pesticide in Arctic aquatic life, and is one of the major contaminants of the .... where t]/2 is the half-life of degradation for pesticides in the soil. Toxaphene is very ...
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 106, NO. D16, PAGES 17,929-17,938,AUGUST 27, 2001
Toxaphene in the United States 2. Emissions
and residues
Y. F. Li and T. F. Bidleman MeteorologicalServiceof Canada,EnvironmentCanada,Downsview,Ontario,Canada
L. A. Barlie AtmosphericChemistryAtmosphericSciencesand GlobalChangeResourcesand EnvironmentalMolecular Sciences Laboratory,PacificNorthwestNationalLaboratory,Richland,Washington
Abstract. Emissionfactorsof toxaphenefor sprayingand tilling eventsare distributedfor the United Stateson a 1øx1olatitudeandlongitudegrid system.By usingthe griddedusageand emissionfactors,inventoriesof griddedtoxapheneemissionsandresiduesin agriculturalsoil in the UnitedStateswith 1/6ø x 1/4ø latitudeandlongituderesolutionhavebeencreated.Total toxapheneemissions were around190 kt between1947 and 1999. At thebeginningof 2000, almost20 yearsafterbanningtheuseof toxaphene,therewere still around29 kt of toxapheneleft in the agriculturalsoil,of which360 t will emit to the air in 2000. The calculatedtoxaphene emissions andresiduesare in generalconsistent with publishedmonitoringdata.The trendsof toxapheneemissionsdueto currentuseandresiduesin agriculturalsoil in the United Statesmatch boththehistoricalatmospheric inputfunctionfor toxapheneextendingoverthe past40 years derivedfrom the compositionof toxaphenein peatcorefrom easternMinnesotato Nova Scotia, andthetrendsof air concentration of toxaphenein the Arctic.This indicatesthattoxaphene residues in theUnitedStatesagriculturalsoilcouldbe a majorsourceof toxaphenein the CanadianArctic and the GreatLakesregion.
1. Introduction
griddedtoxapheneusagein agriculturalsoil and on livestockin the United States with 1/6ø x 1/4ø latitude and longitude Toxaphene is produced by the chlorination of technical resolutionhavebeencreatedby differentcroplanddatasetsand campheneor ct-pineneand can consistof over 3000 compounds cattle numberdata set as surrogatedata [Li, this issue].In this [Vetter, 1993]. This chemical is of concern because it is paper,the griddedannualtoxapheneusagedata setshave been transported globally in the atmosphere, bioaccumulated through usedto calculatethe emissionsand residuesof this compoundin the food chainto top predators(includingpeople).It was found the United States. thattoxapheneis acutelyand chronicallytoxic to aquaticspecies Section2 presentsgridded emissionfactorsof toxaphene. and wildlife and poses a carcinogenicrisk to humans. Of Combiningthe gridded toxapheneusage and emissionfactor, particularconcernin Canadais the occurrenceof toxaphenein gridded toxaphene inventories on a 1/6øxl/4ø latitude and the Arctic and in the Great Lakes. It is the most abundant longitudegrid systemsince 1947 are presentedin section3 for pesticide in Arctic aquatic life, and is one of the major emissions andsection4 for residuesin agriculturalsoil. Section5 contaminantsof the Great Lakes fish. Toxaphene was the is devoted to comparisonbetween trends of emissionsand dominantorganochlorine contaminantin the Lake Superiorfood residueswith monitoringdata in the CanadianArctic and other web, with concentrations 2-15 times higher than total placesin both the United Statesand Canada.The issueof the polychlorinated biphenyls(PCBs) [Kucklickand Baker, 1998]. A new and old sourcesof toxaphenein the Arctic and the Great survey in 1986 showed that concentrationsof toxaphenein Lakes regions is also discussedin this section. Section 6 humanmilk from residentsof northernCanada(Keewatin) were summarizes the paper. approximately ten fold higher than those from the south [Newsomeand Ryan, 1999]. 2. Emission Factors As a general-purposeinsecticide,toxapheneis one of the Emissionfactorsof the pesticidesrepresentthe emission most heavily used organochlorinepesticidesglobally, with an estimated totalusageof 1.33 x 106t [VoMnerand Li, 1993, potentialof pesticidesin a geographicalarea, and are used to Usually,the definitionof emissionfactor 1995], more than 40% of which was used in the United States calculatethe emissions. and the usageof the pesticide [Li, thisissue].The use of toxaphenein the United Statescanbe is givenasthe ratio of emissions dividedinto four differentperiodsbetween1947 and 1986. The [Berdowskiet al., 1997]. In this paper,we usethe definitionof factorsgivenby Li et al. [2000]: totalproductionwas around720 kt ILl, this issue].Inventoriesof theemission
