Additional Case Studies

DDT and Fragile Eggshells
The chemical war on Colombian coca
Fighting the Fiery Serpent:Guinea Worm eradication program
Ebola Hemorrhagic fever

During the 1960s, peregrine falcons, bald eagles, osprey, brown pelicans, shrikes, and several other predatory bird species suddenly disappeared from former territories in eastern North America. What caused this sudden decline? Studies revealed that eggs laid by these birds had thin, fragile shells that broke before hatching. Eventually, these reproductive failures were traced to residues of DDT and its degradation product, DDE, which had concentrated through food webs until reaching toxic concentrations in top trophic levels such as these bird species.

DDT (dichloro-diphenyl-trichloroethane), an inexpensive and highly effective insecticide, had been used widely to control mosquitoes, biting flies, codling moths, potato beetles, corn earworms, cotton bollworms, and a host of other costly and irritating pest species around the world. First produced commercially in 1943, more than 50 million pounds of DDT were sprayed on fields, forests, and cities in the United States by 1950.

But as we have since discovered, there are disadvantages to widespread release of these toxic compounds in the environment. In the case of falcons, eagles, and other top predators, DDT and DDE inhibit enzymes essential for deposition of calcium carbonate in eggshells, resulting in soft, easily broken eggs. As we will discuss later in this chapter, other compounds chemically related to DDT are now thought to be disrupting endocrine hormone functions and causing reproductive losses in many species other than birds.

These effects, coupled with the discovery of a pervasive presence of various chlorinated hydrocarbons in human tissues worldwide, led to the banning of DDT in most industrialized countries in the early 1970s. Peregrine falcons, which had declined to only about 120 birds in the United States (outside of Alaska) in the mid-1970s, now number about 1400, most of them bred in captivity and then released into the wild. Bald eagle reproduction has increased from an average of 0.46 young per nest in 1974 to 1.21 young per nest in 1994 in eastern Canada. Peregrine falcons and bald eagles had recovered enough to be removed from the endangered species list in the eastern United States in 1994.

What have we learned from this experience? Chemical pesticides offer a quick, convenient, and relatively inexpensive way to eliminate annoying or destructive organisms. At the same time, however, excessive pesticide use can kill beneficial organisms and upset the natural balance between predator and prey species. Modern pesticides undoubtedly have saved millions of human lives by killing disease-causing insects and by increasing food supplies. But we must understand what these powerful chemicals are doing and use them judiciously. In this chapter, we will study the major types of pests and pesticides along with some of the benefits and problems involved in our battle against pests.

Colombia to Spray Coca Cops with Stronger Herbicide

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June, 1998

Environmental Consequences Could Be Severe

After more than a decade of pressure, the Colombian government agreed in June to US demands to test a new herbicide for use in the war on cocaine producers. The new herbicide is tebuthiuron, a pelletized herbicide that is more effective, persistent, and environmentally dangerous than herbicides used in Colombia in the past. Critics, including a US General Accounting Office report of February 1998, argue that this new offensive is taking place at the expense of other, possibly more effective, interdiction efforts.

For four years Colombian police have used airplanes to spray fields with liquid herbicides. But several problems have made these treatments relatively ineffective. Applications by air frequently miss target plants, or reach only parts of targeted fields, so that only about 30% of treated plants are killed. Rainfall quickly disperses and dilutes liquid herbicides, further reducing effectiveness. Most important, applications must be done low to the ground, at times of day when there is no rain and little wind to cause drift from the target fields. These low-level applications in fine weather make airplanes especially vulnerable to attack from the ground.

<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::Coulombia2::/sites/dl/free/0072452706/22967/colombia2.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif">Coulombia2 (60.0K)</a>Coulombia2 Colombia's south-central provinces are likely to recieve the greatest focus in the tebuthiuron application program.

In contrast, tebuthiuron comes in pea-sized solid pellets, which can be dropped from higher altitudes even in rainy or windy weather. This makes tebuthiuron applications much safer for pilots. The solid pellets are expected to hit target fields with better accuracy, increasing the effectiveness of applications. Pellets break down and disperse more slowly than liquid herbicides, making the application more likely to kill plants. At the same time, tebuthiuron, which is sold in the United States under the brand name Spike, is a highly toxic, extremely persistent, broad-spectrum herbicide. Labels warn that even slight exposure to roots can kill trees. Persistence means that the chemical compound breaks down slowly, so that the herbicide can remain potent for 15 months. In a moist environment, such as in the rain forests of southern Colombia, water can quickly carry persistent herbicides through the environment. Broad-spectrum herbicides are lethal to a wide variety of vegetation. Tebuthiuron is effective not just against coca plants but also against any broadleaf or woody vegetation--including mature trees, shrubs, and vines.

