Pesticide Residues in the Environment - Pesticides: Evaluation of Environmental Pollution - page 190

and 4.9±0.1×10 9 /Ms, respectively (Wu and Linden 2010). The presence of bicarbonate
ionsreducedthepesticidedegradationratesviascavenginghydroxylradical,butthefor-
mationofcarbonateradicalalsocontributedtothedegradationofthepesticideswithsec-
ond-order reaction rate constants of 2.8±0.2×10 6 and 8.8±0.4×10 6 /Ms, for parathion
andchlorpyrifos,respectively(WuandLinden2010).WuandLinden(2010)describedthe
dualrolesofbicarbonateioninUV/H 2 O 2 treatmentsystem,thatis,scavenginghydroxyl
radicalsandformationofcarbonateradicalsbyusingasimulatedkineticmodel.Results
obtainedbyBaietal.(2010)indicatesthatoxygenplasmatreatmenthasnoticeableeffects
on organophosphorus pesticide with satisfactory degradation eficiency, which mainly
depends on related operating parameters including plasma treatment time, discharge
power, distance from the center of the induction coil, and concentration of organophos-
phoruspesticide.
6.5.3 Carbamate Pesticides
Thiram is an alkyldithiocarbamate compound, which has been widely used as a fun-
gicideinagriculture.Thephotocatalyzeddegradationconditionsofthiraminaqueous
titanium dioxide-suspended solution were optimized under sunlight illumination
(Kanecoetal.2009).Kanecoetal.(2009)investigatedtheeffectofvariousfactors,such
as photocatalyst loading, initial substrate concentration, temperature, pH, sunlight
intensity,andilluminationtimeonthephotocatalyticdegradationofthiram.Thepho-
tocatalyticdegradationofthiramis,apparently,averycomplexprocesswhosemecha-
nism is not yet fully clariied. The photocatalytic degradation pathway of thiram in
water with titanium dioxide on the basis of experimental data obtained by Kaneco
etal.(2009)andthatreportedintheliteratureisillustratedin Figure6.14 .Evaluation
of operational parameters involved in solar photo-Fenton degradation of a pesticide
mixtureincludingtwocarbamateinsecticides(oxamylandmethomyl)wasdescribed
byZapataetal.(2009a,b).
6.5.4 Herbicides
6.5.4.1 Chlorotriazine Herbicides
Persistenceofthreechlorotriazineherbicides,terbuthylazine,simazine,andatrazine,and
methylthiotriazine herbicide prometryn was studied in the river water, seawater, and
groundwatersamplesexposedtosunlightanddarknessunderlaboratoryconditions(127
days)byNavarroetal.(2004).Theresultsshowedthatlighthadlittleeffectontheremoval
ofthefourherbicidesinriverwaterbuthadamarkedeffectontheirremovalfromseawater
andgroundwater.Surprisingly,thisremovalappearedtobeinverselyproportionaltothe
concentrationofdissolvedorganicmaterials(Navarroetal.2004).ProsenandZupančič-
Kralj(2005)describedtheevaluationofphotolysisandhydrolysisofatrazineanditsirst
degradationproductsinthepresenceofhumicacids.Underexposuretosunlight,atrazine,
desethylatrazine, and desisopropylatrazine were converted to 2-hydroxy analogs only
at pH 2 because of acid hydrolysis and possible contribution of photolysis (Prosen and
Zupančič-Kralj 2005). Kiss et al. (2007) described the photolytic degradation of atrazine,
simazine,prometryn,andterbutryn.Hernándezetal.(2008)reportthephotodegradation
ofchlorotriazineherbicides(terbuthylazineandsimazine),methylthiotriazineherbicides
(terbutryn and terbumeton), uracil herbicides (bromacil and terbacil), phenylurea herbi-
cide(diuron),andotherpesticides.