Because of the vast number of trace pollutants and ECs and the breadth of literature on the occurrence, use, and toxicity it is difficult for regulators to evaluate pollutants that pose the greatest risk to human health scientists to improve treatment techniques for higher priority pollutants and the public to modify consumption patterns. Many trace pollutants and ECs are not considered priority pollutants of concern because they are not analyzed in standard water sampling protocols, they are below detection limits of existing analytical techniques, their occurrence in the freshwater environment is not well documented, or their toxicity is not established.