The Atmosphere as a Source of Water-Soluble Volatile Organic Compounds Found in Urban Streams

摘要

Volatile organic compounds (VOCs) are frequently detected in surface waters of theUnited States. To reduce their occurrence in urban streams, it is imperative tounderstand the sources of these pollutants. The atmosphere is a potential source ofselected water-soluble VOCs in urban streams and was investigated in this study. Airand surface-water VOC data collected during 1996 to 2002 from 10 monitoring sitesfrom the U.S. Geological Survey's National Water-Quality Assessment (NAWQA)Program were examined. These sites were selected to evaluate the potential for directtransport of VOCs from the atmosphere to urban streams. Concurrent samples (airand surface water) were collected from eight sites, but two sites had available datathat were compared based on the closest sampling dates. Analytical results of 87VOCs were screened by evaluating the occurrence and concentrations in both air andsurface water using defined categories, and equilibrium concentrations in surfacewater C_w~s were calculated based on the measured air concentrations. Four VOCs(acetone, methyl tert-butyl ether (MTBE), m- and p-xylene, and toluene) were in thecategory of detected in more than 20 percent of surface-water samples and in morethan 10 percent of air samples, with at least 10 percent of C_w~s concentrations greaterthan the aqueous long-term method detection level (LTMDL). One VOC, benzene,was in the category of detected in more than 20 percent of surface-water samples andin more than 10 percent of air samples, with at least 2 percent of the C_w~sconcentrations greater than one-half the aqueous LTMDL. Six VOCs (chloroform,methylene chloride, perchloroethene, p-isopropyltoluene, 1,1,1-trichloroethane, andtrichloroethene) were in the category of detected in more than 20 percent of surfacewatersamples and in more than 10 percent of air samples, with less than 1 percent ofC_w~s concentrations greater than one-half the aqueous LTMDL. Five VOCs wereidentified as having the atmosphere as a possible source of contamination to smallurban streams: acetone, benzene, MTBE, m- and p-xylene, and toluene. Of thesefive VOCs, acetone, benzene, and MTBE were consistently in equilibrium with theatmosphere. Depending on the site and season, the atmosphere can serve as aprobable dominant source for VOC contamination in urban streams.