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date: 03 December 2021

1 Introduction to the Marine Environment and Pollutionfree

1 Introduction to the Marine Environment and Pollutionfree

  • Judith S. Weis
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p. 1What is the marine environment?

As used in this book, the marine environment covers not only the ocean, but estuaries (e.g., bays), which are coastal areas where the seawater is diluted with freshwater coming from rivers and streams, or sometimes groundwater. Much of the pollution is concentrated in these shallow coastal areas, which are often next to urban centers and other concentrations of humans who are responsible for the pollution.

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What are some basics of marine ecosystems and food webs?

Marine ecology is a branch of ecology dealing with the interrelations of organisms living in the oceans, shallow coastal waters, and on the sea shore. Organisms interact through the roles they play as producers, consumers, and decomposers. Primary producers are plants that take in inorganic carbon dioxide and water, and through the process of photosynthesis make organic materials (sugars) using light energy from the sun. They are the first step of the food web. Primary consumers are herbivorous animals that eat the plants; secondary consumers are carnivorous animals that eat the herbivores; p. 2third-level consumers are carnivores that eat other carnivores; and decomposers are microorganisms (such as bacteria and fungi) that break down the organic materials from the plants and animals (excretory products and dead bodies) into inorganic materials, which are eventually reused by producers. The decomposers are concentrated in the sand or mud on the bottom, and play an essential role in recycling materials. There are more producers than consumers, more primary consumers than secondary consumers, and so on up the chain, because at each step in the food chain a great deal of energy is lost—it is not efficient. So top carnivores (for example sharks) are the rarest animals.

The most important primary producers in the ocean are a diverse group of microscopic floating single-celled photosynthetic organisms called phytoplankton. They are the basis of the food web that supports the rest of oceanic life. They are widely distributed in huge numbers, but occur near the surface of the water only down as far as light penetrates, since light is essential for photosynthesis. Phytoplankton are eaten by small floating animals called Zooplankton. Zooplankton consist of a wide variety of different types of generally small animals, some of which spend their whole life as small plankton, while others are larval stages of larger animals such as clams or crabs that will subsequently go to the bottom to live as adults. Zooplankton, in turn, are eaten by small fish, which are eaten by larger fish, which may be eaten by very large fish (or other large animals such as marine mammals). Animals that live on the bottom are called benthos; some benthic animals obtain their food by filtering the plankton, while others consume decaying plant or animal material (called detritus) that sinks down to the bottom.

In shallow coastal areas or estuaries, additional kinds of primary producers are found: larger algae (seaweeds) or rooted plants like seagrasses that live attached on the bottom, since the light can penetrate through the shallow water. These are consumed by various animals, but mostly after they have died and decayed into detritus (Figure 1.1).

Figure 1.1 p. 3Marine food web showing different trophic levels (from Wikimedia)

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Why is there concern about the state of the oceans?

For centuries, it was thought that the oceans were so vast that nothing people could do could possibly have an impact on them. However, contrary to this belief, it turns out that we have been doing so for many years. Back in 1951, Rachel Carson wrote in The Sea Around Us that people could not change the ocean the way we have plundered the continents, but she subsequently changed her opinion. We are now aware that many fish populations are declining from overfishing, that warming is melting the polar ice and raising sea levels, and that portions of the ocean are full of trash—plastic bottles and bags, balloons, and lost fishing nets. We have witnessed disastrous oil spills. We find abnormalities in marine animals due to subtle effects of man-made chemicals and find large coastal areas with water devoid of oxygen, and therefore of marine life, due to wastes released into the waters.

p. 4Marine ecosystems are very important for the health of both marine and terrestrial environments. Coastal habitats account for about one-third of all marine biological productivity, and some estuarine ecosystems (i.e., salt marshes, seagrasses, mangrove forests) are among the most productive regions on the planet. In addition, other marine ecosystems, namely coral reefs, provide food and shelter to the greatest amount of marine biological diversity in the world. The ocean plays a key role in cycles of carbon, nitrogen, phosphorus, and other important chemicals. Ocean chemistry has been changing due to human activities both in coastal waters and in the open ocean. Some of the greatest impacts are on carbon, nitrogen, and dissolved oxygen, which affect biological functioning. Decades of pollution, along with destruction of coastal habitats and overfishing, have had devastating impacts on marine biodiversity and habitats. The increasing demand for seafood worldwide has depleted many fish populations, along with the economies of some coastal communities. On top of this, climate change is altering the oceans in ways that we are only beginning to understand. There is growing scientific evidence demonstrating serious—sometimes disastrous—impacts of pollution in the marine environment. Chemical pollutants of greatest concern are those that are widespread and persistent in the environment, accumulate in organisms, and cause effects at low concentrations. Toxic chemicals are varied and often difficult to detect.

