks on a population’s health. Climate change, air, noise, and water pollution are examples of environmental burdens because they have detrimental effects on the ecosystem and human health. This burden can manifest in a variety of ways, including increased rates of illness, disability, and premature death as well as decreased quality of life and productivity. Health indicators such as mortality rate s, morbidity rates, and disability-adjusted life years (DALYs) are used to measure the impact of environmental hazards on human health and help identify vulnerable populations at risk. Environmental burden considers the cumulative impacts , or the total harm to humans resulting from the combination and interaction of multiple factors such as pollution, socioeconomics, and preexisting conditions. For example, the impact of respiratory illness on an individual living in a community with elevated air pollution will be greater than that on an individual living in a community with clean air.
Bioaccumulation refers to the gradual accumulation of contaminants, such as heavy metals like mercury and lead, within the tissues of living organisms. This process occurs as organisms consume contaminants from their surrounding environment more rapidly than they are able to eliminate or metabolize them. Instead of being excreted, the substances become stored in the organism’s body, leading to increased concentrations as the toxins accumulate. Over time, organisms higher up the food chain, such as humans, may consume food that contains these accumulated pollutants (EPA, 2021b).
A comprehensive approach is necessary to reduce environmental burden; approaches include addressing the underlying causes of environmental hazards, providing education to the public about hazards, and implementing policies to reduce exposure to environmental pollutants. The C/PHN assesses the reports and then works with regulatory agencies and industries to reduce emissions and waste, advocating for clean energy and transportation and supporting policies that protect vulnerable populations from environmental risks.
Read the scenario, and then respond to the questions that follow. This case scenario about Mr. Harper will evolve throughout the chapter.
Mr. Harper, a 68-year-old retired miner, has been experiencing increasing difficulty breathing. His health has deteriorated over the past year with two hospitalizations for chronic obstructive pulmonary disease (COPD) exacerbation and recurrent pneumonia. In addition to working in the mines for 44 years, Mr. Harper has a 20-pack/year history of tobacco use and lives alone in an old, damp, poorly ventilated house. His nurse, Regis, is visiting his home for the first time today.
| Vital Signs | Physical Examination | |
|---|---|---|
| Temperature: | 99.1 |
|
| Blood pressure: | 150/95 | |
| Heart rate: | 104 | |
| Respiratory rate: | 26 | |
| Oxygen saturation: | 92% on room air |
- What signs and symptoms of COPD exacerbation and pneumonia does Mr. Harper present with?
- Identify upstream and downstream factors that could be contributing to Mr. Harper’s deteriorating health.
- What immediate actions should Nurse Regis take while in Mr. Harper’s home?