Milestones in Biology 6 Test Your Knowledge
On the origins of DDT:
a. When was the chemical DDT first widely used, and what was its intended purpose?
b. How effective was it for that purpose?
a: DDT was intended to combat insect-borne diseases, specifically typhus and malaria, among U.S. soldiers during World War II. b: It was very effective, saving the lives of countless soldiers.
On the mechanism of DDT:
a. How does DDT kill insects?
b. How does DDT harm top predator birds?
a: DDT is toxic to the nervous systems of insects. b: It accumulated in organisms up the food chain, and the high concentrations in top predator birds caused reproductive failures—the thinning of eggshells to the point that the eggs were easily crushed before the chicks hatched.
What is biomagnification?
The process by which chemicals (particularly toxic chemicals) increase in concentration with each trophic level. Organisms at the lowest trophic levels have the lowest concentrations and organisms at the highest trophic levels have the highest concentrations.
PCBs (polychlorinated biphenyls), a type of chlorinated hydrocarbon, were used for a variety of purposes (including electrical insulation), until their use was banned in 1979. A 2000 survey of top predator fish in the Great Lakes showed that the concentration of PCBs in these fish ranged from 0.8 to 1.6 ppm. The wildlife protection value (the concentration that should not be exceeded in order to protect the safety of wildlife) is 0.16 ppm. How could there be such high levels of PCBs in top predator fish 21 years after PCBs were banned?
Like DDT, PCBs are very stable in the environment, and degrade only very slowly. Even though they have not been used for decades, they are still present in the environment, and can still magnify up trophic levels.
In 2013, a group of beekeepers launched a lawsuit against the EPA concerning the use of neonicotinoid pesticides and possible unintended impacts on honey bees (see Chapter 22). From what you have read here, what kinds of testing would you want the EPA to require before approving a pesticide applied widely to crops such as corn or soybeans?
Some of the questions to consider and test include: Do the pesticides leave a residue on the plants or in the environment? Are humans, other animals, or nontarget insects affected by exposure to these pesticides even at low levels? How long does it take for the pesticides to degrade? Do the pesticides accumulate in tissues of nontarget insects, wildlife, or humans? If the pesticides accumulate, what are their impacts on the health and behavior of nontarget insects, wildlife, and humans, in both the short term and the long term? If there are any toxic effects, are these reversible with treatment?