The Short-lived Miracle Of Ddt
DDT was a savior in the 1940s and a curse by the 1960s. Its story shows how a technology that does enormous good can also do enormous harm.
EARLIER THIS YEAR A GROUP OF JOURNALISTS ASSEMBLED BY NEW York University voted Silent Spring (1962), by the ecologist Rachel Carson, the second most influential piece of American journalism of the twentieth century. Drawing on a wide range of scientific studies, Carson demonstrated to the public that DDT, the miracle chemical of World War II and the keystone of the World Health Organization’s global antimalaria program in the 1950s, was less a benefit to humanity than a danger to the global ecosystem. Within a decade Carson’s book and the movement it spawned led to the banning of DDT in the United States and in most other industrial countries. The meteoric rise and precipitous decline of DDT is at once an epic of human achievement in war, a dramatic chapter in the long struggle against malaria, and a cautionary story about the outcome of unbridled enthusiasm for new technology.
If not for the frantic search for an effective insecticide early in World War II, there might have been no story to tell. When the United States entered the war, scientists in the Office of Scientific Research and Development (OSRD) knew that one of the greatest threats to troops in wartime has always been disease, especially insect-transmitted diseases that thrive when thousands of people are thrown together in close quarters and new environments. Brig. Gen. Nathanael Greene learned that hard lesson in 1776, when one-third of his Continental Army was stricken with louse-borne typhus during the Long Island campaign. Typhus was also an important factor in the defeat of Napoleon’s Grand Army when it invaded Russia in 1812.
Typhus was an even greater problem in World War I. Millions of soldiers on the Eastern Front were infected, with large numbers dying from the disease. Even after the war, typhus devastated refugees and returnees throughout Eastern Europe. Mosquito-borne malaria was another serious problem in World War I. During the Salonika campaign the British had 162,000 soldiers unfit for combat because of malaria, compared with 28,000 killed or injured in battle. The French army at Salonika at one time had less than 20 percent of its troops ready for combat because of the same disease.
By the close of the War to End All Wars, it was unmistakably clear that insect-carried disease could be disastrous for armies. Yet two decades later none of the combatants entering the next world war had significantly improved their abilities to cope with insects. It was therefore no surprise to any informed observer when, in the first year after the United States entered World War II, the entire 1st Marine Division had to be withdrawn from the Pacific front because more than half its men had contracted malaria. This serious defeat, which occurred without enemy action, came in the summer of 1942, soon after the OSRD had begun collaborating with the Agriculture Department’s Bureau of Entomology and Plant Quarantine to find a way to control or eliminate battle-zone insects. The bureau’s laboratory in Orlando, Florida, became the center for a program to test every known insecticide and insect repellent.
In 1942 the laboratory tried thousands of commercial and noncommercial chemicals and preparations, focusing mainly on lice, which seemed likely to be the greatest enemy. A few lice and a promising chemical would be put on a civilian volunteer’s arm, in a sleeve firmly taped at each end. After 24 hours the sleeve was opened. If the lice had died, new ones were inserted, but no more insecticide was added. This process was repeated until the lice survived. Through most of 1942 only one product killed lice for as long as eight days: pyrethrum, a natural insecticide derived from tropical plants that is widely used today in spray insecticides. Unfortunately, the major sources of pyrethrum were found primarily in war-threatened areas of equatorial Africa and in other tropical areas occupied by enemy troops, such as Indonesia. Moreover, pyrethrum often irritated skin when it was applied directly.
The laboratory at Orlando kept trying every new concoction that came to its notice. Late in 1942 a new insecticide called Gesarol arrived from J. R. Geigy, a chemical dye company in neutral Switzerland. Its active ingredient was dichlorodiphenyltrichloroethane—DDT, for short. The OSRD laboratory tagged the sample and tested it the same way it did everything else.
If the laboratory had known DDT’s recent history, or if it had not already been jaded by the extravagant claims of some other commercial products, it might have pounced on DDT immediately. Geigy, a long-established firm in the city of Basel, had entered the insecticide field in 1935, when it assigned a team of chemists headed by Paul Hermann MÜller to find a product for mothproofing woolens. After testing a wide variety of chemicals on household flies, MÜller and his team hit upon DDT, which had first been synthesized by a German doctoral student nearly 80 years earlier but had gone unnoticed until it was rediscovered by MÜller’s chemists. They found that although DDT was not immediately lethal, it killed everything in a test box within 24 hours. Most distinctive of its properties was its uncanny persistence: It remained effective for days, even weeks, without reapplication.
