Polysaccharides as safer release systems for agrochemicals

21 Pages·2017·1.67 MB·English

Agron.Sustain.Dev.(2015)35:47–66
DOI10.1007/s13593-014-0263-0
REVIEWARTICLE
Polysaccharides as safer release systems for agrochemicals
EstefâniaVangelieRamosCampos&JhonesLuizde
Oliveira&LeonardoFernandesFraceto&BaljitSingh
Accepted:13October2014/Publishedonline:14November2014
#INRAandSpringer-VerlagFrance2014
Abstract Agrochemicalsareusedtoimprovetheproduction Keywords Polysaccharides .Slowreleaseformulations .
of crops. Conventional formulations of agrochemicals can Pesticides .Agrochemical
contaminate the environment, in particular in the case of
intensive cropping. Hence, there is a need for controlled-
release formulations of agrochemicals such as polysaccha- Contents
ridestoreducepollutionandhealthhazards.Naturalpolysac-
charidesarehydrophilic,biodegradablepolymers.Thisarticle 1. Introduction.................................
reviewstheuseofpolysaccharidesintheformofmicro-and 2. Controlled-releaseagrochemicaldeliverysystems
nanoparticles,beadsandhydrogels.Themainpointsare:(1) andtheiradvantages...........................
slowreleaseformulationsminimizeenvironmentalimpactby 3. Polymer-basedcontrolled-releaseagrochemical
reducing agrochemical leaching, volatilization and degrada- deliverysystems/formulations...................
tion.Forexample,50%oftheencapsulatedinsecticidechlor- 4. Classificationsofcontrolled-releaseagrochemical
pyrifos is released in 5 days, whereas free chlorpyrifos is deliverysystems..............................
releasedin1 day. (2) Slow release formulationsincreasethe 5. Commonlyusedbiopolymersforagrochemical
water-holdingcapacityofsoil.(3)Slowreleaseformulations deliverysystems..............................
bettercontrolweedsinthelongrun.(4)Polymer-clayformu- 6. Polysaccharide-basedcontrolled-release
lations store ionic plant nutrients. (5) Polymer hydrogel for- formulationintheformofmicrospheres
mulations reduce compaction, erosion, and water run-off. andnanoparticles.............................
Theyincreasesoilpermeabilityandaeration,infiltrationrates, 7. Polysaccharide-basedcontrolled-release
and microbial activity, and, in turn, plant performance. In formulationintheformofbeadsand
conclusion,polysaccharideformulationscanbeusedforsafer polymericnetworks/hydrogels ...................
useofagrochemicals. 8. Cyclodextrinsascarriersystemtoagrochemicals.....
9. Prospects...................................
10. Conclusion..................................
Estefânia Vangelie Ramos Campos and Jhones Luiz de Oliveira
contributedequallytothiswork Conflictofinterest...........................
:
Acknowledgments...........................
E.V.R.Campos L.F.Fraceto
DepartamentodeBioquímicadaUniversidadeEstadualde References.................................
Campinas,CampinasSP,Brazil
: :
E.V.R.Campos J.L.deOliveira L.F.Fraceto(*)
DepartamentodeEngenhariaAmbiental,UNESP-Universidade
1Introduction
EstadualPaulista,Av.TrêsdeMarço,511,AltodaBoaVista,
Sorocaba,SP,Brazil
e-mail:[email protected] Global demand for food due to the increase of the world
population has encouraged the maximization of agricultural
B.Singh
production, thus has sought the development of high-value
DepartmentofChemistry,HimachalPradeshUniversity,
Shimla171005,India crops, which include the use of pesticides, fertilizers, and
48 E.V.R.Camposetal.
equipment with high technology (Popp et al. 2013; Campos polymeric formulations that make their transportation easy
etal.2014). and reduce chances of inflammation and evaporation (Tsuji
Agrochemicalsplayamajorrole,inordertomaintainthe 2001). In one study, it is reported that the mobility of
increasingdemandoffoodtothegrowingpopulation.How- imidacloprid insecticide in soil from alginate-based con-
ever,harmfuleffectofthesechemicalstotheenvironmentand trolled-releasesystemdecreasedinverticalmobilityofinsec-
healthisamajorlimitationontheiruse.Hence,safehandling ticide from this system (44.7 %) as compared to technical
ofthesechemicalsisalsoverysignificant(AbhilashandSingh product (82.3 %). The volatilization of active ingredient has
2009).Agrochemicalisagenerictermforthevariouschem- alsobeenreportedtoreducewiththeuseofpolymericsystems
icalproductsusedinagricultureincludingpesticides,chemi- (Dailey 2004). In some agricultural application, e.g., seed
calfertilizers,manure,andothergrowthagents.Amongthese treatment,theinitialreleaseofpesticideisnotdesirableasit
chemicals,pesticidesplayaveryimportantroleinagricultural can harm the germinating seed itself. Due to autocatalytic
developmentbycontrollingthepestsbecausemorethan30– hydrolysis of poly lactic acid, it has been used to develop
40%ofthefoodproductionislostduetopests(Swinnenetal. thedelayedreleaseformulations(ZhaoandWilkins2005).It
2000) can be attributed mainly to residual pesticide in soils. Since
In the conventional formulations, the active ingredient is controlled-release systems would not release the AI at once,
mixed with other inert materials for their safer, easier, and this therefore lowers the pesticide residues in soil and thus
moreaccuratehandlingaswellasfortheireffectiveapplica- reducesthephytotoxicity(Moguletal.1996).
tion in the field. However, the immediate release of active Recently, many efforts have been made to develop pesti-
ingredientisthemaindrawbackassociatedwiththeseformu- cides delivery devices by using different materials. These
lations. Consequently, quick loss of these chemicals occurs materials include polymers (Kumar et al. 2014; Paradelo
from the field by various degradation processes including et al. 2014; Chowdhury 2014), silica (Qian et al. 2013;
photolyticdegradation,hydrolyticdegradation,andmicrobial Wanyika 2013; Zhang et al. 2014b), polyphosphates (Cini
degradation.Thesearealsolostbyvolatilization,evaporation, etal.2012),waxes(Rodriguesetal.2014),clay/organo-clay
and leaching that occur after their application to field. As a (Hickey et al. 2011; Sahoo et al. 2014), agro wastes
result,concentrationofactiveagentinthefielddecreasesvery (Petrucciolietal.2011).However,thematerialsusedtopre-
quickly,belowtheminimumeffectiveconcentrationrequired pare release systems should satisfy the some requirements
tomaintainthebiologicalefficacy.Inordertomaintaintheir related to the diffusion/solubility/degradation/fabrications.
