October 2004 DDT - Good or Bad? Everyone has heard of DDT, a chemical initially touted as a “miracle” pesticide and later, after a couple of decades of use, a chemical that was blamed for endangering predatory bird species, causing disease, and degrading ecosystems.
Before commenting on DDT, let’s take a look at the history of the product and its use. DDT (Dichloro-diphenyl-trichloroethane), a chlorinated hydrocarbon, was first synthesized in 1874. Its effectiveness as an insecticide, however, was not discovered until 1939 by Paul Muller, a chemist working for the Swiss chemical firm J. R. Geigy. This discovery marked the beginning of a new era in medical entomology and the use of synthesized chemical compounds as pesticides. Research revealed that DDT was a powerful, persistent, stable chemical that was effective against an exceptionally broad range of insect pests. The main concern was: “Can the chemical be safely used on man?” After months of testing the FDA (Food and Drug Administration) concluded that “DDT was entirely safe for use.”
During World War II, the U. S. Military realized that without a way to control insect-borne diseases such as malaria and typhus, early defeat of the Japanese would not be a realistic expectation, they understood that these diseases would inflict more casualties than the enemy. The federal government assigned the task of finding an effective insecticide (because of the sub-tropical climate) to the State of Florida, Division of Insects Affecting Man and Animals of the Bureau of Entomology’s laboratory in Orlando. After testing over 8,000 chemical compounds they found that pyrethrum, a natural botanical insecticide, extracted from chrysanthemum flowers, was safe and effective. Unfortunately, supplies of pyrethrum were in short and undependable supply. Poor chrysanthemum crops and labor problems in Kenya in 1942 and 1943 resulted in a critical shortage of pyrethrum. Without sufficient supplies, the armed services needed an alternative. Between July and December of 1942, the Orlando lab tested over 900 more chemical compounds, DDT, known as Gesarol at the time, was among them. In May of 1943 the laboratory recommended DDT to the Office of Scientific Research. The military acted immediately, DDT was used for louse control. After using DDT louse powder, the military reported that the troops were “virtually louse free”, while German prisoners that were brought in, were heavily infested. In Naples, Italy, typhus had reached epidemic proportions. After liberating the city, 2.25 million people were deloused between December, 1943 and March of 1944. DDT powder had a miraculous effect, for the first time in medical history a typhus epidemic was stopped in mid-winter.
Testing of DDT continued, it was found that 1 part per million parts of water killed 100% of mosquito larva when used as a larvicide. Used as an aerosol for killing adult mosquitoes, DDT was again found to be extremely effective. While the potency of DDT was being demonstrated, the residual properties were being discovered. Laboratory tests indicated that DDT was exceptionally persistent. Surface treatments would kill adult mosquitoes for months after an application.
DDT’s potency and persistence proved to be true for just about all insect pests. The “icing on the cake” was that it was also very inexpensive to manufacture. DDT was used for public health pest control, agricultural pest control, forest products pest control, structural pest control, turf and ornamental pest control ... if it was an insect pest, DDT was used. DDT was cheap, safe, and effective.
During the 30 years of DDT use, prior to its cancellation, 1,350,000,000 pounds or 675,000 tons of DDT was used in the U. S. Users of DDT were euphoric with the product’s results. Crop production soared, millions of people were saved from the misery of insect-borne disease, our nation’s economy prospered ... it was a golden age for mosquito control and the disease they caused, it was a release from the ravages that insects caused in general, there were thoughts that insect pests that had affected man throughout history, could be eradicated forever, it was a miracle! Then reality struck, life found a way. Insects developed resistance to DDT, it didn’t work anymore. Because of DDT’s persistence, it bioaccumulated in the fatty tissue of living things. The higher up the food chain, the greater the concentration of DDT in the organism. DDT was blamed for cancer, mutation, and the decline of predatory bird populations. DDT was blamed for egg shell thinning. Eggs would break before they could hatch, reducing the number of hatchlings per clutch. The miracle pesticide was showing its bad side ... but was it the chemical or the fact that it was misused? One note here, upon review and recent research, most and perhaps all of these allegations were based on bad science, the only valid fact is that DDT did bioaccumulate, however, high concentrations in man or animals have not been shown conclusively, to cause death or disease.
On June 14, 1972, the EPA issued an order banning the use registration of DDT products in the U. S. except for public health emergencies, quarantine, and a few minor crop uses. DDT could still, however, be produced in the U. S. and exported.
After researching the literature on DDT, I got the impression that DDT was the scapegoat for many of the ills being recognized at the time. Predatory bird populations were on the decline but once the hunting of such was no longer allowed, their populations rebounded - during the height of DDT use. The allegations that DDT caused cancer and mutations was based on biased research of rats subjected to massive doses of DDT, far in excessive of what was in the environment. Subsequent testing has shown DDT not to be carcinogenic or mutagenic. My only experience with chlorinated hydrocarbons was when I was about 8 years old, my dad did a perimeter treatment with chlordane around the foundation of our home because there were ants, lots of ants coming inside the house. After the treatment there were no more ants or any insects for that matter, inside our home for at least the next 20 years ... when my parents sold their home. No one suffered any ill effects and there was no drop off in toads or other creatures, I know this because I was always catching them. I’ve talked to several entomologists that were in the military that have witnessed the effects of DDT use in other parts of the world and their comments have always been favorable.
Having been in the business of applying pesticides for over 2 decades now, the problem I see with the use of DDT in the past was that it was used indiscriminately. It was so effective and cheap that farmers and other pesticide applicators overused it, there was no stewardship in its use. By the time problems started to be recognized, there were tons and tons of the stuff in our environment, and because of DDT’s ability to persist, it wasn’t going to go away overnight.
Rachel Carson’s 1962 book, Silent Spring, was what ignited the environmental movement against the use of pesticides in the U. S. Many of her claims concerning pesticides may not have been completely accurate, but the fact that pesticides were being used indiscriminately, excessively, and in need of better controls, was completely valid.
Today, mosquito control operations have basically 2 groups of chemical compounds from which to choose, the pyrethroids (permethrin, sumethrin, resmethrin, etc.) and the organophosphates (malathion, dibrom, temephos, etc.) for mosquito control. This situation leaves us in a tenuous position because of the possibility of the development of resistance by mosquitoes. As an agency in charge of controlling mosquitoes, we must be prudent with the use of chemical pesticides and very aware of the possible occurrence of resistence in the mosquito population. If resistance occurs, we have only one other choice of chemical pesticides. Needless to say, we need more than one alternative. Presently, chemical manufacturers are looking for alternatives, but mosquito control/public health is a very small aspect of the pesticide industry and not a whole lot of resources (money) are being invested. My thoughts are, with all the advancements since the banning of chlorinated hydrocarbons in the U. S., that, somehow, someway, the government and chemical industry could take another, more prudent look at this group of chemical compounds. I would think, applied under the foundation of a structure, basically out of the environment, these products could provide excellent termite control for decades, with one treatment. Also, I would think, chemical science has advanced enough to formulate these compounds in a way that would maintain their safety level to humans, potency to insects, but reduce their ability to persist in the environment so they can’t bioaccumulate. If chlorinated hydrocarbons are not looked at again for pest control it would be an injustice, a penalty against mankind for our reckless use of these products in the past. We need to learn from our mistakes and apply that knowledge for the betterment of mankind.
By the way, DDT is still being used today in Africa, India, and Southeast Asia, saving hundreds of millions of people from the death and misery inflicted by insect-borne diseases. |