In the late 1930s MÜller and his team tried DDT on cockroaches, mosquitoes, and many agricultural pests. They found that it combined an excellent “knockdown” characteristic (the ability to kill insects on contact) with a superior residual effect (the ability to continue killing insects that landed on surfaces sprayed with the chemical). In 1940 Geigy began selling its new product, Gesarol (DDT at 5 percent strength), as a pesticide. The next year a dust with just a 1 percent concentration proved extremely effective in stopping an infestation of potato beetles in Switzerland. By 1942 a preparation named Neocid was being marketed as a louse killer. It was used with excellent results at Italian refugee camps on the Swiss border.
Because of Switzerland’s neutrality, information on DDT was freely available to all the combatants in World War II. The German army made some use of DDT, spraying it in Greece and Yugoslavia to control mosquito larvae in an attempt to reduce the incidence of malaria. However, it was the Americans who most effectively exploited the new insecticide. In August 1942 about 100 kilograms of Gesarol (half of it 5 percent DDT spray and half of it 3 percent DDT dust) had been exported from Switzerland to Geigy’s subsidiary in New York via a neutral freighter from Portugal. Copies of some of the scientific reports soon followed.
Victor Froehlicher, the head of the Geigy office in New York, laboriously translated the reports into English. They described effects so far beyond those of any existing insecticide that he found them hard to believe. On October 16, 1942, he delivered his translation and a small quantity of Gesarol to an official at the Department of Agriculture in Washington. Following government policy on insecticide research, information about DDT was thereafter treated as a secret in the United States.
Gesarol passed the sleeve test with flying colors, killing lice for nearly three weeks without renewal. Better yet, it did not seem to irritate the skin, and it had no odor. Next DDT was tried in the Orlando countryside. In one remarkable instance the natural conditions of two neighboring ponds were surveyed, and then one pond was sprayed with DDT to kill mosquito larvae. A week later the scientists were puzzled to find that not only were the larvae in the first pond dead or dying, but those in the second pond were too. They realized that even the small quantity of DDT carried from one pond to the other by ducks and other waterfowl was enough to kill the insects.
The scientists now knew that they were dealing with an exceptionally powerful formula, and the OSRD gave the development of DDT-laden insecticides a high priority. A range of concentrations were tested for the manufacture of louse powder, and a variety of solvents were tried for sprays, because by this time it was clear that the war in the Pacific would demand a massive malaria-control effort. One American general called malaria “an enemy more dangerous than the Japanese.” At first DDT had to be imported from Switzerland, but as early as May 1943 a Geigy affiliate, the Cincinnati Chemical Works, started up a pilot plant. The chemical process for synthesis of DDT was not complicated, requiring the reaction of monochlorobenzene (C 6 H 5 Cl) and chloral hydrate (CCl 3 CH(OH) 2 ) to form DDT (CCl 3 CH(C 6 H 4 Cl) 2 ) and water, with sulfuric acid as a catalyst. Production was limited mostly by wartime bottlenecks in the availability of the basic ingredients.
The OSRD decided to experiment with widespread field tests before beginning regular military distribution. It turned to a nonmilitary organization, the Rockefeller Foundation, to carry out much of the fieldwork. Since its creation in 1913 by John D. Rockefeller, with an endowment that eventually reached $183 million, the foundation had become a global leader in public health work, particularly with regard to parasitic and insect-borne diseases. The foundation’s public health program continued one that had been initiated by the Rockefeller Sanitary Commission (1909-12) and the International Health Board (1913-28). The program had first attacked hookworm infestation, an insidious “disease of laziness” that predominantly affected the poor in the rural Southern United States and workers on plantations and industrial settlements throughout the world.
In the 1920s and 1930s the foundation expanded its public health program to include yellow fever and malaria. One of its greatest efforts came in Brazil, where in the late 1930s foundation officers eradicated Anopheles gambiae , a yellow-fever-carrying mosquito species that had inadvertently been introduced from Africa. Soon after the beginning of World War II, but before Pearl Harbor, the foundation created the Rockefeller Foundation Health Commission, composed of foundation staff who had substantial field experience. The commission formed a team that could be deployed in war-damaged regions threatened with epidemics or other public health problems.