-
Copyright2001 by theAmericanGeophysical Union. Papernumber2000JD900823. 0148-0227/01/2000JD900823
$09.00
Ek 'k
,
wherek = s corresponds to a sprayingeventandk = t indicatesa tilling event.In the caseof a sprayingevent,Vs is the current 17,929
17,930
LI ET AL.: TOXAPHENE IN THE UNITED STATES---EMISSIONS AND RESIDUES
applicationand the degradationrates in the soil, are not well known. Within the scopeof the present study, a number of assumptions havebeenmadefor simplicity. Sincetoxaphenewaswidely usedin the preharvesttreatment of cotton [Avendanoet al., 1995] and more than 80% of the toxaphenewasusedon cottonin the United States,all toxaphene usedin agricultureis assumed to be via the sprayingmode. Only one plant/harvest cycle is assumedin a givenyear, and emissionsof toxapheneresiduesin the agricultural soil are assumedto start at the time of tilling in each year. The errors created by these assumptionsare reduced since only annual emissions are considered here. Also the re-emission by toxaphenedepositedon soil and water after transportation in the atmospherehas not been consideredhere. In this sense,only first-time emissionsare estimatedin this paper. Spraying events tend to produce the strongesttoxaphene emissionsbefore 1982, when toxapheneuse was deregistered. Figure 1. Emissionfactorfor spraymode for the United States Since then, the sourcesof emissionsare thoseresiduesleft in the on a 1øxlolatitudeandlongitudegrid system(eachcell hasa size croplandsoil. Besidesemitting to the air, the residuesof the of around20 km x 20 km). pesticidesin the soilare lostovertime by degradation. As an example,considerthe usageU and the corresponding emissionsE in 2 consecutiveyears,year 1 and year 2. Suppose usageof pesticidesas a spray,Es is the amountof pesticides Ua)t of toxaphene areusedin Y•year1, andtheemission in year emittedto the atmosphere in the sprayingevent,andtheemission 1 will be
factorFs is definedastheratioof emission Es andusageVs. In the casefor a tilling event, Vt is the amountof residuesdue to previoususage.E, is the amountof pesticidesemittedto the atmosphere, andthe emissionfactorF, is definedas the ratio of emissionEt and the amountof residuesV,. This definitionis convenientfor consideringthe emissionsdue to consecutive yearsof applicationof pesticides ILl etal., 2000]. It hasbeenrealizedrecentlythat mosttoxapheneemissions from soil residueshappenin summerdue to high temperature [Hamer etal., 2001]. In thiscase,the emissionfactorFt, defined astheratioof annualemission Et to theamountof residues Vt can be treatedas the annualemissionfactor of toxaphenedue to tilling or soil-airexchange. This will not createsignificanterrors sinceonlyannualemissions areconsidered in thispaper. Griddedannualemissionfactorsof toxaphenefor North Americaon a 127 x 127 km polarstereographic grid [Van Heyst etal., 1999]havebeencreatedby usingan air/surface exchange modeland a simplecanopymodel [Scholtzetal. 1997]. On the basis of these annual emission factors, emission factors of toxapheneon a 1øxlø latitude and longitudegrid systemare calculatedandgivenin Figure 1 for sprayingmodeandFigure2 for tilling modeand soil-airexchange.Thesetwo figuresshow that emissionfactorsfor toxapheneare between0.227 and0.375 for spraymodeandfrom 0.0114 to 0.0188 for tilling modeand soil-airexchange.The areaswith the highestemissionfactorsare aroundthe statesof Wyomingand SouthDakota.The reasonsfor thehighestemission factorsin theseregionsareprobablythehot anddry weatherduringmostof thegrowingseason[Scholtzet al, 1997].