concentrationtothedesiredlevel,thesechemicalsneedtobe The polymersingeneral haveall the characteristics required
applied again and again that leads to various environmental to develop the controlled-release formulations (Price et al.
andhealthproblems.Theexcessquantityofpesticidessome- 2014).
times may cause phytotoxicity. Recently, new formulations
havebeendevelopedthatmaymodifyperformanceofactive
compound which have less impact on environment (Fig. 1). 3Polymer-basedcontrolled-releaseagrochemicaldelivery
Theseformulationsreleasethechemicalsslowlyincontrolled systems/formulations
andsustainedmanner(Scher1999;Camposetal.2014).
Polymers,especiallyintheformofhydrogelsandbeads,are
very important in formation of controlled-release systems.
2Controlled-releaseagrochemicaldeliverysystems Theseformulations,besidesprovidingtheslow-releaseprofile
andtheiradvantages to the pesticide, also increase the water-holding capacity of
soil(Royetal.2014).Aftertheirdegradation,thesearehelpful
In a controlled-release system or controlled-release formula- ascompostinthefield(Kumaretal.2014).Naturalpolymers
tions,apesticideorotherbioactiveagentisincorporatedintoa are gainingconsiderableacceptanceoversyntheticpolymers
carrier, generally a polymeric material. These systems are as controlled-release devices because of their eco-friendly
capable of delivering active ingredient slowly and continu- nature,costeffectiveness,easyavailability,andbiodegradabil-
ouslyforlongerdurationtoaspecifiedtargetatadesiredrate ity(Azwaetal.2013).
(Fig.2).Theyminimizetheimpactoftheseharmfulchemicals
ontheenvironmentbyreducinglossesduetoleaching,vola-
tilization,anddegradationandtherebymaintainingbiological 4Classificationsofcontrolled-releaseagrochemical
efficacy of active ingredient (Nair et al. 2010; Gogos et al. deliverysystems
2012;Camposetal.2014).
The encapsulation of pesticides has been reported to en- Based on the concept of combining pesticide with polymer
hancetheirsafetyandhandlingaspects.Themorevolatilized matrices,thesesystemsarebroadlyclassifiedasphysicaland
and flammable liquid pesticides can be converted to solid chemicalcombinations.Thepolymeractsasarate-controlling
Polysaccharidesassaferreleasesystemsforagrochemicals 49
Fig.1 Schematicrepresentation
oftheuseofactiveagentin
agriculture,aswellassomeofthe
problemsrelatedtotheuseof
thesecompoundsinthe
environmentandasanalternative
tosolvetheseproblemstheuseof
controlledreleasesystems
device in physical combination and acts as a carrier for the core material in gelatin (Mohanty and Bohidar 2003). In
active agent in chemical combination (Kenawy 1998). The ionotropic gelation, pesticide containing polymer solution is
physicalcombination broadly comprises oflaminated,reser- poured drop wise into solution of metal ions. For example,
voir,andmonolithicsystems(Scher1999).Therearevarious solution of sodium alginate and pesticide added drop-wise
methods for encapsulation of pesticide in physical combina- intocalciumchloridesolution.
tion (Foy and Pritchard 1996; Scher 1999; Benita 2005; Another way to achieve the controlled-release pesticide
Venkatesan et al. 2009; Bansode et al. 2010). Tefft and formulations is by chemically attaching the active agent to
Friend(1993)havepreparedseriesofpolymericmicrosphere naturalorsyntheticpolymericmaterialsthroughalabilelink,
herbicideformulationsbyusingspray-dryingtechnique.The to regenerate the pesticide by hydrolysis or by enzymatic
best example of simple coacervation is the encapsulation of degradation (Kenawy 1998). These formulations especially
Fig.2 Representationofa
deliverysystembasedon
polysaccharidesforbioactive
compoundstargetingapplications
inagriculture.Asanexamplea
deliverysystemforplantgrowth
factors
50 E.V.R.Camposetal.
based on natural polymers formed by physical combination 5.3Cellulose
haveattractedconsiderableattentionasanexcellentcandidate
fordevelopmentofcontrolled-releasepesticideformulations. Cellulose (Fig. 3) is the most abundant polysaccharide in
nature,anditsusefulpropertiesincludebiodegradability,bio-
compatibility,lowtoxicity,andlowcost.Thecellulosemole-
cule is composed of sequences of β-D-glucopyranose units
5Commonlyusedbiopolymersforagrochemicaldelivery linked by β-(1,4) glycosidic chemical bonds (Beneke et al.
systems
2009).Celluloseanditsderivativesarewidelyusedasdeliv-
erysystemsforbioactivecompounds,sincetheyareenviron-
Polysaccharides are macromoleculescomposed ofmonosac-
mentallyfriendlyandcanbedegradedbymanybacteriaand
charide units linked by glycosidic bonds (Liu et al. 2008;
fungi present in the air, soil, and water (Raafat et al. 2012;
Raemdoncketal.2013).Thesecompoundsarefoundwidely
Akaretal.2012;Hemvichianetal.2014).
