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= E GASOL= <br /> 65-17 <br /> 5raVitatlon and capillary forces decreases evaporation. -'-dueas she <br /> :�" ortanca of some Cranaiorma>cion pathways (see below) , a.z� •r lead co <br /> ott>'td-water contaminat7.an. <br /> TranmiOrmation Processes in Soil/Ground-water System-- <br /> 55.2.2.1 <br /> ystem:65.2.2.1 Chemical Transformation <br /> No data war* available on chemical transformation of } <br /> the environment- However, as discussed in Cha tar 64 gasoiiae in <br /> P phocaoxidacion <br /> has been reported to play a significant role in the chemical <br /> degradation of some petroleum hydrocarbons in the sunlit euvironmenc <br /> (1845,1848,2252.2259) . Alkanes, benzenes. and mono-subs titutad <br /> banzenas have been shown to be relatively resistant to photolysis in <br /> aquaous systems; xylenaz photolyzed slowly While trisnbstitutad <br /> benzenes and naphthalenes photolyzed ac rates competitive with <br /> + volatilization (1845) . Penetration of oil below the soil surface <br /> Iimits exposure cc solar radiation while extensive lateral spreading of <br /> oil over impermeable or roc surfaces may i <br /> 4 rocky promote substantial <br /> phoccoxidative degradation. The oxygenated products of phocaoxidation <br /> era generally more water-soluble than the parent hydrocarbons and are <br /> { thus more Likely to be leached from soil. enhanced toxicity of Cho <br /> oxygenated hydrocarbons has also been observed (2248,2252) . <br /> a !- <br /> 65:2.2.2 Biological Degradation <br /> Natural ecosystems have considerable exposure to petroleum <br /> hydrocarbons from natural emissions. accidental contaodnacionthrough <br /> oil spills and storage tank leaks, and deliberate application to land <br /> is disposal activitias such as land-Farming waste; therefore, their <br /> biodagrada=ion is of environmental importance. Numerous authors have <br /> observed the biodegradation of petroleum hydrocarbons. and several <br /> i extensive reviews aitd reports are available (1846,2252.2255.2249,2253). i <br /> An extensive and diverse group of petroleum hydrocarbon-degrading <br /> bacteria and fungi are widely distributed in the eavironmenz. The <br /> { reader is referred to Chapter 64 for a more detailed summary of the <br /> biodegradation of petroleum. hydrocarbons. <br /> E. <br /> J Tba qualicativa hydrocarbon content of petroleum mixtures largely <br /> 1 determines Chair degradability. in general. microorganisms exhibit <br /> decreasing ability to degrade aliphacim hydrocarbons with increasing <br /> Chain length. n-Alkalies are considered more easily biodegraded than <br /> branched or cyclic, aikana.; aromatics are generally more rapidly <br /> biodegraded than alkanes. The composition of gasoline suggests that <br /> ' most of the aromatic specias will be highly biodegradable. and many of <br /> the aliphatic species chat are not volatilized Will be moderately <br /> 1 biodegradable. In a study of the biodegradation of individual <br /> components of gasoiina using microorganisms isolated from ground water, <br /> the aliphatics and aromatics were shown to be sources of . carbon for <br /> N �9ear and Pseudomonas cultures, respectively (2331) . Vary few of <br /> the remaining components supported bacterial growth; co-oxidation was <br /> t suggested as a possible mechanism for removal of non-growth components. <br /> E, 6/87 <br />