Environmentalists and members of the Colombian government worry that the persistence of the herbicide will make fields useless for subsistence agriculture after the coca plants have been killed. The region's peasants rely on subsistence farming in the forest for survival. Damage to forests surrounding coca fields could be extreme. And further deforestation is inevitable as coca growers--and subsistence farmers--are forced to clear more land for farming after tebuthiuron applications.

Fears of Herbicide Persistence, Water Contamination

One of the most urgent worries, though, is water contamination. The persistent herbicide moves and disperses quickly once it enters streams or groundwater. Although the herbicide is designed to kill plants, it is also poisonous to animals, and dispersal by water poses serious health threats to local farmers and to wildlife. The maker of tebuthiuron, a subsidiary of Dow Chemical Company, insists that the chemical be used only under carefully controlled conditions and where there are no nearby water bodies, streams, or shallow groundwater. But uncontrolled conditions and heavy rainfall are precisely the reasons the US government has insisted on tebuthiuron's use on Colombia's cocaine fields. The company strongly opposes this use of the herbicide.

If approved for use, tebuthiuron could be used on more than 80,000 hectares (nearly 200,000 acres), mainly in the southern provinces of Caqueta, Putumayo, Guaviare, and Meta.

Some Illegal Use Already Underway?

Reports have surfaced that covert tebuthiuron applications have been under way at least since last spring, long before the Colombian government agreed to its testing. Until July the chemical was strictly banned in the country, but early last spring farmers were reporting on finding pea-sized pellets in their fields--pellets that experts contend could only be tebuthiuron. Pellets were found in nearby subsistence food plots, as well as in illegal coca fields.

To read more, see

Environmental Science, A Global Concern, Cunningham and Saigo, 5th ed.
Persistence and mobility of pesticides and herbicides: page 256
Tropical deforestaton: page 297

Environmental Science, Enger and Smith, 6th ed.
Herbicides: page 268

In 1986, the world health community began a campaign to eliminate the guinea worm (Dracunculus medinensis) from the entire world by the year 2000. If successful, this will be only the second global disease ever completely eradicated (smallpox, which was abolished in 1977 was first), and the only time that a human parasite will have been totally exterminated worldwide. Known as the fiery serpent, the guinea worm is a terrible scourge of many tropical countries. Infection starts by drinking stagnant water contaminated with tiny water fleas (called cyclops) containing guinea worm larvae. Inside the human body, the worms grow to as long as one meter (3 ft). After a year of migrating through the body, a threadlike adult worm emerges slowly through a painful skin blister. Most worms come out of the legs or feet but they can appear anywhere on the body. The 8 to 12 weeks of continuous emergence are accompanied by burning pain, fever, nausea, and vomiting. Many victims bathe in a local pond or stream to soothe their fever and pain. When the female worm senses water, she releases tens of thousands of larvae, starting the cycle once again.

As the worm emerges from the wound, it can be rolled around small stick and pulled out a few centimeters each day. Sometimes the entire worm can be extracted in a few days, but the process usually takes weeks. If you pull too fast and the worm breaks off, the part left in your body can die and fester, leading to serious secondary infections. If the worm comes out through a joint, permanent crippling can occur. There is no cure for guinea worm disease once the larvae are ingested. There is no vaccine, and having been infected once doesn't give you immunity. The only way to break the cycle is through behavioral changes. Community health education, providing clean water from wells or by filtering or boiling drinking water, eliminating water fleas by chemical treatment, and teaching infected victims to stay out of drinking supplies are the only solutions to this dreadful problem.

When the eradication campaign was started in 1986, guinea worms were endemic to 16 countries in sub-Saharan Africa as well as Yemen, India, and Pakistan. Every year about 3.5 million people were stricken and at least 100 million people were at risk. With the leadership of former U.S. President Jimmy Carter, a consortium of agencies, institutions, and organizations-including the WHO, UNICEF, the United Nations Development Program (UNDP), the World Bank, bilateral aid agencies, and the governments of many developed countries-banded together to fight this disease. Although complete success has not yet occurred, encouraging progress has been made. Already the guinea worm infections are down more than 96 percent. Pakistan was the first country to be declared completely free of these parasites. Infection rates in Kenya, Senegal, Cameroon, Chad, India, and Yemen are down below 100 cases per year. More than 80 percent of all remaining cases occur in Sudan, where civil war, poverty, drought, and governmental resistance to outside aid have made treatment difficult.