innature,includinginalgae(alginate),plants(cellulose,pec-
tin,cyclodextrin, and starch),microorganisms (dextran), and
animals(chitosan)(Liuetal.2008;Raemdoncketal.2013). 5.4Cyclodextrin
Themoleculescanbelinear(forexample,chitosan)orcyclic
(such as cyclodextrin), and differ in terms of their charge, Cyclodextrins (Fig. 3) are complex polysaccharides com-
which can be neutral, positive, or negative (Hassani et al. posed of glucose units (α-D-glucopyranose) connected by
2012).Advantagesofthesesubstancesincludetheirlowcost α-(1,4) bonds. Enzymatic modification is used to obtain α-
and ready availability, which facilitates the large-scale pro- cyclodextrin(composedofsixglucoseunits),β-cyclodextrin
ductionofproductsderivedfromthem. (seven units), and γ-cyclodextrin (eight units) (Pérez-Martí-
Oneoftheapplicationsofpolysaccharidesisincontrolled- nezetal.1999;PacioniandVeglia2007).Theconicalstruc-
releaseformulationsthatareusedinavarietyofareas,includ- ture,togetherwiththeorientationofhydroxylgroupstowards
ingagriculture.Someofthemainpolysaccharidesemployed theexterior,providesthecyclodextrinswithuniquephysico-
ascarriersinagriculturearedescribedbelow. chemicalproperties,sincetheycanbesolubilizedinanaque-
ousmedium,whileatthesametimetheycantransporthydro-
phobiccompoundsintheinterioroftheircavities(Brittoetal.
5.1Alginate
2004).Cyclodextrinsarewidelyemployedduetotheircapac-
itytoforminclusioncomplexeswithmanymolecules(Pérez-
Alginate(Fig.3),obtainedfrombrownmacroalgae,isalinear
Martínezetal.1999;DeCarvalhoanddeAlvesPinto2012;
polysaccharide composed of 1-4 bonds of β-D-manuronic Morin-CriniandCrini2013;Higuerasetal.2013;Fernandes
acid (M) and α-L-guluronic acid (G), with variations in the etal.2014;Garridoetal.2014).
compositionandsequentialstructurealongthechain(Zhang
andZhao2007;Lertsutthiwongetal.2008).Thepolysaccha-
ride can be used for the sustained release of agrochemicals 5.5Dextran
after passing through an ionotropic gellification process
employing metal ions (Fernández-Pérez 2007; Singh et al. Dextrans (Fig. 3) are polysaccharides derived from bacteria,
2013;WlodarczykandSiwek2013). composedofglucosemonomersconnectedbyα-(1,6)bonds
inthemainchainandbyα-(1,4),α-(1,3),andα-(1,2)bondsin
the branches (Ahmed et al. 2012; Raemdonck et al. 2013).
5.2Starch
Theextentofbranching,molecularmass,andotherproperties
of dextran vary according to the microorganism employed
Starch(Fig.3)isoneofthemainreservecompoundsinplants
(Ahmedetal.2012;DeCiccoetal.2014;MateenandHoare
andisabundantincerealgrains,legumes,roots,andfruits.Itis
2014).
a homopolysaccharide consisting of chains of amylose and
amylopectin.Amyloseisconstitutedofglucoseunitsconnect-
edbyα-(1,4)bonds,formingalinearchain,whileamylopec- 5.6Guargum
tin forms branched structures between the glucose units by
meansofα-(1,4)andα-(1,6)bonds.Therelativeproportions Guargum(Fig.3)isaneutralpolysaccharidecomposedofa
ofthese structuresvaryaccording to the speciesfromwhich main chain of D-mannopyranose residues connected by
the starchisobtained, and there can bevariationswithin the β-(1,4) glycosidic bonds, linked to D-galactopyranose resi-
samespecies,dependingonthedegreeofmaturityoftheplant duesbyα-(1,6)glycosidicbonds.Thesolubilityofguargum
(DenardinanddaSilva2009;Zhongetal.2013;Laycockand in cold water increases in line with the galactose/mannose
Halley2014). molarratio(Vaughnetal.2013;Rutzetal.2013).
Polysaccharidesassaferreleasesystemsforagrochemicals 51
Fig.3 Chemicalstructuresofthe
polysaccharidesusedtoprepare
carriersystemsforbioactive
compoundsemployedin
agriculture
5.7Pectin 6Polysaccharide-basedcontrolled-releaseformulation
intheformofmicrospheresandnanoparticles
Thepectins(Fig.3)areafamilyofpolysaccharidespresentin
the cell walls of higher plants. Their structures consist of D- Avarietyofpolymericnano-andmicroparticlescanbeused
galacturonicacidunitsconnectedbyα-(1,4)bonds,forminga as carriers for bioactive molecules. Depending on the mate-
linearpolysaccharideinterruptedbyhighlybranchedregions. rials and methods used, it is possible to obtain nano- and
The composition of pectin varies according to its botanical microspheres,ornano-andmicrocapsules,whichdifferboth
source(Lvetal.2014;Bayarrietal.2014). structurallyand interms oftheir composition.Nanocapsules
aresystemscomposedofapolymericshellandanoilynucle-
5.8Chitosan us,wheretheactiveprinciplecanbedissolvedinthenucleus
oradsorbedonthepolymericwall.Nanospheresdonotcon-
Thesubstancechitiniswidelyfoundinnature.Itisthemain tainoilintheircomposition,andconsistonlyofapolymeric
componentoftheexoskeletonofcrustaceansandisfoundin matrix.Inthiscase,thereisnodistinctnucleus,andtheactive
thecellwallsofcertainbacteriaandfungi.Chitosan(Fig.3)is principle is adsorbed or retained by the polymeric matrix
a partially deacetylated compound obtained by the (Schaffazick et al. 2003; Anton et al. 2008; Mishra et al.
deacetylation of chitin in an alkaline medium (Senel and 2010).
