PESTICIDES AND INDUSTRIAL ORGANIC CHEMICALS - Marine Pollution: What Everyone Needs to Know - page 102

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Figure 6.1 DDT molecule (in all organic molecules with hexagons, a carbon atom is at each
point of the hexagon)

these, such as DDT, are banned in many countries, but they
nevertheless persist in marine sediments. In some countries
they are still used and continue to run off into aquatic envi-
ronments. Organochlorine chemicals (mostly DDT-related
pesticides, PCBs, and dioxins) have been studied intensively
for decades. Dichlorodiphenyltrichloroethane (DDT) (Figure
6.1), the most powerful pesticide the world had ever known,
can kill hundreds of different kinds of insects.
Its ability to kill insects was identified in 1939 by the chem-
ist Paul Müller, who won the Nobel Prize for Physiology and
Medicine. DDT was used in World War II to clear South Pacific
islands of malaria-causing insects, and was used as a delous-
ing powder. When it became available for civilian use it was
considered a marvel, because it could be applied as a pow-
der on the water in relatively small amounts and would keep
killing mosquito larvae for months after only one application.
It could kill all kinds of insects, was not particularly toxic to
humans, and enjoyed great success until the development of
resistance by both mosquitoes and eventually the public. DDT
and related chemicals are fat-soluble and highly persistent.
Insect populations can develop resistance because not all of
the insects are killed when they are sprayed by the chemical.
The few remaining resistant individuals breed, and their off-
spring are also more resistant to the chemical, an example of
selection—evolution—at work. The insects eventually become