When the United States entered World War II, the OSRD asked the Rockefeller Foundation to establish a laboratory to study lice. This louse lab was set up in New York City using staff from the Rockefeller Institute for Medical Research (now Rockefeller University). The laboratory started its work with a few lice scraped from a patient at Bellevue Hospital. It then began detailed studies of the insects’ biology. In the fall of 1942, after breeding a few generations of the lice and ascertaining that they carried no diseases, samples were taken to New Hampshire to infest volunteers at a conscientious objectors’ camp. The lab then sent a series of promising concoctions to the camp, where they were tested both for their effectiveness in killing the lice and for any problems they might cause by coming in contact with skin. Testing there and in Mexico reinforced the finding that pyrethrum was an effective lousicide. Early tests of DDT in the summer of 1943 suggested that it was even more potent. But with Geigy’s Cincinnati plant still working out its kinks, supplies remained limited. In any case, DDT’s field effectiveness was yet to be proved.
After testing pyrethrum powder in two Egyptian villages in the spring of 1943, the commission moved its North African operations to newly liberated Algeria and Tunisia, where it worked with a branch of the Pasteur Institute in Tunis that had studied epidemic disease in the region since 1893. The scientific leader of this Rockefeller Commission unit was Dr. Fred Soper, an energetic, outspoken veteran of past Rockefeller public health campaigns. He was famous among malariologists for leading the foundation’s successful antimosquito campaign in Brazil a few years earlier. Among the strategies Soper employed there was the widespread and repeated distribution on water surfaces of Paris green, a salt containing copper and arsenic, to kill mosquito larvae. But Paris green is poisonous to humans and is only briefly effective. When Soper began to use DDT, he immediately recognized its superiority over other insecticides. For the next twenty years he energetically pushed DDT as an answer to malaria. But his first mission was to demonstrate the chemical’s effect on lice, a program he drove forward relentlessly and with disdain for anyone who did not see the future as clearly as he did.
In June 1943 Soper and his commission and Pasteur Institute colleagues received their first supplies of DDT. They held their initial tests at the Maison Carrée prison in Algiers, where inmates were dusted with DDT and other insecticides currently used by the Allied forces. That fall DDT was given field tests in an Algerian town with a mixed Arab and European population and at a nearby prisoner-of-war camp. Among other factors, the studies aimed to find out whether DDT powder could be effective against lice when it was dusted into clothing through neck, arm, and leg openings. The commissioners thought this would be faster than requiring each person to disrobe, and they also recognized that in most cultures civilians would be reluctant to strip naked in front of strangers.
The lessons learned from these trials were put to dramatic use in December 1943, when the Allied military command in Italy asked the commission to stop an incipient typhus epidemic in Naples. The American 5th Army had captured the city on October 1 and found public health conditions deplorable; by one estimate, 90 percent of the citizens had body lice. In the next month 25 cases of typhus were identified; 42 were found in November, and 60 in the first half of December. The Associated Press reported the crisis in the United States a few days later and said that a quarter of the cases had resulted in death. Although the troops had not suffered any typhus casualties, humanitarian concerns made it imperative for the Allies to act quickly.
When the Rockefeller Foundation Health Commission was called in, a large quantity of the current production of DDT was earmarked for Naples, with 60 tons dispatched immediately. Commission officers set up five delousing stations in the city, and on New Year’s Day 5,000 civilians were dusted using a hand-operated blower that had been developed and modified in the North Africa trials. By the end of the month 1.3 million residents of Naples and the surrounding region had received insecticidal baths with DDT and pyrethrum. Typhus continued to fester in January, began to decline in February, and in March decreased abruptly to a few cases a day. The epidemic was over.
Nothing like this result had ever been seen before. From then on the British and American armies decreed that “DDT marches with the troops.” It also proved vitally important in liberated German concentration camps, where by the spring of 1945 typhus had become rampant.
Important as these triumphs were, the fight against lice and typhus may ultimately have been less significant than the fight against mosquitoes and malaria. After the Allies liberated Rome and central Italy in June 1944, the Rockefeller Foundation Health Commission was asked to develop a malaria-control program, in part because the retreating German army had destroyed so much of the water-control system that drained low-lying and marshy areas. Some of the Rockefeller officers had experience with a pre-war Rockefeller Foundation antimalaria program in Italy and knew the terrain and the mosquito habitat quite well.