McClure 2004). Chitin is composed of D-glucosamine and
N-acetyl-D-glucosaminemonomers,linkedbyβ-(1,4)glyco-
sidic bonds (Senel and McClure 2004; Lertsutthiwong et al. 6.1Spheresandmicrospheres
2008).Theextentofdeacetylation,thecontentofimpurities,
andthedistributionofthemolarmassofchitosandependson Fernández-Pérezetal.(2000)studiedthemobilityinthesoil
the natural source of the primary material as well as the column of isoproturon released from alginate–bentonite
preparation method (Senel and McClure 2004; Laranjeira spheres. Simulations were made of typical soil structures,
anddeFávere2009). using columns consisting of fractions of sand, peat, altered
Chitosanhasacquiredwidespreadappealforuseinmany soil, and native soil. Sorption and desorption tests wereper-
applicationsindifferentfields,includinginagriculture,since formed for all the fractions. It was found that use of the
it is non-toxic, biodegradable, and biocompatible. As exam- alginate–bentonite formulations resulted in reductions in the
ple,recently,Grilloandcoworkershaspublishedtheprepara- vertical mobility of isoproturon, compared to columns con-
tionofchitosan/tripolyphosphatenanoparticlesascarriersys- tainingtheherbicidealone.Thegreatestsorptioncapacitywas
tems to paraquat herbicides. The results showed that these obtained for the peat layer. The use of alginate–bentonite
nanoparticles were able to decrease the herbicide toxicity could therefore provide an effective system for reducing the
(Grilloetal.2014). amount of herbicide leached through the soil, hence
52 E.V.R.Camposetal.
diminishing possible risks of contamination of underground only 1 day, while 50 % of the encapsulated insecticide was
waterbodies. releasedin5days.
Flores Céspedes et al. (2007) described the synthesis of Jerobin et al. (2012) studied the preparation of alginate
alginate spheres containing different adsorbents (bentonite, spheres containing the pesticide azadirachtin, using glutaral-
anthracite, and activated carbon), and the influence of the dehyde as the reticulation agent and different concentrations
adsorbentsonthe encapsulation efficiencyoftwoherbicides ofneemoil.Twoagents(starchandpolyethyleneglycol)were
(metribuzinandchloridazon),aswellasonthereleaseratesof usedtocoattheparticles.Bothcoatingsretardedthereleaseof
the active principles in aqueous media. The release rates of theactiveprinciple,comparedtouncoatedspheres,although
systems prepared with metribuzim were faster than those starchprovidedthebestmodulationofthereleaseprofile.The
containing chloridazon (which is more hydrophobic than releaseofazadirachtinincreasedwhenhigherconcentrations
metribuzim).Theformulationscontainingtheadsorbentspro- ofneemoilwereused,andtheresultsindicatedthatvariable
videdslowerreleaseofbothherbicides,comparedtotheuse quantitiesoftheoilcouldbesuccessfullyincorporatedinthe
ofthealginatespheresalone.Intermsofreducingtherelease coatedalginatespheres.
rate,themostefficientadsorbentwasactivatedcarbon. Kulkarnietal.(2000)preparedspheresofalginatetocarry
Guan et al. (2008) prepared, characterized, and evaluated azadirachtin, using glutaraldehyde as the reticulation agent.
theinsecticidalactivityofmicrocapsulesofalginateandchi- The formulations were optimized by varying the time of
tosanusedasacarriersystemforimidacloprid.Characteriza- exposuretothereticulationagentandthepercentageloading
tionoftheparticlesemployedconfocallasermicroscopyand of neem oil. Different concentrations were successfully
scanning electron microscopy. Tests investigated the release encapsulated in the alginate spheres. The particles presented
kineticsandphotodegradationoftheinsecticide,andassaysof a highly consistent average diameter, with no significant
the insecticidal activity of the systems employed the adult variations according to changes in the concentrations of the
stageoftheinsectMartianusdermestoideasamodel.Evalu- componentsofthespheres,althoughchangesinbothvariables
ationwasmadeoftheadsorptionofphotocatalystsbasedon affected the encapsulation efficiency of the active principle.
silver nitrate (AgNO ), titanium dioxide (TiO ), and sodium The release rate was faster for higher concentrations of
3 2
dodecylsulfate(SDS),andtheireffectonphotodegradationof encapsulated neem oil, while a longer time of exposure to
theinsecticide(undervisibleandUVradiation).Theparticles thereticulationagentdiminishedthereleaserate.Thevalues
obtainedwerestableandimidaclopridwasencapsulatedwith ofndeterminedbythereleaseoftheneemoilfromthespheres
anefficiencyofaround82%.Inreleaseassays,itwasshown were between 0.70 and 0.94. This result indicates that the
thatthereleasetimeoftheencapsulatedinsecticidewasupto releaseprocesswasgovernedbyFickiantransport.
eighttimeslonger,comparedtothefreeinsecticide,andthat Sopeña et al. (2007) determined the influence of several
alterations in the concentrations of alginate and chitosan af- variablesontheabilityofmicrospherestoreduceleachingof
fected the release profile. Tests with the photocatalysts indi- theherbicidealachlorinsandysoilsinordertoavoidcontam-
cated that the formulation utilizing Ag/TiO /SDS presented inationofundergroundwaterbodies.Themicrosphereswere
2
thebestadsorptioncharacteristicsandphotocatalyticactivity. able to retard the release rate of the alachlor in relation to
In terms of insecticidal activity, the toxicity of 50 % micro- commercial formulation. The percentage of herbicide eluted
capsuleswithimadaclopridandphotocatalyst(Ag/TiO /DSS) following application of the formulation was around 40 %.
2
washigherthanthatof95%freeimidacloprid,asshownby This percentage was less than expected for a soil with low
LD valuesof13.45and9.86mg/Lforthesystemswithout contents of clay and organic matter (since the interaction of
50
and with particles, respectively, demonstrating the effective- alachlorisinfluencedbythesetwosoilproperties).Changesin
nessoftheparticle-basedformulation. theparameterstopreparethemicrospherespromotechanges
Roy and coworkers (2009) investigated the synthesis of inthe release profileofthe herbicide,causing a reduction in
microspherescomposedofsodiumalginateandstarch,foruse leaching,increasethepersistenceandtheconcentrationinthe
asa carrier systemfor the insecticide chlorpyrifos. The con- upper soillayers. Theslowerrelease might alsoassistinthe
centrationsofalginate,starch,andreticulationagent(CaCl ) controlofweedsoverlongerperiods.
