Term

Definition

AAM

American Academy of Microbiology.

Abiotic

Not Living.

Acidophile

Organism that prefers acidic conditions (pH as low as 1 standard unit).

Acidotroph

Microorganism that is able to flourish in very acidic (pH <3.5) conditions. Many are aerobic and function over relatively narrow pH ranges.

Activation Energy

Amount of energy required to bring each molecule in one mole of a substance to their reactive state at a given temperature.

Adaptability

The ability of microorganisms either as individual strains, or as a consortium, to adapt to function in some way within a given environment. Often there is a lag (induction) time before this activity commences.

Adaptation

Change in an organism or population of organisms by which they become better suited to the environment. Adaptation can be genetic and/or physiological.

Advection

The process by which solutes are transported with the bulk motion of flowing groundwater.

Aerobe

Organism that grows in the presence of molecular oxygen.

Aerobic

An environment with a partial pressure of oxygen similar to normal atmospheric conditions.

Aggressivity

The state in which an organism is active and able to compete with other strains for space, nutrients, water and gases.

Alkalophile

Organism that prefers alkaline conditions (pH as high as 10.5 standard units).

Alkane

A non-aromatic saturated hydrocarbon with the general formula CnH(2n+2).

Alkene

An unsaturated, open chain hydrocarbon with one or more carbon-carbon double bonds, having the general formula CnH2n.

ALS

Advanced Light Source.

Anabolism

The process in which energy is used to build organic compounds (e.g., enzymes, nucleic acids) that are necessary for life functions. Energy is derived from catabolism, stored in high-energy intermediate compounds such as adenosine triphosphate (ATP), guanosine triphosphate (GTP) and acetyl-coenzyme A, and used in anabolic reactions that allow a cell to grow.

Anaerobe

An organism that only grows in the absence of molecular oxygen.

Anaerobic

An environment lacking molecular oxygen.

Anaerobic Respiration

Respiratory process by which certain bacteria use inorganic TEAs other than molecular oxygen for energy-yielding oxidative metabolism. Nitrate reduction is an example of anaerobic respiration.

Anoxic

Habitat devoid of molecular oxygen.

Anthropogenic

Derived from human activities.

APS

Advanced Photon Source.

Aquiclude

Very low permeability hydrogeologic unit that effectively stops groundwater flow.

Aquifer

Permeable water-bearing formation capable of yielding exploitable quantities of GROUNDWATER.

Aquitard

Low permeability hydrogeologic unit that retards groundwater flow.

Assimilative Capacity

The ability of in situ conditions to naturally attenuate contaminants in a manner that protects SENSITIVE RECEPTORS (i.e., the greater the assimilative capacity, the greater the ability to attenuate contaminants and protect receptors).

Autotroph

An organism that uses inorganic carbon such as carbon dioxide as its carbon source for growth. (Compare with a HETEROTROPH, which obtains carbon from organic carbon sources.)

Bacteria

A group of diverse and ubiquitous prokaryotic single-celled microorganisms.

Bioaccumulation

Intracellular accumulation of contaminants such as heavy metals by living organisms.

Bioaugmentation

The process of amending contaminated media with microorganisms to destroy/immobilize contaminants of concern. (Compare to BIOSTIMULATION.)

Bioavailability

The availability of contaminants to microorganisms that are capable of biodegrading them.

Biochemical Oxygen Demand (BOD)

The empirically derived molecular oxygen requirement that a biodegradable organic substance exerts upon water assuming an oxidative biological degradation pathway. The BOD test measures the molecular oxygen (in mg/L) consumed by seed microorganisms over 5 days at 20 degrees centigrade.

Biodegradation

The breakdown of organic substances effected by microorganisms.

Biofilter

Equipment engineered to biodegrade VOCs in air by passing VOC-contaminated air through media onto hich biodegrading microorganisms are attached.

Biomass

The amount of biological matter present within a habitat.

Bioremediation

The use of biological mechanisms to destroy, transform, or immobilize environmental ontaminants to protect potential SENSITIVE RECEPTORS.

Biostimulation

The process of modifying environmental conditions to enhance natural biological attenuation. For example, addition of electron acceptors/donors and/or inorganic nutrients, pH adjustment, etc. (Compare to BIOAUGMENTATION.)

Biotic

Living.

Biotransformation

Alteration of the structure of a compound effected by a living organism.

Bioventing

The process of supplying molecular oxygen in situ to oxygen-limited soil microbes by forcing air through unsaturated contaminated soil at low flow rates. Forced aeration stimulates biodegradation and minimizes stripping volatile organic compounds into the atmosphere. Frequently used to remediate soil under structures since it is relatively non-invasive.

BOD

Biochemical oxygen demand.

Brownfield

An abandoned, idled, or under-utilized industrial or commercial facility where expansion or redevelopment is complicated by a real or perceived environmental contamination condition.

BTEX

Acronym for the aromatic petroleum hydrocarbons benzene, toluene, ethylbenzene, and xylenes.

