The word pesticide is a catch-all term for chemicals that kill or control anything that humans have deemed to be a pest. Such chemicals can be grouped according to the kind of organism targeted, such as insecticide (insect), herbicide (weed), fungicide (fungus，菌), or rodenticide (rodent，鼠). Most pesticide compounds in use today are synthetic; that is, they are man-made concoctions（混合物）produced in a laboratory. A danger inherent to the use of synthetic poisons is that once the chemicals are released into the environment, they may harm unintended victims and have unanticipated effects.
On a global scale, over five billion pounds of conventional pesticides are used annually. Twenty-five percent of this total volume, or 1.2 billion pounds, is used in the United States alone. Population declines and extensive mortality of birds strongly indicate that the health of the environment and thus the health of organisms that depend on it suffers due to the prevalence of pesticides. From songbird declines beginning in the 1940’s, to population crashes of peregrine falcons, ospreys, and other predatory birds first detected in the 1960’s, to the more recent deaths of over 5% of the world’s population of Swainson’s Hawks during the winter of 1995, birds have been unwitting victims of pesticide contamination.
In 1962, Rachel Carson’s best-selling book, Silent Spring, drew international attention to the environmental contamination wrought by pesticides, particularly the insecticide DDT. Thanks partly to the fervor generated by Carson’s book and partly to a study done by the National Institutes of Health which found DDT or its by-products in 100% of the human tissues it examined, DDT and most other organochlorines（有机氯杀虫剂）were banned for use in the United States in the early 1970’s. Since the ban, numbers of the more severely affected bird species have slowly recovered. However, the fate of some populations of Peregrine Falcons remains uncertain because DDT, its breakdown products, and other organochlorines are still prevalent in the environment.
If DDT was banned in the United States in the early 1970’s, why is there still a problem today? One reason is that the United States continues to export DDT, along with other pesticides known to be hazardous to the environment and to human health. The countries of Latin America, the wintertime destination for many of the migratory birds that breed in the United States and Canada (including many Peregrine Falcons), are also the destination for many of these exported pesticides.
1. One danger of using pesticides is that ______.
2. The use of pesticides leads to all the following except ______.
3. After DDT and most other organochlorines were banned for use in the United States ______.
4. The word “hazardous” in the last paragraph most probably means ______.
