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READING PASSAGE (3 minutes)
DDT is a human-manufactured chemical once used to control the spread of unwanted insects. It was used during World War II to kill mosquitoes carrying dangerous human diseases, and afterwards to get rid of agricultural pests. Over time, however, scientists discovered that DDT did much more harm than good.
DDT, although designed to protect humans and plants from disease- carrying insects, is itself a hazard to the environment. It accumulates in the soil and in small bodies of water and is then ingested by animals such as fish and birds. Because DDT is not easily digested, it gets stored in the body and builds up over time. Too much DDT can poison and even kill wildlife. It is, for example, a major factor in the decline of the bald eagle.
DDT also endangers the health of humans who consume produce sprayed with DDT Studies have shown that exposure to DDT increases the risk of diabetes, birth defects, and various forms of cancer. The effects of DDT consumption were found to be so severe that the United States eventually banned the chemical.
Finally, DDT has failed to effectively combat disease-carrying mosquitoes, and thus diseases like malaria continue to spread. Not long after DDT was first introduced on the market, mosquitoes began developing a resistance to the chemical. It was not long before mosquitoes could once again easily transmit deadly diseases.
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LECTURE TRANSCRIPT
First of all, DDT can, in some cases, benefit plants and animals. Yes, DDT, when consumed in extremely large quantities, will impair, or even kill, an animal. But in smaller quantities . . . which is how it was most often found to be in environment… it mostly just kills insects, which can spread diseases from plant to plant or animal to animal. Insect-born diseases have been known to wipe out huge populations of species. And so, by preventing insect populations from escalating, DDT prevents certain animal and plant populations from shrinking.
DDT can also benefit human health. Again, DDT can be toxic if you ingest it in large quantities, but even the World Health Organization considers it only "moderately hazardous." Which means that in smaller quantities, DDT doesn't really do much at ail if you happen to ingest it. Sure, there are studies that show a correlation between DDT and things like cancer or reproductive disease, but many of these studies are inconclusive. What DDT does do, though, is kill the insects that spread deadly human diseases, like malaria or typhus. Such diseases have far more devastating effects on human health than DDT ever had. So by reducing their spread, DDT in fact improves public health.
Lastly, DDT has effectively combated diseases; particularly malaria, in the past. Although some mosquitoes have now developed a resistance to DDT, there are many cases in which it successfully wiped out the disease. Sri Lanka, for example, had 1.5 million cases of malaria between 1934 and 1955; 80,000 people died. The year after country completed an intensive anti-mosquito program using DDT, only seventeen cases were reported. Since then, millions of lives have been saved because of the widespread use of DDT.
