Pesticide Residues in the Environment - Pesticides: Evaluation of Environmental Pollution - page 175

R

T MO T N O

kw k MO

MO

0--2cm

W

N

T m

W (t) kw + MO (t) k MO
W (t) + MO (t)

km=

-2- -6cm

M

FIGURE 6.7
Schematicmodelusedforthecalculationofdegradationandtransfersinandbetweensoilfractions:W(water-
extractable fraction), MO (methanol-only-extractable fraction), N (nonextractable fraction), M (methanol-
extractablefraction),R(runoff).(FromSaison,C.,Louchart,X.,Schiavon,M.,andVoltz,M.,Evidenceoftherole
ofclimatecontrolandreversibleagingprocessesinthefateofdiuroninaMediterraneantopsoil. Eur. J. Soil Sci.,
2003,61,576-587.CopyrightWiley-VCHVerlagGmbH&Co.KGaA.Reproducedwithpermission.)

substrates showed faster pesticide dissipation in the presence of lignocellulosic materi-
als, as in garden compost and vine branch straw (Coppola et al. 2011). The adsorption
andtherateofdegradationof 14 C-labeledisoproturonandmecoprop(MCPP)atconcen-
trations from 0.0005 to 25,000 mg/kg were determined in biobed soil (Henriksen et al.
2003).Thebiobedmaterialshowedenhancedabilitytoadsorbthetwoherbicides.K d was
5.2L/kgforisoproturonand1.6L/kgforMCPPinbiobedmaterial,whichishigherthan
innaturalsoil(Henriksenetal.2003).Theinluenceoflipophilicityandformulationon
the distribution of eight pesticides (isoproturon, chlorotoluron, triasulfuron, phenmed-
ipham,pendimethalin,chlorpyrifos,difenconazole,andpermethrin)inlaboratory-scale
sediment-watersystemswasdescribedbyBromilowetal.(2003).Sorptionequilibrium
wasreachedbetween15and30days,theproportionofpesticideinthesedimentrang-
ing from 20% for acidic and therefore polar triasulfuron to 97% for the lipophilic per-
methrin(Bromilowetal.2003).Somedegradationwasobservedforallcompoundsover
90 days; for some compounds and formulations, enhanced degradation occurred after
20-60 days. Degradation rates ranging from relatively high values for phenmedipham
(DT 50 2.5-4days)tolowvaluesfortriasulfuronanddifenconazole(DT 50 >>90days)were
observed.Itisconcludedthatlipophilicityisthechiefdeterminantofpesticidedistribu-
tion in sediment-water systems (Bromilow et al. 2003). Phenmedipham was degraded,
presumably by alkaline hydrolysis, much more quickly in the pond water than in the
sediment,illustratingtheroleofsorptionandalso,possibly,thelowersurfacepHofclay
particles in slowing breakdown (Bromilow et al. 2003). The ability of microorganisms
to degrade isoproturon, atrazine, and mecoprop within aerobic aquifer systems was
describedbyJohnsonetal.(2003).Biodegradationwasconirmedbytheformulationof
monodesmethyl-anddidesmethyl-isoproturon.Mineralizationofplant-incorporatedres-
iduesof 14 C-isoproturoninarablesoilsoriginatingfromdifferentfarmingsystemswas
describedbyvonWirén-Lehretal.(2002). 14 C-isoproturonresidueswereincorporatedin
wheatplantsbygrowingseedlingsfor18daysinquartzsandwithnutrientsolutionthat
wastreatedwithring-labeled 14 C-isoproturon,resultingin 14 C-concentrationequivalent
to 15.4 nmol isoproturon per g of dry shoot mass. The residues were characterized by