GLOSSARY - Bioaugmentation for Groundwater Remediation - page 364

Dehalogenase ‐ Enzyme catalyzing the loss of a halogen (chloride, fluoride, etc.).

Denature ‐ A structural change in macromolecules (such as DNA) caused by extreme
conditions such as high temperatures.

Denaturing gradient gel electrophoresis (DGGE) ‐ A form of electrophoresis that uses a
chemical gradient to denature the sample as it moves across an acrylamide gel. Commonly used
to separate DNA or RNA into smaller fragments.

Dense nonaqueous phase liquid (DNAPL) ‐ A liquid that is denser than water and does not
dissolve or mix easily in water (it is immiscible). In the presence of water, it forms a separate
phase from the water. Many chlorinated solvents, such as TCE, are DNAPLs.

‐ The lowest concentration at which a chemical can reliably be detected.

Detection limit

Dichloroethene (DCE) ‐ An organochloride solvent, also known as dichloroethylene, with
the molecular formula C 2 H 2 Cl 2 . DCE is found as three different isomers: 1,1-dichloroethene;
cis -1,2-dichloroethene; and trans -1,2-dichloroethene.

Diffusion ‐ Dispersive process resulting from the movement of molecules along a
concentration gradient. Molecules move from areas of high concentration to areas of low
concentration.

Dilution ‐ The combined processes of advection and dispersion resulting in a net dilution of
the molecules in the groundwater.

Dispersion ‐ The spreading of molecules along and away from the expected groundwater
flow path during advection as a result of mixing of groundwater in individual pores and
channels.

Electron acceptor ‐ Compound that receives electrons (and therefore is reduced) in the
oxidation-reduction reactions that are essential for the growth of microorganisms and for
bioremediation. Common electron acceptors in the subsurface are oxygen, nitrate, sulfate, iron
and carbon dioxide. Chlorinated solvents (e.g., TCE) can serve as electron acceptors under
anaerobic conditions.

Electron donor ‐ Compound that donates electrons (and therefore is oxidized) in the
oxidation-reduction reactions that are essential for the growth of microorganisms and
bioremediation. Organic compounds (e.g., lactate) generally serve as an electron donor
during anaerobic bioremediation. Less chlorinated solvents (e.g., VC) can also serve as
electron donors. Hydrogen generated in fermentation reactions also can serve as an electron
donor.

Enzyme ‐ A protein created by living organisms to use in transforming a specific compound.
The protein serves as a catalyst in the compound's biochemical transformation.

Ex situ ‐ Latin term referring to the removal of a substance from its natural or original
position, e.g., treatment of contaminated groundwater aboveground.