2
werevaried,andtheeffectsonthereleaseprofileandparticle El Bahri and Taverdet (2007) prepared and characterized
intumescencewereevaluated.Ahigherconcentrationofalgi- microspheresloadedwithethylbenzoateasapesticidemodel.
nateandlowerconcentrationofstarchfavoredintumescence, The microspheres were prepared by a solvent evaporation
asdidhigherpHandtemperature.Thereleaserateincreasedat technique, and double encapsulation was performed using
higher alginate concentrations, but decreased when the con- solvent evaporation followed by coacervation. The matrices
tent of starch was increased. The best release profile was testedincludedethylcellulose,celluloseacetatebutyrate,and
obtained for microspheres containing more alginate and less poly(methyl methacrylate). The microparticles were charac-
starch.Useoftheparticleseffectivelycontrolledthereleaseof terized by scanning electron microscopy (SEM) and Fourier
theinsecticide,since50%offreechlorpyrifoswasreleasedin transform infrared spectroscopy (FTIR), and measurements
Polysaccharidesassaferreleasesystemsforagrochemicals 53
weremadeoftheaverageparticlesize,togetherwithinvitro fertilizerrelease,whichwouldbeusefulindroughtregions,or
release tests and analysis of the parameters involved in syn- wherewatersuppliesarelimited.
thesisofthemicrospheres.Itwasfoundthatuseofthecellu- Han et al. (2009) described a film based on starch and
losederivativesproducedmicrospheresthatweremoreporous polyvinyl alcohol (PVA) for the coating of soluble fertilizer
thanthoseobtainedusingpoly(methylmethacrylate),andthat granules.Evaluationwasmadeoftheinfluenceofthestarch/
thesizeoftheparticleswasstronglydependentofthepolymer PVAratio,permeabilitytowaterandammonium,absorption
matrix, its concentration, and the agitation speed employed capacity,andbiodegradabilityinsoil.Thefilmswerecharac-
during preparation, but less dependent on the emulsifier. terizedusingFTIR,X-raydiffraction(XRD),andatomicforce
Capture of the active principle was strongly dependent microscopy (AFM). The water absorption, permeability to
on the polymeric matrix, the polymer concentration, and water, and permeabilitytoammoniumincreased inlinewith
the polymer/active principle ratio. The release of ethyl the PVA content, while reduced concentrations of starch af-
benzoate could be restricted by using the poly(methyl fected the compatibility of the films. The permeability and
methacrylate) matrix, increasing the polymer concentra- absorption capacity of films reticulated with formaldehyde
tion, or by using coated microspheres (microcapsules). decreased as the formaldehyde concentration increased, due
The use of cellulose matrices to obtain formulations tointramolecularbondingofthehydroxylsofstarchandPVA.
able to deliver sustained release of agrochemicals was After50daysofexposureinthesoil,thefilmsbecamesmall,
therefore proven viable. fragile,andbroken,indicativeoftheirnaturalbiodegradation
Wu and Liu (2008) developed and characterized granules inthesoilenvironment,andtheirfinalweightlossexceeded
ofchitosanandpoly(acrylicacid-co-acrylamide)forthecon- 50%.ThefindingsshowedthatstarchandPVAcouldbeused
trolledreleaseofnitrogen,phosphorus,andpotassium(NPK), toproducefilmstocoatgranulesofsolublefertilizers,dueto
andtheretentionofwater.Thegranuleswerecharacterizedby theirinherentpermeabilityandbiodegradability.
FTIR and atomic absorption spectrophotometry, and tests Guan et al. (2011) investigated the use ofalginate micro-
investigated the in vitro release kinetics and the absorption spheres as carriers of the hormone ecdysone. The micro-
of water. The granules consisted of three layers: a water- spheres were prepared using internal gelification, and were
soluble nucleus containing the NPK nutrient mixture, an characterizedbyconfocalscanninglasermicroscopy(CSLM)
internalcoatingofchitosan,andanexternalcoatingofabsor- andSEM.Invitroreleasetestswereperformed,togetherwith
bent polymer. The granules contained 7.98 % potassium, evaluationofthestabilityofecdysone,eitherfreeorencapsu-
8.14 % phosphorus, and 8.06 % nitrogen, and successfully lated,duringexposuretoultravioletlight.Toxiceffectswere
modulatedthereleaseofthefertilizer,sincelessthan75%of evaluatedusingthelarvaeofM.dermestoidesChevrolat.The
the nutrients had been released after a period of 30 days. alginatemicrospheresshowedahighencapsulationefficiency
Addition of the granules to the soil significantly improved ofaround81%,confirmingtheefficiencyofthepreparation
the water retention capacity. The formulation was therefore technique, and an average diameter of 52.8±9.8 μm. The
shown to be a good slow release fertilizer, with the added concentration of the reticulation agent had a direct effect on
benefitofbeingabletoassistwaterretention.Itcouldthere- theintumescencecapacityoftheparticles.Theinvitrorelease
fore have potential applications in the remediation of arid and photodegradation experiments confirmed that the
regionsandareasaffectedbydesertification. particles were able to modulate the release profile of the
Ni et al. (2009) developed dual-coated particles for the hormone, as well as reduce its photodegradation. The
slowreleaseofureaandtheretentionofwater.Ethylcellulose toxicitystudies showedthatthe microspherescontainingthe
was used for the internal coating, and poly(acrylic acid-co- hormoneweremoretoxicthanfreeecdysone,asreflectedina
acrylamide)fortheexternalcoating.Thestructuralandchem- lower EC value. Finally, the photostability of the
50
ical characteristics of the material were determined using microparticles was indicative of a long useful lifetime when
SEM, FTIR, and differentialcalorimetry(DSC),and evalua- usedinfieldapplications.
tionwas madeofits effectivenessinretarding the release of Paula et al. (2010) prepared and characterized micro-
fertilizerinthesoil,aswellasitsabilitytoabsorbwaterandits spheres composed of chitosan and cashew tree gum, which
degradability.Theparticlesconsistedofthreelayers:anucleus were used as carriers of the essential oil of Lippia sidoides,
containing pure urea, an inner coating of ethylcellulose, and which possesses insecticidal properties. The particles were
an outer coating of the absorbent copolymer. The nitrogen characterized using SEM, infrared spectroscopy, UV-Vis
content was 21.1 %, and the particles were able to absorb a spectroscopy, thermogravimetric analysis (TGA), and DSC.
