Pesticide Residues in the Environment - Pesticides: Evaluation of Environmental Pollution - page 165

a greater sorption potential than the other pesticides (Bondarenko and Gan 2004). Chai
et al. (2009) described the dissipation of acephate, chlorpyrifos, cypermethrin, and their
metabolitesstudiedingreenmustard( Brassica juncea (L.)Coss.)andinsoils.Dissipationof
acephate,chlorpyrifos,andcypermethriningreenmustardsandtopsoilsfollowedirst-
order kinetics, with half-lives between 1.1 and 3.1 days in green mustards and between
1.4and9.4daysintopsoils(26°C)(Chaietal.2009).Themetabolitesmethamidophosand
3,5,6-trichloropyridinol derived from acephate and chlorpyrifos amounted to less than
10% and 25% by mass of the parent compounds in soils. The metabolites methamido-
phosand3,5,6-trichloropyridinolwereobservedatlowlevelsofbelow3.22mg/kgintop-
soilsanddissipatedcompletelyin28and63days,respectively.Thedegradationratesof
pesticides in the soil were equal to or slightly faster than the degradation rates in tem-
perate soils (Chai et al. 2009). The degradation of chlorpyrifos in poultry-, swine-, and
cow-derived efluents and efluent-soil matrices was studied using batch- and column-
incubation studies (Huang et al. 2000). Chlorpyrifos was degraded by aerobic microbial
processesinanimal-derivedlagoonefluents.Microbialcommunityanalysisbydenatur-
ing gradient gel electrophoresis of polymerase chain reaction-ampliied 16S ribosomal
ribonucleicacidgenesshowedthatthesinglebandbecamedominantinefluentduring
chlorpyrifosdegradation.Insoils,bothbioticandabioticdegradationcontributedsignii-
cantlytotheoveralldissipationofchlorpyrifos.Largedifferencesinthedegradationrates
wereobservedbetweensoils,withthefastestrateobservedinsoilwithhigherpHvalues
andcation-exchangecapacity.Theresultsindicatethatefluent-inducedincreasesinsoil-
solutionpHforlow-pHsoilsmayenhancedegradationthroughhydrolysisbyasmallper-
cent(Huangetal.2000).Kravvaritietal.(2010)describedthedegradationandadsorption
ofchlorpyrifosandterbuthylazineinthreedifferentbiomixturescomposedofcomposted
cotton crop residues, soils, and straw in various proportions and also in sterilized and
nonsterilized soils. The results obtained by the authors show that compost biomixtures
degradedthelesshydrophobicterbuthylazineatafasterratethansoil,whiletheopposite
wasevidentformorehydrophobicchlorpyrifos.Theresultswereattributedtotherapid
abiotic hydrolysis of chlorpyrifos in the alkaline soil (pH 8.5), compared with the lower
pHofthecompost(6.6),butalsototheincreasingadsorption(K d =746mL/g)andreduced
bioavailability of chlorpyrifos in thebiomixtures compared with soil(K d =17 mL/g), as
veriiedbytheadsorptionstudies(Kravvaritietal.2010).Apesticidemixturecontaining
chlorpyrifos, isoproturon, pendimethalin, chlorothalonil, epoxiconazole, and dimetho-
atewasincubatedinbiomixandtopsoilatconcentrationstosimulatepesticidedisposal
(Foggetal.2003).Degradationwassigniicantlyquickerinbiomixthanintopsoil.While
degradation of pesticides applied in mixture to biomix was slower than when applied
alone,DT 90 valuesindicatethat,eveninamixture,pesticideswillbedegradedwithin12
months (Fogg et al. 2003). An effective chlorpyrifos-degrading bacterium (named strain
YC-1)wasisolatedbyYangetal.(2006)fromthesludgeofthewastewatertreatingsystem
ofanorganophosphoruspesticidemanufacturer.Basedonthephenotypicfeatures,phy-
logenetic similarity of 16S rRNA gene sequences, and BIOLOG test, the strain YC-1 was
identiiedasthegenus Stenotrophomonas (Yangetal.2006).Theisolateutilizedchlorpyrifos
asthesolesourceofcarbonandphosphorusforitsgrowthandhydrolyzedchlorpyrifos
to3,5,6-trichloro-2-pyridinol.Parathion,methylparathion,andfenitrothionalsocouldbe
degradedbythestrainYC-1whenprovidedasthesolesourceofcarbonandphosphorus
(Yangetal.2006).TheinoculationofthestrainYC-1(10 6 cells/g)tothesoiltreatedwith
100mg/kgchlorpyrifosresultedinahigherdegradationratethaninnoninoculatedsoils.
The results conirmed that the newly isolated chlorpyrifos-degrading bacterium can be
successfullyusedforbioremediationofcontaminatedsoils(Yangetal.2006).