Have the harmful effects of chemicals on man & ecosystems lessened since Silent Spring was published?
It's a complicated question with no simple answer. I live and work in a very agricultural valley, so this issue is paramount in discussions and regulations about this issue. Since Silent Spring's publication in the 1950s, and with the help of the modern environmental movement that followed, the worst pesticides, including the DDT Carson talks about, have been outlawed.
Strict laws in terms of the handling of pesticides and the training of workers who handle them have made today's system better where that is concerned. The fact there are more types of pesticides isn't in and of itself a bad thing, as they have become more specialized for specific uses and benefits, as opposed to blanket pesticides like DDT. While these chemicals are still dangerous and harmful to the environment, streams and rivers, and wildlife not to mention humans, especially when improperly used, I think you can still say it is better than it was in Carson's time.
Government intervention in the wake of Carson's work was documented. The establishment of the Environmental Protection Agency, or the EPA, was enacted in the Nixon Administration. Its focus was to take up the ecological awareness that was initiated by Carson's groundbreaking work. Along these lines, the establishment of public watchdog environmental groups such as Greenpeace have helped to make environmental protection and ecological awareness issues at the forefront of public dialogue. Indeed, business interests have influenced government monitoring and intervention in the area of environmental treatment, but the issue is so pervasive in our culture and in our schooling that businesses and commercial interests are scrutinized in their interactions with the environment to a level that could not have been foreseen in Carson's time.