Pesticide Residues in the Environment - Pesticides: Evaluation of Environmental Pollution - page 164

• Toxicity
• Preferentialuseassubstrate,ascarbonsourcealternativetothepollutant
• Lowpollutantconcentrationintheaqueousphasebyamicellationeffect
• Thepossibilitythatthesurfactantactsasaninterferenceinthemicrobialmetabolic
processes.

ThemodelsproposedbyQuinteroetal.(2005)fortheHCHdegradation,consideringthe
differentsurfactantconcentrations,suggestthatdifferentmicrobialconsortiaareinvolved
inthedegradationofα-andγ-HCHwhilethedegradationofβ-andδ-HCHisaffectedby
diffusionallimitations.
Biodegradationanddetoxiicationofpentachlorophenol(PCP)bythewhite-rotfungus
Phanerochaete chrysosporium wasdescribed(Mendoza-Cantúetal.2000).Resultsobtained
bythem(Mendoza-Cantúetal.2000)showthat Phanerochaete chrysosporium applicationto
bioremediate PCP-contaminated soil is a feasible option, owing to its eficiency and the
productionofinnocuousintermediatesduringtheprocess.
Another very important compound from OCPs is lindane (γ-HCH). An adaptive
mechanism and eflux-transport system of Pseudomonas sp. LE2 counteracting lindane
were investigated to understand the survival mechanism of this microorganism in
lindane-contaminated environment (Kim et al. 2002). The results obtained by Kim et al.
suggestthat Pseudomonas sp.LE2capableofgrowinginthepresenceoflindaneisableto
adapttotheluidizingactionoflindanebyincorporatingthesaturatedfattyacidintomem-
branelipidsandeliminatelindanefromthecellbyanenergy-dependentefluxmechanism.
Dieldrin

(1,2,3,4,10,10-hexachloro-6,7-epoxy-1,4,4a,5,6,7,8,8a-octahydro-1,4,-endo-exo-5,8-
dimethanonaphthalene)isoneofthemostpersistentorganochlorinepesticides,havingan
averagehalf-lifeofbetween5and25yearsinsoilsediment(Vilanovaetal.2001).Therefore,it
islistedasoneofthe12persistentorganicpollutantsintheStockholmConvention.Microbial
degradationisaneffectivewaytoremediateenvironmentalpollutants,includingpersistent
organicpollutants.Thirty-fourisolatesofwood-rottingfungiwereinvestigatedtotesttheir
ability to degrade dieldrin. Strain YK543 was selected as a fungus capable of degrading
dieldrin.Themetabolicpathwayincludes9-hydroxylationreportedinrat'smetabolismcata-
lyzedbylivermicrosomalmonooxygenase(Kameietal.2010).Kameietal.(2010)described
thetransformationofdieldrinto9-hydroxydieldrinbyamicroorganismirst.

6.4.2 Organophosphate Insecticides

Organophosphate insecticides play an important role in the success of modern farming
and food production. Organophosphate insecticides have been widely used throughout
theworldsincetheuseoforganochlorinecompoundswasdiscontinuedinthe1970sand
1980s in most regions. The objectives of the study described by Bondarenko and Gan
(2004) were to evaluate the degradation kinetics of diazinon, chlorpyrifos, malathion,
and carbaryl in urban stream sediments under aerobic and anaerobic conditions and to
understand the time dependence of pesticide sorption in the sediments. The decline of
pesticide concentration over time was itted to a irst-order decay model to estimate the
rateconstant(d −1 )andt 1/2 (d).Theitobtainedbytheauthorsintheexperimentwasgener-
ally good, as evident from the correlation coeficient, except for degradation of carbaryl
and chlorpyrifos under anaerobic conditions. The overall persistence for aerobic degra-
dationfollowedtheorder:chlorpyrifos>diazinon>carbaryl>malathion.Thesorption
coeficientconsistentlyincreasedwithtimeforallpesticides,andchlorpyrifosdisplayed