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What is a contaminant? Is there a difference between a contaminant and a pollutant?

A contaminant is a biological, chemical, or physical substance or energy normally absent or rare in the environment, which is present and which, in sufficient concentration, can adversely affect living organisms. A pollutant is substance or energy introduced into the environment that has undesired effects. So if a contaminant is present in high enough concentration, p. 5it is a pollutant. It could be something that occurs naturally in the environment (e.g., metals) but is in excess, or could be something that is man-made. Pollutants may be classified by their origin, by their effects on organisms, by their properties (such as toxicity), or by their persistence in the environment. Toxic chemicals are very varied, numerous, and expensive to monitor.

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What are the major sources of pollution in the marine environment?

Land-based sources pollute estuaries and coastal waters with nutrients, sediments, and pathogens (disease organisms), as well as potentially toxic chemicals including metals, pesticides, industrial products, and pharmaceuticals. Following the Industrial Revolution, more and more material has been discharged from industries, sewage treatment plants, and agriculture, eventually reaching marine ecosystems. But pollution does not come exclusively from land-based sources. Highly visible events such as the Exxon Valdez oil spill in Alaska and the Deepwater Horizon gusher in the Gulf of Mexico have polluted the seas with oil from ships, and from drilling platforms in the ocean itself. These highly publicized events have raised public awareness of marine pollution. Other water-based sources of pollution are less spectacular, and include discharge of waste from vessels, the leaching of antifouling paints from ships, and leaching of wood preservatives (e.g., creosote or chromated copper arsenate) from wooden bulkheads and dock pilings. Aquaculture operations such as floating cages in which salmon are raised can pollute nearby waters with fish wastes, uneaten food, antiparasite chemicals, and antibiotics. Pollution can also enter the ocean from the atmosphere. For example, the metal mercury is released as a gas into the atmosphere from burning coal, and subsequently can be deposited in the oceans. Nitrogen, in the form of nitrogen oxides from the burning of fossil fuels, is also an air pollutant before p. 6being deposited into the ocean in precipitation and becoming a water pollutant.

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What are the major ways that land-based pollutants enter the marine environment?

“Ocean dumping” refers to transporting materials in a barge and physically dumping them in the ocean. The dumping of industrial, nuclear, sewage, and many other types of waste into oceans was legal in the United States until the early 1970s, when it became regulated; however, dumping still occurs illegally everywhere. The movement to ban ocean dumping of sewage sludge gained momentum in the United States when contaminated wastes from sewage-derived microorganisms were discovered at public beaches, along with unsavory items such as hypodermic syringes and tampon applicators. Most of the chemical pollution in the ocean comes into the water through pipes rather than dumping. While many pollutants are discharged (legally) from industrial or residential areas, others come from agricultural areas. Factories and sewage treatment plants release their wastes into receiving waters through a pipe, referred to as a “point source,” which can be monitored and regulated by environmental protection agencies. Since passage of the Clean Water Act in the United States in 1972, much progress has been made in controlling pollution from point sources. Combined sewer overflow (CSO) occurs in older cities, however, where storm drains connect to pipes going to sewage treatment plants from homes and industries. Heavy rainfall can overwhelm the capacity of the sewage treatment plants, causing everything to go out into the water untreated. The resulting bacterial contamination from sewage leads to beach closures for health reasons.

In recent decades attention has moved from point sources to diffuse runoff and atmospheric deposition (called “nonpoint sources”). Contaminants that wash into the water from soil, streets, construction sites, and so on during rainfall can enter water bodies in many places, as do pollutants from the atmosphere that come down in rainfall. This pollution is not so easily regulated. Nonpoint sources such as farms, roadways, and urban or suburban landscapes remain largely uncontrolled, and are major sources of continuing pollution inputs (Figure 1.2). If it is not directed to sewage treatment plants causing CSO, urban stormwater runs directly into water bodies, bringing with it sediments, grease, litter, oil, polycyclic aromatic hydrocarbons (PAHs), and metals from highways.

Figure 1.2 p. 7Nonpoint source runoff from rural and urban landscapes (permission from Dr. Peddrick Weis)

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Which pollutants enter the ocean from the air?