quantity of water equivalent to 70 times their own weight. Evaluation was made of the encapsulation efficiency, intu-
Releasekineticsexperimentsrevealedthataround75%ofthe mescence, in vitro release profile, and insecticidal activity
activeprinciplehadbeenreleasedafter30daysofincubation against the larvae of Aedes aegypti. The particles showed
withsoil.Theadditionoftheseparticlestosoilcouldtherefore spherical morphologyand were highlyporous. The chitosan
significantly improve water retention while providing slow particles(CT)hadanaveragesizeof1.27μmandanessential
54 E.V.R.Camposetal.
oilencapsulationefficiencyof4.4%,whilethecorresponding assessedintermsofthereleaseprofileoftheactiveprinciple,
valuesforchitosan-cashewtreegumparticles(CT-CTG)were its mobility in a calcareous soil, and the morphology of the
1.53μmand2.4%.TheintumescenceofCTexceededthatof granules. Encapsulation efficiency close to 100 % was
CT-CTG,andCTrequiredashortertimetoreachequilibrium, achievedandthereleaserateoftheactiveprinciplecouldbe
whiletheTGAandDSCanalysesdemonstratedthattheCT- controlledbyadjustingthethicknessofthecoatingagentand
CTGparticlesweremorethermallystablethanCT.Theuseof modifying its surface by addition of the plasticizer. In soil
areticulationagentresultedinapolymericnetworkthatwas mobility experiments, it was shown that coating of the
more rigid, with a low coefficient of diffusion, resulting in granuleswasabletoreduceleachingoftheherbicide.
release that was more prolonged. In the insecticidal activity
assays,bothtypesofparticleshowedlarvicidalactivity,with 6.2Nanoparticles
thelarvaeofA.aegyptibeingsuccessfullyeliminatedafteran
exposure period of 72 h. These findings confirmed the suit- dos Silva et al. (2011) studied the release profile and soil
ability of polysaccharides such as chitosan and cashew tree sorptionofalginate/chitosannanoparticlesusedascarriersof
gum for use as matrices to carry bioinsecticides designed to the herbicideparaquat. Theaverage sizeofthe particleswas
controltheproliferationofinsectlarvae. 635±12 nm, and the encapsulation efficiency was 74.2 %.
Quiñonesetal.(2010)describedtheuseofchitosanmicro- Encapsulationoftheherbicideinthenanoparticlesresultedin
spheres to carry synthetic analogues of brassinosteroids and asignificantchangeinthereleaseprofileoftheherbicide,with
diosgenin derivatives, and tested different ligands in the the release being slower, compared to free paraquat. In soil
reactions. The systems were characterized using FTIR and sorption experiments, it was found that sorption of both the
DSC, and release assays were realized in water at different encapsulatedandfreeformswasdependentonthecontentof
pHvalues.TheFTIRandDSCresultsshowedthattheactive organic matter in the soil, although the sorption profile was
principles had been efficiently encapsulated in the chitosan reducedwhenparaquatwasassociatedwiththenanoparticles,
microspheres. When ethanolic solutions of the steroids were henceimprovingtheherbicidalaction.
used,theencapsulationpercentageincreased,andinthecase Gengetal.(2009)developedandcharacterizednanoparti-
ofthediosgenins,thebestligandwasdicarboxylicacid.The clesofFe0 stabilizedbychitosan(CTO-Fe0),and nanoparti-
release kinetics assay using water revealed that the least clesofFe0synthesizedinanethanol–watermixture(EW-Fe0),
efficiently encapsulated steroids were released fastest from which were tested for the reduction of Cr(VI). Characteriza-
the particles. These results demonstrate that molecular tion was performed using FTIR, XRD, and TEM. They
modificationscanbeusedtodesigneffectivesystemsforthe showed that the size average of the particles was 82.4 nm,
deliveryandreleaseofagrochemicals. and that the nitrogen and oxygen atoms were the sites of
Sopeñaetal.(2011)developedethylcellulosemicrospheres bonding of chitosan on the iron, and were responsible for
fortheprogressivereleaseoftheherbicidenorflurazon(NFZ) the stability of Fe0 in the nanoparticles. The maximum rate
and compared photodegradation rates with those of a com- ofreduction ofCr(VI)wasthree times greater for CTO-Fe0,
mercialformulation.Themicrosphereswereabletoprovidea comparedtoEW-Fe0.Becauseoftheprotectionprovidedby
gradual and sustained release of NFZ, as well as substantial chitosan, CTO-Fe0 presented good stability in terms of
protectionagainstphotolysisoftheherbicide,inbothaqueous oxidation, and retained a high reduction capacity after
solutionandsoil.Theslowreleaseactedtoreducetheamount exposure to ambient air for 2 months. The combination of
of herbicide available for photodegradation. The rate of fast reaction kinetics and good resistance to oxidation
photodegradationinaqueoussolutiondiminishedinthepres- indicates that nanoparticles of Fe0 stabilized with chitosan
enceofcolloidalsoilcomponentssuchasgoethiteandhumic could be used as an effective agent for environmental
acids,duetotheirabilitytoblockUV,whilethiseffectwasnot remediation.