An encouraging outcome of this crusade is the demonstration that public health education and community organization can be effective, even in some of the poorest and most remote areas. Village-based health workers and volunteers conduct disease surveillance and education programs allowing funds and supplies to be distributed in an efficient manner. Once people understand how the disease spreads and what they need to do to protect themselves and their families, they do change their behavior. And when the campaign is completed and guinea worms are completely vanquished, the health workers and volunteers will be available for further community development projects.

In mid-April, 1995, a 36-year-old laboratory technician named Kimfumu checked into the medical clinic in Kikwit, Zaire (now the Democratic Republic of Congo) complaining of a severe headache, stomach pains, fever, dizziness, weakness, and exhaustion. Surgeons did an exploratory operation to try to find the cause of his illness. To their horror, they found his entire gastrointestinal tract was necrotic and putrefying. He bled uncontrollably, and within hours was dead. By the next day, the five medical workers who cared for him, including an Italian nun who assisted in the operation, began to show similar symptoms, including high fevers, fatigue, bloody diarrhea, rashes, red and itchy eyes, vomiting, and bleeding from every body orifice. Less than 48 hours later, they, too, were dead, and the disease was spreading like wildfire throughout the city of 600,000.

As panicked residents fled into the bush, government officials responded to calls for help by closing off all travel--including humanitarian aid-into or out of Kikwit, about 400 km (250 mi) from Kinshasa, the national capital (fig. 9.1). Fearful neighboring villages felled trees across the roads to seal off the pestilent city. No one dared enter houses where dead corpses rotted in the intense tropical heat. Boats plying the adjacent Kwilu River refused to stop to take on or discharge passengers or cargo. Food and clean water became scarce. Hospitals could hardly function as medicines and medical personnel became scarce.

Deadly tropical fevers are an unfortunate fact of life in Central Africa but rarely are they this contagious or lethal. The plague that afflicted Kikwit was Ebola hemorrhagic fever, a viral disease for which there is no known treatment. Within a few weeks, about 400 people in Kikwit had contracted the virus and 350 were dead. Where a 10 percent mortality rate is considered high for most infectious diseases, Ebola kills up to 90 percent of its victims, usually within only a few days after exposure.

The Kikwit Ebola outbreak was neither the first nor last appearance of this dread disease. The first recognized Ebola epidemic occurred in 1976 in Yambuku, Zaire (near the Ebola River, after which the virus was named), where at least 280 people died. Three years later, 22 patients died in Sudan from a slightly different and less virulent form of Ebola. In 1996, about 100 people were killed by Ebola in two separate episodes in Gabon, and in 1999 an outbreak in the gold mining town of Durba in the Democratic Republic of Congo killed at least 63 people.

Ebola is one of two members of a family of RNA viruses called the Filoviridae (fig. 9.2). The other filovirus causes Marburg fever, an equally lethal and contagious hemorrhagic disease, named after a German town where it was first contracted by laboratory workers who handled imported monkeys infected with the virus. Together with members of three other families (arenaviruses, bunyanviruses, and flaviviruses), these viruses cause a group of terrible, episodic diseases including Lassa fever, Rift Valley fever, Bolivian fever, and Hanta or Four-Corners fever (named after the region of the southwestern United States where it was first reported).

The viruses associated with most of these emergent, hemorrhagic fevers are zoonotic. That means a reservoir of viruses naturally resides in an animal host or arthropod vector. No host or vector is known for Ebola but we know that monkeys and other primates can contract related diseases. Why viruses remain peacefully in their hosts for many years without causing much more trouble than a common cold, but then erupt sporadically and unpredictably into terrible human epidemics is a new and growing question in environmental health and risk assessment. In this chapter we will look at some of the changes humans are bringing about in our environment as well as how a variety of environmental factors affect our health. While you're not likely to encounter Ebola unless you venture into the African jungle, studying this material should give you some ideas about what we might do to ensure a safer environment and how you can adopt a healthier lifestyle.