Nitrogen gases, mercury, carbon dioxide, and radioactive isotopes come largely from the atmosphere. Some organic chemical pollutants (e.g., polychlorinated biphenyls, or PCBs) can also be transported long distances in the air before being deposited in the ocean.

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p. 8Can objects in the water cause pollution?

Antifouling paints on vessels are designed to reduce attachment of organisms like barnacles and algae, and do so by being toxic. The chemicals are released slowly from the boat paint and thus deter settlement by the planktonic stages of these organisms. However, the chemicals are also toxic to other organisms nearby. The most popular antifouling chemical that was used in the past was tributyltin (TBT), which is now banned throughout most of the world (and will be discussed in detail in later chapters). Other antifoulants include copper, which is especially toxic to mollusks and algae (it is used as an algicide and molluscicide). Since bans and restrictions on TBT came into effect, researchers have developed and produced new types of chemicals. Irgarol is now a common antifoulant, and is highly toxic to nontarget plants. It is found in water and sediments near marinas at levels that may be high enough to cause changes in phytoplankton communities. Another antifouling biocide, diuron, is also found in water and sediments.

When wooden structures are placed in the water in the form of dock pilings or bulkheads, they are subject to decay by microbes and destruction by wood-boring animals such as some amphipods (gribbles) and shipworms (which are really mollusks). Therefore, the wood gets treated with high concentrations of toxic chemicals, such as creosote or chromated-copper-arsenate (CCA), to prevent this destruction. These chemicals also leach from the wood and can accumulate in the environment and get taken up by nearby plants and animals, causing toxic effects.

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How can aquaculture cause pollution?

Aquaculture is the raising of marine organisms for food—farming the sea—similar to agriculture on land. Fish farms, especially open cage culture of salmon, have been found to p. 9be sources of pollution in local waters. Thousands of fish concentrated in open net pens produce tons of feces. Combined with uneaten food, this waste sinks to the bottom and affects the local environment, polluting the water and smothering plants and animals on the seafloor below the cages. For example, the nutrients in unused fish feed and fish feces can cause local algal blooms, which lead to reduced oxygen in the water, which in turn can lead to the production of ammonia, methane, and hydrogen sulfide, which are toxic to many aquatic species. Low oxygen can also directly kill marine life. Many types of aquaculture use chemical treatments such as antibiotics or antiparasite chemicals for a successful harvest. The amount of these chemicals released into the environment determines their effects on other organisms. A wide range of chemicals is currently used in the aquaculture industry—primarily pharmaceuticals such as antibiotics and antiparasitic chemicals, and antifouling agents such as copper for the cages. In some areas, such as Southeast Asia and South America, overuse of antibiotics has led to increased resistance of bacteria to treatment, which can make them much more harmful to the cultured species and potentially to other species, including humans.

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Once in the water, what happens to the pollutants?

Ocean currents and organisms may redistribute pollutants considerable distances. However, sediments tend to bind metals, and many organic contaminants concentrate in the bottom sediments. The historic use of some chemicals that are no longer manufactured in the United States (e.g., DDT, PCBs) has left a legacy of contamination in the sediments, which remain contaminated with these persistent chemicals that continue to cycle through the environment and affect marine life decades after their input has ceased. Contaminated sediments also pose a problem for dredging operations, because the dredging process can release the contaminants from the sediments p. 10and make them more available to biota. Another thorny issue is where to put the contaminated sediments once they have been dredged up from the bottom. Solving these problems is a major reason for long delays in dredging for deepening ship channels and for cleanups of toxic hot spots. Organisms can take up or bioaccumulate chemicals from the environment. Once taken up into the body, the chemicals can exert toxic effects.

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How do chemicals get into marine animals?

Aquatic animals take pollutants into their body through the skin, gills, and digestive tract, and excrete them in their waste or expel them through the gills. When the rate of uptake is greater than removal, the chemical builds up in the body. Chemicals that have low solubility in water and bind to sediments tend to accumulate to greater concentrations in organisms, especially in their fatty tissues. Chlorinated hydrocarbon pesticides, polychlorinated biphenyls (PCBs), and methylmercury are among those toxic substances with low water solubility that concentrate in organisms and are not readily metabolized or excreted.

