Biomedical Engineering Reference
In-Depth Information
CHAPTER 2
DEHALOCOCCOIDES AND REDUCTIVE
DECHLORINATION OF CHLORINATED SOLVENTS
Frank E. L¨ffler, 1,2 Kirsti M. Ritalahti 1,2 and Stephen H. Zinder 3
1 University of Tennessee, Knoxville, TN 37996; 2 Oak Ridge National Laboratory, Oak Ridge,
TN 37831;
3
Cornell University, Ithaca, NY 14853
2.1 INTRODUCTION
2.1.1 The Chlorinated Ethene Problem
Since the beginning of the twentieth century, short-chain C1 to C3 chlorinated aliphatic
hydrocarbons (CAHs) have been manufactured in large amounts and extensively used in
industrial, military, agricultural and household applications. The widespread use of CAHs is
based on their desirable properties including low cost, easy availability, excellence as solvents,
chemical stability and fire safety (i.e., most chlorinated solvents are nonflammable and do not
form explosive mixtures with air). The widespread use, careless handling and storage, igno-
rance of health effects and environmental dangers, and the lack of regulations over decades of
extensive use led to wide-ranging groundwater contamination.
Exposure to CAHs is of public concern because these chlorinated chemicals are toxic,
several are classified as potential human carcinogens and some, such as vinyl chloride (VC), are
proven human carcinogens (IARC, 1995 ; Kielhorn et al., 2000 ). Today, the United States
Environmental Protection Agency (USEPA) and Occupational Safety and Health Administra-
tion (OSHA) enforce stringent regulatory standards to protect humans from CAH exposure
through contaminated drinking water and other routes (e.g., inhalation). After recognizing the
dangers that CAHs pose in the environment and to human health, handling and use practices
improved so that uncontrolled release has been eliminated in most countries. Although acci-
dental spills of CAHs remain a risk, the majority of CAH sites were contaminated decades ago.
Table 2.1 lists CAHs that were, or still are, being used in industrial, military, agricultural and
household applications, and are commonly encountered at contaminated sites.
The total amount of chlorinated solvents used worldwide in 2002 was approximately
764,000 metric tons ( www.eurochlor.org/ ; accessed June 19, 2012); however, exact amounts
are difficult to obtain, partly because some solvents are co-produced in a single process or are
chemical intermediates, and furthermore not all countries report reliable production numbers.
In 1980, about 282,000 tons of perchloroethene (PCE; also termed tetrachloroethene) was used
in the United States, but the demand declined to approximately 168,000 tons in 2007 (Table 2.2 ).
This decline reflects the much more efficient use of PCE (e.g., reduced evaporation losses,
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