Occurrence and Potential Human-Health Relevance of Volatile Organic Compounds in Drinking Water from Domestic Wells in the United States

Article excerpt

Groundwater is used as a drinking-water supply by about one-half of the U.S. population, including almost all people residing in rural areas. As estimated by the U.S. Geological Survey (USGS) (Hutson et al. 2004), domestic wells provide drinking water to about 43.5 million people, representing 15% of the total U.S. population (Supplemental Material, Figure 1, available online at http://www. ehponline.org/members/2007/10253/suppl. pdf). Estimated withdrawals from domestic wells increased by 60% between 1965 and 2000, with an average withdrawal rate of about 3.6 billion gallons per day in 2000 (Hutson et al. 2004). Between 1995 and 2000, domestic withdrawals increased about 6%, and domestic population increased almost 2% (Hutson et al. 2004), indicating increased use of self-supplied drinking water. In addition, estimates by the National Ground Water Association indicate that > 400,000 new domestic wells used for drinking-water supplies are drilled each year in the United States (McCray KB, personal communication).

As the population and demand for safe drinking water from domestic wells increase, it is important to examine water quality and identify contaminants that occur in water from domestic wells. One contaminant group of concern is volatile organic compounds (VOCs), which are contained in many products used around households, including solvents, paints, adhesives, deodorizers, refrigerants, fuels, and fumigants. A VOC is an organic chemical that has a high vapor pressure relative to its water solubility. The chemical and physical properties of VOCs allow the compounds to move between the atmosphere, soil, surface water, and groundwater. Once in the environment, VOCs can be mobilized, dispersed, diluted, volatilized, adsorbed, and/or degraded. Although many VOCs have relatively short half-lives in certain media due to abiotic and biotic degradation, other VOCs can be persistent, degrading little over years or decades. The production of some synthetic organic chemicals (many of which are VOCs) has increased by more than an order of magnitude between 1945 and 1985 (Ashford and Miller 1991). Some VOCs, such as chlorinated solvents, have been used in industry and commerce for almost 100 years (Pankow and Cherry 1996). Once introduced to groundwater, VOCs may persist and potentially contaminate drinking-water supplies.

The U.S. Environmental Protection Agency (EPA) reported that the presence of elevated VOC concentrations in drinking water may be a concern to human health because some VOCs are carcinogens and/or may adversely affect the liver, kidneys, spleen, and stomach, as well as the nervous, circulatory, reproductive, immune, cardiovascular, and respiratory systems (U.S. EPA 2003, 2007a). Some VOCs may affect cognitive abilities, balance, and coordination, and some are eye, skin, and/or throat irritants. The Agency for Toxic Substances and Disease Registry (ATSDR 2007) provides human-health information that is searchable by individual contaminant, and additional information is provided by the U.S. EPA (2003, 2007a, 2007b).

The USGS's National Water-Quality Assessment (NAWQA) Program recently completed an assessment of 55 VOCs in groundwater throughout the United States. A screening-level assessment used in that study compared VOC concentrations to human-health benchmarks for drinking water to aid in understanding the potential human-health relevance of VOC occurrence (Zogorski et al. 2006). VOC concentrations in samples collected before treatment or blending during 1985-2002 from 2,401 domestic wells were compared with human-health benchmarks when available, including U.S. EPA maximum contaminant levels (MCLs) for regulated contaminants and health-based screening levels (HBSLs) for unregulated contaminants (those without U.S. EPA MCLs) (Toccalino et al. 2003). HBSLs, as well as MCLs, are maximum contaminant concentrations that are not expected to cause adverse health effects over a lifetime of exposure (Toccalino 2007). …