Valence state: The combining capacity of an atom or radical determined by the number of electrons that it will lose, add, or share when it reacts with other atoms.
free product: A NAPL found in the subsurface in sufficient quantity that it can be partially recovered by pumping or gravity drain.
aerobic: Direct aerobic metabolism involves microbial reactions that require oxygen to go forward. The bacteria uses a carbon substrate as the electron donor and oxygen as the electron acceptor. Degradation of contaminants that are susceptible to aerobic degradation but not anaerobic often ceases in the vicinity of the source zone because of oxygen depletion. This can sometimes be reversed by adding oxygen in the form of air (air sparging, bioventing), ozone, or slow oxygen release compound (e.g., ORC(r)).
Aerobic dechlorination may also occur via cometabolism where the dechlorination is incidental to the metabolic activities of the organisms. In this case, contaminants are degraded by microbial enzymes that are metabolizing other organic substrates. Cometabolic dechlorination does not appear to produce energy for the organism. At pilot- or full-scale treatment, cometabolic and direct dechlorination may be indistinguishable, and both processes may contribute to contaminant removal. For aerobic cometabolism to occur there must be sufficient oxygen and a suitable substrate which allows the microbe to produce the appropriate enzyme. These conditions may be present naturally but often in the presence of a source area oxygen and a substrate such as methane or propane will need to be introduced.
Adapted from US. EPA 2006 Engineering Issue: In Situ and Ex Situ Biodegradation Technologies for Remediation of Contaminated Sites
anaerobic: Direct anaerobic metabolism involves microbial reactions occurring in the absence of oxygen and encompasses many processes, including fermentation, methanogenesis, reductive dechlorination, sulfate-reducing activities, and denitrification. Depending on the contaminant of concern, a subset of these activities may be cultivated. In anaerobic metabolism, nitrate, sulfate, carbon dioxide, oxidized metals, or organic compounds may replace oxygen as the electron acceptor.
Anaerobic dechlorination also may occur via cometabolism where the dechlorination is incidental to the metabolic activities of the organisms. In this case, contaminants are degraded by microbial enzymes that are metabolizing other organic substrates. Cometabolic dechlorination does not appear to produce energy for the organism. At pilot- or full-scale treatment, cometabolic and direct dechlorination may be indistinguishable, and both processes may contribute to contaminant removal.
Quoted from US. EPA 2006 Engineering Issue: In Situ and Ex Situ Biodegradation Technologies for Remediation of Contaminated Sites
architecture: "Architecture" refers to the physical distribution of the contaminant in the subsurface. Residuals that take the form of long thin ganglia or small dispersed globules provide a larger surface area that will dissolve much faster than if the same amount of liquid were concentrated in a competent pool.
Sources: For purposes of this discussion, a DNAPL source zone includes the zone that encompasses the entire subsurface volume in which DNAPL is present either at residual saturation or as "pools" of accumulation above confining units. In addition, the DNAPL source zone includes regions that have come into contact with DNAPL that may be storing contaminant mass as a result of diffusion of DNAPL into the soil or rock matrix.
source zone: For purposes of this discussion, a DNAPL source zone includes the zone that encompasses the entire subsurface volume in which DNAPL is present either at residual saturation or as "pools" of accumulation above confining units. In addition, the DNAPL source zone includes regions that have come into contact with DNAPL that may be storing contaminant mass as a result of diffusion of DNAPL into the soil or rock matrix.
focal ulceration: The process or fact of a localized area being eroded away.
metaplasia of the glandular stomach: A change of cells to a form that does not normally occur in the tissue in which it is found.
hyperplasia of the glandular stomach: A condition in which there is an increase in the number of normal cells in a tissue or organ.
histiocytic: Degenerative.
duodenum: First part of the small intestine.
microcytic: Any abnormally small cell.
squamous cell papillomas: A small solid benign tumor with a clear-cut border that projects above the surrounding tissue.
squamous cell carcinomas: Cancer that begins in squamous cells-thin, flat cells that look under the microscope like fish scales. Squamous cells are found in the tissue that forms the surface of the skin, the lining of hollow organs of the body, and the passages of the respiratory and digestive tracts. Squamous cell carcinomas may arise in any of these tissues.
jejunum: The middle portion of the small intestine, between duodenum and ileum. It represents about 2/5 of the remaining portion of the small intestine below duodenum.
ileum: The distal and narrowest portion of the small intestine.
squamous: Flat cells that look like fish scales.
metaplasia: A condition in which there is a change of one adult cell type to another similar adult cell type.
ossification: The process of creating bone, that is of transforming cartilage (or fibrous tissue) into bone.
clastogenesis: Any process resulting in the breakage of chromosomes.
neoplastic: Abnormal and uncontrolled growth of cells.
ulceration: The process or fact of being eroded away.
leucocytosis: An elevation of the total number of white cells in blood.
neutrophils: A type of white blood cell.
chromodulin: A small protein that binds four trivalent chromium ions.
biomagnification: The increased accumulation and concentration of a contaminant at higher levels of the food chain; organisms higher on the food chain will have larger amounts of contaminants than those lower on the food chain, because the contaminants are not eliminated or broken down into other chemicals within the organisms.
exencephaly: Cerebral tissue herniation through a congenital or acquired defect in the skull.
everted viscera: Rotated body organs in the chest cavity.
