Pesticide Residues in the Environment - Pesticides: Evaluation of Environmental Pollution - page 173

supportedbythecapacityforexpressionofarangeofextracellularenzymesatboth−0.7
and−2.8MPawaterpotentials. Phanerochaete chrysosporium wasabletodegradethismix-
ture of pesticides independent of the laccase activity. In soil extract, Trametes versicolor
was able toproduce the samerange of enzymesas Phanerochaete chrysosporium plus lac-
case,evenwhenpresentas30ppmofthepesticidemixture(FragoeiroandMagan2005).
CompletedegradationofdieldrinandtriluralinwasobservedbyFragoeiroandMagan
(2005),whileabout80%ofthesimazinewasdegradedregardlessofosmoticstresstreat-
mentinanutritionallypoorsoilextractbroth.Thecapacityoftoleranceanddegradation
of high concentrations of mixtures of pesticides and production of a range of enzymes,
evenunderosmoticstress,isadvantageousandtheauthors(FragoeiroandMagan2005)
suggestpotentialbioremediationapplications.
6.4.4.2 Triazinone Herbicides
Metribuzin (4-amino-6-tert-butyl-4,5-dihydro-3-methylthio-1,2,4-triazin-5-one) is weakly
sorbedinsoilsandthereforeleacheseasilytolowersoillevels,whichresultsinthelossof
activity.
MetribuzindegradationandtransportdescribedbyMaloneetal.(2004)weresimulated
using three pesticide sorption models available in the Root Zone Water Quality Model
(RZWQM):
• Instantaneousequilibrium-only(EO)
• Equilibrium-kinetic(EK,includessiteswithslowdesorptionandnodegradation)
• Equilibrium-bound (EB, includes irreversibly bound sites with relatively slow
degradation).
Theresultobtainedbytheauthors(Maloneetal.2004)indicatethat
• Simulated metribuzin persistence was more accurate using the EK (root mean
square error, RMSE=0.03kg/ha)andEB(RMSE=0.03kg/ha)sorptionmodels
comparedtotheEO(RMSE=0.08kg/ha)modelbecauseofslowingmetribuzin
degradationratewithtime.
• Simulatingmacroporelowresultedinpredictionofmetribuzintransportinper-
colate over the simulation period within a factor of 2 of that observed using all
threepesticidesorptionmodels.
Moreover, little difference in simulated daily transport was observed between the
three pesticide sorption models, except that the EB model substantially underpredicted
metribuzin transport in runoff and that when macropore low and hydrology are accu-
ratelysimulated,metribuzintransportintheieldmaybeadequatelysimulatedusinga
relativelysimple,EOpesticidemodel(Maloneetal.2004).
Soil amendments play an important role in the management of runoff and leaching
lossesofpesticidesfromagriculturalields.Therefore,theeffectofbiocompostfromthe
sugarcanedistilleryefluentonmetribuzindegradationandmobilitywasstudiedbySingh
(2008) in a sandy loam soil. Metribuzin was more persistent in biocompost-unamended
(T-0) looded soil (t 1/2 −41.2 days) than in nonlooded (t 1/2 −33.4 days) soil. Freundlich
adsorptionconstants(K f )fortreatmentsT-0,T-1,andT-2were0.43,0.64,and1.13,respec-
tively, suggesting that biocompost application caused increased metribuzin sorption