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<br /> ,!, TQMOTM GASOLINE 65-18
<br /> Alth'ougn the mitrooioca of most ^on,concamanacea' 'soils include- '
<br /> maxiv na=urally occurring hydrocaroon-degrading populations, 'the
<br /> addition of petroleum 'selectively enriches that sector able to adapt
<br /> and ut_ _e the new suoscrate Other environmental factors shown to
<br /> have a ajor effect on biodegraaabili=Z are availabLlity of oxygen and
<br /> moaerate temperatures_
<br /> In -s+ mmarv,. biodegradation- of the petroleum -"hydrocaroonsry- -�
<br /> ,ta, - P1 L I
<br /> comnriszng automotive gasolines }" ,is ,` -expected to ba. ' rap zdr` under
<br /> — — -coudLtions—favorable—for—microbial-act vity�,� and—when—fuel.y components are freely avail'ablerto the microorgantsms. Degradation may be Limited
<br /> and/or slow in environm*nts� with few"jdegrading`,organLsms`, ' low "'pH, low
<br /> temperatures, and tihigh� salinity„{e ug:,�='arc=i.c, environments)=. Ft' should
<br /> __ S 'M U y,,,e y ,
<br /> be mentioned that Walker'f e�� �. �, (2257)' ;state that evens under,2,optimum -
<br /> conditions, ` total+and,�co. plete' biodegradation is., occur,
<br /> 'expected<to= occur
<br /> L f i I Wr r',VV A d.s Y,+ w .4w ,{ Ay , n r r f 4 Ilk f `�
<br /> except pbssibly over, an ,,extremely�'long timeperiod. �� �;� t
<br /> , '
<br /> 65.2.3 Primary Routes of 'Exposure from SOL1/Ground=water systems
<br /> "f
<br /> The above discussion, ;of `fate "'achways suggests that the ma)or r
<br /> comoonents of gasoline are highly volatile but vary in their potential
<br /> for bioaccumulation and `tendency to sorb to, soil. * They -range from
<br /> moderately ' to strongly sorb-id. 'to soil, andj ,their bioaccumu' lation
<br /> potential ranges from low ;to high. The "variability in the.properties
<br /> of the components suggests they ,may have somewhat different potential
<br /> expo ure +pathwaysr . I� • '�'� '� ell,
<br /> Spills of gasoline would result in , the ;evaporative, loss of the
<br /> more highly "volatile ,companents leaving= "those ofi;lesser", volatility in
<br /> the, sail., The ;fraction",remaining,,in Eche soil' is expected to,be tela-
<br /> cively�' mobile I and W"Llls fbe carried by gravity to the saturated zone of
<br /> the ,soil., There,z the more, soluble-; components will dissolve , into the
<br /> ground 'water or;form`emaulsLons with 'Lt. 4; ,Thesea`com'ponents tare primarily
<br /> aiomacic Rand lower imole6u' kar, weLght aliphatic,compounds; in one study
<br /> using unleaded gasoline, approximately 951 of the-water soluble frac-
<br /> tion was = benzene and 'subscztuced benzenes (2318) . The insoluble
<br /> fraction of gasoline ' floats as a separate phase, on top of the Water
<br /> table. The movement of- gasoline dissolved in ground water is
<br /> esp - %ally-important because-of its relatively high'solubility (173-200
<br /> mg/L .(2287,2297)) Furthermore, the movement' of dissolved hydrocarbons
<br /> " in,ground water is 'much greater than chat of the separate liquid phase,
<br /> reaching distances o£,hundreds to thousands of meters compared to tens
<br /> of mecersJ for the movement of the separate phase. In the presence of
<br /> cracks_ and fissures. however.,, the flow of the separate hydrocarbon
<br /> phase is greatly enhanced: ' y u
<br /> The movement of gasoline in ground water may contaminate drinking
<br /> water supplies, iIresulting Ln ingestion exposures Ground-wacer dis-
<br /> charges to "surface water or the movement of 'contaminated soil particles
<br /> to, surface `water drinking water supplies may also result in ingescion
<br /> " exposure and' 4in dermal ' exposures from the recreational use of these
<br /> waters The ;potential also exists for the uptake of some gasoline
<br /> 6/87
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