Thomas A. Weil Universitv of Chicago Ch cogo, ino's 6C637 Barbara Q. Weii Chicago State University Chicago, Illinois 60621 Bernard D. Blauslein University of Pittsburgh Pittsburgh, Pennsylvania 15260
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Chemistry- for Nonscientists
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The case of DDT
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Previous articles in this Journal and other journals (1-7) have described new approaches to the education of nonscience students in chemistry. For this group of students, interest and enthusiasm are often lacking. It is essential, therefore, to try to show students, very early in the course, why they should study science. Our highly technological society is faced with many problems; for some of these science will play an important part in working out the solutions. However, students must realize that science cannot solve these problems alone. Economic, social, and political considerations are all part of any solution and nonscientists must better understand these kinds of complex problems. Our introduction to chemistrv for nonscientists discusses one example, the case of DDT. The early successes miracles" in the use of DDT show how "technoloev-borne -. occur. This "miracle," however, caused major problems which went unchecked for a long time. The use of DDT exemplifies the difficulties involved in correcting adverse effects of a procedure once it is established and widespread. Our discussion of DDT is not meant to be the definitive study of DDT; however, the subject is covered in sufficient detail to allow the instructor to emphasize the complex relationships between science and society. Development of DDT 1874 Preparation of DDT reported by 0.Zeidler (8) as part of his PhD thesis. 1939 Potato cmp in Switzerland threatened by Colorado potato beatle. Swiss entomologists tested a number of chemicals and found dichlorodiphenyltrichloroethane (DDT) to he mast effective. 1942 Geigy Company of Switzerland sent samples of DDT to U. S. and American scientists began working with DDT. 1943 The U.S. began large scale manufacture of DDT for use by Armed Forces to combat typhus and most notably malaria. 1945 US. War Production Board released DDT for civilian use. Worldwide use of DDT began with special emphasis on eradicating malaria (9, 10). DDT especially applicable because it was inexpensive. long lasting, easily applied, and nontoxic to people and domestic animals. The effectiveness of DDT for malaria cantml is typified by data for Ceylon: 1.5 million cases and 80,000 deaths resulted from malaria in 1934-35. As a result of widescale use of DDT only 17 cases were reported in 1963 for the entire country. When application of DDT was discontinued, malaria increased and over 600,000 cases were reported during 1968 and the fint quarter of 1969 (11). Further data showing effective use of DDT to control malaria is eiven in reference (121. 19Ai Agrwultural Use: Hemuse it was low in cost, enay to apply and eiferrirc agninsr many ditfcrcnr insert prats \rtdeiprcad use of I)IYI' in nrrirulrure was begun. l'herr ia a good corrclation between pesticide usage and agricultural yield, as shown in the table. However, there are disturbing relationships: Japan which has 2.1 times the yield of food per acre as does the U. S.. uses 7 times as much oesticide. The U. S.. wit" 2.1 limes the yield GI fwd per ark as the average fo; Indin and Afrwa, u i c r 11 1tmt.r asrnurh pcst~t&. 198
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1948 Dr. Paul Mueller received the Nobel prize in medicine for the discovery of the effects of DDT as an insecticide. Problems Associated with DDT Use Chemical Stability DDT's half-life is several years; it resists chemical breakdown by air, water, sunlight, and microbes in the soil; i.e., it is a "hard pesticide." (However, recent reports (13) discuss the photochemical degradation of DDT.) DDT has been found practically everywhere; it has been carried by wind and ocean currents to all parts of the earth and is found in water, air, fish, wildlife, the food we eat, and the human body (14-17). Biological Magnification (16) DDT is not very soluble in water; a saturated solution contains only about 1 x 10-7% DDT (1 ppb). DDT is soluble in fatty materials and is thus concentrated in the fatty tissues of living creatures. Plankton and algae: generally 1 X 10-8-1 x DDT (concentrations 10-100 times t h a t of DDT in water). Small fish, shrimp, clams, etc., herbivores: generally 2 x 10-5-1 x DDT (0.2-1 ppm). Larger fish, carnivores: generally 3 x 10-'-6 x DDT (3-6 ppm) but much higher concentrations have been reported. Flesh eating birds a t the top of their food chain, i.e., gulls, hawks, ospreys, and eagles: general(10-100 ppm) DDT (16). A decline ly 1 x 10-3-1 x in population of these flesh-eating birds has been attrihuted to this high DDT concentration. The effect is not direct killing of adult birds, but drastic reduction in reproduction. I n general, fewer eggs are laid in a mating season and the eggs have thin shells. Scientists believe that DDT inhibits the way in which calcium is metabolized in forming the usually strong material of the egg shell (18). Pesticide Resistance When DDT, or any other insecticide is first used on a specific insect population, as many as 99% of these insects are killed. However, a few remaining resistant individuals are able to reproduce almost without competition (16). Since insects breed a t the rate of several generations a year, a resistant population of insects may soon become Pesticide Usage and Agricultural Yields in Selected World Arear Area or Nation
Pesticide Use Wheetare) (2.47 acres)
Yield (kg/h&le)
-n'rsk~n f r m . "Man's Impact on the (;lobel Env!mment." Yas?arhurrrs cnmh:dgs, nlnunchua~tla,1870. p. 119.