EsO)= UfoFs.
(2)
In the above equationthe subscriptsindicateevents,while the superscript (1) indicatesyear 1. The residuesof all toxapheneapplied are assumedto be mixed and stayin the soil until the next tilling event in year 2. The amountof residues Rt at the nexttilling eventis
R,= (Ur'ø- Esrø)e -•'r,
(3)
wherep is thedecayconstant of thepesticidein thesoil;T is the time periodbetweenthe dayswhenthe pesticideis appliedand the day when the tilling event startedin year 2. The decay
constant p isgivenby In2
/,t -
,
(4)
tl/2
wheret]/2is thehalf-lifeof degradation for pesticides in the soil. Toxapheneis very resistentto degradationin soils with a reportedhalf-lifefrom0.8 year[Adams,1967]to 14 years[Nash
3. Emissionsof Toxaphene According to our knowledge, emission inventories of
toxaphene for the UnitedStateshaveneverbeenreported.It is apparentthat the computationof emissionson a grid system coveringthe whole United Statesrequiresconsiderable human and computerresources. The difficulty in undertakingsucha large numberof computations is that someof the input data Figure 2. Emissionfactorfor tilling mode for the United States requiredfor the computations, suchas the timing and modeof on a 1øx1ølatitudeand longitudegrid system.
17,931
LI ET AL.: TOXAPHENE IN THE UNITED STATES--EMISSIONS AND RESIDUES
Table1. Emissions of Toxaphene in 2000BasedonDifferent Re ionsa ............
Regions
Emission, t Percent ofTotal Emission
Southeast Delta States
157 111
43.1 30.4
Appalachian
30
8.3
SouthernPlains Mountain CornBelt NorthernPlains Northeast Pacific Lake States UnitedStates
27 14 9 6 4 4 2 364
7.4 3.8 2.5 1.6 1.1 1.1 0.55 100
aForthemapof different regions, please seeLi [ thisissue]. Figure3. Totaltoxaphene emissions in theUnitedStatesfrom 1947 to 1999 on a 1/6øxl/4ø latitude and longitudegrid system
(eachcellhasa sizeof around20 km x 20 km).
Eightypercent of toxaphene appliedon cattleis assumed to
emitto the air eachyear[Scholtzet al. 1997],andthe residues are not consideredin the followingyear. The total emissions and Woolson, 1967].In thispaper,10yearsof degradation half- fromtoxaphene usedoncattlewerearound39 kt. life is usedfor toxaphene [Mackayet al., 1997]. Archeret al. [1978]proposed an average emission factorfor In year2, U(2)t of toxaphene areused,andtheemission in toxapheneproductionof 0.28 kg/t, based primarily on year 2 will be
evaporation fromholdingpondsandlagoons. Thismakesthe
duringthe sprayevent,and
totalemissions of toxaphene frommanufacturing sitesto be200t between1947 and 1982(totalproduction: 714 kt). The annual emissions of toxaphene frommanufacturing siteshadlittleeffect
Es(2)= U(2)Fs Et(2)-- g, F,
(5) (6)
on the total annual emissionsin the United States, but could makea big influencelocally.