The commission decided that the most likely areas to suffer from malaria, and thus to impede the war effort in Italy, were the delta of the Tiber River (which included the port of Ostia, a major landing point for supplies for the Allied armies) and the Pontine marshes, which had historically been the source of malaria infestations for nearby Rome. In both areas the commission carried out massive DDT campaigns, hand-spraying the insides of houses and farm buildings and then moving on to swamps and bodies of water. This effort was the first time that DDT (mixed with kerosene or fuel oil) was sprayed from the air to distribute it quickly and widely. Some malaria developed, but there was no epidemic. As the European campaign continued, DDT was also used with effect in battle areas, first by spraying inside barracks and other military structures and then with aerial spraying of mosquito breeding zones near bases.
Now DDT, which had done much to secure victory for the Allies in Europe, had its turn in the Pacific. At first it was used in areas behind the lines, dispensed by hand sprayers. Soon, though, it was laid down in advance of landing forces, sprayed from airplanes over coastal zones so that the invading American forces would not have to worry about insects. With American production of DDT reaching two million pounds per month by the end of 1944 (it was now being manufactured by the giant Du Pont chemical company, among others), malaria was a minor problem in the last months of the war. Other diseases spread by insects were significantly affected by DDT as well. On Saipan, for example, an epidemic of dengue fever broke out soon after American troops landed in the late summer of 1944. It ended after a C-47 sprayed 9,000 gallons of a kerosene solution of DDT over the island.
With all these successes DDT came to public notice as one of the most important tools in the Allied arsenal after the official secrecy about it ended in July 1944, when Victor Froehlicher of Geigy’s New York office published a thorough article about it in a chemical-industry magazine. A month later Britain, where DDT had been received, investigated, and manufactured at about the same pace as in the United States (but in smaller quantities), released a statement about its military uses. Many British civilians first heard of DDT from Winston Churchill on September 28, 1944, when, in one of his frequent radio messages, he rhapsodized about “the excellent DDT powder, which has been fully experimented with and found to yield astonishing results.”
In the context of World War II’s devastation, Churchill’s enthusiastic assessment made perfect sense. Yet even in the glow of impending Allied victory, disturbing evidence had begun to crop up. In 1944 a government installation on a New Jersey island had been sprayed with DDT to rid it of annoying flies. This had worked, but along with the flies, the fish population had been drastically reduced. After the war, when spraying stopped on one Pacific island, mosquitoes returned in greater numbers than before because DDT had wiped out their natural predators. And worse news was on the way.
In 1946 reports from DDT-soaked Italy said that flies and mosquitoes were demonstrating resistance to the pesticide. By 1950 enough was known about DDT’s possible ill effects on humans for the U.S. Food and Drug Administration to state that it was “extremely likely that the potential hazard of DDT has been underestimated.” The FDA had studied DDT and found that it tended to accumulate in the fatty tissues of all animals, including humans. When used on dairy farms for fly control, it quickly showed up in cows’ milk. The FDA also found that massive doses of DDT caused nerve damage, but it was impossible to determine the long-term effects of the low-level exposure most citizens would have.
These early hints of trouble scarcely affected the postwar juggernaut of pesticide production and distribution. In August 1945, just before the Japanese surrender, restraints on civilian sales of DDT ended in the United States, and it quickly spread to household and agricultural uses. Most people chalked up DDT’s occasional problems to experience and figured that adjusting the concentration or the method of application would solve any problems. And even if a few animals might die, the improvements in the quality of human life far outweighed any small costs that might arise.
In the first flush of postwar giddiness, DDT, just like atomic energy and other wartime inventions, seemed a miracle. It was employed against the beetles that carried Dutch elm disease, and in a few years public health authorities were using it in mosquito-control programs throughout the country. Throughout the 1950s the use of DDT for malaria control expanded globally. First the Rockefeller Foundation led an experimental attempt to eradicate mosquitoes from Sardinia, and then the Pan-American Health Organization (led by the insecticide warhorse Fred Soper) and later the World Health Organization entered the fray. Early results were dramatic, as malaria infection rates fell sharply. The age-old scourge was virtually eliminated from the Southern United States; worldwide, reliable estimates suggest that DDT had prevented five million malaria deaths by 1950. In 1948 MÜller was awarded a Nobel Prize for his work in discovering the wonder chemical.
As early as the mid-1950s, though, it became increasingly clear that DDT would not be the only answer to the problem of insect-carried disease. Mosquitoes were not being completely eradicated; in spite of four years of saturation spraying in Sardinia, they survived there. Moreover, insects of all types were developing resistance to DDT. While the common housefly was one of the most resilient, by 1960 some 137 species of insect pests were known to have some level of resistance. The World Health Organization stated in the 1960s that “resistance is at present the most important problem” in its insect-control programs.