~ n a t ~ t uuf'l'whnulwy tr PI-.
abundant. Two years after DDT was first used in Sweden (1946), resistance of the housefly was reported (10). Thirty-eight different species of malaria-carrying mosquitoes have become resistant to insecticides (9), and throughout the world over 200 species of insects are now known to be resistant to one or more types of insecticides. Early Warning o l Adverse Effects 1945 1946
DDT was shown to be toxic to certain animals, especially frogs, snakes, crayfish, and fish 110). Clarence Cottam and Elmer Higgins of the Fish and Wildlife Service wrote of the possible dangers of DDT use to certain beneficial insects, fish, and other wildlife (14).
Large numbers of birds were killed as a result of spraying DDT on trees that had Dutch Elm disease (10). A warning by the National Audubon Society that DDT and other insecticides are harmful to birds and other beneficial animals (19) was issued. 1949-62 Many other reports warning of the dangers of DDT appeared; however, very little attention was paid to these until 1962 (20). 1962 Publication of "Silent Spring" by biologist Rachel Carson. Following this publication more and more attention was given by scientists, the general public, government agencies, legislators, and the courts to the many important questions involved in pesticide use.
1949
Limiting the Use of DDT
As evidence of the hazards of insecticides, as well as their limitations, has been gathered, there have been increasing demands to limit their use. After much debate on the subject, in June 1972, William D. Ruckelshaus, then head of the Environmental Protection Agency (EPA), banned the use of DDT in the United States, effective DeCemher 31, 1972, except for public health emergency, if needed. In his report, he said that (21, 22)
What is needed are safe, effective alternative methods of insect control. Some progress has already been made in the development of such alternative methods (23-33). Most of these alternatives to chemical pest controls use techniques of biological pest control, such as insect predators that prey on other insects, parasites and pathogens that infect specific insect pests, the use of induced sexual sterilitv and genetic defects as a means of controlling insect populations, and the development of insect resiitant crop varieties. Until such time as these are generally available, it is felt by most that we are not yet 6 a position to completely stop the use of chemical pesticides. The preceding account is the type of introduction that we have found to he quite successful in chemistry for nonscientists. The case history of DDT is a scientific "story" that the average student is interested in and can appreciate. It is important to the student personally and requires no previous knowledge of chemistry. With this beginning for the type course we have described, we go to other examples: air pollution, water pollution, the energy shortage, etc., integrating with them the basic chemistry needed for an intelligent and informed discussion. Throughout a course of this kind, it is our aim to point out to the students why they should be familiar with the basic ideas of science. and because of our technoloeicallv oriented society, how they as citizens will be invorved in many science related decisions. This introduction helps to develop manv of our goals in the course and to erase the attitude held h i many students that "it is not necessary to study science." Literature Cited
mum "representation of modem chemistry" tor nonaciance major chemistry
The risks to the environment from continued use of DDT in massive auantities are . . . clearlv established. There is no doubt that DDT runoff (mto streams and rivers) can cause contamination of waters, and, given its propensity to volatilize and disperse durmg application, there is no assurance that even curtailed usage . . . will not continue to affect widespread areas beyond the location of application.
He also said that (22) The evidence of record showine storam (of DDT and its metabolitear in man and m a w ~ i w a t m nin t h e f o d cham i. a naming torhr prudtnr rhat m-m ma) h< cxyos~n: h m 4 l t o s wbstnnre rhnr may ulrimnrely have ieriuusefterrion hm hcslth.
In his report i t was noted that there is a possibility that DDT can cause cancer in man, although evidence is inconclusive. Near total or total bans on DDT have been enacted in manv countries. includine. Denmark. New Zealand, wede en; USSR, and ~ e r m & y . Many "nderdevelooed countries of the world. however. cannot do without DDT. These countries still use it, ess&tially because they have no practical, economic choice. Faced with the conflicting consequences of both using and banning DDT and other similar agents, we must find other means of controlling insects and diseases.
Enuirnnmenf." Zlafional Academy af ~ydroearbons 'Ln the M& Sciences. Washineton. D. C.. 1971. 1151 "Man's Impact on the Global Environment," Massachueattr Institute of Technologv P ~ J I Cambtidge, . Masaehusetrs, 1970. 1161 Wagner, R. H.. "Environment and Man." W. W. Norton and Co., New York. (141 'Thl&;ed
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117) Ferwson.O.E..Enuimn.. 14!6).30!1972). 1181 Rakall. P.D., Sci. A m e r , 222, 72 (1970). (191 NewYorkTimes,p.24,May2,119491. 1201 Carson, 8.."Silent Spring," Houghton Miflin Co., NewYork, 1962. 121) U.S. Neus and WorldRegorl. 72.75 IJune 26, 1972). 1221 Gilierte. R..Srienra, 176, 1313 11972). (231 1rving.G. W.. Science, 168, 1119 11970). (241 Miller.S.,andKnapp.C., Environ.,Sri. Terho1.,5,398(19711. 1251 a an in the ~ i u i n g~ n u i r o n m m t . " he ~nstituteof ~ c o l o g yR e p * of the workshoo on Global Ecoloeical Problsms. 1971.
my ofScipncer. Washington. D.C.. Msrch 1973. (33) Archan-Treiehd. J., ScienceNews, 104.40 (1973).
Volume 57, Number 3, March 1974
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