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Introduction <br />Total petroleum hydrocarbons (TPH) is a term used to describe a large family of several <br />hundred chemical compounds that originally come from crude oil. The TPH in this study consists <br />of mainly aliphatic hydrocarbons ranging from Coo-CZS with undecane, dodecane, tridecane and <br />tetradecane being present in larger percent. Many studies have been conducted that address the <br />properties of organic compounds and their fate in the environment (1-37). For most <br />hydrocarbons, biodegradation was not a significant removal process (15; 30; 31). For JP8jet fuel, <br />disappearance from soil appeared to be due to both evaporation and biodegradation (21). <br />[n a study of the fate of JP-4 in soil (I5), hydrocarbons with molecular weights equivalent <br />to decane or lower disappeared from soil in both active and sterile treatments by the first <br />sampling time, indicating that evaporation was the major removal process for these hydrocarbons. <br />Hydrocarbons with molecular weights higher then decane like undecane, dodecane, tridecane and <br />tetradecane were not removed as rapidly from soil as the more volatile hydrocarbons and traces of <br />these hydrocarbons persisted until the end of the experimental period. It was also found from the <br />same study that for undecane, dodecane and hexadecane, no significant differences in <br />disappearance were noted between the active and sterile treatments. <br />Volatilization and biodegradation are the two major processes that determine the fate of <br />TPH components in soil. While volatilization is expected to be the dominant fate process for <br />these fuels from soil surfaces, biodegradation will become increasingly dominant as the soil depth <br />increases. Some components of these fuels may migrate through the soil to groundwater. <br />When dodecane is released into the soil, it may biodegrade to a moderate extent. Because <br />of sorption and low solubility in water, dodecane is not expected to leach into groundwater. When <br />released into water, it may evaporate and/or biodegrade to a moderate extent. In the atmosphere. <br />dodecane is expected to be readily degraded by reaction with photochemically produced hydroxyl <br />radicals. When released into the air, it may be removed from the atmosphere to a moderate extent <br />by sorption (26). <br />For mixtures of TPH, their movement in the environment is actually a function of the <br />chemical and physical properties of the component hydrocarbons. Following release of TPH to <br />air, water, or soil, the component hydrocarbons partition relatively independently of each other <br />based on their respective vapor pressures, solubilities, and Henry's law and sorption constants. <br />For TPH mixtures, these values are ranges based on the component hydrocazbons. Information on <br />the specific physical and chemical properties of several of the component hydrocarbons (e.g. <br />undecane, dodecane, tridecane, tetradecane, etc.) can be found in Material Safety Data Sheets <br />(MSDS) obtained from Acros Organics (2) and Fisher Scientific (18) and other sources. These <br />values and sources are presented in Table 1. Humphrey (20) has reviewed and addressed the <br />solubility of these hydrocarbons with respect to their biodegradation. Erickson et al. (17) have <br />reviewed the literature on microbial growth when two liquid phases are present. <br />In general, using carbon dioxide (COZ) evolution to measure biodegradation is a reliable <br />technique and actually provides data on the mineralization of a test chemical. Here we describe a <br />simple microcosm method, based on COZ production and TPH depletion, for determining the <br />aerobic biodegradability of organic chemicals in soils. The experiment involves extraction of <br />TPH components from soil and subsequently identifying them using analytical techniques. The <br />concentration of COZ in the gas phase is measured at regular time intervals using a gas <br />