observed for clay (montmorillonite) and fulvic acids, for Laoetal.(2010)producedanewamphiphilicderivativeof
which the results were similar to those obtained for the mi- chitosan, N-(octadecanol-1-glycidyl ether)-O-sulfate chito-
crospheres alone. The use of ethylcellulose in sustained re- san,asacarrierfortheinsecticiderotenone.Characterization
leaseformulationscanthereforereducethedosesofherbicide was performed using FTIR and nuclear magnetic resonance
required,sincelossesbyphotolysisareminimized.Theeffects (NMR), and the critical micellar concentration (CMC) was
could be especially advantageous during the first hours fol- investigated, together with the release kinetics in water. The
lowing foliar and soil applications, with reductions in losses FTIRandNMRresultsconfirmedthesuccessfulsynthesisof
duetoleachinganddissipation. NOSCS, and the CMC was between 3.55×10−3 and 5.50×
Flores-Céspedes et al. (2009) studied the preparation and 10−3mg/mL.Thepolymericmicellesformedwerespherical,
characterization of granules of the herbicide chlorsulfuron with a size range of between 167 and 204 nm, and the
coated with ethylcellulose and with addition of a plasticizer nanoparticleswereformedbyself-assemblyinaqueoussolu-
(dibutyl sebacate). The effects of the amendments were tion.Theencapsulationofrotenoneincreaseditssolubilityin
Polysaccharidesassaferreleasesystemsforagrochemicals 55
water 1,300-fold, while in vitro release assays demonstrated dichlorprop was more toxic to Scenedesmus. The use of
thatthenanoparticlesprovidedsustainedreleaseoftheinsec- chitosannanoparticlesresultedinagreaterreductionintoxic-
ticide. The properties of nanomicelles based on NOSCS en- itytoScenedesmus,comparedtoplainchitosan,whileinthe
able them to be used as carriers to encapsulate and case of Chlorella, the opposite was observed. The chiral
subsequently release insoluble pesticides employed in selectivityoftheherbicidetothetwoalgaewasalteredwhen
agriculture. itwascomplexedwitheitherplainchitosanorthenanoparti-
Wen et al. (2010) studied the bioavailability of the chiral cles,whichcouldbeexplainedbydifferencesinthephysico-
herbicidedichlorproptothegreenalgaChlorellapyrenoidosa, chemicalpropertiesofthetwomaterials,orbydifferencesin
in the absence and presence of chitosan nanoparticles. The thecellwallsofthetwoalgae.
particleswerecharacterizedbyFTIR,X-rayspectroscopy,and Celis et al. (2012) used different methods to prepare a
TEM,andtestsofthetoxicityanddissipationoftheherbicide bionanocompositematerialbasedonchitosanandclay(mont-
were performed. The average diameter of the chitosan parti- morillonite),usedasanadsorbentfortheherbicideclopyralid
cles was smaller than 100 nm. In the absence of chitosan, present in an aqueous solution or in a mixture of water and
dissipationoftheS-enantiomerinaChlorellavulgarisculture soil.ThenanoparticleswerecharacterizedusingFTIR,X-ray
medium was faster than that of the R-enantiomer, while the spectroscopy, and SEM. The bionanocomposites showed
order of dissipation was reversed when the polysaccharide goodherbicideadsorptioncapacityatpHlevelsatwhichthe
was used. In the absence of chitosan, the R-enantiomer was anionicformoftheactiveprinciple and the cationicformof
moretoxictothealgae,whiletheSformwasmoretoxicinthe chitosan predominated. Removal of the herbicide from
presence of chitosan. These observations provided a clear aqueous solution was more effective when a higher
indication that chitosan was able to modify the concentrationofchitosanwasusedinthebionanocomposite.
enantioselectivebioavailabilityoftheherbicide,whichcould At slightly acid pH, the composites effectively adsorbed
beofuseinenvironmentalprotectionapplications. clopyralid from soil. The use of this type of formulation
Liu et al. (2011) evaluated the capacity of complexes of could help to limit the mobility of anionic pesticides in the
polymers and cyclodextrinstoadsorband removepesticides environment,reducingrisksofcontamination ofsurface and
present in water. Seven different formulations were synthe- subterraneanwaterbodies.
sizedusingepichlorohydrinasareticulationagent,andwere FengandPeng(2012)synthesizedanewcompoundbased
then characterized using SEM, IR spectroscopy, and DSC. on chitosan, using carboxymethyl chitosan (CM-C) with
The synthesized particles presented a homogeneous porous ricinoleicacid(RA).Investigationsweremadeofthereaction
spherical morphology. The ability of the particles to adsorb conditions required for its formation, and the products were
pesticides was confirmed using adsorption kinetics and iso- characterizedwiththeaimofproducingaformulationsuitable
therm assays, in the presence of a mixture of 10 pesticides. foruseasacarrierofthebiopesticideazadirachtin(AZA).The
Theadsorptionoccurredduetomultipleinteractionsincluding concentrationsofthecomponentswerevaried,andthestabil-
inclusioninthecyclodextrins,hydrogenbridges,andphysical ityoftheresultingformulationswasdeterminedbymeasure-
adsorption, among others. Multivariate regression analysis mentsofparticlesize,polydispersion,andzetapotential.The
enabledidentificationoftheparticlepropertiesthatweremost particleswereanalyzedusingIRspectroscopyandSEM,and
significantintermsofadsorptionpotential:cyclodextrincon- the release of AZA was measured in an aqueous medium.
tent,swellingability,andporesize.Amixtureofthreetypesof Under suitable conditions, the liposoluble group of RA
particlesthatshowedthebestadsorptionpotentialwasusedto reactedwiththehydrosolublegroupofCM-C,producingthe
determinetheremovalofthepesticidesfromwater,sincethis amphiphiliccompoundRA-CM-C,amicellarpolymerthatis
combination was most suitable for the range of pesticide self-assembling in water. The concentrations of the compo-
concentrations likely to be found in the environment. The nentsinfluencedthestabilityoftheformulations.Theparticles
goodabilityofparticlesbasedonpolymersandcyclodextrin presented good polydispersion, with a size range of 200–
toadsorb pesticides isindicative oftheir potential for use in 500 nm, as well as smooth spherical morphology and high
waterremediation. zeta potential.The AZA encapsulationefficiencywas 56%,
Wen et al. (2011) synthesized and characterized chitosan and the particles were able to release the pesticide over a
complexesandnanoparticlesofchitosancontainingthechiral periodof11days.Theuseofthecarrierassistedthesolubili-
herbicidedichlorprop,withtheaimofreducingthepotential zation in water of this lipid-soluble pesticide, and could
forleachingandcontaminationofsubterreaneanwaters.The thereforeofferadvantagesinagriculturalapplications.