Contaminants are transferred through food webs from prey to predator (trophic transfer), and some chemicals tend to become more concentrated during this process—a phenomenon called biomagnification. Persistent organic chemicals like PCBs and DDT, as well as methylmercury, tend to build up or biomagnify as they go from prey to predator, causing the largest, long-lived top predator to have the highest levels (Figure 1.3). An animal in a polluted area accumulates toxic chemicals from each item of contaminated food that it eats; concentrations are higher in consumers than in their food, and are highest in the top carnivores such as large fish, fish-eating birds, marine mammals, and humans. Because of biomagnification, methylmercury levels can be quite high in large carnivorous fish like swordfish and tuna, even though they live in the open ocean far from any source of mercury. It is recommended that people (particularly pregnant women and young children) not eat a lot of these fish. Chlorinated pesticides, PCBs, and dioxin also undergo biomagnification, but metals other than methylmercury do not do so.

Figure 1.3 p. 11Biomagnification of contaminants up the food web (© Walther-Maria Scheid, Berlin, Germany, for World Ocean Review 2010)

The sex of a fish may affect how much of a contaminant it accumulates. Egg yolk is a fat-rich substance that can store large quantities of organic contaminants, and some females put large amounts of these fat-soluble chemicals into eggs, reducing the levels in their bodies. This maternal transfer of contaminants is found in egg-laying birds and reptiles as well as fishes. While it is a good for the females to reduce their own pollutant level, it certainly does not benefit the offspring to start out their lives already loaded with toxic chemicals.

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What is toxicity?

A toxic substance is one that harms living things at low concentrations. (Almost anything can be harmful if there is p. 12enough of it!) Toxic effects have been studied primarily in laboratory experiments (bioassays), although there have been some field studies of effects on populations of marine organisms. Early studies of pollutant effects relied on tests that measured lethality (death). The LC50—the concentration of a chemical that caused 50% of the test animals to die (typically in 96 hours)—was the benchmark. Regulations under laws such as the US Federal Insecticide Fungicide and Rodenticide Act (FIFRA) for developing safe levels of pesticides to protect aquatic life require the standard LC50, which is of little ecological relevance. Toxicity tests are required for a few species: rainbow trout, bluegill, and daphnids—one cold-water fish, one warm-water fish, and one crustacean, all freshwater species. Unfortunately, even today, over half a century later, this approach—measuring what percentage of the animals die in 96 hours—is still considered most useful in a regulatory context. These tests do not consider sublethal effects that occur over longer periods of time, or toxicity that is delayed, or differences in life history among species. Knowing about effects of longer-term, lower-dose exposures on physiology, behavior, and development is essential for understanding overall impacts of pollutants in nature.

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What effects can pollutants have besides killing living things?

Extensive research has shown that toxic chemicals can disrupt metabolic, regulatory, or disease defense systems, and reduce reproduction. Behavior, development, and physiology are all sensitive to pollutants. Learning about these sublethal effects can help us understand the mechanisms of action of different chemicals, and also to understand ecological effects in the real world. We have learned that early life processes and stages—eggs and sperm, fertilization, embryonic development, and larvae—are very sensitive to contaminants, so setting “safe” levels based on how much of a chemical will kill adults will not protect these young stages. The hormonal control of p. 13reproduction can be affected by many chemicals, now called “endocrine disruptors.” Exposures during early life may cause effects that do not appear until later, sometimes many years later. Thus, long-term delayed effects and indirect effects are important. There has been some progress toward greater ecological realism, but advances have been mainly in freshwater ecosystems.

The effects of chemicals on individuals may cause changes in populations and result in reduced population growth rate, lower population size, reduced birth rates, and higher death rates, producing a population dominated by younger, smaller individuals with reduced genetic variability. Reduced genetic variability happens when the more susceptible individuals disappear from the population and the more pollution-tolerant ones become predominant, as has been seen with insecticide-resistant insects or antibiotic-resistant bacteria.

Toxic effects appear first at the biochemical level, and later at the cellular level, then the level of the whole organism, the population, and eventually the ecological community as a whole. Initial biochemical changes observed can be altered enzymes, changes in DNA and RNA, or the production of particular proteins that can detoxify the chemical. At the cellular level, chromosome damage, cell death, abnormal structures, or cancer can occur. Some chemicals affect the immune system and increase susceptibility to infectious diseases. At the level of the whole organism, changes in physiology, development, growth, behavior, or reproductive capacity may occur, and at high concentrations, the animal or plant can die.

