Pesticides
Pesticides are chemicals used to kill insects that feed on crops and vegetation. The first documented use of pesticides was by the ancient Greeks. Pliny the Elder (23–79 A.D.) reported using common compounds such as arsenic, sulfur, caustic soda, and olive oil to protect crops. The Chinese later used similar substances to retard infestation by insects and fungi. In the 1800s Europeans used heavy metal salts such as copper sulfate and iron sulfate as weed killers.
The invention of DDT (dichloro-diphenyl-trichloroethane) in 1939 marked a revolution in the war against pests. DDT was effective, relatively cheap, and apparently safe for people—on the face of it, a miracle chemical that promised a world with unprecedented crop yields. Its discoverer, Paul Muller, received a Nobel Prize for discovering the high efficiency of DDT as a contact poison against pests. In the United States, pesticide use in agriculture nearly tripled after 1965, as farmers began to use DDT and other pesticides, herbicides, and fungicides intensively and began to accept these chemicals as essential to agriculture.
For many years, it was thought that if pesticides were properly used, the risk of harm to humans and wildlife was slight. As the boom in pesticide use continued, however, it eventually became apparent that pesticides were not safe after all. The fundamental reason that pesticides are dangerous is that they are poisons purposely designed to kill living organisms. Part of the problem is biomagnification—a predator that eats organisms with pesticides in their bodies ends up concentrating all those pesticides in its own tissues. Eventually, the concentration of pesticides causes serious problems. DDT was eventually shown to have harmed numerous bird species, particularly those high in the food chain, such as bald eagles and peregrine falcons. DDT caused the production of eggs with shells so thin they could not protect the developing chick.
As the dangers of pesticides became more apparent in the 1960s and 1970s, some of the most dangerous, like DDT, were banned in the United States. However, the use of other chemical pesticides increased until the 1980s. Use levels have generally held steady since then. Farmers continue to apply about one pound of pesticide per year for every person on Earth. The majority of pesticide use—75 percent—occurs in industrialized countries. Unfortunately, the primary reason that pesticide use has leveled off in recent decades is not concern regarding its safety, but declines in its effectiveness. This is due to the fact that pest species quickly evolve resistance to pesticides. Worldwide, the number of resistant pests continues to climb. Unfortunately, increased resistance has only created a demand for more, and more powerful, chemicals.
FIGURE 5.1
Aquatic/wetland species at risk, 1996
FIGURE 5.2
National watershed characterization, September 1999
Pesticides degrade numerous aquatic ecosystems after seeping into the ground as runoff from watering or rain. The U.S. Fish and Wildlife Service reports that pesticides harm about 20 percent of the country's threatened and endangered animal and plant species.
Fertilizers
For decades, farmers have tried to increase the productivity of their land by using ever-increasing amounts of fertilizers. Fertilizers are biological products or chemicals applied to increase crop growth. Fertilizers may seep into water and collect in lakes, streams, and groundwater. While fertilizers are not poisonous by nature, large quantities of fertilizers can cause serious health problems in aquatic animals. Fertilizers also encourage the growth of aquatic plant life, disrupting food webs and biological communities. Aquatic plants and algae may grow so rapidly that they block off sunshine or deplete nutrients essential to other species.
Oil Spills and Runoff
Oil spills represent regular and devastating accidents to aquatic life. Oil spilled into the ocean floats on the water surface, cutting off oxygen to the sea life below and killing mammals, birds, fish, and other animals. The dangers presented by oil spills have grown worse over the years. In 1945 the largest tanker held 16,500 tons of oil. Now, supertankers the length of several football fields regularly carry more than 550,000 tons.
In 1989 the tanker Exxon Valdez ran aground on the pristine Alaskan coastline, spilling 11 million gallons of oil into the bay and killing millions of animals. In 1994 a federal jury assessed $5 billion in punitive damages and $3.5 billion in criminal fines and cleanup costs against Exxon. The Valdez spill led to additional safety requirements for tankers, including double hulls. Larger oil spills than the Valdez have occurred both before and since, but the incident alerted many people to the damage that can be done to marine habitats. Many species impacted by the spill, particularly seabird species, have yet to recover more than a decade later.
In January 2001 the tanker Jessica released 150,000 gallons of fuel near the Galapagos Islands, a biologically rich area harboring numerous unique species including Darwin's famous finches, marine iguanas, and a tropical penguin population. There was widespread relief when winds blew the oil slick seaward rather than towards the islands. Sea bird and sea lion deaths numbered in the dozens, and it was believed that a true catastrophe had been avoided. Ongoing studies of the Galapagos' unique marine iguanas, however, revealed in June 2002 that numerous iguanas likely died due to oil-related injuries after the spill. In particular, 60 percent of the marine iguanas on Santa Fe Island died in 2001, despite the fact that oil contamination was relatively low, with only about one quart of oil per yard of shoreline. Similar deaths were not found on another island where there was no contamination. Scientists believe that the deaths occurred when oil contamination killed the iguanas' gut bacteria, making them unable to digest seaweed and causing them to starve. Marine iguanas have no natural predators and generally die either of starvation or old age.
