DDT Time Lapse Sequence
One of the most effective, if deadly, pesticides, this organochlorine insecticide is certainly the most historically significant, due to its effects on the environment, agriculture, and human health. Although banned in the United States and many other countries around the world since the 1970s, humans and animals in the United States are still exposed to DDT and its derivatives because it continues to be manufactured and applied in underdeveloped nations where some of North America's food supply is grown.
In her landmark 1962 environmental book Silent Spring, Rachel Carlson, a former federal marine biologist, wondered rhetorically where all the songbirds had gone. She clearly placed the blame on the insecticide DDT, and so set the world's stage for the environmental movement. The first chlorinated organic insecticide to be synthesized, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane, or DDT, was highly effective at eradicating disease-laden mosquitoes responsible for huge outbreaks of malaria, as well as human lice that carried typhus.
First synthesized in 1873 by a German biochemistry graduate student of Adolph von Bayer, Othmar Zeidler, it was not until after 1939 when Swiss Nobel Prize Laureate Paul Muller of Geigy Pharmaceutical discovered the effectiveness of the synthetic chlorinated hydrocarbon as an insecticide, that commercial production skyrocketed. During World War II through its ban in 1973, this inexpensive but highly effective insecticide may have saved more than 25 million people from fatal diseases. DDT (molecular weight of 355) disrupts the delicate ionic balance between sodium and potassium within an insect's neurons, leading to paralysis and death.
The properties that make DDT a highly effective insecticide also make it the bane of ecological and human health. It is fat-soluble, bioaccumulates, and once in the food chain, grows to concentrations many times greater than the applied or ambient concentrations (biomagnification). In populations of bald eagles and peregrine falcons, piscivorous birds at the top of the aquatic food web, concentrations reached critical levels that resulted in behavioral anomalies and eggshell thinning that led to complete reproductive failure. The manner in which biomagnification functions is through a compound's persistence in a relatively unaltered form, allowing it to be passed to higher levels in a food chain. Initially, aquatic insects feeding on other aquatic invertebrates and algae concentrated DDT at levels greater than those found in the water column and sediments. Insectivorous fishes, including small minnows and larger species such as the Great Lakes whitefishes and trouts, accumulated an increased concentration in their fatty tissues (not necessarily fatal to them), as the DDT moved up another rung in the food chain. The fish-eating bald eagles and osprey feasted on these pesticide-laden "time bombs", concentrating the fishes' lifetime accumulation of DDT in their fatty tissues, and passing along a portion to their embryos and the yolk that provided the embryo's nourishment while in the egg. People consuming fish were also accumulating at least a portion of each fish's lifetime dose of the toxic organic compound and its metabolites, DDE (1,1-dichloro-2,2-bis(chlorophenyl)ethylene) and DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane).
Although banned in the United States and many other countries around the world since the 1970s, people and animals in the U.S. are still exposed to DDT and its derivatives because it continues to be manufactured and applied in underdeveloped nations where some of the U.S. food supply is grown. Additionally, migratory species of Neotropical birds, and far-ranging fish species such as mackerel and tuna, as well as the winds, carry the toxic contaminant from areas of use into other environments.
DDT Time Lapse Sequence #1
A time-lapse sequence of 18 images acquired using polarized illumination illustrates the growth of spherulitic crystallites from the melt. Their formation is restricted at the edge of the melt region where a different crystal structure occurs.
DDT Time Lapse Sequence #2
A number of large highly birefringent spherulites form from the melt and merge in this 30-image time-lapse sequence.
DDT Time Lapse Sequence #3
Multiple large spherulites, exhibiting violet to blue birefringence, grow and fill the viewfield in a sequence of 23 time-lapse images.