A vast array of chemical compounds are in wide commercial use in the United States, and the potential ecological and human-health effect of exposure to chemical mixtures has been identified as a high priority in environment health science. Awareness of the potential effects of low-level chemical exposures is rising. The U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, conducted a study in which samples were collected from 38 streams in 25 States to provide an overview of contaminants found in stream water across the Nation. Additionally, in this study, biological screening assays were used to help determine any potential ecological or human-health effects these chemical mixtures could cause. Details are provided on the sampling methodology, analytical methodology, quality assurance procedures, and an extensive appendix provides details for each sampling site. Some of the highlights of the book include: US Geological Society and US Environmental Protection Agency collaborative report on the chemical composition of contaminants in US streams, 38 US stream waters in 25 states sampled and tested, Methodology, procedure, and sampling details are described, Physical parameters and inorganic results recorded on field sheets for each site, Over 60 references cited for further research