Environmental Engineering Reference
In-Depth Information
varietyofinteractionsamongmicroorganisms,soilconstituents,andthepesticides(Arias-
Estévezetal.2008;Toppetal.1997).Thus,degradationratesdependonmanymicrobio-
logical, physical, and chemical properties of the soil and physicochemical properties of
thepesticides(Arias-Estévezetal.2008;Raoetal.1983).Degradationofpesticidescanbe
throughseveralmechanisms,suchasoxidation,reduction,orhydrolysis.
Sorptionplaysafundamentalroleintheadvective-dispersivetransportdynamics,per-
sistence,transformation,andbioaccumulationofpesticides(Arias-Estévezetal.2008;De
Jonge et al. 1996). The sorption processes depend on the properties of the analytes, for
example, base-acid properties, pK
a
. The sorption process is different for nonionic and
ionicanalytesorweaklyacidic,weaklybasic,andneutralpesticidesbecausethesorption
ofthesepesticidesdependsonthesoilpH,electriccharge,andionicstrength.Othersoil
constituentsthanorganicmatter,includingclaysandironoxides,areimportantsorbents
forthesorptionofioniccompounds.Themolecularnatureofsoilorganicmatterhasbeen
provedtobeimportantindeterminingsorptiononnonionicpesticides.Numerousstudies
have determined sorption isotherms in order to investigate the inluence of soil param-
eters(organicmattercontent,claycontent,pH,etc.)onthesorptionofweaklyacidic,basic,
orneutralpesticidesbyawidearrayofsoils(Arias-Estévezetal.2008).Figure6.1showsa
schematicdiagramofthesorptionreactions(smallkvalues)andinstantaneoussorption
equilibria(capitalK),whichmayoccurwithapesticideinsoilwater,asneutral,basic,or
acidicmolecules.Slowsorptionreactionsmayalsooccurwithcationicoranionicspecies.
-
K
ads
P
-
P
-
P
abs
o
K
abs
k
abs
P
abs
P
w
k
des
k
bind
bound
P
s
+
+
P
w
P
s
+
K
ads
Aqueous
phase
Soil
phase
FIGURE 6.1
Schematicdiagramofthesorptionreactions(smallk)andinstantaneoussorptionequilibria(capitalK),which
may occur with a pesticide in soil water, as neutral, basic, or acidic molecules. Slow sorption reactions may
also occur with cationic or anionic species. Ps and Pw are the potentially available adsorbed-phase and dis-
solved-phasepesticidelevels.(Reprintedfrom
Agric. Ecosyst. Environ.,
123,Arias-EstévezM.,López-Periago,E.,
Martínez-Carballo,E.,Simal-Gándara,J.,Mejuto,J.-C.,andGarcía-Río,L.,Themobilityanddegradationofpesti-
cidesinsoilsandthepollutionofgroundwaterresources,247-260,(2008),withpermissionfromElsevier.)
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