complexes were characterized by FTIR, and the inhibition Tao et al. (2012) synthesized chitosan modified with 1-
ability of the herbicide was evaluated using two different naphthylaceticacid,whichisanimportantplantgrowthhor-
algae, C. vulgaris and Scenedesmus obliquus. It was found mone. The material was characterized using FTIR, thermo-
that the sensitivity of the algae varied according to species, gravimetricanalysis,andNMR.Inthemodifiedchitosan,the
with S-dichlorprop being more toxic to Chlorella, while R- main polysaccharide chain contained both amino and
56 E.V.R.Camposetal.
naphthylacetyl groups. The release of the 1-naphthylacetic formulationsofpesticidesafterionotropicgelationwithmetal
acid was strongly dependent on pH and temperature, and ions(Işıklan2007).Althoughtheionotropicgelationofalgi-
couldcontinuefor55daysatpH12and60°C.Despitethis natewithmetalionisasimpleandfastwayofobtainingbead
dependence, the formulation offers potential for the slow formulationsbutitisassociatedwithalimitationwhichisloss
releaseofagrochemicalssuchashormones. ofactiveingredientduringbeadpreparation(FerreiraAlmeida
Zhongandcoworkers(2013)developedasuperabsorbent andAlmeida2004;GeorgeandAbraham2006).Onewayto
polymer based on sulfonated maize starch (SMS) and poly circumvent this limitation is to prepare bi-polymeric bead
(acrylicacid) (PAA) for the incorporation ofrockphosphate formulationbyusingsomeothernaturalpolysaccharidealong
(RP).ThecomplexesformedwerecharacterizedusingXRD withalginate.Itisworthtomentionherethatalginateinsoil
and FTIR, and in vitro release assays and water absorption undergoes enzymatic or radiolytic degradation to produce
experiments were performed. It was found that RP could be plant growth promoter oligo-alginates which were found to
satisfactorilydispersedintheSMS-PAAmedium,andthatthe elicitgermination,shootelongation,androotgrowthpromot-
waterabsorptioncapacitywasinfluencedbytherelativeratios ingactivity(AbdEl-Rehim2006).Thepresenceofalginatein
ofthedifferentcomponents(SMS,PAA,andRP).Thesystem pesticide formulations also helps in crop growth. Various
wasabletoprovideasustainedreleaseofphosphate,aswell clays have been used as the modifiers or additives in
asexcellentwaterretention,makingitpotentiallyvaluablefor polymer-based controlled-release systems to further control
useincropproduction. thereleaseprofilethepesticides(Flores-Céspedesetal.2009;
Table 1 provides a summary of the main polysaccharides BergayaandLagaly2013).FloresCéspedesetal.(2013)have
usedinthestudiesdescribedabove,togetherwiththetypesof used bentonite as modifying sorbents in alginate-based con-
carriersystemsandactiveprinciples. trolled-releaseformulations.Theyhaveobservedthedecrease
the rate of release of active compound as compared to the
market product. Apart from controlling the release rate, the
incorporationofbentoniteinalginatehasalsobeenfoundto
7Polysaccharide-basedcontrolled-releaseformulation increasethegranuleyields,thereforeresultsinmoreefficient
intheformofbeadsandpolymericnetworks/hydrogels andcheaperformulation(BergayaandLagaly2013).Theclay
also helps in retaining nutrient ions and thus make soil as a
Hydrogelsarehydrophilicpolymericnetworksthatareableto usefulmediumforthegrowthofplantsdueitsionexchange
retain large quantities of water without losing their three- nature(Dixon1991).
dimensional structure (in other words, without dissolving). Alginates-basedcontrolled-releaseformulationshavebeen
Cross-bondingbetweenthepolymericchainsformsthetridi- investigated with various herbicides such as monolinuron,
mensionalstructure,andthenetworkcanbebuiltindifferent desmetryn, chloridazon, atrazine, simazine, and chloroxuron
ways,bymeansofcovalentbonds,hydrogenbridges,vander as active ingredients. Release rate from these formulations
Waals forces, or physical interactions (Yoshida et al. 1993; showed sufficient retardation of herbicide release (Pfister
Andrianov andPayne 1998;Qiu and Park2012).Hydrogels etal.1986).PeppermanandKuan(1993)haveobservedthe
are prepared by using natural/synthetic polymers. Those ob- alginate formulations have decreased the rate of release of
tained from natural polymers possess mechanical properties metribuzin herbicide compared to the conventional formula-
that cannot be controlled, due to the inherent variability. On tion.Inanotherstudy,thereleaserateofisoproturonherbicide
the other hand, hydrogels derived from synthetic polymers fromthe alginateformulationalsodecreasedascomparedto
have consistent defined properties, although most of these the technical product (Villafranca-Sánchez et al. 2000). The
substances are not biodegradable (Hoffman 2012). There is useofcontrolled-releasesystemshasalsoreducedthevertical
currently a move towards the use of “intelligent” hydrogels mobility of herbicide into the soil (Fernández-Pérez et al.
that are able to respond to environmental stimuli (such as 2000). Further, the utility of these systems can be improved
light,pH,temperature,orthepresenceofspecificmolecules), bycombiningmorethanoneherbicidesorcombiningherbi-
resulting in structural changes in the hydrogel and the con- cide and fertilizer in a single formulation (Johnson and
comitant release of the active agent (Soppimath et al. 2001; Pepperman 1998). The application of pesticide mixture in
QiuandPark2001). agriculture is also desirable to provide effective pest control
Alginate is a water-soluble linear polysaccharide can be andtocounterthedevelopmentofresistanceinthepathogens
used to prepare the agrochemical loaded beads formulation (Birch and Shaw 1997). After comparing, release rates and
throughionotropicgelation(ErtesvågandValla1998;Mørch mechanismsofherbicidesfromsimpleconventionalformula-
etal.2006).Alginatebeadsarepreparedbydroppingasolu- tions completely finished within single day, whereas release
tionofsodiumalginatecontainingthedesiredactiveingredi- fromalginatebasedoncontrolled-releasesystemslastedupto
entintheformofdroplets,intoametalionsolutionwhichacts 2weeks.Hence,itispossibletocontroltherateofpesticide
as crosslinker. These have been used as controlled-release releasebysuitablymodifyingandadjustingtheexperimental