To Be Considered: Documents, such as federal or state guidances, that are not legally binding but may be relevant to the topic in question.
gaining: A gaining surface water body is one where groundwater flows into it.
losing: A surface water body is losing when there is a permeable sediment bed that is not in contact with the groundwater allowing the surface water to seep through it.
fluvial: Of or pertaining to flow in rivers and streams.
lacustrine: Of or pertaining to a lake as in lacustrine sediments—sediments at the bottom of a lake.
lipid: Any class of fats that are insoluble in water.
lipophilic: Able to dissolve in lipids—in this case fatty tissue.
organelles: A part of a cell such as mitochondrion, vacuole, or chloroplast that plays a specific role in how the cell functions and membranes.
RfD: The RfD is an estimate of a daily exposure of the human population (including sensitive sub-groups) to a substance that is likely to be without "the appreciable risk of deleterious effects during a lifetime." An RfD is expressed in units of mg/kg-day.
autonomic: That part of the nervous system that controls non-conscious actions such as heart rate, perspiration and digestion.
ataxia: Lack of muscle coordination.
funnel-and-gate configuration: A system where low-permeability walls (the funnel) placed in the saturated zone direct contaminated ground-water toward a permeable treatment zone (the gate)
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Coal tar creosote; coal tar; and heavy fuel oil (HFO), such as bunker oil, heavy fuel oil 6, and marine oil, are complex mixtures that vary due to the type of feedstock and manufacturing method used to produce them. Nevertheless, they all contain some common groups of compounds, such as polycyclic aromatic hydrocarbons (PAHs) and other heterocyclic ring compounds that contain elements, such as oxygen, sulfur, or nitrogen. The proportions of each class of compound vary, with creosote containing greater proportions of the lighter phenols, cresols, and PAHs than coal tar and HFO. Coal tar and HFOs contain greater proportions of 5- and 6-ring PAHs and other more complex, polar, ring structures. Due to the variability of these complex mixtures, their toxicology is difficult to study. The toxicology of an individual component of the mixture may be potentiated or antagonized by other components of the same mixture, making it difficult to predict the behavior of a particular compound in a mixture even when the toxicology of that compound is well known.
Occupational exposure to creosote, coal tar, and HFOs is likely to occur from dermal exposure or possibly inhalation pathways when heated mixtures vaporize. As the use of HFOs is limited to heavy industry and marine applications, there is little expectation that the general population will be exposed, other than in the case of dermal exposure to HFOs washed onto beaches after an oil spill. Coal tar and creosote are more widely used, and the general population might be exposed to them by contact with some pharmaceutical products or freshly creosoted landscaping timbers or other creosote-preserved timber. In addition, the public may be exposed to coal tars and creosotes through the ingestion of contaminated ground water (when used for drinking water purposes) and contaminated fish or shellfish. There is some evidence to suggest that PAHs, present in coal tars, creosote, and HFOs, can bioaccumulate. The presence of these compounds in the breast milk of lactating mothers provides a route of exposure to nursing infants.
No studies are available on the human health effects of the HFOs. However, short-term animal studies (dermal route of exposure) indicate dermal and hepatic toxicity, plus proliferative changes in the epithelium of the bladder. Chronic (2-year) animal studies have shown that HFOs induce tumors in test animals. Numerous studies of occupational exposure to coal tars are available, leading to the conclusion that coal tars are known human carcinogens. Epidemiological studies link creosote exposure to an increased incidence of cancers of the bladder, lung, and multiple myeloma. This mixture also is considered to be a probable human carcinogen.
HFOs have not shown an effect on the fertility of male or female rats. However, dermal exposure of pregnant rats to HFOs resulted in maternal toxicity even at low doses. Furthermore, fetal resorptions were increased and fewer viable offspring were produced. Abnormal development was noted in both living and dead fetuses. In general, it may be concluded that coal tar exerts developmental toxicity in rats and mice by all routes of exposure. These effects are severe and include an increased incidence of abnormalities and prenatal mortality. By contrast, the reproductive and developmental toxicity of creosote is not well understood due to the lack of adequate studies.
Ecological Toxicity
There is no informaton on the ecological toxicity of the coal tars for either the terrestrial or aquatic environments. Although the toxicity of creosote to aquatic organisms is well documented, minimal information exists on its effects on terrestrial organisms. Fish are adversely affected by creosote in surface water and adverse reproductive and developmental effects have been reported. Aquatic crustaceans and mollusks are also sensitive to creosote. The mixture also exhibits toxicity towards aquatic plants. Some studies indicate that HFOs are toxic to fish. Among ecological receptors, HFOs have been observed to penetrate the cellular matrix of marsh plants causing heavy mortality, but after a few years, normal growth was re-established. Studies performed on the eggs of mallard ducks showed that HFO applied to the shell greatly reduced hatching success and survival. However, minimal information exists on the effects of HFOs on terrestrial receptors.
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