Fortunately, we have seen in many locations that when the input of pollutants decreases or toxic waste sites are cleaned up, the incidence of diseases and other problems diminishes. Tolerance to the contaminants may be lost as well. In a contaminated marsh near a former battery plant close to the Hudson River that released cadmium for decades, Jeffrey Levinton and colleagues from Stony Brook University showed p. 14that the worms in the sediments had become highly tolerant to cadmium. Some years after the pollution was cleaned up, as required by the Environmental Protection Agency (EPA), the scientists revisited the site and found that the worms had lost their cadmium tolerance over relatively few generations.

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How is the degree of toxicity measured?

“The dose makes the poison.” It is important to have accurate measurements of how much of a given chemical causes a given effect. Contaminants generally occur in low concentrations, but small concentrations such as parts per million and parts per billion can cause effects. A part per million (ppm) seems like a very small amount—and it is. One ppm (or mg/l) is equivalent to one drop of a substance in about 13.2 gallons of water. One ppb (or jig/l) is one part in 1 billion—much smaller than a ppm. One drop in one of the largest tanker trucks used to haul gasoline would be 1 ppb. Some chemicals, including dioxin and tributyltin are toxic at levels below 1 ppb. It is difficult and expensive to measure these low concentrations of contaminants. Sophisticated equipment such as atomic absorption spectrophotometers or gas chromatograph/mass spectrometers is needed.

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How can field studies be used to understand toxicity?

Integrated field approaches are important, along with laboratory studies to provide insights into effects at the population and community level. Field experiments can investigate contaminated environments—but hardly ever, only under very restricted conditions, may scientists release known amounts of chemicals in the field to observe effects in controlled experiments. Attempts to bring the field closer to the lab include studies on multiple species placed together in microcosms (small containers) or mesocosms (large containers), which can be used to investigate community level effects of contaminants. They p. 15allow for replication, so dose-response relationships under controlled conditions can be studied. These kinds of studies can show the differential sensitivity of different species and can be used to learn about biological interactions. There is much to be learned from such approaches. However, dosing of complex mesocosms with known concentrations of specific chemicals still does not really duplicate the natural environment in which organisms are subjected to many different pollutants at different concentrations (which vary over time), and where some of the species may have evolved increased resistance to some contaminants. Thus, there remains uncertainty with ecological risk assessments and with translating mesocosm results to real-world field situations.

It is usually very difficult to attribute problems seen in the field to particular contaminants, because generally there are many different contaminants at a site. In some rare cases, observations on natural populations in the field called attention to effects of certain chemicals. This was the case with tributyltin’s (TBT) effects on oysters in Europe (see Chapter 8). Since the abnormalities produced by TBT are unique and not produced by other chemicals, the causal connection between observed effects (abnormal shells in oysters) and the particular chemical (TBT) could be seen more easily.

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Why are some species more sensitive to pollution than others?

Differences in sensitivity are due to differences in physiology, generation time, and life cycle among species, which can all affect initial responses and the ability to recover from the effects. Species that are short-lived and produce large numbers of offspring can exploit changing environments, including contaminated ones. Such species with short generation times also are more likely to be able to evolve tolerance to contaminants. High metabolic rates can lead to more rapid breakdown of pollutants. In contrast, species that are long-lived, slow to mature, and have relatively few offspring are less likely to be p. 16able to evolve resistance to contaminants. Also, long-lived species tend to be higher up on the food web, fewer in number, and to accumulate higher levels of contaminants over a long period of time. Their slow reproduction makes potential population recovery from declines very slow. Slow reproduction, combined with high accumulation of contaminants, makes them particularly vulnerable to reproductive effects. Transfer of fat-soluble contaminants (e.g., PCBs, DDT) from females into the yolk of developing eggs exposes the next generation to these chemicals even before they are hatched.

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What laws regulate marine pollution?

