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Volatile organic compounds (VOCs) are organic compounds with chemical and physical properties that allow the compounds to move freely between water and air. Many products contain VOCs including fuels, solvents, paints, glues, adhesives, deodorizers, refrigerants, and fumigants. Because of human-health concerns, many VOCs have been the focus of national regulations, monitoring, and research during the past 10 to 20 years. The selection procedure for VOC target analytes for emphasis in the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program, completed in 1994-96, involved three sequential phases: (1) initial selection and preliminary screening of 130 candidate compounds on the basis of available information; (2) laboratory studies to ascertain the feasibility of analysis by purge-and-trap gas chromatography/ mass spectrometry; and (3) analysis of groundTvater, surface-water, and quality-control samples to ascertain the performance of laboratory methods on environmental samples. Preliminary screening considered several factors including: (1) physical properties; (2) human cancer rating; (3) noncancer human-health risk; (4) toxicity to freshwater aquatic organisms; (5) occurrence data for VOCs in ground water, surface water, and drinking water; (6) potential for atmospheric ozone depletion; (7) bioconcentration in aquatic organisms; and (8) use or potential use as a fuel oxygenate in gasoline. As a result of the selection procedure, 55 VOC target analytes were identified for additional study including 21 halogenated alkanes, 10 halogenated alkenes, 3 aromatic hydrocarbons, 9 alkyl benzenes, 6 halogenated aromatics, 4 ethers, 1 aldehyde, and 1 nitrile. Of the 55 VOC target analytes, 29 have a national enforceable drinking-water regulation; 28 are classified as known, probable, or possible human carcinogens; 35 have noncancer humanhealth effects; and 33 are known to impart taste and odor to water. For the protection of freshwater biota, 33 of the 55 VOC target analytes have water-quality guidelines established by the U.S. Environmental Protection Agency, and 17 have water-quality guidelines established by Environment Canada. Important physical, chemical, and biological properties governing aquatic behavior and fate of the VOC target analytes include: aqueous sc Nubility, vapor pressure, Henry's law constant, octanol-water partitioning coefficient, sorption coefficient, half-life, and bioconcentration factor. This report (1) describes the step-by-step procedure used to select NAWQA's VOC targe* analytes, (2) lists the VOC target analytes, and (3) provides human-health criteria, drinking-water regulations, aquatic toxicity criteria, and other information on each target analyte. Abstract

Selection procedure and salient information for volatile organic compounds emphasized in the National Water-Quality Assessment Program