Unintended Consequences

Solutions to environmental problems occasionally create unintended consequences, that is, solving one problem creates another. Scientists and engineers must carefully evaluate potential negative results before implementing new remediation programs. For example, burying wastes in landfills may cause groundwater contamination, incinerating wastes reduces waste volumes but can cause air pollution, and excavating abandoned waste sites as part of a remediation effort may expose workers to contamination. Recycling can have a net negative environmental impact if air pollution associated with transportation outweighs environmental benefits. Stimulating the biodegradation of trichloroethylene (TCE) in contaminated groundwater can lead to the formation of vinyl chloride, a more hazardous chemical. Two examples are described here: MTBE and disinfection by-products.


Methyl tertiary-butyl ether (MTBE) is a fuel additive that has improved air, but degraded groundwater. Its primary use in the United States began in the 1990s as a fuel oxygenate added to gasoline to help meet the requirements of the Clean Air Act. By providing a source of oxygen during gasoline combustion, MTBE reduces carbon monoxide levels. It has been used in a number of localities to help combat significant air pollution problems, and studies have identified important air quality and public health benefits from its use.

Unfortunately, the addition of MTBE to fuels resulted in unintended consequences. MTBE is highly soluble in water and relatively nonbiodegradable. It has been detected in groundwater across the United States, primarily from fuel leaks and spills. For example, the U.S. Geological Survey (USGS) analyzed drinking water information from over one thousand community water systems (CWS) in the Northeast and Mid-Atlantic regions of the United States for the period from 1993 to 1998. MTBE was found in drinking water from 8.9 percent of the CWSs. Levels over 20 μg/l were determined in 1 percent of those same cases. Once introduced to groundwater, MTBE's high solubility makes it very mobile. The U.S. Environmental Protection Agency (EPA) did issue a drinking water advisory for MTBE in 1997. Although there are no data on the effects of drinking MTBE-contaminated water on humans, cancer and other deleterious effects occur in animals at high exposure levels. Furthermore, MTBE has an unpleasant taste and odor.

Disinfection By-Products

Disinfection, one of the primary tools of water treatment, is the removal and inactivation of pathogenic microbes, that is, small organisms such as viruses, bacteria, and protozoa, that can cause disease. Disinfection has historically been accomplished using chlorination, the destruction of microbes by hypochlorous acid and the hypochlorous ion, formed by the reaction of chlorine gas and water or added directly as hypochlorite salts. Large improvements in public health occur when pathogen-free waters are available for human consumption, and significant portion of the life span increase achieved in the modern era is the result of safe drinking water.

However, there have been unintended consequences of disinfection by chlorination. If organic compounds are present in the water, halogenated disinfection by-products (DBPs) may be formed. Two halogenated DBPs regulated by U.S. drinking water standards are trihalomethanes (THM) and haloacetic acids. Both can increase the risk of cancer. THMs can also cause liver, kidney, and central nervous system problems. A USGS study found THMs in the drinking water of 45 percent of some 2,000 CWSs randomly selected in the Northeast and Mid-Atlantic regions of the United States. Fortunately, there are a number of ways CWSs can limit the generation of halogenated DBPs, including using water sources with low organic content, removing organic compounds before chlorination, and using disinfectants that produce fewer or no halogenated DBPs, such as ozone or chloramines.



Grady, S., and Casey, G. (2001). "Occurrence and Distribution of Methyl tert -Butyl Ether and Other Volatile Organic Compounds in Drinking Water in the Northeast and Mid-Atlantic Regions of the United States, 1993–98." Washington, D.C.: U.S. Geological Survey.

U.S. Environmental Protection Agency. (1997). "Drinking Water Advisory: Consumer Acceptability Advice and Health Effects Analysis on Methyl Tertiary-Butyl Ether (MtBE)." EPA-822-F-97-009. Washington, D.C.: U.S. Environmental Protection Agency.

U.S. Geological Survey, Water Resources Investigations Report 00-4228.

Internet Resources

Davis, J. Michael. "How to Avert the Problems of MTBE." Available from http://www.epa.gov/ord .

Reshkin, K. "EPA Student Center." Available from http://www.epa.gov/students .

Jess Everett

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