The ocean, as well as marine pollution from land-based sources, is governed by legal frameworks at the international, national, state, and local levels. Multilateral and bilateral treaties and other agreements are in place for fishery management, shipping, protecting biodiversity, and pollution. The multinational treaty on pollution is the International Convention for the Prevention of Pollution from Ships, commonly known as MARPOL, which regulates discharges into the ocean. MARPOL is a comprehensive treaty that regulates pollution from ships. Six annexes to the treaty set out regulations for different aspects of pollution. Annex I covers prevention of pollution by oil from operational measures and from accidental discharges; Annex II regulates pollution by noxious liquid substances carried in bulk (some 250 substances were evaluated and included in the list); Annex III specifies requirements for the issuing of detailed standards on packing, marking, labeling, documentation, stowage, and quantity limitations for “harmful substances”; Annex IV contains requirements to control pollution by sewage (the discharge of sewage is prohibited, except when the ship has an approved sewage treatment plant or is discharging disinfected sewage using an approved system); Annex V governs garbage and bans discharge of plastic from ships; and Annex VI limits sulfur oxide and nitrogen p. 17oxide emissions from ship exhausts and prohibits emissions of ozone depleting substances into the air. MARPOL, administered by the International Maritime Organization (IMO), creates obligations for both flag states (the country certifying a vessel, from which a vessel launched, or under which a vessel sails) and port states (where a vessel lands). Both flag states and port states may inspect vessels to make sure they are in compliance with the treaty and can impose sanctions if it is in violation of the terms. In the United States, the Coast Guard has the primary responsibility.

Like marine-based sources, land-based sources are regulated by all levels of government. The United Nations Convention on the Law of the Sea (UNCLOS) is an international treaty that covers many aspects of ocean governance and includes obligations to control land-based sources of pollution. In addition to UNCLOS, regional treaties and domestic laws attempt to control land-based pollution. For example, the Cartagena Convention’s Protocol Concerning Pollution from Land-Based Sources and Activities seeks to prevent land-based solid waste from coming into the Caribbean Sea. The terms of this treaty include preventing “persistent synthetic and other materials” from harming the ocean. Treaties like this provide both a legally enforceable framework and a forum in which countries can come together to exchange best practices and voluntary approaches to combat pollution.

In the United States, the Clean Water Act (CWA) seeks to control land-based sources of pollution. The CWA made it unlawful to discharge any pollutant from a point source (pipe or man-made ditch) into navigable waters unless a permit was obtained. It is enforced by the EPA. The EPA’s National Pollutant Discharge Elimination System (NPDES) is a permit program that controls point source discharges into the aquatic environment. Individual homes that are connected to a municipal system, use a septic system, or do not have a surface discharge do not need an NPDES permit; however, industrial, municipal, and other facilities must obtain permits if their discharges go p. 18directly to surface waters. The CWA also provided funding for municipalities to construct or upgrade sewage treatment plants. The EPA has implemented pollution control programs such as setting wastewater standards for industry, and has set water quality standards for a large number of contaminants in surface waters. Beyond this, there are additional controls for waters that are impaired by pollution. Section 303 of the Clean Water Act authorizes states to identify impaired waters and calculate limits on the levels of various pollutants that can enter the impaired water. These limits are called total maximum daily loads (TMDLs). In 2007, California created a TMDL for the Los Angeles River in an attempt to reduce the amount of garbage entering that river, which would in turn reduce the amount of garbage entering the Pacific Ocean. The CWA will be discussed further in Chapter 11.

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Why are some contaminants that have been banned still a problem?

National and international laws can regulate or ban chemicals, but “legacy pollution” from persistent contaminants (e.g., DDT, PCBs, metals) can remain in sediments for decades after their use or discharge has been banned, and sediments are a continuing source of contaminants to organisms. In addition, many pollutants are still not regulated, and there are inadequate controls on nonpoint sources. Environmental regulations and the level of compliance vary widely among countries. Nevertheless, much has improved in US waters as a result of the Clean Water Act, which stimulated many municipalities to build or upgrade sewage treatment plants.

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How extensive and severe is marine pollution around the world?

While humans depend on the oceans for a variety of goods and services, we have altered and impaired the oceans both directly and indirectly. A Global Map of Human Impact on Marine p. 19Ecosystems, a high-resolution map and atlas combining numerous data sets of the world’s oceans, was published a few years ago by a large study group. It reveals that human activities have strongly affected approximately 40% of the marine area and have left only about 4% relatively pristine. It covers 17 different types of human activities, including climate change and fishing, as well as pollution. The authors compiled data from a variety of sources and fed them into a model that assigned a single number to each square kilometer of ocean, reflecting the overall human impact at that spot. The most highly affected marine areas are the eastern Caribbean, the North Sea, and Japanese waters, and the least affected ones are around the poles. The most heavily affected types of environments are continental shelves, rocky reefs, coral reefs, seagrass beds, and seamounts. There are few areas of coral reefs, mangroves, or seagrass beds in the world that are relatively unaffected. While not all affected areas are affected by pollution, many of them are. The major types of pollution are excess nutrients (eutrophication), marine debris, oil spills, and toxic contaminants.