CAH

Chlorinated aliphatic hydrocarbon.

Carbolic acid

PHENOLS.

Catabolism

The process by which energy is extracted from organic compounds by breaking them down into their individual components.

CERCLA (Superfund)

Comprehensive Environmental Response, Compensation, and Liability Act.

Chain-of-Custody

Record documenting name of individual having physical custody of samples, the duration of that custody, and the nature of security conditions, if any.

Chemical Oxidation

Remediation strategy in which strong chemical oxidizing agents are supplied to contaminated soils/groundwater to oxidize contaminants. In the case of CAHs, chemical oxidation yields carbon dioxide, water, and inorganic chloride.

Chemical Oxygen Demand (COD)

Measurement of the molecular oxygen equivalent of chemically-reduced matter, typically assumed to be organic carbon. COD includes only matter susceptible to chemical oxidation by strong oxidant.

Chlorinated Aliphatic Hydrocarbon (CAH)

A straight chain hydrocarbon containing at least one chlorine atom and either a single or double carbon bond (i.e., alkane or alkene, respectively).

CISB

Committee on In Situ ioremediation, Water Science and Technology Board, Commission on Engineering and Technical Systems, National Research Council.

COD

Chemical oxygen demand.

Cometabolism

The process by which a contaminant is fortuitously degraded by an enzyme or cofactor produced during microbial metabolism of another compound. Typically, there is no apparent benefit to the microorganism involved.

Consortium

Two or more members of a natural assemblage in which each organism benefits from the other. The group may collectively carryout some process that no single member can accomplish independently.

Creosote

An antifungal wood preservative often used for treating utility poles and railroad ties. Creosote consists of coal tar distillation products, including PHENOLS and PAHs.

Daughter

Chemical products that result from the biochemical transformation of chemical reactants. For example, cis-/trans-1,2-DCEs, 1,1-DCE, and VC may be daughters of PCE and/or TCE under certain conditions.

DCA

Dichloroethane.

DCE

Dichloroethene.

Dehalorespiration

Bacterial growth-coupled utilization of a chlorinated compound as a TEA (oxidant substitute) and molecular hydrogen, or simple organic compound, as electron donors. DEHALORESPIRATION occurs only under anaerobic, chemically reducing conditions, and the process is also referred to as metabolic REDUCTIVE DEHALOGENATION.

Dehydrohalogenation

Elimination of a hydrogen ion and a halide ion that results in the formation of an alkene.

Denitrification

The formation of gaseous nitrogen and/or oxides of nitrogen from nitrate or nitrite by certain bacteria during ANAEROBIC RESPIRATION. Denitrification only occurs in ANAEROBIC or MICROAEROPHILIC conditions when there is sufficient organic carbon to support reaction. Denitrification may be used as a treatment technology to remove nitrogen oxides from liquid waste streams. See DISSIMULATORY NITRATE REDUCTION.

Dihaloelimination

Reductive elimination of two halide substituents that results in formation of an alkene.

Dispersivity

A property quantifying mechanical dispersion in a medium.

DNA

Deoxyribonucleic acid.

DNAPL

Dense non-aqueous phase liquid that is denser than water and therefore can penetrate the water column. (Compare to LNAPL.)

DPTA

Diethylenetriaminepentaacetic acid.

EDTA

Ethylenediaminetetraacetic acid.

Eh

Redox potential.

Electron Acceptor

An oxidant that accepts electrons during oxidation-reduction reactions. Microorganisms obtain energy by transferring electrons from electron donors such as organic compounds or reduced inorganic compounds to an electron acceptor. Electron acceptors are chemically oxidized compounds, including molecular oxygen, nitrate, iron (III), manganese (IV), sulfate, carbon dioxide, or in some cases CAHs such as PCE and TCE, which become chemically reduced during transformation.

Electron Donor

Compound capable of supplying electrons during oxidation-reduction reactions. Microorganisms obtain energy by transferring electrons from electron donors such as organic compounds or reduced inorganic compounds to a TEA. Electron donors are chemically reduced materials such as fuel hydrocarbons or naturally occurring organic carbon, which become chemically oxidized during transformation.

Elimination

Reaction in which two atoms such as chlorine and hydrogen are lost from adjacent carbon atoms and a double bond is formed in their place.

Enhanced Bioremediation

Engineered bioremediation performed to clean up, and eventually close, a contaminated site.

Enhanced Rhizosphere Biodegradation

Enhanced biodegradation of contaminants near plant roots where compounds exuded by the roots increase biological activity. Other plant processes such as water uptake by the plant roots can enhance biodegradation by drawing contaminants into the root zone.

Enrichment

Technique for culturing microorganisms in a liquid medium that results in an increase of that population relative to others. The liquid medium frequently contains substances that encourage growth of the selected microorganism (e.g., the contaminant for a metabolic degradation pathway).

Enzymes

Proteins acting as biological catalysts.