Thetotalgridded emissions fortoxaphene between1947and for thesingleyear Theusagedata[Li, thisissue]andtheannualemission factors 1999aregivenin Figure3 andtheemissions emissions are194 have been localizedon a 1/6øxl/4ø latitude and longitudegrid of 2000aregivenin Figure4. Totaltoxaphene system,and combined to estimate toxaphene emissions to the kt between1947 and 1999, 80% of which is contributedby the in agriculture, and20%of whichis contributed atmosphere. For thepresent study,griddedusageof toxaphene useof toxaphene dueto tilling andsoil-airexchange.
from 1947 to 1985 has beenusedfor estimatingboth emissions bytheuseonlivestock. Asshown inFigure4, in 2000,almost 20
yearsafterbanning theuseof thispesticide, therewill bearound emittedfromthe agricultural soil in the onlyaccount for thepresent year'sapplication but alsoresidual 360 t of toxaphene United States.Table 1 gives the amountsof emissionfrom pesticide in thesoildueto annualapplication started in 1947. differentregions.Almost90% of total nationaltoxaphene and residues.The resultingemissionand residueestimates not
emissionsare from the Southeaststates,the Delta states,and the Appalachianstates.
4. Residuesof Toxaphenein Agricultural Soil Inventoriesof pesticideresiduesin agriculturalsoil are important for somemodels[Harneret al., 2001;Scholtzet al., 1997] to predict pesticidevolatilization.Although direct measurements of soilsamples in representative agricultural lands in theUnitedStatescanbehelpfulin determining thereservoir of pesticides available for emission, theyarelaborintensive and costly.Residues in thecropland in theUnitedStateshavebeen calculatedbetween1947and2004 accordingto equation(3). The
Figure4. Toxaphene emissions in theUnitedStatesin 2000on a 1/6øxl/4ø latitudeandlongitudegrid system.Around90% of
toxaphene residues in agricultural soilin theUnitedStates at the beginning of 2000arepresented in Figure5. It indicates thatthe agricultural landsmostcontaminated by toxaphene are in the southeastern partof theUnitedStates,with residues as highas 150t percellin someplaces. Thetotaltoxaphene residues leftin the agriculturalsoil in the United Statesand ready for
total emissionsare from the southeastern part of the United
volatilizationat the beginningof 2000 are around29 kt, among
States.
which360 t will be emittedin 2000 (Figure4).
17,932
LI ET AL.' TOXAPHENE
IN THE UNITED
STATES
EMISSIONS
AND RESIDUES
Toxaphene residues (Unit:t/cell)
[] [] •
100 10 I
to 150 to 100 to 10
!-"-•:: 0.1 to ::iiii::ii < 0.1
1
.....
o
Figure5. Toxaphene soilresidues in theUnitedStatesin 2000ona 1/6øxl/4 ølatitudeandlongitude gridsystem. 5. 2. ToxapheneResiduesin Agricultural Soil
5. Results and Discussions
5.2.1. Toxapheneresiduesby states. The National Soils MonitoringProgram(NSMP) wasinitiatedin 1968 by the U.S. Departmentof Agricultureand is administered by the U.S. Figure6 presentsthe temporaltrendsof toxapheneemissions EnvironmentalProtectionAgency. In this program,pesticide andcroppingdatawerecollectedin 1971 from 1473 and residuesin agriculturalsoil in the United Statesbetween application 1947 and 2004. Both annual emissions and residues reached samplingsitesin 37 states[Carey et al., 1978a, 1978b].The in eachstateof the United States highestvalues in 1975 (160 kt for soil residuesand 11 kt for averagesoil concentrations emissions).In 2004, around260 t of toxaphenewill be emitted, from the NSMP are shownin Figure 7. The stateswith highest (> I mg kg4 dry weight) were South and residuesleft in soil will still be as high as 20 kt. Between soil concentrations Carolina,Georgia,Mississippi,andLouisiana. 2000 and 2004, around8 kt of toxaphenewill be lost, 1.2 kt of We estimatethe averagesoil concentrations in eachstateas which are due to volatilization,and 6.8 kt are due to degradation. This indicatesthat over the long term, it is degradation,not follows. First, the total toxapheneresiduesin each state are volatilization,that removesmost of the toxaphenefrom soils. calculatedfrom the griddedresiduedata.Then the croplandof Thereforea significantamountof toxaphenewill stayin cropland the United States based on states for 1969 is obtained from the soils in the United States for at least another decade. U.S. Departmentof Agriculturewebsite(http://usda. mannlib. 5. 1. Trends of Toxaphene Emissions and Residuesin Agricultural Soil
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