Silent Spring: Chapter 4 Summary & Analysis

Water has become the most precious natural resource in this modern age, but humanity is indifferent to and unaware of the dangers facing this environmental system. There are many kinds of pollutants affecting the water supply, but it is the mixture of these chemicals that is particularly threatening, since the interactions between these chemicals are poorly understood. Rolf Eliassen, a professor at M.I.T. testified to this effect at a congressional hearing on water purity, warning those assembled that we do not know what is in our water.

Insecticides are being applied directly to water systems, or indirectly via aerial spraying that then becomes mixed in with agricultural runoff water, making these systems toxic to fish. Further, discoveries of DDT traces in fish upstream of contamination or spraying sites suggest that once these chemicals get into the groundwater that the groundwater transfers the chemicals all throughout the system. This means that all water is threatened by contamination anywhere.

Chemicals from agricultural runoff have been found to contaminate drinking water even after the runoff has passed through water purification plants. Chemists have little understanding of what chemical combinations might be reaching the public, how to test for them, or what their effects might be.

Carson recounts the story of a farming district in Colorado contaminated by chemicals that had leached into the water table from the Rocky Mountain Arsenal—a factory that produces pesticides—located several miles away. Over seven or eight years, these chemicals had traveled through the groundwater to pollute local wells. Most alarmingly, wells tested positive for a synthetic chemical called 2,4-D, a weed killer that had apparently formed spontaneously in when certain chemicals combined, independent of human oversight.

In another example, at key wildlife refuges in Oregon and Northern California, agricultural runoff of DDD and DDE caused mass poisonings of migratory birds within ‘protected’ zones. The poisons were passed up the food chain from plankton to waterfowl, as fish that ate infected plankton accumulated a larger dose, and waterfowl that ate infected fish concentrated the poison within their own bodies further still. This process in which poisonous chemicals become more focused as they move up the food chain, is known as bioaccumulation or biomagnification, and is particularly dangerous because of its impact on humans, who are often at the top of the food chain.

In Clear Lake, California, fishermen chose to dose ‘gnat-infested’ waters with DDD, even though the gnats were not especially harmful. Despite ‘careful planning’, the operation had to be repeated, and the following winter revealed that other species had been affected. The western grebe, a bird of “spectacular appearance,” died out completely in the area, having eaten fish that had in turn eaten infected gnats and plankton, again accumulating increasingly concentrated doses of the chemical. Because the chemicals had passed from the lake into the tissues of its inhabitants, initial tests of the water had suggested that it was safe.

Carson questions the wisdom of using substances with such strong biological effects that can impact the drinking supply. Dr. Hueper has warned that cancer hazards in public drinking water are increasing, and there is evidence to support his claim. The complex, interconnected nature of the water system, especially, supports Carson’s claim that “in nature nothing exists alone.”