Epoxidation

The reaction by which an oxygen molecule is inserted into a carbon-carbon double bond to form an epoxide. For example, epoxidation is the mechanism by which microorganisms cometabolize TCE in the presence of a suitable primary substrate such as methane in aerobic, chemically oxidizing settings.

Equipment Blank

Sample of distilled/de-ionized water rinseate that is washed over sampling equipment and submitted to an analytical laboratory to evaluate for potential contamination owing to improper equipment decontamination procedures.

Eutrophic

Natural waters enriched with inorganic nutrients such as nitrogen and phosphorus. (Compare with OLIGOTROPHIC.)

Eutrophication

The process by which natural waters become enriched of with inorganic nutrients such as nitrogen and phosphorous.

Ex Situ

Out of the original position, such as a stockpile of excavated soil.

Facultative Aerobes

Facultative aerobes are microorganisms that are only VIABLE in anoxic environments if alternative TEAs, such as nitrate and sulfate, are present (i.e., they use nitrate and sulfate as TEAs for respiration once oxygen has become depleted).

Fermentation

An energy-yielding metabolic pathway that involves a series of oxidation-reduction reactions in which the substrate and TEA are organic compounds. Fermentation occurs within a wide variety of bacteria and fungi.

FST

Fractionation separation technology.

Fungi

A group of diverse and widespread unicellular and multi-cellular eukaryotic organisms. Some species are important in the natural decomposition of plant litter.

GC/MS

Gas chromatography/mass spectroscopy.

GEMS

Genetically engineered microorganisms .

Groundwater

Subsurface water occupying the saturated zone.

Groundwater System

Water-bearing formation capable of transmitting and storing GROUNDWATER.

Halophilic

Organisms that prefer elevated salt concentrations in excess of other organisms.

Heterotroph

An organism that obtains carbon and energy from growth-coupled metabolism of organic carbon. (Compare with an AUTOTROPH, which obtains carbon from inorganic carbon.)

HPLC/MS

High-pressure liquid chromatography/mass spectroscopy.

Hydraulic Conductivity

A measurement of the ability of a given volume of soil, sediment, or rock to transmit water.

Hydraulic Gradient

The maximum change in hydraulic head per unit distance.

Hydraulic Head

The height above a datum plane of the surface of a column of water. In groundwater flow systems, hydraulic head has two components consisting of elevation head and pressure head.

Hydrodynamic Dispersion

The natural process that mixes contaminants with the fluid phase in porous media. Hydrodynamic dispersion is due to both mechanical dispersion (i.e., mechanical mixing due to the presence of soil grains and interstitial space between grains) and molecular diffusion (e.g., physical-chemical mixing due to concentration gradients that spread contaminants in the absence of fluid motion).

Hydrogenolysis

A reductive reaction where a carbon-halogen bond is broken, and hydrogen replaces the halogen substituent.

Hydroxylation

Addition of a hydroxyl group to a CAH.

In situ

In place, the natural or original position.

Inoculum

Material used to introduce a microorganism into a suitable situation for growth.

Intrinsic Bioremediation

The natural attenuation of contaminants of concern mediated by native microorganisms, typically bacteria.

Isoenzyme

An enzyme that can occur in more than one form within a given species. Also called an ISOZYME.

Isozyme

An enzyme that can occur in more than one form within a given species. Also called an ISOENZYME.

Lignin

A complex polymer that occurs in the woody material of higher plants. It is highly resistant to chemical and enzymatic degradation. The WHITE ROT FUNGI are known for their lignin-degrading capability.

LNAPL

Liquid that is lighter than water and floats on top of the water column. (Compare to DNAPL.)

LNAPL

LIGHT NON-AQUEOUS PHASE LIQUID.

Mechanical Dispersion

A physical process of mixing along a groundwater flow path resulting solely from differences in path length and pore velocity.

Medium

Material that is supportive of biological growth.

Mesophile

An organism that prefers temperature ranges of about 20 – 45 degrees centigrade. (Compare with THERMOPHILE and PSYCHROPHILE.)

Metabolism

Growth-coupled reaction in which microorganisms use electron donor for organic carbon and energy and electron acceptor to collect electrons released during the reaction.

Methane-Producing Bacteria

METHANOGEN.

Methanogen

Bacteria that oxidize hydrogen to methane and water using carbon dioxide as the TERMINAL ELECTRON ACCEPTOR under anaerobic conditions. These bacteria may occur in anaerobic muds, ponds, sewage sludge, and other similar environmental settings.

Methanotrophs

Obligate aerobic bacteria that use methane as electron donor and typically molecular oxygen as the TEA. Methanotrophs are responsible for the co-oxidation of certain chlorinated solvents at the expense of methane.

Microaerophilic

An environment with low molecular oxygen content, but which is not anaerobic.

Microbe

Microorganism.

Microcosm

A smaller unit representative of a larger one.

Microflora

The microorganisms associated with a given environment.

Micronutrient

Chemical element necessary for biological activity found in trace amounts,