The U.S. National Research Council warns that, even without large catastrophic oil spills, many marine habitats are regularly exposed to oil pollution. Harbors and aquatic habitats near developed areas are in particular jeopardy. The U.S. National Research Council estimates that approximately 8.4 billion gallons of oil enter marine waters each year from street runoff, industrial liquid wastes, and intentional discharge from ships flushing their oil tanks. As little as one part of oil per million parts of water can be detrimental to the reproduction and growth of fish, crustaceans, and plankton.
Ocean Dumping and Debris
Ocean debris comes from many sources and affects diverse marine species. Waterborne litter entangles wildlife, masquerades as a food source, smothers beach and bottom-dwelling plants, provides a means for small organisms to invade non-native areas, and contributes to toxic water pollution. Records of interactions between ocean debris and wildlife date back to the first half of the twentieth century. Northern fur seals entangled in debris were spotted as early as the 1930s. In the 1960s, various seabirds were found to have plastic in their stomachs. By the early twenty-first century, a total of 255 species were documented to have become entangled in marine debris or to have ingested it.
Some scientists once thought it was safe to dump garbage into the oceans, believing the oceans were large enough to absorb sludge without harmful effects. Other scientists argued dumping would eventually lead to the pollution of the oceans. Metropolitan centers such as New York City once loaded their sludge and debris onto barges, took the vessels out to sea, and dumped the refuse, in a practice called ocean dumping. Problems with ocean dumping were not fully recognized until floating plastic particles were found throughout the Atlantic and Pacific Oceans.
The perils of ocean dumping and debris struck home both literally and figuratively in the summer of 1988, when debris from the ocean, including sewage, garbage, and biohazards from medical waste, washed up on the Atlantic seaboard, forcing an unprecedented 803 beach closures. In some cases authorities were alerted to beach wash-ups when children turned up hypodermic needles in the sand. Aquatic species also faced serious dangers from these materials, including absorbing or ingesting hazardous waste substances, and ingesting needles, forceps, and other dangerous solid debris. In 1994 hundreds of dead dolphins washed up on Mediterranean beaches, killed by a virus linked to water pollution. Scientists pointed to this event as an indication of what may happen to other marine animals (and humans) if pollution continues.
At the urging of the Environmental Protection Agency (EPA), the dumping of potentially infectious medical waste into ocean waters from public vessels was prohibited in 1988. In 1992 the federal government banned ocean dumping. In 1995 the EPA stepped up efforts to educate people about the dangers of polluting coastal waters through improper disposal of trash on land, sewer overflows to rivers and streams, and dumping by ships and other vessels. The EPA further warned that marine debris poses not only a serious threat to wildlife, but remains in the environment for many years. (See Table 5.1.)
Mercury and Other Toxic Pollutants
Mercury poisoning is a problem in many lakes and oceans. Mercury can cause brain damage and other serious health problems in wild species and in humans. During the 1990s scientists began to report widespread mercury contamination in fish, including those inhabiting remote lakes that were assumed pristine. As a result, many states now warn people against eating certain types of fish.
The Environmental Protection Agency's National Fish and Wildlife Contamination Program reported that in 2002 mercury was the cause of 2,140 fish and wildlife consumption advisories. This represented an 11 percent increase from mercury consumption advisories in 2001. Scientists believe that the main source of mercury pollution is rain-water that carries mercury from coal-burning power plants, incinerators that burn garbage, and smelters that make metals. Because mercury becomes concentrated in organic tissues like DDT, even small concentrations of mercury in the water can be harmful to health. (See Figure 5.3.)
While it is not the only pollutant causing fish and wildlife consumption advisories, mercury is the fastest-growing
TABLE 5.1
How long does marine debris stay in the environment?
| Cardboard box | 2 weeks |
| Paper towels | 2-4 weeks |
| Newspaper | 6 weeks |
| Cotton glove | 1-5 months |
| Apple core | 2 months |
| Waxed milk carton | 3 months |
| Cotton rope | 3-14 months |
| Photodegredable 6-pack ring | 6 months |
| Biodegradable diaper | 1 year |
| Wool glove | 1 year |
| Plywood | 1-3 years |
| Painted wooden stick | 13 years |
| Foam cup | 50 years |
| Tin can | 50 years |
| Styrofoam buoy | 80 years |
| Aluminum Can | 200 years |
| Plastic 6-pack ring | 400 years |
| Disposable diapers | 450 years |
| Plastic bottles | 450 years |
| Microfilament fishing line | 600 years |
| Glass bottles/jars | Undetermined |
| SOURCE: Adapted from "Marine Debris Timeline," U.S. Environmental Protection Agency, Gulf of Mexico Program, Stennis Space Center, MS, October 9, 2003 [Online] http://www.epa.gov/gmpo/edresources/debris_t.html [accessed February 17, 2004] | |
contaminant. Figure 5.4 lists the pollutants for which advisories were published between 1993 and 2002. The number of lake acres affected by advisories issued due to DDT, chlordane, and PCBs remained relatively stable during the ten-year tracking period, while those affected by mercury increased dramatically.
Figure 5.5 shows the total number of fish consumption advisories in each state in 2002, from mercury as well as other pollutants. The percentage of lake acres and river miles under advisory between 1993 and 2002 are shown in Figure 5.6. Pollution in aquatic environments has increased steadily in the past decade.
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