Environmental regulation of pollution in the United States is often maligned as costly and ineffective. Pollution continues to plague and degrade the natural resources in the United States, and U.S. waters in particular. Nonpoint source pollution is currently the most significant source of water pollution, but it is also the most unregulated. While other discharges into U.S. waters have been dramatically reduced since the Federal Water Pollution Control Act (FWPCA) was enacted, nonpoint source pollution—caused most by runoff from agricultural operations—has increased.

One of the most fundamental tenets of toxicology is that "the dose determines the poison." This simple phrase provides the basis for the belief that all agents—chemicals and physical phenomena that are capable of producing some effect—have the potential to cause toxicity. Whether toxicity actually occurs is principally a matter of dose: the greater the exposure to a given agent, the more pronounced or severe the response of a cell or organism.