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anaerobicconditionsisDDD.Theclosenessofk conv,1 tothedegradationrateconstantfor
theconversionfromp,pʹ-DDTtop,pʹ-DDEandp,pʹ-DDDisgovernedbyaparallelreaction
(Noegrohatietal.2008).
Inanotherstudy,JuhaszandNaidu(2000)screenedthecontaminatedsoilsanduncon-
taminatedplantandfecalmaterialformicroorganismswiththeabilitytodegradeDDT.
Fivesoilswereusedfortheisolationofxenobiotic-degradingmicroorganisms.Microbial
communitiesenrichedonthebasalsaltmedium—BSM(containedperliter:0.4gK 2 HPO 4 ,
0.4 g KH 2 PO 4 , 0.4 g (NH4) 2 SO 4 , 0.3 g NaCl, 5 mL trace elements solution, 5 mL vitamin
solutionand5mLmagnesium/calciumsolution(0.4gMgSO 4 ×7H 2 Oand0.4gCaCl 2 ×2
H 2 O))—containing peptone (1 g/l) and DDT (100 mg/l) were tested for their ability to
degradeDDT,DDD,andDDEafterthreesuccessivetransfersintheenrichmentmedium
(Juhasz and Naidu 2000). A decrease in the concentration of DDT over the incubation
period was observed for all microbial communities; a 5%-14.6% decrease was observed
after28daysofexposuretoDDT.SmalldecreasesintheconcentrationofDDDwerealso
observedformicrobialcommunitiesintherangeof7.3%-9.8%.DDEwasgenerallyrecal-
citranttomicrobialattack(JuhaszandNaidu2000).ThedegradationofDDT(100mg/l)by
isolateAJR 3 9,504resultedina35%decreaseinDDTconcentrationafter28dayswithacon-
comitantincreaseinDDDconcentration(JuhaszandNaidu2000).GuenziandBeard(1968)
reportedtheaccumulationofDDDinanaerobicsoilsystemsseededwithalfalfa-amended
Pawneesiltloam;onlytracesofsixotherdegradationproductsweredetected.Although
strain AJR 3 9,504 could not be positively identiied, other Gram-negative organisms and
“Pseudomonas-like”organismshavebeenshowntotransformDDTtoDDD.Inpurecul-
turesystems,dechlorinationofDDTby Escherichia coli , Enterobacter aerogenes , Enterobacter
cloacae , Klebsiella pneumoniae , Pseudomonas aeruginosa , Ps. Putida , Hydrogenomonas , and
Aerobacter aerogenes hasbeenreported(Wedemeyer1967;Plimmeretal.1968;Aislableetal.
1997).DDDformationbyAJR 3 9,504probablyresultedfromthereductiondechlorination
of the aliphatic part of the DDT molecule. In another paper, Plimmer et al. (1968) pro-
posedthatinthecaseof Aerobacter aerogenes ,conversionofDDTtoDDDoccurredwiththe
replacementofchlorinebyhydrogenorhydrideion.
Other authors (Strompl and Thiele 1997) demonstrated that DDE remained refractory
for105dayswhenaddedtoaerobicoranaerobicbatchreactorsinoculatedwithbacterial
consortiafrom,forexample,anaerobicgranularsludgeandDDE-contaminatedsoiland
suggestthatDDEisextremelyrecalcitranttomicrobialdegradation.
OneoftheOCPswithstrongsorptioncharacteristicsishexachlorocyclohexane(HCH),
amixtureofisomers:α-,β-,γ-,andδ-HCH.Theuseofsurfactantsmayincreasethepollut-
ant'sdesorptionfromthesoil.Quinteroetal.(2005)describedtheuseofthreesurfactants,
TritonX100,Tween80,andsodiumdodecylsulfate(SDS),ontheHCHdesorptionfrom
asandyloamsoil.TritonX100exertedthebestdesorptionofHCHisomers,followedby
Tween80,whereasSDScausednosigniicantdesorptionoftheisomers(Quinteroetal.
2005).Thedesorptionassaysshowthatβ-andδ-HCHhavestrongerhydrophobiccharac-
teristicsthanα-andγ-HCH,astheypresentalowerdesorptionpercentage.Thiscouldbe
inluencedbythefactthatβ-HCHislesssolublethantheotherisomers.Thesurfactant
Triton X100 showed the highest extraction eficiency among the three surfactants con-
sidered and the concentrations corresponding to the two phases well correlated with a
linearmodel(Quinteroetal.2005).Otherpapers(Parketal.2003;Sunetal.1995)report
the capability of Triton X100 to desorb other OCPs present in the soil: DDT and penta-
chlorophenol(PCP)correlatedwithlinearmodels.Theinhibitoryeffectofasurfactanton
thebiodegradationcapabilitymayhaveitsorigininthefollowing(Quinteroetal.2005;
Volkeringetal.1998)
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