Critical Thinking Discussion

Module 6 - Critical Thinking Discussion 1414 unread replies.1414 replies.

Arguably, the most notable circumstance that factored into the foundation of the modern environmental movement was the discovery and use of dichlorodiphenyltrichloroethane, or DDT, as a broad-spectrum insecticide during World War II. In that conflict, it was used to control mosquitoes, lice, ticks, and fleas, which carried human diseases such as typhus, malaria, and dengue fever. Due it its unparalleled success, DDT was approved for use after the war as not only a commercial pesticide, but also an agricultural one. By the 1950s, DDT was is wide use throughout world, and is cited as being a key factor in reducing human fatalities from insect-borne diseases.

However, it came at a cost.

DDT is hydrophobic compound (difficult to dissolve in water), but also lipophilic (dissolves really well in fats and oils). It is also difficult to breakdown in the environment, taking up to 30 years to break apart on the molecular level. This means that when it soaks into soils and aquatic sediments, it doesn't wash away, and can persist for many decades, allowing any organism that comes into contact with it -- such as fish who eat sediment-dwelling plants and crustaceans -- to cause DDT to accumulate in their tissues. Once DDT enters the food chain, animals higher-up in the food web will collect greater and greater doses of it in a process called biomagnification. 

By the 1960s, the populations of many birds, especially predatory birds, plummeted drastically, as DDT was found to be the cause of a previously-unknown side effect: Birds who had the chemical accumulate in their metabolisms laid eggs that had shells which were too thin to survive to hatching. This side effect was a factor in the drastic decline of North American bald eagles to the point where they became an endangered species in the United States. With DDT being demonstrated as the culprit, numerous other side effects were discovered such as toxicity to shellfish and fish, endocrine disruption in mammals, and cancer in humans. As it happens, the chemical DDT was rushed to market after World War II without much consideration to any long-term affects to humans and the environment.

At the time, concerns about DDT were voiced by naturalists, scientists, and the U.S. government as to the dangers of the chemical and its improper application by those who purchased it. However, it wasn't until 1962 when a naturalist named Rachel Carson published a book entitled Silent Spring that action was taken to limit DDT use. These limits -- and the eventual ban on DDT in the United States -- did not go unchallenged by the chemical industry.  Lawsuits were filed and misinformation was spread, and despite Carson's death in 1964 from breast cancer, the controversy surrounding DDT continues to this day. 

Read:

In the Hunt Library, download and read the article The Wild Life of 'Silent Spring' by Eliza Griswold from the New York Times Magazine (Note: You must be logged into ERNIE to use the Hunt Library). 

Post:

Discuss among your peers the effect of Silent Spring on the government, private individuals, and the chemical industry. Consider the following questions in your discussion: Was Carson qualified to characterize the effects of DDT on the environment? Did she present specific evidence for the effects of DDT? Did she vehemently defend her work against all opposition? Or was she more concerned about how her book would be received? Consider Carson's opposition: What did Carson claim as the reasoning for expanded use of DDT after World War II? Is this reasoning justified? What did chemical manufacturers specifically do after Silent Spring was published? How did Carson view the government's role versus the rights of individuals in DDT and it's application? Did she argue for stricter government controls? What compromise was struck between chemical manufacturers and the government about DDT? How is Carson's book viewed today by her critics? Are they justified in their opinion?

Respond:

Respond to the posts of at least 2 of your fellow classmates in a thoughtful and courteous manner, and stay objective and open-minded with your point-of-view. You are welcome to bring your own opinions into this discussion, but they must be viewed through the lens of science, and you will be graded on how you utilize Critical Thinking Habits-of-Mind in your dialog.