But resistance was actually only part of the problem—the lesser part, as it turned out. More frightening was the steady accumulation of evidence that DDT was wreaking environmental damage on a large scale. Early fish kills following spraying raised concern, but it took some time for scientists to understand why the fish had died: some by direct poisoning, but more because the DDT had killed off their food supply. Rachel Carson wrote about a massive DDT campaign to control a spruce budworm infestation in a watershed in the Canadian province of New Brunswick. Virtually all the young salmon were killed in a few days, largely because the insects in the water, on which they fed, were as susceptible to DDT as the winged insects it was aimed at.
Over the years, environmental testing revealed that DDT use had an even more insidious hazard, one that resulted from the very quality that made it so effective: its persistence. Because it deteriorated very slowly, DDT was not just killing insects but was spreading far up the food chain. By the time Silent Spring appeared, in 1962, there were signs that some birds of prey, particularly fish eaters, were seriously affected by environmental DDT. Bald eagles and ospreys—large, beautiful, soaring birds whose nests were familiar landmarks in coastal waters and inland lakes—had been driven close to extinction.
As early as 1947 observers found these birds producing few or no young in areas where a few years before each nest had regularly yielded one or two fledglings. Eventually scientists found evidence that DDT accumulation had interfered with the egg-making process. In some cases none at all were laid; in others, eggs were produced but were so fragile that sitting adults crushed them. Public outcry about the endangerment of the bald eagle, a national symbol, was a major reason DDT was banned in the United States in 1972. (By then, of course, epidemics of insect-borne disease were mostly a thing of the past in this country.) Since the ban, ospreys and other birds of prey threatened with extinction have managed to restore their numbers.
In other parts of the world, DDT is still a primary insecticide, and eliminating it is less simple. In fighting the scourge of malaria, which has been resurgent in the last quarter-century, DDT is far more affordable and effective than anything else available. About two dozen developing nations (including China, India, and Mexico), which together account for nearly half the world’s population, still use DDT for house-spraying campaigns. A United Nations organization has been moving to get DDT banned worldwide within the next decade, but the Malaria Foundation International, an organization of more than 350 doctors and scientists, vehemently opposes such a quick cutoff.
The foundation argues that since malaria kills 2.7 million people a year, the price in human life of such a ban would be too high, especially since the amounts of DDT being used today are much lower than in the past. (Spraying all the high-risk houses in a nation the size of Guyana, for example, requires no more DDT in a year than would once have been used on a thousand-acre cotton field.) So there may be unavoidable public health reasons to continue using DDT for nonagricultural purposes for at least a while longer.
The pesticide story is not just a matter of DDT use, however. One billion pounds of pesticides and herbicides will be used by American farmers in 1999, and against all the benefits that they bring must be balanced the serious environmental damage they will cause. Approximately 67 million wells in the United States are contaminated by pesticides in some degree. Worldwide, after a half-century of heavy use of DDT and its successors, at least 535 insects have demonstrated resistance to insecticides.
Alternatives to artificial pesticides are being examined seriously and applied extensively in agriculture, though the situation in disease control is less promising. The use of predatory insects to control pest species has grown rapidly, and scientists are researching naturally occurring pesticides. In March 1999, for example, a newspaper reported that the federal government’s Agricultural Research Service had found that “the natural oil that gives peaches their perfume also kills fungus and other pests in the soil.”
None of these alternatives is likely to be a safe, all-purpose magic bullet, any more than DDT was. Insect immunity will continue to crop up, and for many applications the simplicity and killing power of artificial pesticides will make them hard to resist. As choices proliferate, however, and scientists, farmers, and the general public gain an everdeeper understanding of the intricate web of life that makes up the global ecosystem, we can hope that ways will be found to keep damage to nontarget species to a minimum and to ensure that there is no cost in human life.
In early 1999 motorists heading east near Orlando on 1-4 could see a row of tall power-line towers, each fitted with a platform at the top to encourage osprey nesting. There were a dozen or more platforms, and on almost every one was a pair of ospreys, newly arrived from their Caribbean wintering grounds. Their presence creates at least a partial closing of the circle. In the place where DDT was first introduced into the American environment, one of the species believed to be most seriously threatened by it has made a strong comeback. The Jekyll-and-Hyde chemical that saved soldiers, sailors, marines, and civilians in World War II and served as a potent weapon against malaria, is now fading from the global ecosystem that found it to be an unprecedentedly serious intrusion.