The Beginning of the Synthetic Era
In the 20th century, several things changed. The World's population grew exponentially (as is its habit), and more food was needed to feed everyone. The World Wars occurred, and many scientific efforts were directed to the creation and dispersal of weaponized chemical agents. This research eventually led to the making of synthetic pesticides.
Now times really began to change. Scientists were able to make specific pesticides directed at specific organizations, such as algicides, bactericides, fungicides, and insecticides. While in many ways these were safer than the general poisons farmers used before, the new pesticides also tended to be much more powerful, and sometimes misdirected.
An excellent example of these early pesticides is the infamous DDT (dichlorodiphenyltrichloroethane), which showcases both the benefits of these new pesticides and their inherent dangers. When DDT was first invented by a Swiss chemist, it was found to be inexpensive (a huge plus), potent specifically toward insects, long-lasting, and insoluble. Soon it was being used to rid homecoming soldiers of lice and clear up mosquito/malaria problems in multiple nations.
Only later were the detriments of DDT investigated and made popular by Rachel Carson's "Silent Spring". Specifically, the pesticide was found to be toxic to a wider range of animals than previously thought, including most importantly young fish and crabs. Because of DDT's synthetically induced insolubility, it also had a habit of sticking around—permanently. Scientists were able to find evidence of DDT bioconcentration in the tissues of animals, increasingly more in larger animals such as large fish and the osprey feeding on them. While there were few visible effects on the environment or the food chain, scientists determined that there prolonged use of DDT could pose significant dangers.